WO1991001534A2

WO1991001534A2 - Access control apparatus and key means

Info

Publication number: WO1991001534A2
Application number: PCT/GB1990/001061
Authority: WO
Inventors: Alistair Macdonald Henderson
Original assignee: Alistair Macdonald Henderson
Priority date: 1989-07-10
Filing date: 1990-07-10
Publication date: 1991-02-07
Also published as: AU5939690A; WO1991001534A3

Abstract

The invention provides for means for controlling the accessing apparatus (28), for example, a television set (56) and key means (10) suitable for use in such control apparatus (28), the key means (10) being arranged to interfere with radiation instant thereon so as to reflect or retransmit radiation identifying that particular key (10). The key (10) may be used in control apparatus (48) for enabling/disabling operation of a television set (56) so that the length of time the television set (56) is in operation can be controlled having regard to the identity of the user wishing to use the television apparatus (56).

Description

ACCESS CONTROL APPARATUS AND KEY MEANS TECHNICAL FIELD

The present invention relates to access contro apparatus and to key means which may be used with suc apparatus. In particular, but not exclusively, the inventio relates to apparatus for controlling accessing o equipment such as a television, video player/recorde and/or computer unit.

Over recent years, television has become a majo part of the entertainments industry and has becom entrenched into societies general way of life

Further, as the ease with which television sets can b used, for example with the introduction of infra-re remote control devices and direct video programming b way of bar-codes located along side programmes liste in magazines such as The Radio Times, televisio continues to become ever more popular. With the adven of satellite and cable TV, the number of hours spen watching television is likely to increase considerabl in the near future. Further, the improved quality o television systems provided by the NICAM systems an

High Definition Television (HDTV) will rende television even more popular as will the ease wit which television sets and video recorders can be use by way of remote control devices.

In addition to displaying television programmes, television sets are commonly used to display compute graphics or a video recording and this serves t increase the length of time spent viewing a televisio screen or similar equipment such as a separate VDU o the computer unit.

It has long been suggested that children spend too much time watching television rather than taking part in other activities thought of as necessary, for example reading, outdoor activities and, in particular, studying. It is also considered that TV viewing can be addictive.

Some countries have taken action to ban television on a certain day each week, however, with the advent of satellite television this method of limiting the amount of television received by a television set is inappropriate.

In addition to the difficulties faced in regulating the actual number of hours children spend watching television, it is also difficult to censor which particular programmes they watch. Although there is a general rule that programmes not suitable for children are broadcast after 9.00pm, this in no way prevents children from watching these programmes. Further, although parents may ensure that children do not watch late evening programmes at the time of broadcast, it is possible that children will video such programmes in order to watch them the next day without parental knowledge. There is thus a need for a simple, secure device to help families, particularly those with young children, regulate their children's TV viewing habits. It is important that such a device can operate with standard national/region broadcasts, satellite broadcasts, cable TV, with TV sets showing video recordings or displaying computer graphics and separate

VDUs of computer systems.

Equipment of this nature demands that a cheaply manufactured, secure and large variety of key means are available for such, and other apparatus where accessing of the apparatus is to be controlled. The prese invention also seeks to provide such a key means alo with associated key identification apparatus. DISCLOSURE OF THE INVENTION The present invention seeks to provide apparat for selectively controlling the accessing predetermined equipment.

According to one aspect of the present inventi there is provided access control apparatus includi means for identifying a prospective user of apparat to be accessed and means for selectively enabling u of the apparatus on the basis of the identification the user.

Preferably, the apparatus may include means f recording the amount of time for which a user h accessed the apparatus.

Advantageously, the means for selectively enabli use of the apparatus includes means for indicating t period for which a particular user has accessed t equipment so that appropriate apparatus disabling step can be taken.

Preferably , the control apparatus is arranged t enab le u s e of the apparatus to be a c c e s s ed b controlling a signal to the apparatus . Advantageously the control apparatus acts so as to selectively connec an aerial to a TV set .

Preferably, the apparatus includes a switch fo enabling operation of the television set which switc may comprise a latched R.F. relay or a switched gai amplifier or other semiconductor switch.

The control apparatus may act so as to selectivel connect the power supply to the apparatus. Suc control apparatus is particularly advantageous for us with apparatus not having a signal line, for example television set where the aerial is fixedly connected t the television set or a self contained computer unit.

If the apparatus to be enabled/disabled has a fixed internal signal source, for example a portable TV, the switch may be arranged to short-out the signal cable such that when the switch is attached to the external aerial plug, it causes a required degrading of the signal An interference signal could also be introduced to an external signal line to block the internal signals. Preferably, the control apparatus is arranged to received a key means. As such, the key means may comprise a conventional key or some form of identification card having magnetic data stored thereon. Advantageously, the key comprises a member which is arranged to interfere with radiation incident thereon so as to modify the incident radiation to provide radiation identifying that particular key. As such, the control apparatus includes a radiation source and means for detecting a radiation signal obtained by way of the key member. Also, the modification may comprise filtering, absorbing, refracting or reflecting the incident radiation.

Also, the radiation detection means may be arranged to receive a plurality of keys so that the device can share the equipment usage time amongst each user when a corresponding plurality of users are accessing the equipment.

Alternatively, the detection device may be arranged to receive only one key. In this case, the device includes micro-processor control means whereby a prospective TV viewer who enters the room in which the television is operating can remove the key already held in the device and then log-on with his/her own key. If the detection device is arranged to receive a plurality of keys, a common source may direct radiatio by way of prisms or mirrors onto each of the ke members. The resulting radiation pattern obtained fro each key member can then be read by a plurality o detection means under micro-processor control Alternatively, a plurality of radiation devices, eac associated with one key, may be controlled by a micro processor such that only one of the plurality of key experiences radiation at a particular time and i detected by a common detector.

In this way, the invention may prevent a viewe tagging on to another viewer's viewing time. Also, th user having the greatest time period credited t his/her key, may be given priority over other users fo deciding which programme is viewed.

Advantageously, the apparatus includes a band-pas filter so as to prevent particular channels bein watched during predetermined time periods. Preferably, the band-pass filter is associated with micro-processo control means wherein the time of transmission o particular programmes on particular channels can b directly input into the apparatus so as to preven those programmes being watched by a particular TV user.

The programme information may be down loaded from a external source. For example, a home computer may b arranged to display programme information and provide for a user-friendly selection and display procedure.

The data relating to programme timings may be provided via current Prestel or Oracle services. Particularly, if programme information is represented in bar-code, an optical scanning device can be employed to input the required programme information into the control processor. As an alternative to such a filter, a narrow-band signal generator may be employed to generate an interference signal to be superimposed onto the signal to interfere with a particular programme channel.

Advantageously, the control micro-processor will allow each user to have a preset time allocation, and will allow for the decrementing of the allocated time period so that once the period is exhausted, that particular key will not allow the required accessing.

Preferably, this allocated time period may be automatically reset to maximum after one week. Alternatively, the apparatus of the present invention may also provide for a system whereby parents are able to monitor the accumulated amount of time each child has been watching television without access being denied to any user so that the necessary sanctions can then be taken. As such, the insertion of a control key means into the apparatus initiates the counting of a timer which stores a running total of minutes or hours watched by a particular child as identified by the key means. The apparatus of the present invention may be readily adapted for use to prevent excessive time spent watching videos or playing computer games. In either case, control apparatus may be located between the video recorder/computer game module and the VDU, whether it is a television set or not, so as to break the connection therebetween in response to a control signal from the control processors. However, with a computer the control apparatus is generally located between the power supply and the computer/VDU. According to another aspect of the present invention, a means of communicating certain data between a plurality of such apparatus is required. For example, where there is more than one entertainment system to be controlled within a household, apparatus may be employed to control the access and use of that system. It is advantageous to allow all key members be programmed in at least one of the plurality o apparatus, and used in any other control apparatus a required. In addition, use of an allotted time peri is communicated between each control apparatus t ensure that an individual's allocation is decremente when accessing any one of the plurality of contro apparatus.

A signal path allowing for such communication ma be advantageously provided by the signal cabl providing for enabling or disabling of the equipment Communication between each control apparatus may b effected by a coded digital message, modulated at frequency which does not interfere with the signa required to enable operation of the controlle equipment. This modulated message may be injected ont the signal cable, and may communicate between apparatu by way of a standard communications protocol, such as Half Duplex Link Communication (HDLC). Alternatively, communication may be effecte between apparatus by a separate interconnecting wire or where control is to be provided by means of th power cable, by means of a modulated message carrie over the ring mains by one of a number of know methods.

According to yet another aspect of the presen invention, the apparatus may be used to monitor th total time equipment is used by individuals, such a for example in hotel rooms where pay television i available. In this case, on use of a suitable ke member, access is given immediately, and the period o use recorded, displayed and reported to a central unit.

Further, the apparatus of the present inventio may be arranged to simultaneously control a pluralit of equipment units, for example, a television set an video recorder. Such control may be achieved by using a two-pole switch within the apparatus so as to prevent an unlimited length of broadcast being recorded or an unlimited number of prerecorded video-tapes being watched.

Preferably, the key member comprises a plastic material formed of a plurality of randomly arranged coloured regions which interfere with the radiation passing therethrough. The particular coloured pattern formed in the key member provides a unique signature by which the owner of that key member can be identified.

Further, the key means may comprise a key pad by way of which an identifying serial number can be input to the control apparatus. A sample function may also be included whereby a user may access the apparatus for a predetermined short time so as to sample use of the apparatus at that time.

