JPS6330924A - Coordinate input device utilizing elastic wave - Google Patents

Abstract

PURPOSE:To obtain an exact longitudinal wave propagation time, and to obtain a tablet having high accuracy by calculating (frequency) X (plate thickness) by which the difference of the advancing distance of a longitudinal wave and the advancing distance of lamb wave exceeds one wavelength of the longitudinal wave in a coordinate input effective area, so that only the longitudinal wave of a first arriving wave can be detected. CONSTITUTION:When an exciting voltage VF is applied, and an input pen is contacting an input plate 1, a longitudinal wave is delayed by a propagation time and is appeared. In such a case, since the group velocity of the Lamb wave is reduced, the first arriving wave consists of only the longitudinal wave. For instance, when the input plate 1 is formed of soda lime glass, when the minimum of (frequency) X (plate thickness) of the So wave is determined by a graphical differentiation by substituting 5,500m/sec for the velocity of the longitudinal wave and 3,500m/sec for the velocity of the transverse wave, and calculating the phase speed distribution, it becomes about 2mmMHz. Accordingly, when the plate thickness of the soda line glass plate, and the propagation frequency are set to 4mm and 500KHz, respectively, the velocity of the Lamb wave becomes smaller than the transverse wave velocity, and a part (b) becomes the area of only the longitudinal wave. Therefore, even if the propagation time becomes short, as for the first arriving wave, only the longitudinal wave is detected exactly, and the propagation time can be measured with high accuracy.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an elastic wave coordinate input device, and particularly relates to an elastic wave coordinate input device suitable for a handwriting input device for inputting information to computers and the like. be.

[Conventional technology]

Conventional elastic wave application coordinate input device is a paper of the 11th Image Engineering Conference! 5-7. 1980, Plot-1
Among the waves that propagate in an elastic wave medium, as disclosed in Akira Ishii et al.'s ``Acoustic Wave Tablet Using Plate Waves,'' which is described in When applying this, it was necessary to set a propagation frequency with a small difference between the phase velocity and group velocity.

For this reason, it was necessary to reduce the thickness of the medium for elastic wave propagation and to lower the propagation frequency.

However, making the medium thinner leads to a decrease in the strength of the input board, and lowering the frequency slows down the rise of the detected wave, making it vulnerable to noise.

For this reason, the frequency was determined from a compromise of (frequency) x (plate thickness). Therefore, a difference occurs between the phase velocity and the group velocity, and this difference limits the area of the input board.

Furthermore, coordinate input devices that use longitudinal waves have been proposed as a method that does not use Lamb waves, but no consideration has been given to frequency selection.

[Problem that the invention seeks to solve]

Although the above-mentioned prior art discloses a frequency selection method for an acoustic wave tablet using Lamb waves, it does not consider a frequency selection method for a longitudinal wave application tablet.

In tablets that apply longitudinal waves, when detection is performed at a relatively low frequency, longitudinal waves and Lamb waves overlap, making it impossible to accurately detect longitudinal waves, which is a factor in reducing the accuracy of the tablet.

The present invention has been made in order to solve the problems of the prior art described above, and is provided in an input board of a coordinate input device.

Among the elastic waves that propagate, longitudinal waves and Lamb waves are distinguished by not including any Lamb waves in the first arriving wave at the detection point, and the distance between the elastic wave transmission point and the elastic wave detection point is small. The object of the present invention is to provide an elastic wave application coordinate input device that can measure the longitudinal wave propagation time with sufficient accuracy and improve the precision of the device.

[Means for solving problems]

In order to achieve the above object, the configuration of the elastic wave applied coordinate input device according to the present invention includes an isotropic medium for propagating elastic waves and an input pen, and is excited by an electric signal output from a pulser circuit to generate elastic waves. The input pen includes an elastic wave transmitting element that generates a wave, and an elastic wave detecting element that converts the elastic wave into an electric signal, and the input pen includes the elastic wave transmitting element, and the plurality of ends of the isotropic medium an elastic wave applied coordinate input device, wherein the elastic wave detecting element is disposed at the end of the isotropic medium, or the input pen is equipped with the elastic wave detecting element, and the elastic wave transmitting element is disposed at the end of the isotropic medium. In the above, when the elastic wave transmitted from the elastic wave transmitting element and propagating in the isotropic medium reaches the elastic wave detecting element, the difference between the traveling distance of the longitudinal wave and the traveling distance of the Lamb wave is: It has an arithmetic and constraint circuit that calculates and selects the frequency of the propagating elastic wave and the plate thickness of the isotropic medium so that the frequency of the propagating elastic wave and the plate thickness of the isotropic medium are equal to or more than at least one wavelength of the longitudinal wave within the effective coordinate input area.

