JPH03276221A - Ultrasonic coordinate input device - Google Patents

Abstract

PURPOSE:To prevent the misinput of coordinates due to the switching noise by starting the measurement of various data which are actually used for input of coordinates after the switch of a sensor and after the signal variance is eliminated on a signal input line. CONSTITUTION:A pen driving circuit 100 drives a pen 1, and a driving waveform generating circuit 101 generates the driving waveform of the pen 1. Then a tg/tp detection circuit 200 is provided to detect the group arriving time tg and the phase arriving time tp of the ultrasonic signals out of the signals received from the sensors 2a - 2c together with a counter circuit 201 which decides the transmission time of the ultrasonic wave based on the signals tg and tP. A pen driving signal is outputted when a fixed time passed after the switch of sensors. At the same time, the circuit 201 is actuated for measurement of the arriving time of the ultrasonic wave. Thus it is possible to prevent the mismeasurement of the switching noise and to always secure the measurement of the normal tg and tp.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ultrasonic coordinate input device, and generally to various applied devices incorporating a distance measurement technique that utilizes the propagation of ultrasonic waves.

[Prior Art] One of the devices devised as an applied device for ultrasonic distance measurement is an ultrasonic coordinate input device. Hereinafter, the present invention will be explained using this device as an example.

FIG. 8 is a schematic diagram of a commonly devised ultrasonic coordinate input device. Reference numeral 1 denotes a coordinate indicating tool (hereinafter referred to as a pen), which has a piezoelectric element incorporated therein and is a transmitter that transmits a desired ultrasonic signal from its tip. 2a, 2b, 2
A sensor c is a receiver that receives an ultrasonic signal emitted from the pen via the propagation body 3. 3 is a propagation body, which is made of glass, aluminum, etc., and serves as a propagation medium for ultrasonic waves. Reference numeral 4 denotes a vibration isolating material, which is set for the purpose of preventing reflected waves other than direct waves from the pen 1 from entering the sensors 2a to 2c. In the ultrasonic coordinate input device configured as described above, the coordinates of the indicated point are calculated from the distances between each of two or more plurality of sensors and the indicated point.

Various methods have been devised to calculate the distance between the sensor and the pointing point, but basically the distance is calculated based on the time it takes for the ultrasonic signal emitted from the pen to reach the sensor. When using transverse ultrasonic waves with different group and phase velocities, take the envelope of the received waveform, find the group arrival time, and roughly calculate the distance, and if more precision is required, detect the phase at an appropriate position. , the phase arrival time is determined to achieve finer accuracy.

Next, a procedure for calculating the distance γ between the pen and the sensor from the two time information of the group arrival time and the phase arrival time will be explained.

First, when a voltage as shown in FIG. 9 is applied to the piezoelectric element in the pen, the signal received by the sensor becomes as shown in FIG. 10. On the other hand, when the peak position is detected as the group arrival time t8, as shown in FIG. 11, the first stage amplifier 5. Full wave rectifier6. A comparator 9 detects the zero cross of the differential signal through the low-pass filter 7 and the differential circuit 8, and recognizes the time as the group arrival time t1.

With this, γ can be calculated from γ=v,・t, but since the method detects time based on the envelope, there is inevitably some fluctuation △t due to the influence of the signal output size and filter characteristics. occurs. Therefore, in general, it is possible to obtain a value with less fluctuation by detecting a specific phase zero-crossing point to determine the time.

Therefore, if the detection point is defined as the group arrival time t and the phase zero cross point immediately after the determination, then ■8≠■
, and since the phase within the group shifts with the distance γ, a step-like phase as shown in FIG. 12 is observed as the phase arrival time 1p. This stage indicates the movement of the phase detection point, and the joint between each stage is a parallel shift of the signal synchronization T. If Vg and V are equal and a constant phase detection point can always be observed, such a staircase will not be possible and a phase arrival time t2 as shown by straight line a will be obtained.

Therefore, it is sufficient to convert 1p obtained stepwise into the original straight line a.

In other words, Master tpIl (vg/vp) jg-tof(t,,:
However, since the group arrival time t9 has a large fluctuation, tpl = (vg/vp) tg-tar
-jp (n is an integer), tpa "tplTX Int(tpt/T+0.
5)=tt+Tx Int[((vg/vt)tg-
taf-t, )/T+o,s].

Using this t-, the pen-sensor distance γ is determined by the following formula: %r'' Vp4pa-rot (rot: offset value) = At, +B
E+0.5)+FA: V.

B: v, ・T=λ C: (vg/vp)/T=f・(v,/v,)D
: -1/T-f E : -t, r/T F : -mar
...0 By the method described above, the group arrival time t and phase arrival time t of the ultrasonic vibrations from the pen 1 through the propagation body 3 to the sensors 2a to 2C are measured. In a coordinate input device using multiple sensors, these 1. ．． 1. will be measured by the number of sensors,
In the example of the coordinate input device shown in FIG. 8, three sensors 2a to 2C are used. Thereby, the measured group and phase arrival times are also j g−, j tb,
t□. and t□+ j p b + j p c.

By the way, methods for measuring these multiple groups and phase arrival times include (1) one tz for one sensor;
, to measurement circuits are provided, and (2) a method in which a plurality of sensors are switched and measurement is performed using one measurement circuit. In method (1), one input of ultrasonic vibration simultaneously activates multiple sensors. ．． 1. Because it can measure, inputs where the pen moves, such as handwritten input, can be processed with high precision and at high speed.

Furthermore, method (2) requires only one measuring circuit, which has the advantage of significantly reducing costs.

[Problem to be Solved by the Invention] However, in the conventional example (2) above, noise is generated during sensor switching and is input to the measurement circuit, so this noise signal defines tg and tp. , there were cases where it was not possible to input the correct coordinates.

The present invention eliminates the above-mentioned conventional drawbacks, and after sensor switching,
To provide a highly reliable ultrasonic distance measuring device that eliminates erroneous measurements of tg and tp due to noise caused by sensor switching by providing a means for delaying the time and starting actual measurement of the arrival time of an ultrasonic signal. .

[Means for Solving the Problem] In order to solve this problem, the ultrasonic distance measuring device of the present invention is an ultrasonic coordinate input device that inputs coordinates based on distance measurement by propagation of ultrasonic vibrations. an input selection means for sequentially selecting input signals from ultrasonic receivers arranged at a plurality of locations on the ultrasonic propagation medium; and a distance measurement means for measuring a distance based on the input signals selected by the input selection means. The distance measuring means starts measuring the distance after a predetermined time has elapsed when the input selecting means switches the sensor.

Here, the distance measuring means delays the start of ultrasonic vibration of the ultrasonic oscillation source for a predetermined period of time.

Further, the distance measuring means starts measuring the distance after a predetermined time delay from the arrival of the ultrasonic vibration.

[Function] In this configuration, when the input selection means switches the sensor, the distance measuring means starts measuring the distance after a predetermined time has elapsed, thereby eliminating erroneous measurements of 1, 1p due to noise caused by the sensor switching. .

[Example] The present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a block diagram showing the configuration of the ultrasonic distance measuring device of this embodiment. In the figure, 100 is a pen drive circuit that drives the pen 1, 101 is a drive waveform generation circuit that generates the drive waveform of the pen 1 as shown in FIG. The detection circuit 201 is a counter circuit for determining the propagation time of the ultrasonic wave based on the t and t signals.

202 operates sensors 2a to 2 according to instructions from the CPU 300.
This is a switching circuit that can be admired.

Further, 300 is a CPU that controls the waveform generation of the drive waveform generation circuit 101 and calculates the distance from the output of the counter circuit 201, and a timer 300a that waits the pen drive for a predetermined time after the switching circuit 202 switches the sensor.
have.

301 is an RO that stores the control program for the CPU 300
M, 302 is a RAM for auxiliary storage, and 400 is an output unit that outputs, for example, coordinates based on the calculated distance.

FIG. 2 is a flowchart showing the operating procedure of the ultrasonic coordinate input device of this embodiment.

When a sensor for measuring the arrival time of ultrasonic waves is selected in step S21, a weight is applied in step S22, and after a certain period of time has elapsed, the pen 1 is driven to generate ultrasonic waves in step S23. By starting the pen drive at this time,
Two timer counter circuits (the fourth one) of the counter circuit 201
(details in the figure) starts measuring the arrival time. One of the counters has a hardware circuit configuration such that it detects the rising edge of the specified signal t and stops, and the other counter detects the first fall of the specified signal t and stops. Step S
Reference numeral 24 waits for the spread processing until these counters stop, and is configured to proceed to the next processing when it is detected that the counters have stopped and data regulation has been completed.

