JPH1165745A - Coordinate input device and vibration arrival timing detection method thereof - Google Patents

Abstract

(57) [Problem] To provide a coordinate input device which maintains a good input feeling and enables stable vibration detection, and has high accuracy and a wide selection range of components. In a coordinate input device having a vibration transmission plate and a vibration input pen for inputting elastic wave vibration on the vibration transmission plate, a vibration sensor (6a) converts the elastic wave vibration applied to the vibration transmission plate into an electric signal. I do. The high-pass filter 420
Among the electric signals from the vibration sensor 6a, signals having a frequency equal to or lower than a predetermined frequency including a frequency band in which an unnecessary signal component exists are attenuated. A timing signal tg for detecting a group delay time based on the electric signal obtained through the high-pass filter 420
Is obtained. On the other hand, a timing signal tp for detecting a phase delay time is obtained based on the electric signal from the vibration sensor 6a. The arithmetic control circuit calculates the group delay time and the phase delay time based on tg and tp, and calculates the distance from the vibration input point to the vibration sensor 6a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coordinate input device and a method for detecting a vibration arrival timing thereof. More specifically, the elastic wave vibration input from the vibration pen is detected by a plurality of sensors provided on the vibration transmission plate, and based on the transmission time of the elastic wave vibration input from the vibration pen to the vibration transmission plate, the vibration pen The present invention relates to a coordinate input device for detecting the coordinates of a vibration input point and a method for detecting a vibration arrival timing.

[0002]

2. Description of the Related Art As an ultrasonic coordinate input device, there is known an ultrasonic coordinate input device which detects an input vibration value on a coordinate input plate to obtain an input coordinate value. For example, Japanese Patent Publication No. 5-60615
In the coordinate input device disclosed in the above, the vibration pen is brought into contact with the vibration transmission plate to input vibration to the vibration transmission plate, and the inputted vibration is transmitted on the vibration transmission plate, and provided on the vibration transmission plate. The contact coordinate position of the vibrating pen is calculated based on the delay time required to reach the sensor.

A vibrating pen of this type of coordinate input device has a built-in vibrator, and its vibration frequency is selected to a value that can generate a plate wave on a vibration transmission plate made of a glass plate or the like. In addition, when driving the vibrator, a mode in which the vibrator vibrates in the vertical direction with respect to the vibration transmission plate is selected, and the vibration frequency of the vibrator is set to the resonance frequency including the pen tip, thereby enabling efficient vibration conversion. .

In order to improve the input feeling (writing sensation) of the coordinate input device, the material of the pen point and the surface material of the glass plate (surface treatment state, when laminating on glass, the material of the laminate) are as follows: A material having a predetermined coefficient of friction has been selected.

[0005]

However, depending on the material of the vibration transmitting plate (when laminating on glass, the material of the laminate), unnecessary low-frequency sound waves are generated by friction with the vibration input pen. For this reason, in addition to the frequency component of the ultrasonic vibration determined by the vibration input pen and the vibration transmission plate that should be originally detected, the above-described unnecessary sound wave is detected. In general, when an unnecessary sound wave is detected, the detection circuit determines that the detection is erroneous, and performs an operation of not outputting a coordinate value, so that a substantial sampling rate is reduced.

Also, there is a trade-off with the feeling of input,
It is also conceivable to select a material for the laminate that does not generate unnecessary sound waves. However, since the coordinate input device is a general-purpose device, it is not known how an unspecified number of users will use it. As an example of use of the coordinate input device, there is a case where a work such as placing a paper such as a document on an input plate and tracing from there is performed. In such a case, if the original is a paper such as a coated paper, a rubbing noise is also generated, an unnecessary sound wave is generated, and the same problem as described above occurs.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides a coordinate input device and a vibration arrival timing detecting method for maintaining a good input feeling and enabling stable vibration detection. An object of the present invention is to realize a coordinate input device having a wide selection range of components.

