JPS5816509B2 - Coordinate detection device using elastic waves - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a coordinate detection device using elastic waves, and more particularly to a coordinate input device that obtains position coordinates by counting the delay time of elastic waves.

Conventionally, the distance from the radiation point to the detection point is calculated by counting the delay time required for the elastic wave to propagate from the radiation point to the detection point and finding the product of the sound speed and the delay time, and then calculating the position of the radiation point or detection point. There are three types of coordinate input devices for determining coordinates, which are roughly classified depending on the method of propagation of elastic waves.

The first is a method that propagates through the air, the second is a method that uses surface acoustic waves (Leley waves) that propagate on solid surfaces such as glass, and the third is a method that uses a uniform plate thickness that is thinner than the wavelength of the elastic wave. This method uses plate acoustic waves (Lamb waves) that propagate through a oriented substrate.

A typical example of the first method is a "sonic pen" which is used to specify the positional coordinates to be detected.The tip of the input pen is electrically discharged, and the generated elastic waves (sound waves) propagate through the air and are placed on two sides of the coordinate detection plane. Sound waves are detected using a rod-shaped microphone.

If there is an obstacle such as a hand on the coordinate detection plane, it will impede the propagation of sound waves and interfere with the coordinate detection operation, resulting in difficulty in operability.

In the second method, the propagation of surface acoustic waves is fundamentally influenced by the surface condition of the propagation medium.

The input pen has a built-in piezoelectric element, which receives elastic waves excited from two sides of the coordinate detection plane of the solid surface by the input pen pressed against any point on the same plane, and converts them into electrical signals. Detects elastic waves and reads coordinates of arbitrary points.

If you place your hand, etc. on the coordinate detection plane while specifying coordinates with the input pen, the operation may be impaired.

Furthermore, it is impossible to use a coordinate detection method that is important in practice, such as placing a sheet of paper on a coordinate detection surface and drawing characters or figures to find the coordinates that make up the letters or figures.

In this way, the second method is easy to operate as a coordinate detection device.
I must say that it is quite limited in terms of functionality.

Next, in the third method, the wavelength of the elastic wave is relatively long;
Since elastic waves propagate not only on the surface of the flat plate that serves as the coordinate detection plane, but also inside the flat plate, they are almost unaffected by the surface condition.When a sheet of paper is placed on the coordinate detection plane, characters are read using an input pen that combines a ballpoint pen and a piezoelectric element. Coordinates can be detected while drawing or drawing shapes.

Furthermore, even if you place your hand on it, it will not interfere with its operation.

As described above, the third method is considered to be extremely superior to other methods in function and operability as a method for inputting coordinates of figures and characters into information processing machines such as computers.

However, there are still technical problems that must be solved before this method can be put into practical use.

Because this method uses elastic waves with a low frequency of about 100-odd kilohertz, it is difficult to perform anti-reflection termination treatment at the ends of the flat plate in order to suppress the reflected waves at the ends of the coordinate detection flat plate, where the elastic waves propagate, to a sufficiently low level. be.

This is because the wavelength of the elastic wave is long, so the non-reflection termination of an appropriate size will not absorb the elastic wave sufficiently.

Therefore, a conventionally considered countermeasure is to use a plate material such as an acrylic plate that has a large attenuation constant for elastic waves.

Since the attenuation constant is large, if the coordinate detection period is set long enough for practical use, the reflected waves will repeat multiple reflections within the coordinate detection plate, and will be sufficiently attenuated within the coordinate detection period to generate the next wave. It can be made sufficiently small that it does not affect the coordinate detection operation.

Additionally, polymeric materials with large attenuation constants, such as acrylic plates, generally have a low sound velocity, which has the advantage of increasing coordinate detection accuracy.

However, while high attenuation materials have the above advantages, there is a problem in that the amplitude of the detection signal of the elastic wave varies depending on the detection coordinates due to attenuation.

This has been a factor that impairs the stability of detection operation when conventionally detecting elastic waves by threshold processing.

