JPH05150891A - Wireless coordinate reader - Google Patents

Abstract

PURPOSE:To prevent the miscalculation of the coordinates of a wireless coordinate reader by detecting whether a metallic foreign matter exists on a tablet or not. CONSTITUTION:An exciting circuit 7 produces an exciting signal s3 of plural frequencies including the resonance frequency of a resonance circuit of a coordinate pointer 4. The scanning circuits 5 and 6 select an exciting line 1 and a sense line 2 respectively, and the pointer 4 or a metallic foreign matter is set at the crossing part of both lines 1 and 2. Thus an induction signal s1 is produced on the line 2. The amplitude of the signal s1 is increased only when the amplitude is excited by the resonance frequency with the indicator 4 set at the crossing part. Meanwhile a big difference is not produced by the exciting frequency with a foreign matter set at the crossing part respectively. A foreign matter detector circuit 9 compares the signal s1 with an amplitude signal s2 to decide the presence or absence of a foreign matter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coordinate reading device for inputting coordinates to an external device such as a computer,
In particular, the present invention relates to a wireless coordinate reading device that does not require a signal line to connect between a tablet and a coordinate indicator.

[0002]

2. Description of the Related Art A configuration diagram of a conventional wireless coordinate reading device is shown in FIG. The operation will be described based on this figure. The coordinate reading unit 103 includes an excitation line 101 and a sense line 102.
Are laid orthogonally, and the scanning circuits 105 and 106 are respectively provided.
Connect to and select sequentially. First scanning circuit 1
Since the excitation signal s103 is supplied from the excitation circuit 107 to 05, the selected excitation line is the excitation signal s10.
An alternating magnetic field is generated by 3. Since the coordinate indicator 104 has a tuning circuit that tunes to the frequency of the excitation signal s103, when this is placed on the coordinate reading unit 103, the excitation line 101, the coordinate indicator 104, and the sense line 102.
The induction signal s101 is generated in the sense line 102 by the combination of the three. The guidance signal s101 is sequentially selected by the second scanning circuit 106, and the signal processing circuit 108 is selected.
To an amplitude signal s102, and this signal is input to the coordinate calculation circuit 110 to calculate coordinates from the distribution state of the guidance signal s101. The above is the operation principle of the wireless coordinate reading device.

When attention is paid to only one selected excitation line and one selected sense line, a model as shown in FIG. 9 can be obtained. The drawing shows a configuration in which a scanning circuit is omitted and one excitation line is directly excited to observe an induction signal generated in one sense line. As shown in FIG. 9A, the coordinate indicator 1
When 04 approaches the intersection of the excitation line 101 and the sense line 102, the induction signal s101 having a relatively large amplitude is generated on the sense line 102. The amplitude of the induction signal is compared with the threshold value Vth, and when exceeding the threshold value Vth, it is determined that the coordinate indicator 104 is present on the tablet, and the coordinates are calculated.

[0004]

However, in the conventional coordinate reading device of this type, the metallic foreign matter is detected by the coordinate reading unit 10.
Even when placed on position 3, there is a problem that the excitation line 101 and the sense line 102 are coupled and the coordinates are erroneously calculated. As shown in FIG. 9B, when the foreign matter 12 approaches the intersection of the excitation line 101 and the sense line 102, an induction signal s101 having an amplitude of a certain magnitude is generated, though not so much as the coupling by the resonance circuit. The threshold value Vth may be exceeded.

The present invention has been made to solve the above-mentioned problems in the conventional coordinate reading apparatus, and the first one thereof is
The purpose of is to realize a wireless coordinate reading device capable of recognizing, when a metallic foreign matter is placed on the coordinate reading unit, the foreign matter. A second object is to realize a wireless coordinate reading device which prohibits calculation of coordinates when it is recognized that a foreign object is placed.

[0006]

In order to solve the above problems, in the first invention, an alternating magnetic field is generated from the tablet and generated in the tablet by electrical coupling between the tablet and a coordinate indicator having a tuning circuit. In the wireless coordinate reading device for calculating the position where the coordinate indicator is placed based on the induction signal, an exciting circuit for generating an exciting signal of a plurality of frequencies including the tuning frequency of the tuning circuit in the tablet, and a plurality of frequencies. And a foreign substance detecting means for detecting whether or not a binding substance other than the coordinate indicator is placed on the tablet by comparing the amplitudes of the induction signals for the wireless coordinate reading device.

In the second aspect of the invention, in addition to the above-mentioned configuration, a wireless coordinate reading device is provided which is provided with means for prohibiting coordinate calculation when the foreign matter detecting means detects that a foreign matter is placed on the tablet. ..

