JP4564680B2 - Position detection device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a position detection device that obtains an indication position of a position indicator based on a magnetic field, an electric field, or an electromagnetic field exchanged between a position detection unit and a position indicator.
[0002]
[Prior art]
A conventional position detecting device of this type is disclosed in Japanese Patent Laid-Open No. 63-70326.
[0003]
In the position detection apparatus described above, the coordinate value of the position indicated by the position indicator is obtained by exchanging radio waves between the position detector and the position indicator. According to this, a plurality of sense units constituting the position detection unit, specifically, a plurality of loop coils arranged in parallel in the position detection direction are sequentially selected to radiate radio waves and provided to the position indicator. The radio wave re-radiated from the resonance circuit is received, and the coordinate value (coordinate position) of the indicated position is obtained from the distribution of the received signal intensity.
[0004]
This type of position detection device is usually called a digitizer and used as a computer input device as it is together with a display device such as a CRT, or as an input / output device integrated with a flat display device made of liquid crystal or the like. Since it is used, noise from these display devices is also detected, and this causes a problem that coordinate values cannot be detected stably.
[0005]
In order to suppress the influence of such external noise, many of the conventional position detection devices detect only a desired frequency component by providing a band-pass filter in a circuit that receives a signal from the position indicator. (First conventional example).
[0006]
In addition, as a removal method that does not depend on the frequency component of noise, in Japanese Patent Laid-Open No. 7-31647, a period for receiving a signal from a position indicator and a period for detecting only noise are provided, respectively. A configuration is proposed in which the influence of noise is removed by subtracting the noise level value from the signal level value from the device (second conventional example).
[0007]
Furthermore, there has been one in which the influence of noise is reduced by increasing the transmission power of radio waves and strengthening the reception signal from the position indicator (third conventional example).
[0008]
[Problems to be solved by the invention]
However, depending on the CRT, the liquid crystal, or their control circuit, a noise component having a frequency close to the use frequency of the position detection device may be radiated. In this case, noise could not be removed by a bandpass filter or the like (problem in the first conventional example).
[0009]
Further, noise generated from a display device or the like generally has a pulse-like waveform, and its signal level changes in real time. In this case, as described above, a sufficient effect cannot be obtained by processing the signal reception period and the noise detection period in a time-sharing manner (problem in the second conventional example).
[0010]
Furthermore, there is a limit in increasing the transmission power and there are problems such as an increase in cost (problem in the third conventional example).
[0011]
In view of these problems, the present invention provides a position detection device that can detect a coordinate value stably without being affected by noise generated from a display device or the like regardless of the frequency component of external noise. Objective.
[0012]
Another object of the present invention is to provide a position detection device that can detect a coordinate value stably with little influence on pulse-like noise generated from a display device or the like or noise that changes in real time. To do.
[0013]
It is another object of the present invention to provide a position detection device that can detect a stable coordinate value even with a small transmission power.
[0014]
Another object of the present invention is to provide a position detection device that can detect stable coordinate values with a low-cost configuration.
[0015]
[Means for Solving the Problems]
In the present invention, in order to achieve the above object, one of the plurality of sense units of the position detection unit is selected for a certain period of time, and during that period, the signal is generated according to the magnetic field, electric field or electromagnetic field exchanged with the position indicator. In a position detection apparatus that obtains signal levels for all or a part of the plurality of sensing units and repeats a position detection operation for detecting the indicated position of the position indicator from these signal levels, prior to the position detection operation, during the selection time period. Means for performing a noise level detection operation for detecting a noise level generated when no magnetic field, electric field or electromagnetic field is exchanged with the position indicator, and when the detected noise level exceeds a predetermined value Means for repeating the noise level detection operation and performing the position detection operation only when the noise level detection operation is below a predetermined value.
[0016]
According to the above configuration, when a magnetic field, an electric field, or an electromagnetic field is not exchanged with the position indicator, the signal level generated in the sense unit of the position detection unit, that is, the level of external noise is detected, and this exceeds a predetermined value. If it is, it is determined that noise from the display device or the like is mixed, and the operation for detecting the noise level is repeated without shifting to the position detecting operation. If the noise level is equal to or lower than a predetermined value, it is determined that no external noise is mixed, and the process proceeds to a position detection operation to detect a coordinate value. By processing in this way, detected coordinate values are not affected by external noise.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
[First Embodiment]
(Configuration of the first embodiment)
FIG. 1 shows the hardware configuration of the first embodiment of the position detection apparatus of the present invention.
