JP2608901B2 - Coordinate input device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a coordinate input device using radio waves or magnetism.

(Conventional technology) Conventionally, in this type of coordinate input device, a shield plate is placed below a sensing portion of a tablet to avoid the influence of unnecessary external interference radio waves, terrestrial magnetism, and the like.

(Problems to be Solved by the Invention) However, if the shield plate and the sensing portion are brought too close to each other, the level of the detection signal becomes small, and the position cannot be detected. Therefore, there is a problem that the thickness of the tablet cannot be reduced.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a coordinate input device capable of eliminating the above-mentioned problems and making the thickness of a tablet extremely thin.

(Means for Solving the Problems) In the present invention, in order to solve the above problems, radio waves or magnetism is exchanged between the sensing unit of the tablet and the position indicator, and at least the position connected to the sensing unit of the tablet. In a coordinate input device for detecting input coordinates by a detection circuit, a shield plate made of silicon steel containing 4.0 to 7.0% by weight of silicon is provided below a sensing part of a tablet.

(Operation) According to the present invention, the shield plate provided below the sensing portion of the tablet eliminates the influence of unnecessary external interference radio waves and geomagnetism, but the shield plate is made of silicon.
Since it is made of silicon steel containing 0 to 7.0% by weight and has little loss with respect to radio waves and magnetic fields exchanged between the sensing unit and the position indicator, it can be arranged close to the sensing unit.

FIG. 11 shows the experimental results of the detection signal voltage obtained when the distance between the sensing part of the tablet and the shield plate was changed. In the figure, 4 is a 0.35 mm thick 6.5% silicon steel (I). 5 indicates the characteristics when using 0.5% thick 6.5% silicon steel (II), and 6 indicates the characteristics when using 0.5 mm thick conventional silicon steel (III). Show. Table 1 shows the composition and magnetic properties of the above silicon steels (I), (II) and (III).

According to the graph shown in FIG. 11, the conventional silicon steel (II
It can be seen that the voltage that could not be obtained with the shield plate according to I) unless it was separated by 5 mm from the sense part was obtained at 0 m with 6.5% silicon steel, that is, in the state of being in close contact. Next, the silicon content of the shield plate was changed FIG. 12 shows the experimental results of the detection signal voltage obtained occasionally. FIG. 12 shows the result of measuring the detection voltage in a state where the shield plate is in close contact with the sensing portion, and the plate thicknesses of all the shield plates are 0.35 mm. As is clear from FIG. 12, the silicon content is 4.0 to
Detection signal voltage 4 (Vp
p) is obtained.

For the shield plate, Ni, Co, Al should be added to improve the magnetic properties. C0.01 wt%, Mn0.3 wt%, P0.1 wt%, S0.02 wt% ,
It is also preferable to set N 0.01% by weight and 00.01% by weight.

FIG. 1 shows an outline of a coordinate input device according to the present invention.
In the figure, 1 is a tablet for inputting coordinates, 2 is a position indicator for specifying a position, for example, a stylus pen,
Reference numeral 3 denotes a position detection circuit that detects a coordinate value on the tablet 1 designated by the stylus pen 2.

As shown in FIG. 2, the tablet 1 is provided with reinforcing plates 12 and 13 of about 2 mm in thickness such as acrylic and vinyl chloride above and below a flat sensing part 11 of about 0.8 mm in thickness. , A thickness of about 0.35 mm between the sense part 11 and the reinforcing plate 13
A shield plate 14 made of 6.5% silicon steel is provided so as to be in close contact with the lower surface of the sensing portion 11, and the entire thickness is 0.1 mm.
It is laminated with vinyl 15 of about 5 mm, and the overall thickness is about 5 mm.

