JPH03276222A - Ultrasonic distance measuring device - Google Patents

Abstract

PURPOSE:To accurately decide whether an input is regular or not and to prevent the wrong input by invalidating the measurement of distance when it is estimated the pressing force is less than a prescribed level. CONSTITUTION:A coordinate pointing device 1 is provided together with a sensor 2, a pen drive circuit 100, a driving waveform generating circuit 101, a tg/tp detection circuit 200, a counter circuit 201, a CPU 300, etc. Then a signal level is read out and at the same time the distance is measured between a vibration generating means and the sensor 2. Based on the relation between the result of the distance measurement and the signal level, the pressing force of the vibration generating means is estimated. Then the result of the distance measurement is validated only when the pressing force of the vibration generating means is larger than a prescribed level. Thus it is possible to evade the input of an extreme tilt state of the vibration generating means regardless of the distance relation between the vibration generating means and the means 2. Then the measurement of distance is always attained with the constant pressing force.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an ultrasonic distance measuring device, and generally to various applied devices incorporating a distance measuring 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. 12 is a schematic diagram of a commonly devised ultrasonic coordinate input device. 1 is a coordinate indicator (hereinafter referred to as a pen)
It is a transmitter that has a piezoelectric element built into it and transmits a desired ultrasonic signal from its tip. 2a, 2b,
2c is a sensor, which is a receiver that receives ultrasonic signals emitted from the pen via the propagation body 3. Reference numeral 3 denotes a propagating 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, the envelope of the received waveform is taken, the group arrival time is determined, and a rough distance calculation is performed, and if more precision is required, the phase at an appropriate position is detected. , the phase arrival time is determined to achieve finer accuracy.

Next, a procedure for calculating the pen-sensor distance γ from two pieces of time information, the group arrival time and the phase arrival time, will be explained. First, when a voltage as shown in FIG. 13 is applied to the piezoelectric element in the pen, the received signal waveform of the sensor becomes as shown in FIG. 14. On the other hand, the peak position is defined as the group arrival time t,
When detecting the sensor output signal as shown in FIG. 15, the first stage amplifier 5. Full wave rectifier6. Low pass
A comparator 9 detects the zero cross of the differential signal through each circuit of the filter 7 and the differentiating circuit 8, and recognizes the time as the group arrival time t.

As a result, r can be calculated using γ=v, ・tl, but since the method is based on detecting time based on the envelope, a certain amount of fluctuation △t will inevitably occur due to the influence of the signal output size and filter characteristics. do. Therefore, in general, it is possible to obtain a value with less fluctuation in time determination power by detecting a specific phase zero crossing point.

Therefore, if the detection point is defined as the phase zero cross immediately after the group arrival time 1g is determined, v5≠V, and the phase in the group shifts with the distance γ, so the phase arrival time t is as shown in Figure 16. A step-like structure is observed. This stage shows the movement of the phase detection point, and the joint between each stage is a parallel shift by the period T of the signal. 7 If V and V are equal and a constant phase detection point can always be observed, then , such a staircase is not possible, and a phase arrival time t like the straight line a is obtained.

Therefore, it is only necessary to convert the stepwise obtained t into the original straight line a.

In other words, tpa 4 (Vt/Vjtg-tar (tof: offset value), but since the group arrival time t has a large fluctuation, tpl = (vg/vp) t, -tar-tp
(n is an integer) =tp"TX Int (tp+/T"0.5)=1.
◆TX Ir+t [((Vl/VD) tg-taf
-tp)/T+0.5].

Using this tp''', the pen-sensor distance r can be calculated using the following formula: %r = Vp'tearof (rot: offset value) = Atp+B X Int(Ct, +Dtp+
E+0.5)+FA: V.

9: V,・T=λ C: (v z / v −) / T・(v, /v
,) D: -1/T=-f E: -t, f/T F: -rot Here, 1. ．． 1. This is the start time of the measurement, which is determined by taking advantage of the fact that the level of the waveform detected by each sensor changes depending on the degree of close contact between the pen and the propagating body.

That is, when the pen is pressed against the propagating body and the degree of mutual contact increases and the detected waveform level becomes greater than a certain reference value, it is determined that the input state is present and 1. ．． 1. Start measuring.

FIG. 17 shows an example of the circuit. FIG. 17 is a block diagram of a recently used detection circuit. Also, Figure 18(a)
, (b) show signals at various parts of the circuit of FIG.

