CA1101961A - Graphics table particularly for a telewriting system - Google Patents

Graphics table particularly for a telewriting system

Info

Publication number
CA1101961A
CA1101961A CA317,681A CA317681A CA1101961A CA 1101961 A CA1101961 A CA 1101961A CA 317681 A CA317681 A CA 317681A CA 1101961 A CA1101961 A CA 1101961A
Authority
CA
Canada
Prior art keywords
wires
pen
signal
electric current
detector
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
CA317,681A
Other languages
French (fr)
Inventor
Jean-Claude Rahuel
Jean-Paul Dagneilie
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Telediffusion de France ets Public de Diffusion
Original Assignee
Telediffusion de France ets Public de Diffusion
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Telediffusion de France ets Public de Diffusion filed Critical Telediffusion de France ets Public de Diffusion
Application granted granted Critical
Publication of CA1101961A publication Critical patent/CA1101961A/en
Expired legal-status Critical Current

Links

Classifications

    • GPHYSICS
    • G06COMPUTING; CALCULATING OR COUNTING
    • G06FELECTRIC DIGITAL DATA PROCESSING
    • G06F3/00Input arrangements for transferring data to be processed into a form capable of being handled by the computer; Output arrangements for transferring data from processing unit to output unit, e.g. interface arrangements
    • G06F3/01Input arrangements or combined input and output arrangements for interaction between user and computer
    • G06F3/03Arrangements for converting the position or the displacement of a member into a coded form
    • G06F3/041Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means
    • G06F3/046Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means by electromagnetic means

Abstract

Graphics Table Particularly For A Telewritinq System Abstract of the Disclosure A graphic table comprising a non-conductive plate supporting two crossing layers of wires and a pen for writing on a sheet disposed on the plate. The wires are successively scanned by an electric current which creates a field to be detected by the pen. The electric current is a current of high frequency, for example of the order of ten megahertz, and the wires are switched at a frequency of for example one hundred kilohertz. The pen is followed by a selective amplifier of ten megahertz, by a filter, by a detector, and by a circuit for determining the instant when the picked up signal passes through a peak. Notably useful in telewriting systems.

Description

11~1961 The present invention relates to a graphics table particularly useful in the telewriting system.
From day to day, the importance of and interest in -telewriting apparatus is increasing. It will be recalled that a telewriting system consists of graphics acquisition means, connected to one of a transmission line or channel, which can take various forms such as a graphics table, a light pen, a ball point etc. whose co-ordinates are periodically retrieved, then coded and transmitted via the transmission line or channel tc the receiving end, where display means such as cathode ray tubes, plasma panels, tracing tables, special printing machines, etc. are available to display the sketch or written information.
More particularly, this invention relates to a graphics table comprising a non-conductive plate including a set of horizontal wires and a set of vertical wires, all insulated from the others, the wires of one set being sequentially, one by one, scanned by an electric current, then the wires of the other layer are one after the other similarly sequentially scanned by an electric current, and so on, and a type of ball point pen which allows the writing or the drawing on a sheet of paper covering the non-conductive plate, the aforenoted ball point pen comprising the meanC sensitive to the electric field which is built up by the current passing in the aforenoted wires, which delivers an output signal allowing the derivation of the co-ordinates of the end of said ball point pen.
One such graphics table has been described in a technical article entitled "A WRITING TABLET FOR CONVERTING CURRENT
HANDWRITING INTO ELECTRICAL SIGNALS", by L. R. Nieuwkerk in the Dutch reviez "Tijschrift van het Nederlands Electronica- en Radiogenootschap" 38, No. 6, 1973, pages 139 to 143. In that table the electric current which scans the horizontal current which limits the amplitude of the signal detected by the ball point pen through the sheet of paper. In other respects, for various reasons, the wire scanning frequency is required to be chosen between 100 and 200 kilohertz and it results in a light noise level disturbing the signal detected by the pen. The accuracy in the measurement of the co-ordinates is thus limited by the weak signal-to-noise ratio of the apparatus.
One object of the present invention is the provision of a graphics table of this type, but without the drawbacks noted above, in allowing the improvement of the amplitude of the signal-received in the pen and particularly the signal-to-noise ratio.
According to a feature of the present invention, there is provided a graphics table comprising a non-conductive sheet supporting two crossings sets of wires and a pen capable of writing on a sheet of paper placed on the non-conducting plate, the wires of one set, then the other being successively scanned by an electric current of high frequency, and said pen comprising the means for reception of an electric field built up by the electric current scanning the sets of wires successively.
According to another feature, the frequency of the current applied to the said wires i9 of the order of about 10 meagahertz, the wires scanning frequency being of the order of about one hundred kilohertz.
According to another feature, the signal which is picked up by said pen is detected in a coherent detection process.
According to another feature, the signal detected by said pen is amplified in a selective amplifier of which the passband is centered at the frequency of the current applied to the said wires.