FIG. 3 shows details of the loop coil group 16 in the X direction and the loop coil group 17 in the Y direction, which constitute the sensing unit 11. Each of the X-direction loop coil groups 16 has a substantially rectangular shape, and a large number of, for example, 48 loop coils 16-1, arranged such that their long sides are parallel to each other along the Y-direction and partially overlap each other. 16-2,..., 16-48, and the loop coil groups 17 in the Y direction are also substantially rectangular, and their long sides are parallel to each other along the X direction, and a part of each is overlapped. A large number of 48 loop coils 17-1, 17-2, ... 17-
The loop coil group 16 in the X direction and the loop coil group 17 in the Y direction are closely overlapped with each other (however, they are drawn apart for easy understanding in the drawings). The loop coil groups 16 and 17 are composed of patterns on a double-sided board, for example. Here, each loop coil is constituted by one turn, but may be constituted by a plurality of turns as necessary.

FIG. 4 shows a stylus pen (hereinafter simply referred to as a pen).
2 shows a detailed structure, in which a core 22 such as a ball-point pen and a core 22 such as a ball-point pen can be slidably housed inside a pen shaft 21 made of a non-metallic material such as a synthetic resin from its tip. Through hole
Ferrite core 23 with 23a, coil spring 24, switch 251, coil wound around ferrite core 23
A tuning circuit 25 consisting of a capacitor 252 and capacitors 253 and 254 is integrally incorporated and built in, and a cap 26 is attached to the rear end.

The coil 252 and the capacitor 253 are connected in series with each other as shown in FIG. 5 so as to constitute a well-known resonance circuit. The phase of the current is set to a value that resonates (tunes) in phase. Also the capacitor
254 is connected in parallel to both ends of the capacitor 253 via a switch 251, and when the switch 251 is turned on,
The phase of the current in the above-described resonance circuit is delayed, and the phase of the received signal described later is delayed by a predetermined angle. The switch 251 holds the pen shaft 21 by hand or the like, and pushes the tip of the core body 22 into the pen shaft 21 by, for example, pressing the tip of the core 22 on the upper surface of the tablet 1.
It is pressed through 24 and turned on.

FIG. 5 shows the details of the position detection circuit 3 together with the tuning circuit 25. In the figure, reference numeral 301 denotes a control circuit, 302 denotes a signal generating means (circuit), and 303x and 303y denote X and Y direction selecting means (circuits). Also, 304x and 304y are transmission / reception switching circuits, 305 is an XY switching circuit, and 306 is a reception timing switching circuit, and these constitute connection switching means. Also,
307 is a bandpass filter (BPF), which constitutes a signal detecting means. Reference numeral 308 denotes a detector, and reference numeral 309 denotes a low-pass filter (LPF), and these constitute a coordinate detecting means including processing in the control circuit 301 described later. Also, 310,311
Is a phase detector (PSD), 312 and 313 are low-pass filters (LPF)
These constitute switch ON / OFF discriminating means including the processing in the control circuit 301 described later. Further, 314x and 314y are drive circuits, and 315x and 315y are amplifiers.

Next, the operation of the device will be described together with its configuration.
First, how radio waves for position detection are transmitted and received between the tablet 1 and the pen 2 and the signals obtained at this time will be described with reference to FIG.

The control circuit 301 includes a well-known microprocessor or the like, controls the signal generation circuit 302,
Selection circuits 303x and 303y according to the flowchart shown in FIG.
The switching of each loop coil of the tablet 1 is controlled via the XY switching circuit 305 and the reception timing switching circuit 3
Control the switching of the coordinate detection direction for 06.
The output values from the low-pass filters 309, 312, and 313 are converted from analog to digital (A / D), the arithmetic processing described later is executed to calculate the coordinate value of the position specified by the pen 2, and the state of the switch is identified. To a host device (not shown) such as a host computer.

The selection circuit 303x sequentially selects one loop coil from the X-direction loop coil group 16, and the selection circuit 303y sequentially selects one loop coil from the Y-direction loop coil group 17. And operates based on information from the control circuit 301.

The transmission / reception switching circuit 304x alternately connects the selected one loop coil in the X direction to the driving circuit 314x and the amplifier 315x, and the transmission / reception switching circuit 304y connects the selected one loop coil in the Y direction. Are alternately connected to a drive circuit 314y and an amplifier 315y, which operate according to a transmission / reception switching signal described later.