In FIG. 17, 10 is a received wave zero-cross comparator for detecting the phase state of the received waveform, and 11 is a received wave zero-cross comparator for detecting the phase state of the received waveform. Old gh“
A reference level comparator 12 that maintains the output is a reference level comparator that maintains the "high" output while the output of the differentiating circuit 8 exceeds a certain reference level. The envelope waveform (2) output from the low-pass filter 7 is taken into the differentiating circuit 8 and the reference level comparator 11. The envelope waveform taken into the first differentiating circuit 8 is output as a differentiated waveform, and is input to the reference level comparator 12 and the second differentiating circuit 8'. The output of the second differentiating circuit 8' is then input to the zero-cross comparator 9. The zero-cross comparator 9 detects the falling zero-crossing of the input differential waveform and outputs a "high" level, and further detects the rising zero-crossing and outputs the "I2ow level. The output obtained by this is ■.

On the other hand, the reference level comparator 12 receives the input 1
While the second differential waveform is at a level higher than the reference, “h ig
The output signal obtained by this is @. tl is the time from the generation of the pen drive signal to the rise of the output ■ obtained from the AND of the outputs @ and ■. In other words, 1 is not output unless the first-order differential waveform output from the first differentiating circuit 8 is greater than the reference level set in the reference level comparator 12. and ■
By taking the logical product of , the comparator output due to noise appearing in ① is eliminated, and it is possible to always measure the correct t.

By doing this, the specified point of t becomes the first inflection point of the output of the low-pass filter, and it is specified at an earlier position that is less susceptible to reflection than in the case of a single-stage differentiation circuit. It has become. In other words, the ultrasonic signal emitted from Ben 1 may directly enter the sensor 2 or may be reflected by the vibration isolating material 4 on the propagation body 3 and enter the sensor 2, and the difference between the two causes the reflected waves to be may directly overlap the waves. The degree of this overlap is determined by 1. In order to avoid the influence of the reflected waves as much as possible, the reflected waves will overlap in front of the direct waves as the intermingling difference between the two becomes shorter. ．． 1. To measure , it is desirable to take the specified points of t and t as early as possible in the signal waveform.

In addition, by doing this, the area ratio of the effective area to the ineffective area on the propagation body 3 (the area where the reflected waves overlap the specified points of tg and tp, making it impossible to measure 1..1. correctly) is increased. You can take it.

The above principle 1g is also used. However, in the case of t, measurement, the output signal 0 obtained from the logical product of the output signal ■ obtained by inputting the received waveform to the zero-cross comparator 10 and the output signal ■ of the reference level comparator 11 1p is defined by detecting the first falling edge of .

The reasons for this are 1. In the case of measurement, unless the reference level comparator output does not go to the "high" level, the zero-cross comparator output signal for t always rises while the output signal @ maintains the "high" state. In contrast, in the case of 1p, the output signal 0 of the zero-cross comparator for t may rise after the output signal 0 of the zero-cross comparator becomes "high."
This is because a normal t may not be defined at the rising edge of the output signal @. Therefore, when measuring t, t is determined by detecting the fall of the output signal 0.

As described above, the coordinates are not input unless Ben is pressed against the propagation body with a certain amount of pressure or more.

[Problems to be Solved by the Invention] In the conventional example described above, the input state was detected by utilizing the fact that the received signal level changes depending on the pressure of the ben 1 against the propagation body 3. That is, when the Ben 1 is pressed against the propagation body 3 with a pressure above a certain level, and the received signal level (or other signal level based on it, such as the output of a low-pass filter) becomes larger than a certain reference value, This was detected and determined to be an input state.

However, since the received signal level varies depending on the distance between Ben 1 and sensor 2 and the angle of inclination of Ben 1, if the range of variation in the distance or angle of inclination is large, the pressing of Ben 1, which is determined to be an input state, is The range of fluctuation is also large. Therefore, in a place close to sensor 2, Ben press without input intention is in the state (
If the pen is tilted (ambiguous input) or the distance cannot be measured accurately, the distance measurement may start in the state (tilt is input), or if the pen is far away from the sensor 2, the pressure may not be applied even though it is in the formal input state. There were problems such as a poor operational feel and the inability to specify the correct input behavior, such as not being able to input without raising the level.