[0008]

In the coordinate reading device thus constructed, when the exciting line is excited sequentially with a plurality of frequencies and the amplitude of the induction signal generated in the sense line is observed, when the coordinate indicator is placed, it is incorporated. The amplitude of the induction signal is large only when the excitation signal has the tuning frequency of the tuning circuit, and the amplitude is small when the excitation signal has another frequency. On the other hand, when a metallic foreign substance is placed, it does not have a clear frequency characteristic as in the resonance circuit, and therefore the difference in the amplitude of the induction signal for each frequency tends not to be as large as in the coordinate indicator. The magnitude of the amplitude of the guidance signal is determined by the foreign matter detecting means, and it is determined whether the placed object is the coordinate indicator or the foreign matter.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. First, the configuration will be described. FIG. 1 is a block diagram of a coordinate reading device according to the present invention. In the figure, 1 is an excitation line, 2 is a sense line, 3 is a coordinate reading unit, and the excitation line 1 and the sense line 2 are laid at equal intervals and are orthogonal to each other to form a coordinate reading unit 3. is doing.

Reference numeral 4 is a coordinate indicator having a resonance circuit.
A circuit diagram of the circuit of the coordinate indicator 4 is shown in FIG. Figure 2
, 41 is a coil and 42 is a capacitor L
A C resonance circuit is constructed. Now, let the resonance frequency fr of this resonance circuit be f1. Returning to FIG. 1, 5 is a first scanning circuit for sequentially selecting the excitation line 1, and 6 is a second scanning circuit for sequentially selecting the sense line 2. The scanning circuits 5 and 6 are composed of a plurality of electronic switching elements,
One of the excitation line 1 and the sense line 2 is selected by the selection signal input from the control circuit 11 and connected to the circuit connected to the common terminal of the switch element. The first scanning circuit 5 selects one of the excitation lines 1 by the selection signal dad and connects it to the excitation circuit 7.
Further, the second scanning circuit 6 selects one of the sense lines 2 by the selection signal sad and connects it to the signal processing circuit 8.

Reference numeral 7 indicates an excitation signal s3 on the selected excitation line.
It is an exciting circuit for supplying. The structure of the excitation circuit 7 is shown in FIG. In FIG. 3, reference numeral 71 is a frequency dividing circuit, and the control circuit 1
The basic clock clk input from 1 is divided to output signals of a plurality of frequencies. The figure shows two signals clk1 and c
lk2 is output, and the frequency of clk1 is f1 and the frequency of clk2 is f2. 7
Reference numeral 2 is a first waveform shaping circuit for shaping the signal clk1 which is a rectangular wave and converting it into a sine wave, and 73 is also the signal clk.
It is a second waveform shaping circuit for shaping the waveform of 2 and converting it into a sine wave. A switching circuit 74 selects one of the two signals converted into the sine wave according to the frequency switching signal fsel input from the control circuit 11. An amplifier circuit 75 amplifies the selected signal and outputs it as an excitation signal s3.

Returning to FIG. 1, reference numeral 8 is a signal processing circuit for processing the induction signal s1 generated in the selected sense line and outputting the amplitude signal s2. The configuration of the signal processing circuit 8 is shown in FIG. In the figure, 81 is an amplifier circuit and 82 is a detection circuit. The detection circuit 82 is a general AM detection circuit and detects the amplified induction signal s1 and outputs an envelope signal thereof. Reference numeral 83 is an A / D conversion circuit, which digitizes the voltage of the envelope signal and outputs it as an amplitude signal s2.

Returning to FIG. 1, reference numeral 9 is a foreign matter detection circuit for detecting whether or not a foreign matter is placed on the coordinate reading section 3 based on the amplitude signal s2, and 10 is a coordinate for calculating coordinates based on the amplitude signal s2. It is a calculation circuit. Reference numeral 11 denotes a control circuit, which outputs a control signal to each section as described above. These foreign matter detection circuit 9, coordinate calculation circuit 10, control circuit 11
Is composed of a microprocessor.

Next, the operation will be described. The technology related to coordinate calculation is not the object of the present invention. The principle of operation has been briefly described in the prior art, and therefore the operation of the foreign matter detection circuit 9 will be mainly described here. As shown in FIG. 5, it is assumed that one excitation line 1 and one sense line 2 are selected. The selected excitation line 1 is connected to the excitation circuit 7 to generate an alternating magnetic field. The excitation circuit 7 uses the frequency switching signal fse
It is a circuit that outputs an excitation signal s3 of frequencies f1 and f2 by l.

