WO1992007336A1

WO1992007336A1 - Apparatus for determining the position of an indicating object above a reference surface

Info

Publication number: WO1992007336A1
Application number: PCT/NL1991/000196
Authority: WO
Inventors: Johannes Jacobus Duimel
Original assignee: Exact Dynamics B.V.
Priority date: 1990-10-10
Filing date: 1991-10-10
Publication date: 1992-04-30
Also published as: AU8748391A; NL9002205A

Abstract

Apparatus for determining the position of an indicating object above a substantially rectangular reference surface, comprising two series of light emitting means positioned near the circumference of said reference surface for emitting light at least substantially parallel to the reference surface and at short distance thereof, and light detecting means positioned near the corners of the reference surface for detecting the light emitted by said light emitting means and for generating a therewith corresponding electrical signal. One of the series of light emitting means can be replaced by a mirror, providing an apparatus with significantly reduced number of components which can be accommodated in an easy to handle housing.

Description

Apparatus for determining the position of an indicating object above a reference surface.

The invention relates to an apparatus for determining the position of an indicating object above a substantially rectangular reference surface, comprising: light emitting means positioned near the circumference of said reference surface for emitting light at least substantially parallel to the reference surface and at short distance thereof, light detecting means positioned near the circumference of the reference surface for detecting the light emitted by said light emitting means and for generating a therewith corresponding electrical signal, driving means for activating the light emitting means, signal processing means for processing the signals generated by said light detecting means, and a processor circuit for selectively activating the driving means and the signal processing means to identify those combinations of light emitting means and light detecting means between which the light path is interrupted because of an indicating object positioned near the reference surface.

Such an apparatus is known from the American patent US 4,703,416. In this prior art system the light detection means are embodied as two elongated series of light sensors arranged along the two opposite sides of the rectangular reference surface and at short distance above this surface. The light emitting means are embodied as four light sources, which are.positioned at the four corners of the rectangular reference surface each adjacent to the respective ends of the two series of light detection means. Both light emitters, which are present near the ends of the one series of light detection means emit light in the direction of the other series of detection means and vice versa. The light detection means are each connected to a signal processing circuit for amplifying, filtering and eventually shaping of the relatively weak signal delivered by the actual sensor. The processor circuit is used to scan the various light detectors in a predetermined order whereby the light transmitters, directed to these detectors, are in operation, such that in case an n a ng o ec suc as , brought near the reference surface the combination of transmitter and light detector can be determined whereby the light path between both is interrupted. After these combination(s) is (are) determined, the position of the indicating object above the reference surface can be derived by solving a number of goniometrical position determination equations. For that purpose use can be made of a programmed processor of a computer.

A first disadvantage of this prior art apparatus is that light is emitted by four light transmitters which are positioned near the corners of the reference surface whereas two series each with a relatively large number of light sensors are used to accumulate and detect this light. Each of this light sensors is during operation connected to a circuit by means of which the signal delivered by the respective sensor is shaped, amplified, filtered to eliminate as far as possible any ambient influences and otherwise shaped to adapt the signal for further processing. Especially such a circuit has to be able to discriminate between the relatively weak light pulses from the light transmitter and the ambient light. That implies that very sensitive and selective circuits have to be applied. Especially in case the light sources are transmitting relatively weak light pulses and the light sensors there¬ fore will deliver relatively weak signal levels such signals can be relatively expensive. In many cases each of these circuits has to be adjusted separately and sometimes also a screened housing is necessary to exclude disturbing external influences.

It is indicated in said US patent that a multiplexer can be used to connect the various detectors to a common detector circuit, but this multiplexer has to be able to switch the relatively weak detector signals and therefor has to fulfil very stringent requirements. In the described embodiment of the apparatus an AD-converter is used to realize a comparator function which is necessary to distinguish the desired light pulse from the ambient noise. Also this AD-converter does not add to the simplicity of the apparatus.

The object of the invention is now to indicate in which way these disadvantages can be eliminated. This object is fulfilled in the apparatus described in the heading paragraph in that the light emitting means comprise two series ^"of light sources, which during operation are arranged along opposite edges of the references surface and at said stance a ove the re erence sur ace, t at t e ig t etect ng means comprise light detection elements which during operation are positioned near the ends of the series of light sources near the respective corners of the reference surface and at said distance above the reference surface, and that the apparatus comprises selection means for selecting the drive means in a predetermined order to activate thereby the. corresponding light sources.