The signal generating circuit 301 has a predetermined frequency f0, for example, a rectangular wave signal A of 500 kHz, a signal A '(not shown) obtained by delaying the phase of the rectangular wave signal A by a predetermined angle, a predetermined frequency fk, for example, 15.
A 625 kHz transmission / reception switching signal B and a reception timing signal C are generated. The rectangular wave signal A is sent to the phase detector 310 and is converted into a sine wave signal by a low-pass filter (not shown).
Or 314y, the square wave signal A 'is sent to the phase detector 311, the transmission / reception switching signal B is sent to the transmission / reception switching circuits 304x and 304y, and the reception timing signal C Is the reception timing switching circuit 30
Sent to 6.

Now, assuming that information for selecting the X direction is input from the control circuit 301 to the XY switching circuit 305 and the reception timing switching circuit 306, the sine wave signal is transmitted to the driving circuit 314x, converted into a balanced signal, and further transmitted and received. The signal is transmitted to the switching circuit 304x, and the transmission / reception switching circuit 304x switches and connects one of the drive circuit 314x and the amplifier 315x based on the transmission / reception switching signal B, and is output from the transmission / reception switching circuit 304x to the selection circuit 303x. The signal is at time T (= 1 / 2fk), here every 32 μsec
The signal D is a signal D that outputs or does not output a signal of 500 kHz.

The signal D is sent to the X of the tablet 1 through the selection circuit 303x.
It is transmitted to one loop coil 16-i (i = 1, 2,..., 48) in the direction, and the loop coil 16-i generates a radio wave based on the signal D.

At this time, when the pen 2 is held in a substantially upright state, that is, in a used state on the tablet 1, the radio wave excites the coil 252 of the pen 2 and causes the tuning circuit 25 to generate an induced voltage synchronized with the signal D. E is generated.

Thereafter, when the signal D enters a period of no signal, that is, a reception period, and the loop coil 16-i is switched to the amplifier 315x side, the radio wave from the loop coil 16-i immediately disappears, but the induced voltage E becomes lower. It gradually attenuates according to the loss in the tuning circuit 25.

On the other hand, the current flowing through the tuning circuit 25 based on the induced voltage E causes the coil 252 to emit radio waves. Since the radio wave excites the loop coil 16-i connected to the amplifier 315x in reverse, an induced voltage due to the radio wave from the coil 252 is generated in the loop coil 16-i. The induced voltage is transmitted from the transmission / reception switching circuit 304x to the amplifier 315x and amplified to become the reception signal F only during the reception period, and further the reception timing switching circuit
Sent to 306.

Either the selection information in the X direction or the Y direction, here the selection information in the X direction, and the reception timing C which is substantially the inverted signal of the transmission / reception switching signal B is input to the reception timing switching circuit 306. When the signal C is at the high (H) level, the reception signal F is output, and during the low (L) level, nothing is output. Therefore, the signal G is output at the output (substantially the same as the reception signal F). Is obtained.

The signal G is transmitted to the band filter 307. The band filter 307 is a ceramic filter having a frequency f0 as a unique frequency, and a signal having an amplitude h corresponding to the energy of the frequency f0 component in the signal G. H (strictly, in a state where several signals G are input to the bandpass filter 307 and converge) are transmitted to the detector 308 and the phase detectors 310 and 311.

The signal H input to the detector 308 is detected and rectified to be a signal I, and a low-pass filter 309 having a sufficiently low cutoff frequency has a voltage value corresponding to almost half of the amplitude h, for example, Vx And transmitted to the control circuit 301.

The voltage value Vx of the signal J is the pen 2 and the loop coil 16-i.
A value dependent on the distance between the two, and here a value that is approximately inversely proportional to the fourth power of the distance, and changes when the loop coil 16-i is switched. By converting the value Vx into a digital value and performing an arithmetic process described later on these, the pen 2
Is used to calculate the coordinate value of the designated position in the X direction. In addition,
The coordinate value of the designated position in the Y direction by the pen 2 is calculated in the same manner.

On the other hand, the rectangular wave signal A is input to the phase detector 310 as a detection signal. At this time, the switch 251 is off and the phase of the signal H substantially matches the phase of the rectangular wave signal A. In this case, a signal (in substantially the same as the signal I) obtained by inverting the signal H to the positive side is output. This signal is converted into a DC signal (substantially the same as the signal J) having a voltage value corresponding to almost half of the amplitude h by the low-pass filter 312 as described above, and sent to the control circuit 301.

The rectangular wave signal A 'is input to the phase detector 311 as a detection signal.
Is off and the phase of the signal H is advanced by a predetermined angle with respect to the phase of the rectangular wave signal A ', a signal having components on the positive side and the negative side is output. This signal is converted into a DC signal by the same low-pass filter 313 and sent to the control circuit 301.Since the output signal of the phase detector 311 has components on the positive side and the negative side, the low-pass filter 313 The output voltage value is considerably smaller than the output voltage value of the low-pass filter 312.

Here, when the switch 251 of the pen 2 is turned on, the phase of the current flowing through the tuning circuit 25 is delayed with respect to the induced voltage E,
The phase of the received signal F is also delayed by a predetermined angle, that is, almost coincides with the phase of the rectangular wave signal A '. Accordingly, the output H of the bandpass filter 307 at this time is converted into a signal having components on the positive side and the negative side by the phase detector 310, and the lowpass filter 31
The output of 2 has substantially the same voltage value as the output of the low-pass filter 313 when the switch 251 is off, but the phase detector 3
The signal is inverted to the positive side by 11 and the low-pass filter 31
The output of 3 is a DC signal having a predetermined voltage value corresponding to approximately 1/2 of the amplitude h, as described above.

Thus, when the switch 251 is off, the low-pass filter 3
A predetermined voltage value is obtained at the output of 12 and the switch 251
Is ON, a predetermined voltage value is obtained at the output of the low-pass filter 313.
By monitoring the output values of 12 and 313, switch 251
Can be identified as being off or on.

The information indicating the on (or off) state of the switch 251 identified here is used as information for specifying a value to be actually input among the coordinate values of the position specified by the pen 2.

Next, the coordinate detection operation in the position detection circuit 3 and the state of the pen 2 according to FIGS.
The operation of the entire apparatus will be described together with the details of the on / off state identification operation of 251.

First, when the power of the entire apparatus is turned on and the measurement is started, the control circuit 301 sends information for selecting the X direction to the XY switching circuit 305 and the reception timing switching circuit 306, and the loop coil of the tablet 1 in the X direction. 16-1 to 16-
Of the 48, information for selecting the first loop coil 16-1 is sent to the selection circuit 303x, and the loop coil 16-1 is connected to the transmission / reception switching circuit 304x.

Based on the transmission / reception switching signal B described above, the transmission / reception switching circuit 304x drives the loop coil 16-1 with the driving circuit 314x and the amplifier 315x.
In this case, the drive circuit 314x is switched to 32 μm.
In the transmission period of sec, 500 as shown in FIG.
The 16 sine wave signals of kHz are sent to the loop coil 16-1.

The switching between transmission and reception is repeated seven times for one loop coil, here 16-1, as shown in FIG. 8 (b). The seven transmission and reception repetition periods correspond to one loop coil selection period (448 μsec).

At this time, an induced voltage is obtained from the output of the amplifier 315x every seven reception periods for one loop coil, and this induced voltage is supplied to the bandpass filter 307 via the reception timing switching circuit 306 as described above. Transmitted and averaged, detector 3
08, transmitted to the control circuit 301 via the phase detectors 310, 311 and the low-pass filters 309, 312, 313.

The control circuit 301 performs A / D conversion of the output value of the low-pass filter 309 and inputs it, and temporarily stores the detection value as a detection voltage depending on the distance between the pen 2 and the loop coil 16-1, for example, Vx1.

Next, the control circuit 301 sends information for selecting the loop coil 16-2 to the selection circuit 303x, connects the loop coil 16-2 to the transmission / reception switching circuit 304x, and connects the pen 2 and the loop coil 16-2.
Obtain the detection voltage Vx2 depending on the distance to and memorize it,
Thereafter, similarly, the loop coils 16-3 to 16-48 are sequentially connected to the transmission / reception switching circuit 304x, and depend on the distance in the X direction from the pen 2 for each loop coil as shown in FIG. 8 (c). The detected voltages Vx1 to Vx48 (however, only a part thereof is shown in an analog expression in FIG. 8C) are stored.

As shown in FIG. 9, the actual detection voltage is obtained only in the several loop coils before and after the center (xp) where the pen 2 is placed.

The control circuit 301 checks whether or not the maximum value of the plurality of stored detection voltages is equal to or higher than a predetermined fixed detection level, for example, the detection level shown in FIG. 9. The selection of each loop coil in the X direction and the voltage detection are repeated again, and if it is equal to or higher than a certain detection level, the process proceeds to the next process.

Next, the control circuit 301 sends selection information in the Y direction to the XY switching circuit 305 and the reception timing switching circuit 306, switches the selection circuit 303y and the transmission / reception switching circuit 304y in the same manner as described above, and controls the low band when transmitting and receiving radio waves. The pen 2 obtained by A / D conversion of the output value of the filter 309 and each of the Y-direction loop coils 17-1 to 17-1
The detection voltage depending on the distance to 17-48 is temporarily stored. Thereafter, a level check is performed in the same manner as described above, and if the maximum value of the detection voltage is equal to or lower than a predetermined detection level, X
Returning to the selection of each loop coil in the direction and the voltage detection, and if the voltage is equal to or higher than a predetermined detection level, the coordinate values of the designated positions of the pen 2 in the X and Y directions will be described later based on the stored voltage values. Is calculated.

Next, the control circuit 301 controls the loop coil 16- in the X direction.
1 to 16-48 (or Y-direction loop coils 17-1 to 17-4)
8) The information for selecting the loop coil for which the maximum detection voltage is obtained is transmitted to the selection circuit 303x (or 303y), and the transmission and reception of the radio wave is repeated a plurality of times, for example, seven times. A / D output value obtained from 312 and 313
Then, as described above, it is detected whether any of these values is equal to or greater than a predetermined value, and the on / off state of the switch 251 is identified.

The on / off identification result of the switch 251 is transferred to the host device together with the coordinate values of the designated positions of the pen 2 in the X and Y directions.

When the first coordinate detection operation and the state identification operation are completed in this way, the control circuit 301 performs the second and subsequent coordinate detection operations as shown in FIG. Among the 16-48, the selection circuit selects information for selecting only a certain constant before and after the loop coil at which the maximum detection voltage is obtained, for example, only 10 loop coils.
303x, and the Y-direction loop coils 17-1 to 17-1
Of the −48, the loop coil for which the maximum detection voltage is obtained is centered, and a constant number before and after the loop coil, information for selecting only the ten loop coils is sent to the selection circuit 303y, and the output value is output in the same manner as described above. Then, the coordinate detection operation of the pen 2 in the X direction and the Y direction and the identification operation of the ON / OFF state of the switch 251 are performed, and the obtained coordinate values and the identification result are transferred to the higher-level device.

In addition, if the level check described above is explained in detail,
Check whether the maximum value of the detection voltage has reached the detection level and which loop coil has the maximum value of the detection voltage, and stop the subsequent coordinate calculation and the like if the detection level has not been reached. This is a process of setting the center of the loop coil to be selected in the next coordinate detection operation and state identification operation.

X-direction or Y-direction coordinate values, for example, as one method of calculating the coordinate value xp, approximate the waveform near the maximum value of the detection voltage Vx1 ~ Vx48 with a suitable function, the coordinates of the maximum value of the function There is a way to ask.

