COORDINATE INPUT APPARATUS

Abstract: A system for detecting the types and status of position designating devices is incorporated in a coordinates input apparatus having a tablet (1) constituting a coordinates input section, a plurality of position designating devices (2) of different types, and a position detecting circuit (3) for driving the tablet and detecting positions at which coordinates are input by the position designating devices. The system has an antenna coil (13) disposed around a coordinates input range of the tablet, and a tuning circuit (22) disposed in each of the position designating devices for transmitting radio waves in response to an external signal at an individual frequency determined in accordance with the type of the corresponding position designating device. An AC signal of predetermined frequencies is applied to the antenna coil so that it transmits radio waves. The types and status of the position designating devices are detected by judging the condition of the position designating circuits from signals within the antenna coil while the transmission of the radio waves is suspended. With this system, the types and status of a plurality of position designating devices can be detected without having to connect the devices to other circuits via cords or provide them with complicated signal generating circuits and power sources such as batteries.

Description: BACKGROUND OF THE INVENTION The present invention relates to detection of the status of a plurality of position designating devices of different types which are used in a coordinates input apparatus, and more particularly to a system for detecting the status and type of each of the position designating devices which has designated only a position at which coordinates are to be input. Description of the Related Art: Hitherto, a system has been incorporated in a coordinates input apparatus for detecting the status (hereinafter referred to as the "pen-down status") of a position designating device which has designated only a position on a tablet at which coordinates are to be input. The arrangement of this system has been such that a switching means is provided in the position designating device and is turned on (or off) only in the pen-down status, and that timing signals based on the ON (or OFF) condition of the switching means are transmitted to a position detecting circuit via a cord or by the use of ultrasonic waves or infrared rays. However, with the arrangement in that timing signals are transmitted from the position designating device via a cord, there has been a drawback in that the cord causes a hindrance to the operating efficiency of the position designating device. In addition, with the arrangement in that timing signals are transmitted by the use of ultrasonic waves or infrared rays, a transmitter, a signal generating circuit, a battery, and the like must be provided in the position designating device per se. Hence, the above-described conventional arrangement involved the following problems. The arrangement of the position designating device becomes complicated and large in size and weight, thereby lowering the operating efficiency of the position designating device. In addition, there has been no means to differentiate, with ease, between a plurality of position designating devices of different types. SUMMARY OF THE INVENTION A primary object of the present invention is to provide a system which is, when used, capable of differentiating between the types of position designating devices, and capable of detecting factors concerning the position designating devices, such as the position and status thereof, without causing any decrease in the operating efficiency of the position designating devices. In order to achieve this object, according to the invention, there is provided a system for detecting the status of a position designating device, such as a stylus pen, in a coordinates input apparatus having a tablet constituting a coordnates input section, and a position detecting circuit adapted to drive said tablet and detect positions at which coordinates are input by said position designating device, characterized in that said tablet is provided with an antenna coil, and each one of a plurality of position designating devices of different types is provided with a tuning circuit including a coil and capacitors working cooperatively to transmit radio waves in response to an external signal at an individual frequency predetermined in accordance with a corresponding type of position designating device, wherein an AC-signal having a plurality of frequencies each being identical to an individual frequency of one of said tuning circuits is intermittently and sequentially applied to said antenna coil so that radio waves are transmitted by said antenna coil, and, when the transmission of said radio waves is suspended, signals generated by said tuning circuits in response to said radio waves are received by said antenna coil to enable the detection of the respective positions and operating statuses of said position designating devices, and wherein a determination of the correspondence of the frequencies of the received signals with the types of position designating devices is used to effect a differentiation between the different types of said position