JPH06100654B2 - Ultrasonic rangefinder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention uses a digital correlator to accurately measure the difference between the transmission time and the reception time, and to measure the difference from the transmission point to the reflection point or the reception point. The present invention relates to an ultrasonic range finder for measuring a distance.

(Prior Art) An ultrasonic distance meter measures a distance from a transmission point to a reception point by using a difference between an ultrasonic wave transmission time and an ultrasonic reception time and a sound velocity. At this time, if the reception time is not accurately measured, a large error will occur in the distance. For example, the speed of sound underwater is about 1.5 km / sec, so 10
An error of 1/00 second causes an error of 1.5 m in distance.

Now, when examining the received signal, it is determined that the received time is the time when the received signal exceeds a certain threshold value in order to avoid the influence of noise.

FIG. 4 shows the case where noise is not mixed in the received signal, and FIG. 5 shows the case where noise is mixed in the received signal. In FIG. 4, noise is not mixed, but there is a difference in the time when the reception level exceeds the threshold value between when the reception level is high and when the reception level is low. Therefore, a difference in distance occurs due to the difference in reception level. In FIG. 5, since the received signal contains noise, there are two times at which the threshold level is exceeded, as shown by the thin solid line, t1 and t2. Depending on which is the correct time, t1
A time difference of ~ t2, that is, a distance difference is generated.

(Problems to be Solved by the Invention) An error occurs in FIG. 4 due to the influence of tidal current in the water, bubbles, water temperature change, and shaking of the transceiver when ultrasonic waves are transmitted into the water.

In FIG. 5, the noise level fluctuates depending on the size of the distance to the reflection point, so that the error increases or decreases.

An object of the present invention is to improve the above-mentioned drawbacks and to provide an ultrasonic range finder which is less affected by noise and fluctuations in reception level.

(Means for Solving the Problem) FIG. 1 is a diagram showing a principle configuration of the first invention. In FIG. 1, 1 is a transmitter, 2 is a receiver, 3 is means for obtaining a reference wave, 4 is means for A / D converting and storing the received wave, 5 is a digital correlator, 6 is an arithmetic circuit, and 7 is Indicates a reflection point. In FIG. 1, the alternate long and short dash line indicates that each of the constituent blocks on the right side thereof is installed at the receiving point.

The first invention has the following configuration in an ultrasonic range finder that measures the distance from the transmission point to the reflection point by a time difference when the transmitted ultrasonic wave is reflected from the reflection point 7 and received. That is, storage means for storing a signal waveform corresponding to the waveform of the transmitted ultrasonic wave as a reference wave, storage means for storing data obtained by A / D converting the received wave, and reading the data stored in the storage means. , The digital correlator 5 for comparing with the reference wave read from the storage means, and the generation time of the reference wave for which the maximum correlation value is obtained for the output of the digital correlator is determined as the reception time, and the time difference from the transmission time is Calculation circuit 6 for calculation
And measures the distance from the transmission point to the reception point.

Further, FIG. 6 is a diagram showing a principle configuration of the second invention. Sixth
As shown in the figure, in the second invention, the receiving point is installed away from the transmitting point, and the transmitting point and the reception condition are different from each other due to the time difference when the transmitted ultrasonic wave is directly received instead of the reflected wave at the reflecting point. An ultrasonic range finder for measuring the distance between the two is configured similarly to the first invention.

Therefore, among the reference numerals shown in FIG. 6, the same reference numerals as those in FIG. 1 indicate the same reference numerals as those in FIG.

(Operation) In FIG. 1, the ultrasonic wave is transmitted from the transmitter 1, and the signal reflected at the reflection point 7 is received by the receiver 2. The receiver 2 A / D converts the received signal and stores it in a storage device, etc. 4
To store. On the other hand, the means 3 for obtaining the reference wave is installed, for example, at the receiving point and stored in the storage means for storing the signal waveform corresponding to the waveform of the ultrasonic wave to be transmitted as the reference wave. Next, the digital correlator 5 reads out the data of the storage means 3 to be stored as the reference wave and the original one of the means 4 for A / D converting the received wave and storing it, and obtains the correlation value between them. 2A shows a reference wave formed by 32 time series values in the time axis direction, and FIG. 2B shows a received waveform. When the reference wave is a waveform formed with 32 time-series values, for example, the same number of data is read from the time TO at which the received wave data also starts to be stored, the correlation value is obtained, and the correlation value is stored in the digital correlator. Store in the device address TO. FIG. 2 is a diagram for explaining this situation with analog waveforms.