Preferably, the control apparatus includes a micro-processor control unit. In this case, the micro- processor control unit is used to store information relating to each key. As such, the micro-processor control unit can be programmed by, for example the parents, such that the key means can only enable operation of the TV set for a predetermined amount of time. Thus, since each child is issued with a unique key, the amount of time that each child watched television can be monitored and controlled.

The control apparatus may be battery powered or power may be provided by way of battery eliminators or mains transformer units. In particular, when a plurality of apparatus is required, the aerial cable may be employed to distribute d.c. power to each apparatus by way of a single battery eliminator.

The plastics key member arranged to interfere with radiation is particularly advantageous for use with domestic appliances such as in the control apparatus the present invention since a large number of uniq key members can be provided at low cost. Each key m comprise a random pattern of material. Also, various features may be included to prote against attempts to overcome the security of t apparatus, for example, the apparatus can be reset if signal plug is removed, the programming of th apparatus can be prevented other than by a master-k user and also the addition or removal of furthe apparatus can be detected.

Removal of the signal plug from the contro equipment may be detected in a plurality of ways. I particular, the capacitance of the signal line may b monitored for sudden changes which would accompan removal. This may be achieved by applying a d.c charge between the core and the sheath of the cable a regular intervals, and measuring the time constant a the charge decays. A substantial reduction in thi decay time would indicate tampering. Alternative form of capacitance measurement may also be used.

As mentioned above the present invention als relates to an identification key.

At present, numerous identification keys ar available to provide for the automatic identificatio of the key holder. For example, such keys are used t access bank cash dispensing machines and also to allo access through security doors.

These known keys commonly comprise cards having magnetic strip which stores the necessary informatio required to identify the card holder. When used, th card is inserted into an associated part of the machin to be accessed, or the door to be opened, and th magnetic data is "read", thus enabling the machine o door lock to be activated. Further information fo identifying the card holder may also be input by way of a keyboard.

Other known apparatus includes mechanical key switches and systems operating by use of passwords, voice recognition and bar code scanning.

A further development of known keys or cards is the so called 'SMART' card which, in addition to a data storage medium, also includes integrated electronic circuitry for enhancing the card's information storage and retrieval capabilities.

Although these known identification keys or cards have found wide applications, the expense involved in producing such cards disadvantageously restricts their use in 'domestic' situations. Further, the cost of producing systems for detecting the card are also disadvantageously costly. Also, the cards are easily damaged or broken, as is the electronic circuitry or data medium. Known apparatus may also be disadvantageously easily copied, be of an inconvenient size and shape and have little aesthetic quality. Also repeated use may lead to malfunction and also the detection apparatus is readily reprogrammable.

When choosing a key system for a particular application, many factors must be taken into consideration. For example, the cost of the keys, the ease of manufacture of variants, the number of variations possible, the ease of copying the keys, the vulnerability of the key to damage when used, wear with time or use, the size, weight and aesthetic features of the key, the ability to store information and the repeatability of identical key manufacture. Further considerations are the cost of the key detector system, the repeatability and accuracy of detection, the ease of use, the security of the detector against unauthorized use, the number of keys accepted by each detector, the ease of programming for use of new ke and the dependence on a power source.

It would therefore be advantageous if identification key could be provided which does n exhibit these disadvantages. The present inventi therefore seeks to provide an identification key whi can be economically produced, is not prone to damage breakage, and which provides for the uniq identification of each of a suitable number of su keys.

According to another aspect of the prese invention there is provided an identification k comprising a key member arranged to interfere wi radiation from a radiation source so as to modify t incident radiation for identifying the key member.

The key member may block, reflect, filte refract, enhance or otherwise alter or interfere wi the radiation so as to provide an identifying radiati signal. The difficulty in copying the random pattern the key increases security and also the various typ of environment in which the key can be successful employed.

The key member may be formed of a randomly varie density plastics material, the material having variety of refractive indices.

Also, the key member may be arranged to interfer with the incident radiation by the inclusion of plurality of opaque particles or elements in a rando pattern. Further, the particles or elements may als be reflective so as to reflect the incident radiatio as required.

Preferably, the key member is formed of a plastic material, for example plastics resin that is introduce into a key mould in liquid form. As such, th particles or elements may be set in the plastics material when in a liquid state.

Advantageously, the key member is of plastics material of variegated pattern to interfere with the incident radiation. Different regions of the key member then exhibit different degrees of translucency. The key member may comprise portions of at least two plastics which are transparent or translucent to light of one or more wavelengths to different degrees. The density of the plastics material may be varied so that a variety of refractive indices are provided in the material. Each unique variation of density will provide for a unique radiation signal to be detected by the detection means. The key member may be provided in any required shape, however to advantageously optimise reception of the radiation from the source, the key shape should allow for a 90° angle of incidence with the radiation.

According to an alternative key, an electric or electromagnetic field can be used as the source of radiation, and the key formed from random patterns of electromagnetically sensitive material then used to alter or disturb this radiation field in some way, with detectors measuring the resultant field produced. The key member may be produced by using particular densities of iron filings to dope liquid plastic material. Various densities of doped plastic may be produced, and various other ferromagnetic materials used for the doping. The plastic may be poured into a mould in liquid form and mixed with the ferromagnetic material. On hardening, a solid key member is formed with a randomly varied three-dimensional ferromagnetic pattern.

This embodiment of the key need not have a concave surface, and is not damaged by scratching or dirt. Although a concave surface is not required, accura positional placing is still important. Also, the k must be shielded from electromagnetic interference.

The radiation source may be provided by one more coils located around a key member slot which, wh electrically energised, will produce an electromagnet field. The field produced will vary in proportion the current flowing in the coils, the number of tur in the coil, and the size, density, and magneti permeability of the key member. Thus key members different density will produce different fields. Th field produced will comprise an identifiable three dimensional pattern relating to that key member. Th field may be detected by one or more magnetic fiel strength detectors, such as a Hall effect device. further feature of the electromagnetic radiatio sensitive key lies in its ability to vary the radiatio intensity and direction. Using an a.c. source in th coil produces a varying field. In this case, a alternative form of detection may be provided by secondary coil located around the key member, which i used to measure an induced a.c. voltage dependent o the key member. By using further coils in a differen plane, and driving them at 90° out of phase, a rotatin electric field can be produced. In the presen invention, the rotating field allows a signature to b produced dependent on the three-dimensional shape an density of the key, thus allowing for precis identification of one of may key members. One particular type of key means makes use of th capacitance provided by two parallel conductive plate having a dielectric medium located therebetween. Th capacitance is dependent on the size of the plate (cross sectional area), the distance between the plate and the coefficient of permitivity of the materia between the plates . The insertion of each of a plurali ty of key members of randomly dif f ering permitivity between capacitor plates provides for a range of unique identification keys . If an electric field of E volts per meter is applied to the plates , a

2 charge density of D coulombs per m will result, in which D= u,kE, and where u, is the electric permitivity of a vacuum, and is the relative dielectric constant of the material of the key member. As such, the key is identified by measuring the "capacitance" with the key member inserted.

The key member may be formed from a liquid plastic material having a known dielectric contant. The plastic may be heavily doped with at least one other material having a dielectric constant different from the plastic to produce a random three-dimensional pattern in the plastic material. The key so formed has a varied dielectric pattern between any particular two points thereof. For example, PVC has a dielectric constant of 7, silica 4 and polyethylene 2.3 and so such materials may be introduced as small particles or elements into the liquid plastic prior to solidifying to form the key.

The detection mechanism may be formed by one or more conductive plates placed around a key member holder. Any particular pattern of plates can be employed. The measurement of capacitance, needed to identify the key, may be carried out in any one of a plurality of ways. For example, a voltage may be applied to the plates, and the time constant of the capacitor measured. Alternatively, the response of the capacitor to a plurality of different applied frequencies can be monitored. Further, the device may be used as an element in a capacitance controlled oscillator. Also, since values of dielectric constant va with temperature, a reading may be taken from th detector without a key inserted and then a furthe reading taken after key insertion and the two reading compared to obtain a final reading. Also, variation in temperature between the dielectric and the devic including the capacitor plates may be compensated by microprocessor and temperature sensitive element i contact with the key member. Further, the properties of some known piezo electric materials, for example BaTio. may be used Such materials polarise when an electric field i applied thereto, and relax over a period of time havin an associated time constant T when the field i removed. Certain materials with time-constants o hundredths of a second may thus be provided in rando patterns within a key member. A number of differen materials with different time-constants may be locate in various random portions of the key and a variety o densities. As such, an electric field may be applie which is sufficient to polarise the variou ferroelectric regions in a common direction. O removal of the field, the polarisation within th material gradually decays. The level of polarisatio at various points of the key member may be measured a various times to determine several values of T at eac point, thus identifying the key member. The radiatio may be produced by an electric field developed by tw parallel plates. The modification provided by the ke member is an enhancement of the field by retaining th field pattern after removal of the source of the field.

Further, an a.c. field may be employed, in whic case phase shift of frequency response may comprise th measured characteristics. In a similar way, various ferromagnetic materials, such as the common iron filings, may be embedded into a key member in a variety of random three-dimensional patterns. The key member may then be excited with an electromagnetic field produced from one or more coils or otherwise. The resultant static magnetic fields produced will have a complex flux pattern, dependant on the dispersion of the ferromagnetic material within the key member, which may be detected by means of Hall effect devices. By varying the excitation via a plurality of coils, further scope for variation of a random identification pattern within the key is obtained.