This apparatus comprises only four light sensors with corresponding sensitive signal processing circuits, whereas in the prior art apparatus this number can be many tenth's. The applied series of light sources can be activated in a predetermined order for instance by means of very simple digital multiplexer or another digital selection circuit which is known as such without the necessity to use very sensitive or otherwise electronic components. In relation to the prior art apparatus a significant reduction in the number of relatively expensive electronic components is obtained. The major part of the necessary components is of a commonly available type which do not have to fulfil stringent requirements. This will lead to a reduction of the cost of the apparatus as a whole. In the above described embodiment of the apparatus according to the invention both series of light sources are arranged along opposite edges of the reference circuit. That implies that wires are necessary to connect the respective series of light sources and the thereto adjacently positioned light detectors to the remaining electronic circuits, especially to the processor circuit. Depending on the circumstances this can be considered as a disadvantage. In a further embodiment of the invention it appears to be possible to substantially eliminate the use of wires. This embodiment of the invention is characterized in that the apparatus comprises two processor circuits, that the first series of light sources together with the light detection elements which are positioned near the ends thereof are connected to a first processor through the driving means the selection means and the signal processing means assigned to these light sources and light detection elements, that the second series of light sources together with the light detection elements which are positioned near the ends thereof are connected to a second processor through the driving means and the signal processing means assigned to these light sources and light detection elements, and that one of the light sources from the first series in combination with one of the light detection elements adjacent to the second series as well as one of the light sources from the second series in combination with one of the light detection elements adjacent to the first series are used to establish a communication connection between both processors. This apparatus requires two processor circuits, but the thereto related costs are more than outbalanced by the reduction in costs caused by the elimination of the wires. Furthermore this embodiment of the apparatus consists in fact of two identical sub apparatuses, which both are positioned opposite each other along the respective sides of the reference surface.

Therewith the manufacturing of the apparatus as a whole is simplified. Furthermore it is possible to connect a separate display unit to each of the processors, for instance in the form of a multicharacter display unit, so that the position determining data which are produced by the apparatus, can be made easily readable from different directions for two persons- It is remarked that with the use of a template onto the reference surface the apparatus according to the invention can be used for instance as a kind of keyboard. In that case the processors can be embodied such that instead of position determining data for instance characters or digits can be made visible depending on the part of the "keyboard", which is momentarily indicated.

In a further embodiment the number of necessary electronic circuits for operating the above described apparatus can be reduced significantly in that one of said series of light sources together with the adjacent light detecting elements is replaced by a mirror, positioned perpendicular to the reference surface and along the respective edge of said reference surface, by means of which mirror light, emitted by the light sources in the other series of light sources, can be reflected to the light detection elements adjacent thereto.

With this measure the number of light transmitters and light receivers is divided into half and furthermore the number of necessary electronic components is significantly reduced. Especially the number of sensitive circuits for processing the light sensor signals is reduced from four to two.

Nothing is said above about the internal structure of the series of light sources. For an expert in this field it will be obvious to use one series of light sources which are all positioned at the same short distance above the reference surface. However, if a dimension is assigned to the series of light sources perpendicular to the reference surface than it is not only possible to detect indicating objects which are not in contact with the reference circuits but are positioned just above the surface and furthermore it is possible to obtain information about the attitude of the indicating object. A preferred embodiment of the invention has in connection therewith the characteristic that both series of light sources are divided in rows of light sources positioned above each other and parallel to the reference surface, whereby each of said rows has a different distance to the reference surface. Preferably this embodiment has the further characteristic that the mutual distance between the various rows of light sources, which together are forming one of the series of light sources, are equal. With the exception of the mirror all components of the circuit which during operation of the apparatus have to be located at a predetermined position are approximately located on a line along one edge of the reference surface. That provides the possibility to accommodate all these components in one housing which as a whole can be positioned adjacent to the respective edge of the reference surface. The positioning of the mirror along the opposite edge of the reference surface is than to only action necessary to bring the apparatus in a condition ready for operation. In other words, it is preferred that the light emitting means the light emitting means and light detecting means to be arranged along one edge of the reference surface together with the corresponding driving means, selection means and signal processing means are accommodated in an elongated housing of which the length is approximately equal to the distance between both light detection elements, of which the height is approximately equal to said distance and of which the width is preferably selected such that the whole housing can be manipulated by hand easily.

It is furthermore preferred that the dimensions of the mirror are selected such that the length and height of the mirror are not larger than respectively the length and height of the housing. Therewith it is possible to store the mirror together with the housing for instance in a casing or something like that. Preferably however, the housing itself may function as casing in which case preferably the housing comprises means for clamping, inserting or otherwise storing the mirror if the apparatus is not in operation.

To prevent eventual adjustment problems during the preparation of the apparatus to make it ready for operation it is preferred that the housing and the mirror comprise attachment means for attaching distance elements by means of which during operation the mirror is maintained at a predetermined distance of the light sources and light detection means which are present in the housing and parallel to said series of light sources. _

The invention will be explained in more detail with reference to the attached drawings.

Figure 1 illustrates a first embodiment of an apparatus according to the invention comprising two series of light sources which are positioned opposite each other along the respective sides of a reference surface, as well as four light detectors present at the corners of the reference surface.

Figure 2 illustrates in which way the position of an indicating object above or onto the reference surface can be determined based on the interruption of at least two light paths between one of the light detectors and one of the light transmitters. Figure 2a illustrates a preferred embodiment of a selection circuit, such as the selection circuits 16 and 18 in figure 1.