As shown in FIG. 5 (A), a coordinate indicator 4 is placed at the intersection of the excitation line 1 and the sense line 2, and the excitation line 1 is excited by switching the above two frequencies. At this time, the resonance frequency fr of the coordinate indicator 4 is connected to the sense line 2.
Is f1, the induction signal s1 having a large amplitude is generated when excited at the frequency f1, and the induction signal is hardly generated when excited at the frequency f2.

As shown in FIG. 5B, when a metallic foreign substance 12 is placed in place of the coordinate indicator 4, this foreign substance does not have a clear frequency characteristic as much as the coordinate indicator 4. , Even if excited at frequency f1, or frequency f2
Even if excited by, the amplitude of the induction signal s1 does not significantly differ. The foreign matter detection circuit 9 attempts to distinguish between the coordinate indicator 4 and the foreign matter 12 by utilizing the difference in appearance of the induction signal due to the difference in frequency characteristics. As described above, the foreign matter detection circuit 9 includes the coordinate calculation circuit 10 and the control circuit 11.
Since it is also constituted by a microprocessor, the identification processing is realized by a program.

FIG. 6 is a flowchart of the foreign matter detection processing.
A timing chart of each signal is shown in FIG. FIG. 7A shows a coordinate indicator 4 at the intersection of the excitation line 1 and the sense line 2.
FIG. 7B is a timing diagram when the
FIG. 6 is a timing diagram when a is placed. The foreign matter detection operation will be described with reference to these drawings. First, the case where the coordinate indicator 4 is placed will be described. In step 1, the control circuit 11 sets the frequency switching signal fsel to 0. If the exciting circuit 7 outputs the frequency f1 when fsel = 0 and the frequency f2 when fsel = 1, in this step, fsel is output.
When = 0 is input, the excitation signal s3 having the frequency f1 is output.

The frequency f1 is the resonance frequency f of the coordinate indicator 4.
Since it is equal to r, the induction signal s1 becomes a signal with a large amplitude. The induction signal s1 is supplied to the amplitude signal s by the signal processing circuit 8.
Converted to 2. In step 2, the foreign matter detection circuit 9 inputs the amplitude signal s2. Since the frequency switching signal fsel = 0 is also input to the foreign matter detection circuit 9, it is recognized from this signal that the current excitation frequency is f1, and the input amplitude signal s2 is stored in the storage area s2 corresponding to the excitation frequency f1. Store in (f1).

Subsequently, in step 3, the control circuit 11 sets the frequency switching signal fsel to 1. The exciting circuit 7 receives this signal and outputs the exciting signal s3 having the frequency f2. At the frequency f2, the resonance circuit of the coordinate indicator 4 does not resonate, so that the induction signal s1 is hardly generated. In step 4, the foreign matter detection circuit 9 inputs the amplitude signal s2. Since the frequency switching signal fsel is 1 this time, it is recognized from this signal that the current excitation frequency is f2, and the input amplitude signal s2 is stored in the storage area s2 (f2) corresponding to the excitation frequency f2.

In step 5, the absolute value dV1 of the difference between the amplitude signal s2 stored in s2 (f1) and the amplitude signal s2 stored in s2 (f2) is determined, and this value is used as the threshold value dVref.
Determine whether it is larger or smaller. When the coordinate indicator 4 is placed, this value dV1 is large, so the determination is no, and it is determined that the object is not a foreign substance. The threshold value dVref used for the determination is set to an appropriate value in advance by an experiment.

When the foreign matter 12 is placed as shown in FIG. 7B, the induction signal s when excited at two frequencies.
The magnitude of the amplitude signal s2 of 1 is not as large as when the coordinate indicator 4 is placed. Since the absolute value dV2 of the difference between the amplitude signal s2 stored in s2 (f1) and the amplitude signal s2 stored in s2 (f2) is smaller than the threshold value dVref, the determination in step 5 is yes and it is determined to be a foreign substance. ..

In this way, it is determined whether the coordinate indicator 4 or the foreign matter is placed at the intersection of the excitation line 1 and the sense line 2. The foreign matter detection process described above has been described as being performed with a specific excitation line and sense line selected, but in the actual process, the largest induction line in the sequential selection of the excitation line and the sense line. This is performed for the set of excitation line and sense line that generated the signal. However, the reason why the maximum induction signal is used is that there is an advantage that the S / N can be made high, and it is not always necessary to use the group that has generated the maximum induction signal.