Also, mutual inductance may be exploited according to the invention. In this case, an energising coil is coupled to a secondary coil by way of the mutual inductance dependant on the key member. An a.c. voltage in the excitation coil will produce a corresponding a.c. voltage and current in the secondary coil, which is dependant on the number of turns in both coils, and the mutual inductance. The mutual inductance is in turn dependant on the dispersion and density of the ferromagnetic elements included in the linking key member. Again a plurality of detection coils may be used to improve detection sensitivity and so increase the number of key means which can be employed with the identification apparatus.

Further means may provide for "moving" the electromagnetic field relative to the key member. Two coils may be located at an angular separation of, for example 90 and then energised with respective a.c. voltage supplies which are out of phase by, for example, 90°. This provides a rotating field which impinges various different cross-sectional regions of the key member. Measurements are taken at known points in this excitation phase and a two-dimensional map of the dispersion of the particles of the key member ma be obtained at low cost. Further phase shifted coil may also be added to increase the sensitivity an selectivity of this arrangement as required. As outlined above, the optical embodiment of th key system of the present invention can be based on th interference caused to a beam of light, causing detector to produce a particular reading. Th detectors can be arranged to identify th characteristics of the light with which the ke interferes, such as particular colours, and in this wa a range of low cost keys and detectors can be produce meeting the particular requirements noted above.

According to yet another aspect of the presen invention there is provided an identification ke comprising a key member having a random pattern forme of at least two regions each of which is selectivel transparent or translucent to radiation of one or mor wavelengths so as to selectively transmit, block o attenuate radiation identifying that key.

Preferably, the key member is formed of polythen resin which may be impregnated with translucent dye.

Selective reflection may be obtained by the rando inclusion of reflective particles or elements in one o more of the regions.

Preferably, the key member is arranged to b selective of visible radiation. As such, the at leas two regions comprise regions of different colour.

The key comprises a random non-regular pattern o plastics material of at least two colours, in the manner of a typical cloud.

The radiation source, key member and detector may be arranged in one of a number of advantageous ways , depending on the particular application of the apparatus. One particularly simple arrangement which can be adapted to suit many applications involves the radiation passing from the source to the detector by way of a key which is situated therebetween.

According to a further aspect of the present invention there is provided a method of producing an identification key member comprising introducing at least two materials , of different radiation affecting properties , into a mould and allowing at least one material to harden and form the key member. The materials may comprise liquid plastic and in particular liquid plastics resin which may be mixed with a translucent dye material, ferromagnetic material or other elements , so as to produce a unique random pattern. Advantageously, the plastics resin comprises ultra -violet l ight curable and durable resin of different colours .

Pref erably , the introduction of the coloured plas ti cs material i s controlled by mean s o f a microprocessor so that an optimum number of keys , each having sufficiently discrete unique pattern, can be produced . The coloured plastics materials may be poured or injected into the mould, such that clouds of each variety of material are randomly formed.

Automated liquid dispensing apparatus may be provided which allows for rapid inj ection of measured quantities of liquid plastics at precise positions in each mould.

Advantageously, the optical embodiment of the key according to the present invention is formed of a pattern of the three primary colours . Further , particular agents may be introduced into the liquid plastics to ensure immisability between each colour.

The key member may be constructed in many physical shapes depending on its application and the arrangement o f th e rad i a t i on s our c e and d e te c tor me an s . Positioning of the key member in a detector important to obtain consistent identifying reading In fixed position systems, ie where there is relative movement between the key member and t radiation source and detector during the reading of t radiation, a variety of shapes are suitable which all the key to be held tightly in the detection apparat and to be located only in one particular orientatio Small lugs or flanges may be provided on the surface the key member so as to allow for a snap-fit into t detection apparatus.

In order to ensure maximum transmission of sour radiation into the key member, a shape providing a 90 incidence of radiation to the source is preferred f the optical embodiment. In this respect, a conca surface is provided on the key member so as to provi a 90 angle of incidence to the maximum possible amou of radiation. Also, radiation which passes through th key member should be transmitted to the detector mean with maximum efficiency. This may also be achieved t best effect by the use of a concave surface on the ke member. The concave surface also provides protectio against general wear and abrasion of the key surface

According to still a further aspect of the presen invention there is provided a method of producing a identification key member comprising introducing liqui plastics material into a mould and also randoml introducing at least one radiation opaque member int the liquid plastics. Preferably, the liquid plastic resin will be pre mixed with either translucent dye material or othe particles as required. One or more of these mixes ma then be injected into moulds to harden. Know automated liquid dispensing systems are readil available for use in this process and allow rapi injection of precisely measured quantities of liquid at precise locations within each mould. Computer control may also be incorporated. The control programme can ensure that each of a number of different dyes are injected in a variegated way to form unique random patterns. A further factor affecting the pattern produced in the key is the introduction of agents into the liquid plastic to ensure immisability between each colour. The liquid plastic material may be hardened according to the method of the present invention to form a solid key member as required. A two-part chemical resin may be used, whereby the mixture formed hardens within a fixed time period. Other methods such as injection of catalysts at the final stage of production may also be used. Use of a two-part resin may cause problems due to the automatic hardening process which may block the liquid injection equipment. One advantageous solution to this problem is the use of a U.V. light curable liquid plastic resin. In this case, the resin remains in the liquid state in storage, during the injection process and also once introduced into the mould. The mould may then be passed under a U.V. light source in order to harden the key member. U.V. curable plastic resins are readily obtainable.

The variously doped materials may be allowed to mix so as to provide greater variations of effect.

Further, particles of radiation translucent, luminescent or reflective material may be introduced into the key member.

The present invention also provides apparatus for use in identifying such a key which comprises a device arranged to receive the key, at least one radiation source and at least one radiation detector. Preferably, for the optical embodiment, the apparatus includes three radiation sources each which emits a respective one of the three prima colours and the detectors may be wavelength selectiv Also, the apparatus may include a wide band detecto capable of detecting radiation in the bandwidth of ea of the three sources.

The apparatus may also emit and detect radiati which exists outside of the visible spectrum.

The radiation source may be located so as to be the opposite side of the key to the detector Preferably, however, the radiation source and detecto may be located on a common side of the key. As suc the radiation emitted from the source is arrange to transmitted through the key and then reflected ba therethrough so as to impinge on the detectors.

In many cases, for all embodiments of the key, is useful to take a plurality of readings of t radiation signal provided by the key member, f example, to improve security. This may be achieved using multiple sources, multiple detectors or adjusting the relative positions of the key membe source and detector between or during readings.

Multiple readings may be obtained by usin multiple sources, multiple detectors or by moving t source, detector or key.

A multiple detector array may be used i conjunction with a wide beam radiation source so as t obtain multiple readings and thus increase the possibl variation in the key members. Alternatively, radiation may be swept across a ke and onto an array of detectors by use of a movabl reflector. As such radiation is emitted from th source onto the reflector which may be pivoted or move linearly as required. The key identification is the dependent on a physical effect such as the movement o the reflector.

Further, multiple sources may be employed and switched so as to produce a range of radiation patterns. Typically, each source will provide radiation of a particular band width and will thus produce a different response at a wideband detector. Such an arrangement is particularly advantageous in the optical embodiment due to the low cost of narrow band width L.E.D. sources. A slide member may also be provided which houses the radiation source and detector and which is arranged for movement in the region of the key member. Such a slide member allows for low cost manual scanning of a key to obtain maximum analysis of the key's characteristics.

Alternatively, the key member may be arranged to move past a stationery radiation source and detector. As such, the key member may be moved under the influence of gravity and may move independently or may be located or loaded onto a shuttle member.

The detector and source may be housed in a common unit which is moved into and out of the region of the key member or alternatively the key member may be moved into and out of the region of the radiation by means of gravity or otherwise. The key may be attached to some other object, particularly to facilitate movement of the key through the region of the radiation. The detectors may comprise light dependent resistors, photo diodes, photo transistors, photo darlingtons, Hall effect devices and pick-up coils and may be used in association with appropriate filters.

Preferably, the apparatus for use in identifying a key member includes means for determining whether the key position within the detection apparatus is correct. Further, the apparatus may also comprise means for detecting entry of the key member therein. Key ent may be detected by monitoring radiation from radiation source, which radiation is interrupted entry of the key into the apparatus. Alternatively, micro-switch may be employed which changes state due physical contact with the key member introduced in the detection apparatus. Further, the key member m be provided with a magnetic material for exampl magnetizable liquid resin injected into the memb which, once the key is located in the detect apparatus, acts so as to change the state of a magnet reed switch or Hall effect device.

Means for determining correct positioning of t key member within the detection apparatus i particularly advantageous for use with a detecti system in which the key member and the radiation sour and detectors move relative to one another duri detection of the radiation. In a situation where t key member is allowed to move under the influence gravity, the leading edge of the key is detected Precise key positioning can then be calculated on t basis of the time taken for a particular portion of t key member to reach a particular location within th detection apparatus. In a situation where the speed o relative movement between the key member and th radiation source and detector is not constant or known the key member is provided with a regular pattern o characteristics so as to aid calibration of the system As such, a portion along the length of the key ma include a series of opaque and translucent lines o regions dyed with one particular colour. A detecto may be tuned to the bandwidth of that particular colou so as to indicate the precise moment for readings to b taken by other detectors as the key member move relative to the radiation source and detector. The detector apparatus may also include means for compensating for ambient radiation . A separate detector may be provided to detect ambient radiation and thus adjust the reading obtained by the key member identification detectors so as to allow for the ambient radiation which enters the detection apparatus . Further , mechanical design of the detector apparatus may be such that negligible ambient radiation enters the apparatus . Advantageous ly , the identification apparatus includes a microprocessor, or like circuitry, which is arranged to store information relating to each key and provide a contro l f unction dependent on the key inserted in the identification apparatus . The control function may also include automatic calibration to allow for variation in the sensitivity of the detectors or the output from the sources so as to allow the key to have a useful life irrespective of the s light variations in the key position within the detection apparatus , the variation source intensity with time and damage to the key due to dirt and frictional contact with other surfaces or the like.

As such , any variations must be compensated for in the detector circuit . Thus the output from the d etector i s f ed into a micro-proces sor and the variations in source intensity can be nulled by reference to a control signal obtained directly from the source.

One compensation system includes a key detector and compensation detector. The compensation detector receives radiation directly from the source and this va lue , along with the value obtained by the key detector forms a ratio which is stored in a memory device. This measurement sequence is repeated and if the readings are within the required tolerance, the reading is accepted. At a further date, when the ke is again inserted in the apparatus, another sequence o readings is obtained and providing they are within th allowed tolerance, the reading is accepted. The ne reading may be set as the centre reading and correspondingly new tolerance band calculated Variations in key quality with time are thu compensated for. In particular, the following sequenc may be arranged to be required: (i) Switch on source;

(ii) Wait for source to stabilise; (iii) Take first reading, (iv) Wait for predetermined period; (v) Take second reading; and accept reading if within tolerance band.

If the readings are not within the tolerance band the steps (iv) and (v) are repeated.

The key of the present invention, in overcomin many of the above disadvantages, opens up new areas o application for key control systems. Particula critical features of the design of the key are th lowest combined cost of key and detector production, a infinite variety of key, an extreme difficulty i copying a key and a physically tough but aestheticall pleasing key size and shape.

In particular, the key system of the presen invention is suitable for low cost domestic situation where a reasonable degree of security is required. Typical applications may include, domestic applianc control, computer access control, door entry control systems, moving object identification systems and toke detection systems, in addition to high-security applications.

According to yet a further aspect of the present invention, the key member and identification apparatus form part of an enable/disable system for controlling operation of specified apparatus. The specified apparatus may comprise any domestic appliance or commercial apparatus or alternatively any particular apparatus machine or location to which access is to be selectively prevented, for example a television set as outlined before.

Thus, the present invention can provide for an enable/disable system comprising identification apparatus for identifying a key as described above, which system enables or disables the use of a television.

The television set may of course be used for displaying computer graphics or a video recording. Preferably, the identification apparatus of the system includes a microprocessor as outlined above.

Advantageously, the identification apparatus controls a switch for enabling or disabling a picture and or sound on the television. As such, the switch may be provided so as to selectively connect the aerial to the television. In this case, the switch preferably comprises a latched R.F. relay or may comprise a switched gain amplifier or semiconductor switch.

As a further advantage, the microprocessor may be arranged to indicate if either of the identification apparatus or associated connections have been tampered with.

By providing a microprocessor having a timing function, it is thus possible to provide a system for monitoring how long a particular person watches a television s et , and also to prevent that person watching the set if they have been watching it for more than a pre-determined time.

Accordingly, in addition to preventing operation of the television set once a predetermined time period has been exceeded, the apparatus of the invention m allow further viewing of the television set in exce of that predetermined time period, which excess however, is measured by the control processor. Thus the apparatus can then store and display the exces time period so that the parents can take the necessar sanctions against that particular viewer.

Further, the apparatus of the present inventio may be programmable with the time and channel o transmission of a particular programme of interest due to its unsuitability for viewing by children o otherwise. In this manner, the parents can be warne of a particular programme of interest appearing on channel by way of a visual or audible signal emitted b the television set at the time of transmission of tha programme. Thus, if so desired, the parents can switc to that channel or, if appropriate, ensure that thei children do not switch to that channel. As previously the information relating to the time and channel o broadcast of the programme of interest can be inpu into the apparatus by way of an optical scanning devic and a bar-code data source.

Further, such programme information can be fe into the control processor and then down-loaded onto video recorder such that the programme of interest ca be recorded by the video recorder without need fo manual setting of the recording period Advantageously, the programme information can be down loaded to the control processor from a currentl available television subscriber service for exampl Prestel or Oracle.

The ease with which a video recorder can be pre programmed thus makes it particularly necessary t provide means for preventing use of the equipment b children, as outlined according to the presen invention.

Thus, the present invention allows for the economic provision of a control system for monitoring and limiting the time children spend watching television.

The key and its associated identification apparatus of the present invention can be produced at low cost and allow for an infinite number of discreet keys to be produced. Each key is particularly difficult to copy and the keys and identification apparatus can be used in a wide variety of domestic and commercial situations. Other typical applications include domestic appliance control, computer access control, door entry control and moving object control. Typically, the identification key may be associated with a human, animal or some inanimate object, for example a car, which is to be identified.

According to still another aspect of the present invention there is provided apparatus for enabling/disabling the operation of a television, which apparatus comprises means for disconnecting an aerial from the television and means for maintaining the aerial in its disconnected state.

As an alternative, the apparatus may include means for disconnecting the mains supply from the television in addition to or instead of the aerial disconnection means .

The disconnection means may comprise a switch which itself may comprise a latched R.F, relay or a unity gain amplifier.

Preferably, the aerial may be connected, as required, by the use of key means. The key means may be as described hereinbefore. BRIEF DESCRIPTION OF THE DRAWINGS The invention is described further hereinafter by way of example only, with reference to the accompanyi drawings in which:

Fig. 1 is a perspective view of one embodiment an identification key according to the prese invention;

Fig. 2a is a diagrammatic plan view of o embodiment of identification apparatus according to t present invention;

Fig. 2b is a diagrammatic side elevation of t identification apparatus of Fig 2a;

Fig. 3 is a diagrammatic representation of on embodiment of enable/disable apparatus according to t present invention for use in controlling the operatio of a television; Fig. 4 is a diagrammatic plan view of anothe embodiment of identification apparatus and it associated micro-processor control system;

Fig. 5 is a perspective view of a key embodyin the present invention; Figs. 6a-6d illustrate various further embodiment of the key member of the present invention;

Fig. 7 is another annotated diagrammati representation of apparatus embodying the invention;

Fig. 8 is a schematic drawing of electromagneti identification apparatus according to one embodiment o the present invention;

Fig. 9 is a schematic drawing of electromagneti identification apparatus according to anothe embodiment of the present invention; Fig. 10 is a schematic drawing of electromagneti identification apparatus according to a furthe embodiment of the present invention;

Fig. 11 is a schematic drawing of electromagneti identification apparatus according to yet anothe embodiment of the present invention; Fig. 12 is a schematic drawing of electromagnetic identification apparatus according to still another embodiment of the present invention; and

Fig. 13 is a diagrammatic illustration of domestic equipment employing apparatus embodying the present invention. BEST MODE OF CARRYING OUT THE INVENTION

Fig. 1 illustrates an identification key 10 formed of a three dimensional pattern of different coloured plastics material 12-26 disposed in a random pattern. The random pattern of the key member is a particular feature of the present invention since it allows for the cheap manufacture of a plurality of discrete keys which cannot be readily copied. Such a key 10 is formed by the controlled pouring of different coloured liquid plastics material into a mould. The different colours then form a random pattern of coloured plastic which is unique to that particular key. Thus, if a light source is directed at one side of the key 10, a coloured image representing the particular pattern of colours is transmitted from the other side of the key 10. This image is unique to the particular key and by measuring the spacial characteristics of the image any one of a number of keys can be identified. The base region of the key 10 includes a magnetic material 47. The material 47 may comprise a liquid magnetic material which can be light-hardened.

Figs 2a and 2b diagrammatically illustrate apparatus 28 which is arranged to receive and identify such a key 10. The apparatus 28 includes a slot 42 into which the key 10 is introduced. Biased support lugs 32a, 32b project into the slot 42 and are displaced as the identification key 10 moves into the slot 42. The resilience of the support lugs 32a, 32b holds the key 10 against a reflective panel 30. The key 10 is thus held stationary with respect to thr radiation sources 34-38 and a wideband radiatio detector 40. Each of the three sources 34-38 compris a narrow band light emitting diode or the like, whi combine to provide a wide band source with low pow consumption. The signal obtained from the detector 4 is output from the identification apparatus 28 by wa of connection 44 and socket 46. The base region of th slot 42 includes a magnetic reed switch which is close by action of the magnetic material 48 when the key 1 is positioned in the slot 42. The reed switch control the power supply to the sources and detector such tha the detection apparatus is only activated when the ke 10 is fully received in the slot 42. In this manner, "wake up" signal is sent to a control processor whic switches the processor from a dormant state to a ful power-up state, thereby reducing the power consumptio of the apparatus.

