JPS59195776A - Electromagnetic induction type coordinate reader - Google Patents

Abstract

PURPOSE:To detect quickly the position coordinates of a coordinate indicator by switching the gain of an amplifier amplifying an induction signal induced in a sense wire depending on the level of the induction signal. CONSTITUTION:A gain switching circuit 23 switching the gain of an amplifier 8 amplifying the induction signal induced in sensor wires Xi, Yi and a level discriminating circuit 16 discriminating the level of the amplified inducing signal are provided respectively. The gain of the amplifier circuit 8 is set maximum by an operation control section 15 when a coordinate indicator 4 approaches a tablet face 1. Further, when the level of the inducing signal is larger than a prescribed level, the gain of the amplifier 8 is switched to be minimum by the operation control section 15. Thus, the position coordinates of the coordinate indicator are detected quickly.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention applies an alternating magnetic field generated from a coordinate indicator to a conducting wire laid on a tablet, and detects the magnitude of the induced voltage induced in this conducting wire to determine the position of the coordinate indicator. The present invention relates to a coordinate reading device for determining coordinates, and in particular to a novel improvement for detecting the approach of a coordinate indicator to a tablet with high sensitivity.

A coordinate reading device used for a certain type of purpose is required to have a mechanism that quickly detects the position coordinates of a coordinate indicator when the coordinate indicator approaches a tablet surface.

In conventional coordinate reading devices, the sense lines are scanned at high speed, and the induced signal level induced in each sense line by the alternating magnetic field applied by the excitation winding of the coordinate indicator is converted into digital information using an A/D converter. A method has been proposed in which, after conversion, it is determined whether the line is at a predetermined level or not, and the position coordinates of the sense line when the level exceeds the predetermined level are detected and detected as the position coordinates of a coordinate indicator. .

However, this method has the drawback that it takes a long time to detect the position of the coordinate indicator because the conversion speed of the A/D converter is several tens of microseconds or more.

In order to eliminate the above-mentioned drawbacks, the present invention provides a gain switching circuit that can set the gain of an amplifier that amplifies the induced signal induced in the sense line in several stages, and the level of the analog signal input to the A/D converter. When the coordinate indicator approaches the tablet surface, the sense line is scanned at high speed and the gain of the amplifier circuit is set to the maximum, so that the level of the signal induced by the sense line is set to the maximum. The position coordinates of the coordinate indicator are detected at a point in time when the guidance signal is small, that is, at an early point when the coordinate indicator approaches the tablet surface, and then A
/ A level determination circuit directly determines the level of the analog signal before inputting it to the D converter, allowing the sense line to be scanned at extremely high speed without being restricted by the conversion speed of the A/D converter. This allows the position coordinates of the coordinate indicator to be detected.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

As shown in FIG. 1, the basic structure of the tablet 1 consists of a plurality of folded X-axis sense lines on the surface side of a suitable insulating substrate 2.
...
3,...Yn) are laid in parallel at the same pitch.

One end of each X-axis sense line Xt is connected to each analog switch S of the X-axis scanning circuit 3x consisting of a group of analog switches, and one end of each Y-axis sense line Yj is connected to each analog switch S of the Y-axis scanning circuit 3Y. It is connected to the. Furthermore, each analog switch S is connected to a common output line α. Further, the other ends of each of the senses gXi and Y are connected to a common ground line and grounded. As described later, the scanning circuits 3X and 3Y operate from x1 to x2...
...→xrrL-+Y1→Y2...→Y%
In this order, the analog switches S are sequentially closed so as to connect each sense line to the common output line a.

An excitation winding 5 is attached to the coordinate indicator 4. 6 is a predetermined frequency f. 7 is an amplifier that amplifies the output of the oscillator 6. The excitation signal amplified by the amplifier 7 is supplied to the excitation winding 5, and an alternating magnetic field with a frequency of 10 is generated from the coordinate indicator 4. do.

When the coordinate indicator 4 that generates an alternating magnetic field approaches the tablet 1, the coordinate indicator 4
The frequency f is on the sense lines xi and y in the vicinity of . AC signals are induced. The induced signals induced in the sense lines xi and Yj are generated only when the analog switch 8 connected to the sense lines Xi and Yj is selected by the scanning circuits 5X and 3Y.
It is derived to the output line α. That is, as the sense lines are scanned, the induced signals from each sense line appear in order on the output line α.