designating devices. Further developments of the system according to the invention are indicated in the dependent claims 1 to 6. The invention further provides a method of distinguishing between different types of position designating devices, as is specified in claim 7 In accordance with a preferred embodiment, each of the tuning circuits is provided with a switch, and, when each of the switches is turned on, each of the tuning circuits in the corresponding designating devices transmits a signal in response to the signal of the frequency that is identical with the individual frequency of the tuning circuit of the corresponding position designating device, from among signals of different frequencies sequentially transmitted by the antenna coil. The antenna coil receives these signals, thereby enabling detection of the position and operating status of the position designating devices. The correspondence of the received signals with the types of the position designating devices is determined, thereby differentiating between the types of the position designating devices. By virtue of this arrangement of the system in accordance with the present invention, no cord is necessary between the position designating devices and other circuits. It suffices to provide tuning circuits each including a coil and capacitors, thus making unnecessary any complicated signal generating circuit or battery, which the prior art necessitated. In addition, since the type of each of the position designating devices is also detected without using any cord, the position designating devices can have a very high operating efficiency, while the position designating devices may be input pens of different types in terms of. for instance. display color they correspond, thereby enabling selection of the display color by means of the switches. The above and other objects, features, and advantages of the present invention will become apparent from the following description. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view schematically illustrating a coordinates input apparatus to which an embodiment of the present invention is applied; Fig. 2 is a sectional view of an input pen; Fig. 3 is a block diagram of a timing control circuit; Fig. 4 is a diagram illustrating waveforms of signals from various parts shown in Fig. 3; and Fig. 5 is a timing chart showing the relationship between the reception and the transmission of signals shown in Fig. 4. DESCRIPTION OF THE PREFERRED EMBODIMENT Fig. 1 illustrates a coordinates input apparatus in which a system for detecting the status of position designating devices in accordance with an embodiment of the present invention is incorporated. In this figure, reference numeral 1 denotes a tablet; 2, a plurality of position designating devices (hereinafter referred to as the "input pens") of different types, only one of which is shown in the figure; 3, a position detecting circuit; and 4, a timing control circuit. The tablet 1 comprises a casing 11 of a non-magnetic metal, and a tablet body 12 and an antenna coil 13 which are accommodated in the casing 11. The tablet 12 is connected to the position detecting circuit 3, while the antenna coil 13 is connected to the timing control circuit 4. The tablet body 12 is driven by the position detecting circuit 3 and constitutes a detecting section for detecting positions designated by the input pens 2. The tablet body 12 is disposed substantially in the center of the casing 11. The casing 11 has a frame 14 which is drawn thereon to indicate a range within which coordinates can be input thereto. As for the tablet body 12 and the position detecting circuit 3, it is possible to use, for instance, those described in Japanese Patent Application No. 238532/1983 "Coordinate Position Detection Device" (see Japanese Patent Laid-Open No. 129616/1985) and Japanese Patent Application No. 33083/1984 "Position Detection Device" (see Japanese Patent Laid-Open No. 176134/1985), both filed by the present applicant. The arrangement of the former device is such that a multiplicity of magnetostrictive transmitting media are disposed parallel with the surface of a tablet body 12 in such a manner that some of the magnetostrictive transmitting media are disposed at right angles with others, and magnetostrictive vibrations are periodically imparted to each of these media from one end thereof to the other end. When an input pen 2 approaches the media, the magnetostrictive vibration at that location is enhanced by means of a bar magnet provided in the pen. By making use of this phenomenon, a position detection circuit 3 detects the X-Y coordinates of the location on the basis of the time duration of propagation to that location. On the other hand, the arrangement of the latter device is such that magnetostrictive media, some of which are disposed at right angles with others, are excited by an AC current, and voltages induced therein are detected by detection coils. X-Y coordinates are detected by making use of the phenomenon in which, when a similar input pen approaches the media, the permeability of the magnetostrictive media changes locally thereby causing a resultant change in the induced voltages. The antenna coil 13 comprises a conductive wire which is provided with an insulation coating such as polyvinyl chloride