, , ~10~96~
The above mentioned features of the present invention, as well as others, will become very clear in the following description of an embodiment, the said description having been made in relation to the diagram of the graphics table shown in the single accompanying figure.
The graphic table of the single figure is comprised of a non-conductive plate 1, which is preferably a printed circuit board supporting a set of vertical regularly spaced wires 2 on one face and, on the other face, a set of horizontal wires 3 equally regularly spaced, the spaces between the wires of one or the other set being equal. Each wire 2 is connected to the output of an electronic switch or AND gate 4 while each wire 3 is connected to the output of an electronic switch or AND gate 5. Each AND gate 4 has one input connected to the output of an oscillator 6 and the other input connected to the output of the corresponding stage of the shift register 7 comprising as many stages as wires 2. Each AND gate 5 has one input connected to the output of oscillator 6 and the other input connected to the output of the corresponding stage of a shift register 8 comprising as many stages as wires 3. The shift input register 7 is connected to the output of a counter-divider or divider 9 while the data input of its first stage is connected to the reset output of a cyclic counter 10. Between the last stage of register 7 and the first stage of register 8, is inserted a third shift register 11 comprising a reduced number of stages.
In practice the registers 7, 11 and 8, connected in series, operate a single shift register, that is to say that the bit "1", which is introduced into the first stage of 7 when the reset output of 10 is activated, is successively shifted through 7, 11 and 8, to the output of the last stage of 8, at the rate of the clock pulses provided by divider 9.
Counter 10 has its counting input connected to the output of divider 9.
The graphics table is also comprised of a pen 12, which is in practice , . ~