Next, from the time T1 when the received wave data is delayed by one, the same number is read out to obtain the correlation value, and the correlation value is stored in the next address T1 of the storage device.

By repeating the process of obtaining the correlation value in this manner until the end of the received wave, a time series of correlation values can be obtained. Next, the time of occurrence of the received wave data that has the maximum value in this time series
Tx is obtained and sent to the arithmetic unit 6. In this case, the initial correlation value is low and the correlation value is maximum at Tx. The arithmetic circuit 6 integrates the sampling time interval of the time-series data and the number of repetitions until the maximum value of the correlation value of the received wave data is obtained to obtain the time when the correlation value becomes maximum from the start of the memory, and further the start of the memory of the reception data from the transmission. Calculate the value with the time added to. This value is the exact time it took from sending to receiving. Then, the distance from the transmission point to the reception point can be calculated from this value and the sound velocity.

In the second invention, the receiving point is installed apart from the transmitting point, and the ultrasonic wave can be received without passing through the reflecting point. The process including the reference wave and reaching the distance calculation is the same as in the case of the first invention.

(Embodiment) In the embodiment of the present invention, the storage means for storing the reference wave is installed at the receiving point. Alternatively, when it is installed at a transmission point and compared by a digital correlator, data is transmitted from the transmission point through a communication line and used as a reference wave. The received wave is always stored in memory after A / D conversion. For the data to be compared in the digital correlator, if the data stored in the memory is read and the correlation value is directly calculated, the calculation time will be too long. Waveforms slightly before the time when the threshold is exceeded are moved to the buffer. If the data in the buffer is read and the correlation value with the reference waveform is obtained, the time required to obtain the correlation value can be shortened.

Next, FIG. 3 is a block diagram for calculating the distance. In FIG. 3, block 11 is a distance calculation unit, 12 is maximum correlation time data, 13 is recording start time data, and 14 is transmission time data. Reference numeral 15 is a distance output unit. The distance calculation unit 11 first obtains the time difference between the time data 14 and 13 and the time difference between 13 and 12, respectively.

The distance can be obtained by adding these values and then integrating the sound velocity. The distance output unit 15 outputs the value.

(Effect of the invention) According to the invention of the present application, by using a memory for a signal that receives an ultrasonic wave and obtaining a correlation value with a reference wave, it is possible to accurately know a reception time that is not affected by noise, The exact distance between the transmitting point and the receiving point or the reflecting point can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a principle configuration of the present invention, FIG. 2 is a diagram for explaining the operation of FIG. 1, FIG. 3 is a block diagram for explaining calculation of a distance as an embodiment of the present invention, 4 and 5 are diagrams for explaining the operation of the conventional ultrasonic rangefinder, and FIG. 6 is a diagram showing the principle configuration of the second invention. 1 ... Transmitter 2 ... Receiver 3 ... Means for obtaining reference wave 4 ... A / D conversion / storing means 5 ... Digital correlator 6 ... Arithmetic circuit

Claims (2)

[Claims] 1. An ultrasonic range finder for measuring a distance from a transmission point to a reflection point by a time difference when a transmitted ultrasonic wave is reflected by a reflection point and received, and a signal corresponding to a waveform of the transmission ultrasonic wave. Storage means for storing a waveform as a reference wave, storage means for storing data obtained by A / D converting the received wave, read data stored in the storage means, and compare with the reference wave read from the storage means And a calculation circuit that determines the generation time of the reference wave for which the maximum correlation value is obtained for the output of the digital correlator as the reception time and calculates the time difference from the transmission time. And ultrasonic range finder. 2. An ultrasonic range finder for measuring a distance between a transmitting point and a receiving point by a time difference when the transmitted ultrasonic wave is received by installing the transmitting point and the receiving point apart from each other. Storage means for storing the signal waveform corresponding to the waveform of the reference wave as a reference wave, storage means for storing the data obtained by A / D converting the received wave, and the data stored in the storage means are read out from the storage means. A digital correlator that compares the read reference wave with an arithmetic circuit that determines the generation time of the reference wave for which the maximum correlation value is obtained for the output of the digital correlator as the reception time and calculates the time difference from the transmission time. An ultrasonic range finder characterized by: