JPS6117081A - Ultrasonic sensor - Google Patents

Abstract

PURPOSE:To enable the detection of distance to an object with an ultrasonic sensor, by moving an ultrasonic vibrator at a uniform speed in the direction of transmitting or receiving waves to differentiate the transmission frequency from the oscillation frequency equivalently. CONSTITUTION:An FSK modulation cycle setting section 14 corrects the FSK cycle Ta corresponding to a measuring distance to calculate the residual epsilon between the measuring distance and the FSK cycle based on the output of a phase comparator 10 and performs an adjustment to keep the epsilon below a specified value so that the output of a repetitive FSK demodulating section 9 may remain H continuously. By so doing, the distance to an object corresponding to the FSK cycle Ta reduces gradually to the H level. At this point, the position of an object to be detected is obtained by zero method mode and a signal of the distance to the object with an absolute value output signal convertor section 17. If so, the output of the absolute value output signal convertor section 17 gives the distance to the object as it is unless the object moves. An ultrasonic vibrator is moved at a uniform speed in the direction of transmitting and receiving waves to differentiate the transmission frequency from the oscillation frequency equivalently thereby enabling the detection of distance to an object.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an ultrasonic sensor that transmits ultrasonic waves to an object and detects the distance to the object based on the time it takes to obtain a reflected signal.

Prior art and its problems In the case of a CW type ultrasonic sensor, it is difficult to detect a stationary object using one ultrasonic transducer element. According to the pulse drive method that drives the ultrasonic transducer periodically, the sensing response time is limited by the pulse period, making it impossible to detect objects near the sensor, and requiring a gate circuit to extract the received signal. There is a problem in that the process becomes complicated and automatic measurement becomes difficult. In addition, by providing a constant frequency diaphragm on the object to be detected as a reflector, it is possible to transmit and receive waves using a single ultrasonic transducer element using the CW method. Since power supply is required, the structure becomes complicated and there is a problem in that it cannot be easily detected. Furthermore, as a means to realize a sensor using a single transmitting and receiving oscillator using the CW method, we have developed a technology widely known as a radio wave altitude needle for instrument navigation in the field of wireless measurement (Yoshimura and Fujimori, Keigaku Publishing, ``Radar Optics''). A conceivable method is to drive an ultrasonic transducer with an FM signal whose frequency changes continuously, and to determine the propagation time based on the beat frequency that is the difference from the frequency component of the delivered signal.

However, resonant electrostrictive transducers are widely used as ultrasonic transducers, but these transducers cannot convert broadband signals and are not applicable to such FM-type ultrasonic sensors. The problem was that it could not be done.

The purpose of the invention has been made in view of the problems of ultrasonic sensors as described above.The invention is based on the above-mentioned problem of ultrasonic sensors. An object of the present invention is to provide an ultrasonic sensor that can detect the distance to an object.

Structure and Effects of the Invention The present invention is an ultrasonic sensor that sends ultrasonic waves to an object and detects the distance to the object. A drive signal generator with an output, an actuator that holds an ultrasonic vibrator and is driven by the output of the drive signal generator to perform constant reciprocating motion along the wave transmission direction of the ultrasonic vibrator, and generates ultrasonic waves at a constant frequency. An ultrasonic oscillator that drives a transducer, a difference frequency signal detection means that extracts a signal of a difference between the transmitting and receiving frequencies based on a reflected signal from a detected object obtained by the ultrasonic transducer, and reciprocating motion of an actuator. and a phase difference detection means for comparing the phase of the transmitted and received wave difference signal obtained by the difference frequency signal detection means, and configured to detect the position of the object by the output of the phase difference detection means. It is something to do.

According to the present invention having such characteristics, since the ultrasonic transducer itself is vibrated at a constant velocity in the wave transmission direction and its frequency is changed by the Doppler effect, it is possible to use a resonant ultrasonic transducer. Ultrasonic waves with a frequency different from the frequency of the vibrator can be transmitted. Furthermore, it is possible to easily extract the Doppler frequency band of the received signal and provide an ultrasonic sensor with a high S/N ratio. In addition, it is possible to detect the absolute position of an object using the zero position method mode, and by setting the period for vibrating the ultrasonic transducer back and forth according to the distance to the object position, the output from the phase comparison circuit can be detected. can be maintained at a predetermined value, and the object position can be easily detected by extracting the displacement from that position as a phase difference. Therefore, it is possible to provide an easy-to-use ultrasonic sensor that is integrated with a control system such as a robot arm.

Description of the embodiment [Configuration of the embodiment] Fig. 1 shows an embodiment of the ultrasonic sensor according to the present invention fj11.
FIG. In this figure, ultrasonic oscillator 1
is an oscillator that oscillates an ultrasonic signal with a constant frequency fo, and its oscillation output is given to the directional coupler 2. The directional coupler 2 is composed of a three-winding transformer or an electronic circuit having the function thereof, and when it transmits an ultrasonic signal to the ultrasonic transducer 3, it transmits a reflected wave signal to another output end. The ultrasonic transducer 3 transmits and receives ultrasonic waves, and is driven by an actuator 4 at a constant speed back and forth in the wave transmission direction.

This actuator 4 is driven by a triangular wave drive signal from a triangular wave generator 5. The received signal obtained by the ultrasonic transducer 3 is then given to the mixer 6 via the directional coupler 2. The mixing B6 is formed by a nonlinear circuit and generates a signal containing a frequency that is the difference between the transmitting and receiving frequencies, and uses a multiplier, a balanced demodulator, and the like. The output of the mixer 6 is given to a band pass filter 7 which extracts a signal of the difference between the transmitting and receiving frequencies, and the output of the band pass filter 7 is given to an amplitude limiting section 8. The amplitude limiter 8 removes noise caused by the influence of wind, etc. by limiting an input signal having an amplitude greater than a predetermined width to a predetermined width, and its output is F
The signal is given to the SX demodulator 9. The FSK demodulator 9 obtains a binary signal whose potential changes depending on the frequency of the received signal, and its output is given to the phase comparator 10. The phase comparator 10 compares the phase of the frequency change of the transmitted ultrasonic signal with the phase of the received ultrasonic signal, and its output is sent to the signal converter 11, correction amount detector 12, and mode switching control. Section 13. The signal conversion unit 11 converts a signal into a distance signal in accordance with a given phase amount, and outputs the distance signal as a displacement amount. The correction amount detection section 12 determines the correction amount for making the phase difference 0 based on the phase difference signal, and provides its output to the frequency variable control section 15. The mode switching control section 13 also sets initial conditions, determines conditions regarding mode switching control between zero mode and displacement mode, which will be described later, and maintains internal state after state transition.

Now, the period corresponding to the detection distance to the detected object is set by the FSK modulation period setting section 14. The cycle may be set by receiving a signal from a manual setting switch or another automatic control system formed integrally with this ultrasonic sensor. Then, this signal with the set period is given to the frequency variable control section 15, and the actuator 4
The frequency for driving the silkworm is determined, and its output is given to the variable frequency oscillator 16 to form a driving frequency signal. For example, when the variable frequency oscillator 1G is a V/F converter, the variable frequency controller 15 generates a voltage corresponding to the frequency, and when the variable frequency oscillator 16 is a counting type circuit, the variable frequency controller 15 generates a voltage corresponding to the frequency. It shall be converted into a hexadecimal code.

The output of the variable frequency oscillator is the triangular generator 5 mentioned above.
The actuator 4 is driven by the triangular wave signal. Now, the oscillation output of the variable frequency oscillator 16 is also given to the phase comparator 1o and the absolute value signal output converter 17 at the same time. The absolute value conversion signal output section 17 outputs an absolute value output signal and a data valid signal after the variable frequency control has converged, and the signals correspond to the distance to the object. Reference numeral 18 denotes a test signal generator that sends out a pseudo reflected wave when there is no object to be detected or when the ultrasonic transducer 3 is separated to test the circuits of each part of the ultrasonic sensor.

As shown in FIG. 2, the actuator 4 has a horn 2o for adjusting the spreading direction of the ultrasonic beam and a yoke 21 formed inside the horn 2o, and a permanent magnet 22 is formed at the center thereof. A cylindrical cup 23 is provided on the outer periphery of the permanent magnet 22, and a coil 24 is further formed on the outer periphery of the permanent magnet 22. A spring 25 is provided integrally with the cup 23, and a spring 25 is provided at the opening of the horn 20 in the direction of the arrow A. An electromagnet part is formed to be able to vibrate freely. At the center of the spring 25 is an ultrasonic transducer 3 that sends ultrasonic signals in the direction of arrow A.
is retained. By using the actuator 4 thus formed, by driving the coil 24 with a predetermined signal, the spring 25 integrated with the coil 24 can be vibrated by a predetermined interval in the axial direction.

[Operation of the embodiment]

Next, the operation of this embodiment will be explained with reference to waveform diagrams. FIG. 3 is a waveform diagram showing waveforms of each part of the block diagram of FIG. 1. First, it is assumed that a period corresponding to the detection distance to the detected object is set in the FSK modulation processing setting section 14 from the outside. Then, the setting signal is transmitted to the variable frequency control section 15, and the oscillation frequency of the variable frequency oscillation section 16 is determined.

FIG. 3(a) shows the output of the variable frequency oscillator 16, which is given to the triangular wave generator 5 and converted into a triangular wave signal. Then, as shown in FIG. 2, the coil 24 of the actuator 4 is driven by the triangular wave signal shown in FIG. Here, the ultrasonic oscillator 1 has a frequency f as described above.
O's electric signal is oscillated, but since the ultrasonic vibrator 3 itself that converts this signal into an ultrasonic wave vibrates back and forth, the third
As shown in FIG. fe), the frequency of the ultrasonic signal transmitted from the ultrasonic transducer 3 to the front of the horn 20 fluctuates due to the Doppler effect. That is, when the ultrasonic transducer 3 is displaced at a constant speed V in the direction of the arrow as shown in FIG. 3 (cl), if the Doppler shift frequency is fm, then fm=V/
c (c: speed of sound in the medium). Therefore, when moving forward in the direction of arrow A, the transmission frequency is fo + f
m, and when retreating, fo - fm. If such a signal is transmitted toward the object to be detected, the ultrasonic wave will travel back and forth to the object after the propagation time Td (=2D/c, D: object distance) and the ultrasonic transducer 3 will receive ) The received signal is obtained as shown in (). Then, by receiving this received signal using the same ultrasonic transducer 3 and converting it into an electric signal, a step-like transfer signal is obtained as shown in FIG. 3 (el). The frequency of the signal is the third
The transmitting and receiving frequencies in Figure (C1, (d) cancel each other out, and as shown in the figure, the frequencies fo+2fm, fo, f
This results in a signal having a frequency that fluctuates between o -2fm. When this signal is given to the mixer 6, the frequencies fO and f
o + '2 fm.

A signal with a difference of fo 2fm is obtained, and its output is passed through a bandpass filter 7 and an amplitude limiter 8' to F'S
The signal is given to the K demodulator 9. Therefore, the FSK demodulator 9 generates a square wave signal that goes to "L" level during the time period when the frequencies of the transmitted and received waves are equal, and goes to "H" level during the time period when the frequencies of the transmitted and received waves are different, as shown in FIG. 3+ri. This will be obtained. The phase comparator 10 is connected to the F
'The phases of the output of the SK demodulator 9 and the oscillation output of the variable frequency oscillator 16 are compared, and an output based on the phase difference is provided to the signal converter 11. Therefore, by converting the phase difference by the signal converter 11, the position output of the object can be obtained.