Step S25 is a step of determining whether t8 and t of all sensors are defined, and the processes of steps S21 to S25 are repeated until measurement of all sensor data is completed. When it is confirmed in step S25 that measurement of all sensor data has been completed, the process proceeds to step S26, where a coordinate calculation is performed using the data, and a display is performed based on the result in step S27.

Figure 3 shows the drive signal waveform, detection signal waveform, t,
A time chart of the prescribed signal waveform, t, and the prescribed signal waveform is shown. In the diagram, from the top, the noise that occurs when switching the sensor in the detection signal, which is the pen drive signal, the detection signal, the tf regulation signal, t, and the regulation signal, is referred to as switching noise. At the time of switching, t,·t is noise that jumps into the detection signal line of the detection circuit 200. This noise signal is subjected to a predetermined process in the t,·t2 circuit 200, and outputs a t1 specified signal and a t, specified signal. These are the "t5 regulation signal due to noise" and the "t, regulation signal due to noise" in the figure.

Conventionally, the pen drive signal is outputted immediately after sensor switching, as shown by the broken line in the figure, and at the same time as 1. ．． 1
．． The measurement counter was working. As a result, the rise of "1 due to noise, standard signal" and the rise of "t due to noise,
At the first falling edge of the specified signal, an incorrect t□ in the figure is detected.
” and “There were cases where an incorrect tpJ was specified and correct coordinate detection was not possible.

Therefore, in this embodiment, as shown by the solid line in the figure, the pen drive signal is output after a certain period of time has elapsed after sensor switching, and at the same time, a counter for measuring the arrival time is activated, thereby making it possible to avoid errors caused by switching noise. Prevents measurement and always maintains regular 1, . 1. This allows measurements to be taken.

In the figure, what is indicated as a sensor detection signal is an ultrasonic signal received by the switched sensor. This signal is subjected to predetermined processing through the detection circuit 200, and outputs "t, specified signal according to the detection signal" and "t, specified signal according to the detection signal", and at the rising edge of the former, t , and the latter falls to define t, and the counter of the counter circuit 201 is stopped. As shown in the figure, this shows that 1. ．． 1. measurements are taken and the coordinates are always input correctly.

Here, FIG. 4 will be explained. Figure 4 shows t6 and t
, is a block diagram of a counter circuit 201 that measures .

In the figure, 300 is the control and coordinate calculation 1 of the above-mentioned control circuit.
100, which is a control circuit (CPU) that controls display etc.
is a pen drive circuit that actually drives the pen based on signals from the CPU 300. Timer/counter circuit 33.34
are timer/counter circuits, t and t, respectively.

Count and measure. 33.34 is 5TRT (start), 5TP (stop) terminal, RD (lead) terminal, R
It has an ST (reset) terminal, etc., and by inputting a pen drive signal from the CPU 30o to the 0.5TRT terminal, the counter is started at the rising edge of the signal, and the S
t input to the TP terminal, from the rising edge of the specified signal or t
.

It is configured to detect the fall of the specified signal and stop the counter. Here, the counted data is C
Under the control of the PU 300, when a signal is input to the RD terminal, it is sent from the DATA terminal to the CPU 300, and when the CPU 300 receives the above data, it sends it to the RS.
A signal is input to the T terminal to reset the timer/counter circuit to its initial state.

In this embodiment, a software timer is used to apply a wait between sensor switching and counter start. 1. ．． 1. Although this is intended to prevent erroneous measurements, it is also possible to use a hard timer instead of the soft timer.

[Other Examples] Here, a method using dummy counts will be described. In other words, ignore the first count data counted immediately after switching the sensor, reset the timer/counter circuit, drive the pen for the second time in the same state (without switching the sensor), and use the data at that time. It was designed to do so. That is, the first data is read blankly and the second data is used for measurement, but the number of blank readings may be set by looking at the actual detected waveform.

FIG. 5 shows a flowchart of the control procedure in this case. This is an example of one empty read.

The sensor is switched in step 541, and the reading count data is reset in step S42.

In step S43, the pen is driven and a timer/counter is started, and in step S44, the process waits until the data definition is completed. Data measurement is completed at t.

It may be detected based on the state of the 1p regulation signal.

Subsequently, the number of readings is incremented by 1 in step S45, and the number of measurements is checked in step S46. If it is the first measurement, the process returns to step S43, the timer count is reset, and steps S43 to S46 are performed again.

Furthermore, if it is the second measurement, the data at this time is made valid and stored in the RAM 302. Next, in step S47, the above processing is repeated until all sensor data is obtained, and once all sensor data is obtained, coordinate values are calculated in step S48, and processing such as display is performed in step S49.