In operation, the identification key 10 i received in the slot 42. The sources 34-38 each emi radiation of different bands of wavelength which i directed towards the key 10. Each of the sources 34-3 emit radiation in turn. A first radiation source 3 emits radiation. A reading is then taken on the ke detector 40 and on a compensation detector (not shown)

The ratio of the key detector/compensation detecto output is computed and this value stored. Th radiation source 34 is then switched off and the sourc

36 switched on. A key-detector reading an compensation-detector reading is again taken and further ratio obtained for the source 36. The sourc

36 is then switched off and the procedure repeated fo the source 38. The whole sequence of readings is the repeated and the three ratio values are compared wit the previous results. If the successive ratio value obtained for each detector are within a tolerance of 5%, the readings are accepted. If the readings fall outside this tolerance level, they are repeated up to five times until the readings fall within the acceptable range. The readings then form the characteristic of the key and are stored. When the key member is next used, the above procedure is repeated and the new reading compared with the one previously stored. Generally, the readings will be similar for similar conditions. However, variations in position of scratches on the surface of the key may produce variations in the readings obtained. In order to cope with the residual variation of the radiation obtained from the key member, an adaptive band acceptor is set up. As such any new reading is compared with the previously stored reading and is accepted if it is within 5% of the stored reading. The new reading is then stored and the previously stored reading removed from the memory. In this way, progressive scratching of the key causes the band of acceptability to drift allowing for compensation within the system. The regions of different coloured plastic each act as a filter allowing only one particular wavelength of light to pass therethrough. Thus, a coloured image corresponding to the pattern of coloured plastics of the key 10 is transmitted from the side of the key 10 adjacent the reflective panel 30. This image is then reflected at the panel 30 and transmitted back through the key 10. The image then emerges and the characteristics thereof are measured by the detector 40. Since the pattern of coloured plastic of each key 10 is unique to that key, the image impinging on the detector 40 and thus the signal produced by the detector is also unique to that particular key. Although not illustrated, a predetermined pattern may be provided in a portion of the key member of thi invention to provide a signal indicating correc positioning of the key within the identificatio apparatus. As illustrated in Fig 3, this unique signal is fe to a microprocessor 48 which has been preprogramme with control functions which operate in response to th particular key identified. The main control functio of the microprocessor 48 is that it controls a switc 50 inserted between two lengths 52a, 52b of coaxia cable which lead from an aerial 54 to a television set 56. The switch 50 comprises a switched gai amplifier and is controlled by the microprocessor 48 t be switched between two states. In one state, the aerial 54 is connected to the television set 56 and i the other, the aerial is disconnected therefrom. I this manner, the selective disconnection of th television aerial 54 from the television set 56 serve so as to prevent a picture being displayed on th screen of the television set 56. Alternatively, th switch 50 may control solely the audio output of th television set.

According to the apparatus of the invention, multi-pole switch relay may be used to effect contro of a plurality of apparatus simultaneously.

The microprocessor 48, on identifying a particula key 10, is preprogrammed to prevent the televisio being viewed by a particular key holder. Also, th microprocessor 48 may include a timing function whereb the television can be operated by a particular ke holder only for a predetermined number of hours o minutes. In this way, the time that a person, especially a child, spends watching television eac day, can be controlled. Fig. 4 illustrates a television set 10 having a aerial 12 connected thereto. The aerial 12 is connected to the television 10 by way of a radio frequency latching relay 14 which in turn is connected by way of control lines 15 to a micro-processor control unit 16. A key identification system 18 is connected by way of lines 21 to the micro-processor 16. The identification system 18 comprises an output radiation unit 20, a radiation detector 22 and a reflective backing member 30 spaced from the source unit 20 and detector 22. The source unit 20 comprises three L.E.D. sources, one of which emits red light, another of which emits yellow light and the other of which emits green light.

A key member 28 is illustrated disposed between the source unit 20 and the reflective backing 30. The key member 28 is formed of transparent plastics material arranged to interfere with the radiation emitted from the L.E.D. source of source unit 20. The radiation emitted from the source unit 20 travels through the key 28 and is reflected back therethrough by way of the reflective backing member 30 so as to finally impinge on the detector 22. The detector 22 is a single wideband detector suitable for detecting light from each of the three L.E.D. sources in the source unit 20.

The key 128 has a portion thereof provided with magnetic material (not shown) which influences a magnetic reed switch 40 located in the region of the base of the slot into which the key 28 is located. Thus, once in position, the magnetic material in the key 28 closes the magnetic reed switch 40 so as to indicate that the key 28 is in position within the detector system 18. On closing, the magnetic reed switch 40 sends a signal along lines 42 to the micro- processor control unit 16. The three L.E.D.'s of the source unit 20 also emit radiation towards a dire reading detector 32. The value obtained at the dire reading detector 32 is used to calibrate the k identification system such that a variation in t intensity of radiation output from the source unit 2 does not affect the accurate operation of the syste A standard analogue to digital converter 34 is locat between the output of the direct reading detector 3 and the detector 22 so as to feed digital informati into the micro-processor control unit 16. A pus button panel 54 and liquid crystal display 52 ar connected to the micro-processor control unit 16 by wa of control lines 50.

In use, a parent programmes the micro-processo control unit by way of the push button panel 54 an liquid crystal display 52 to allow a certain key 28 t enable operation of the television 10 for predetermined amount of time only. Thus, with particular key 28 located in the detection system 18 and thus the micro-processor control unit 16 receivin that key's unique identifying signal by way of th detector 22 and the analogue to digital converter 34, parent can input for example three hours. Thus, whe the child whose key that is wants to watch television the key 28 must be inserted into the detection syste 18. Since the micro-processor control unit reads tha there are three hours in credit for that particula key, the aerial 12 is connected to the television se 10 by control of the radio frequency latching relay 14 The child will then be able to watch the television However, if the child watched three hours television o watched one hour and then returns to watch a furthe two hours, that child will have used up all of th three hours credit that was previously programmed int the micro-processor control unit 16 and the unit 1 will open the radio frequency latching relay so as to disconnect the aerial 12 from the television set 10. Thus, that particular child has only been able to watch three hours television. The control unit 16 then inhibits use of the television until the end of the week, when the key 28 is automatically re-credited with the three hours for use during the next week. At any time of course, the parent may reprogramme the micro¬ processor unit 16 so as to credit the childs' key 28 with more viewing time.

The liquid crystal display 52 is also included so as to improve the practicalities of the present invention. As such, a child can insert key 28 and, by way of the liquid crystal display 52, may investigate how much viewing time they have left on credit and thus plan ahead which particular programmes they want to watch.

The micro-processor control unit 16 is extremely versatile since it also allows a parent to prevent a child using the television apparatus after a particular time. Also, since a television programme can be recorded directly onto a video recording machine, a similar unit can also be provided to prevent use of such machines during particular times of the day or night.

From the above, the illustrated embodiment of the present invention provides the family with the ability to preset the amount of viewing time available to each member of the family. The apparatus can also be used as a policing device rather than an absolute control device.

The apparatus may also be provided with an override button, incorporated so as to allow any person to sample the television programmes on offer without the necessity of inserting a key. To improve the effectivness of the apparatus the present invention a security device 43 is connect by way of line 46 to the micro-processor control un

16 so as to indicate if the apparatus has been tamper with.

As can be seen from the above, the apparatus the present invention provides for the followi advantageous features:

A method of positively identifying each user; method of setting up and programming the apparatus; method of using the apparatus to watch programmes; method of inhibiting programmes from being watched wh not authorised and a method of detecting and indicati interference or tampering with the apparatus. The optical key system forms the basis of particularly advantageous embodiment of the prese invention. The key is generally longitudinal with hexagonal cross-section, one of the faces of t hexagonal key being concave in shape. The concave fa improves the security of the location of the key with the detection system 18. The key 28 is formed of random variegated pattern produced from three prima coloured translucent dyes. Also, the detector 22 m comprise a light dependent resistor or a single phot darlington transistor.

A particularly advantageous sequence of events fo taking a key measurement are as follows:

Detect magnetic reed switch 40 closure on key 2 entry; Wake up micro-processor 16;

Wait 0.5 seconds to avoid residual key vibratio on placement;

Turn on red L.E.D. and wait 100ms for stability; Measure output from detector 22; Measure output from direct beam detector 32; Calculate and store ratios, together with upper and lower boundaries of acceptability; Display information to user; Repeat with yellow and green L.E.D.'s; Put micro-processor to sleep until when next required.

Thus, the micro-processor is now "primed" such that the next time that particular key is inserted into the detection system 18 the micro-processor will be able to associate that key with the necessary information relating to the number of hours watched, the time of day the television was watched and the channel that was watched.

According to an alternative embodiment, the control apparatus may act so as to selectively connect the power supply to the television set. As such, the mains may be switched by way of a thyristor triac switch.

The tamper detector device 48 may operate so as to monitor the capacitance of the aerial so as to record a sudden change in the capacitance thereof. Such monitoring can be carried out by monitoring for voltage changes or current changes in a trickle current input into the cable or by observing for a change in frequency of a capacitance controlled oscillator.

The invention is not restricted to the details of the foregoing embodiment. For example, any particular key means may be used to enable use of the television apparatus. Fig. 5 illustrates a preferred optical embodiment of a key member according to the invention. The key comprises a tongue portion 60, one side of which is provided as a convex surface 62 and the other side 64 of which is flat. The flat side 64 has a concave groove 72 formed in its surface and one end of the tongue member is provided with handling means 66. Th tongue portion 60 is advantageously formed of plastic material suitably adapted or arranged to interfere wit radiation incident thereon in accordance with th invention. The groove 72 provides a concave optica surface which is not readily contacted, and thu damaged by, key mounting means or otherwise.

A variety of shapes of the optical key membe according to the present invention is illustrated i Figs 6a - 6d. Fig. 6a shows a key member for use in typical domestic application. The key member having a hexagonal key body 86 is provided at one end with a magnet 88 and at the other end with an ambient light shield 90. A hand grip 92 extends from the side of the ambient light shield remote from the key body 86. The hexagonal shape allows for accurate location of the key member in associated detector apparatus. One of the faces of the key body 86 is provided with a concave surface so as to ensure constant orientation of the key member in detection apparatus and also to provide for efficient radiation transmission

Fig. 6b shows the shape of a key member according to the present invention which is particularly suitable for a security door system. The key member is arranged to be worn as a ring and comprises an annular ring body 94 carrying a key body 96 which includes a multi¬ coloured crystal-cut surface. A back plate 98 extends from the ring body 94 and acts so as to block ambient light when the key body 96 is inserted into the detector apparatus.