The present invention provides an ultrasonic distance measuring device that eliminates the above-mentioned conventional drawbacks, accurately determines whether or not the input is official, and eliminates erroneous input.

Furthermore, the present invention provides an ultrasonic distance measuring device that accurately determines whether or not input is official over a wider range.

[Means for Solving the Problem] In order to solve this problem, the ultrasonic distance measuring device of the present invention is an ultrasonic distance measuring device that measures distance using the propagation of ultrasonic waves, and includes a sensor means. Based on the signal level of the ultrasonic vibration outputted from the ultrasonic vibration signal level and the distance information measured at that time, the pressing force of the ultrasonic generation means against the propagation means is predicted. and a measurement invalidation means for invalidating the distance measurement at that time when the distance measurement is predicted to be weaker than the distance measurement value.

Further, in the ultrasonic coordinate input device, the sensor means are arranged at a plurality of predetermined locations on the propagation means, and the selection method selects the sensor means having the shortest distance to the ultrasonic generation means from among the plurality of sensor means. It further includes means.

[Function] In this configuration, at the same time as reading the signal level, the distance between the vibration generating means and the sensor means at that time is measured, and the pressing pressure of the vibration generating means is predicted from the relationship between the measurement result and the signal level. By validating the distance measurement results only when the pressing pressure is greater than a specified value, no matter what distance relationship there is between the vibration generating means and the sensor means, extreme inclinations of the vibration generating means will not occur. This allows distance measurement to be performed using constant pressure while avoiding the need for input.

Furthermore, when the above configuration is incorporated into a coordinate input device using a plurality of sensor means, by selecting the sensor means with the shortest distance between the vibration generating means and the sensor means, it is possible to make accurate predictions using only one sensor. Accurate pressing makes it possible to predict the pressure even in a wide range.

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

<Press is the principle of pressure judgment> Figure 5 shows the distance X between Ben 1 and sensor 2 and sensor 2.
signal level A received at (or the signal level of another signal based on it, e.g. amplifier circuit 5. low-pass
Output signals of filter 7, differentiating circuit 8, etc.)
The graph shows the pressure of Ben 1 on the propagation body 3 using pressure P (pen pressure) as a parameter. In this example, the signal level A is the output of the low-pass filter, and the signal level A is [■
], the distance X is expressed as [mm], and the pressing pressure P is expressed as [gfl]. This relationship is equivalent to the generally known attenuation of the sound pressure of a spherical wave with respect to distance X expressed using pressure P as a parameter, and therefore, the state of this attenuation is expressed by equation (1).

A.

A (x) =-esu8...(1)A
o and y are constants, and 80 is a constant determined by Ben 1's pen pressure P when e -''/x = l.

FIG. 6 shows a graph showing the relationship between Ben 1's pen pressure P and signal level A(x,) at a certain point a on the propagator 3. This shows that the signal level increases as the degree of closeness increases, and it also means that the signal level does not increase when Ben is leaning.

The present invention attempts to manage Ben's pen pressure by utilizing the above property, and for this purpose, the signal level A and the distance X at that time are measured, and from the relationship of equation (1), the pen pressure P It is determined whether or not the value is greater than a specified value, and depending on the result of the determination, it is determined whether the distance measurement result is valid or invalid.

<Configuration of this embodiment> FIG. 1 is a block diagram showing the configuration of the ultrasonic distance measuring device of this embodiment. In FIG. A drive waveform generation circuit 200 generates a drive waveform for the pen 1 as shown in FIG.
tl·t, which detects tl and t from the received signal of
The detection circuit 201 is a counter circuit for measuring the propagation time of the ultrasonic wave based on the t and t signals.

t, ·t, the signal level at a predetermined part of the detection circuit 200 is C
It is output to PU300. Further, 300 is a control circuit for waveform generation of the drive waveform generation circuit 101 and a counter circuit 201.
A CPU that calculates the distance from the output of t, t, and determines the pen pressure based on the signal level from the detection circuit 202.
, 301 is R for storing the control program of the CPU 300.
OM, 302 is a RAM for auxiliary storage, and 400 is an output unit that outputs coordinates and the like based on the distance calculated when the pen pressure is equal to or higher than a predetermined value.

FIG. 2 shows an example of a distance measuring circuit using this embodiment.

In the figure, numerals 5 to 14 are the same as those described in the conventional example.