and is disposed around the coordinate input range of the tablet body 12, i.e., in this embodiment, on the rear surface of the upper panel 11a of the casing 11 around the frame 14. Although the conductive wire is given one turn in the illustrated example, a plurality of turns may be provided, as required. Each of the input pens 2 accommodates therein a magnetism generator for designating a position, which is, for instance, a bar magnet 21, and a tuning circuit 22 including a coil and capacitors. Fig. 2 illustrates details of the structure of the input pen 2. A pen shaft 23 is formed of a non-metal material such as a synthetic resin and receives therein an integral structure formed by combining a core member 24, such as a ball-point pen, the bar magnet 21 having a through-hole slidably receiving the core member 24, a coil spring 25, and the tuning circuit 22 constituted by a switch 221, a coil 222 wound around an iron core, two capacitors 223 as shown in FIg. 3, and a variable capacitor 224 provided for the fine tuning. A cap 26 is provided at the rear end of the pen shaft 23. The arrangement of the switch 221 is such that, when the tip of the core member 24 is pressed against the surface of the tablet so that the core member 24 slides into the pen shaft 23, the switch 221 is turned on by being pressed by the rear end of the core member 24 via the coil spring 25. As is also shown in Fig. 3, the capacitor 223 and the variable capacitor 24 are connected to each other in parallel so as to form a parallel circuit. One end of the coil 222 is connected to one end of the parallel circuit via the switch 221, while the other end of the coil 222 is connected to the other end of the parallel circuit, thereby constituting the parallel resonance circuit 22. The resonance circuit 22 provided within each of the input pens 22 has an individual resonance frequency determined in accordance with the type of the corresponding input pen 2, for example, in accordance with the predetermined different display color of the input pen 2. More specifically, the capacities of the capacitors 223 of the resonance circuits 22 are varied so that the resonance circuit 22 of the input pen for producing displays in "black" has a resonance frequency of 450 KHz, the resonance circuit 22 of the input pen for producing displays in "red" has a resonance frequency of 500 KHz, and the resonance circuit 22 of the input pen for producing displays in "blue" has a resonance frequency of 550 KHz. It should be noted that values of each of the resonance circuits 22 are selected in such a manner as to resonate (to be tuned) with the radio waves of the identical frequency from among radio waves transmitted from the antenna coil 13 at respective frequencies determined in accordance with the types of the input pens 2. Fig. 3 shows details of the arrangement of the timing control circuit 4. In the drawing, reference numeral 401 denotes an oscillator (OSC); 402, a frequency demultiplication counter; 403 and 404 denote NAND gates; 405 denotes a transmission terminal; 406, a reception terminal; 407 and 408 denote reception changeover switches; 409, 410a, 410b, 410c, 411a, 411b and 411c, amplifiers; 412a, 412b and 412c, mechanical filters; 413a, 413b and 413c, phase detectors (PSDs); 414a, 414b and 414c, low-pass filters (LPFs); 415a, 415b and 415c, comparators; and 416a, 416b and 416c, output terminals. Fig. 4 is a waveform diagram of signals in various parts shown in Fig. 3. Hereinafter, a detailed description will be made of operation. The oscillator 401 sequentially generates a plurality of groups of clock pulses each comprising a predetermined number of clock pulses having the frequency of 0.9 MHz, 1 MHz, or 1.1 MHz. The frequency demultiplication counter 402 demultiplies the frequencies of the clock pulses into 1/2 and 1/32. A pulse signal A having the frequencies of 450 KHz, 500 KHz, and 550 KHz, which has been obtained by demultiplying the frequencies of the clock pulses into 1/2, is input to one input terminal of the NAND gate 403, while a pulse signal having the frequencies of 28.12 KHz, 31.25 KHz, and 34.38 KHz (the respective pulse durations being 17.8 µs, 16 µs, and 14.5 µs), which has been obtained by demultiplying the frequencies of the clock pulses into 1/32, is input to the other input terminal of the NAND gate 403. The output of the NAND gate 403 is sent to the NAND gate 404, and becomes a signal B which intermittently sends pulses having the pulse duration of 17.8 µs and the frequency of 450 KHz, pulses having the pulse duration of 16 µs and the frequency of 500 KHz, and pulses having the pulse duration of 14.5 µs and the frequency of 550 KHz, as shown in Fig. 4. The changeover in frequency of the clock pulses output from the oscillator 401 takes place in conformity with the period of the pulses obtained by the frequency demultiplication into 1/32. In Fig. 4, the widths of the pulses having different frequencies are illustrated as the same width for the convenience's sake of the illustration. The signal B is sent to the antenna coil 13 via the transmission terminal 405 and is transmitted therefrom as radio waves. At this point, if the switch 221 is turned on in the tuning circuit 22 of the selected input pen 2, the tuning circuit 22 resonates with the radio waves of the