JPH04233487A - Ultrasonic distance measuring apparatus - Google Patents

Abstract

PURPOSE:To provide an ultrasonic distance measuring apparatus without erroneous measurement otherwise caused by ultrasonic noises. CONSTITUTION:A control circuit 6 is provided and an excitation signal 6A with a specified frequency is outputted to an ultrasonic vibrator 1 to emit an measuring ultrasonic wave toward a target. Reflected wave from the target is inputted into the ultrasonic vibrator 1 and a receiving signal 2A is amplified to be inputted into a receiving pulse generation circuit 5 from an envelope detector 4 while being inputted into a receiving pulse generation circuit 8. A pulse signal 5A synchronous with the inputting of the received signal is outputted from the receiving pulse generation circuit 5 and a control circuit 6 measures a distance to the target based on a time to be elapsed after the outputting of switching signal 6B to an analog switch 2 before the inputting of the above pulse signal 5A. A pulse signal 8A corresponding to the frequency of the received signal 2A is outputted from the receiving pulse generation circuit 8 and the control circuit 6 performs the measurement of the distance only when the frequency of the received signal 2A coincides with the frequency of an excitation signal 6A and the results are shown on a display device 7.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an ultrasonic distance measuring device.
In particular, the present invention relates to a measuring device that does not cause erroneous measurements due to ultrasonic noise.

0002

[Prior Art] Ultrasonic distance measuring devices measure the distance to a target based on the return time of ultrasonic waves from the target, and are mounted on vehicles and used for purposes such as collision avoidance when parking. ing. For the reception and transmission of ultrasonic waves, small piezoelectric ceramic vibrators with a simple structure are often used, but since the band in which such vibrators can obtain high sensitivity is relatively narrow, as the number of users increases, it becomes difficult to use the same frequency. There is a risk of interference between devices that use the Furthermore, there is a risk of erroneous measurements occurring in vehicles and the like with poor noise environments.

[0003] For example, Japanese Patent Publication No. 58-40148 discloses a method of sequentially and randomly changing the transmission interval and identifying whether or not the reflected wave is due to the self-transmission based on the results of several pulse transmissions and receptions. ing.

0004

[Problem to be solved by the invention] However, the propagation speed of ultrasonic waves is extremely slow compared to radio waves, and when the above method is used for ultrasonic distance measurement, it takes time to transmit and receive, resulting in a significant drop in responsiveness. There is a problem.

SUMMARY OF THE INVENTION The present invention has been made to solve this problem, and an object of the present invention is to provide an ultrasonic distance measuring device that does not cause erroneous measurements due to ultrasonic noise including interference and has sufficient responsiveness.

[0006]

[Means for Solving the Problems] The configuration of the present invention will be explained with reference to FIG. 7. The ultrasonic distance measuring device includes an excitation means for emitting an excitation signal of a predetermined frequency to cause the ultrasonic transmitting means to transmit ultrasonic waves, and an ultrasonic distance measuring device. an ultrasonic receiving means for obtaining a received signal by receiving the reflected wave of the ultrasonic wave reflected by the target; and a distance for measuring the distance to the target from the time from emitting the excitation signal to obtaining the received signal. It comprises a measuring means and a control means for activating the distance measuring means only when the received signal has a certain relationship with the excitation signal.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, reference numeral 1 denotes an ultrasonic transducer which serves both as ultrasonic transmitting means and ultrasonic receiving means, and is selectively connected to a control circuit 6 and an amplifier 3 by switching an analog switch 2. Therefore, the switching signal 6B from the control circuit 6 becomes "
At the "H" level, the analog switch 2 is switched to the transmitting side, a high frequency excitation signal 6A is given to the ultrasonic transducer 1, and ultrasonic waves are emitted toward the target. Switching signal 6
When B goes to the "L" level, the analog switch 2 switches to the receiving side, and the received signal 2A output from the ultrasonic transducer 1 due to the reflected wave from the target is input to the amplifier 3.

The output of the amplifier 3 is input to an envelope detector 4 and a reception pulse generation circuit 8, and the output 4A of the detector 4 is input to a reception pulse generation circuit 5. Outputs 5A and 8A of both reception pulse generation circuits 5 and 8 are input to the control circuit 6, respectively. Note that three types of frequencies of the excitation signal 6A outputted from the control circuit 6 are selected in a procedure described below.

FIG. 2 shows a time chart of each of the above signals. The received signal 2A is amplified by the amplifier 3 to become the signal 3A, which is input to the reception pulse generation circuit 8, where the portion above the threshold level V1 is converted into a pulse signal 8A having the same frequency as the reception frequency, and is output to the control circuit 6. . On the other hand, the output signal 4A of the wave detector 4 is transmitted to the reception pulse generation circuit 5.
It is converted into a pulse signal 5A having the same length as the portion above the threshold level V2, and is output to the control circuit 6.

