JPH11237948A - Position detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a position detecting device which has high detecting accuracy despite its simple constitution. SOLUTION: The signals which are received from a position indicator A of a position detecting device B are detected at a sensor part 21, held by a sample-and-hold circuit 29 via a transmission/reception switching circuit 25, a receiving operational amplifier 26, a detection circuit 27 and a low pass filter 28 and then converted into the digital signals by an A/D (analog/digital) converter 30. These digital signals undergo the arithmetic processing via a CPU 31 and the coordinate position of the indicator A is calculated. Meanwhile, the largest voltage that is outputted from the circuit 29 in the preceding scanning mode is held by a peak holding circuit 32, and the voltage conversion range of the converter 30 varies according to true said largest voltage. Thus, the converter 30 is set at a point near its voltage conversion range and the highly accurate position detection is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position detecting device for detecting the position of a position indicator by transmitting and receiving signals to and from the position indicator by electromagnetic coupling or the like.

[0002]

2. Description of the Related Art A position detecting device called a tablet or a digitizer generally includes a loop coil or a wire, which is a sensor that responds to an electromagnetic field or an electrostatic field, in the X-axis direction and the Y-axis direction over the entire coordinate detection surface. Arrange multiple pieces in each direction,
By determining which sensor has detected the strongest signal, the coordinate position of the position indicator on the coordinate detection surface is detected.

In such a position detecting device, first, the signal from the position indicator is detected by performing an all scan for scanning the sensor in the X-axis direction and the Y-axis direction over the entire area of the coordinate detection surface. Then, rough position information of the position indicator is obtained. Next, based on rough position information of the position indicator obtained by the all scan, a plurality of sensors near the position indicator are set to X.
A signal from the position indicator is detected by performing a sector scan for scanning in the axial direction and the Y-axis direction, and detailed position information of the position indicator is obtained.

At this time, the strength of the detected signal and the signal strength from the sensor adjacent thereto are detected to interpolate the position between the sensors, thereby improving the position detection accuracy. Further, in order to accurately perform the interpolation, a well-known analog / digital (A / D) conversion circuit is used. The detected analog signal is once converted into a digital value, and the coordinate value is obtained by calculation. .

[0005]

The above-mentioned A / D
The conversion circuit is generally configured such that a conversion range of an analog voltage to be converted is determined by externally applying a DC voltage called a reference voltage. Since the signal detected by the sensor is weak, the signal is amplified by using an amplifier circuit in a conventional device in order to make the voltage within the conversion range. Also,
In order to improve the coordinate detection accuracy, particularly the resolution of the coordinate detection, the amplification degree of the amplifier circuit is set so that the voltage detected from the strongest sensor of the aforementioned signal is as close as possible to the maximum voltage value of the voltage conversion range. I try to adjust it.

However, there is a problem in that if the amplification degree is to be adjusted accurately, the configuration becomes complicated and the apparatus becomes expensive. In order to solve this problem, a method of switching the amplification stepwise according to the signal strength is often used.However, even if the amplification degree is adjusted, a considerable level difference occurs and uniform performance is obtained. However, there is a problem that it is difficult to perform high-accuracy position detection.

An object of the present invention is to provide a highly accurate position detecting device with a simple configuration.

[0008]

SUMMARY OF THE INVENTION A position detecting device according to the present invention has a coordinate detecting surface in which a plurality of sensors are arranged in a plurality of different directions. A position detection device that detects a coordinate position of the position indicator on the coordinate detection surface based on a generated signal; a signal detection unit that outputs a detection signal of an analog voltage based on a signal generated by the sensor; An analog / digital conversion circuit for converting a detection signal into a digital signal; coordinate value detection means for obtaining a coordinate position of the position indicator based on an output signal of the analog / digital conversion circuit; And a peak hold means for holding for a certain period as a reference voltage,
A voltage conversion range of the analog / digital conversion circuit is set based on the reference voltage.

Since the reference voltage for determining the voltage conversion range of the analog / digital conversion circuit changes following the maximum voltage value of the detection signal, the position of the analog / digital conversion circuit is maximized by utilizing the voltage conversion range. The coordinate position of the indicator can be obtained.

If the peak hold means is configured to hold the threshold voltage as the reference voltage when the detection signal is equal to or lower than a predetermined threshold voltage, erroneous recognition of the position indicator is prevented. be able to.

Further, if the peak hold means is configured to update the reference voltage every one cycle of scanning,
The control of the peak hold means can be simplified,
Detection accuracy can be improved. Further, the scanning may be an all scan or a sector scan.

The peak hold means includes a first peak hold circuit for generating a reference voltage for scanning the sensors arranged in the first direction, and a sensor arranged in the second direction. With the second peak hold circuit that generates a reference voltage for scanning, the detection accuracy of the position indicator can be improved.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same parts are denoted by the same reference numerals. FIG. 1 is an overall configuration diagram showing an embodiment of the present invention. In FIG. 1, a pen-type position indicator A includes a resonance circuit 1 including a coil 11 and a capacitor 12, and the resonance frequency of the resonance circuit 1 is set to f0.

On the other hand, a position detecting device B for detecting the coordinate position of the position indicator A includes a sensor unit 21 for transmitting and receiving signals to and from the resonance circuit 1 of the position indicator A, and a sensor unit 21. A signal to the position indicator A via
A circuit for calculating a coordinate position of the position indicator A based on a signal received by the sensor unit 21 is provided.

The sensor section 21 includes an X-axis direction loop coil group 21a and a Y-axis direction loop coil group 21b arranged in a plurality of different directions, for example, the X-axis direction and the Y-axis direction. The loop coil group 21a is X
It is composed of a plurality of loop coils X1 to X40 arranged in parallel in the axial direction substantially parallel to each other, in this case, forty loop coils X1 to X40.
2 and each other end is commonly grounded. The Y-axis direction loop coil group 21b is composed of a plurality of loop coils Y1 to Y40 arranged side by side substantially in parallel with each other in the Y-axis direction, in this case, forty loop coils Y1 to Y40. , The other ends of which are commonly grounded. Each of the loop coils X1 to X40 and Y1 to Y40 forms a sensor.

Note that the sensor section 21 is disposed over substantially the entire upper surface of the tablet, and forms a coordinate detection surface. The selection circuit 22 is connected to a common terminal of a transmission / reception switching circuit 25 constituted by a changeover switch.

On the other hand, an oscillator 23 for generating an AC signal having the same frequency f 0 as the resonance frequency of the resonance circuit 1 is connected to a transmission terminal T of a transmission / reception switching circuit 25 via a current driver 24. The reception side terminal R of the transmission / reception switching circuit 25 includes a reception operational amplifier 26, a detection circuit 27, a low-pass filter (LP
F) 28, sample hold (S / H) circuit 29 and A
Central processing unit (CPU) 31 via / D conversion circuit 30
Is connected to the input section. Here, the receiving operational amplifier 26, the detection circuit 27, the low-pass filter (LPF) 28, and the sample-and-hold (S / H) circuit 29 constitute a signal detecting means, and the CPU 31 constitutes a coordinate value detecting means.

Each output unit of the CPU 31 is connected to the selection circuit 22,
Transmission / reception switching circuit 25, sample hold circuit 29, A / D
It is connected to each control input of the conversion circuit 30 and a peak hold circuit 32 as a peak hold means. The output section of the sample hold circuit 29 is connected to the input section of the peak hold circuit 32, and the peak hold circuit 3
The output section 2 is connected to the control input section of the A / D conversion circuit 30.

FIG. 2 is a circuit diagram showing an example of the peak hold circuit 32. In FIG. 2, the output of the buffer operational amplifier 201 whose input is connected to the sample-and-hold circuit 29 is connected to a voltage holding capacitor 205, an input of the buffer operational amplifier 202 and an analog switch via a backflow prevention diode 204. 207. The output of the buffer operational amplifier 202 is connected to the voltage holding capacitor 2 via the analog switch 208.
Reference numeral 06 and its output are connected to the input of the buffer operational amplifier 203 connected to the control input of the A / D conversion circuit 32.

On the other hand, the connection point of the resistors R1 and R2, which are connected in series between the power supply VCC and the ground and constitute a voltage dividing circuit, is connected to the analog switch 20 via a buffer operational amplifier 200.
7 is connected. Analog switches 207, 208
Are connected to the output unit of the CPU 31.