The induced signal appearing on the output line α is amplified by an amplifier 8 and supplied to a band F wave generator 9 whose passband is a frequency 10. As a result, the induced signal caused by the alternating magnetic field is discriminated, and only the induced signal is output from the bandpass filter 9. This output is amplified by an amplifier 10, rectified by a rectifier circuit 11, and further smoothed by a low-frequency F wave filter 12. This smoothed output corresponds to the induced signal level of each sense line. The output of the low-pass F wave generator 12 is input to the A/D converter 14 via the amplifier 13, and is converted into an A/D converter 14.
The data converted by the D converter 14 is input to the calculation control section 15. Furthermore, the output of the amplifier circuit 16 is the level judgment circuit 1.
6 is input. The level determination circuit 16 includes a reference voltage generation circuit 117 and a level comparison circuit 18. The level comparison circuit 18 compares the reference level output from the reference voltage generation circuit 17 and the induced signal level output from the amplifier circuit 13. When the induced signal level becomes higher than the reference level, the output of the level comparison circuit 18 is output to the arithmetic control section 15.
is input. This arithmetic control unit 15 is mainly composed of a microcomputer implemented in firmware, and includes a microprocessor 19. Memory 20. It consists of interfaces 21°, 20, etc. This arithmetic control section 15 is
In addition to controlling the gain switching circuit 23, which will be described later, it also controls scanning of the sense lines Xi and Yj via the address register 24, and at the same time performs processing to obtain coordinate values based on the output of the A/D converter 14. It performs input/output processing between external devices 25, etc.

Next, the operation of detecting the position coordinates of the coordinate indicator 4 will be described. There are basically two operations for detecting position coordinates. One is the operation of scanning the sense lines Xi and Yj over the entire surface of the tablet 1 when the coordinate indicator 4 approaches the tablet 1, and detecting the rough position coordinates of the coordinate indicator 4. This operation scans only the sense lines near where the coordinate indicator 4 is located, calculates the guidance signal level of each sense line, obtains the interpolated position, and detects the detailed position coordinates of the coordinate indicator 4. The present invention relates to a mechanism that quickly detects the rough position coordinates of the coordinate indicator when the coordinate indicator approaches the tablet.
The operation of detecting detailed positional coordinates of the coordinate indicator described later is similar to the operation of a conventional coordinate reading device of this type, and detailed explanation will be omitted. Therefore, the operation of detecting the rough position coordinates of the coordinate indicator 4 when the coordinate indicator 4 is brought closer to the tablet 1 will be described in detail with reference to FIGS. 2 and 3. In Figure 2 (α), the coordinate indicator 4 is the tablet 1.
FIG. 2(b) shows the level of the induced signal induced in the sense line Xi at that time. When the coordinate indicator 4 approaches h1 to h2 on the surface of the tablet 1, a signal is induced on the sense line Xi and the induced signal level V appearing on the terminating resistor Re changes from vl to v2.
increases quadratically to . In order to quickly detect the proximity of the coordinate indicator 4 to the tablet 1, it is necessary to be able to detect when the induced signal level υ is small, and it is desirable to increase the gain of the amplifier circuit 8. Therefore, in this embodiment, a gain switching circuit 23 capable of switching the gain of the amplifier circuit 8 in three stages is connected to the amplifier circuit 8 to provide the gain characteristic shown in FIG. 2(C). The gain switching circuit 23 is composed of a 0-MOS analog switch, etc., and is controlled by the arithmetic control section 15. The VTR in FIG. 2(C) has a level determination circuit 16.
This corresponds to the level output from the reference voltage generation circuit 17 of Level judgment time f
Output from #116 to the calculation control unit 15
The gain switching circuit 23 can be controlled by the following.

Next, the operation will be explained in more detail according to the flowchart shown in FIG.

First, in step 1, the coordinate indicator 4 is excited, the arithmetic control section 15 controls the gain switching circuit 23, and the gain of the amplifier 8 is set to A1. Next, in step 2, the arithmetic control section 15 sequentially controls the analog switches 8 of the scanning circuits 3X and 3Y via the address register 24, and the sense line X'+
Y) is scanned over the entire surface of the tablet 1. In step 3, the value of V in FIG. 3(C) corresponding to the induced signal level induced in the sense line is checked, and V≧VT
If the result is H, proceed to step 4, and otherwise repeat steps 1 to 3. The operation in step 3 is to monitor the output of the level determination circuit 16 by comparing the level of the induced signal amplified with the gain A1 and the reference level VTR by the arithmetic control unit 15. In step 4, the arithmetic control section 15 controls the gain switching circuit 23 to set the gain of the amplifier 8 to A3. This is because when the coordinate indicator 4 rapidly moves from hl to A2, that is, when the induced signal rapidly changes from vl to υ2, the induced signal level is saturated at the gain A1, and the gain is changed to A.