Fig. 6c illustrates a member having an elongate key body 100 which has a weighted bottom end 102. Such a key is arranged to pass through detector apparatus under the influence of gravity. Fig. 6d illustrates a key member arranged to be attached to a moveable shuttle or other carriage member, which key member comprises a body 104 having a regular pattern 106 formed on the underside thereof, which pattern is used to calibrate the detection apparatus as the key member moves therethrough.

From the above, it is apparent that the key of the present invention is ideally suited for applications where low cost security is required, such as in domestic situations. In particular, it is suitable for applications where a community of users of an appliance must be individually identified. For example, the control of TV or video apparatus where there is a desire to limit or control the access of a group, in particular children, to the equipment. A further example of a domestic application is within a telephone hand-set, so that individual users can be identified and billed separately.

The system is also suitable for integrating within computer terminals, cash registers and personal computers as a means for identifying the users and for authorising access to the apparatus. Further, a key fixed to a moving vehicle provides a unique fingerprint when scanned by a roadside detector.

When used for the control of television operation, the key detection control apparatus may be used in association with a common aerial feeding a plurality of television sets. As such, use of all the sets may be controlled by the control apparatus, or alternatively the control apparatus may control each individual aerial feed to each television set.

Also, as an alternative to enabling use of the television set by way of controlling the aerial or power connection to the television set, the set may be selectively enabled/disabled by selectively introducing interference to the required channel. As such, it is possible to block out the television's reception of on or more channels for a predetermined period, In thi manner, and in combination with the identification ke and system outlined above, a reliable televisio monitoring system is provided.

When preventing use of a television set, th system is only effective as a means of control if i prevents even the most intelligent children fro gaining uncontrolled access without being detected Although the key and detector are secure, other area must be protected.

If the batteries are removed and replaced, th system powers up in the programming mode. Whilst thi will allow the user to watch television or chang allocation, keys can only be programmed if located i the detector. As soon as a genuine user attempts t use a master key, it will be rejected and the attempte tampering with the device will become obvious.

A more obvious method of tampering with the syste is to remove the aerial leads. The vital lead t protect is the lead from the device to the television.

A simple method is to fix a plastic clip between the cable and the television chassis, such that the plug cannot be removed without breaking the clip. A more satisfactory method is to monitor the cable for violations as previously described. This can be monitored by checking for current changes in a trickle charge into the cable, or by checking for a change in frequency of a capacitance controlled oscillator. If the key of the present invention is seen by a potential system misuser, the key cannot be readily copied. If the key is stolen, its loss can be reported and authorisation for that key readily removed.

Cash registers in shops and other commercial uses are generally equipped with a mechanical key to authorise changing of till rolls and till disablement etc. Such a key is combined with a numerical codeword typed into the register. A key system according to the present invention which detects and identifies each of a number of users, giving each a particular level of access, further improves the capability of the system.

The device allows users to log-on to a computer hardware unit by insertion of a key into a terminal. Programming flexibility is fully available to programme the access available to each key. It is also possible for a key to be used in any one of a number of separate detectors on different terminals.

The device comprises a small module which can be supplied to terminal manufacturers, personal computer manufacturers, or cash register manufacturers, as an O.E.M. module for incorporation into their products. As such, the system comprises a set of user keys and a compact stand-alone detector module.

The key and detector systems previously described is also suitable for this application. However, simplification can be provided for. The module can remain in power-on mode whenever the terminal is on. Key entry detection can be accomplished by way of optical key-detection means. The additional element which is required is a means of communicating with the system processor. A suitable protocol can be devised for each system, either with a simple AUTHORISE/DENY output, or with a more complex serial or parallel control link. Advantageously, this can be by way of a serial link to the main computer. In the case of a remote terminal, the existing terminal link can be used. In the case of a P.C. or cash register, a separate link is preferred. It is possible to read and store key characteristics in the module, carrying out any ratio calculations required, and informing the system when a new key has been entered. The syste processor can be charged with storing all ke characteristics, reading modules on demand, determinin acceptability, and allowing the appropriate termina access. This is simply accomplished through a application program running on the system.

In some situations it may be more useful to trea the key module as a peripheral device, equipping i with a parallel bus for direct access to the syste bus. In either way, the system communicates with th module using I/O commands to read or set register within the module. An interrupt line to inform th system of key entry is also advantageous.

In such a way a very low cost module is possible comprising electro-optical devices and a bus compatibl Analogue/Digital converter, with all processing an intelligence residing in the main system.

An access control system is illustrated by way o the annotated diagram in Fig. 7. In some situations it is necessary to contro access to a particular location, and a programmabl system, capable for use with a wide range of users, i required. In some complex multi-area systems, different users have access to different areas. Suc systems are in common use in many locations, generall using swipe card technology. This solution i unsatisfactory, however, since such cards ar vulnerable to damage, are easily lost or misplaced, security is low and the detectors are relativel expensive. A low cost high security reliable syste employing the key means of the present invention is particularly advantageous.

The system is designed to maximise security and reliability and minimise cost, while being convenient and simple to use. The system can either be designed as a stand-alone access control module, to be mounted into a gate control mechanism or door, or it can be designed as a module which reports to a centralised wide area access control system. Programming of the system is possible from a detector, or if organised as part of a system, from one designated detector.

Each key can be detected in each of a number of separate detectors with minimum deviation of the measured signal.

The system can comprise the following elements: a means for positively identifying users; a means for setting up and programming the devices; - a means for using the device.

The optical key device hereinbefore described is suitable for this application; the key being particularly arranged to be carried on a keyring. A particularly advantageous key, however, comprising a micro-key, mounted on a ring and worn on the users finger. The key device consists of a variegated pattern of translucent colours, with each key having a slightly different pattern. The shape of the key surface is crystal cut to give an attractive appearance, and to aid accurate placement in the detector. The key is mounted on a metal ring, with a reflective coating between the key crystal and the ring mounting. In this way, when the key is placed into the detector, the source beam is reflected back to the detector. The key is designed to ensure only one orientation of the key in a detector is possible.

The source detector mechanism must be modified for this application. In this case, it is not acceptable to have to wait the short time required to switch between a number of restricted bandwidth L.E.D. outputs. The preferred solution is to use a wi bandwidth Tungsten filament lamp at the centre of t ring crystal, with a number of filtered detecto surrounding. In this way, a number of simultaneo readings can be taken, providing a high degree security. Each detector is generally accurate to bits. An array of 6 detectors would provide for 2.5 10 to power 15 potential variants.

The detector must ensure that the direct optic path between the Tungsten bulb and the detector arr is blocked, and that the ring mount backing effectivel shield the detectors from all ambient radiation. seventh detector is required to provide direc monitoring of the bulb output to enable the necessar ratios of direct signal/reflected signal to b calculated.

The detector measurement and calculation proces is identical to that previously described; with th results being passed on to the door lock or gat control device or to a centralised controller i required.

Fig. 8 is a schematic drawing illustratin electromagnetic means for reading the identification o a key member 260. The key member 260 has a randoml varied pattern of dielectric material such that whe the key is located in between two parallel plates 261

262 of a capacitor device, the capacitance of tha device is altered in accordance with the electri permitivity of the key member 260. As can be seen i the drawing, one of the capacitance plates 26 comprises a plurality of smaller plates thereby formin a corresponding plurality of capacitors. Th capacitance of each capacitor will be dependent upo the portion of the key member 260 located between tha particular plate and the larger plate 261. The valu of capacitance can be measured by obtaining values of the time-constant t, that is the time for the capacitor to gain or lose 63% of its final charge. The value of the time constant t is then used in the equation t = cr, where c is the capacitance and r the known value of resistance disposed in series with the capacitor arrangement. As above, since the value of capacitance measured at each small plate capacitor is dependent on the random pattern of the dielectric medium in the key member 260, the values of capacitance obtained will be a unique value relating to that particular key^' member. A capacitance measurement device 266 is connected to the large plate 261 via connection lines 267 and to each of the small plates 262 by way of connections lines 264 and a selection switch device 265. As a further development, the temperature sensitive detector 263 is included and connected to a micro-processor controller so as to compensate for variations in the dielectric constant of the dielectric medium with fluctuations in the temperature thereof.

Fig. 9 illustrates apparatus which employs the characteristics of piezo-electric materials for the purpose of the present invention. The apparatus comprises two parallel plates 269, 270 in between which a key member 260 is located for identification. The key member 260 is formed of a random pattern of piezo¬ electric materials and the parallel plates 269, 270 are connected to a voltage supply 273 which develops an electric field across the plates. When the electric field is applied to the key member 260, the piezo¬ electric materials polarise and then relax once the electric supply field is removed. The gradual relaxing of the polarises materials occurs over a period of time which may be of the magnitude of hundredths of a second. The measurement of the polarisation at vario locations in the key member 260 may be obtained by w of Hall effect devices 271 located adjacent the low regions of the parallel plates 269, 270. The relaxi of the polarisation and thus the measurements taken the devices 271 will be dependent upon the particul random pattern of each key member 260 and wil represent a signal by which a key member 260 can b identified. The apparatus operates under control of micro-processor to which signals are fed from th devices 271 by way of an analogue/digital converte 272. The voltage supply 273 is connected to th parallel plates 269, 270 by supply lines 274.