Figure 3 illustrates an embodiment in which the light transmitters and light receivers are not, as in figure 1 , connected to one single processor, but are connected to two different processors, whereas furthermore communication between both processors is possible. Figure 4 illustrates an embodiment of an apparatus according to the invention in which the number of necessary light transmitters and light receivers is significantly reduced by making use of a mirror along one side of the reference surface. Figure 5 illustrates in which way the detection is performed in an apparatus of the type illustrated in figure 4.

Figure 6 illustrates in a similar manner as in figure 2 in which manner the position of an indicating object above or onto the reference surface can be determined in case the indicating object has larger dimensions and results in interruption of a larger number of light paths.

Figure 7 illustrates in a similar manner the situation which arises in case the user of the apparatus for instance rests with his _ larger number of light sources from the corresponding light receivers.

Figure 8 illustrates an embodiment of a series of light transmitters in a multilayer structure. Figure 9a illustrates a view on the front surface of this multilayer structure.

Figure 9b illustrates the signal pattern which results from the positioning of a finger in a predetermined attitude in relation to the multilayer structure in figure 9a. Figure 9c illustrates another positioning of a finger onto the reference surface.

Figure 9d illustrates the signal pattern which corresponds to the position of the finger into the reference surface in the way as illustrated in figure 9c. Figure 10 illustrates a possible embodiment of the housing in which the apparatus according to the invention can be accommodated.

Figure 1 illustrates a first embodiment of an apparatus according to the invention. This apparatus comprises a first series of light transmitters or light emitters 12a, 12b, 12n, which with predetermined mutual distance are positioned in a series along the left edge of a reference surface 10 and at short distance above said surface. The apparatus furthermore comprises a second series of light transmitters or light emitters 14a, 14b, 14n, which also with predetermined mutual distance are arranged in a series alongside the right edge of the already mentioned reference surface 10. The various light transmitters 12a, 12b, 12n in the series which in the following will be generally indicated by the reference number 12, are connected to the outputs of a selection circuit 16. In a corresponding manner the various light transmitters 14a, 14b, 14n from the series of light transmitters which in the following will be indicated in general as the series 14, are connected to the outputs of selection circuit 18. The selection circuits 16 and 18 receive control signals from a processor 20. In figure 1 it is presumed that each of the light transmitters 12a 12n consists of a light source, for instance a laser diode or a LED, coupled to a corresponding driving circuit which in turn can be controlled under influence of selection signals from the circuit 16. A similar comment can be provided in relation to the light transmitters 14a 14n. The apparatus furthermore comprises two light detectors or light receivers 22 and 26 positioned near the ends of the light emitter series 12, as well as two light receivers or light detectors 24 and 28 positioned near the ends of the light emitter series 14. Each of the light receivers 22, 24, 26, 28 is connected to a comparator circuit in which the signal level delivered by the receiver is compared with a threshold value to determine whether or not if a light pulse is detected. These circuits are indicated by the reference numbers 30, 32, 34 and 36. Each of these circuits is connected to the input of the processor 20 and delivers a signal thereto which indicates whether or not light is received from one of the light sources. The processor 20 is connected to a display unit 38, for instance^' embodied as a multicharacter display.

The operation of the apparatus in figure 1 will be explained in more detail with reference to figure 2. During normal operation the various light transmitters in the series 12 and in the series 14 are activated successively by suitable signals from the processor 20, which by means of the selection units 16 and 18 are translated in sequential control signals for the various light transmitters. In a possible operation manner sequentially first the light transmitters 12a,

12b, .... 12n of the series 12 are each activated for a short period after which the light transmitters 14a, 14b, 14n of the series 14 are activated, after which again the transmitters of the series 12 are activated, etc. The light receivers 22, 24, 26 and 28 are operating continuously. As long as no indicating object is positioned above the reference surface 10 to interrupt the light path between at least one of the light transmitters and one of the light receivers each of the light receivers will in each combination receive light from one of the light transmitters and will generate a thereto corresponding signal through the corresponding signal processing circuit 30 to the processor 20.

