JPS6388479A - Ultrasonic measuring apparatus - Google Patents

Abstract

PURPOSE:To accurately measure the distance up to an object, by providing a reference voltage setting means for setting the reference voltage level at the time of the present measurement to the limit value of a set range 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 and 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 a comparator 9 through the interface 6 and a D/A converter 8, and the reference voltage is compared with a receiving signal by the comparator 9 and, when the received signal exceeds the reference voltage, detection data is outputted. When measurement is impossible at the time of the previous measurement, a reference voltage level is set to a limit value by a reference voltage setting means. By this method, the reference voltage level at the time of the present measurement is set to a value suitable for a received signal level and a distance can be measured accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial field of application This invention provides an ultrasonic wave that can be applied to an object by measuring the time it takes for an ultrasonic wave transmitted from a transmitter to be reflected by an object and received by a receiver. The present invention relates to an ultrasonic measurement device that determines the distance to an object.

(b1 Summary of the Invention In summary, the ultrasonic measuring device according to the present invention includes a storage means for storing measured distance data and a storage means for accurately and reliably measuring the distance ^1 between the object and the object. a first reference voltage setting means for setting a reference voltage level based on stored measurement distance data; and a first reference voltage setting means for setting a reference voltage level during time measurement to a limit value when the received signal does not exceed the reference voltage. When setting the reference voltage level for the current measurement, the reference voltage level is set based on the previous history of the measured distance, and when the distance could not be measured last time, it is set to the limit value. It is set to an appropriate value for the measurement distance and is designed to prevent continuous unmeasurable conditions.

(C1 Conventional technology Ultrasonic measuring devices generally receive reflected waves of ultrasonic waves transmitted from a transmitting unit to a target object in a receiving unit, and the distance between the transmitting unit and the target object is determined based on the time lag between the transmitting timing and the receiving timing. Measures the distance.The receiving section includes a comparison section that compares the received signal and the reference voltage, and the reception timing is when the received signal exceeds the reference voltage in this comparison section.This means that the receiving section receives the This is to remove noise components from the signal. However, ultrasonic waves cause loss when propagating through the air, and the waveform of the received signal attenuates as the distance from the object increases. Therefore, if a received signal is always detected 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 device disclosed in Japanese Patent Application Laid-Open No. 59-218973, a means is provided to change the level of the reference voltage in the comparator (comparison section) according to the propagation distance of the ultrasonic wave, that is, the time elapsed during measurement. ing. 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+ Problem to be solved by the invention The waveform of the received signal in the receiving section of the ultrasonic measurement device is affected not only by the distance to the object but also by the state of the reflective surface of the object. If the reflecting surface of the receiver is flexible or the direction of reflection does not match the receiver, the waveform of the received signal at the receiver will be 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 make the reference voltage level corresponding 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 the voltage level and reliably measure the distance to an object.

(Means for Solving Problem e1) 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 references them as a received signal. a receiving section including a comparison section for comparing the voltage with the reference voltage; In the device, a storage means for storing measurement distance data from the previous measurement or up to the previous measurement, and a first reference voltage for setting a reference voltage level for the current measurement based on the measurement distance data stored in the storage means. A setting means and a second reference voltage setting means are provided for setting the reference voltage level at the time of the current measurement to the limit value of the setting range when the receiving section did not receive the reflected wave at the time of the previous measurement. It is characterized by

(f) Effect According to the present invention, measured distance data from the previous measurement or up to the previous measurement is stored in the storage means. During the current measurement, the reference voltage level is set based on the measured distance data stored in the storage means. When setting the reference voltage level for the current measurement, if the received signal at the receiver did not exceed the reference voltage during the previous measurement, the reference voltage level is set at the limit. Therefore, when the level of the received signal changes relatively slowly, the reference voltage level is set based on the previous measurement distance or the previous measurement distance, and the target voltage level is set based on the time when the received signal exceeds this reference voltage. Measure distance. On the other hand, if the level of the received signal changes rapidly and the distance cannot be measured because the received signal does not exceed the reference voltage, the reference voltage level is set to a limit value so that the receiving signal No. 43 exceeds the reference voltage.