The purpose of the present invention is to solve these problems by compensating for the attenuation of elastic waves in threshold processing in a coordinate detection device using plate wave elastic waves with a coordinate detection flat plate made of a high attenuation material. An object of the present invention is to provide a coordinate detection device that can detect plate wave elastic waves with high precision.

The coordinate detection device using elastic waves according to the present invention is characterized by being provided with a threshold generation circuit that attenuates to an exponential function of 1 with delay time in accordance with the attenuation characteristics of elastic waves.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a configuration diagram of a coordinate detection device using plate waves.

The coordinate detection flat plate 1 is an acrylic plate with each X-axis piezoelectric element 2 and Y-axis single piezoelectric element 3 bonded to the ends of both the X and Y axes, and PZT piezoelectric ceramic is used as the piezoelectric elements 2 and 3. can.

The X-axis single piezoelectric element 2 and the Y-axis single piezoelectric element 3 are alternately pulse-driven by an X-axis drive circuit 4 and a Y-axis drive circuit 5, respectively, to alternately generate mechanical vibrations, that is, plate waves, in the X-axis direction and in the acrylic plate. Emit in the Y-axis direction.

The plate wave has a vibration frequency determined mainly by the shape and material of the piezoelectric element, takes a constant propagation mode determined by the elastic constant and thickness of the coordinate detection flat plate 10, and propagates at a constant speed.

When the X-axis single piezoelectric element 2 is pulse-driven, a plate wave propagates at a constant speed in the X-axis direction, and this plate wave is detected by the input pen 7 pressed against the coordinate detection flat plate 1 and detected from the pulse drive. The time interval until then is counted by the method described later, and the X coordinate of the pen position is obtained.

Next, the Y-axis single piezoelectric element 3 is pulse-driven, and the X coordinate of the pen position is obtained by the same process as for the X-axis.

Note that the lengths of the piezoelectric elements 2 and 3 are respectively determined by the coordinate detection area 6.
By making the length of each side larger than the length of each side of Can be done accurately.

The input pen 7 has a structure in which a ballpoint pen 9 is press-fitted into the narrow end of a brass conical horn 8, and a piezoelectric element 10 for vibration detection is glued to the thick end of the horn. The tip receives the signal, transmits it efficiently through the horn 8, and imparts vibration to the piezoelectric element 10.

The applied vibration is converted into an electric signal by the piezoelectric element 10 and amplified by the amplifier circuit 11, and then sent to the coordinate detection circuit 1.
2 is input.

FIG. 2 is a block diagram of an embodiment of a coordinate detection device to which the present invention is applied, excluding the coordinate detection plate 1 and input pen 7.

Portions other than the X-axis and Y-axis drive circuits 4 and 5 and the amplifier 11 constitute the coordinate detection circuit 12 shown in FIG.

The output pulse of the reference clock pulse generator 41 is frequency-divided by a frequency dividing circuit 42, and the frequency-divided output causes a flip-flop circuit 43 to repeat setting and resetting at an appropriate repetition period.

This repetition period is set by the X coordinate and the detection period of the X coordinate.

The output of the frequency dividing circuit 42 is supplied to the X-axis drive circuit 4 and the X-axis drive circuit 5, and the X-axis drive circuit 4 and the X-axis drive circuit 5 operate alternately according to the state of the flip-flop circuit 43, and The X-axis single piezoelectric element 2 or the Y-axis electric element 3 is driven.

On the other hand, the output of the frequency dividing circuit 42 is also supplied to a counting circuit 44 and a detection signal threshold processing circuit 45, which are respectively set to an initial state and started to operate.

The counting circuit 44 calculates the delay time from when the piezoelectric elements 2 and 3 are driven until the plate wave actually reaches the coordinate detection area 6 of the coordinate detection flat plate 1, and the delay time when the plate wave reaches the tip of the input pen 7. This is to remove the delay time from the time to detection by the piezoelectric element 10 from the overall propagation delay time for position coordinate determination.

The signal converted into an electrical signal by the piezoelectric element 10 in the input pen 7 is amplified by the amplifier 11 and then input to the detection signal threshold processing circuit 45 .