However, if an indicating object is positioned onto or directly above the reference surface 10 then a situation will be created in which a number of the possible light paths are interrupted, as in more detail will be described with reference to figure 2. It is presumed in figure 2 that an indicating object 40 is positioned above the reference surface 10 at such a height that at least a part of the possible light paths between the light transmitters and the light receivers are interrupted. Such an indicating object may for instance be a pencil, a pen, an indicating stick or just a finger or something else. If in the above-described manner now successively first the light transmitters 12a, 12b, 12n are activated whereby the light detectors 24 and 28 are continuously operating then, as soon as the light transmitter 12x is activated a situation will arise in which the light receiver 24 receives light from the light transmitter 12x, but the light receiver 28 will not receive light from the light transmitter 12x, because the indicating object 40 is present in the light path between the light transmitter 12x and the light^" receiver 28. The respective light paths are in figure 2 indicated by arrows 42 and 44. The fact that the combination of light transmitter 12x and light receiver 28 does not provide a signal forms a first indication for the fact that the respective indicating object is present on the line which can be drawn between the light transmitter 12x and the receiver 28. During the further switching process of the series of light transmitters a similar situation will arise when the light transmitter 14x is activated. The light path 46 between the light transmitter 14x and the receiver 22 is not interrupted and this receiver will therefor send a corresponding signal to the processor 20. The light path 48 between the transmitter 14x and the receiver 26 is interrupted. That means that the indicating object 14 is present on the line between the transmitter 14x and the receiver 26. The cross-point of both lines 44 and 48 determines therefore the sought position of the indicating object 40. If it is now assumed that the whole geometry of the apparatus is known, in other words the distance L1 between the light transmitter 12x and the light receiver 26 is known, the distance L2 between the light transmitter 14x and the light receiver 28 is known and also the width B of the reference circuit 10 is known, in other words the distance between the series 12 and the series 14 is known, than it will be clear for the expert in this field that with the help of some goniometrical equations it will be possible in a relatively simple manner to determine the exact position of the indicating object 40. It is considered superfluous to provide further details of these calculations in this description.

Figure 2b illustrates a preferred embodiment of one of the selection circuits 16 and 18 in figure 1. In this preferred embodiment the various light sources are realized in the form of light emitting diodes which are arranged into an array. In the illustrated example this array consists of eight columns and eight rows. One of the diodes in the array 130 can be selected by activating one of the outputs of the selection circuit 132 and one of the outputs of the selection circuit 134. By means of the selection circuit 132 a negative voltage can be supplied to one of the columns of the array 130 whereas by means of the selection circuit 134 a positive voltage can be supplied to one of the rows of the array. The selection circuit 132 as well as the selection circuit 134 is controlled by a three bit control signal. It will be clear that the diode, which is present at the cross-point of the selected row and the selected column will start emitting light. The circuit in figure 2 is significantly simpler than the relatively complicated multiplexer circuit which according to the prior art is necessary to process the signals of the therein used light sensitive receivers.

•It is remarked that it is preferred in relation to the continuity of the pattern of light paths, which are possible across the reference surface between the light transmitters and the light receivers, that the distance between each light receiver and the respective adjacent light transmitter is equal to half the intermediate distances between the mutual light transmitters, or an odd multiple of this half intermediate distance.

Figure 3 illustrates a second embodiment of an apparatus according to the invention. This embodiment comprises around the reference surface 10 a number of components which are identical to the correspondingly identified components in figure 1. More specifically these components are the series of light transmitters 12 and the series of light transmitters 14, the light receivers 22 until 28, the corresponding signal processing circuits 30, 32, 34 and 36 and the selection circuits 16 and 18 for selecting the various light transmitters 12a 12n, respectively 14a 14n.

The difference between the figures 1 and 3 is to be found in the use of two separate processors 50 and 52 each eventually connected to a corresponding display unit 56 respectively 54. The selection circuit 16 is controlled by the processor 52 and the signals, delivered by the signal processing circuits 30 and 34 are supplied to this processor 52. In a similar manner the processor 50 controls through the selection circuit 18 the various light transmitters 14a 14n, whereas signals derived from the signal processor circuits 32 and 36 are received by this processor 50. To assure that the operation of this embodiment does not significantly differ from the operation of the embodiment in figure 1 there should be a possibility to establish communication between both processors 50 and 52. The special feature of the embodiment in figure 3 is now that this communication between the processors 50 and 52 is established by means of one of the light transmitters 12a 12n in combination with one of the opposite light receivers 24 or 28 respectively. One of the light transmitters 14a 14n and one of the opposed light receivers 22 or 26. As example the light transmitter 12a is used in combination with the light receiver 24 and the light transmitter 14a in combination with the light receiver 22. These four components offer together a bidirectional communication path between the processors 50 and 52, whereby of course measures have to be taken to activate the respective light transmitters 12a respectively 14a through the selection circuits 16 respectively 18 as well as to modulate the transmitted light.

As is schematically indicated in figure 3 the light transmitter 12a can be connected to a separate section of the selection means 16 to which a modulation signal can be supplied from the processor 52 such that after activating the light source 12a the thereby transmitted light can be modulated. A similar connection is realized between the light source 14a and the processor 50. If use is made of pure digital on/off modulation of the light transmitter 12a respectively 14a than it is not necessary to add a separate section to the selection means. In that case it is only necessary to adapt the software in the processors 52 and 50 such that during the communication connection only selection signals for the light transmitters 12a and 14a are selected and such that these light transmitters 12a and 14a are switched on and off in the desired modulation rithm.