Additionally, the above object is achieved by slowing down the group velocity of Lamb waves among the elastic waves propagating in the input plate of the coordinate input device.

[Effect]

The concept behind the development of the present invention and the principle of operation by the above means will be explained with reference to FIGS. 3 to 6.

Figure 3 is a mode diagram of a general Lamb wave, Figure 4 is a phase velocity distribution diagram of a Lamb wave, Figure 5 is a velocity distribution diagram of various elastic waves propagating in the input board, and Figure 6 is a diagram of the velocity distribution of various elastic waves propagating in the input board. , is a comparison diagram of detected waves of longitudinal waves and Lamb waves.

In general, a plate wave or Lamb wave that propagates at low frequency is a typical elastic wave that propagates in a thin plate related to the input plate, and is a 3rd wave.
As shown in the figure, there are an S wave group mode and an A wave group mode, which are expressed by the following equations.

Letting the phase velocity of the S-wave group mode be C, where C is the transverse wave velocity of the thin plate, CD is the longitudinal wave velocity, f is the propagation frequency, and d is the thickness of the thin plate. Further, if the phase velocity of the A wave group mode is C4, it is given by:

When the phase velocities of the S wave group and the A wave group are calculated from equations (1) and (4), the distribution is as shown in FIG. 4.

In Fig. 4, the horizontal axis shows (frequency) x (plate thickness), and the vertical axis shows phase velocity, showing the S wave group of So to S4.

It shows the phase velocity of the A wave group from Ao to A4.

Here, phase velocity is the velocity of a point in a wave phenomenon that moves with the wave while maintaining a certain phase, and group velocity is the velocity of a group of waves with slightly different frequencies and phase velocities.
It refers to the overall speed of propagation.

The group velocity is given by the differential amount of the phase velocity.

Waves higher than the second harmonic (A+, Az,...
, St , S2, . . . ) have small amplitudes, and application of these waves must be excluded from selection because it will significantly reduce the accuracy of the tablet regarding coordinate input it.

So, if we pay attention to So waves and Ao waves, Ao waves are S
O-waves (relative phase velocity) are extremely slow, so when detected with a tablet, they occur in reverberant waves and cannot be distinguished.

Based on the above, when we focus on So waves and compare waves other than Lamb waves, that is, longitudinal waves, transverse waves, and surface waves, we get a distribution as shown in Figure 5.

The group velocity C9 of the So wave is shown as a differential amount of the phase velocity C2 as shown by a broken line.

Here, how the change that occurs in the detected wave appears when the phase velocity and the group velocity are different will be explained with reference to FIG. 6.

Let L be the distance from the elastic wave generation point to the elastic wave detection point.

The propagation time of the longitudinal wave group velocity Cf from the elastic wave generation point to the elastic wave detection point at any distance is given by the longitudinal wave velocity CD,
It is given by Tr = L/C. In addition, the phase of a longitudinal wave is given by T2 = L/C using the phase velocity, and since the phase velocity C7 and group velocity C1 of longitudinal waves propagating through a thin plate are equal, T+ = T2, and there is always a first wave on the + side. The arriving wave (shaded area) appears.

When the distance increases slightly, the propagation time of the group velocity C1 of the longitudinal wave at L + Δt is given by ΔT3 = J L/C, and the phase of the longitudinal wave is given by ΔT < = d t/C-, and the propagation The amount of increase in time is ΔT3-ΔT4, and the detected waves appear in the same phase.