Alternatively, a random distribution o ferromagnetic materials can be provided in a key membe and key detection carried out by way of apparatus a illustrated in Fig. 10. According to this apparatus the key member 53 having the random distribution o ferromagnetic materials disposed therein, for exampl iron filings, is introduced into a key receiver 5 having a plurality of energising coils 57 locate around its periphery. The energising coils 57 ar arranged to produce a static magnetic field having complex flux pattern dependent on the dispersion of th ferromagnetic material in the key member 53. This flu pattern is detected by means of Hall effect devices 5 connected via a selector switch and analogue/digita converter to the micro-processor via lines 63 Electrical connection lines 61 connect the energisin coils to the micro-processor also. Since each of large plurality of key member 53 will have a uniqu random distribution of the ferromagnetic materials each key produces a unique flux pattern which can b read by the Hall effect devices 59 so as to identif that particular key member 53. As illustrated in Fig. 11, the present invention may also provide for key identification apparatus exploiting the mutual inductance between two coils. In this case, a key member 275, having a random distribution of ferromagnetic materials therein, is received in a key holder 276 having an energisation coil 278 and three detection coils 277 located therearound. The energisation coil 278 is connected by way of line 281 to an alternating voltage source 280, which connection may be controlled by a micro¬ processor. The detection coils are connected by way of lines 282 through a current/voltage detector 279 and to the micro-processor. The arrangement of the apparatus is such that the energising coil 278 is connected to each of the detection coils 277 by way of a mutual inductance which is dependent on the magnetic properties of the key member 275. The particular magnetic properties of the key member 275 being provided by the random distribution of the ferromagnetic materials therein. Accordingly, an alternating voltage supplied by way of voltage source 280 and line 281 in the excitation coil 278 will induce a corresponding alternating voltage in the detection coils and the value of the voltage so induced is representative of the dispersion of the ferromagnetic materials in the key member and so provide identification of that particular key member 275. The greater the number of detection coils employed in the apparatus of Fig. 11 , greater is the detection sensitivity of the apparatus which increases the number of key means which can be employed with that apparatus.

Fig. 12 illustrates apparatus arranged to produce relative movement between the electric field and the key member 275. The apparatus comprises a key holder 276 for receiving the key member 275 around which two excitation coils 283, 284 are located in a mutuall perpendicular location. The excitation coil 284 i connected by way of connection lines 288 to a alternating voltage source 287 and the excitation coi 283 is connected by way of lines 290 to an alternatin voltage source 289. The two voltage sources 287 an 289 generate a.c. signals which are 90 out of phase A Hall effect device 285 is located adjacent the lowe region of the key holder 276, as shown in the drawing and is connected by way of lines 290, an analogue digital converter 286 and lines 291 to a micro processor. The micro-processor is also connected t the alternating voltage sources 287, 289 via lines 292. The phase shift between the a.c. signals provided b the sources 287, 289 and the mutual location of th excitation coils 283, 284 provides for a rotatin electric field which impinges on various regions of th key member 275 as it rotates. Measurements of th electric field, as influenced by the rando distribution of ferromagnetic materials in the ke member 275, is taken at predetermined times during th period of the a.c. signals and a two-dimensional map o the dispersion of the ferromagnetic materials in th key member is obtained. The details of such a map provide for apparatus which can accurately read the various random dispersions of the ferromagnetic materials of a large plurality of key members.

Fig. 13 is a diagrammatic illustration of apparatus according to an embodiment of the invention as employed in a domestic situation, wherein it is desired to control access to a main television 801 , a portable television 120, a video system 100 and a home computer 905.

Three sets of apparatus 140, 150 and 160 are required to effect control. A household aerial cable 180 is used for communication between each apparatus to ensure consistency. Each control apparatus 140, 150 and 160 is configured slightly differently to interact in an optimum way with the surrounding equipment and environment. Control apparatus 140 is configured to control the main television 801 and the video 100, and as such is arranged to switch two signal leads simultaneously via a relay device 304. Control apparatus 160 is used to control the portable television 120 and, as such, is arranged to switch an interference signal from a microprocessor unit 105 via a link field 556 and into the television 120. Control apparatus 150 is used to control the mains driven home computer 90 and, as such, is arranged to switch a mains electricity supply 170. Alternatively, the control apparatus is arranged to short-out the aerial connection and so disable the television apparatus.

An incoming signal from the aerial 110 is carried by a coaxial cable 180 to each of the control apparatus 140, 150 and 160 via an optional power supply unit 130.

Normally, the aerial cable 180 is connected directly to the video system 100, and then onto the television 801. This configuration allows unrestricted use of the equipment. However, in Fig. 11, the aerial cable.180 is connected to a socket mounted internally within the apparatus 140 and the cable 180 is held therein by a clamp so that the plug can only be removed from the socket by gaining access to the internal area within the apparatus 140 by removing an inspection panel 704. The signal is passed from the coaxial cable 180 onto a switching device 304 which, in this embodiment, comprises a latching relay. The signal then passes via a fixed coaxial cable 454 to the video system 100 aerial input plug. The apparatus 140 may now be used to control the recording of programmes by the video 100 and input by way of the aerial 110.

The video output socket from the video unit 100 i connected to the apparatus 140 via a further interna coaxial socket. This particular signal line leads to second switching pole on the latching relay 304. Th output from the latching relay 304 is fed, via a secon fixed coaxial lead, to the aerial input socket on th television 801.

In this manner, the apparatus 140 can be used t simultaneously enable or disable use of both the vide unit 100 and he television 801.

The latching relay 304 is controlled via control lines 254, by a microprocessor unit 104. The microprocessor unit 104 is typically a readily available single chip device containing programme memory, data memory, input output lines, LCD driver, keyboard scanner, time of day clock, interrupt lines, a serial Input/Output (I/O) port and other features. Such a device advantageously has a low power consumption and may be put into a "sleep mode" (Minimum power consumption) and awakened by interrupt only when required for use. Such a device, together with a latching relay 304, allows for the use of battery powered apparatus. The microprocessor unit 104 makes use of its scanning circuits to input information from a keypad 354 thereby allowing users to programme operating the mode of the apparatus.

The display driver outputs of the microprocessor unit 104 are used to drive a custom LCD display device 404 to provide the user with basic information on the status and operation of the apparatus.

An identification, or key, system 154 is used for the identification of an individual user of the apparatus 140. The identification system 154 may be a magnetic card reader, key switches, or some other means as hereinbefore described. Alternatively, a code is assigned to each user and entered via the keypad 35.

The control apparatus 140 has detection devices 206 connected to the output signal lines 456 thereof. The devices 206 are used to detect attempts at interfering with the operation of the system by removing aerial plug from the apparatus 140 and replacing it with alternative signal source. The devices 206 monitor for changes in capacitance or impedance in the coaxial lines 45 by various known means particularly as hereinbefore described.

Communication between the microprocessor 104 of apparatus 140 and microprocessors 106, 105 respectively, is effected by making use of the serial Input/Output (I/O) lines on the microprocessor units 104, 105, 106 modulated by respective circuits 504, 505, 506, to a frequency outside the range of the signals input to the systems being controlled. This modulated signal is thus transmitted along the aerial cable 180 to each of the control apparatus 140, 150 and 160.

Access to the components of the apparatus 140 is by way of an access panel 704 only. As such, any attempt to remove the panel will force a reset of the system by removal of power from a battery 754 via access panel 704 to the microprocessor unit 104. Alternatively, the access panel 704 may be used to drive a rest line to the microprocessor 104. If it is required to control a portable television 120 having its own integral signal source, a different configuration must be used. In this case, either the power supply to the equipment is controlled, or the external aerial socket from the portable television 120 is connected to the apparatus 160, as in apparatus 140. If this is done, the television 120 may be controlle either by arranging for the latching relay 306 t short-out the signal cable 456 sheath to core, or ma introduce an interference signal from an oscillato device on the microprocessor 106 a via link field 55 and relay 306 onto the signal line, thereby making th signal unusable.

If it is required to control a device via th power supply, as in the case of the home computer 905 the apparatus may be arranged according to apparatu 150. In this case, a mains latching relay 305 is use to control the equipment 905, by enabling and disablin a power supply from the source 170. Communicatio between the apparatus 150 and other control apparatu 140, 160 within the household, may be possible b connecting the apparatus 150 to the aerial cable 180. As a further optional feature, a mains power unit 13 is connected to the aerial cable 180 to provide a lo voltage d.c. power source via the aerial cable 180 t each control apparatus 140, 150, 160, thus removing th need for an internal power source. The circuit 65 ensures correct polarity, and regulation/curren limiting features. Note that if this feature is used, the method of detecting interference via capacitiv monitoring of the aerial cable is not preferred.

Each display 404, 405, 406 is also included so a to improve the practicalities of the present invention. As such, a user can insert their particular key o identification means into the detector 154, 155 and b way of the liquid crystal display 404, 405, 406 ma investigate how much usage time they have left o credit and thus plan ahead which particular activitie or programmes they want to access.

From the above, the illustrated embodiment of the present invention may provide a family with the ability to preset the amount of usage time available to each member of a family. The device can also be used as a policing device rather than an absolute control device, whereby usage times are displayed, but access is never denied.

In use, the system must first be programmed to identify all potential users, and programmed with the authorised parameters for each user.

