JPS593794B2 - digitizer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a digitizer that measures the position of a cursor using an electromagnetic coupling method.

Digitizers are suitable for deriving digital data from analog displays such as drawings, but there are various types depending on the method used to measure the position of a cursor or pen, which is a positioning element. Typical examples include mechanical, electrostatic, electromagnetic, acoustic, and optical means. Among these, the mechanical type has the disadvantage of operability, the electrostatic type and the optical type are limited by the material of the daisy medium, and the acoustic type is easily affected by changes in temperature, etc., so the electromagnetic type is currently the most versatile. It is said to be rich and have few drawbacks. There are various types of electromagnetic type, that is, electromagnetic coupling type, and FIG. 1 shows an example of a digitizer using the conventional electromagnetic coupling type. FIG. 1 is an explanatory configuration diagram particularly showing the main parts of the position detection section. That is, the flat plate 1 shown in FIG.
The zigzag-shaped two-phase detection loop (detection loop consisting of XcOs line and Xsin line) 2 and 3 formed in
This is to detect the position of. In this case, the relationship between the relative position of the cursor 4 and the electromotive current of the detection loop 2 is as shown in FIG. 1, and the relative position can be detected from the electromotive current. However, in the case of loops as shown in Fig. 1A, it is impossible to distinguish between the two pitches located one pitch next to each other, so another set of area detection loops 5 as shown in Fig. 1C is installed in parallel to enable discrimination. It is configured as follows. Therefore, a large number of lube substrates are required, which has the disadvantage that the circuit becomes not only complicated but also expensive as a whole.

An object of the present invention is to eliminate such drawbacks and provide an inexpensive digitizer that can read position coordinates with an accuracy comparable to that of conventional digitizers.

The present invention will be explained in detail below using the drawings.

FIG. 2 is a diagram showing the main part of an embodiment of the digitizer according to the present invention. In FIG. 2, 20 is an insulating board such as a printed board or glass, and a plurality of conductor loops 21 are formed on the surface of the board (six loops 211 to 216 are shown in the figure).
are arranged to have a single pole. Conductor loop 21
is connected to a switch 22, which switches the loop 2 in synchronization with the pulse P2 applied to the input terminal 24.
11 to 216 in sequence. FIG. 3A shows the pulse P2 applied to the input terminal 24 and the timing of current supply to the loops 211-216.
Furthermore, this switch 22 is also driven by the pulse P1 inputted to the input terminal 23, and the supplied current is interrupted in synchronization with the pulse P1 as shown in the opening of FIG. The pulse P1
and P2 are obtained by appropriately frequency-dividing the reference clock of the oscillator 26 in FIG.
This is a pulse whose frequency is divided by the second frequency divider 28. In this case, as is clear from the beginning of FIG. 3, the second frequency divider 28 performs 1/2 frequency division. Reference numeral 30 denotes a magnetic flux detection cursor for detecting the magnetic flux produced by the conductor loop 21, which has at least one magnetic flux detection coil (not shown), and has an index such as a cross-shaped mark for positioning (not shown) in the center of the cursor. ), and is configured so that the operator can move on the insulating plate 20 in any direction.

32 is an amplifier which amplifies the output of the tuning circuit 31 provided above.

The tuning circuit 31 has a bandpass characteristic as shown in FIG. It attenuates and eliminates harmonics generated by medium pulse excitation of the power signal, and acts to pass only signals near the tuning frequency. 33 is a polarized detector, for example, a synchronous detector can be used.

34 is a band pass filter which extracts only the fundamental wave (the opening in FIG. 6) of the output of the detector 33.

The output of the wave detector 33 has a waveform as shown in FIG.
It corresponds to the separation distance from 35 is a counter for detecting the time of this occurrence, which counts the clock of the oscillator 26 during the time from the start of current drive in the loop 21 until the output signal of the filter 34 crosses zero when moving from positive to negative. It's getting old.

In this case, the point that crosses zero is 90 degrees from the cursor 30 position.
Since the deviation is 0, the conductor loop 211 that is excited first
An excitation signal generated at a position shifted by 90 degrees is given as a start pulse, whereby the counter 35 starts clock counting. The operation of the present invention in such a configuration will be described next.