[0008]

A coordinate input apparatus according to the present invention for achieving the above object has the following arrangement. That is, a vibration transmission plate, vibration input means for inputting elastic wave vibration on the vibration transmission plate, and a conversion means for converting the elastic wave vibration applied to the vibration transmission plate from the vibration input means to an electric signal, Attenuating means for attenuating a signal having a frequency equal to or lower than a predetermined frequency among the electric signals obtained by the converting means, and the elastic wave vibration for determining a group delay time based on the electric signal obtained through the attenuating means. First detection means for detecting an arrival timing, second detection means for detecting an arrival timing of the elastic wave vibration for determining a phase delay time based on an electric signal obtained from the conversion means, and the vibration input means On the vibration transmission plate instructed by the vibration input means based on the time from when the vibration is applied to when the first and second detecting means detect the arrival timing. And a calculating means for calculating a target position.

Further, a vibration arrival timing detecting method according to the present invention for achieving the above object includes the following steps.
That is, a method for detecting a vibration arrival timing of a coordinate input device having a vibration transmission plate and vibration input means for inputting an elastic wave vibration on the vibration transmission plate, wherein the vibration input timing is applied to the vibration transmission plate from the vibration input means. A conversion step of converting the elastic wave vibration into an electric signal, an attenuation step of attenuating a signal having a frequency equal to or lower than a predetermined frequency among the electric signals obtained in the conversion step, and an electric signal obtained through the attenuation step. A first detecting step of detecting the arrival timing of the elastic wave vibration for determining the group delay time, and the arrival of the elastic wave vibration for determining the phase delay time based on the electric signal obtained from the conversion step A second detection step of detecting timing.

[0010]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

<Overall Configuration of Coordinate Input Device> FIG. 1 is a diagram showing the structure of a coordinate input device according to the present embodiment. In the figure, reference numeral 1 denotes an arithmetic control circuit for controlling the entire apparatus and calculating a coordinate position. 2 is a vibrator drive circuit,
The vibrator in the vibration input pen 3 is vibrated. 3
Is a vibration input pen, which generates vibration at the pen tip by a drive output from the vibrator drive circuit 2.

Reference numeral 8 denotes a vibration transmission plate, which is made of a transparent member such as an acrylic or glass plate. On the upper surface of the vibration transmission plate 8, a film (laminate) made of PET or the like for preventing scattering when the vibration transmission plate 8 is broken is disposed via an adhesive layer. The coordinate input by the vibration input pen 3 is performed by touching the vibration transmission plate 8. Actually, the user designates the area within the area indicated by the symbol A (hereinafter referred to as the effective area) indicated by a solid line with the vibration input pen 3. A vibration isolator 7 is provided on the outer periphery of the vibration transmission plate 8 to prevent (reduce) the reflected vibration from returning to the center, and a mechanical vibration such as a piezoelectric element is applied to the boundary at the boundary. Are fixed.

Reference numeral 9 denotes a signal waveform detection circuit which outputs a signal indicating that vibration has been detected by each of the vibration sensors 6a to 6d to the arithmetic and control circuit 1. Reference numeral 11 denotes a display, such as a liquid crystal display, capable of displaying in dot units, and is disposed behind the vibration transmission plate. The display is driven by the display drive circuit 10 to display a dot at a position traced by the vibration input pen 3 and to see it through the vibration transmission plate 8 (made of a transparent member).

<Description of Arithmetic Control Circuit> In the above-described configuration, the arithmetic control circuit 1 operates every predetermined period (for example, 10 ms).
Each time), a start signal for driving the vibrator in the vibration input pen 3 is output to the vibrator drive circuit 2 and time counting by the internal timer (constituted by a counter) is started. The vibrator driving circuit 2 drives the vibrator of the vibration input pen 3 according to the start signal, and generates vibration from the vibration input pen 3. The vibration generated from the vibration input pen 3 reaches each vibration sensor with a delay according to the distance between the vibration sensors 6a to 6d.

The signal waveform detecting circuit 9 includes the vibration sensors 6a to 6a.
The signal from 6d is detected, and a signal indicating the timing of arrival of vibration at each vibration sensor is generated by a waveform detection process described later. The arithmetic and control circuit 1 receives this signal for each sensor and detects the arrival time of the vibration of each of the vibration sensors 6a to 6d. Then, the coordinate position of the vibration input pen 3 is calculated based on the vibration delivery time. The arithmetic control circuit 1 drives the display drive circuit 10 based on the calculated position information of the vibration input pen 3 to control the display on the display 11 or to send the coordinates to an external device by serial or parallel communication. Output (not shown).

FIG. 2 is a diagram showing a detailed configuration of the vibration input pen according to the present embodiment. As described above, the vibrator 4 built in the vibration input pen 3 is driven by the vibrator drive circuit 2. The drive signal of the vibrator 4 is supplied from the arithmetic and control circuit 1 as a low-level pulse signal (start signal), and is applied to the vibrator 4 after being amplified by a predetermined gain. The electric drive signal is converted into mechanical ultrasonic vibration by the vibrator 4 and transmitted to the vibration transmission plate 8 via the pen tip 5. In the present embodiment, the elastic wave transmitted to the vibration transmission plate 8 as described above is a plate wave, which is less susceptible to the effects of scratches and obstacles on the surface of the vibration transmission plate than surface waves. Having.

FIG. 3 is a block diagram showing a schematic configuration of the arithmetic and control circuit 1 of the present embodiment. Hereinafter, referring to FIG.
Each component and its operation outline will be described.

In the figure, reference numeral 31 denotes a microcomputer for controlling the arithmetic and control circuit 1 and the entire coordinate input device, and includes an internal counter, a ROM storing a control program, a RAM used for calculation and the like, and a nonvolatile memory storing constants and the like. CP for executing a control program stored in a memory or a ROM
U and the like.

Reference numerals 32a to 32d denote counters for measuring a reference clock (not shown). Time counters 32a to 32d
The vibrator driving circuit 2 includes a vibrator 4 in the vibration input pen 3.
A start signal for starting the driving of the device is input, and the timing is started. As a result, the start of timing and the detection of vibration by the sensor are synchronized, and the sensors (6a to 6d)
Thus, the delay time until the vibration is detected can be measured. Other circuits constituting each component will be described in order.

The vibration arrival timing signals from the vibration sensors 6a to 6d output from the signal waveform detection circuit 9 are input to the counters 32a to 32d via the detection signal input circuit 34. Each of the counters 32a to 32d latches the count value at that time when the vibration arrival timing signal is input. Note that the counters 32a to 32d
Correspond to the vibration sensors 6a to 6d, respectively.

When the determination circuit 33 determines that all the detection signals have been received, it outputs a signal to the microcomputer 31 to that effect. When the microcomputer 31 receives the signal from the determination circuit 33, it reads the vibration arrival time to each of the vibration sensors latched by the counters 32a to 32d, performs a predetermined calculation (described later), and performs The coordinate position of the upper vibration input pen 3 is calculated.

Then, by outputting the calculated coordinate position information to the display drive circuit 10 via the I / O port 35, for example, a dot or the like can be displayed at a corresponding position on the display 11. Alternatively, by outputting the coordinate position information to the interface circuit via the I / O port 35, the coordinate value can be output to the external device.

<Description of Vibration Propagation Time Detection (FIGS. 4 and 5)
Next, the principle of measuring the time required for the vibration to reach the vibration sensors 6a to 6d will be described. First, detection of the arrival timing of vibration will be described.

FIG. 4 is a block diagram showing a configuration of the signal waveform detection circuit 9. FIG. 5 is a diagram for explaining a detection waveform input to the signal waveform detection circuit 9 and a process of measuring a signal transmission time based on the detection waveform. Hereinafter, the case of the vibration sensor 6a will be described, but other vibration sensors 6b to 6b will be described.
The same applies to d.

As described above, the measurement of the vibration transmission time to the vibration sensor 6a is started simultaneously with the output of the start signal to the vibrator drive circuit 2. At this time, the drive signal 51 is applied from the transducer drive circuit 2 to the transducer 4.
The drive signal 51 is a short (for example, two) rectangular pulse. According to the signal 51, the ultrasonic vibration transmitted from the vibration input pen 3 to the vibration transmission plate 8 proceeds over a time corresponding to the distance to the vibration sensor 6a, and is detected by the vibration sensor 6a as a short detection waveform. You. The reason why the drive signal 51 is set to a short pulse is to prevent erroneous detection due to interference (superposition) between an unnecessary reflection component mainly at the end face of the vibration transmission plate 8 and the vibration to be detected, and to reduce the size of the entire apparatus. is there. FIG.
A signal 52 indicates a signal waveform detected by the vibration sensor 6a.

From the signal waveform 52 detected by the vibration sensor 6a, a group signal indicated by 521 and a phase signal indicated by 522 are obtained, and each signal is processed by a procedure described later.

First, the group signal 521 is processed using the signal after passing through the high-pass filter 420. Since the processing of the group signal 521 that is easily affected by the reflected wave is performed, the high-pass filter 420 is used only for the envelope detection.
The short detection signal after passing is used. FIG. 6 is a diagram illustrating the results of measuring the detected vibration and the unnecessary vibration detected by the vibration sensor 6. As can be seen from the experiment (result of FIG. 6), the vibration frequency due to friction between the vibration input pen and the vibration input surface is about 20 to 40 kHz. That is, the frequency of the unnecessary vibration is 20 to 40 kHz. The detected vibration is about 300 kHz or more. In practice, the high-pass filter 420 is about 30 dB from the frequency of the detection signal.
It is designed to have a frequency characteristic that goes down. “Having a frequency characteristic that reduces the frequency by 30 dB” is a numerical value set based on the experimental result shown in FIG. 6, and is a high-pass filter having a frequency characteristic that attenuates unnecessary vibration by 30 dB. It means to compose.

The detection signal after passing through the high-pass filter 420 is detected by an envelope
3 is taken out. Note that the envelope signal extracted based on the signal 52 is the signal 53. The time lag between the signal 52 and the signal 53 is caused by the processing time of the envelope detection circuit and the like. The extracted envelope signal 53 is input to an envelope inflection point detection circuit 422, where a twice-differential output waveform 58 is generated. Also, the extracted envelope signal 53 is
The signal is also input to the gate signal generation circuit 43. The gate signal generation circuit 43 attenuates the input envelope signal 53 to an appropriate amplitude, adds a certain offset thereto,
A reference level signal 541 is generated. Further, the second-order differential output waveform 54 from the envelope inflection point detection circuit 422 is also input to the gate signal generation circuit 43. The gate signal generation circuit 43 outputs a gate generation signal 542 by comparing the twice differentiated output waveform 54 with the reference level signal 541. The monostable multivibrator 44 outputs a gate signal 56 having a predetermined pulse width to the tg comparator 423 and the tp comparator 452 from the rising timing of the input gate generation signal 542.

The tg comparator 423 outputs the gate signal 5
6 and the second-order differential waveform 54 are input, and a tg signal is generated with the zero-cross point while the gate signal 56 is open as the inflection point of the envelope.

Next, the processing relating to the phase signal will be described. The waveform 522 is converted into a signal having a frequency component having a predetermined width by the narrow band-pass filter 450, and the slice circuit 451 slices the waveform to a predetermined amplitude level or lower (waveform level compression). When the output of the phase signal 58 and the gate signal 56 are input to the tp comparator 452, the tp comparator 452 converts the phase signal (the output signal 57 of the slice circuit 57) of the phase signal while the gate signal 56 is open. The zero-crossing point of the rising edge corresponding to the order is detected, and the phase delay time signal tp is calculated by the arithmetic and control circuit 1.
To supply. In the example of FIG. 5, tp is the second rising zero-crossing point.

Here, the reference level signal 541 for outputting the gate generation signal 542 may be a variable level synchronized with the drive pulse 51 in accordance with the distance between the vibration input pen 3 and the vibration sensor 6a. When the fluctuation range of the detection level is large depending on the distance, setting the variable level is effective because the detection point is stabilized. This is because the gate signal generation circuit 43
In this case, it can be realized by changing the attenuation rate when the envelope signal is attenuated and the level of the offset.

Next, the calculation of the vibration transmission delay time will be described. Since the vibration used in the device of the present embodiment is a plate wave, the relationship between the envelope 521 of the detected waveform and the phase signal 522 with respect to the transmission distance in the vibration transmission plate 8 is as follows.
During vibration transmission, it changes according to the transmission distance. Here, the traveling speed of the envelope 521, that is, the group velocity is V
g, and the speed at which the phase signal 522 advances, that is, the phase speed is Vp. The distance between the vibration input pen 3 and the vibration sensor 6a can be detected from the group velocity Vg and the phase velocity Vp.