frequency that is identical with the resonance frequency of its own, from among the radio waves transmitted from the antenna coil 13. It is assumed, for example, that the selected input pen 2 corresponds to the display color of "black" and that the tuning circuit of this input pen 2 resonates with radio waves of 450 KHz. Since the tuning circuit 22 continues to resonate while its output being attenuated even after the transmission from the transmission side has been suspended, the tuning circuit 22 generates a signal C as shown in Fig. 4. The signal C is transmitted as radio waves from the coil 222 and is received by the antenna coil 13. Since the reception changeover switches 407 and 408 have already been changed over by the pulse signal obtained by the aforementioned frequency demultiplication into 1/32, these switches 407 and 408 receive signals from the reception terminal 406 only during the period in which the transmission is suspended. The thus received signal will be a signal D as shown in Fig. 4 if the switch 221 of the tuning circuit 22 is turned on, while it will be a signal D' as also shown in Fig. 4 if that switch 221 is turned off. Fig. 5 illustrates the timing at which various signals are output from the transmission side and the reception side. As shown in this figure, the reception signal D is generated in repeated response to the transmission signal B transmitted from the antenna coil 13, in such a manner that the tuning circuit 22 of the input pen 2 corresponding to the display color of "black" responds to the pulses of 450 KHz, the tuning circuit 22 of the input pen 2 corresponding to the display color of "red" responds to the pulses of 500 KHz, and the tuning circuit 22 of the input pen 2 corresponding to the display color of "blue" responds to the pulses of 550 KHz. The reception signal D is amplified by the amplifiers 409, 410a, 410b, and 410c, so as to become a signal E (signals Ea, Eb, and Ec on the output side of the amplifiers 410). These signals Ea, Eb, and Ec are passed through the mechanical filters 412a, 412b, and 412c, respectively, in which noise components are removed while the signal components of the respective resonance frequencies are passed therethrough. The signals are then sent respectively to the phase detectors 413a, 413b, and 413c via the amplifiers 411a, 411b, and 411c. The amplifiers 410a, 410b, and 410c have the auto-level-control function and act to make the amplitude of the signals to a constant level. The pulse signal A has already been input to the phase detectors 413a, 413b, or 413c. Accordingly, if the phase of the input signal E coincides with the phase of the pulse signal A, these phase detectors output a signal F (signals Fa, Fb, or Fc on the output side of these phase detectors 413). A lower half of the signal F is inverted, as shown in Fig. 4. The signal F is converted into a flat signal by means of the low-pass filters 414a, 414b, and 414c each having a sufficiently low cut-off frequency and is input to one input terminals of the comparators 415a, 415b, and 415c. A predetermined threshold voltage +VT has been input to each of the other input terminals of the comparators 415a, 415b, and 415c, and the output of the low-pass filters 414a, 414b, and 414c is compared with the threshold voltage +VT. In this example, the signal Fa, which has passed through the mechanical filter 412 et seq. in accordance with the signal of 450 KHz, is fed to the output terminal 416a as a high (H) level signal Ga. At the same time, signals Gb and Gc of low (L) level are fed to the other output terminals 416b and 416c, thereby keeping these two output terminals at "0" level. From these facts, it is determined that the input pen 2 in use is the one corresponding to the display color "black". On the other hand, if the signal D' is received, both signals E and F will be at "0" level, so that signals Ga, Gb, and Gc (not shown in Fig. 4), which are also at low (L) level, are generated, thereby enabling the operating status of the switches 221 to be detected. If the arrangement of the system is such that the signals Ga, Gb, and Gc are sent to the position detecting circuit 3 on the basis of a definition that, when one of these signals is at high level, this means that the corresponding input pen 2 is in the "pen-down" status, and that, when the signal is at low level, this means that the corresponding input pen is not in the "pen-down" status, the input of a position can be effected by operating the input pens 2 with respect to the tablet 1 and simply by pressing the tip of one of the input pens 2 against the tablet 1 at a position where coordinates are to be input. Although in the foregoing embodiment, the signal E is detected by distributing it to three lines in accordance with the resonance frequencies, it is possible to provide an alternative arrangement in which a single line is provided by using a mechanical filter having the range of between 450 KHz and 550 KHz in place of the three mechanical filters 412a, 412b, and 412c, and in which the oscillator 401 is adapted to generate a signal for discriminating each of the frequencies or a timing signal for changing over the frequencies, so that the types of the input pens can be also discriminated therebetween from the timing and the output of the comparator.