In addition, 15 converts the output signal of the low-pass filter 7 into an A/D
This is an A/D converter. CPU300 is A/
Controls the D converter, distance calculation, press pressure (pen pressure) prediction calculation, pen drive 1 display output, data communication, etc.

The A/D converter 15 receives the STC signal outputted at the same time as the pen is driven by the CPU 300, and starts A/D conversion of the output of the low-pass filter. A/
When the D conversion is completed, an EOC signal is output to the CPU 300, and the CPU 300 receives this and outputs the EOC signal to the A/D converter 15.
Outputs the OE scratch signal. The A/D converter 15 is OE
When the flaw signal is received, the conversion result is output to the CPU 300, and the CPU
U3oO temporarily stores this data and generates the STC signal again to start the next A/D conversion.

When the CPU 300 receives the next data, it compares it with the previous data stored at - time and temporarily stores the larger one again. The A/D converter 15 and the CPU 300 repeat the above operations, and within a certain period of time (the longest time from when the pen is driven and the ultrasonic wave is input, the ultrasonic vibration will arrive at the sensor 2). The maximum A/D converted voltage value (■) is detected. FIG. 3 shows each signal.

On the other hand, when detecting ■, the group arrival time t8 and the phase arrival time 1p are simultaneously measured by the input ultrasonic vibration, and the CPU 300 calculates the pen-sensor distance X based on this.

Assuming the above signal level to be A, substitute the obtained ■2 and distance
0 on the LCD or output to an external device as OUT DATA. For example, if you want the pressing force to be 100 [gf] or more, the specified value can be determined in advance by calculating the constant A + oo when the pressing pressure is 100 [gf] and storing it in the program of the CPU 300. .

FIG. 4 shows a control flowchart when the present invention is applied to a coordinate input device using a plurality of sensors.

In step S401, the first sensor signal is first set to be guided to the measurement circuit. In step 5402, the pen is driven to generate ultrasonic vibrations, and in step 5403, the distance between the first sensor and the pen is calculated. Check whether all sensors have been selected in step 5404, and if there are still selected sensors, sensor selection is performed in steps S401 to 5403.
Repeat this for the number of sensors to obtain distance data. In step 5405, the sensor with the shortest distance is determined, the sensor signal of the determined sensor is set to be guided to the measurement circuit, and the pen is driven again.

In step 5406, the maximum value of the signal based on ultrasonic vibration (for example, the output signal of a low-pass filter) at this time is
, and in step 5407, 1. ．． 1p
The pen-sensor distance X is calculated from Step 540
8 is a routine that calculates pen pressure using V and X obtained in steps 5406 and 5407. Step 5409
Then, it is determined whether the resulting writing pressure is equal to or greater than a specified value. If the value is greater than or equal to the specified value, it is assumed that the input is normal, and in steps 410 to 5413, the pen-to-sensor distances of other sensors necessary for coordinate calculation are measured and calculated. Once you have the necessary distance data, proceed to step 5.
In step 414, the measurement result is converted into coordinate values, and in step 5415, it is displayed on the LCD or communicated with an external device to make the measurement result valid.

On the other hand, if it is determined in step 5409 that the pen pressure does not reach the specified value, it is assumed that no formal input has been made, and the process returns.

[Second Embodiment] FIG. 7 shows a block diagram of a measuring circuit of a second embodiment using the present invention. In the figure, 17 is a comparator that compares the output of the low-pass filter with a certain reference level, 18 is a multiplexer that switches the reference level according to a command from the CPU 300, and 19 is the "h" output from the comparator.
This is an RS flip-flop for holding the "high" level.The operation thereof will be explained below with reference to FIG.

In response to a command from the CPU 300, the multiplexer 18 first changes the reference level of the comparator 17 to the lowest voltage value (the eighth
Set to V+) in the figure. When the pen is driven and ultrasonic vibrations are input, the vibrations are converted into electrical signals by the sensor 2, passed through the amplifier 5 and full-wave rectifier 6, and appear at the output of the low-pass filter (the output level of the low-pass filter is determined by the sensor). It goes without saying that it is proportional to the received signal level of 2). This output signal is input to a comparator 17 and compared with a reference level set by a multiplexer 18. As a result of the comparison, the output of the low-pass filter is
When it becomes larger than this reference level, comparator 1
7 changes from the "120W level" to the "high" level, and the RS flip-flop 19 detects the rising edge of this change and sets the "high" level at its output terminal.

