JPS6345622A - Ultrasonic tablet - Google Patents

Abstract

PURPOSE:To prevent the misinput caused by the change of the writing pressure of an input pen by adding a gate circuit to a time counting circuit to detect the peak value of the wave detected first out of the detected voltage. CONSTITUTION:A counter circuit 6 is set at '0' when a start signal is supplied and at the same time an elastic wave is outputted from a pen. This elastic wave is detected by a detecting element via an input plate and converted into digital signals by a zero-cross circuit 1 to be used as a DO signal. In this case, A and B signals are produced by gate A and B circuits 4 and 5 respectively. The A signal shows the time needed for the rise edge of the detected wave and produces a C' signal via an AND circuit C to a CK signal. While the B signal produces a D' signal via an AND circuit D to the output of a 1/2 clock circuit 3. The sum of both C' and D' signals show the peak point of the detected waveform. Thus, an OR circuit E is provided and the E' signals of the circuit E can be counted by the circuit 6.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ultrasonic tablet, particularly to a time counting circuit for an ultrasonic tablet.

[Conventional technology]

Conventionally, regarding the Tabbouleh-Soto time counting circuit applying ultrasonic waves, see IE Transactions, C.H.I. 1344 (1978), Vol.
Pages 98 to 200 (IEEE.

Trans, CH1344 (1978) PL98-20
0).

This uses surface waves among elastic waves propagating in a medium, and the detection voltage is a group of several waves, with the peak value of the detection voltage at the center of the group.

The position of this peak value does not change even if the writing pressure of the input pen changes, so the pen coordinates are calculated by measuring the time to this point.

[Problem that the invention seeks to solve]

In the above-mentioned conventional technology, the waveform of the detected voltage is temporarily shaped by a sample and hold circuit, and then digitized by a comparator circuit. However, this is a technology that is possible when surface waves are used, that is, when reverberation waves can be sufficiently removed.
When using other waves, such as longitudinal waves, Lamb waves, and sound waves,
It was difficult to suppress the amplitude of the reverberating waves, making it impossible to detect accurate coordinates, and there was a possibility that only accurate coordinate input could be made.

An object of the present invention is to provide an ultrasonic tablet that uses waves other than these surface waves, especially elastic waves, and that allows accurate coordinate input without depending on pen pressure.

[Means for solving problems]

The above object is achieved by providing a gate circuit that detects the peak point of the first detected wave, ie, the first arriving wave, of the detected voltage.

[Effect]

In ultrasonic tablets, it is difficult to remove the reverberation of elastic waves. Therefore, it is necessary to calculate the coordinates using the time until the first arriving wave.

This will be explained using FIG. The elastic wave is generated along with the start signal, and when the input pen is pressed against the tablet surface,
The elastic wave propagates through the medium and is detected with a delay of time T0. Here, the amplitude of the detected voltage changes depending on the writing pressure of the input pen, so the threshold level of the comparator V, h
When digitized using , the first arriving wave may be ignored and erroneously input, as shown by the solid line. This problem can be solved by using a zero-cross detection circuit so that even if the input pen pressure is small, it can always be converted into a digital signal. Furthermore, when the writing pressure changes, the propagation time changes as Ta+ and Tb+ due to the offset of the zero-cross detection circuit. Therefore, if we take the peak value of the first arriving wave and calculate the coordinates at time T.

The time T, which is related to the writing pressure of the input pen (accurate coordinate input is possible), is expressed by the following equation.

T = = (Tat + Ta2) / 2
(1) If the period of the reference clock is To, the count value N up to T is = 2 = Kodan Tokodan 'I'o 2T.

T al T *2 T al -□Ya□ ・・・・・・(2) T, 2
T.

It can be expressed as In other words, T is the period up to the rising edge of the detection voltage. It is calculated by counting the period from the rising edge to the falling edge with the period To/2.

With the above method, accurate coordinate input is possible regardless of the pressure of the input pen.

