JPH0460247B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a coordinate input device, and in particular, a coordinate input device that calculates the position coordinates of elastic wave generation on the coordinate input panel by measuring the delay time of elastic waves. It is related to the device.

[Prior Art] In a conventional device of this kind, a start signal is sent from an amplification calculation circuit to a pulse generator, and the pulse generator generates a pulsed electric signal in response to the start signal. Driven by this pulse signal, the vibration generated by the piezoelectric element is propagated through the horn to the vibration propagation body as a plate wave elastic wave, which is detected as a piezoelectric voltage by the piezoelectric element for sensor, and the start signal is synchronized to By repeatedly measuring the delay time required for vibration propagation, the position coordinates of the vibration oscillation source were detected. Incidentally, when detecting the propagating vibration at this time, time was measured by detecting the pulse with the maximum peak level in the pulse group, which is the detected waveform.

[Problems to be solved by the invention] However, since the propagating elastic wave is a plate wave, the group velocity and phase velocity differ due to the influence of dispersion, so the above detection method causes an error of at most one wavelength in the phase velocity wavelength. was unavoidable.

The present invention has been made in view of the above-mentioned conventional technology, and by calculating the maximum value of the envelope of the pulse group that is the detection signal, it is possible to input coordinates with higher resolution by correcting the timed delay time value. The purpose is to provide equipment.

[Means for solving the problem] As a means for solving this problem, the present invention has the following configuration.

That is, a vibration input means that propagates an elastic wave to the vibration propagation body by contacting a desired position on the vibration propagation body, and an elastic input means that is fixed at a predetermined position of the vibration propagation body and propagates through the vibration propagation body. a receiving means for receiving a wave and converting it into a pulse signal group; and a time value for measuring a time value until a pulse signal of the maximum peak level of the pulse signal group is received based on the pulse signal group converted by the receiving means. a detection means for detecting the peak level of each pulse signal of the pulse signal group received by the receiving means, based on the peak level of each pulse signal of the pulse signal group detected by the detection means, and a correction means for calculating the peak position of the group velocity waveform for the pulse signal group and correcting the time value obtained by the time measurement means using the obtained peak position.

[Function] In this configuration of the present invention, the coordinate position of the position specifying means is determined using the time value corrected by the correction means.

[Examples] Examples according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a block diagram of the coordinate input device of this embodiment.

In the figure, 1 is a vibrating pen, and a pulse generator 10
It is composed of a piezoelectric element 2 that vibrates even with a signal from the center, and a horn 3 that amplifies the vibration. 4 is a tablet-type signal input board, and 5 is a vibration propagator. 6 is a contact point between the horn 3 and the vibration propagation body 5. Further, 7a to 7c are piezoelectric elements for vibration detection, which convert elastic waves into electrical signals. 8 is a lead wire, 9 is a vibration absorbing material for preventing reflection of elastic waves, 1
Reference numeral 1 denotes an amplification calculation circuit which instructs the pulse signal generator 10 to generate a pulse signal and receives an electric signal from the lead wire 8. Reference numeral 12 denotes a control unit that controls the entire device, and a memory 12a that stores therein a program for calculating the coordinate position of the grounding point 6 using time values that have been measured and corrected, and a program shown in FIG. 6, which will be described later. It is equipped with

To explain the operation in the above-mentioned configuration, first, a start signal is output from the amplification calculation circuit 11 to the pulse generator 10, and in response to this, the pulse generator 1
0 generates a pulsed electrical signal. As this frequency increases, the resolution increases, but the attenuation rate also increases, so 300 to 500 KHz is appropriate. In response to this electrical signal, the piezoelectric element 2 of the vibrating pen 1 expands and contracts (vibrates) at that frequency. This vibration is amplified by the horn 3, and the vibration is transmitted to the vibration propagation body 5 at the contact point 6, where it propagates as a plate wave elastic wave. Note that the material of the vibration propagation body 5 may be a transparent plate such as glass or acrylic. Now, the propagated plate wave elastic wave is detected as a piezoelectric voltage by three piezoelectric elements 7a to 7c provided for vibration detection (this elastic wave detection processing will be described later), and is transmitted to an amplification calculation circuit via a lead wire 8. Sent to 11. At this time, the delay time required for vibration propagation is detected in synchronization with the start signal generated from the amplification calculation circuit.
The above operation is repeated, for example, 50 to 150 times per second, and the position coordinates of the contact point 6 of the vibrating pen 1 are calculated using the delay times obtained at the three vibration detection piezoelectric elements 7.

Note that this calculation method is shown below.

As shown in FIG. 2, the position coordinates of the vibrating pen 1 are (x, y), and three piezoelectric elements 7 for vibration detection are used.
The respective coordinates Pa to Pc of a to 7c are Pa (x ₁ , y ₁ ) = (0, 0) Pb (x ₂ , y ₂ ) = (x ₂ , 0) Pc (x ₃ , y ₃ ) = ( 0, y ₃ ), the position coordinates (x, y) of the vibrating pen 1 can be obtained as shown in the following equation.

x=x ₂ /2+2・x ₂ /v ²・(t1+t2)・(t1−t2) y=y ³ /2+v ² /2・y ³・(t1+t3)・(t1−t3) However, t ₁ ~ t ₃ : Propagation time of elastic wave v: Propagation velocity of elastic wave By performing the above calculations in the amplification calculation circuit 11, the position coordinates of the vibrating pen 1 can be obtained.

Note that when the vibration in the vibration propagation body 5 reaches the vibration absorber 9, the amplitude of the elastic wave is attenuated here. In this embodiment, the vibration absorbing material 9 is made of silicone rubber mixed with metal powder in order to have a large attenuation rate and match the natural acoustic impedance with glass, but the material is not limited to this. It's not a thing. Furthermore, regarding the plate thickness of the vibration propagation body 5, it is appropriate that the thickness be 0.3 to 2.0 mm. This is because as the plate thickness decreases, the amplitude of the propagated and detected elastic waves increases, but the strength of the material decreases.

A method for detecting a vibration signal waveform in the above coordinate input device will be described.

FIG. 3 is a diagram showing the relationship between the propagation distance, propagation time, and signal waveform of elastic waves.
The waveform converted into an electrical signal by, for example, the piezoelectric element 7a for detection in the "state" is "A'".
At this time, t _A indicates the delay time corresponding to the propagation distance x _A of the elastic wave from the time the start signal is generated (point C).
It is. Therefore, when the vibrating pen 1 is moved to "B state", the propagation distance becomes x _B , so the detection signal becomes "B'"
and the delay time becomes _tB .

The problem here is that the detected vibration waveforms "A'" and "B'" may have different phases, as shown in FIG. In this case, in the past, the time when the pulse with the maximum peak level was detected was taken as the time of elastic wave detection, so there is no problem in the case of the detection signal "A'", but in the case of the detection signal "B'", the time of t _B ' minute is detected. This will result in a time error.
This difference in phase occurs because the plate wave acoustic wave has dispersion, so when pulse driving is performed, the group velocity and phase velocity in the detection signal waveform are different. There is a plate wave (Lamb wave) in the elastic wave that propagates in a vibration propagation body, and in this example, the plate wave acoustic wave is used in that the amplitude does not decrease significantly like a surface wave even if it touches the surface of the plate. This is caused by an error of up to one wavelength in the phase velocity wavelength between the ideal detection point corresponding to the group velocity of the detection signal waveform and the maximum pulse level in the pulse group. be.

In order to correct this time error, in this embodiment, the peak position of the envelope of the waveform of the detection signal is set as the detection time point. The method for calculating the envelope will be explained below.

FIG. 4 is a pattern diagram of the detection signal waveform. In this embodiment, since the phase velocity is slower than the group velocity, when the propagation distance increases, that is, when the vibrating pen 1 moves from "state A" to "state B" in FIG. The detection signal waveform changes as follows. It can be seen that there are four patterns in the waveform. In other words, if the peak levels on the upper side of the waveform in Figure 4a are a, b, c, d, and e in order from the left, then the size of the peak is c>b=d c>b>d (2(c-b )=c-d) b=d b>c>a (2(b-c)=ba) b>a=c It can be seen that the patterns are classified as follows. The relationship between the peak levels a to e, propagation distance, and propagation time is shown in FIG. In this figure, v _g is a straight line corresponding to the group velocity, and a to e are straight lines corresponding to each peak level shown in FIG. 4, which is a part of the phase velocity. The slopes of these straight lines indicate 1/v (v is the propagation velocity), which means that the phase velocity is slower than the group velocity.

Further, in FIG. 5, v _p indicates one wavelength of the phase velocity, and 1/f indicates one period of the phase velocity (f: drive frequency). Therefore, if we move by x _a in the propagation distance, the phase in the group velocity will return to its original state.

Here, x _a =V _p ·V _g /f · (V _g −V _p ) (V _p : phase velocity). Therefore, it is sufficient to divide X _a as shown in ~ in Figure 5 in correspondence with each of the waveforms in Figure 4 a to e, and add the corresponding time correction to the propagation time at the phase velocity. become. That is, when the detected waveform is between .about. in FIG. 5, it is divided into four patterns, such as between .about.

Therefore, in this embodiment, the correction amount is determined as follows based on the magnitudes of the peaks of the pattern waveforms shown in FIGS. 4a to 4e.

That is, (~): 2(c-b)>c-d≧c-b (~):0<2(c-b)≦c-d (~):0≦2(b-c)<b -a (~): 2(b-c)≧b-a>b-c In the above pattern ~, the following correction is made (see Fig. 4).

() The correction in the propagation time for the maximum peak level position c of the pulse group is 0 () The correction in the propagation time for the maximum peak level position c of the pulse group is -(0.25×1/f) () The maximum peak level position of the pulse group The correction in the propagation time for b is + (0.5 x 1/f) () The correction in the propagation time for the maximum peak level position b of the pulse group is + (0.25 x 1/f) As shown above, the maximum peak level in the pulse group By adding or subtracting a correction value to the detected time value, it is possible to improve the accuracy to at least a time value of 1/4 of the phase velocity for one wavelength.

A flowchart for performing signal waveform detection including the above correction using an amplification calculation circuit is shown in Fig. 6.
The processing procedure will be explained. Note that n is the detected count number of the peak of the detection signal waveform, and f(n) is the size of the peak in the count.

First, in step S1, set n to “1” as an initial value.
and read f(n) in step S2. Next, f(n) read in step S3 is stored in the memory 12a.
Store in. In step S4, n is incremented, and in step S5, f(n) is read and memory 1 is
2a (step S6). Next step
In S7, the previously read peak level (f(n-
1)) and the peak level (f(n)) read this time, and repeat steps S4 and subsequent steps until the peak level read this time becomes smaller than the peak level read last time. Incidentally, at this time, the two peak levels previously stored are unnecessary and are therefore deleted (step S8). Now, if it is determined in step S7 that the peak level read this time is smaller than the peak level read last time, that is, if it is determined that the pulse read last time is the pulse with the maximum peak level in the pulse group, step S9
Moving on, the above-described correction will be performed in the following steps.

First, in step S10, it is determined whether the following inequality is true.

2 {(n-1)-f(n-2)}>f(n-1)-f(n
) If this inequality is satisfied, step S12
However, if this is not the case, the process moves to step S10, where correction is made by subtracting 1/4 of the period of the phase velocity wave from the time value at which the maximum peak level (f(n-1)) is detected, and the process is corrected at step S11. Coordinates are calculated and output using the corrected time values.

Further, in step S12, it is determined whether the following inequality is true.

f(n-1)-f(n)≧f(n-1)-f(n-2) If this inequality is not satisfied, step S14
However, if satisfied, the process moves to step S13, and the coordinates are calculated and output in step S11 without adding or subtracting anything to the time value at which the maximum peak level (f(n-1)) was detected. become.

Furthermore, in step S14, the following inequality is also used for determination.

2 {f(n-1)-f(n)}≧f(n-1)-f(n-
2) If this inequality is satisfied, step S15
Then, the time value at which the maximum peak level (f(n-1)) was detected is corrected by adding 1/4 of the period of the phase velocity wave, and if the inequality is not satisfied, the maximum peak level (f(n-1)) is corrected in step S16. The time value at which the peak level (f(n-1)) is detected is corrected by adding one half of the period of the phase velocity wave. Next, in step S11, coordinates are calculated using the corrected time values and output.

As explained above, according to this embodiment, the time value at which the maximum peak level pulse of the detected pulse group in the elastic wave is detected is corrected by the time value of the difference between the peak position of the envelope of the pulse group. This makes it possible to detect the input coordinates of the vibrating pen with higher precision.

In addition, the coordinate input device in this embodiment is not affected by fluctuations in the amplitude of the detection signal waveform due to pen pressure, etc., and is not affected by changes in the amplitude of the detection signal waveform due to pen pressure etc.
Since there is little magnetic field influence, stable position coordinate detection is possible.

In this example, the detected waveform pattern is 4.
However, it is not limited to this, and it is possible to subdivide the elastic waves as long as the detection accuracy of the elastic waves allows. Further, if the waveform detection calculation speed becomes faster, the number of detected waveform patterns will be further increased, and the resolution can be further improved. Further, in this embodiment, three peaks of the detection signal waveform were compared, but if the number of peaks is increased to five or seven, the resolution can be increased as described above if the waveform detection calculation speed can catch up.

In addition, in this example, only the positive peak of the detection signal waveform was detected, but the absolute value peak,
That is, if the lower half of the waveform is detected by folding it upward, the resolution can be doubled with a simple configuration.

In addition, in the flowchart of Fig. 6, f
(n-1) is the pulse with the maximum value peak in the pulse group, and this detection point and the maximum value of the envelope of the detection signal waveform should originally match, but in order to improve accuracy, the detection signal waveform filter the
The accuracy can be further improved by checking the detection point of f(n-1) using the detection point at the maximum value of the envelope obtained by differentiation.

[Effects of the Invention] As explained above, according to the present invention, the time value at which the maximum peak level pulse of the pulse group in the elastic wave is detected is corrected by the time value of the difference in the peak position of the envelope of the pulse group. By doing so, it becomes possible to detect the input coordinates of the vibrating pen with higher precision.

[Brief explanation of the drawing]

Figure 1 is a block diagram of the coordinate input device according to this embodiment, Figure 2 is a diagram showing the delay time between the input pen and each receiving piezoelectric element, and Figure 3 is the propagation distance and propagation time of elastic waves. Figures 4a to 4e are pattern diagrams of detected signal waveforms,
FIG. 5 is a diagram showing the relationship between each peak level a to e of the detected waveform, the propagation distance, and the propagation time, and FIG. 6 is a flowchart for determining the correction value for the detected time value. In the figure, 1... vibrating pen, 2... piezoelectric element, 3...
... Horn, 4 ... Signal input board, 5 ... Vibration propagation body, 6 ... Contact point, 7a to 7c ... Piezoelectric element for vibration detection, 8 ... Lead wire, 9 ... Vibration absorber,
10...Pulse signal generator, 11...Amplification calculation circuit, 12...Control unit, 12a...Memory.

Claims (1)

[Scope of Claims] 1. Vibration input means that propagates elastic waves to the vibration propagation body by contacting a desired position on the vibration propagation body; a receiving means for receiving an elastic wave propagating through the body and converting it into a group of pulse signals; and a receiving means for receiving an elastic wave propagating through the body and converting it into a group of pulse signals, based on the group of pulse signals converted by the receiving means, until a pulse signal of the maximum peak level of the group of pulse signals is received. clocking means for measuring the time value of; detecting means for detecting the peak level of each pulse signal of the pulse signal group received by the receiving means; and a peak level of each pulse signal of the pulse signal group detected by the detecting means. a correction means for calculating the peak position of the group velocity waveform for the pulse signal group based on the level, and correcting the time value obtained by the time measurement means using the obtained peak position, A coordinate input device characterized in that the coordinates of the contact position of the vibration input means on the vibration propagation body are determined based on the time value corrected by the correction means. 2. The correction means adds or subtracts a time value obtained by dividing a time corresponding to one wavelength of a pulse signal in a group of pulse signals received by the reception means to a time value measured by the time measurement means. 2. The coordinate input device according to claim 1, wherein the coordinate input device performs the correction according to the following.