Next, the second invention will be described. In the present invention, the coordinate calculation processing is performed according to the result of judgment as to whether the coordinate indicator 4 or the foreign matter 12 is placed on the coordinate reading unit 3 as described above. Is executed / not executed. In the actual processing, coordinate calculation processing is performed by adding coordinate calculation processing to a branch that is determined not to be a foreign matter in the flowchart of FIG. 6, and this processing is not performed when it is determined to be a foreign matter. Although this part is not shown, it can be easily understood.

Next, some other embodiments related to the above embodiment will be described. First, the configuration of each circuit is not limited to the configuration described in the above embodiment. For example, the excitation circuit 7 may have a function of outputting the excitation signals s3 having a plurality of frequencies in response to the frequency switching signal fsel, and therefore, the internal configuration may be other than the configuration shown in FIG. Further, although the foreign matter detection circuit 9 is configured by the microprocessor together with the coordinate calculation circuit 10 and the control circuit 11, it goes without saying that an equivalent circuit may be configured by hardware.

Further, the processing of the foreign substance detection circuit 9 is not limited to the flowchart of FIG. Since the essence of this processing is to compare the amplitude signal s2 when excited at two frequencies, this processing does not prescribe how to store the input signal. Further, since the essence of the present invention is to switch the excitation frequency and evaluate the amplitude of the induction signal at each frequency, the principle of coordinate calculation itself is not limited. Various wireless coordinate reading devices have been proposed in addition to the principle described in this embodiment. A coordinate indicator has a frequency characteristic, and a tablet and a coordinate indicator are selectively coupled with a signal of a specific frequency. The present invention can be implemented on any principle as long as it is a coordinate reading device based on the principle of calculating coordinates.

[0026]

As described above, according to the present invention, the amplitude of the induction signal generated in the tablet when excited at each frequency is compared with the excitation circuit that generates the excitation signal of a plurality of frequencies, and the foreign matter on the tablet is compared. Since the foreign substance detection circuit for detecting whether or not the foreign substance is placed is provided, it is possible to realize a wireless coordinate reading device capable of detecting the foreign substance when the foreign substance is placed on the tablet. In addition, it is possible to realize a wireless coordinate reading device that does not erroneously calculate coordinates when a foreign object is placed because a means for prohibiting coordinate calculation when a foreign object is detected is provided. I was able to.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a wireless coordinate reading device according to the present invention.

FIG. 2 is a circuit diagram of a coordinate indicator used in the wireless coordinate reader according to the present invention.

FIG. 3 is a configuration diagram of an exciting circuit of the wireless coordinate reading device according to the present invention.

FIG. 4 is a configuration diagram of a signal processing circuit used in the wireless coordinate reading device according to the present invention.

FIG. 5 is an explanatory diagram of a guidance signal of the wireless coordinate reading device according to the present invention.

FIG. 6 is a flowchart of a process of a foreign matter detection circuit of the wireless coordinate reading device according to the present invention.

FIG. 7 is a timing diagram of each signal of the wireless coordinate reader according to the present invention.

FIG. 8 is a configuration diagram of a conventional wireless coordinate reading device.

FIG. 9 is an explanatory diagram of induction signal generation in a conventional device.

[Explanation of symbols]

 1, 101 Excitation line 2, 102 Sense line 3, 103 Coordinate reading unit 4, 104 Coordinate indicator 5, 6, 105, 106 Scanning circuit 7, 107 Excitation circuit 8, 108 Signal processing circuit 9 Foreign matter detection circuit 10, 110 Coordinates Calculation circuit 11, 111 Control circuit 12 Foreign matter 71 Frequency divider circuit 72, 73 Waveform shaping circuit 74 Switching circuit 75, 81 Amplification circuit 82 Detection circuit 83 A / D conversion circuit s1 Induction signal s2 Amplitude signal s3 Excitation signal fsel Frequency switching signal

Claims (2)

[Claims] 1. An alternating magnetic field is generated from a tablet, and the coordinate indicator is placed on the basis of an induction signal generated in the tablet by electrical coupling between the tablet and a coordinate indicator having a tuning circuit. In a wireless coordinate reading device for calculating a position, an excitation circuit that generates an excitation signal of a plurality of frequencies including the tuning frequency of the tuning circuit in the tablet and the induction signals for the plurality of frequencies are compared, and the tablet is compared. A wireless coordinate reader, further comprising foreign matter detection means for detecting whether or not a binding substance other than the coordinate indicator is placed thereon. 2. The wireless coordinate reader according to claim 1, further comprising means for prohibiting coordinate calculation when the foreign matter detecting means detects that a foreign matter is placed on the tablet.