JPH0481751B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Field of Industrial Application This invention provides an ultrasonic wave transmitted from a transmitting section that measures the time it takes for an ultrasonic wave to be reflected on an object and received by a receiving section. The present invention relates to an ultrasonic measuring device that measures the distance to an object.

(b) Summary of the invention The ultrasonic measuring device according to this invention can be summarized as follows:
In order to accurately and reliably measure the distance to the object, there is a storage means for storing the measured distance data, and when the received signal exceeds the reference voltage, reference is made based on the measured distance data stored in the storage means. a first reference voltage setting means for setting the voltage level within the settable range; and a first reference voltage setting means for setting the reference voltage level during the current measurement to the minimum value within the settable range 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 during the previous measurement, the reference voltage level is set to the minimum value within the settable range. In this way, the reference voltage level is set to an appropriate value for the measurement distance, and the measurable state does not continue.

(c) Prior art In general, an ultrasonic measuring device receives reflected waves of ultrasonic waves transmitted from a transmitter to an object at a receiver, and determines the distance between the object and the object based on the time lag between the transmission timing and the reception timing. Measure distance. The reception section includes a comparison section that compares the reception signal and a reference voltage, and the reception timing is determined when the reception signal exceeds the reference voltage in this comparison section. This is to cut out noise components from the signal received by the receiver. 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 decreases 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 makes it possible to compare the received signal with a high-level reference voltage at short distances where the amplitude is large, and to compare it with a low-level reference voltage at long distances where the amplitude is small. This makes it possible to reliably measure the distance between objects.

(d) Problems to be Solved by the Invention The waveform of the received signal at 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 match the receiving section, the waveform of the received signal at the receiving section 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,
Ultrasonic measurement allows the reference voltage level to be set not only in response to changes in the distance to the object, but also in response to changes in the object's reflectance, allowing reliable measurement of the distance to the object. The goal is to provide equipment.

(e) Means for Solving the Problems The ultrasonic measuring device of the present invention includes a transmitter that transmits ultrasonic waves to an object at a predetermined period, and a receiver that receives reflected waves from the object. and a receiving section including a comparison section for comparing the voltage and the reference voltage, and measuring the distance to the object based on the time from the transmission timing to the time when the received signal at the receiving section exceeds the reference voltage. In a sonic wave measurement device, a storage means for storing measured distance data from the previous measurement or up to the previous measurement, and when the receiving section receives a reflected wave during the previous measurement, the measurement distance data stored in the storage means is used. a first reference voltage setting means for setting the reference voltage level for the current measurement within a settable range; and a first reference voltage setting means for setting the reference voltage level for the current measurement when the receiver did not receive a reflected wave during the previous measurement A second reference voltage setting means is provided for setting the reference voltage to the minimum value of the settable range.

(f) Effect In the present invention, measured distance data from the previous measurement or up to the previous measurement is stored in the storage means. When the received signal exceeds the reference voltage during the previous measurement, the first reference voltage setting means sets the reference voltage level within a settable range 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 for the current measurement can be set using the second reference voltage setting means. Set to the minimum value of the range. 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. Distance is measured. On the other hand, if the level of the received signal changes rapidly and it becomes impossible to measure the distance without the received signal exceeding the reference voltage, the reference voltage level is set to the minimum value of its settable range, and the received signal exceeds the reference voltage. Try to surpass it.

(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 I/O 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 target object 21 is received by the receiver, amplified by the amplifier 12, and then sent to the detection circuit 1.
1 and is input to the comparator 9. During distance measurement, the CPU 3 outputs reference voltage data to the D/A converter 8 via the I/O 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 area M of RAM5 connected to CPU3
1 to M13 are assigned to the reference voltage level Vs, flag F, reception time T, measured distance L, 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 outputs this data to the D/A converter 8. When control data is output to the ultrasonic generation circuit 7 during distance measurement, a timer (not shown) is activated and measures the time until the comparator 9 outputs the detection data. The time during this period is stored as reception time T in memory area M3. 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 sets it as the measured distance L. Memory area M4
to be memorized. Further, a flag F assigned to the memory area M2 is set when the receiver 2 does not receive a reflected wave within a predetermined period of 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 from the past measured distances stored in the memory areas M5 to M13, the measured distance L previously stored in the memory area M4 is changed to the past measured distance L1 in the memory area M5.
The measured distance L1 stored in the memory area M5 is stored as the measured distance L2 in the memory area M6. In this way, the ten measured distances are always stored in the RAM 5 and are updated every time the distance is measured.