The output of the comparator 17 becomes "high" at the moment the output of the low-pass filter 7 becomes smaller than the reference level.
The level returns to the "f2ow" level, but since the output terminal of the RS flip-flop 19 is held at the "high" level, the CPU 300 determines that this level is "high".
“or” I2. By reading “OW”, it can be known whether the output of the low-pass filter 7 is greater than the reference level set by the multiplexer 18.

When the output of the RS flip-flop 19 is "high", the CPU 300 resets it (RS flip-flop output "120W") and issues a command to the multiplexer 18 to set the reference level of the comparator 17 to the next level. 18 sets the reference level to the next level according to this command, the CPU 300 drives the pen again for a certain period of time (a certain period of time longer than the longest time it takes from the time the pen is driven until the vibration is received). ), read the output signal of the RS flip-flop 19 and check whether the level is “high” or “βOW”.
” to determine whether.

Repeat the above operation and determine in which range the peak level of the output of the low-pass filter is (in Figure 8, ~Vt, V+ ~V2Vz ~Vs...Va
~Vt, Vt ~Va, Vs
~) is read. Also, t measured during the above period.

and I3 to calculate the pen-sensor distance X, and from these two data it is determined whether the pen pressure is equal to or greater than a specified value.

FIG. 8 illustrates the relationship between the reference level and the range of distance X when writing pressure is defined as 100 [gf] to 150 [gf] or more.

In the figure, the effective range of distance X is shown. ~Tate 8. As a result, the pen-sensor distance X is approximately 1. ~dan, when
The output of the low-pass filter is over 78! 11-tan 2
77 or higher.

J12~Bun, v6 or higher,..., J17~Dan8
If you treat it as an official input state when the value is 73 or higher, you can set the minimum pen pressure to 100 [gf3 to 150].
[gf can be specified.

Also, cross. , Ql, intersection 2. Dan 5. ...28 and V+,
Vz, Vs...■. The setting may be determined by setting 0 and γ to the constants in equation (1) and calculating, or may be determined by actually measuring - degrees.

FIG. 9 shows a control flowchart for detecting the maximum output voltage of the low-pass filter when the measuring circuit of FIG. 7 is used.

First, in step 5601, the RS flip-flop 19 is reset, and in step 5602, the reference level of the comparator 17 is set by setting the multiplexer 18. In step 5603, the pen is driven and ultrasonic vibrations are input, and in step 5604, a wait is performed for a fixed time longer than the longest time it takes from the time the pen is driven until the vibration is received, and then the step At step 5605, it is determined based on the output level of the RS flip-flop 19 whether the output of the comparator 17 has reached the "high" level.

If the level of the RS flip-flop 19 is "high", it is determined that the output of the low-pass filter 7 is higher than the reference level, and it is determined in step 5606 whether the reference level is the maximum one. do.

If it is the maximum level, it is determined in step 5607 that the maximum level is greater than or equal to the reference value, and control proceeds to the subsequent steps.

On the other hand, if it is not the largest, step 5601
Return to step 5602 and set the next reference level.
Repeat the following control. If the comparator output is not "high" in step 5605, it is determined in step 5607 that the output of the low-pass filter 7 is lower than the current reference level and higher than the previous reference level. .

In the above embodiment, a case has been described in which the constants Ao and γ in equation (1) are set constant, but the invention is not limited to this. For example, the writing pressure is set to 100 gf.

Constants (A+o., γ1°.), (A!..., γ2°.) (A
,. . , γ3°. ), (A4°., γ4°.) may be set and switched freely, so that the operation can be selected. It is also possible to calculate an approximate expression for the relationship between distance X - signal level A and pen pressure level - signal level A from the actual measurement results without using equation (1), and use this to manage pen pressure including distance. good.

[Third Example] FIG. 10 shows a third example using the present invention. In the figure,
Reference numeral 20 denotes a peak hold circuit provided at the output of the low-pass filter, which allows the A/D comparator 15 to ensure that the peak value of the output of the low-pass filter is transferred to the A/D.
It is now possible to convert. Also, in this case A/D
Since conversion only needs to be performed once for each pen drive, a low-speed A/D converter can be used.