For example, in FIG. 8 (c), the maximum detection voltage Vx3
And the detection voltages Vx2 and Vx4 on both sides thereof can be calculated as follows by approximating the coordinate values of the center position of each loop coil 16-1 to 16-48 by x1.
X48, and the interval is Δx. ). First, from each voltage and coordinate value, Vx2 = a (x2-xp) ² + b (1) Vx3 = a (x3-xp) ² + b (2) Vx4 = a (x4-xp) ² + b ... ... (3) Here, a and b are constants (a <0).

X3−x2 = Δx (4) x4−x2 = 2Δx (5) Substituting the equations (4) and (5) into the equations (2) and (3) and rearranging it, xp = x2 + Δx / 2 ｛(3Vx2-4Vx3 + Vx + 4) / (Vx2-2Vx3 + Vx4)｝ ... (6) .

Therefore, the maximum value of the detection voltage obtained at the time of the level check and the detection voltages before and after that are extracted from each of the detection voltages Vx1 to Vx48, and these and the one of the loop coil from which the maximum value of the detection voltage is obtained. The coordinate value xp of the designated position of the pen 2 can be calculated by performing an operation corresponding to the above-described equation (6) from the coordinate value (known) of the previous loop coil.

As described above, according to this embodiment, there is no need to connect the tablet and the pen with a cord, and a coordinate input device with excellent operability can be realized.

Note that the number of loop coils and the arrangement thereof in the embodiment are merely examples, and it is needless to say that the present invention is not limited to this. Further, in the above embodiment, the shield plate and the sensing portion are brought into close contact with each other, but they may be separated by an appropriate distance. Furthermore, the present invention relates to Japanese Patent Application No.
The same can be applied to the "position detecting device" of 32244 (see JP-A-60-176133).

(Effects of the Invention) As described above, according to the present invention, the shield plate provided below the sensing part of the tablet eliminates the influence of unnecessary external interference radio waves, geomagnetism, and the like. Is made of silicon steel containing 4.0 to 7.0% by weight of silicon, and has a small loss to radio waves and magnetic fields exchanged between the sensing unit and the position indicator, so that it can be arranged close to the sensing unit. Therefore, the thickness of the tablet can be made extremely small as compared with the conventional tablet, and when this is incorporated in another device (for example, a keyboard), the storage volume can be reduced, and when the tablet is used alone, There is an advantage that a compact one having a small volume can be provided.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an outline of a coordinate input device of the present invention, FIG. 2 is a cross-sectional view of a tablet, FIG. 3 is a detailed configuration diagram of a sensing unit of the tablet, FIG. FIG. 5 is a diagram showing details of a tuning circuit and a position detecting circuit of the stylus pen, FIG. 6 is a signal waveform diagram of each part in FIG. 5, FIG. 7 is a flowchart of a process in a control circuit of the position detecting circuit, FIG. FIGS. 9A, 9B and 9C are timing charts showing a basic position detecting operation in the position detecting circuit, and FIG. 9 shows detected voltages obtained from each loop coil at the time of the first position detecting operation. FIG. 10, FIG. 10 is a timing chart showing the second and subsequent position detection operations and state identification operations, and FIG. 11 is an experiment of a detection signal voltage obtained when the distance between the sensing part of the tablet and the shield plate is changed. Graph showing the results,
FIG. 12 is a graph showing an experimental result of a detection signal voltage obtained when the silicon content of the shield plate was changed. DESCRIPTION OF SYMBOLS 1 ... Tablet, 2 ... Stylus pen, 3 ... Position detection circuit, 11 ... Sense part, 14 ... Shield plate.

Claims (1)

(57) [Claims] 1. A coordinate input device for exchanging radio waves or magnetism between a sensing part of a tablet and a position indicator and detecting input coordinates by a position detecting circuit connected to at least the sensing part of the tablet. A coordinate input device, wherein a shield plate made of silicon steel containing up to 7.0% by weight is provided below the sensing part of the tablet.