Next, an example will be described in which the signal on the detection signal input line of the measurement circuit is monitored and actual measurement is performed after confirming that signal fluctuations due to switching noise have subsided.

As shown in FIG. 6, a high-speed A/D converter 203 is connected in parallel on the detection signal input line of the detection circuit at 1°t, and its output is input to the CPU 300 in FIG. CPU30
At 0, until this input settles to a constant value, or (
(Considering the influence of minute noise), the output of the A/D converter 203 is repeatedly read until it falls within a certain tolerance value.
Then the actual t.

1. Start measurement.

The flowchart in FIG. 7 shows the control procedure at this time. The routine shown in steps S51 to S54 is a feature of this embodiment, and the rest is similar to that in FIG. 2, so a description thereof will be omitted. First, in step S51, the A/D converted value of the signal on the detection signal input line after sensor switching is read, and this is set as Dl.

Subsequently, in step S52, the second A/D conversion value of the same signal is read and is set as D2. DI in step S53
It is checked whether D+=D2 (or whether the difference between Dl and D2 is within the allowable value), and if D+=D2 is not the case, D2 is moved to Dl in step S54 and the process returns to step S52. As a result, steps S52 to S
54 loop and when D+=Dz, it is determined that the signal fluctuation on the detection signal input line has calmed down, pen drive is started, and the actual 1. ．． It is controlled to start 1° measurement. In addition, in the above example, two consecutive A
Although the detection signal input line is considered to be stable when the A/D conversion values become equal, the number of A/D conversion values to be compared is not limited to this.

As explained above, in an ultrasonic coordinate input device with a sensor switching function, measurement of various data for actually used coordinate input is started after signal fluctuations on the signal input line have subsided after sensor switching. By doing so, it is possible to prevent erroneous coordinate input due to switching noise while maintaining the low cost that is an advantage of the sensor switching method.

[Effects of the Invention] According to the present invention, by providing means for delaying time and starting actual measurement of the arrival time of an ultrasonic signal after sensor switching, 1, 1. due to noise caused by sensor switching is provided.
It is possible to provide a highly reliable ultrasonic distance measurement device that eliminates erroneous measurements.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of the ultrasonic coordinate input device of this embodiment, FIG. 2 is a flowchart showing the control procedure of the embodiment, and FIG. 3 is a signal time chart for explaining this embodiment. Figure 4 shows 1. ．． A block diagram of a counter circuit for 1p measurement, FIG. 5 is a flowchart showing the control procedure of another embodiment, FIG. 6 is a block diagram of a signal detection part of still another embodiment, and FIG. 7 is a block diagram of still another embodiment. A flowchart showing an example control procedure, FIG. 8 is a schematic diagram of the ultrasonic coordinate input device, FIG. 9 is a diagram showing a pen drive signal, FIG. 10 is a diagram showing a sensor reception signal, and FIG. 11 is a diagram showing a 1 ．．
．． 1. A schematic configuration diagram of the prescribed detection system, and FIG. 12 is a diagram for explaining the distance calculation method. In the figure, 1...coordinate indicating tool (pen), 2a to 2c...
Sensor, 3... Transmission body, 4... Vibration isolating material, 5... First stage amplifier, 6... Full wave rectifier circuit, 7... Low pass.
Filter, 8...Differential circuit, loo...Pen drive circuit, 101...Drive waveform generation circuit, 200...tyo/t, detection circuit, 201...Counter circuit, 202
---Switching circuit, 300-CPU, 300a-
=Timer, 301・ROM, 302...RAM,
400... Output section.

Claims (3)

[Claims] (1) An ultrasonic coordinate input device that inputs coordinates based on measurement of distance by the propagation of ultrasonic vibrations, which sequentially selects input signals from ultrasonic receivers placed at multiple locations in an ultrasonic propagation medium. and distance measuring means that measures the distance based on the input signal selected by the input selecting means, and the distance measuring means measures the distance after a predetermined period of time when the input selecting means switches the sensor. An ultrasonic coordinate input device characterized by starting measurement. (2) The ultrasonic coordinate input device according to claim 1, wherein the distance measuring means delays the start of ultrasonic vibration of the ultrasonic oscillation source for a predetermined period of time. (3) The ultrasonic coordinate input device according to claim 1, wherein the distance measuring means starts measuring the distance after delaying the arrival of the ultrasonic vibration by a predetermined time.