First, focusing only on the envelope 521, the speed is Vg, and a point on a specific waveform,
When an inflection point is detected, the distance between the vibration input pen 3 and the vibration sensor 6a is given by d = Vg · tg (1), where tg is the vibration transmission time. This equation is for one of the vibration sensors 6a, but the same equation gives the other three vibration sensors 6a.
The distance between b to 6d and the vibration input pen 3 can be similarly obtained.

Further, in order to determine coordinates with higher accuracy, processing based on detection of a phase signal is performed. From the time tp detected from the phase waveform signal 522 as described above, the distance between the vibration sensor and the vibration pen is as follows: d = n · λp + Vp · tp (2) Here, λp is the wavelength of the elastic wave, and n is an integer.

From the above equations (1) and (2), the above integer n
Is represented as n = [(Vg · tg−Vp · tp) / λp + 1 / N] (3)

Here, N is a real number other than "0", and an appropriate value is used. For example, if N = 2, then n can be determined if it is a change such as tg within ± 1/2 wavelength. Then, the distance between the vibration input pen 3 and the vibration sensor 6a can be accurately measured by substituting n obtained as described above into the expression (2).

Although the circuit described above is for the vibration sensor 6a, the other vibration sensors are provided with the same circuit.

<Description of Coordinate Position Calculation (FIG. 7)> Now, four vibration sensors 6a to 6a
When 6d is provided at the positions of the symbols Sa to Sd, the linear distances da to dd from the position P of the vibration input pen 5 to the positions of the respective vibration sensors 6a to 6d can be obtained based on the principle described above. (FIG. 7). According to the coordinate point calculation method according to the present embodiment, the coordinate points can be calculated if the distances to the three sensors are known. Therefore, in the present embodiment, a coordinate point is calculated by using three sensors having a short distance among the four sensors (the sensor located farthest from the input point is not used). In the arithmetic and control circuit 1, the coordinates (x, y) of the position P of the vibration input pen 3 are based on the detected linear distances da to dd (dc is not used in the example of FIG. 7).
Is obtained from the three-square theorem as follows.

X = X / 2 + (da + dd) · (da−dd) / 2X (4) y = Y / 2 + (da + db) · (da−db) / 2Y (5) where X and Y are respectively The distance between the vibration sensors 6a and 6d and the distance between the vibration sensors 6a and 6b.

As described above, unnecessary sound waves due to friction between the vibration input pen 3 and the vibration transmission plate 8 are removed, stable detection is possible, and coordinates can be detected in real time.

Even if the present invention is applied to a system composed of a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), an apparatus (for example, a copying machine, a facsimile, etc.) composed of one device. Device).

Another object of the present invention is to provide a storage medium storing a program code of software for realizing the functions of the above-described embodiments to a system or apparatus, and to provide a computer (or CPU) of the system or apparatus.
And MPU) read and execute the program code stored in the storage medium.

In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiment, and the storage medium storing the program code constitutes the present invention.

As a storage medium for supplying the program code, for example, a floppy disk, hard disk, optical disk, magneto-optical disk, CD-ROM, CD
-R, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.

When the computer executes the readout program code, not only the functions of the above-described embodiment are realized, but also the OS (Operating System) running on the computer based on the instruction of the program code. ) May perform some or all of the actual processing, and the processing may realize the functions of the above-described embodiments.

Further, after the program code read from the storage medium is written into a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, based on the instructions of the program code, It goes without saying that the CPU included in the function expansion board or the function expansion unit performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

As described above, according to the above embodiment, the delay time until the elastic wave vibration input to the vibration transmitting plate 8 by the vibration input pen 3 reaches the vibration sensors 6a to 6d is detected. In a coordinate input device that calculates and outputs coordinate positions (vibration application positions) on the vibration transmission plate 8 based on the delay time, a group of signals output from the vibration sensors 6a to 6d is processed using a high-pass filter. Performs signal processing related to delay time. Since the high-pass filter removes the frequency component of the unnecessary vibration generated on the vibration input surface of the vibration input pen 3 and the vibration transmission plate 8, the signal after the unnecessary vibration is removed is subjected to the processing related to the group delay signal.
Therefore, a stable and highly accurate coordinate input device can be provided.

[0048]

As described above, according to the present invention, a good input feeling can be maintained and stable vibration detection can be performed, and a coordinate input device with high accuracy and a wide selection range of components can be realized.