The detection signal threshold processing circuit 45 outputs a detection pulse indicating the correct detection time of the plate wave and a pen down signal indicating that a correct detection operation has been performed through threshold processing to be described later.

The Noritsubu flop circuit 46 is set by the carry output of the counting circuit 44, reset by the detection pulse of the detection signal threshold processing circuit 45, and is set during the propagation delay time for determining the position coordinates.

The counting circuit 47 counts the reference clock pulses while the flip-flop circuit 46 is set, and outputs the counting result.

For example, the frequency of the reference clock pulse is f (MHz), the desired coordinate resolution is n (lines/mm), and the sound velocity of the plate wave is e (m
m/μs), if f = n x c, the counting result of the counting circuit 47 indicates the line number of the input pen position,
The multiplied value indicates the absolute coordinates (unit function) of the pen position.

For example, when the fundamental mode of a plate wave (symmetrical Lamb wave) is propagated through an acrylic plate with a thickness of 3 m 1 rt, the actual measured value of the sound speed is c = 2.35 (km/S) = 2.35.
Cmm/p S ) is obtained, and if n=4 (lines/mm), the clock frequency f is 9.4 (MHz>).

FIG. 3 is a diagram showing an embodiment of the detection signal threshold processing circuit 45.

Further, FIG. 4 is a time chart showing the relationship between input and output signals in each component of the detection signal threshold processing circuit shown in FIG. 3, and explaining the elastic wave detection operation by threshold processing.

FIG. 4 shows a typical detection signal V processed by the device of the present invention.
8 (output of the amplifier 11), and particularly shows the wavefront portion A of the waveform in detail.

The drive circuit for the piezoelectric element at the end of the coordinate detection flat plate and the acoustic wave detection amplifier following the input pen block DC components, and also block higher-order modes and high-frequency noise other than the fundamental mode of the plate wave propagating through the plate. Since the high-frequency gain of the detection amplifier is sufficiently suppressed, the transverse ratio waveform of the plate wave acoustic wave generated by pulse driving generally takes the form of a high-frequency pulse as shown in Fig. 4, and the detection signal v8 has several peaks. It comes to have a value.

In the present invention, in the wavefront portion A, excluding the first undulation with a small precursor amplitude, the main peaks include the first peak (■), the second peak (■), and the third peak, as shown in FIG. The peaks (■) and numbers will be assigned sequentially.

Two thresholds are provided, El and E3, such that El<E2, and El
It is assumed that a plate wave is correctly detected only when E2 detects the first peak and E2 detects the second peak, and a pen down signal indicating reliable press contact of the input pen with the coordinate detection plane is output.

When the pressing pressure is small, as shown in FIG. 5, the threshold value E1 captures the second peak, giving a larger delay time than when capturing the first peak, which causes an error in the coordinate values. At this time, if the value of the threshold value E3 is set appropriately large, the threshold value E2 can be prevented from capturing any peak, and the pen-down signal can be prevented from being output by logic circuit processing.

Such normal pen-down determination processing determines that the level difference between the first peak and each peak after the second and third peaks is larger than the level difference between each peak after the second and third peaks. This is because the first peak exists in the rising section of the envelope of the plate wave detection signal waveform.

With the pen-down process described above, coordinate detection is always performed using the first peak, and it is possible to avoid skipping of detected coordinates during the coordinate detection operation due to fluctuations in pressing pressure.

Furthermore, since it is necessary to go through two threshold processes in order to perform coordinate detection, there is an advantage that the possibility of erroneously detecting an isolated noise signal is significantly reduced.

An alternative to the pen-down process described above is to equip the input pen with a special pen-down detection element, such as a mechanical microswitch operated by press pressure, as used in conventional coordinate sensing devices, to The pen-down signal is not output unless pressing pressure is applied, and while the pen-down signal is being output, the first peak of the plate wave detection signal waveform is at the threshold E.
It is also possible to always exceed 1 and perform correct coordinate detection operation using the first peak.

