JPH03201019A - Ultrasonic distance measuring instrument - Google Patents

Abstract

PURPOSE:To prevent the mismeasurement of a distance due to the drop of a signal level by providing a pulse generating means which outputs a pulse having the prescribed width longer than the one period of a received ultrasonic signal. CONSTITUTION:A fixed width pulse generating circuit 13 is contained in a tg/tp detecting circuit which detects the group reaching time tg and the phase reaching time tp, and detects the rise of the output received from a reference level comparator 12, and generates the 'high' signals for a fixed time. The pulse width of the 'high' signal is set longer than the one period of the output pulse of a tp-use zero-cross comparator 10. Therefore the first fall of the AND output (tp output(9)) secured between an output signal (8) and an output signal 6 of the comparator 10 is always caused by the signal (6) including the phase information. Thus the fall of the output (9) is defined as a tp detection point. Thus the normal tp is always detected. Then it is possible to prevent the mismeasurement of distances due to the drop of the signal level.

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

FIG. 6 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 transmits a desired ultrasonic signal from its tip. Sensors 2a, 2b, and 2c receive ultrasonic signals emitted from the pen via a propagation member 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 arrival time of the ultrasonic signal emitted from the pen to 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 calculated using the following steps to achieve even finer accuracy.

Next, a procedure for calculating the pen-sensor distance r from two pieces of time information, the group arrival time and the phase arrival time, will be described. First, when a voltage as shown in FIG. 7 is applied to the piezoelectric element in the pen, the received signal waveform of the sensor becomes as shown in FIG. 8. On the other hand, when the peak position is detected by group arrival time t, the first stage amplifier 5. Full wave rectifier6. The zero cross of the differential signal is detected by a comparator 9 through the low-pass filter 7 and the differentiating circuit 8, and the arrival time is recognized as the group arrival time t8.

As a result, r can be calculated from r=v, ・t, but since the method is based on detecting time based on the envelope, a certain amount of fluctuation Δt is inevitable due to the influence of the signal output size and filter characteristics. Occur. Therefore, numerically, it is better to determine the time by detecting the zero-crossing point of a specific phase to obtain a value with less fluctuation.

Therefore, if we define the detection point as the phase zero crossing point immediately after the group arrival time t g'-determination, then
,≠■, and the phase within the group shifts with the distance r, so a step-like phase as shown in FIG. 10 is observed as the phase arrival time t. This stage indicates the movement of the phase detection point, and the joint between each stage is a parallel shift by the period T of the signal. If Vp is equal to (2) and a constant phase detection point can always be observed, such a staircase will not be possible and a phase arrival time 1p as shown by straight line a will be obtained.

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

D knee 1/T +=-f In other words, tam 4 (Vg/Vp) tg-tar (tc
+c: offset value), but since the group arrival time T has large fluctuations, tp+ = (Vg/Vp) jg-
Using the property of tof-tp (n is an integer), jan "tp"T X Ir+t (tpt/T"0
．． 5)=t,+T x rnt[((vg/vp)tg
-toy-tp)/T+o, sl.

Using this tp, the pen-sensor distance r is calculated using the following formula: % ) ) : ) : Here, 1. ．． 1. The measurement start point is determined based on 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 entered.1. ．． 1. Start measuring.

FIG. 11 shows an example of a circuit that also takes into account the measurement start point. In the following explanation, positive logic will be used as an example, but it is not limited to this.

In the figure, 10 is a received wave zero-cross comparator for detecting the phase state of the received waveform, and 11.12 is a low-pass comparator.
This is a reference level comparator that maintains a "high" output while the envelope output from the filter 7 exceeds a certain reference level.

The operation will be explained below using the output waveforms from each circuit in FIG. 11 shown in FIGS. 12(A) and 12(B). The envelope waveform (2) output from the low-pass filter 7 is taken into the differentiating circuit 8 and reference level comparators 11 and 12.

The envelope waveform taken into the differentiating circuit 8 is output as a differentiated waveform, and is inputted to the zero-cross comparator 9. Zero cross comparator 9 detects the falling zero cross of the input differential waveform and outputs a "high" level, and further detects the rising zero cross and outputs "4".
Output ow level. The output obtained by this is the waveform ■.

On the other hand, the reference level comparator 11 outputs "hi" while the input envelope waveform is at a level higher than the reference.
The output obtained by this is the waveform ■. t is the time from the generation of the pen drive signal to the rise of the output signal ■ obtained from the logical product of the output signal ■ and ■. That is, if the envelope waveform output from the low-pass filter 7 does not become larger than the reference level set in the reference level comparator 11, t.

is not output.

The above principle is also used for t. However, in the case of t measurement, the first of the output signal ■ obtained from the AND of the output signal ■ obtained by inputting the received waveform to the zero-cross comparator 10 and the output ■ of the reference level comparator 12. t is defined by detecting the falling edge. The reason for this is that when measuring t, unless the reference level comparator output signal ■ does not go to the "high" level, the rise of the zero-cross comparator output signal ■ for t always means that the output signal ■ high
” occurs while the state is maintained, whereas in the case of 1p, the output signal of the zero-cross comparator for t is “
This is because the output signal ■ may rise after going high, so it may not be possible to specify a normal t at the rise of the output signal ■.Therefore, when measuring t, the output signal The falling edge of (2) is detected to define t.

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

[Problems to be Solved by the Invention] However, in the above conventional example, the output signal of the reference level comparator obtained by comparing the output signal of the low-pass filter with a predetermined reference level, the received wave and the
The t9 output signal (■) is obtained by ANDing the output signal (■) of the zero-cross comparator, and the first fall of the signal (■) is detected to define the As shown in Figure 12 (C), when the level of the output signal ■ of the low-pass filter becomes comparable to the reference level of the reference level comparator, the pulse width of the output signal ■ of the reference level comparator becomes equal to that of the zero-cross comparator for 1p. The falling edge of the output signal ■, which is shorter than the pulse synchronization of the output signal ■ and is unrelated to the output signal ■ containing phase information, is detected and defined as 1p, resulting in a normal error. There was a problem that 1p could not be detected. Therefore, when distance calculations and coordinate value calculations are performed using such 1p, there is a problem in that a large error occurs in the calculation results.

The present invention provides an ultrasonic distance measuring device that eliminates the above-mentioned conventional drawbacks and eliminates erroneous distance measurement due to a decrease in signal level.

[Means for Solving the Problem] In order to solve this problem, the ultrasonic distance measuring device of the present invention uses an ultrasonic distance measuring device that manages the measurement start timing of the ultrasonic arrival time based on the amplitude level of the received ultrasonic signal. The sonic distance measuring device includes a level detecting means for detecting that the amplitude level of the ultrasonic signal exceeds a predetermined reference value, and a method that detects that the amplitude level of the ultrasonic signal is longer than one cycle of the received ultrasonic signal based on the detection by the level detecting means. and pulse generating means for outputting a pulse of a predetermined width.

Here, the signal forming means is provided to form a signal based on the phase state of the received ultrasonic signal, and the signal forming means is enabled while the pulse signal is output from the pulse generating means, and the arrival time of the ultrasonic wave is Detection is performed.

[Function] In this configuration, there is provided a level detecting means for detecting that the amplitude level of the ultrasonic signal exceeds a predetermined reference value, and a level detecting means for detecting that the amplitude level of the ultrasonic signal exceeds a predetermined reference value;
By providing a pulse generating means that outputs a pulse with a predetermined width longer than the period, it is possible to reliably measure the normal arrival time including phase information while maintaining the function of managing the measurement start time of the ultrasonic signal arrival time. This is what I did.

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

FIG. 1A 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 Ben 1, 101 is a drive waveform generation circuit that generates a drive waveform for pen 1 as shown in FIG. 7, and 200 is a sensor 2.
t, t, which detects tg and 1p from the received signal of
A detection circuit 201 is a counter circuit for measuring the propagation time of the ultrasonic wave based on the t5 and t signals.

Further, 300 is a CPU that controls waveform generation of the drive waveform generation circuit 101 and calculates the distance from the output of the counter circuit 201, 301 is a ROM that stores a control program for the CPU 300, and 302 is a RAM for auxiliary storage. 40
0 is an output unit that outputs, for example, coordinates based on the calculated distance.

FIG. 1B is a block diagram showing the configuration of the detection circuit 111 of this embodiment. What differs from the conventional example is a constant width pulse generation circuit 13 provided after the reference level comparator 12, which detects the rising edge (or "high" level, etc.) of the output from the reference level comparator 12. This circuit includes a multi-vibrator that generates a "high" signal for a certain period of time. In this circuit, the generation time (pulse width tw) of the output "high" signal is set by the resistor R and the capacitor C, and is longer than one period jpw of the output pulse of the zero-cross comparator 10, as shown in FIG. determined by the value. As a result, the first fall of the logical product output (tp output ■) of this output signal ■ and the output signal ■ of the zero-cross comparator for t, is always the output signal of the zero-cross comparator for t, which includes phase information. ■This is caused by t9.
By using it as a detection point, it is possible to always detect a normal 1p.

FIG. 3A shows a specific example of the constant width pulse generation circuit 13.

The circuit shown in the figure is an example having two constant width pulse generation circuits, and one can be used as the t8 side and the other as the t, side. Here, an example using an integrated circuit rLs221J with two built-in multi-vibrators will be shown. First, let's focus on the path from human power 1 to output 1. 1. The 2nd bin is the trigger input, the 1st bin is GND, and the 2nd bin is input 1, so the rising edge of the input l is detected,
A pulse signal is generated from the 13th bin. The pulse width of the pulse output at this time is determined by the resistor R+ and capacitor CI connected to the 14th and 15th bins, and the arithmetic expression for its calculation is expressed by the following equation.

tw=(C1・R1−Tate n2)×(1±0.1) t,
>The third bin is a reset terminal, which activates the circuit when it is at a "high" level. That is, the input and output are as shown in FIG. 3B.