[0020]
In FIG. 1, reference numeral 1 denotes a position detection unit, and a plurality of sense units, here, 40 loop coils are arranged as loop coils X1 to X40 and loop coils Y1 to Y40 in the X axis direction and the Y axis direction, respectively. It has become. These loop coils are connected to a selection circuit 2 that selects each loop coil.
[0021]
Each loop coil of the position detection unit 1 is created by etching or the like on a printed board (not shown), and the position detection unit 1 includes a display unit (not shown), for example, a display unit of a known planar liquid crystal display device, It is assumed that the coordinate detection area by each loop coil and the display area are arranged so as to be exactly the same area.
[0022]
The selection circuit 2 is connected to a transmission / reception switching circuit 3, the reception side (R) of the transmission / reception switching circuit 3 is connected to an amplifier 4, and the amplifier 4 is connected to a detection circuit 5. The detection circuit 5 is connected to a low pass filter 6, and the low pass filter 6 is connected to a sample hold circuit 7. The sample hold circuit 7 is connected to an A / D conversion circuit 8, and the A / D conversion circuit 8 is connected to a CPU (central processing unit) 9.
[0023]
Reference numeral 10 denotes an oscillator that generates an AC signal having a constant frequency f0. Reference numeral 11 denotes a current driver that converts the AC signal into a current. The output of the driver is connected to the transmission side (T) of the transmission / reception switching circuit 3. An alternating magnetic field having a frequency of f0 is radiated from one selected loop coil in 1.
[0024]
The CPU 9 sends a control signal (information) to the selection circuit 2, the transmission / reception switching circuit 3, the sample hold circuit 7 and the A / D conversion circuit 8, respectively.
[0025]
Reference numeral 12 denotes a position indicator, in which a coil 13, a writing pressure sensor 14, and a writing pressure detection circuit 15 are provided. The coil 13 is connected to a capacitor (not shown) to form a resonance circuit having a frequency f0. The pen pressure detection circuit 15 is composed of an electronic circuit including an IC, converts an analog signal from the pen pressure sensor 14 into a time-division digital signal, and returns the digital signal to the position detection unit 1 through the coil 13. . Since the operation of this position indicator is disclosed in, for example, Japanese Patent Laid-Open No. 5-313439, it is omitted here.
[0026]
The hardware configuration described above is almost the same as that of the conventional position detection apparatus. As will be described below, this embodiment is different from the conventional example in that the CPU 9 detects the level of external noise, particularly noise from the display device, by software processing, and performs the position detection operation only when it is below a predetermined value. This is the point that was made.
[0027]
(Operation of the first embodiment)
FIG. 2 shows the software configuration of the first embodiment of the present invention, that is, the flow of processing by the CPU 9.
[0028]
A display device, particularly a liquid crystal display device, generates a high-speed pulse in a liquid crystal driving circuit disposed therein for displaying an image due to its principle, and this generates electromagnetic field noise. The transmission source of this noise moves in a constant pattern according to scanning on the display unit. In the present embodiment, this is used to detect the coordinates while avoiding noise from the liquid crystal display device.
[0029]
First, a full scan operation is performed to roughly detect where the position indicator 12 is placed on the position detector 1.
[0030]
This full scan operation transmits and receives radio waves while sequentially switching all 40 loop coils in the X-axis direction and Y-axis direction (s1), and detects whether a signal level exceeding a predetermined threshold is received. (S2) Further, a loop coil (peak coil) having the highest signal level is extracted (s3).
[0031]
This full scan operation is to detect the peak coil with the highest signal level, that is, the loop coil closest to the position indicator 12, in other words, to detect where the position indicator 12 is located. Therefore, the influence of noise from the liquid crystal display device side does not matter. Therefore, it is performed in the same manner as the conventional apparatus.
[0032]
Next, the noise level detection operation and the partial scan operation after the approximate position of the position indicator 12 is known by the full-surface scan operation will be described.