Based on the pulses Pl and P2 obtained by dividing the clock of the oscillator 26 in the first and second frequency dividers 27 and 28, the conductor loops 211 to 216 are activated by the switch 22 at the timing shown at the beginning of FIG. Sequential current drive. loop 2
The magnetic fluxes sequentially generated at points 11 to 216 are detected by the positioned cursor 30. After harmonics are removed from the output of the cursor 30 via a tuning circuit 31, it is appropriately amplified by an amplifier 32 and guided to a polar detector 33. This alternating current signal is detected here and becomes a pulsating current signal as shown in FIG. Subsequently, the fundamental wave of the pulsating flow signal is detected by the bandpass filter 34 to obtain a sinusoidal output as shown at the beginning of FIG. On the other hand, the counter 35 starts counting the clocks from the oscillator 26 in response to a start pulse given from the output end 25 of the switch 22 as shown in FIG. Stop the counting operation as shown in c. Since the count value of the counter 35 at this time corresponds to the distance of the cursor 30 from the conductor loop 211, the position of the cursor 30 on the insulating plate 20 can be detected in this way. The embodiment shown in FIG. 2 is for measuring the one-dimensional position of the cursor 30, but when measuring the two-dimensional position, the configuration shown in FIG. 7 may be used.

That is, one more set of insulating plates 20 shown in FIG. 2 is used,
Arrange the conductor loops so that they are perpendicular to each other. The new insulating plate 20a is current-driven by a switch 22a similar to the switch 22. The switch 22a is also driven by the pulses Pl and P2, but the switch 22 and the switch 22a are configured to be driven alternately in a time division manner. For example, if the insulating plate 20 reads the position of the cursor 30 in the X-axis direction, and the insulating plate 20a reads the position of the cursor 30 in the Y-axis direction, the Can be detected alternately. In this case, the detection systems 31 to 35 are used for both X-axis coordinate detection and Y-axis coordinate detection, but two sets of these detection systems may be prepared and configured to measure each coordinate simultaneously. Furthermore, the insulating plate may be a single piece, and conductor loops perpendicular to each other may be formed on the front and back sides of the insulating plate.

Further, the switches 22 and 22a can also be combined into one set and operated in the same manner. In FIGS. 2 and 7, the detector 33 is of a polar type, but if the filter 34 has a sufficiently large Q and can attenuate and eliminate harmonics, a non-polar detector such as a diode may be used. It can also be used to simplify configuration. However, in a digitizer based on this principle, the bandpass filter 34 has the greatest potential for error. That is, when the center frequency of the filter changes due to temperature changes, changes in components over time, etc., the phase of the passing frequency changes, which directly causes a measurement error in the cursor position. In order to solve this problem, as an example, an amplifier 32 and a polar detector 33 (
Or an analog switch 4 is connected between the non-polar detector 33a)
1 is inserted and connected, and the configuration is configured so that the detection system can be calibrated using simulated input. According to such a configuration, as shown in FIG. 9, the switch 41 is switched to the calibration mode during position measurement of the cursor 30, and a simulated input for calibration is applied to the detector 33a via the switch 41. By measuring the time difference and calibrating the detection system including the filter 34, the actual measured value of the cursor position can be corrected. In this case, the calibration mode does not necessarily have to be provided every time after measuring the cursor position as shown in FIG. 9, but may be set at appropriately thinned out intervals in consideration of the stability period of the detection system. Note that instead of giving the simulated input, a fixed magnetic flux detection cursor 30a is placed at a predetermined position on the back side of an insulating plate (not shown) as shown in FIG.
Calibration can also be carried out by selectively switching the outputs of the force soles 30 and 30a with the switch 41a and taking the difference between the outputs. Figure 11 shows the error curve when measuring using the digitizer shown in Figure 2 or Figure R. The vertical axis is the error, and the horizontal axis is the cursor position (position in the ).

The error is small in the center of the Daisy Dozen area, but the error increases rapidly as it approaches the edges. As is clear from FIG. 12, as the cursor 30 approaches the edge,
This is because the side rope on one side decreases because the conductor loop is finite, and a phase shift occurs between the peak of the output signal after passing through the filter 34 and the peak of the signal before passing through the filter 34.
FIG. 13 is a block diagram showing an embodiment of the digitizer shown in FIG. 11, which has an expanded range of small errors, so-called usable range, and shows a variable threshold rectifier circuit 51 inserted and connected between the detector 33 and the filter 34. It is the same as the one in FIG. 7 except for.

The output waveform of this rectifier circuit 51 is shown in FIG. 14th
A in the figure shows the output waveform (solid line part) when a polar type is used as the wave detector 33 and the threshold level of the rectifier circuit 51 is set to zero. The output waveform (solid line portion) is shown when the detector 33a is used and the threshold level is appropriately raised. In short, by using this rectifier circuit 51, the side rope, which is information from the conductor loop located outside the cursor, is removed, and the loop 21,
The influence of the fact that 21a is finite can be removed. FIG. 15 is an error distribution diagram actually measured in the digitizer of FIG. 13, and shows that substantially the entire surface is within the usable range. FIG. 16 is another embodiment of the present invention, which is a block diagram of a digitizer that can measure the cursor position while keeping the output voltage of the filter 34 constant and the threshold level of the rectifier circuit 51 constant. .

