JPS6388478A - Ultrasonic measuring apparatus - Google Patents

Abstract

PURPOSE:To accurately measure the distance up to an object, by providing a reference voltage setting means for changing the reference voltage level at the time of present measurement by definite quantity when a receiving part receives no reflected wave at the time of the previous measurement. CONSTITUTION:Control data is outputted to an ultrasonic wave generating circuit 7 from CPU3 through an I/O interface 6. The ultrasonic wave generated from the circuit 7 is transmitted to an object 21 on the basis of said control data through an amplifier 10 and a transmitter 1 The reflected wave from the object 21 is inputted to a comparator 9 through a receiver 2, an amplifier 12 and a detection circuit 11. At the time of the measurement of a distance, CPU3 outputs reference voltage to the comparator 9 through the interface 6 and a D/A converter 8 and the comparator 9 compares the reference voltage with a received signal and, when the receiving signal exceeds the reference voltage, detection data is outputted. When a receiving part does not receive the reflected wave, the reference voltage level at the time of the next measurement changes by definite quantity by a reference voltage setting means. By this method, the reference voltage level corresponding to the level of the received signal can be set.

Description

Detailed Description of the Invention ta) Industrial Application Field This invention measures the time it takes for an ultrasonic wave to be transmitted from a transmitter, reflected by an object, and received by a receiver, and The present invention relates to an ultrasonic measuring device that measures the distance between.

(b) Summary of the Invention In summary, the ultrasonic measuring device according to the present invention improves distance measurement accuracy by applying a reference voltage at the time of the current measurement when the receiver did not receive a reflected wave during the previous measurement. By providing a reference voltage setting means that changes the level by a certain amount, it is possible to cope with the attenuation of the reception signal 43 caused by changes in the reflectance of external objects.

(C) Conventional technology Ultrasonic measurement devices generally use a receiver to receive the reflected waves of ultrasonic waves transmitted from a transmitter to a target object, and detect the target object based on the time lag between the transmission timing and the reception timing. The receiving section includes a comparing section that compares the received signal and the reference voltage, and the reception timing is set when the receiving signal exceeds the reference voltage in this comparing section.This means that the receiving section This is to cant the noise component of the received signal. However, ultrasonic waves generate noise when propagating through the air, and the waveform of the received signal attenuates as the distance between the object and the object increases. If an attempt is made to detect a received signal by comparison with a reference voltage of the same level, the measurement accuracy will decrease as the measurable distance range becomes wider.

For this reason, for example, in the method disclosed in Japanese Patent Application Laid-Open No. 59-218973, there is a means for changing the level of the reference voltage in the comparator (comparison section) according to the propagation distance of the ultrasonic wave, that is, the elapse of time during measurement. has been established. This allows the received signal to be compared with a high-level reference voltage at short distances where the amplitude is large, and to be compared with a low-level reference voltage at long distances where the amplitude is small. This makes it possible to reliably measure the distance between.

(d) Problems to be Solved by the Invention The waveform of the received signal in the receiving section of the ultrasonic measuring device is affected not only by the distance to the object but also by the state of the reflecting surface of the object. That is, if the reflecting surface of the object is flexible or the direction of reflection does not reach the receiving section, the waveform of the received signal at the receiving section is attenuated.

However, in the conventional ultrasonic measuring device described above, since the change in the reference voltage level over time is constant, if the propagation distance of the ultrasonic wave, that is, the distance to the target object is the same, the comparison with the received signal is made. The reference voltage also remains constant. Therefore, if the waveform of the received signal is attenuated due to a decrease in reflectance of the object, the received signal may not exceed the reference voltage, and the distance to the object may not be measured.

The purpose of this invention is to set the reference voltage level for the current measurement based on the previous history of the measurement distance, and to adjust the reference voltage level not only to changes in the distance to the object but also to changes in the reflectance of the object. An object of the present invention is to provide an ultrasonic measuring device that can set a level and reliably measure the distance to an object.