Among the modes switched by the mode switching control unit 13, the displacement method mode detects the displacement of an object from a predetermined position by the above-described operation, but the zero-position method mode detects the displacement of an object from a predetermined position by further varying the frequency at which the actuator is driven. The distance to the fixed position is detected. That is, the output of the phase comparator 10 is given to the correction amount detection section 12, and the FSK cycle Ta is changed so that the output of the FSK demodulation section 9 shown in FIG. When the driving FSX period Ta and the round trip propagation time Td have the following relationship - Td = nTa (n = 1.2.----), the Doppler deviation amount 4; L2fm and -2fm
Transition the value of. FS due to the correction by the correction amount detection unit 12
If the K period Ta becomes an integral multiple of Td, there will be no phase difference, so the output of the FSiK recovery section 9 will always be at the "H" level.
The distance to the object can be obtained based on the oscillation frequency of the variable frequency oscillator 16. It is assumed that the distance to the object is limited in advance to a predetermined range so that n becomes 1.

Then, by giving the output of the variable frequency oscillation section 16 to the absolute value output signal converting section 17, it is possible to obtain an absolute value signal of the distance to the object.

[Operation of the embodiment in conjunction with the control system]

Next, using the flowchart of FIG. 4 and the time chart showing the movement of an object in FIG. 5, the operation when controlling the zero position mode and the displacement mode in series will be explained. When the operation starts after time to, first, in step 30 of this flowchart, the system waits for a localization signal indicating that the detected object exists at a fixed position from an automatic control system or the like outside the system. If this signal is given to the FSX modulation cycle setting unit 14 at time t1, the process proceeds to step 31, where the FSK modulation cycle setting unit 14 sets the FSX cycle Ta for the maximum detection distance. First, the absolute position of the object is determined using the zero position method mode.

That is, in step 32, the FSK period Ta is corrected in accordance with the measured distance, and in step 33, the residual ε between the measured distance and the FSK period is calculated based on the output of the phase comparator 10, and the residual ε is calculated. It is checked in step 34 whether or not the value is less than a predetermined value. If this exceeds the predetermined value, return to step 32 and repeat the same process to adjust so that the transmitting and receiving frequencies are always different, that is, the output of the FSK demodulator 9 is continuously at the "H" level. conduct. Then, the distance to the object corresponding to the FSX period Ta gradually decreases as shown by the broken line N in FIG. 5(a). Step 32 to step 3 in current drug t2
4, the position of the object to be detected is obtained by the zero-order method mode, and as shown in FIG.
s is obtained. Then, if the object does not move, the output of the absolute value output signal converter 17 will directly become the distance to the object.

Next, if the localization signal stops at time t3 as shown in FIG. Move to law mote.

In this mode, first in step 37 the FSK period T
The displacement is determined by comparing the phases of a and the signal obtained from the FSK demodulator 9. Then, in step 38, it is checked whether there is a displacement output, and if there is a displacement output, the signal converter 11 transfers the proportional control output signal to the automatic control system.

Assuming that the object to be detected moves as shown by the solid line M from time t4 in the time chart for object movement in FIG. 5(a), the output of the FSK demodulator 9 is " The signal is not an H'' level DC component, but a signal with a different duty ratio depending on the amount of movement of the object.

Therefore, the phase difference is given to the signal converter 11 by the phase comparator 10, and the signal converter 11 outputs an output corresponding to the phase difference to follow the displacement of the object as shown in FIG. It becomes possible to provide a proportional control output. Then, between time t5 and t6, the object returns to its original position and the displacement signal becomes zero, so the signal converter 1
1, the displacement output is not output, but after time t6 and time t7
Since there is a displacement output up to this point, a proportional control signal is given to the control system from the signal converter 11 as shown in step 39.