[0033]
In general, this type of liquid crystal display device scans at a high speed in the main scanning direction (horizontal direction) and has a low period of about 60 to 80 Hz from the top to the bottom in the sub-scanning direction (vertical direction), like the CRT. Scanning at a low frequency of about several tens of kHz). For this reason, almost no noise is mixed in the loop coil (X-axis coil) arranged in parallel in the horizontal direction, and noise is mixed in the loop coil (Y-axis coil) arranged in parallel in the vertical direction. Therefore, in the present embodiment, the processing of the present invention is applied only when the coordinate value in the Y-axis direction is detected. The loop coil in the Y-axis direction will be described with the uppermost side being Y1.
[0034]
FIG. 3 shows the noise level detection operation and the partial scan operation in the present embodiment. Here, the transmission coil (coil for transmitting radio waves) and the reception coil in the noise level detection period and the coordinate detection period by the partial scan are shown. The numbers of (coils that receive radio waves) and the received signal levels corresponding to them are shown. Here, the position indicator 12 is placed near the intersection of the loop coils Y15 and X7, that is, the peak coil in the Y-axis direction is Y15, and the peak coil in the X-axis direction is X7. explain.
[0035]
First, in order to detect the noise level, the CPU 9 causes the selection circuit 2 to select the loop coil two before the peak coil, that is, Y13, and causes the transmission / reception switching circuit 3 to select the reception side. At this time, the CPU 9 reads the signal level output from the A / D conversion circuit 8 and stores it. Next, the CPU 9 causes the selection circuit 2 to select the peak coil Y15 and causes the transmission / reception switching circuit 3 to select the reception side in order to detect the noise level. At this time, the CPU 9 reads the signal level output from the A / D conversion circuit 8 and stores it (s4).
[0036]
Since the signal levels obtained by the two loop coils Y13 and Y15 thus obtained are detection levels when no radio wave is transmitted to the position indicator 12, these are the noise levels detected by the loop coils. Corresponds to the level. When one of these two levels exceeds a predetermined value (s5), the liquid crystal display is scanning around the loop coil Y13 or Y15, and the position where the position indicator 12 is placed is the center. It is determined that noise is mixed in the signal level obtained from a plurality of, in this case, five, loop coils for detecting the coordinate value in the Y-axis direction.
[0037]
Therefore, the CPU 9 repeats the above-described operation of selecting the loop coils Y13 and Y15 again and detecting the received signal level (s4, s5). This operation is one of the features of the present invention.
[0038]
FIG. 3 shows a case where this operation is repeated five times. However, if the received signal levels from both loop coils are both equal to or less than a predetermined value in the first detection, the noise detection operation is performed only once. Good. In FIG. 3, since the signal levels from the loop coils Y13 and Y15 are both equal to or lower than a predetermined value for the first time after the fifth reception, the operation shifts to the partial scan operation.
[0039]
This partial scan operation is performed in the same manner as in the conventional apparatus. That is, for each of the Y-axis direction and the X-axis direction, a signal level that is received by sequentially selecting a plurality of loop coils (here, five loop coils) centering on the loop coil (peak coil) closest to the position indicator 12 is set. Obtaining (s6), detecting whether or not a signal level equal to or higher than the predetermined threshold is received (s7), re-extracting the loop coil (peak coil) having the highest signal level (s8), and these five The coordinate values in the Y-axis direction and X-axis direction of the indicated position of the position indicator 12 are calculated by a known method from the signal level distribution from the loop coil (s9).
[0040]
At this time, at the time of transmission, the loop coil closest to the position indicator 12 is selected, that is, Y15 is selected for the Y-axis direction, X7 is selected for the X-axis direction, and Y13 to Y17 are selected for the Y-axis direction when receiving. The loop coils X5 to X9 are operated so as to scan sequentially.
[0041]
Here, the reason why the partial scan for detecting the coordinate in the Y-axis direction is started from the uppermost loop coil Y13 is that the scanning direction of the liquid crystal display device is from the top to the bottom as described above. This is because it is preferable to scan the loop coil in the same direction as this because the frequency of noise mixing is reduced.