On the other hand, in the case of a Lamb wave, the propagation time of the distance is given by T+'=L/C- using the group velocity C1 of the Lamb wave. Further, the phase at this time is given by Ti = L/C- using the phase velocity C2. Here C, < C,
Therefore, 'L'<T;. Therefore, the phase of the detected wave does not match that of the longitudinal wave, and the first arriving wave (shaded area) is on the negative side.

Furthermore, in the case of L + Δt, the propagation time of the Lamb wave is ΔT i =
ΔL/C, the phase at this time is given by ΔT4=Δt/C7, ΔT3'>ΔT4, and this time the first arriving wave is on the + side. In this way, the detected wave in the case of a Lamb wave changes in phase. For this reason, it becomes impossible to detect a stable first arriving wave, making it difficult to improve the accuracy of the tablet.

Now, if we look carefully at the velocity distribution diagram in Figure 5 again, we can see that the group velocity of the Lamb wave is fast where (frequency) x (plate thickness) is small. Generally, the amplitude of the Lamb wave is several times larger than the amplitude of the @1 wave. Therefore, if the difference between the longitudinal wave velocity and the Lamb wave velocity is small, and the elastic wave generation point and the elastic wave detection point are close, it will be difficult to accurately detect only the longitudinal waves.

Therefore, the difference between the traveling distance of the longitudinal wave and the traveling distance of the Lamb wave is
If you calculate (frequency) x (plate thickness) that is at least one wavelength of longitudinal waves within the effective coordinate input area, and make it possible to detect only longitudinal waves as the first arriving wave, accurate longitudinal wave propagation time can be obtained. This makes it possible to improve the precision of the tablet.

The present invention has been made based on this idea.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 1 is a configuration diagram of a tablet using elastic waves according to an embodiment of the present invention, and FIG. 2 is a voltage waveform diagram when converted into an electric signal by an elastic wave detection element.

In FIG. 1, reference numeral 1 denotes an input plate related to a uniform isotropic medium for propagating elastic waves, and this input plate is made of soda lime glass.

Elastic wave detection elements 2a, 2b, and 2C12d are installed at the four corners of the input board, and are used to detect elastic waves propagating within the input board 1 and convert them into electrical signals.

3 is an input pen, and 4 is a pulser circuit for applying excitation voltage to the input pen 3. The input pen 3 includes an elastic wave transmitting element that is excited by the electric signal output from the pulser circuit to generate an elastic wave.

10 is an external device installed at the bottom of the input board 1, such as a liquid crystal display device. The input panel 1, the elastic wave detection elements 2a to 2d, the input pen 3, the slider 4, and the liquid crystal display device 10 constitute an input operation section 11.

12 is a signal control section, and the signal control section 12 includes an amplifier circuit 5,
It is composed of a waveform shaping circuit 6, a time counting circuit 7, a microcomputer 8, etc.

In the tablet of this embodiment, when the elastic wave transmitted from the elastic wave transmitting element in the input pen 3 and propagating through the input plate 1 reaches the elastic wave detecting elements 2a to 2d, the traveling distance of the longitudinal wave and the Lamb wave Calculate (frequency) x (plate thickness) so that the difference from the traveling distance is small (one wavelength or more of the longitudinal wave) within the valid coordinate input area, and the first arriving wave can detect only the longitudinal wave. It is equipped with a pulser circuit configured as follows.

The operation of the tablet with such a configuration will be explained.

An excitation voltage is applied from the pulser circuit 4 to the input pen 3, and an elastic wave is generated from the input pen 3. Input pen 3 to input board 1
By making contact with the input board 1, elastic waves propagate through the input board 1, and are converted into electrical signals by the elastic wave detection elements 2a to 2d installed at the four corners.

Each propagation time is calculated from the detected electrical signal through an amplifier circuit 5, a waveform shaping circuit 6, and a time counting circuit 7, and is calculated as a reference clock count value by a microcomputer 8.
will be forwarded to. The microcomputer 8 calculates (X, Y) coordinates from each count value, and transfers it to the liquid crystal display device I by the liquid crystal control circuit.

FIG. 2 shows voltages detected by the elastic wave detection elements 2a to 2d and converted into electrical signals.

When an excitation voltage V is applied and the input pen 3 is in contact with the input board 1, a longitudinal wave appears with a delay of the propagation time.