Next, the coordinate detection operation will be explained in more detail using FIGS. 3 and 4.

In FIG. 3, 51 is the detection signal V8 which is the output of the amplifier 11.
A pulse train V whose rising and falling points are the numbered points.

This is a comparator that outputs . 51' is a pulse train V.

A single pulse at the falling point of V.

It is a single pulse generator that outputs . Pulse V.

indicates the point of occurrence of a subsequent point of acceptance among the two acceptance points of each peak of the detection signal V8, and provides a candidate for the point of time at which the delay time counting circuit stops counting.

52 is a comparator that compares the threshold value E1 and the detection signal V8 and outputs a pulse train Vl including the detection output of the first peak.

When the flip-flop 53 is in a reset state and its mutual terminal output Vi is Vi=1 (Q=O1Q=1), the output Vl of the comparator 52 passes through the AND gate and sets the flip-flop 54, making the detection valid. The signal Vu is output.

The detection valid signal vu indicates the point at which delay time counting is stopped.

candidate signal sequence V.

A delay time counting stop signal is detected by an AND gate from among the signals, and a desired detection pulse Vd is generated.

At the same time, at the falling edge of the pulse signal ve, the Noritsubu flop 54 is reset to stop the detection valid signal Vu.

suppresses the generation of detection pulses caused by In addition, the detection pulse V
d sets the flip-flop 53, sets its output Vi to Vi = 0 (Q = 1, q = 0), prevents the output Vl of the comparator 52 from passing through the AND gate, and outputs the detection valid signal Vu.
- Suppressing new generation of the detection pulse Vd.

The detection pulse Vd obtained in this way gives the desired σ acceptance point of the first peak, and the Noritsubu flop 4 in FIG.
6, the delay time counting operation of the counting circuit 4γ is stopped, and a correct and stable counting result of the propagation delay time of the plate wave is provided.

On the other hand, the detection pulse Vd is the monostable multivibrator 5
5, and generates a pulse signal vm having a pulse width corresponding to the time domain in which the second peak of the detection signal v8 occurs.

56 is a comparator that compares the threshold value E 2 and the detection signal V8 and outputs a pulse train V2 including the second peak detection output.

When the output V2 and the pulse signal Vm are input to the AND gate, the second peak detection output that occurs subsequent to the detection pulse vd indicating the first peak customer reception time is extracted.

This AND gate output indicates that a positive pen-down has occurred and causes the flip-flop 57 to rotate, producing a pen-down signal V at its output.

The above operation is repeated by resetting the flip 70 knobs 53 and 57 by the output of the frequency dividing circuit 42 in FIG. Outputs detection pulses alternately,
Flip-flop 46 is driven as described in connection with FIG. 2 to alternately count the X and X coordinates.

The above threshold processing is performed correctly only when a detection signal v8 of a constant amplitude is obtained under a constant pressing pressure, but if the plate wave is accompanied by attenuation due to propagation,
The amplitude of the detection signal v8 at a distant position is attenuated by propagation, so even with the same pressing pressure, the amplitude of the detection signal v8 at a position close to the piezoelectric elements 2 and 3 is smaller than the amplitude of the detection signal at a position close to the piezoelectric elements 2 and 3, just like the case where the pressing pressure is small as shown in FIG. Similarly, plate waves may not be detected at far positions.

In view of this point, the present invention provides the threshold value E1. E2 is made to vary depending on the distance from the piezoelectric element 2°3 of the coordinate detection position.

By the way, it has been experimentally confirmed that plate wave elastic waves attenuate exponentially with respect to the propagation distance and the equivalent propagation delay time.

Therefore, the threshold E1. A signal that decays exponentially with respect to the delay time may be supplied as E2.

Such a signal can be realized by a charging/discharging circuit such as the embodiment shown in FIG.
If the reciprocals of R are matched, the amplitude of the plate wave detection signal and the threshold value E1. under a constant pressing pressure, regardless of the detection position. E2
can maintain a constant relationship with

In Fig. 6, the input V of the charging/discharging circuit. i is synchronized with the output pulse of the frequency divider circuit 42 in FIG. 2, and the input voltage V.