(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 measurement paths tIL1 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 become the past measured distances iL1.
is stored in memory area M5 as
The measured distance L1 stored in is stored in the memory area M6 as measured distance [,2. In this way, R.A.
In M5, 10 measured distances are always written, α, while being updated periodically on the distance side.

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

When the ultrasonic measuring device operates and the measurement timing reaches every 50 ms (n 1 ), the CPU 3 outputs control data to the ultrasonic generating circuit 7 and starts the timer T (n2). As a result, the ultrasonic generation circuit 7 outputs ultrasonic waves having the waveform shown in FIG. 4(A). Here, from time tQ to time t
5 is 50m5. 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 set to its maximum value V until time t1 has elapsed.
Set it to m (n3.n4). This time t1 is the time required for the vibrations caused by the transmission of the ultrasonic waves to converge, and is approximately 0.4 ms. When time t1 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 Ml is updated every time ts. At this time, the measurement distance stored in memory area M4 and the past measurement path/1L stored in memory areas M5 to M13
The average value Lm of 1 to L9 is calculated (n8). ROM
The relationship between the measurement path, 1, and the reference voltage level is stored in 4, and the reference voltage level corresponding to the average value Lm of the measurement 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 in 1., the maximum value Vm is maintained from the measurement start time tQ until time t1 has elapsed. Thereafter, it is set to the set value Vs.

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. Note that since the received signal is amplified by the amplifier 12 and then detected by the detection circuit 11, the comparator 9 has a fourth
A received signal 43 (envelope signal) having a waveform indicated by a broken line in FIG. 3(B) is input.

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 (nil), and if the set value Vs is not the minimum value Vn, the set value vS@minimum value Vn is changed. n12), check reception of reflected waves (n
13). Incidentally, when the flag F is in the reset state or when the set value Vs is the minimum value Vn, the reception of a directly reflected wave 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 twice the maximum distance that can be measured by an ultrasonic measuring device, and can be calculated from the fact that an ultrasonic wave travels 340 mm in 1 ms. For example, if the maximum measurable distance is 150 cm, the ultrasonic wave must travel 300 cm to detect that distance, which requires approximately 8.8 ms. In reality, it is appropriate to add a slight error to this and make it 10 m5.

In the above, M4 to M13 of the RAM 5 correspond to the storage means of the present invention, n8 and n9 correspond to the first reference voltage setting means, and nlo to n15 correspond to the second reference voltage setting means. As described above, when time t1 has elapsed after the start of distance measurement, n5~nlo (ni
The operations 1, n12)→n13→n14→n5 are repeated, and reception of reflected waves is checked using the set value Vs as a 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
Proceed to lo → nil, n12, and the reference voltage level is shown 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 set to the minimum value Vn 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, the distance can be reliably measured.

In this embodiment, the past measurement paths +C1tL1 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 measurement distances. The set value Vs of the reference voltage level may be set only from the previous measurement distance stored in the memory area M4.

(h) Effects of the Invention According to the present invention, when setting the reference voltage level for the current measurement, the first reference type point setting means refers to the measured distance data from the previous measurement or up to the previous measurement, and If measurement was not possible during the previous measurement, the second reference voltage setting means sets the reference voltage level to the limit value. This makes it possible to set the reference voltage level at the time of the current measurement to a value suitable for the received signal level, and also prevents continuous unmeasurable states, making it possible to accurately and accurately measure the distance to the object. It can be carried out

[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 13 waves transmitted by the ultrasonic measuring device, and FIG. 4(B) and (C) 2 is a diagram showing a reference voltage and a waveform of a received signal in a comparison section of the same ultrasonic measuring device. FIG. 1- transmitter, 2- receiver, 9- comparator.

Claims (1)

[Claims] (1) comprising a transmitter that transmits ultrasonic waves to a target object at a predetermined period; a receiver that receives reflected waves from the target object; and a receiver that includes a comparison unit that compares the receiver and a reference voltage; An ultrasonic measurement device that measures the distance to an object based on the time from the transmission timing until the time when the received signal exceeds the reference voltage at the receiver section stores measurement distance data from the previous measurement or up to the previous measurement. first reference voltage setting means for setting a reference voltage level for the current measurement based on the measured distance data stored in the storage means; and second reference voltage setting means for setting the reference voltage level at the time of the current measurement to the limit value of the setting range.