Via the communication connection with which is established in this way between the processors 50 and 52 on the one hand synchronization signals have to be transferred to assure that the activation of the various light transmitters is performed at moments in time whereby the opposite light receivers are switched active and the respective processor is ready to receive and process the signals generated by these light receivers. Furthermore data signals have to be transmitted via these communication connection to exchange data which are accumu ate n o processors. Pre era y s exc ange a es p ace in two directions so that both processors at the end of a full scan period comprise the full data set and both processors are able to calculate independent of each other the position of an indicating object above the reference surface 10. It will be clear for the expert in this field that in the circuit according to figure 3 all means are present to establish a communication connection between both processors, on the condition that both processors comprise sufficient software to direct this communication. As such, however, the realization of communication between two processors via a transmission path in-which light is the transmission medium, is considered as known and therefore no further details will be provided.

In practice such a circuit as is illustrated in figure 3 may function as follows: 1 ) during a first period which can be considered as the initialization period, a connection is established between the processors 50 and 52 through the described communication path and in the processors the decision is taken which processor will function as master and which processor will function as slave. Furthermore eventual synchronization signals are exchanged to assure that in the following second period the correct light transmitters and correct light receivers will be activated at the desired moments in time.

2) during a second period sequentially in a predetermined pattern the light transmitters 12a....12n are activated and by means of the light receivers 24 and 28 signals are generated which after processing thereof will be supplied to the processor 50. At the end of this period eventual synchronization signals will be exchanged between the light transmitter 12a and the light receiver 24 as preparation for the following third period.

3) during the following third period the light transmitters

14a .14n are activated in a predetermined pattern and by means of the light receivers 22 and 26 signals are generated which after processing thereof are supplied to the processor 52. Also at the end of this third period eventual synchronization signals are exchanged between the processor 50 and the processor 52 through the bidirectional communication connection.

4) during a following fourth period a data communication connection transmitter 12a and the light receiver 24 as well as the light transmitter 14a and the light receiver 22, and data concerning the signals received in the preceding two periods are exchanged such that in any case one of both processors 50 or 52 is able to calculate the momentaneous position of an eventual indicating object above the reference surface 10. (Eventually both processors may carry out the same calculation as mutual check) . If necessary the results are mutually exchanged for comparison reasons through the same communication route. This comparison option offers the possibility to check the correct functioning of both processors 50 and 52 and to correct eventual deviations. Furthermore the results are made visible on both display units 54 and 56 and thereafter the circuit continues with a first period in which the transmitters 12a 12n are activated in a predetermined order, etc.

Figure 4 illustrates a further embodiment of an apparatus according to the invention in which a significant reduction of the number of necessary components is realized. In this embodiment light transmitters and light receivers are only positioned at one side of the reference surface 10. In the underlying embodiment the light transmitters 12a 12n and the light receivers 22 and 26 with the corresponding circuit 30 respectively 34. The light transmitters are controlled by a selection circuit 16 receiving control signals from a processor 58. At the right side of the apparatus according to figure 4 a mirror 62 is positioned perpendicular to the plane of the drawing which mirror is able to reflect light which is transmitted by one of the light transmitters 12a, 12b, 12n in a plane parallel to the reference surface 10 in the direction of the light receivers 22 and 26. The operation of the apparatus in figure 4 will now be explained in more detail with reference to the schematical drawing in figure 5.

Figure 5 shows at the left side of the reference surface 10 only the light transmitters 12a....12n as well as the light receivers 22 and 26. These light transmitters and light receivers will be mirrored because of the presence of the mirror 62, creating the virtual light sources 12a', 12b' 12n' as well as virtual light detectors 22' and

26'. If now an indicating object 64 is positioned above the reference surface 10 and if the light transmitters 12a 12n are activated in a predetermined order then two situations will arise in which the light path between a transmitter and a receiver is interrupted.

The first of these situations arises when the light source 12y is activated. The light emitted by the light source 12y is able after reflection against the mirror 62 to reach the light receiver 22 as is indicated by the arrow 64. Looking at the virtual receiver 22' it can also be stated that light, transmitted by the light transmitter 12y is able to reach along a rectilinear path the virtual light receiver 22' . This is indicated in figure 5 by means of a dashed line. An eventual light path between the light transmitter 12y and the light receiver 26 is indicated by the arrow 66. Considered as a straight line this light path extends between the light source 12y and the virtual light receiver 26' . Because of the reflection against the mirror 62 the actual light path will run in the direction of the actual light receiver 26. This light path is, however, blocked as a result of the presence of the indicating object 64 as illustrated in figure 5. Therefor this receiver 26 will not provide a signal. The fact that during the activation of the light source 12a a signal will be supplied by the light receiver 22, but no signal will be supplied by the light receiver 26 makes clear that an indicating object is present somewhere in the light path which is indicated by the reflected arrow 66.