The purpose is to input the unsaturated induced signal level to the A/D converter 14. The address detection in the next step 5 is to detect which sense line Xi is being scanned by the arithmetic control unit 15 at the time when the level judgment circuit 16 outputs the signal. - If it turns out that the level determination circuit 16 outputs an output while controlling the C\axis sense line Y, then it is possible to determine that the coordinate indicator 4 is located near the intersection of the sense lines xlltYls. The position coordinates of the coordinate indicator 4 can be detected. In this way, the rough position coordinates of the coordinate indicator 4 can be detected in steps 1 to 5, and the rough position coordinates of the coordinate indicator 4 can be detected in an unprecedented short distance.

Steps 6 to 14 are pre-processing for entering the coordinate detection routine [step 15] of a conventional coordinate reading device of this type for detecting the detailed position coordinates of the coordinate indicator 4.
This shows a routine in which the level of the induced signal input to the converter 14 is set to an optimum level by the gain switching circuit 23. The area scan in step 6 scans only the sense lines in the vicinity of the sense line address detected in step 5, and the induced signals induced in each sense line are sequentially derived. In step 7, the A/D converter 14 is activated at an appropriate timing when the level of the induction signal becomes stable. In the next step 8, wait for a conversion end signal from the A/D converter 14, and when the conversion is completed, proceed to the next step 9.
, the digitally converted detection voltage VP is taken in.

In steps 1o and 11, the level of this detection voltage vp is determined. If vP≦Vb, the process proceeds to step 13, and if the gain is not set to A1, the gain is changed from A3 to A2 in step 14, or Allgara A1
Thus, the gain is set one step higher, and the process returns to step 6. If the gain has already been set to A1, it is determined that the reading medium 26 placed on the tablet 1 is thick and the guiding signal level is small, and the process moves to the coordinate detection routine 15. In step 11, Vp≧
If it is determined to be VH, the gain is set to a smaller gain by one step, such as from A1 to A2 or from A2 to A3, in step 12, and the process returns to step 6. Therefore, in step 10.11, even if the thickness of the reading medium 26 placed on the table left 1 changes, the detection voltage Vp is changed to Vp.
The level is adjusted by the gain switching circuit 23 so that the state becomes p (V p (V H), and it becomes possible to proceed to the coordinate detection routine 15.

Note that VH and VL are set to provide appropriate hysteresis to changes in gain characteristics to prevent chattering in gain changes.

As described above in detail, the coordinate reading device according to the present invention includes a gain switching mechanism that can set the gain of the amplifier that amplifies the induced signal induced in the sense line in several stages, and an induced signal level determination mechanism. This is achieved by the arithmetic control unit, so the position coordinates of the coordinate indicator can be detected extremely quickly. Furthermore, the guidance signal is amplified with the optimum gain and input to the A/D converter, allowing the position coordinates to be determined with high accuracy. It has the effect of being able to be detected.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the overall configuration of the coordinate reading device according to the present invention, Fig. 2 (α) is a perspective view showing the state between the coordinate indicator and the tablet, and Fig. 2 (b) is a sense line. FIG. 2 (CC) is a gain characteristic diagram, and FIG. 3 is a flowchart of the basic operation according to the present invention. 1...Tablet 2...Insulating substrate 5X, 5'l...Scanning circuit 4...Coordinate indicator 5...Excitation winding Line 6... Oscillator 7, 8, 10-, 13... Amplifier 9...
... Bandwidth F wave device 11 ... Rectifier circuit 12 ... Low band F wave device 14 ... A / D converter 15 ... Arithmetic control Section 16...Level judgment circuit 17...Reference voltage generation circuit 18...Level comparison circuit 23...Gain switching circuit Xi, Yj...Sense Line α... Output line b... Ground wire S... Analog switch Fig. 2 (a) $20 (G) Fig. 2 (C,) So v2 Figure 3 TART Main position Oj completed JFA, += t, vl-2仝rX1人1 No1./T), S, V 4"Shoulder 4"'Break address attack! Otsu 1 Soa Li 9, A/9 Responsibility 5 OH” [+ Sude 7/
4 sI=t=toO Ire 6
3 #Jψshito1 stay 7+ 12 11.1. Ya, 7. Eye VL
"N. Yes VMko//

Claims (1)

[Claims] A tablet comprising a large number of sense wires laid at regular intervals, a coordinate indicator having an excitation winding for applying an alternating magnetic field to the tablet, and an induction signal induced in each sense wire by the alternating magnetic field. In a coordinate reading device equipped with an arithmetic control unit that detects the position of a coordinate indicator generating an alternating magnetic field from the level of the induced signal, the gain of an amplifying circuit for amplifying the induced signal is adjusted to a plurality of values. a gain switching circuit that switches between stages, and a level determination circuit that determines the level of the induced signal amplified by the amplifier circuit; The electromagnetic induction type is characterized in that the gain of the amplifier circuit is set to be maximum, and when the level of the induction signal becomes higher than a predetermined level, the gain of the amplifier circuit is switched to be the minimum by the arithmetic control section. Coordinate reading device.