Claims: A system for detecting the status of a position designating device (2), such as a stylus pen, in a coordinates input apparatus having a tablet (1) constituting a coordinate input section, and a position detecting circuit (3) adapted to drive said tablet and detect positions at which coordinates are input by said position designating device, characterized in that said tablet (1) is provided with an antenna coil (13), and each one of a plurality of position designating devices (2) of different types is provided with a tuning circuit (22) including a coil (222) and capacitors (223,224) working cooperatively to transmit radio waves in response to an external signal at an individual frequency predetermined in accordance with a corresponding type of position designating device, wherein an AC-signal having a plurality of frequencies each being identical to an individual frequency of one of said tuning circuits is intermittently and sequentially applied to said antenna coil so that radio waves are transmitted by said antenna coil, and, when the transmission of said radio waves is suspended, signals generated by said tuning circuits in response to said radio waves are received by said antenna coil to enable the detection of the respective positions and operating statuses of said position designating devices, and wherein a determination of the correspondence of the frequencies of the received signals with the types of position designating devices is used to effect a differentiation between the different types of said position designating devices. A system according to claim 1, further comprising a switch (221) disposed in each of said tuning circuits (22) for turning on or off the connection between said coil and said capacitors, wherein, when it is required to designate only a position at which coordinates are to be input, said position designating devices are used by turning on or off said switches. A system according to claim 1, wherein said tablet further comprises a casing (11) made of a non-metallic material such as a synthetic resin, and a tablet body (12), in addition to said antenna coil (13), said casing accomodating said tablet body and said antenna coil. A system according to claim 1, wherein each of said position designating devices further comprises a magnetism generator (21) for designating positions, in addition to said tuning circuit. A system according to claim 1, wherein said antenna coil (13) comprises a conductive wire provided with an insulation coating such as polyvinyl chloride, said conductive wire being disposed around a coordinates input range (14) of said tablet. A system according to claim 1, wherein said tuning circuit has a variable capacitor (224). A method of distinguishing between different types of position designating devices (2) used for inputting coordinates in a coordinate input apparatus which has a tablet (1) constituting a coordinate input section, and a position detecting circuit (3) adapted to drive said tablet and detect positions at which coordinates are input by said position designating device, each position designating device comprising a tuning circuit (22), wherein said tuning circuits (22) are adapted to transmit radio waves in response to an external signal at an individual frequency determined in accordance with the type of position designating device, AC-signals having frequencies identical with said individual frequencies are successively transmitted from said tablet, signals which are re-transmitted in response to said transmitted signals from the tuning circuit of the position designating device being used are received in said tablet, and the correspondence of the received signals with the types of position designating devices is determined, thereby distinguishing between the types of position designating devices.

Inventors: SENDA, TOSHIAKI 303 MAESHIMA-MANSION, YAMANAMI, TSUGUYA 303 MAESHIMA-MANSION
Applicants: WACOM CO., LTD.
Application year: 1987
Main classification: G06K11
IPC codes: G06F3