The second of said situations will arise when the light source 12z is activated. The light which is emitted by the light source 12z in the direction of the mirror 62 and which is able to reach the receiver 22 after reflection against the mirror 62, is in figure 5 not illustrated in detail. What is illustrated is the light path, which could exist between the light transmitter 12z and the light receiver 26. This light path is indicated by the arrow 68. The light path 68 extends, considered in a linear sense, between the light transmitter 12z and the virtual light receiver 26'. In reality the light should reach the light receiver 26 after reflection against the mirror 62. As appears from figure 5 the actual light path is blocked by the presence of the indication object 64 so that the real light receiver 26 will not deliver a signal. Also in this situation the light receiver 22 will deliver a signal whereas the light receiver 26 will not deliver signal.

Because also in this case the full geometry of the apparatus is known and more specifically the distance between the light transmitter 12y and the light receiver 26 (more specifically the corresponding distance between the light transmitter 12y' and the virtual light receiver 26') is equal to L2, the distance between the light transmitter 12z and the light receiver 26 is equal to L1 and furthermore the distance between the real transmitters and receivers and the virtual transmitters and receivers is equal to 2B, it is possible using simple goniometrical equations to calculate the exact location of the indicating object 64 above the reference surface 10. Also in this case a detailed discussion of these calculations is considered superfluous, because these calculations are within reach' of^"the expert in this field. Above it is assumed that each time only two specific light paths are interrupted in case an indicating object is positioned on or above the reference surface. That applies only in case the dimensions of the indicating object are relatively small, such as a thin pencil or something similar. However, if a somewhat larger or courser indicating object is used, such as for instance a human finger, than in general more light paths will be interrupted as is illustrated in figure 6. Figure 6 shows a cross-section through an indicating object 70 of significantly larger dimensions than is assumed in the preceding figures. As appears in figure 6 all light paths between the light receiver 28 and a series of light transmitters situated between the light transmitter 12m and the light transmitter 12o are interrupted, whereas on the other hand all light paths between the light receiver 26 and a series of light transmitters situated between the light transmitter 14m and the light transmitter 14o are interrupted. The data which are collected in this situation in the processor circuit (or circuits) are, however, sufficient-to be able to calculate the position of the center of the indicating object 70 with sufficient accuracy. The basic data which are collected comprise the dimensions 1 and 2, indicating the positions of the light transmitters 12m and 12o, the dimensions L3 and L4 determining the position of the light transmitters 14m and 140 and the width dimension B. Using algorithms which are considered as known to the expert an average L5 can be calculated from L1 and L2 and an average L6 can be calculated from L3 and L4. The combination of L5, L6 and B provides sufficient data to be able to calculate the center of the indicating object 70 with sufficient accuracy.

Instead of a finger, a pencil, a pen, an indicating stick or a something similar it is also possible to use an "wireless" mouse as indicating object, in other words, to use an object which can be manipulated and handled by hand very easily and which roles or glides over the reference surface and can be moved very easily in all directions. The advantage of such a mouse is that the positioning thereof can be established very stable also by persons which are suffering from trembling fingers or persons who have problems with the coordination of their hand or finger movements. If in such a case a mouse is used ^"which offers additional support and simultaneously is able to be moved very easily over the reference surface, then that will appear to be a good aid to obtain a correct indication.

Not only relatively thick and voluminous indicating objects can be detected in this way. Also objects of significantly larger dimensions can lead to a correct positioning indication. If instead of a finger someone places for instance a whole hand or even a whole arm on the reference surface then this will lead to a completely different situation then is discussed above. As an example it is assumed in figure 7 that both the arm and the hand of a person are resting on the reference surface and that with a finger a predetermined position on the reference surface is indicated. As is illustrated in figure 7 the arm 72, the hand 74 and the finger 76 will cause interruption of a large number of possible light paths. In fact the light receiver 24 is only able to receive light from the light transmitter 12p and all light transmitters which are positioned between the transmitter 12p and the receiver 22, whereas the receiver 22 is only able to receive light from the light transmitter 14p and all light transmitters which are positioned between the transmitter 14ρ and the receiver 24. However, the fact that a series of light transmitters from the edge of the reference surface up to a predetermined light transmitter are completely screened implies the situation as illustrated in figure 7. The software, applied in the processors 50 and 52 for processing the received signals, can be adapted such that this specific fact forms the reason to search only for the position of the last visible light source, in other words the position of the light sources 12p and 14p. These light sources are, as will be clear from the above description, determining the place of the end of the finger 76 and will determine therewith the position on the reference surface 10 which, is indicated by the user of the apparatus.