onstituted by a section of coaxial cable open at its end 13 near table 1, such as to constitute a field pick up. At that end 13, the sensor can be slightly pojected out for connection to an external conductor to improve the effectiveness oE the pick up~ At the other end 14, the coaxial section is extended to the input of an amplifier 15, of which the output is connected to the input of a passband filter 16 of which the output is connected to the input oP a detector 17. The output of detector 17 is connected to the input of circuit 18 which is designed to determine the instant when the signal coming Prom 17 passes through a maximum and to provide a signal at that instant. The output of circllit 18 is connected to the write input of a memory 19 of which the data input is connected to the count outputs of counters 9 and 10. Memory 19 can be cyclically read under the control of control circuit 20, data read from 20 being delivered to a communication line 21.
The end 13 of pen 12 is provided with a pencil lead or an inked ball allowing drawing od writing on a sheet of paper 22 applied on plate 1 as with an oridinary pen.
In the embodiment described, the oscillator 6 provided a signal at a frequency oP 10 megahertz and divider 9 has a division ration equal to one hundred. It results in divider 9 providing a continuous train of clock pulses at the repetition frequency of one hundred kilohertz and wires 2 and 3 are scanned, when their supply AND gates 4 and 5 are on, by a 10 megahertz signal instead of a continuous current as in the graphics table described in the technical article mentioned above.
One can suppo~ that at the initial instant counter 10 attains its maximim count for which the reset output applied a bit ~1" to the first stage of shift register 7. The Pirst gate 4 is on and the ~10 magahertz signal is applied to the first wire 2. As the following clock pulse is received from 9, the bit "1" is shifted into the second stage of 7 and the second vertical wire
2 receives the 10 megahertz signal is applied to the second vertical wire 2, and son and. When all the wires 2, that is to say all the stages of 7, have been successively scanned the bit "1" passes into the shift register 11.
The shift register 11 comprises a few stages only and is purposed for clearly separating the scanning of vertical wires 2 and the scanning of horizontal wires 3.
Therefore, from the output of register 11, the bit "1" passes into the shift register 8 ans provided the successive supply of a signal at 10 Megahertz to wires 3. Then bit "11l leaves the last stage or cell of 8, a little ahead llV~61 of the counter 10 attaining its maximum count. In effect, the amximum count of 10 is equal to the number of stages v of 7, plus the number of stages k of 11, plus the number of stages h of 8, and an arbitrary constant k'.
~uring the application of the 10 megahertz signal to a wire 2 or 3, it radiates an electromagnetic field which is partly pick up by the pen 12 through the sheet 13 on which ~2 is applied at the instant of writing the signal applied from pen 12 to amplifier 15 depending on the distance of end 13 of pen 12 to the radiating wire 2 or 3. Theoretical considerations relating to the interpretation of the signals received by the pen have been given in the technical article already cited, notably on the subject oE the interpretation of the position of the end of the pen between two wires, and these considerations described with respect to a DC table are still valid for a high frequency table because they do not involve the frequency of the signal applied to the wires.
In short it is recalled that the utilized signal results from the sampling that virtually shifts at constant speed on the table or plate 1, either horizontally or vertically. The samplign is carried out at a frequency that is twice the maximum frequency of the bell sha~ed signal which is virtually shifted to satisEy Sha~non~s law. The samples are stored in a capacitor for reconstituting the signal, the capacitor being Pormed by the input impedance of amplifier 15. The width at mid-hight of the bell shaped curve is equal to a/v where a is the distance between the wires 2 or 3 and v is the efPective speed of shifting determined by the pulse frequency of shift registers 7 or 8, i.e 100 kilohertz. The signal is ampliEied in amplifier 15, then filtered in passband filter 16 of which the passband has a width of 200 kilohertz and is centered at 10 megahertz. It should be noted that in this manner the low frequency noise that is obtained in the current table of the technical article cited above is ~e~iminated.
The output signal oE 16 is detected in 17, which delivers the bell shaped signal. It should be noted that detector 17 can be a coherent detector of which the reference input is then connected from the output of 6 for causing a synchronous detection which again improves the signal-to-noise ratio. Tje maximu~ determination circuit 18 can be a conventional differentiation circuit associated with a conventional zero crossing detector which allows the deter-mination of the time whe~ the beel shaped signal provided by 17 passes through its maximum.
In the memory 19, the received signal from 18 is an write order which initiated write operation of the contents of 10 into 19 at the same time as well as write operation in 19 of the contents of counter-divider 9. It will become apparent that the content of 10 at the maximum time indicates the ; number of the radiating wire 2 or 3 ~hile th~ contents of 9 that can vary ..

6: l from 0 to 99 gives the distance of the end 13 to that wire.
The memory 19 is cyclically read under the control of circuit 20 and delivers its contents to line 21. The read control circuit 20 can be operated Prom 10 through the current path 2~ during the count oP the last k'pulses at the end oP each cycle.
It will be understood that the use oP a supply current at 10 megahertz provided many advantages over a DC supply. In the first place the capacitor constituted by the pen tip the paper 22, the dielectric oP plate 1 and the radiating wire has much lower impedance. TherePore with equal peak voltage, the voltage picked up in the coaxial structure of the pen~ is more important with an improved signal-to-noise ratio~ The spectrum oP the received signal is symmetrical around 10 megahertz which allows the provision oP a simple structure for the ampliPier 15. The low Preyuency noises are ~liminated.
Finally use of a coherent detection becomes possible to increase the distance between the wires oP the plate and/or to increase the dimensions oP the plate.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1) A graphic table comprising a non-conductive plate carrying two orthogonal sets of wires and a pen capable of writing on a sheet of paper placed on the non-conducting plate, the wires of one set and of the other being successively scanned by an electric current, and said pen comprising reception means of a field created by the electric current successively scanning the set wires, characterized in that said electric current is at a high frequency of the order of ten megahertz, the scanning frequency of said wires being of the order of one hundred kilohertz.
2) A graphic table according to claim 1, characterized in that the signal picked up by the pen is applied to coherent detector.
3) A graphic table according to claim 1, characterized in that the signal picked up by the pen is amplified in a selective amplifier having a passband centered at the frequency of the current applied to said wires.
41 A graphic table according to one of claims 1 to 3, characterized in that it is comprised of an oscillator delivering a high frequency output signal, electronic switching means for applying sequentially to the wires of the sets, the said oscillator output signal, a first counter-divider for providing control pulses to said switching means, a maximum signal detector connected to a detector which is connected to said pen, said detector causing the state of said first counter-divider to be read each time the signal which is applied thereto passes through the maximum.
CA317,681A 1977-12-21 1978-12-11 Graphics table particularly for a telewriting system Expired CA1101961A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR7739395A FR2412997A1 (en) 1977-12-21 1977-12-21 GRAPHIC TABLET ESPECIALLY FOR TELEWRITING SYSTEMS
FR7739395 1977-12-21