[0042]
The reason why the above-described noise detection is not performed for all the loop coils Y13 to Y17 is that the noise generated from the display device is simultaneously detected by several adjacent coils, so that all the loop coils are not selected. This is because it is possible to know whether or not the noise source from the liquid crystal display device passes near the position indicated by the position indicator 12.
[0043]
The reason why noise detection is not performed for the lowermost loop coil Y17 for detecting the coordinate in the Y-axis direction will be described. In this embodiment, the loop coils Y13 to Y17 are sequentially selected after noise detection by the coils Y13 and Y15. For this reason, the time when the loop coil near Y17 is selected is the time that has passed for a while after the noise detection. Therefore, if the noise level from the loop coil Y15 is sufficiently low, the probability of noise being mixed during reception by the loop coil Y17 is low.
[0044]
After obtaining the coordinate values in the Y-axis and X-axis directions, an operation for detecting the writing pressure value applied to the pen tip of the position indicator is performed. This operation is described in Japanese Patent Laid-Open No. 5-313439 described above. Since it is clear in the issue, etc., it is omitted.
[0045]
(Extension of the first embodiment)
Although an example using a liquid crystal display device is described in this embodiment mode, the present invention can be similarly applied to a case where a display device of another system such as a plasma display or an organic EL display is used. Further, in this embodiment, a method is used in which a loop coil is provided in the position detector and the electromagnetic induction action with the position indicator is used. However, another method may be used. In this embodiment, the loop coil is formed on the printed board, but this may be incorporated in the display device.
[0046]
In this embodiment, the noise detection loop coil and the coordinate detection loop coil are used in common, but they may be separated. In this embodiment, two loop coils for noise detection are used, ie, a scan start coil at the time of coordinate detection and a coil closest to the position indicator. It may be changed according to the noise generation pattern. Further, in the present embodiment, noise detection by the loop coil in the X-axis direction is not performed, but this may be performed as in the Y-axis direction.
[0047]
[Second Embodiment]
(Configuration of Second Embodiment)
The hardware configuration of the second embodiment (but not included in the scope of claims) is the same as that of the first embodiment shown in FIG. As described below, this embodiment is different from the first embodiment in that the CPU 9 detects the level of external noise, particularly noise from the display device, by software processing, and subsequently detects the position and coordinates. The value is obtained, but only when the noise level is a predetermined value or less, the obtained coordinate value is treated as valid.
[0048]
(Operation of Second Embodiment)
FIG. 4 shows the software configuration of the second embodiment of the present invention, that is, the flow of processing by the CPU 9.
[0049]
First, a full scan operation for roughly detecting where the position indicator 12 is placed on the position detector 1 is performed in the same manner as in the first embodiment (s11, s12, s13).
[0050]
Next, as in the case of the first embodiment, the process proceeds to a noise level detection operation and a partial scan operation.
[0051]
FIG. 5 shows a state of the noise level detection operation and the partial scan operation in the present embodiment. Here, the numbers of the transmission coil and the reception coil in the noise level detection period and the coordinate detection period by the partial scan, and corresponding to them are shown. The received signal level is shown. Further, here, it is assumed that the position indicator 12 is placed near the intersection of the loop coils Y22 and X14, that is, the peak coil in the Y-axis direction is Y22 and the peak coil in the X-axis direction is X14. explain.
[0052]
First, in order to detect the noise level, the CPU 9 causes the selection circuit 2 to select the loop coil two times before the peak coil, that is, Y20, and causes the transmission / reception switching circuit 3 to select the reception side. At this time, the CPU 9 reads the signal level output from the A / D conversion circuit 8 and stores it. Next, the CPU 9 also causes the selection circuit 2 to select the peak coil Y22 and causes the transmission / reception switching circuit 3 to select the reception side in order to detect the noise level. At this time, the CPU 9 reads the signal level output from the A / D conversion circuit 8 and stores it (s14).
[0053]
Next, the CPU 9 continues the partial scan operation. This partial scan operation is performed in the same manner as in the first embodiment, and the coordinate values in the Y-axis direction and the X-axis direction of the indicated position of the position indicator 12 are obtained (s15, s16, s17, s18).
[0054]
In the present embodiment, the noise detection operation and the subsequent partial scan operation are repeated, and the noise level and the coordinate value are continuously detected. The CPU 9 averages the detected coordinate values over a plurality of times (for example, four times), and then outputs them as coordinate data to a host computer (not shown). This averaging is a process for reducing the jitter of the output coordinate values.