It is assumed above that both series of light sources are structured as a monolayer of light sources which are all positioned a acent to each other at the same height direct y a ove t e re erence surface. However, it is also possible to apply a multilayer structure as is schematically illustrated in the three dimensional view of figure 8. The series 80 of light transmitters has in this example a three layer structure of which the lower layer comprises the light transmitters 82a,

82b, 82n, the middle layer comprises the light transmitters 84a,

84b, ...... 84n, and the upper layer comprises the light transmitters 86a, 86b, 86n. Figure 8 shows furthermore the reference surface

10 with the light receivers 90 and 92 which are positioned along the other edge of the reference surface 10. For the sake of clearness the second series of light transmitters (between the receivers 90 and 92) is not illustrated and the same applies to the further receivers which should be positioned near the ends of the illustrated series of light transmitters. The light transmitters are positioned such that the light, emitted by the light transmitters, can be detected by the two light receivers 90 and 92.. The advantage of such a multilayer structure is that information will be obtained about the attitude of the indicating object in the three dimensional space, as will be explained with reference to figure 9. Figure 9 illustrates a view on the multilayered series of light sources 82a' 86n, seen from the direction of the arrow 94 in figure 8, with in front thereof the schematically illustrated finger 96 which is positioned on the reference surface 10 (the reference surface 10 is perpendicular to the plane of the drawing in this figure). By positioning the finger 90 in the manner as is illustrated in figure 9a the light paths between the light receivers and a number of light transmitters in the rows 82, 84 and 86 are interrupted. Assuming that the finger 96 is present at some distance of the series of light transmitters 82, 84 and 86 the light rays emitted by two groups of light transmitters will be interrupted. These two groups are schematically indicated in figure 9b. The combination of both patterns of interrupted light sources enables the processor circuit or circuits in the apparatus to decide on the one hand that there is an indicating object above the reference surface 10 and to decide on the other hand in which position this indicating object is present above the reference surface 10, especially using the data obtained from the light sources on the row 82 (in cooperation with the corresponding information from the other series of light sources which is not shown in this example) and enables furthermore to obtain information about the attitude of the indicating object above the reference surface as will be clear from the figure. Figure 9c illustrates a similar view as in figure 9a, however, now with a finger which is present somewhat above the reference surface and has another oblique attitude. The corresponding patterns of the light transmitters which are screened from the opposite light receivers because of the presence of the finger are illustrated in figure 9d. As appears from this figure it is possible to decide on the basis of-the interrupted light paths in the first place that there is an indicating object above the reference surface 10, in this case at a distance which correspond to the height of the lower series of light sources, and furthermore it can be decided that the indicating object has in general an oblique attitude.

It is remarked that the sub-patterns in the figures 9b and 9d of those transmitters, which are invisible for each of the light sources, are identical, however, depending on the position of the indicating object also somewhat different patters may be created.

With a suitable choice of the number of layers of the structure and with a suitable dimension of each of the light sources it is therefore possible to obtain detailed information not only about the position of the tip of the indicating object above the reference surface, but also about the spacial orientation of the indicating object as a whole in the three dimensional space in relation to the reference surface. Apart from the coordinates of the tip of the indicating ιobject, which provide two degrees of freedom (the x- and y-coordinate) in the embodiments with one single row of light transmitters, or three degrees of freedom (x-, y- and z-coordinate) in the embodiments with multilayered series of light transmitters, in this embodiment with multilayered light transmitters two further degrees of freedom can be determined (the oblique attitude viewed from two different directions). If furthermore an indicating object is used which has not a rotation symmetrical shape then from the mutually clearly different light path interruption patterns information can be obtained about the eventual rotation of an indicating object around its longitudinal axis. In other words, it is possible to assign a kind of joystick-function to the indicating object.

Finally figure 10 shows a possible practical housing in which the apparatus according to the invention, especially an embodiment comprising a reflecting mirror, could be accommodated. The apparatus comprises a housing 100, in which the light transmitters, light receivers and all other electronic circuits are accommodated. The housing is through two distance elements 102 and 104 coupled to a mirror 106 of which the mirror surface is parallel to the front surface 100a of the housing 100. In this front surface 100a the series of light transmitters 108 is positioned whereas at both sides of these series both light receivers 110 and 112 are positioned. In the upper surface 100b of the housing 100 a display panel 114 is installed, for instance comprising a display unit for displaying various alphanumeric characters, which display unit is known as such. The housing 100 may comprise furthermore an on/off switch for the power supply inside the housing 100 (for instance in the form of an accumulator or battery) and may comprise further connections for connecting the processor for instance to a further display, a personal computer, a printer or other peripheral.

The distance elements 102 and 104 are preferably attached to the housing 100 and to the mirror 106 such that they can be decoupled very easily. It is preferred that the distance elements 102 and 104 and also the mirror 106 have such dimensions that these components can be stored for instance into an empty space inside the housing 100 destined thereto. If the apparatus is not in use, it forms a compact unit which can be handled very easily by the user.

In the operative condition the apparatus as a whole is positioned above the reference surface, whereby the part of the reference surface which is present within the frame determined by the housing 100, the distance element 102, the mirror 106 and the distance element 104 delimits the actual surface above which the presence of an indicating object can be detected by the apparatus. Furthermore in figure 10 a practical application of the apparatus is illustrated schematically. On the reference surface a piece of paper 116 or another suitable carrier is positioned onto which in this case 10 digits are placed in a predetermined pattern. If this pattern is known within the processor of the apparatus and one of the digits is indicated for instance by means of a finger, than it will be clear that this apparatus is able to translate the position of the indicating finger directly into the corresponding digit data. The respective digit can be displayed onto the display panel. If the apparatus is connected through a modem to a telephone network then this apparatus may act as selector unit for a telephone by mean of which a handicapped person which is not able to operate a normal telephone apparatus, is able to communicate by telephone. It will be clear that the apparatus is not restricted to the shown embodiments but that other embodiments will be covered by the invention as well.