(Means for Solving the eJ Problems) The ultrasonic measurement device of the present invention includes a transmitter that transmits ultrasonic waves to an object at a predetermined period, and a transmitter that receives reflected waves from the object and uses the received signal and reference a receiving section including a comparison section for comparing the voltage with the reference voltage; ff) Effects According to the present invention, the device is characterized in that it is provided with a reference voltage setting means for changing the reference voltage level at the time of the current measurement by a certain amount when the receiving section did not receive the reflected wave at the time of the previous measurement. If the receiver did not receive the reflected wave during the previous measurement,
The reference voltage setting means changes the reference voltage level during the current measurement by a certain amount. Therefore, even when the received signal is attenuated without a change in distance, the reference voltage compared in the comparison section changes, and the reference voltage level corresponding to the level of the received signal, that is, the reflectance of the object is set.

(g) Embodiment FIG. 1 is a block diagram of an ultrasonic measuring device which is an embodiment of the present invention.

Control data is output from the CPU 3 to the ultrasonic generation circuit 7 via the I10 interface 6. The ultrasonic generation circuit 7 generates ultrasonic waves according to this control data, and the ultrasonic waves are amplified by the amplifier 10 and transmitted from the transmitter 1 to the target object 21.

The reflected wave from the object 21 is received by the receiver, amplified by the amplifier 12, and then input to the comparator 9 via the detection circuit 11. During distance measurement, the CPU 3 outputs reference voltage data to the D/A converter 8 via the I10 interface 6. The D/A converter 8 inputs a reference voltage corresponding to this data to the comparator 9. Comparator 9 compares the reference voltage and the received signal, and outputs detection data when the received signal exceeds the reference voltage.

Memory areas M1 to M of RAM5 connected to CPU3
13 is assigned to the reference voltage level Vs, flag F, reception time T, measured distance, and past measured distances L1 to L9, respectively, as shown in the memory map of FIG.

The CPU 3 reads the reference voltage level Vs stored in the memory area M1 during distance measurement, and sends this data to the D/D.
Output to A converter 8. Ultrasonic generation circuit 7 when measuring distance
When the control data is output, a timer (not shown) is activated and measures the time until the comparator 9 outputs the detection data. The time during this time is defined as the reception time T and the memory area M
Store in 3. The ROM 4 connected to the CPU 3 stores the relationship between the reception time T and half the distance that the ultrasonic wave propagates during this time, and the CPU 3 reads out the distance corresponding to the reception time T and uses it as the measured distance. Memory area M
Store in 4. Further, the flag F assigned to the memory area M2 is set when the receiver 2 does not receive a reflected wave within a predetermined time.

Furthermore, past measured distances L1 to L9 are stored in memory areas M5 to M13 of the RAM 5.

When a new distance is measured, the past measured distances stored in the memory areas M5 to M13 are changed to the past measured distance L1.
is stored in memory area M5 as
The measured distance L1 stored in is stored in the memory area M6 as the measured distance L2. In this way, RAM
5, 10 measured distances are always stored while being updated periodically on the distance side.

FIG. 3 is a flowchart showing the operation of the ultrasonic measuring device.

When the ultrasonic measurement device operates and the CPU 3 reaches the measurement timing every 50 ms (nl), it outputs control data to the ultrasonic generation circuit 7 and starts the timer T (n2). 4. Output ultrasonic waves having the waveform shown in FIG. 4(A). Here, the time from time to to time t5 is 50 ms. Once the control data is output from the CPU 3 to the ultrasonic generation circuit 7, a 70 kHz pulse signal is output. Further, the timer T measures the time from the transmission of the ultrasonic wave until the reception of the reflected wave. After this, the reference voltage level of the comparator 9 is kept at its maximum value Vm until time t1 has elapsed ((n 3. n 4) *This time t1 is the time required for the vibrations caused by ultrasonic transmission to converge. When the zero time t1, which is about 9.4 ms, has elapsed, the reference voltage level is set to the set value Vs stored in the memory area M1 (n5).

The set value Vs of the reference voltage level stored in the memory area M1 is updated every time ts. At this time, the measured pressure iL stored in the memory area M4 and the past measured pressure ML1 stored in the memory areas M5 to M13
The average value Lm of ~L9 is calculated (n8). The relationship between the measured distance and the reference voltage level is stored in the ROM 4, and the reference voltage level corresponding to the average value Lm of the measured distance is read out and stored in the memory area M1 as the set value Vs (
n9). Here, the reason why the set value Vs is updated every time ts is to prevent the reference voltage level from changing frequently, and it is considered that approximately IS is appropriate as the time tsO value.