The wave width T of i is set equal to the delay time for the plate wave to reach the starting edge of the coordinate detection area 6, and the output of the charging/discharging circuit changes to the amplitude of the plate wave from the starting edge of the coordinate detection area to the terminal edge. It decays proportionally and exponentially.

FIG. 7 shows the threshold values E1. of the comparators 52, 56 in the detection signal threshold processing circuit shown in FIG. This shows an embodiment in which the above-mentioned exponentially attenuating signal is supplied as E2.

Reference numerals 58-1 and 58-2 are the charging and discharging circuits shown in FIG. 6, and an output amplitude adjustment circuit is added to the output stage, and each of them supplies threshold values E, , E2 that decay exponentially.

The input of 513-1.5B-2 is the frequency divider circuit 42 (Figure 2)
The output V of the monostable multivibrator 59 driven by the output of .

i, the pulse width T can be freely set by adjusting the circuit constants, and the desired threshold signal as shown in FIG.
1, 5 [Output from 2.

As explained above, according to the present invention, the threshold value is made to attenuate exponentially with respect to the delay time. Detection is possible, and attenuation is reduced by using a plate with a low sound velocity as the coordinate detection plate, which is less affected by reflected waves.
There is an advantage that a stable coordinate detection device with high coordinate detection accuracy can be realized.

[Brief explanation of drawings]

Fig. 1 is a diagram showing a typical configuration example of a coordinate detection device;
3 is a block diagram illustrating the operation of the coordinate detection device, FIG. 3 is a diagram illustrating a configuration example of the detection signal threshold processing circuit of the coordinate detection device, and FIG. 4 is a time chart illustrating the operation of the detection signal threshold processing circuit, FIG. 5 is a diagram showing the relationship between the threshold value and the elasticity detected signal when coordinates are not detected, and FIG. 6 is a diagram showing an embodiment of a charging/discharging circuit that supplies a threshold signal that decays exponentially with delay time in the device of the present invention. FIG. 7 shows an embodiment of a circuit for supplying an exponentially decaying threshold to a comparator in the detection signal threshold processing circuit of the apparatus of the present invention. 1: Coordinate detection flat plate, 2: X-axis circumferential piezoelectric element, 3: X-axis circumferential piezoelectric element, 4: X-axis drive circuit, 5: Y-axis drive circuit, 6: Coordinate detection area, 7: Input wall/, 8: Brass conical horn,
9: ballpoint pen, 10: piezoelectric element for vibration detection, 11: amplifier, 12: coordinate detection circuit, 41: reference clock - pulse generator, 42: frequency dividing circuit, 43: flip-flop circuit, 44: counting circuit, 45 :Detection signal threshold processing circuit, 4
6: Flip-flop circuit, 47: Counting circuit, 51: Comparator, 51': Single pulse generator, 52: Comparator, 53
．． 54: Flip-flop circuit, 55: Monostable multi-bi break, 56: Comparator, 57: Flip-flop circuit, 5B-1, 58-2: Charge/discharge circuit, 59: Monostable multi-bi break.

Claims (1)

[Claims] 1. To count the propagation delay time from the emission position of the plate wave elastic wave to the elastic wave detection position by the input pen, and to pulse drive the piezoelectric element at the end of the coordinate detection flat plate in order to detect the position coordinates of the input pen. In a coordinate detection device that detects the wave crest of an elastic wave by detecting two large and small peaks forming the wave crest of a high frequency pulsed plate wave elastic wave obtained by using two comparators with different large and small threshold values. , a coordinate detection flat plate having a constant attenuation constant is provided, and two large and small threshold generation means are provided, which attenuate exponentially with propagation delay time in accordance with the attenuation characteristics of a plate wave elastic wave propagating through the coordinate detection plate,
A coordinate detection device using elastic waves, which is provided corresponding to the two large and small thresholds, and supplies thresholds that decay exponentially with propagation time to the two comparators for wave front detection.