The control circuit 6 calculates the distance to the target based on the time from the rise of the switching signal 6B to the rise of the pulse signal 5A, but at the same time calculates the distance to the target based on the period of the pulse signal 8A (T in FIG. 2). The frequency of the received signal 2A is calculated and it is determined whether it is due to reception of ultrasonic noise according to the procedure described below. If it is due to ultrasonic noise, the distance calculation in the control circuit is stopped.

Details of the processing procedure of the control circuit 6 in this case will be explained below with reference to FIGS. 3 to 5. In FIG. 3, in step 101, the frequency of the excitation signal 6A is set. Next, the counter n is reset (step 102), and it is checked whether there is a received signal 2A (step 103). Since the received signal 2A before being transmitted is due to ultrasonic noise, if the received signal 2A is present, the process proceeds from step 103 to step 104 and a determination 1 routine is executed. The judgment 1 routine is shown in FIG. 4, and in step 111 it is judged whether the frequency Fx of the received signal 2A is the same as the frequency Fo of the set excitation signal 6A, and if they are the same, the Change the set frequency of the excitation signal 6A. The set frequency is selected from three types: F1, F2, and F3.

At step 105 in FIG. 3, the excitation signal 6A is output at the set frequency, and the ultrasonic transducer 1 emits ultrasonic waves toward the target object. Subsequently, it is determined whether there is a received signal 2A (step 106), and if there is a received signal 2A, a determination 2 routine is executed. Details of the determination 2 routine are shown in FIG. 5, and in step 121 it is checked whether the frequency Fx of the received signal 2A matches the frequency Fo of the excitation signal 6A. This confirmation is to determine whether the frequency Fx at which the frequency is maximum matches the frequency Fo of the excitation signal 6A from the frequency frequency distribution of the received signal 2A determined from the period T of the pulse signal 8A. As shown in FIG. 2, when there is no ultrasonic noise, among the three frequencies (F1 to F3) of the excitation signal 6A, the frequency that coincides with this frequency in the vicinity thereof has the highest frequency.

[0013] Only when the received signal frequency Fx matches the excitation signal frequency Fo in step 121, the distance is calculated and displayed on the display 7 (step 122). In this way, distance calculation is not performed depending on the received signal 2A due to ultrasonic noise input at another frequency, so that erroneous measurements will not occur due to ultrasonic noise.

In step 108, a counter n is incremented, and ultrasonic transmission and reception are repeated until the count value n reaches a predetermined value k. After repeating the transmission and reception of ultrasound a certain number of times, step 102 and subsequent steps are executed again to check whether or not ultrasound noise is received.

As described above, by detecting the level and frequency Fx of the received signal 2A, it is possible to check for the presence of ultrasonic noise before starting distance measurement and perform measurement at a different frequency, and also to detect the frequency of the received signal 2A. Since distance measurement is stopped when Fx is different from the frequency Fo of the excitation signal 6A, erroneous measurements due to ultrasonic noise can be effectively avoided.

[0016] In the above embodiment, the coincidence between the excitation signal and the received signal is detected using the maximum frequency, but the average value or the like may also be used, or the phase or the like may be detected instead of the frequency. In short, it is sufficient that the excitation signal and the received signal have a certain predetermined relationship. Of course, frequency switching of the excitation signal is not limited to three types.

The control operation of the control circuit can be realized by hardware logic, and if the control circuit can directly detect the rise of the pulse signal 8A, it is not necessary to provide the detector 4 and the pulse generator 5.

If the frequency of the ultrasonic noise is necessarily different from the frequency of the ultrasonic waves used for measurement, steps 102 to 104 in FIG. 3 are unnecessary.

[0019]

As described above, according to the ultrasonic distance measuring device of the present invention, distance measurement is performed only when the transmitted ultrasonic wave and the received ultrasonic wave have a certain relationship. Even if sonic noise is received, there will be no error in distance measurement, and accurate distance measurement is always possible even when installed in a vehicle or the like with a poor noise environment.

[Brief explanation of the drawing]

FIG. 1 is an overall block diagram of a distance measuring device.

FIG. 2 is a time chart of various signals of the distance measuring device.

FIG. 3 is a processing flowchart of the control circuit.

FIG. 4 is a processing flowchart of the control circuit.

FIG. 5 is a processing flowchart of the control circuit.

FIG. 6 is a frequency distribution of reception frequencies.

FIG. 7 is a claim correspondence diagram.

[Explanation of symbols]

1 Ultrasonic transducer 2 Analog switch 3 Amplifier 4 Envelope detector 5 Reception pulse generation circuit 6 Control circuit 7 Display 8 Reception pulse generation circuit

Claims (1)

[Claims] 1. Excitation means for emitting an excitation signal of a predetermined frequency to cause the ultrasonic transmission means to transmit ultrasonic waves; and ultrasonic waves for receiving reflected waves of the ultrasonic waves reflected by a target object to obtain reception signals. a receiving means; a distance measuring means for measuring the distance to the target object from the time from when the excitation signal is emitted until the received signal is obtained; and a distance measuring means for measuring the distance to the target object only when the received signal has a certain relationship with the excitation signal. An ultrasonic distance measuring device comprising a control means for operating a measuring means.