At this time, the group velocity of the Lamb wave is slowed down.

It can be seen that the first arriving wave is only a longitudinal wave, and no other waves are superimposed. For example, if the input board 1 is made of soda lime glass, the longitudinal wave velocity is 5500 m/sec and the shear wave velocity is 35 m/sec.
00 m/sec, calculate the phase velocity distribution, and differentiate it on the diagram to find the minimum So wave (frequency) x (plate thickness), which is approximately 2 '' mm Hw. Therefore, for example, soda lime The thickness of the glass plate is 4 mm, and the propagation frequency is 5.
00 KH, the Lamb wave will be slower than the shear wave velocity,
The part (bl) in Figure 2 is an area where only longitudinal waves exist. Therefore, even if the propagation time becomes short, only the longitudinal waves are accurately detected for the first arriving wave, making it possible to measure the propagation time with high accuracy. It becomes possible.

According to this embodiment, among the waves propagating in the input board of the tablet, it is easy to distinguish between longitudinal waves and Lamb waves.
The elastic wave transmission point and the elastic wave detection point, that is, the input pen 3
Even if the distance between the device and the elastic wave detection elements 2a to 2d is small, it is possible to measure the longitudinal wave propagation time with sufficient accuracy and improve the precision of the tablet.

In the above-mentioned embodiment, the isotropic medium for propagating elastic waves was a soda lime glass input plate, but it may be an acrylic plate or a polycarbonate plate.

In addition, although we have shown an example in which elastic wave detection elements are arranged at four locations,
It goes without saying that coordinate calculation is possible if there are two or more locations.

Furthermore, similar effects can be expected by arranging the elastic wave transmitting element at the end of the input board and configuring the elastic wave detecting element to be provided on the input pen side.

〔Effect of the invention〕

As described above, according to the present invention, among the elastic waves propagating in the input board of the coordinate input device, Lamb waves are completely excluded from the first arriving wave at the detection point, so that longitudinal waves and Lamb waves are not included. An elastic wave application coordinate input device that can distinguish between waves and measure the longitudinal wave propagation time accurately even if the distance between the elastic wave transmission point and the elastic wave detection point is small, increasing the accuracy of the device. can be provided.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a tablet using elastic waves according to an embodiment of the present invention, FIG. 2 is a voltage waveform diagram when converted into an electric signal by an elastic wave detection element, and FIG. , a mode diagram of a general Lamb wave, Figure 4 is a phase velocity distribution diagram of a Lamb wave, Figure 5 is a velocity distribution diagram of various elastic waves propagating in the input board, and Figure 6 is a diagram of longitudinal waves and FIG. 3 is a comparison diagram of detected waves of Lamb waves. DESCRIPTION OF SYMBOLS 1... Input board, 2a, 2b, 2C12d, ..., elastic wave detection element, 3... Input pen, 4... Pulser circuit,
6... Waveform shaping circuit, 7... Time counting circuit, 8...
・Microcomputer, 11...Input operation section, 12
...Signal control section. Agent Patent Attorney Masaru Ogawa Omata-' Dormitory 3 Prisoner Dormitory 40 Dormitory Closed

Claims (1)

[Claims] 1. An elastic wave transmitting element that is equipped with an isotropic medium that propagates elastic waves and an input pen, that is excited by an electrical signal output from a pulser circuit to generate an elastic wave, and that converts the elastic wave into an electrical signal. an elastic wave detection element, the input pen is provided with the elastic wave transmission element, and the elastic wave detection elements are arranged at a plurality of ends of the isotropic medium, or the input pen is provided with the elastic wave transmission element; In an elastic wave application coordinate input device comprising a detection element and the elastic wave transmitting element disposed at an end of the isotropic medium, an elastic wave transmitting element transmits an elastic wave and propagates in the isotropic medium. Outputting a propagating elastic wave in which, when the wave reaches the elastic wave detection element, the difference between the traveling distance of the longitudinal wave and the traveling distance of the Lamb wave is at least one wavelength of the longitudinal wave within the effective coordinate input area. An elastic wave application coordinate input device characterized by being equipped with a pulser circuit.