[0055]
At this time, in this embodiment, when the noise level from the two detected Y-axis coils exceeds a predetermined value (s19), the coordinate value detected immediately after that is discarded as invalid ( s20). For example, if one of the four coordinate values to be averaged is invalid, the remaining three coordinate values are processed to be averaged (s21).
[0056]
By performing processing in this way, coordinate values affected by noise from the liquid crystal display device can be removed. This operation is one of the features of the present invention.
[0057]
Here, the reason why partial scanning for coordinate detection in the Y-axis direction is started from the uppermost loop coil Y20, the reason why noise detection is not performed for all the coils of the loop coils Y20 to Y24, The reason why noise detection is not performed for the lowermost loop coil Y24 for coordinate detection is the same as in the case of the first embodiment.
[0058]
The operation for detecting the pen pressure value applied to the pen tip of the position indicator is also apparent from Japanese Patent Laid-Open No. 5-313439, etc., as in the first embodiment, and is therefore omitted.
[0059]
(Extension of the second embodiment)
Although an example using a liquid crystal display device is described in this embodiment mode, the present invention can be similarly applied to a case where a display device of another system such as a plasma display or an organic EL display is used. Further, in this embodiment, a method is used in which a loop coil is provided in the position detector and the electromagnetic induction action with the position indicator is used. However, another method may be used. In this embodiment, the loop coil is formed on the printed board, but this may be incorporated in the display device.
[0060]
In this embodiment, the noise detection loop coil and the coordinate detection loop coil are used in common, but they may be separated. In this embodiment, two loop coils for noise detection are used, ie, a scan start coil at the time of coordinate detection and a coil closest to the position indicator. It may be changed according to the noise generation pattern. In this embodiment, noise detection by the X-axis side loop coil is not performed, but this may be performed in the same manner as in the Y-axis direction.
[0061]
In this embodiment, the coordinate values are averaged, but this may not be performed and invalid data may not be output.
[0062]
【The invention's effect】
As described above, according to the present invention, prior to the position detection operation, the noise level generated when no magnetic field, electric field, or electromagnetic field is exchanged with the position indicator is detected, and the noise level is a predetermined value. when beyond the repeated noise level detection operation by the TURMERIC line position detecting operation only when was below the predetermined value, detecting a coordinate value of the indicated position that is not affected by noise radiated from the display device or the like can do.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a first embodiment of a position detection apparatus of the present invention. FIG. 2 is a process flow chart showing a first embodiment of a position detection apparatus of the present invention. FIG. 4 is a flowchart showing a noise level detection operation and a partial scan operation in the embodiment. FIG. 4 is a process flow diagram showing a second embodiment of the position detection apparatus of the present invention. Diagram showing detection and partial scan operations [Explanation of symbols]
1: position detection unit, 2: selection circuit, 3: transmission / reception switching circuit, 4: amplifier, 5: detection circuit, 6: low-pass filter, 7: sample hold circuit, 8: A / D conversion circuit, 9: CPU, 10 : Oscillator, 11: Current driver, 12: Position indicator, 13: Coil, 14: Pen pressure sensor, 15: Pen pressure detection circuit.

Claims (3)

One of the plurality of sense units of the position detection unit is selected for a certain period of time, and the signal level generated in response to the magnetic field or electric field or electromagnetic field exchanged with the position indicator during that period is all of the plurality of sense units. Or in a position detection device that repeats a position detection operation for obtaining a part and detecting the indicated position of the position indicator from these,
Prior to the position detection operation, means for performing a noise level detection operation for detecting a noise level generated when no magnetic field or electric field or electromagnetic field is exchanged with the position indicator during the selection time;
A position detecting device comprising: means for repeating the noise level detecting operation when the detected noise level exceeds a predetermined value and performing the position detecting operation only when the detected noise level is equal to or lower than the predetermined value. Noise level detection operation position detecting device according to claim 1 Symbol placement and performing the at least one sense portion around the indicated position of the position indicator at the time. Position detecting unit position detecting device according to claim 1 or 2, wherein the is arranged a display unit and overlaid integrally of a display device.

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