The same goes for the route from input 2 to output 2.
The 5th bin is the output terminal, the 6th and 7th bins are the timing terminals,
The 8th bin is GND, the 9th and 10th bins are input terminals, the 11th bin is a reset terminal, and the 16th bin is a power supply terminal. Note that the 4th and 12th bins are negative logic output terminals 1 and 2, respectively.
It is.

[Other Embodiments] In the above embodiments, a case has been described in which a constant width pulse is generated by detecting that the low-pass filter output exceeds the reference level set in the reference level comparator. A constant width pulse may be generated by detecting that the output level of the first stage amplifier exceeds the reference level. Figure 4 shows a block diagram of the detection circuit in this case. The timing and timing of each output signal in this case is shown in Figure 4. The chart will look like Figure 5.

When the output signal [phase] of the first-stage amplifier 5 is directly input to the reference level comparator, a pulse-like output as shown in ■' is obtained. When this signal ■' is input to the constant width pulse generation circuit 13, it detects the first rise of the output ■' and outputs a constant width pulse of tw, and when the output ends, the first rise of the output ■' is output. Detected and outputs a constant width pulse again. This operation is constantly repeated to obtain the output signal ■'.

The output signal ■' and the output signal ■ of the zero-cross comparator for t and t are logically ANDed.

Obtain the output signal ■′. Detecting this first falling edge
If p is defined, 1. Normal t,− based on the phase information of the received waveform without losing the ability to control the measurement start timing.
can be measured reliably.

In addition, the full-wave rectifier circuit 6 is used to generate the constant width pulse as described above.
It is also possible to use the output of or the output of the differentiating circuit 8,
The same effect as this example can be obtained.

As explained above, depending on the magnitude of the ultrasonic signal received by the sensor, whether or not to measure desired data is determined based on the amplitude level of the ultrasonic signal in a functional ultrasonic distance measuring device. By providing a pulse generation circuit that detects that the ultrasonic signal has become larger than the ultrasonic signal level and outputs a pulse signal with a width longer than one period of the ultrasonic signal, the ultrasonic signal is always The phase position can now be detected, and it is possible to reliably measure normal time data while maintaining the function of managing the measurement start time of desired data using the amplitude level of the ultrasonic signal.

[Effects of the Invention] According to the present invention, it is possible to provide an ultrasonic distance measuring device that eliminates erroneous distance measurement due to a decrease in signal level.

[Brief explanation of drawings]

FIG. 1A is a block diagram showing the configuration of the ultrasonic distance measuring device of this embodiment, and FIG. 1B is a block diagram showing the configuration of the ultrasonic distance measuring device of this embodiment. -1. A block diagram of the detection circuit, Fig. 2 is a timing chart of the outputs of each part of the above circuit, Fig. 3A is a diagram showing a specific example of a constant width pulse generation circuit, and Fig. 3B is an example of input/output signals of the circuit of Fig. 3A. FIG. 4 is a diagram showing 111. of another embodiment. A block diagram of the detection circuit, Fig. 5 is a timing chart of each output of the above circuit, Fig. 6 is a schematic diagram of the coordinate input device, Fig. 9 is a block diagram of the detection circuit that determines the ultrasonic signal arrival time, Fig. 7 Figure 8 is a diagram showing a pen drive signal, Figure 8 is a diagram showing a sensor reception signal, Figure 10 is an illustration of a distance calculation formula, and Figure 11 is a block diagram explaining a conventional t, t, measurement timing determination circuit. FIGS. 12(A) to 12(C) are timing charts of outputs of each part to explain the operation of the circuit of FIG. 11. In the figure, 1...coordinate indicator, 2...sensor, 3...
Propagator, 4... Vibration isolation material, 5... First stage amplifier, 6...
・Full-wave rectifier circuit, 7...Low-pass filter, 8...
・Differential circuit, 9...1. Zero-cross comparator for 10...tl, zero-cross comparator for 11
. . . Reference level comparator, 12 . . . Reference level comparator, 13 . . . Constant width pulse output circuit. Figure 5 Figure 12 (A) Figure 12 CB) Figure 12 (C)

Claims (2)

[Claims] (1) An ultrasonic distance measuring device that manages the timing to start measuring ultrasonic arrival time based on the amplitude level of a received ultrasonic signal, and detects when the amplitude level of the ultrasonic signal exceeds a predetermined reference value. An ultrasonic distance measuring device comprising: a level detecting means for detecting the level; and a pulse generating means for outputting a pulse having a predetermined width longer than one period of a received ultrasonic signal based on the detection by the level detecting means. (2) A signal forming means is provided for forming a signal based on the phase state of the received ultrasonic signal, and the signal forming means is enabled while the pulse signal is output from the pulse generating means, and the arrival time of the ultrasonic wave is 2. The ultrasonic distance measuring device according to claim 1, wherein the ultrasonic distance measuring device detects: