JPH0431406B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a coordinate detection device using an electromagnetic drive method.

[Conventional technology]

There are various types of coordinate detection devices using an electromagnetic drive method. Among these, a coordinate detection device that is commonly used will be explained with reference to the drawings.

FIG. 3 is a block diagram of a conventional coordinate detection device. In the figure, 1 is a tablet, 2 is a magnetic field generating device such as an electromagnetic pen or cursor (hereinafter referred to as an electromagnetic pen), and 3 is a pen drive circuit for generating a magnetic field in the electromagnetic pen 2. Above tablet 1
An X-axis detection lead wire and a Y-axis detection lead wire are wired to detect the coordinates of the electromagnetic pen 2 on the tablet 1. The pen drive circuit 3 is driven by a clock signal c from a clock generator (not shown), and supplies a sine wave current to the electromagnetic pen 2 in synchronization with the clock signal c. The electromagnetic pen 2 generates a magnetic field in response to this, which generates a sinusoidal voltage in each detection conductor of the tablet 1 in accordance with the position of the electromagnetic pen 2.

4 is a waveform detection circuit, which is composed of a waveform processing circuit 5 and a filter 6. Waveform processing circuit 5
inputs the sine wave voltage of each detection conductor of the tablet 1, and outputs a sine wave signal whose phase is shifted according to the magnitude of the voltage. The filter 6 is provided to remove noise mixed in from inside and outside the coordinate detection device, and is composed of a capacitor and a resistor. A comparator 7 converts the sine wave signal from the filter 6 into pulses corresponding to the sine wave signal.
A counter 8 detects the phase difference between the clock signal c and the output signal from the comparator 7, and outputs a corresponding number of pulses. Reference numeral 9 denotes a data processing circuit composed of a microcomputer, which performs necessary calculations and controls based on the output pulses of the counter 8, and calculates the coordinates of the electromagnetic pen 2.

Since a coordinate detection device having such a configuration is already known, a more detailed explanation will be omitted.

[Problem that the invention seeks to solve]

In the above coordinate detection device, the waveform detection circuit 4
Since the filter 6 is provided in the position, the influence of noise is removed and accurate coordinate values can be detected. However, the filter 6 must prevent itself from causing a phase shift in the output signal of the waveform processing circuit 5. For this reason, the filter 6 has restrictions such as the need to use a highly accurate capacitor and resistor that change little with respect to temperature changes. In particular, it is naturally effective to use a filter whose resonant circuit has a sharp sharpness Q for noise removal, but it is difficult to use such a filter in the conventional coordinate detection device described above. The reason for this will be explained using FIGS. 4a and 4b.

FIGS. 4a and 4b are frequency characteristic diagrams of the filter, and in each figure, the horizontal axis represents frequency, and the vertical axis represents signal level and phase. The solid line in the figure shows the frequency characteristics of the filter at a certain temperature.As shown in Figure 4a, if the sharpness Q is sharp, signals that slightly deviate from the resonant frequency will be cut out, which will reduce noise. are sufficiently removed. Here, if the temperature changes from the above-determined temperature,
The frequency characteristics of the filter vary as shown by the broken line in the figure. Due to such fluctuations, the phase of the signal passing through the filter changes by a value of 4Θ, as shown in FIG. 4b. This phase change 4Θ is large even for a slight change in frequency characteristics, so a filter with a sharp sharpness Q cannot be used, and as a result, noise removal cannot be performed ideally. was occurring.

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the prior art described above and to provide a coordinate detection device in which a filter can be arbitrarily configured without considering phase shift.

[Means for solving problems]

In order to achieve the above object, the present invention includes a magnetic field generating device such as an electromagnetic pen or cursor that is driven by a drive signal of a predetermined frequency, and a plurality of detection leads that output signals according to the position of the magnetic field generating device. , a waveform processing circuit that processes the waveform of the output signal from these detection conductors, a filter, and a phase difference detection means that detects a phase difference between the waveform signal from the waveform processing circuit that has passed through the filter and the drive signal. , and data processing means for processing the output signal of the phase difference detection means, the waveform signal from the waveform processing circuit and the drive signal for driving the magnetic field generation device are selected and input to the filter. When the drive signal from the signal switching means is input to the filter, the waveform signal is input to the filter by the signal switching means and the correction value detection means for obtaining a correction value based on the output signal of the phase difference detection means. The present invention is characterized in that it includes a correction means for correcting the output signal of the phase difference detection means with the correction value obtained by the correction value detection means when inputted.

[Effect]

During coordinate detection operation, when the signal switching means selects a drive signal of a predetermined frequency, this drive signal is input to the phase difference detection means through a filter, and the phase is compared with the drive signal directly input to this phase difference detection means. and a signal corresponding to the phase difference between them is output from the phase difference detection means. The correction value detection means calculates a correction value based on the signal from the phase difference detection means.
This correction value is 0 when no phase shift occurs in the filter, and becomes a value proportional to the phase shift when a phase shift occurs due to temperature change or the like. Next, when the signal switching means selects a waveform signal from the waveform processing circuit, this waveform signal is inputted to the phase difference detection means through a filter, and the phase difference between it and the drive signal is detected. This detected phase difference is corrected by the above correction value by the correction means and output as accurate coordinate values.