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

When the ultrasonic measuring device operates and the CPU 3 reaches measurement timing every 50 ms (n1), it outputs control data to the ultrasonic generating circuit 7 and starts the timer T (n2). As a result, the ultrasonic generating circuit 7 outputs ultrasonic waves having the waveform shown in FIG. 4A. Here, the time from t0 to t5 is 50 ms. CPU3
Once the control data is output from the ultrasonic generating circuit 7, it outputs a 70kHz pulse signal. 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 (n3, n4). This time t1 is the time necessary 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 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 average value Lm of the measured distance L stored in the memory area M4 and the past measured distances L1 to L9 stored in the memory areas M5 to M13 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). The reason why the set value Vs is updated every time ts is to prevent the reference voltage level from changing frequently, and approximately 1 s is considered to be an appropriate value for the time ts.

During distance measurement, the reference voltage level changes from measurement start time t0 to time t1, as shown by waveform 42 in FIG. 4B.
is set to the maximum value Vm until
Become Vs. This can prevent noise that directly propagates from the transmitter 1 to the receiver 2 during ultrasonic transmission to be mistakenly detected as a received signal. Incidentally, since the received signal is detected by the false detection circuit 11 which is amplified by the amplifier 12, the comparator 9 is
A received signal 43 (envelope signal) having a waveform shown by a broken line is input to.

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 of the settable range (n11), and the set value Vs is the minimum value Vn.
If not, set value Vs is set to minimum value Vn (n12), and reception of reflected waves is checked (n13).
Incidentally, when the flag F is in the reset state or when the set value Vs is the minimum value Vn, reception of a directly reflected wave is checked.

Checking whether the reflected wave has been received means checking whether there is detection data from the comparator 9. If the reflected wave has not been received, it is checked whether the 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 about 8.8 ms. In reality, it is appropriate to add a slight error to this and set it to 10 ms.

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 n10 to n15 correspond to the second reference voltage setting means. As described above, when the distance measurement start time t1 has elapsed, the operation of n5 to n10 (n11, n12) → n13 → n14 → n5 is repeated, and reception of reflected waves is checked using the set value Vs as the reference voltage level. . When the reflected wave is received, flag F is reset (n16), and the value of timer T at this time is read out and stored in memory area M3 (n17). Next, the measurement distance L 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 time of the next distance measurement, the process proceeds from n10 to n11 and n12, and the reference voltage level becomes as shown in the waveform 44 shown in FIG. 4C. In other words, if no received signal was detected during the previous measurement, the set value of the reference voltage level will be changed during the current measurement.
Vs is set to the minimum value Vn. Thereby, even if the reflectance of the object 21 changes and the received signal is attenuated without changing the measurement distance, 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 distance L stored in the memory area M4.

(h) Effects of the Invention According to this invention, when setting the reference voltage level for the current measurement, the first reference voltage setting means refers to the measurement distance data from the previous measurement or up to the previous measurement, and If measurement is not possible during measurement, the second reference voltage setting means sets the reference voltage level to the minimum value of the selectable range. 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, prevent continuous unmeasurable states, and accurately measure the distance to the object. It can be done reliably.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the control section of an ultrasonic measuring device that is an embodiment of the present invention, Fig. 2 is a memory map of the main part of the RAM that constitutes a part of the control block of the ultrasonic measuring device, and Fig. 3 is a flowchart showing the operation of the same ultrasonic measuring device, FIG. 4A is a diagram showing the waveform of the transmitted wave of the same ultrasonic measuring device, and FIGS. 4B and C are reference voltages in the comparison section of the same ultrasonic measuring device. FIG. 3 is a diagram showing a waveform of a received signal. 1...Transmitter, 2...Receiver, 9...Comparator.

Claims (1)

[Claims] 1. A receiving unit including a transmitting unit that transmits ultrasonic waves to a target object at a predetermined cycle, and a comparing unit that receives reflected waves from the target object and compares the receiving unit 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, A storage means for storing measured distance data, and a reference voltage level for the current measurement based on the measurement distance data stored in the storage means when the receiving section received a reflected wave during the previous measurement. a first reference voltage setting means that sets the reference voltage level within the settable range; and a second reference voltage setting means that sets the reference voltage level for the current measurement to the minimum value of the settable range when the received wave did not receive the reflected wave during the previous measurement. An ultrasonic measuring device comprising a reference voltage setting means.