That is, a peak voltage detector 61 and a comparator 62 are added to the digitizer of FIG. 13 described above, and the amplifier 32 is further replaced with a variable gain amplifier 32a. This peak detector 61 detects the peak of the output voltage of the filter 34, and the comparator 62 compares this with a comparison voltage. Based on the comparison result, the gain of the variable gain amplifier 32a is controlled to keep the output voltage of the filter 34 constant. Therefore, the magnitude of the signal input to the rectifier circuit 51 is always constant, and even if the distance between the cursor and the conductor loop increases and the output voltage of the cursor decreases, the threshold remains at a constant level. You can measure the position without changing the position. FIG. 17 shows another embodiment, which is the same as that shown in FIG. 7 except that a threshold control circuit 71 is used.

This threshold control circuit 71 determines a threshold voltage in relation to the peak value output of the band pass filter 34. For example, when the peak value of the filter 34 becomes 1/2, the threshold voltage of the rectifier circuit 51 is also halved. As a result, it is possible to perform a measurement in which the influence of the side lobe of the cursor signal is removed, as described above. The resolution of the digitizer described above is mainly determined by the short-term stability of the filter 34.

This short-term stability refers to phase fluctuations on the order of several tens to hundreds of KH2, and slow phase changes such as drift can be removed by adopting the calibration mode described above, but this short-term stability is generally There is no reasonable solution other than taking several period measurements and averaging them. For example, 3
In order to measure 60 h with a resolution of 0.1, the short-term stability of the phase must be 0.1 or less, but this is quite difficult to realize. Figure 18 shows a configuration to solve this problem.The difference from Figure 17 (including Figures 7, 13, and 16) is that the mode variable type is used for current 1 drive of the conductor loop. This is because current switches 81 and 81a are used. The switches 81 and 81a have a mode in which the same current can be applied to a plurality of loops spaced apart at a certain interval. Figure 19 shows this situation. In mode A (fine measurement) shown in Figure A (fine measurement), the same current flows through N loops in the measurement range, and in mode B (rough measurement) shown in Figure 19, the same current flows through one loop. It is shown that current flows only through the loop. The waveform shown by the broken line in the figure shows the output of the filter 34, and in mode A, the measurement range is 1/N of mode B due to the phase change of 3600, so the resolution is improved accordingly. be able to. However, in this case, as is clear from FIG. 19A, in mode A alone, they cannot be distinguished from each other at positions 360 degrees out of phase, so mode B is used to make this distinction.

However, since mode B only needs to be able to make the above distinction, it does not require particularly high resolution. Figure 20 shows an example of the operation transition, in particular, by mixing the above-mentioned calibration modes, in X-axis position measurement, the X-axis position measurement is performed using the Bose mode → Mode A →
Mode B. Calibration mode → Mode A in Y-axis position measurement
The position measurement operation is shown in the order →Mode B. In the digitizer shown in FIG. 18, the frequency of the output waveform of the filter 34 in mode A is N times that in mode B.

Therefore, it is necessary to prepare another set of detection systems suitable for the N times higher frequency signal as a detection system, but in order to simplify the system and reduce the cost, the current switches 81 and 81a are set to mode A.
By configuring one input pulse P2 to be further frequency-divided to 1/N and inputted only in this case, the detection system can be made into one set. As explained above, according to the digitizer of the present invention, the position coordinates of a cursor can be measured with high precision and high speed without using a conductor loop for detecting an area, which is required by conventional digitizers. In addition to being able to use inexpensive digital elements to drive one conductor loop, there is no need for an expensive AD converter for signal detection, and an output proportional to position can be directly obtained, making interpolation and nonlinear correction completely unnecessary. Since this is not necessary, a high-speed and inexpensive digitizer can be realized.

Furthermore, even if the cursor output becomes smaller due to the distance between the cursor and the conductor loop, the phase is detected, so the magnitude of the output will not cause an error, making it possible to create a digitizer that is less susceptible to environmental conditions. .

Furthermore, by calibrating a simulated input or by arranging a conductor loop and cursor positioned in advance, it is possible to easily eliminate the influence of phase changes due to detection system drift, etc. This has great practical effects, such as the ability to easily improve resolution through measurements and rough measurements without increasing the density of conductor loops, etc.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the main parts of a conventional digitizer, Fig. 2 is a block diagram of main parts showing an embodiment of the digitizer according to the present invention, Fig. 3 is a diagram showing the timing of current drive of the conductor loop, and Fig. 4 5 is a diagram showing the frequency characteristics of the tuning circuit 31, FIG. 5 is an output waveform diagram of the detector 33, FIG. 6 is a diagram for explaining the operation of the counter 35, FIGS. 7, 13, 16, 1st
7 and 18 are main part configuration diagrams showing other embodiments of the present invention, FIGS. 8 and 10 are main part configuration diagrams of the parts adopted when realizing the calibration mode, and FIG. 9 is a calibration diagram. 11 and 15 are diagrams showing the relationship between the cursor position on the insulating plate and the error, and FIG. 12 is the diagram showing the relationship between the input and output of the bandpass filter 34. 14 is a diagram for explaining the function of the rectifier circuit 51, FIG. 19 is a diagram for explaining mode A and mode B implemented in the digitizer of FIG. 18, and FIG. 20 is a diagram for explaining the function of the rectifier circuit 51. FIG. 3 is an operation transition diagram of the digitizer of FIG. 20, 20a...Insulating plate, 21, 21a, 21
1 to 216, 21c... Conductor lube, 22, 2
2a...Switch, 26...Engineer,
27...First frequency divider, 28...Second frequency divider
Frequency divider, 30, 30a... Magnetic flux detection cursor, 31... Tuning circuit, 32, 32a...
・Amplifier, 33, 33a...Detector, 34...
... Band pass filter, 35 ... Counter, 41, 41a ... Analog switch, 51
... Rectifier circuit, 61 ... Peak voltage detector, 62 ... Comparator, 71 ... Threshold control circuit, 8L81a ... Current Switch.

Claims (1)

[Scope of Claims] 1. A frequency dividing means for dividing a reference clock to obtain a clock pulse of a predetermined frequency, an insulating plate formed by arranging a plurality of conductor loops so as to have a single pole, and said dividing means. a switch for sequentially driving the plurality of conductor loops with current in the order of arrangement from one end in synchronization with pulses applied from a circumferential means; a magnetic flux detection cursor for detecting magnetic flux generated from the conductor loops; a detection means for detecting an output signal; a bandpass filter that passes only the fundamental wave output from the detection means; a counting operation is started by a signal from the switch; and a counting operation is started based on the output signal from the bandpass filter. A digitizer comprising: a counter configured to stop the clock and counting the clock; and a position of the cursor on the insulating plate can be detected from the count of the counter. 2. The digitizer according to claim 1, wherein the detection means is a polarized detector. 3. The digitizer according to claim 1, wherein the detection means is a non-polar detector. 4. The detection means is configured so that the input from the magnetic flux detection cursor or the simulated input for calibration can be selected as an alternative, and when the simulated input for calibration is selected, the detection system can be calibrated. A digitizer according to claim 1, characterized in that: 5. The digitizer according to claim 1, wherein the detection means is calibrated so as to be able to rectify at an arbitrary threshold level. 6. According to claim 1, the detection means is capable of amplifying and controlling the input signal in relation to the output of the bandpass filter and rectifying it at a constant threshold level. digitizer. 7. The digitizer according to claim 1, wherein the switch is a switch capable of driving the conductor loops at regular intervals with the same current. 8. Prepare a frequency dividing means for dividing the reference clock to obtain a clock pulse of a predetermined frequency, and two sets of insulating plates each having a plurality of conductor loops arranged so as to have a single pole, and insert these into the conductor loops. are arranged so that the conductor loops are orthogonal to each other, and drive the two sets of plurality of conductor loops with current sequentially in the order of arrangement from the end of the insulating plate in synchronization with the pulses given from the frequency dividing means; A magnetic flux detection cursor that respectively detects the magnetic flux generated from the conductor loop, a detection means that detects the output signal of the magnetic flux detection cursor, a bandpass filter that passes only the fundamental wave of the output from the detection means, and a bandpass filter that passes only the fundamental wave of the output from the detection means; The counter includes a counter that counts the clock and is configured to start counting operation based on a signal from the band-pass filter and stop counting operation based on an output signal from the band-pass filter, and the count value of the counter is used to determine the position of the cursor on the insulating plate. A digitizer characterized by being able to detect two-dimensional positions. 9 Two signal processing systems consisting of the detection means, the bandpass filter, and the counter are provided corresponding to each of the insulating plates, and the signals from the magnetic flux detection cursor are individually received and processed, and the signals on the insulating plates are Claim 8, characterized in that the two-dimensional position of the cursor can be detected.
Digitizer as described in section.