This programming stage may be effected on any control apparatus 140, 150 or 160, only by the holder of a master key or identification code. Prior to programming, each control apparatus is in a reset state, but aware of the state of the other apparatus due to the serial data link via the aerial cable 180 between the connected apparatus.

When the first key or identification code is entered via the key detector 154, 155, 156 or alternatively via the keypad 354, 355, 356 respectively, the key or identification code is recognized henceforth as a master identification key or code by each control apparatus. The apparatus used to first identify this key or code is also defined to be the master apparatus for communication protocol purposes. From that time, further access keys or codes may be programmed from any connected apparatus, but only under authorisation from the master key. If the master key is lost or otherwise misplaced, the system must be reset by removing the access panel 704, 705, 706 or battery 754, 755, 756. This procedure allows a new master key to be programmed. Attempts by unauthorised users to foil the system by causing a reset, allowing for programming to a new master key will be detected and foiled, since keys cannot be programmed unless present, and the holder of the original master key would subsequently find access barred to the old master key, making detection of th interference inevitable.

A regular "watchdog" communication message is sen between all connected apparatus to ensure that n existing apparatus is removed from the circuit, an that no new apparatus has been added. Such an actio will set an alarm message on the display 404, 405, 40 which can only be reset by use of a master key.

The master key also allows access to the keyboar 354, 355, 356 which may be used together with th display 40 to preset each users' parameters.

For example, a parent may set a childs' key t allow 15 hours of use, which must not be taken befor

5.30pm, or later than 8.00pm. These parameters ar shared amongst each control apparatus 140, 150 and 160

The child may wish to watch the main television 801 but first wants to find out which programmes ar currently showing. A special "sample" button, (no shown) located on the keyboard 354 may be used fo this. On pressing the sample button, immediate acces is given to the equipment 801 and 100 by way of th apparatus 140. This access is given without referenc to any key or identification system, but is restricte to a fixed time for example, one minute, which may no be repeated more than once in a set period, for exampl

5 minutes.

Having decided that one of the programme currently showing on the television 801 is wort watching, the child may insert its identification ke into detector 154, or provide the access code into th keypad 354. At this point, the pre-authorised usage parameters are checked. If these parameters are accepted, the relay 304 is switched on to give access to the equipment 801. The remaining time available to that user is displayed continuously on the LCD 404, allowing each user to note usage of their time allocation, and so control that usage. This time allocation is decremented each minute until the key is removed, thereby inhibiting use of the equipment 801. The rates of usage are communicated directly to each control apparatus 140, 150 and 160, so allowing the child to use up their allocation as required on any of the available equipment 801, 100, 120 or 90. For example, a child may use up five hours on the main television 801, seven hours on the portable television and three hours on the home computer and thereby exhaust their allotted accessing period. The apparatus will then bar access to all connected equipment until the end of a preset period, usually a week, whereupon the authorised usage is reset to the original value for the next period of, for example, one week.

As can be seen from the above, the apparatus of the present invention provides for the following advantageous features: A method of positively identifying each user of household equipment, a method of setting up and programming the said apparatus, a method of using the apparatus to access the equipment, a method of inhibiting television programmes from being watched when not authorised and a method of detecting and indicating interference or tampering with the apparatus.

The invention is not restricted to the details of the foregoing embodiment. For example, various identification systems may be used and the apparatus may also be used to control other equipment where control of shared usage is a problem such as access to bathrooms or other particular locations.

Claims

1 . A key compris ing a key member arranged t modify radiation from a radiation source so as t provide radiation identifying the key member.

2. A key as claimed in claim 1 , wherein th member comprises material having non-uniform refractiv index.

3. A key as claimed in claim 2, wherein th material is of non-uniform density.

4. A key as claimed in claim 1, 2 or 3, wherei the key member comprises wavelength selective material

5. A key as claimed in claim 5, wherein th member comprises material of at least two differen colours.

6. A key as claimed in any one of claims 1 to 5 wherein the member includes a plurality of opaqu elements.

7. A key as claimed in claim 6, wherein at leas one opaque element is radiation reflective.

8. A key as claimed in any one of claims 1 to 7 wherein the key member includes a fluorescent material

9. A key as claimed in any preceding claim wherein the key member is formed of plastics material.

10. A key as claimed in claim 9, wherein the ke member is formed from light curable plastics material.

11. A key as claimed in any preceding claim wherein the key member has a concave surface providin a radiation entry or exit region.

12. A key as claimed in claim 1, arranged t interfere with electromagnetic radiation.

13. A key as claimed in claim 12, wherein the ke member has a dielectric material therein.

14. A key as claimed in claim 12, wherein the key member has a piezo-electric material therein.

15. A key as claimed in claim 12, wherein the key member has a ferromagnetic material therein.

16. A key as claimed in any preceding claim wherein the key member includes a random pattern of material for modifying the radiation.

17. A method of forming a key member comprising introducing at least two materials, of different radiation reactive properties, into a mould and allowing at least one of the materials to harden.

18. A method as claimed in claim 17, wherein the materials filter light of different wavelengths.

19. A method as claimed in claim 18, wherein the materials are mixed with a translucent dye.

20. A method as claimed in claim 17, 18 or 19, wherein at least one of the materials comprises a plastics material.

21. A method as claimed in claim 20, wherein the at least one material comprises liquid plastics resins.

22. A method as claimed in any one of claims 17 to 21 , wherein one of the materials includes an opaque material.

23. A method as claimed in claim 22, wherein the opaque material comprises a plurality of opaque elements.

24. A method as claimed in any one of claims 17 to 23, wherein the material to be hardened is light curable.

25. A method as claimed in any one of claims 17 to 24, wherein the materials are introduced to the mould under the control of micro-processor control means.

26. A method as claimed in any one of claims 17 to 25, wherein at least one material is introduced so as to form a random pattern.

27. Access control apparatus comprising means fo identifying a prospective user of apparatus to b accessed and means for selectively enabling use of th apparatus on the basis of the identification of th user.

28. Control apparatus as claimed in claim 2 including means for recording the amount of time a use has accessed the apparatus.

29. Control apparatus as claimed in claim 27 o 28, wherein the means for selectively enabling use o the apparatus includes means for indicating the perio for which a user has accessed the apparatus so tha apparatus-disabling steps can be taken.

30. Apparatus as claimed in claim 27, 28 or 29, wherein the apparatus to be accessed comprises television receiver apparatus.

31. Apparatus as claimed in claim 30, which enables use of the television apparatus by controlling the display function of the television screen.

32. Apparatus as claimed in claim 31, arranged so as to selectively connect a television aerial to the television apparatus.

33. Apparatus as claimed in any one of claims 30 to 32, wherein the means for selectively enabling use of the television apparatus includes a latched R.F. relay switched gain amplifier, or semiconductor switch.

34. Apparatus as claimed in claim 30 or 31 , arranged to control the electrical power supply to the television apparatus.

35. Apparatus as claimed in any one of claims 27 to 34, arranged to be enabled by key means.

36. Apparatus as claimed in claim 35, wherein the key means includes a numerical key pad.

37. Apparatus as claimed in any one of claims 27 to 35, arranged to receive key means as described in any one of claims 1 to 16.

38. Apparatus as claimed in claim 37, including radiation source and detector means.

39. Apparatus as claimed in claim 37 or 38 arranged to receive a plurality of key means.

40. Apparatus as claimed in any one of claims 27 to 39, including a band-pass filter for selectively filtering signals received by the apparatus to be accessed.

41. Apparatus as claimed in any one of claims 27 to 40, including timer means for presetting activation of the enabling/disabling means.

42. Apparatus as claimed in any one of claims 27 to 41 , including monitor means for monitoring the length of time the apparatus is used after being enabled by at least one of a plurality of users.

43. Key identification apparatus comprising means for receiving a key, at least one radiation source and at least one radiation sensitive detector for detecting radiation from the source which has been interfered with by the key.

44. Apparatus as claimed in claim 43, including three radiation sources, each of which emits a respective one of the three primary colours.

45. Apparatus as claimed in claim 43 or 44, wherein the radiation source and radiation detector are located on a common side of the key means and the apparatus includes radiation reflector means located on the opposite side of the key means to the source and detector.

46. Apparatus as claimed in any one of claim 43, 44 or 45 and arranged to provide relative movement between the key means and radiation emitted from the source.

47. Apparatus as claimed in claim 46, includin movable radiation reflection means for moving th radiation relative to the key means.

48. Apparatus as claimed in claim 47, wherein th radiation reflection means comprises a mirror or prism

49. Apparatus as claimed in claim 46, includin carriage means for passing the key means therethrough.

50. Apparatus as claimed in claim 49, wherein th key means is arranged to move under the influence o gravity.

51. Apparatus as claimed in claim 43, having capacitor device arranged to receive the key mean between plates thereof and means for measuring th capacitance of the device.

52. Apparatus as claimed in claim 43, having coil means for developing an electric field across the key means.

53. Apparatus as claimed in claim 52, having means for measuring the electric field as influenced by the key means.

54. Apparatus as claimed in claim 53, having means for developing moving electric field.

55. Apparatus as claimed in claim 52, having a plurality of coil means and means for measuring the mutual inductance between at least two of the coil means.

56. Apparatus as claimed in claim 43 having means for measuring the time constant of a relaxing polarised piezo-electric material.

57. Apparatus as claimed in any one of claims 43 to 56, including means for detecting the correct location of the key means therein.

58. Apparatus as claimed in any one of claims 43 to 50, including ambient radiation compensation means.

59. Apparatus as claimed in any one of claims 43 to 58 and arranged to receive a key as claimed in any one of claims 1 to 16.