Claims

1. Apparatus for determining the position of an indicating object above a substantially rectangular reference surface, comprising: - light emitting means positioned near the circumference of said reference surface for emitting light at least substantially parallel to the reference surface and at short distance thereof, light detecting means positioned near the circumference of the reference surface for detecting the light emitted by said light emitting means and for generating a therewith corresponding electrical signal, driving means for activating the light emitting means, signal processing means for processing the signals generated by said light detecting means, and - a processor circuit for selectively activating the driving means and the signal processing means to identify those combinations of light emitting means and light detecting means between which the light path is interrupted because of an indicating object positioned near the reference surface, characterized in that, the light emitting means comprise two series of light sources, which during operation are arranged along opposite edges of the references surface and at said distance above the reference surface, that the light detecting means comprise light detection elements which during operation are positioned near the ends of the series of light sources near the respective corners of the reference surface and at said distance above the reference surface, and that the apparatus comprises selection means for selecting the drive means in a predetermined order to activate thereby the corresponding light sources.

2. Apparatus according to claim 1, characterized in that the apparatus comprises two processor circuits, that the first series of light sources together with the light detection elements which are positioned near the ends thereof are connected to a first processor through the driving means the selection means and the signal processing means assigned to these light sources and light detection elements, that the second series of light sources together with the light detection elements which are positioned near the ends thereof are connected to a second processor through the driving means and the signal processing means assigned to these light sources and light detection elements, and that one of the light sources from the first series in combination with one of the light detection elements adjacent to the second series as well as one of the light sources from the second series in combination with one of the light detection elements adjacent to the first series are used to establish a communication connection between both processors.

3. Apparatus according to clόim 1 , characterized in that one of said series of light sources together with the adjacent light detecting elements is replaced by a mirror, positioned perpendicular to the reference surface and along the respective edge of said reference surface, by means of which mirror light, emitted by the light sources in the other series of light sources, can be reflected to the light detection elements adjacent thereto.

4. Apparatus according to one of the preceding claims, characterized in that-both series of light sources are divided in rows of light sources positioned above each other and parallel to the reference surface, whereby each of said rows has a different distance to the reference surface.

5. Apparatus according to claim 4, characterized in that the mutual distance between the various rows of light sources, which together are forming one of the series of light sources, are equal.

6. Apparatus according to one of the preceding claims, characterized in that the processor circuit, respectively at least one of the two processor circuits, is connected to a display panel onto which the position data related to the indicating object above the reference surface or thereto related data can be displayed after processing thereof in the processing circuit(s) .

7. Apparatus according to claim 6_f referring back to claim 2, 3, 4 or 5, characterized in that both processor circuits are connected to the display panel.

8. Apparatus according to one of the preceding claims, characterized in that, the distance between a light detector and the adjacent light emitter belonging to a series of light sources is equal to half the mutual distance between the light sources or an odd multiple thereof.

9. Apparatus according to one of the preceding claims, characterized in that, the light emitting means and light detecting means arranged along one edge of the reference surface together with the corresponding driving means, selection means and signal processing means are accommodated in an elongated housing of which the length is approximately equal to the distance between both light detection elements, of which the height is approximately equal to said distance and of which the width is preferably selected such that the whole housing can be manipulated by hand easily.

10. Apparatus according to claim 9 referring back to one of the claims 3-8, _. characterized in that the dimensions of the mirror are^' selected such that the length and height of the mirror are not larger than respectively the length and height of the housing.

11. Apparatus according to one of the preceding claims 9 or 10, characterized in that the housing comprises means for clamping, inserting or otherwise storing the mirror if the apparatus is not in operation.

12. Apparatus according to one of the claims 9-11, characterized in that the housing and the mirror comprise attachment means for attaching distance elements by means of which during operation the mirror is maintained at a predetermined distance of the light sources and light detection means which are present in the housing and parallel to said series of light sources.

13. Apparatus according to one of the claims 9 until 12, characterized in that said means are supplied from a battery or accumulator which is positioned within the housing.

14. Apparatus according to one of the preceding claims, characterized in that the apparatus comprises connecting means through which the apparatus can be connected to a computer and/or to a printer and/or to a modem and/or to a standard bus.

15. Apparatus according to one of the preceding claims, characterized in that the light sources are arranged in an array of n-rows and m- columns, whereby through a one out of n-selector one of the rows can be selected and through a one out of m-selector one of the columns can be selected such that through said selectors a voltage of one polarity can be supplied to a selected row and a voltage of the other polarity can be supplied to a selected column.