In addition, although this example shows a driving mechanism of an ultrasonic vibrator similar to the voice coil of a speaker as an actuator,
For example, a nearmorph may be used as long as it is configured to reciprocate at a constant speed, and an ultrasonic transducer can be installed at the tip of the robot arm to drive the robot arm at a constant speed. The distance to the object may also be detected.

In addition, a reflector plate is provided in front of the farthest end of the ultrasonic sensor according to this embodiment, and by operating the cycle setting corresponding to that position as a test mode, the sensor can be adjusted by appropriately switching during operation, and furthermore, the sound velocity can be adjusted. It is also conceivable to perform correction according to the following.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the ultrasonic sensor according to the present invention, Fig. 2 is a sectional view showing the structure of an actuator that vibrates the ultrasonic transducer, and Fig. 3 is a waveform of each part of this embodiment. 4 is a flowchart showing the procedure for operating this ultrasonic sensor in successive zero position mode and displacement method mode, and 5 is a time chart showing the movement of the object and the corresponding signal. It is a chart. 1------1 ultrasonic oscillator 2-----unidirectional coupler 3------1 ultrasonic vibrator 4--=-actuator 5-----triangle wave generator 6.-----1 -Mixer 7---Band pass filter 8---One amplitude limiter 9-・-FS' and demodulator 10---
--- Phase comparator 11 --- Signal converter
12-----Correction amount detection section 13・-・--・-・
Mode switching control section 14-----FSK modulation period setting section 15-------1 Frequency variable control section 16------1 Variable frequency oscillation section 1, 7-1-- ---・Absolute value output signal conversion section 18・----
-・Test signal generator patent applicant Tateishi Electric Co., Ltd. agent Patent attorney Yoshiki Okamoto (1 person) Figure 1

Claims (6)

[Claims] (1) An ultrasonic transducer that converts an electric signal and an ultrasonic wave, a drive signal generator that outputs a signal at a constant frequency, and an ultrasonic transducer that holds the ultrasonic transducer and is driven by the output of the drive signal generator. an actuator that performs uniform reciprocating motion along the transmission direction of the ultrasonic transducer; an ultrasonic oscillator that drives the ultrasonic transducer at a constant frequency; difference frequency signal detection means for extracting a signal of a frequency difference between the transmission and reception frequencies based on the reflected signal; and comparing the phase of the reciprocating motion of the actuator with the phase of the transmission and reception difference signal obtained by the difference frequency signal detection means. An ultrasonic sensor comprising: phase difference detection means, and configured to detect the position of an object based on the output of the phase difference detection means. (2) The actuator has a coil driven by the drive signal generator, and a spring connected to the coil to vibrate and hold the ultrasonic transducer. The ultrasonic sensor according to item 1. (3) The ultrasonic sensor according to claim 1, wherein the drive signal generator is an oscillator that oscillates a triangular wave. (4) The drive signal generator is a variable frequency oscillator, and includes phase control means for controlling the oscillation frequency of the drive oscillator so that the phase difference between the output of the phase comparator and the drive oscillator is always constant. The ultrasonic sensor according to claim 1, characterized in that: (5) The drive signal generator is a variable frequency oscillator, and the oscillation frequency of the variable frequency oscillator is predetermined so that the phase difference of the phase comparison difference detection means is zero, and the oscillation frequency of the variable frequency oscillator is determined in advance so that the phase difference of the phase comparison difference detection means is zero, and the oscillation frequency of the variable frequency oscillator is set in advance. 2. The ultrasonic sensor according to claim 1, wherein the amount of displacement of an object is detected by the phase difference detection means. (6) A patent claim characterized in that the drive signal generator is set so that the period of uniform reciprocating motion is twice the sound wave propagation time corresponding to the distance to the object to be measured, and the phase difference is zero. The ultrasonic sensor according to item 5.