(A) is a transmission signal transmitted from the sensor unit 21 to the position indicator A, (B) is an induced voltage generated in the resonance circuit 1, (C) is a reception signal received from the resonance circuit 1, (D) is a detection signal output from the sample and hold circuit 29. (E) shows the peak hold circuit 3
(F) is a peak hold signal output from the operational amplifier 202, (g)
Is a transmission switch signal for controlling the analog switch 208 to be closed, and (h) is a reference voltage output from the peak hold circuit 32 to the A / D conversion circuit 30.

The reset signal (e) supplied to the analog switch 207 is a control signal for resetting the voltage held in the capacitor 205 to a predetermined threshold voltage, and is supplied from the CPU 31. The operational amplifier 200 supplies a threshold voltage when resetting is performed by a reset signal (e), and the threshold voltage is determined by a voltage dividing ratio of the resistors R1 and R2. That is, when the maximum value of the detection signal (d) of the sample and hold circuit 29 is smaller than the threshold voltage, the operation is performed so that the reference voltage (h) does not become smaller than the threshold voltage. The reason for this is to avoid erroneous recognition when the position indicator A is not on the tablet.

The operational amplifier 202 is connected to the capacitor 20
5 is output as a peak hold signal (to). The analog switch 208 outputs the maximum voltage output as the peak hold signal (f) to the capacitor 20.
A control signal for transmitting the signal to and holding the signal in the closed state is supplied from the CPU 31 as a transmission switch signal (g).

The operation of the peak hold circuit 32 will now be described briefly. The peak hold circuit 32 holds the maximum voltage value of the voltages generated at the output of the sample hold circuit 29 during one coordinate detection period. This voltage is supplied to the A / D conversion circuit 30 as a reference voltage (h) during the next coordinate detection period.

That is, as shown in FIG. 2, the detection signal (d) output from the sample and hold circuit 29 is supplied to the capacitor 20 via the operational amplifier 201 and the diode 204.
5 is held. At this time, when the maximum value of the detection signal (d) is smaller than the threshold voltage which is the output of the operational amplifier 200, the threshold voltage is continuously changed to the capacitor 205.
And operates so that the reference voltage (h) does not become lower than the threshold voltage. This makes it possible to avoid erroneous recognition when the position indicator A is not on the tablet.

The operational amplifier 202 outputs the maximum voltage held in the capacitor 205 as a peak hold signal (to). The analog switch 208 is closed in response to the transmission switch signal (G) from the CPU 31, and transmits the peak hold signal (F) to the capacitor 206 and holds it. The holding voltage of the capacitor 206 is
A / D conversion circuit 30 as a reference voltage (h) via
Is output to

FIG. 3 is a flowchart showing the processing of the CPU 31. FIG. 4 is a timing chart when all scans are performed in the X axis direction, FIG. 5 is a timing chart when all scans are performed in the Y axis direction, and FIG. 6 is a sector scan in the X axis direction and the Y axis direction. It is a timing chart in the case of performing. 4 and 5, the loop coils X1 to X40 and Y1 to Y40 are indicated by "T" when connected to the transmission side T, and "R" when connected to the reception side R.

Hereinafter, the operation of the present embodiment will be described in detail with reference to FIGS. First, the CPU 31 sends a signal for selecting the first loop coil of the X-axis direction loop coil group 21a, for example, the loop coil X1, to the selection circuit 22 at the timing shown in FIG. A signal to be connected to the transmitting side T is transmitted. The AC signal of the frequency f0 output from the oscillator 23 is converted into a current by the current driver 24, and supplied to the loop coil X1 selected by the selection circuit 22 via the transmission / reception switching circuit 25. As a result, a radio wave having a frequency f0 is generated from the loop coil X1. At this time, when the position indicator A is placed on the sensor unit 21, the radio wave excites the resonance circuit 1 and generates an induced voltage having a frequency f0.

The CPU 31 sends the transmission / reception switching circuit 25 to the transmission side T.
Is transmitted for a predetermined period of time, the receiving side R
Is transmitted to eliminate the radio wave generated from the loop coil X1. At this time, the induced voltage generated in the resonance circuit 1 of the position indicator A gradually attenuates in accordance with the loss and emits a radio wave of the frequency f0, which excites the loop coil X1 described above in reverse. Position indicator A
And an induced voltage corresponding to the distance between the loop coil X1 and the loop coil X1.

The CPU 31 supplies the transmission / reception switching circuit 25 to the reception side R.
Is transmitted for a certain period of time, information for selecting the second loop coil of the X-axis direction loop coil group 21a, for example, X2, is transmitted to the selection circuit 22, and transmission and reception of radio waves similar to the above are performed. The third to fortieth loop coils of the X-axis direction loop coil group 21a, for example, the loop coils X3 to X40 are selected by sequentially scanning, and the same radio waves are transmitted and received as described above. Thus, the all-scan in the X-axis direction is performed (step S1).

At the time of the all scan, instead of selecting all the loop coils of the X-axis direction loop coil group 21a, it is also possible to select one after another, such as every other one. Further, it is not necessary to sequentially scan from the loop coil X1 to the loop coil X40, and the scanning may be performed by changing the order in a predetermined order. Furthermore, transmission / reception of radio waves to / from one loop coil may be performed a plurality of times. Note that the transmission time for each of the loop coils X1 to X40 and the reception time for each of the loop coils X1 to X40 must be equal, but the transmission time and the reception time do not necessarily have to be the same.

The induced voltage generated in each of the loop coils X1 to X40 of the X-axis direction loop coil group 21a during the above-described reception period is amplified by the operational amplifier 26 via the selection circuit 22 and the transmission / reception switching circuit 25, and the reception signal C) is output. The received signal (c) is detected by the detection circuit 27 and sent to the low-pass filter 28. The low-pass filter 28 has a cutoff frequency sufficiently lower than the frequency f0, converts the output signal of the detection circuit 27 into a DC signal, and sends it to the sample-and-hold circuit 29. The sample and hold circuit 29 has a CP
According to the sampling control signal supplied from U31,
The DC signal is sampled and held at a predetermined timing, specifically, a voltage value at a predetermined timing during a reception period.

The held detection signal (d) is an analog signal corresponding to the induced voltage. The detection signal (d) is converted into a digital signal by the A / D conversion circuit 30 and sent to the CPU 31 as a digital voltage value.
At this time, as shown in FIG. 4, the CPU 31 sends the transmission switch signal (g) and the reset to the peak hold circuit 32 every one cycle of the all-scan, that is, every time one X-axis all-scan operation is performed. The signal (e) is supplied to update the reference voltage (h). That is, the analog switch 208 is closed by the transmission switch signal (g), and the voltage of the peak hold signal (f) output from the operational amplifier 202 (the maximum voltage in the previous all-scan operation) is held in the capacitor 206; Operational amplifier 2
The signal is output as a reference voltage for the A / D conversion circuit 30 at the time of the next all-scan operation by being output from the A / D converter 03.

Next, in order to hold the maximum voltage in the next all-scan operation, the analog switch 207 is closed by the reset signal (e), and the capacitor 2
05 is temporarily changed to the operational amplifier 200
Reset to the output threshold voltage. Since the reference voltage (h) changes following the maximum value of the received signal (c), the maximum value of the value output by the A / D conversion circuit 30 usually has the A / D conversion circuit 30. Almost the maximum value of the conversion range is output.

However, when the position indicator A is not on the tablet or is separated from the tablet surface, there is no received signal (c), so that the detection signal (d) has the resistances R1, R2.
Does not reach the preset threshold voltage, and the reference voltage (h) becomes equal to the threshold voltage. Therefore, A /
The value output by the D conversion circuit 30 is the A / D conversion circuit 3
It does not reach near the maximum value of the conversion range of 0. If the maximum value output from the A / D conversion circuit 30 does not reach the fixed value, the position indicator is determined not to be on the tablet, and the process of step S1 is repeated (step S2).

By the all scan step, A /
If there is a loop coil whose maximum value output from the D conversion circuit 30 reaches a certain value, a loop coil (peak coil) having the maximum output voltage is extracted, and its number,
In the example of FIG. 4, X7 is stored (step S3).

Next, the CPU 31 sequentially scans each loop coil of the Y-axis direction loop coil group 21b and transmits and receives the same radio waves as described above to perform an all-scan in the Y-axis direction (step S4). A peak coil in the Y-axis direction is extracted and its number is stored (step S
5).

FIG. 5 shows an example of the waveform of each part in the above-described Y-axis all-scan operation, and each signal is the same as in FIG. In the case of FIG. 5, the peak coil extracted by the Y-axis all scan is the loop coil Y5. still,
Before the Y-axis all-scan operation, the reference voltage (h) is not updated, and the voltage set in the previous step S1 is maintained as the reference voltage (h). As a result, the control of the peak hold circuit 32 can be simplified and a high position detection accuracy can be obtained.

Next, the CPU 31 determines a predetermined number of the X-axis direction loop coil group 21a centered on the peak coil, for example, two before and after the loop coil X7.
The sector scan in the X-axis direction is performed by sequentially scanning the total of five loop coils from the smaller number to the larger number (or the larger number to the smaller number) and transmitting and receiving radio waves in the same manner as in the all scan. (Step S
6). Further, a predetermined number of loop coils around the peak coil of the Y-axis direction loop coil group 21b, for example, two loop coils before and after the loop coil Y5, that is, a total of five loop coils, from the smaller number to the larger number (or larger) (Step S7) by sequentially scanning from the smaller one to transmitting and receiving radio waves in the same manner as in the all-scan operation (Step S7).

FIG. 6 shows the aforementioned X-axis sector scan and Y-axis sector scan.
It shows an example of the waveform of each part in the axis sector scan. In the X-axis sector scan and the Y-axis sector scan, as shown in FIG. 6, each time a one-cycle sector scan is performed in each of both the X-axis direction and the Y-axis direction, the transmission switch signal (G) and Reset signal (e)
To update the reference voltage (h).

That is, first, the analog switch 208 is closed by the transmission switch signal (g), the voltage output from the operational amplifier 202 (the maximum voltage in the previous sector scan operation) is held in the capacitor 206, and the operational amplifier 203 And supplies it as a reference voltage (h) of the A / D converter 30 in the next all-scan operation.

Next, in order to hold the maximum voltage in the next sector scan operation, the analog switch 207 is closed by the reset signal (e) to set the capacitor 20.
5 is temporarily reset to the threshold voltage output from the operational amplifier 200.

As described above, since the reference voltage (h) changes following the maximum value of the received signal (c), the A / D
The maximum value output by the conversion circuit 30 is A /
Almost the maximum value of the conversion range of the D conversion circuit 30 is output. For this reason, the resolution in calculating the coordinate values can be improved.

Here, if the position indicator has been removed from the tablet or moved away from the tablet surface, there is no received signal (c), so that the detection signal (d) is
1, the capacitor 205 does not reach the preset threshold voltage, and the capacitor 205 is continuously maintained at the threshold voltage.
Therefore, the value output by the A / D conversion circuit 30 is A / D
It does not reach near the maximum value of the conversion range of the D conversion circuit 30. If the maximum value output from the A / D conversion circuit 30 does not reach the fixed value, it is determined that the position indicator A has left the tablet, and the process returns to step S1 (step S8).

If it is determined that the position indicator A is on the tablet, the X-axis and Y-axis peak coils are extracted from the detection values obtained by the X-axis and Y-axis sector scans and stored. (Step S9). Based on the maximum value of the signal voltage obtained from each of the peak coils and the detected value of the signal voltage obtained from the loop coil adjacent to the peak coil, the above-described well-known coordinate calculation is executed, and the position indicator A
Are obtained in the X-axis direction and the Y-axis direction (step S
10) Then, the process returns to step S6, and the sector scan operation is repeated to perform a detection operation following the locus of the position indicator A as shown in FIG.

As described above, according to the present embodiment, the reference voltage (h) that determines the voltage conversion range of the A / D conversion circuit 30 changes following the peak value of the detected signal. Therefore, it is possible to always perform the coordinate calculation using the voltage conversion range of the A / D conversion circuit 30 to the utmost, thereby enabling position detection with high resolution.

Further, a peak hold circuit 3 for holding the maximum voltage value of the voltages detected from the respective sensors for a certain period.
This can be realized with a simple configuration in which only 2 is added.
In the present embodiment, a common reference voltage (h) is used for scanning in the X-axis direction and scanning in the Y-axis direction. However, two peak hold circuits are provided, that is,
A first peak hold circuit that holds the maximum value of the detection signal (d) when scanning in the X-axis direction, and a second peak that holds the maximum value of the detection signal (d) when scanning in the Y-axis direction If a hold circuit is provided so that the reference voltage is switched and supplied to the A / D conversion circuit 31 during scanning in the X-axis direction and scanning in the Y-axis direction, respectively, a more accurate coordinate can be obtained. Detection becomes possible.

In this embodiment, the case where the resonance circuit 1 and the loop coils X1 to X40 and Y1 to Y40 are electromagnetically coupled has been described. However, the present invention can also be applied to the case of magnetic coupling or electrostatic coupling. Further, the frequency f of the signal output from the oscillator 23
Although 0 is set to match the resonance frequency of the resonance circuit 1, the two frequencies do not necessarily have to match completely, and may be any frequency that is close enough to transmit and receive signals.

[0049]

As described above, according to the present invention,
With a simple configuration that simply adds a peak hold unit that holds the maximum voltage value of the voltages detected from the sensors for a certain period, it is possible to perform coordinate calculation using the maximum voltage conversion range of the analog / digital conversion circuit. Therefore, there is an effect that the coordinate detection accuracy, particularly the resolution of the coordinate detection can be improved.

Further, when the detection signal is equal to or lower than a predetermined threshold voltage, the peak hold means holds the threshold voltage as a reference voltage, thereby preventing erroneous recognition of the position indicator. Further, the peak hold means updates the reference voltage every scanning cycle, thereby simplifying the control of the peak hold means and improving the coordinate detection accuracy.

Further, the peak hold means may include a first peak hold circuit for generating a reference voltage for scanning the sensors arranged in the first direction and a sensor arranged in the second direction. With the configuration including the second peak hold circuit that generates the reference voltage for scanning, the detection accuracy of the position indicator can be further improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of a peak hold circuit used in the embodiment of FIG. 1;

FIG. 3 is a flowchart showing processing of a CPU used in the embodiment of FIG. 1;

FIG. 4 is a timing chart of an X-axis all scan operation in the embodiment of FIG. 1;

FIG. 5 is a timing chart of a Y-axis all-scan operation in the embodiment of FIG. 1;

FIG. 6 is a timing chart of a sector scan operation in the embodiment of FIG. 1;

[Explanation of symbols]

A ··································································································································· X1 to X40, Y1 to ... Loop coil as a sensor 27... Detector circuit constituting signal detecting means 28... Low-pass filter constituting signal detecting means 29. Sampling and holding circuit 30 that constitutes detecting means Analogue / digital conversion circuit 31 CPU as coordinate value detecting means 32 Peak as peak holding means Hold circuit

Claims (5)

[Claims] 1. A coordinate detection surface comprising a plurality of sensors arranged side by side in a plurality of different directions, and based on a signal generated by the sensors due to an interaction with a position indicator, the coordinate detection surface includes a plurality of sensors. In a position detecting device for detecting a coordinate position of the position indicator, a signal detecting means for outputting a detection signal of an analog voltage based on a signal generated in the sensor; and an analog / digital conversion for converting the detection signal into a digital signal. A circuit; a coordinate value detecting means for obtaining a coordinate position of the position indicator based on an output signal of the analog / digital conversion circuit; and a peak holding means for holding a maximum voltage value of the detection signals as a reference voltage for a certain period of time. Wherein the voltage conversion range of the analog / digital conversion circuit is set based on the reference voltage. Detection device. 2. The position detecting device according to claim 1, wherein said peak hold means holds said threshold voltage as said reference voltage when said detection signal is lower than a predetermined threshold voltage. . 3. The position detecting device according to claim 1, wherein said peak hold means updates said reference voltage every one cycle of scanning. 4. The position detecting apparatus according to claim 3, wherein the scanning is one of an all scan and a sector scan. 5. The peak hold means includes: a first peak hold circuit for generating a reference voltage for scanning a sensor arranged in a first direction; and a sensor arranged in a second direction. 5. The position detecting device according to claim 1, further comprising a second peak hold circuit for generating a reference voltage for scanning.