FIG. 11 shows a time chart. The peak hold circuit 2o always holds the peak of the output of the low-pass filter, except when it receives the (7) PHR signal from the CPU 300 and is in a reset state. A/
The D converter 15 operates for a sufficient time t(
After a period of time (from when the pen is driven until the vibration reaches the sensor 2), the output of the peak hold circuit 20 is A/D converted by the STC signal.
When the D conversion is completed, an EOC signal is output to the CPU 300. The CPU 300 receives the EOC signal, resets the peak hold circuit 2o, performs predetermined processing, and then performs the next pen drive.

As explained above, while reading the signal level of the output signal from the sensor means or another signal based on the output signal, the distance between the vibration generating means and the sensor means at that time is measured, and the measurement result and the signal A prediction means for predicting the pressure when the vibration generating means is pressed in relation to the level; a judgment means for determining whether the pressure predicted by the prediction means is equal to or higher than a certain specified value; As a result of the judgment, the pressure is always constant regardless of the distance relationship between the sensor means and the vibration generation means. By pressing the button, distance measurement is started using pressure, and ambiguous input or tilting of the vibration generating means is prohibited.
This has the effect of promoting accurate distance measurement and improving the operational feel.

Further, in the coordinate input device having the above configuration and using a plurality of sensor means, there is provided a selection means for selecting the sensor means having the shortest distance to the vibration generation means, and a pressure prediction of the vibration generation means using the selection sensor means. By providing a control means for executing this, it is possible to predict the pressure in a wide range that cannot be predicted by a single sensor, and to encourage accurate coordinate input of the coordinate input device, and to improve the operation feeling. It has the effect of improving

[Effects of the Invention] According to the present invention, it is possible to provide an ultrasonic distance measuring device that accurately determines whether or not the input is official and eliminates erroneous input.

Furthermore, it is possible to provide an ultrasonic distance measuring device that accurately determines whether or not input is official over a wider range.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the configuration of the ultrasonic distance measuring device of this embodiment, Fig. 2 is a diagram showing the circuit configuration of the first embodiment, and Fig. 3 is a diagram showing waveforms of the first embodiment. , FIG. 4 is a control flowchart of the first embodiment, FIG. 5 is a diagram showing the relationship between distance X and signal level A using writing pressure as a parameter, and FIG. 6 is a diagram showing the relationship between writing pressure and signal level A. Figure 7 shows the circuit configuration of the second embodiment; Figure 8 shows the circuit configuration of the second embodiment;
FIG. 9 is a control flowchart of the second embodiment, FIG. 10 is a diagram showing the circuit configuration of the third embodiment, FIG. 11 is a time chart of the third embodiment, and FIG. FIG. 12 is a schematic diagram of the coordinate input device, and FIG. 13 is a diagram showing pen drive signals. FIG. 14 is a diagram showing the sensor reception signal, and FIG. 15 is a diagram showing the sensor reception signal. ．． 1. A schematic diagram of the prescribed circuit, FIG. 16 is an explanatory diagram of the distance calculation method, and FIG. 17 is the conventional 1. ．． 1. The block diagram of the regulation circuit, FIGS. 18(a) and 18(b), is the conventional 1. ．． FIG. 3 is an explanatory diagram of the operation of the 1° regulation circuit. In the figure, 1--coordinate indicator (pen), 2--sensor,
5... Amplifier, 6... Full wave rectifier circuit, 7... Low pass filter, 15... A/D converter, 17...
... Comparator, 18 ... Multivibrator, 1
9... RS flip-flop, 20-... peak hold circuit, 100... pen drive circuit, 101... drive waveform generation circuit, 200... t, ·t, detection circuit, 2
01...Counter circuit, 300...CPU. 301...ROM, 302-RAM, 302 a
”-pen pressure threshold, 400 . . . output section.

Claims (2)

[Claims] (1) An ultrasonic distance measuring device that measures distance using the propagation of ultrasonic waves. A pressing force prediction means for predicting the pressing force of the generating means to the propagation means; and a measurement invalidation means for invalidating the distance measurement at that time when the pressing force is predicted to be weaker than a predetermined value. Ultrasonic distance measuring device. (2) An ultrasonic coordinate input device in which the sensor means are arranged at a plurality of predetermined locations on the propagation means, and the sensor means having the shortest distance to the ultrasonic generation means is selected from among the plurality of sensor means. The ultrasonic distance measuring device according to claim 1, further comprising selecting means.