〔Example〕

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

FIG. 1 is a circuit block diagram of the present invention.

Gate A circuit 4, Goo 68 circuit 5,
Counter circuit 6 that counts time using a reference clock
(time counting circuit) is reset. Ultrasonic waves are generated simultaneously with the generation of this start signal. When the generated ultrasonic waves are pressed against the ultrasonic medium surface (tablet surface) with an input pen, they propagate through the medium and are converted into voltage by the detection element. The detected voltage is digitized by a zero cross detection circuit l. The zero cross detection circuit consists of a normal comparator and flip 7.
It is composed of 0 tubes. Digital signal D○ is gate A
Circuit 4 and Gate) B circuit 5 respectively output the time from the start signal to the rising edge of the detection voltage and the detection time of only the first arriving wave as gates. The counter 6 counts by the reference clock circuit 2 during the gate A, and counts by the clock circuit 3 for 1/2 period of the quantity reference clock of the gate B.

These operations will be explained using the timing chart of FIG.

GK is a clock signal output from the reference clock circuit 2. Counter circuit 6 when the start signal is input
becomes "Oo," and at the same time, an elastic wave is output from the pen. The elastic wave propagates through the input board, is captured by the detection element, and is converted into a digital signal by the zero-cross circuit 1 to become the Do signal.

At this time, the gate A circuit 4 and the goo 68 circuit 5 generate an A signal and a B signal, respectively. The A signal indicates the time to the rising edge of the detected wave, and is the AN of the CK multiplied signal.
D circuit C obtains a C'-fold signal. On the other hand, the B signal is ANDed with the output of the 1/2 clock circuit 3 to obtain the D' signal. As mentioned above, the sum of the C' multiplied signal D' signal indicates the peak point of the detected waveform, so an OR circuit E is installed and this O
It is good if the E' signal from the R circuit E is counted by the counter circuit 6.

By the above operation, the time until the peak value of the first arriving wave of the detection voltage is counted. That is, even if the writing pressure of the input pen changes, the correct elastic wave propagation time is measured, making it possible to calculate accurate coordinates.

〔Effect of the invention〕

According to the present invention, in an ultrasonic tablet with reverberant waves, it is possible to accurately measure the elastic wave and propagation time up to the peak value of the first arriving wave, thereby preventing erroneous input due to changes in the pressure of the input pen. .

[Brief explanation of drawings]

FIG. 1 is a circuit block diagram of an embodiment of the present invention, FIG. 2 is a timing chart thereof, and FIG. 3 is an explanatory diagram of erroneous input due to changes in pen pressure of an input pen. DESCRIPTION OF SYMBOLS 1...Zero cross detection circuit, 2...Reference clock generation circuit, 3...1/2 frequency divider circuit, 4...Rising edge trigger gate circuit, 5...Gate circuit, 6...Counter circuit (time counting circuit). Agent: Patent Attorney Katsuo Ogawa, ″・□ Figure 1 Figure 2 Figure E'

Claims (1)

[Claims] 1. An ultrasonic transmitting element that is excited by an electric signal to generate an ultrasonic wave, an input pen that propagates the ultrasonic wave and is equipped with the transmitting element, and a uniform isotropic medium that propagates the ultrasonic wave from the input pen. , consisting of a plurality of detection elements installed at the end of the medium and converting the propagated ultrasonic waves into electrical signals,
An ultrasonic tablet or input pen that has a time counting circuit that counts the time it takes for ultrasonic waves to propagate from an input pen to a detection element using a reference clock, and calculates the position coordinates of the input pen from the count value. is provided with the detection element, and a plurality of ultrasonic transmitting elements are provided at the end of the medium,
In an ultrasonic tablet, the time counting circuit counts the time it takes to sequentially excite them and detect the input pen, and calculates the position coordinates of the input pen from the counted value. home,
An ultrasonic tablet characterized by being equipped with a gate circuit that detects the peak value of the first detected wave.