〔Example〕

Hereinafter, the present invention will be explained based on illustrated embodiments.

FIG. 1 is a block diagram of a coordinate detection device according to an embodiment of the present invention. In the figure, parts that are the same as those shown in FIG. 3 are given the same reference numerals, and explanations thereof will be omitted. 1
0 is a switch that selectively switches between the waveform signal output from the waveform processing circuit 5 and the clock signal c. This switch 10 is provided before the filter 6, so that when either the waveform signal or the clock signal c is selected, the signal passes through the filter 6. 11 is the data processing circuit 9 shown in FIG.
The data processing circuit corresponds to the calculation,
correction value detection means for obtaining a correction value during the control means;
A correction means for correcting the detected coordinate values using the obtained correction value and a means for controlling the switching device 10 are added.

Next, the operation of this embodiment will be explained with reference to the flowchart shown in FIG. First, in this coordinate detection device, whether the filter 6 is in a state where a phase shift occurs or not, and if it is in a state where a phase shift is caused, what is the magnitude of the phase shift (correction value with which the coordinate detection value should be corrected)? Correction value detection is performed to detect whether the value is as follows (step S ₁ shown in FIG. 2). This correction value detection is performed as follows. That is, the data processing circuit 11 outputs a command to the switch 10 to switch the switch 10 to the side that selects the clock signal c. As a result, the clock signal c is inputted to the counter 8 through the filter 6 and the comparator 7.
On the other hand, a clock signal c is simultaneously input to the counter 8, and in this counter 8, the clock signal c that has passed through the filter 6 and the clock signal c that has not passed through the filter 6 are compared. As a result of this comparison, if there is no phase shift in the filter 6, the output pulse from the counter 8 will be 0, and
When a phase shift occurs in the filter 6, the number of output pulses from the counter 8 is proportional to the magnitude of the phase shift. This number of output pulses is input to the data processing circuit, and the value is temporarily stored as a correction value.

Next, the data processing circuit 11 switches the switch 10 to the side that selects the waveform signal from the waveform processing circuit 5, whereby XY coordinate detection is performed by the same means as in the prior art (step S ₂ ). Then the detected XY
The coordinate values are corrected using the correction values obtained in step S ₁ described above (step S ₃ ), and the corrected values are output as XY coordinate values (step S ₄ ). In detecting the next XY coordinate value, steps S ₁ to _{S 4} are repeated again.

In this way, in this embodiment, a phase shift in the filter is detected every time a coordinate value is detected, a correction value proportional to the phase shift is determined based on this, and the detected coordinate value is corrected using this correction value. Therefore, accurate coordinate values can be obtained regardless of whether or not there is a phase shift in the filter.
From this, it is possible to select a filter with a sharpness Q,
Effective noise removal can be performed, and highly accurate and reliable coordinate detection can be performed. Furthermore, since there is no need to consider the temperature characteristics of resistors, capacitors, etc., there is no need to use expensive resistors, capacitors, etc., and the cost of the device can be reduced.

Furthermore, if the temperature characteristics of the filter are known, the temperature can be determined by detecting the phase difference, and based on this, temperature compensation of other parts and devices can be considered.

In addition, in the description of the above embodiment, an example was explained in which a correction value is detected every time coordinates are detected, but correction value detection can also be performed every several times.

〔Effect of the invention〕

As described above, in the present invention, a correction value proportional to the phase shift of the filter is detected, and the detected coordinate values are corrected using this correction value, so even if there is a phase shift, accurate coordinate values can be obtained. can be detected. Therefore, it is possible to configure a filter arbitrarily without considering phase shift, and this allows effective noise removal using a sharp filter with sharpness Q, further improving the accuracy and reliability of coordinate detection. can be improved. Furthermore, since there is no need to use expensive resistors, capacitors, etc. that have severe temperature characteristics, the cost of the device can be reduced.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a coordinate detection device according to an embodiment of the present invention, FIG. 2 is a flowchart explaining the operation of the device shown in FIG. 1, and FIG. 3 is a block diagram of a conventional coordinate detection device. Figures 4a and 4b are frequency characteristic diagrams of the filter. DESCRIPTION OF SYMBOLS 1... Tablet, 2... Electromagnetic pen, 3... Pen drive circuit, 5... Waveform processing circuit, 6... Filter, 7... Comparator, 8... Counter, 10...
...Switcher, 11...Data processing circuit.

Claims (1)

[Claims] 1 A magnetic field generator driven by a drive signal of a predetermined frequency, a plurality of detection leads that output signals according to the position of the magnetic field generator, and a waveform processing circuit that processes the waveforms of output signals from these detection leads. , a filter, a phase difference detection means for detecting a phase difference between the waveform signal from the waveform processing circuit that has passed through the filter and the drive signal, and a data processing means for processing the output signal of the phase difference detection means. In the coordinate detection device, the signal switching means selectively inputs the waveform signal and the drive signal to the filter, and when the drive signal is selected by the signal switching means, the output signal of the phase difference detection means A correction value detection means for obtaining a correction value based on the correction value, and a correction means for correcting the output signal of the phase difference detection means with the correction value when the waveform signal is selected by the signal switching means. Coordinate detection device.