[0049]

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a structure of a coordinate input device according to an embodiment.

FIG. 2 is a diagram illustrating a detailed configuration of a vibration input pen according to the embodiment.

FIG. 3 is a block diagram illustrating a schematic configuration of an arithmetic control circuit 1 according to the embodiment.

FIG. 4 is a block diagram showing a configuration of a signal waveform detection circuit 9;

FIG. 5 shows a detection waveform input to a signal waveform detection circuit 9;
It is a figure for explaining measurement processing of signal transmission time based on it.

FIG. 6 is a diagram showing the results of measuring detected vibration and unnecessary vibration detected by the vibration sensor 6.

FIG. 7 is a diagram illustrating a method of calculating a coordinate position.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Operation control circuit 2 Vibrator drive circuit 3 Vibration input pen 4 Vibrator 5 Pen tip 6a-6d Vibration sensor 7 Vibration-proof material 8 Vibration transmission board 9 Signal waveform detection circuit 10 Display drive circuit 11 Display

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Katsuyuki Kobayashi, Inventor 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Ryozo Yanagisawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inside the corporation

Claims (9)

[Claims] 1. A vibration transmitting plate, vibration input means for inputting an elastic wave vibration on the vibration transmitting plate, and a conversion for converting the elastic wave vibration applied from the vibration input means to the vibration transmitting plate into an electric signal. Means, an attenuating means for attenuating a signal of a predetermined frequency or less among the electric signals obtained by the converting means, and the elasticity for determining a group delay time based on the electric signal obtained through the attenuating means. First detection means for detecting the arrival timing of the wave vibration; second detection means for detecting the arrival timing of the elastic wave vibration for determining a phase delay time based on the electric signal obtained from the conversion means; The vibration transmission instructed by the vibration input means based on the time from when the vibration is applied by the vibration input means to when the first and second detection means detect the arrival timing. A coordinate input device comprising: a calculating unit that calculates a coordinate position on a plate. 2. The vibration input means applies an elastic wave vibration having a frequency higher than unnecessary vibration generated when the vibration input means and the vibration transmission plate come into contact with each other. The coordinate input device according to claim 1, comprising a high-pass filter having a frequency characteristic of attenuating the coordinate. 3. The coordinate input device according to claim 2, wherein said attenuating means is a high-pass filter having a frequency characteristic that is substantially 30 dB down from the frequency of the detection signal. 4. The apparatus according to claim 1, wherein the first detecting means detects an envelope of the electric signal having passed through the attenuating means, and detects an arrival timing of the elastic wave vibration based on a characteristic point of the envelope. 2. The coordinate input device according to 1. 5. A vibration arrival timing detecting method for a coordinate input device, comprising: a vibration transmission plate; and a vibration input means for inputting an elastic wave vibration on the vibration transmission plate, wherein the vibration transmission means detects the vibration arrival timing. Converting the elastic wave vibration applied to the electric signal into an electric signal; attenuating the signal having a predetermined frequency or less among the electric signals obtained in the converting step; A first detection step of detecting an arrival timing of the elastic wave vibration for determining a group delay time based on a signal; and the elastic wave for determining a phase delay time based on an electric signal obtained from the conversion step. A second detection step of detecting an arrival timing of the vibration. 6. The method according to claim 5, further comprising an acquisition step of acquiring a time from an application timing of the vibration by the vibration input means to an arrival timing detected in the first and second detection steps. Vibration arrival timing detection method. 7. The vibration input means applies elastic wave vibration having a frequency higher than unnecessary vibration generated when the vibration input step and the vibration transmission plate come into contact with each other.
The vibration arrival timing detecting method according to claim 6, wherein the electric signal obtained in the conversion step is supplied to a high-pass filter having a frequency characteristic for attenuating the unnecessary vibration. 8. The vibration arrival timing detecting method according to claim 7, wherein the high-pass filter has a frequency characteristic that is approximately 30 dB down from the frequency of the detection signal. 9. The method according to claim 1, wherein the first detecting step detects an envelope of the electric signal that has passed through the attenuation step, and detects an arrival timing of the elastic wave vibration based on a characteristic point of the envelope. 5. The method for detecting vibration arrival timing according to item 5.