JPH0460246B2 - - 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 corrugated plate, the group velocity and phase velocity differ due to the influence of dispersion, so the above detection method causes an error of up to one wavelength in the phase velocity wavelength. was unavoidable.

The present invention has been made in view of the above-mentioned prior art, and by calculating the maximum value of the envelope of a group of pulses that are detection signals, 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 provided 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 based on the pulse signal group converted by the receiving means, measuring a time value until a pulse signal with the maximum amplitude of the pulse signal group is received. a timer; and a correction means for calculating the peak position of the group velocity waveform for the pulse signal group converted by the receiving means and correcting the time value obtained by the timer using the obtained peak position. Equipped with.

[Function] In the configuration of the present invention, the time value until the receiving means receives the elastic wave propagating from the position designated by the position specifying means is measured by the time measuring means, and the electric signal generated by the receiving means is measured. The calculation means calculates the peak position of the envelope of the pulse group, and the correction means corrects the time value measured by the clock means using this calculation result, thereby determining the coordinate position of the position specifying 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 that 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 stores therein a program for calculating the coordinate position of the grounding point 6 based on the measured time value and a program for operating the flowchart shown in FIG. 6, which will be described later. A memory 12a is provided.

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 process 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.

The 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+v ² /2・x 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 absorbing material 9, the vibration 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 t _B.

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 a maximum of one wavelength error in the phase velocity wavelength when the ideal detection point corresponding to the group velocity of the detection signal waveform and the maximum pulse level in the pulse group are detected because propagation is adopted. It is something.

In order to correct this time error, in this embodiment, the peak level of the pulse signal immediately after the pulse signal with the maximum peak level in the pulse group is set as the threshold value.
By comparing the pulse signal with the maximum peak level, the time error of the generated pulse width is continuously corrected. The correction processing means and its principle will be explained below.

FIG. 4 shows the relationship between propagation distance and propagation time in the detection signal waveform. v _G is a straight line corresponding to group velocity, and a to e are straight lines corresponding to phase velocity. The slope of this straight line is 1/v (v indicates the propagation velocity). Therefore, as can be seen from this figure, the phase velocity is slower than the group velocity. In addition, in the propagation distance, λ _P is one wavelength of the phase velocity, and 1/f is one period of the phase velocity (f: driving frequency). Fourth
In the figure, you can see that if you move x _A (→) over 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, the points in FIG. 4 and the points in FIG. 4 are in the same phase. Therefore, if the propagation time is corrected by h at the point, the propagation velocity will match the propagation velocity at the group velocity v _G.

Based on the above, the details of correction in signal waveform detection will be explained below.

FIGS. 5a to 5e are typical pattern diagrams of detection signal waveforms. In this example, since the phase velocity is slower than the group velocity, when the propagation distance increases, that is, when moving from "state A" to "state B" in FIG. 3, the waveforms shown in FIGS. 5a to 5e are formed. The detection signal waveform changes continuously.

Here, the detection signal waveform is passed through a low-pass filter to form an envelope, which is differentiated, and the maximum value of the phase velocity waveform peak is detected from this zero crossing point.
If this continues, a maximum deviation of one wavelength will occur as described above. Therefore, while holding this maximum value, the next peak of the maximum value is detected and this level is set as the threshold value, and the pulse width corresponding to the time domain of the intercept of the maximum waveform that crosses this level as shown in Fig. 5 a to e. Generates a “Z” pulse signal. In this way, the pulse width "Z" increases or decreases continuously in response to the phase shift, as shown in FIGS. 5a to 5e, and returns to 0 after one wavelength shift. This continuously changing pulse width Z is detected and converted into
By correcting each time to the point at the maximum value of the peak, the detection point of this signal waveform can be made to coincide with the propagation time at the group velocity v _G.

Therefore, by detecting this pulse width "Z", the position of the envelope of the pulse group can be continuously determined.

In other words, when the time required to detect the pulse with the maximum peak level in the pulse group is "t", it corresponds to the difference between the pulse position of the maximum peak level and the peak position of the envelope of the pulse group. By adding or subtracting the time value to "t", it becomes possible to calculate the position coordinates of the vibrating pen 1 even at the time when the peak of the envelope of the pulse group is detected.

The relationship when the corrected time is "T" and the time correction value corresponding to the pulse width "Z" is P(Z) is shown below.

T=t+P(Z) Also, this P(Z) is the pulse width when pulse 50 in the pulse group shown in Figure 5a is taken as the threshold.
When Z ₀ , this Z ₀ becomes the maximum value, so 0<
There is a relationship of Z<Z ₀ .

Therefore, P(Z)=-1/f×Z/Z ₀ where 1/f is one period of the phase velocity.

Therefore, 0≦Z/Z ₀ <1, and the time value can be corrected within one wavelength of the phase velocity.