Publications (1)

Publication Number Publication Date
CA1101961A true CA1101961A (en) 1981-05-26

Family

ID=9199398

Family Applications (1)

Application Number Title Priority Date Filing Date
CA317,681A Expired CA1101961A (en) 1977-12-21 1978-12-11 Graphics table particularly for a telewriting system

Country Status (9)

Country Link
US (1) US4225750A (en)
JP (1) JPS5491150A (en)
CA (1) CA1101961A (en)
CH (1) CH626463A5 (en)
DE (1) DE2854398A1 (en)
FR (1) FR2412997A1 (en)
GB (1) GB2038482B (en)
NL (1) NL7812284A (en)
SE (1) SE7813073L (en)

Families Citing this family (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2476876A1 (en) * 1980-02-21 1981-08-28 Telediffusion Fse TRANSPARENT GRAPH TABLET FOR TELEECRITURE SYSTEM
JPS5983238A (en) * 1982-11-04 1984-05-14 Sony Corp Position detector
JPS617917A (en) * 1984-06-22 1986-01-14 Nec Corp Coordinate input device
FR2589599B1 (en) * 1985-10-31 1991-01-11 Morin Francois TELE-WRITING TERMINAL
JPH0646377B2 (en) * 1985-11-30 1994-06-15 ぺんてる株式会社 Transparent tablet device
JPH05233147A (en) * 1992-02-21 1993-09-10 Mitsubishi Electric Corp Display incorporating type tablet
GB9219918D0 (en) * 1992-09-21 1992-11-04 Vernon Gauging Systems Limited Position recognition apparatus
US5918384A (en) 1993-08-17 1999-07-06 Akeva L.L.C. Athletic shoe with improved sole

Family Cites Families (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS576608B2 (en) * 1974-07-26 1982-02-05
US4088842A (en) * 1975-05-23 1978-05-09 Kabushiki Kaisha Daini Seikosha Automatic coordinate determining device
US3992579A (en) * 1975-06-02 1976-11-16 Ibm Corporation Tablet system with digital activation
US3999012A (en) * 1975-07-07 1976-12-21 Ibm Corporation Graphic entry tablet with improved addressing
US4080515A (en) * 1975-06-17 1978-03-21 Gtco Corporation Successively electromagnetically scanned x-y grid conductors with a digitizing system utilizing a free cursor or stylus
US4054746A (en) * 1975-10-22 1977-10-18 Data Automation Corporation Electronic coordinate position digitizing system
US4039747A (en) * 1976-02-05 1977-08-02 Telautograph Corporation Apparatus for converting the position of a manually operated instrument into an electrical signal
US4138592A (en) * 1977-09-16 1979-02-06 Capehart Jack D Electromagnetic detection line digitizer

Also Published As

Publication number Publication date
SE7813073L (en) 1979-06-22
JPS5491150A (en) 1979-07-19
US4225750A (en) 1980-09-30
DE2854398A1 (en) 1979-07-05
GB2038482B (en) 1982-08-25
GB2038482A (en) 1980-07-23
FR2412997B1 (en) 1983-03-18
FR2412997A1 (en) 1979-07-20
NL7812284A (en) 1979-06-25
CH626463A5 (en) 1981-11-13

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