The reference voltage level during distance measurement is shown in waveform 42 in Figure 4 (B).
As shown, the maximum value Vm is maintained from the measurement start time to until time tl has elapsed, and then the constant value Vs is maintained. Thereby, it is possible to prevent noise that directly propagates from the transmitter 1 to the receiver 2 during upper tone transmission from being mistakenly detected as a received signal. Incidentally, since the received signal is amplified by the amplifier 12 and then detected by the detection circuit 11, a received signal 43 (envelope signal) having a waveform shown by a broken line in FIG. 4(B) is input to the comparator 9.

Next, the state of flag F is checked (n10).

If the flag F is set, it is checked whether the set value Vs is the minimum value Vn (n11), and if the set value Vs is not the minimum value Vn, the set value VsO value is set to α.
subtract n12) and check the reception of the reflected wave (
n13). Incidentally, when the flag F is in the recent state or when the set value Vs is the minimum value Vn, the reception of direct reflected waves is checked.

The check for reception of reflected waves is a check for the presence or absence of detection data from the comparator 9, and if no reflected waves are received, it is checked whether time t2 has elapsed (n14). The time t2 measured here is a time determined according to the maximum distance that the ultrasonic measuring device can measure. That is, it is the time required for an ultrasonic wave to propagate through a distance that is twice the maximum distance that an ultrasonic measuring device can measure, and can be calculated from the fact that an ultrasonic wave travels 340 mm in 1 ms. For example, when the maximum measurable distance is 150 cm, the ultrasonic wave must travel 3QQcm to detect that distance, which requires about 8.8 ms. In reality, it is appropriate to add a slight error to this and make it 10 m5.

In the above, nlO to n15 correspond to the reference voltage setting means of the present invention. As described above, when time t1 elapses after the start of distance measurement, n5 to n10 (n11.
The operation of n12)→n13→n14→n5 is repeated, and the reception of the reflected wave is checked using the set value Vs as the reference voltage level. When the reflected wave is received, the flag F is reset (n16), and the value of the timer T at this time is read out and stored in the memory area M3 (n17). Next, the measurement distance is calculated from the reception time T (n18), and the start of the next distance measurement is waited.

When time t2 elapses without receiving a reflected wave after the start of measurement, flag F is set. Therefore, at the next distance measurement, n
lo→ni1. Proceed to n12 and set the reference voltage level in Figure 4 (
The waveform 44 shown in C) is obtained. That is, if no received signal was detected during the previous measurement, the set value Vs of the reference voltage level is decreased by α during the current measurement. As a result, even if the reflectance of the object 21 changes and the received signal is attenuated without a change in the measurement distance, an appropriate reference voltage level can be set, and the distance can be reliably measured.

In this embodiment, the past measured distances L1 to L9 are stored in the memory areas M5 to M13, and the set value Vs of the reference voltage level is determined based on the average Lm of the past 10 measured distances. The set value Vs of the reference voltage level may be set only from the previous measured pressure ML stored in the memory area M4.

(H1 Effect of the Invention According to this invention, when the receiving section does not receive a reflected wave, the reference voltage setting means changes the reference voltage level at the next measurement by a certain amount. Therefore, the reflection of the object If the received signal is attenuated without changing the measured pressure (k) due to a change in the amount or reflectance, the reference voltage level can be set according to the level of the received signal, and the distance to the object can be determined with certainty. Moreover, it can be measured accurately.

[Brief explanation of the drawing]

3 is a flowchart showing the operation of the ultrasonic measuring device, FIG. 4(A) is a diagram showing the waveform of the transmitted wave of the ultrasonic measuring device, and FIG. 4(B) and (C) are FIG. 3 is a diagram showing a reference voltage and a waveform of a received signal in a comparison section of the same ultrasonic measuring device. 1- transmitter, 2- receiver, 9- comparator.

Claims (1)

[Claims] (1) Comprising a transmitter that transmits ultrasonic waves to a target object at a predetermined cycle, and a receiver that receives reflected waves from the target object and includes a comparison unit that compares the received signal and a reference voltage, In an ultrasonic measurement device that measures the distance to an object based on the time from the transmission timing to the time when the received signal at the receiver exceeds the reference voltage, the receiver did not receive a reflected wave during the previous measurement. An ultrasonic measurement device that is provided with a reference voltage setting means that changes the reference voltage level at the time of the current measurement by a certain amount.