It is assumed that this Z ₀ has been measured and input in advance.

Next, the time value correction process will be explained according to the flowchart of FIG. In the following explanation, f(n) represents the peak level of each pulse of the pulse group.

First, in step S1, n is set to "1" as an initial value.
and read f(n) in step S2. Next, in step S3, n is incremented, and in the next step S4, f(n) is read, and the previously read f
(n-1) and f(n) are compared (step S5).
If f(n) is larger than f(n-1) in this determination, the process returns to step S3. Therefore, from step S3 to step S5, the pulse with the maximum peak level in the pulse group is determined. Now, in the determination at step S5, f(n) is f
(n-1), step S
6, find the intercept Z of the n-1th pulse using f(n) as the threshold value. Next, in step S7, f(n-
Add correction -1/f x Z/Z ₀ to the detection point in 1).
Next, based on the time value corrected in step S8, the position coordinates of the vibrating pen 1 are determined and output using the formula described above (step S8).

As explained above, in this embodiment, the pulse width “Z”
Although the peak level of the pulse immediately after the maximum peak level was used as the threshold value for detection, the present invention is not limited to this.

For example, as shown in Figure 7, hold the third peak from the maximum peak level in the pulse group, set the level of the third peak from this maximum value as the threshold, and compare the two waveforms before crossing this. A similar effect can also be obtained by generating a pulse signal with a pulse width corresponding to the time domain of the intercept of , and detecting the ratio of the two pulse widths (Z ₁ , Z ₂ ).

In this case, the corrected time value P(Z ₁ , Z ₂ ) is as follows.

P(Z ₁ , Z ₂ )=-1/f×Z ₂ /Z ₁ As shown in Figure 6, this ratio also increases continuously in response to the phase shift, and when the shift is one wavelength, Also, go back. This continuously changing pulse width
By detecting Z ₁ and Z ₂ and correcting them each time to the point at the maximum value of the peak, the detection point of this signal waveform coincides with the propagation time at the group velocity v _G.

In this embodiment, only the positive peak of the detection signal waveform is detected, but if the peak of the absolute value, that is, the lower half of the waveform is detected by folding upward, the resolution can be doubled.

Further, in this embodiment, if the number of waveforms used for correction is further increased, a detection method with even higher accuracy and higher resolution can be obtained.

As explained above, according to this embodiment, the maximum position of the envelope of the pulse group and the maximum peak level of the pulse group are determined by the time value until the maximum peak level in the pulse group, which is the detection signal, is detected. By correcting the time corresponding to the difference from the peak position of
It becomes possible to calculate coordinates with higher resolution.

Furthermore, the detection method in the embodiment has the advantage that continuous correction can be performed instead of piecemeal correction.

Furthermore, in the detection method that takes the ratio of the time domain of two waveform intercepts that cross a threshold, it is possible to detect position coordinates that are not affected by fluctuations in the amplitude of the detected waveform signal due to pen pressure or the like.

[Effects of the Invention] As explained above, according to the present invention, the time value until the maximum peak level in the pulse group which is the detection signal is detected is determined by the maximum position of the envelope of the pulse group and the maximum peak level in the pulse group. By correcting the time corresponding to the difference between the maximum peak level and the peak position,
It becomes possible to calculate coordinates with higher resolution.

[Brief explanation of drawings]

Figure 1 is a schematic configuration diagram showing the coordinate input device of 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 of elastic waves. A diagram showing the relationship between time and signal waveform,
FIG. 4 is a diagram showing the relationship between propagation distance and propagation time in the detection signal waveform, and FIGS. 5a to 5e are pattern diagrams of the detection signal waveform. FIG. 6 is a flowchart showing the time value correction process according to this embodiment;
Figures a to e are pattern diagrams of detection signal waveforms of other embodiments. 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 absorbing material, 1
0...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, and a vibration input means provided at a predetermined position of the vibration propagation body, a receiving means for receiving an elastic wave propagating through a propagation medium and converting it into a group of pulse signals; and a receiving means for receiving an elastic wave propagating through a propagation medium 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 with the maximum amplitude of the group of pulse signals is received. a timer for measuring the time value of the time value; and a timer for calculating the peak position of the group velocity waveform for the pulse signal group converted by the receiving means, and calculating the time obtained by the timer at the position of the obtained peak. A coordinate input device comprising: a correction means for correcting a value, and determining the coordinates of a contact position of the vibration input means on the vibration propagation body based on the time value corrected by the correction means. 2. The correction means compares the maximum amplitude pulse signals using, as a threshold, the amplitude level value of one pulse signal before and after the maximum amplitude pulse signal in the group of pulse signals received by the reception means. 2. The coordinate input device according to claim 1, wherein the time value obtained by the time measuring means is corrected using a pulse width modulated signal.