JPS5928273B2 - distance measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device that uses sinusoidally modulated light to measure the distance to a stationary or moving object.

A conventional device that transmits and receives sinusoidal modulated light and determines the distance to an object that reflects the transmitted modulated light from the phase difference θ between the signals has a configuration as shown in the block diagram of FIG.

In other words, the configuration of the optical system consists of one beam splitter 1
The light-emitting element 2 and the light-receiving element 3 are arranged orthogonal to each other with the center at or reflected by a moving reflective object 5,
The light returns to the beam splitter 1 again, the optical path is changed by the beam splitter 1, and the light is received by the light receiving element 3.

In order to determine the phase difference between the transmitted and received signals with this device, the phase of the signal received from the light receiving element 3 is measured using the phase measuring device 6, using the signal phase from the oscillator 4 as a reference. Signal phase fluctuations such as phase drift occur in the drive circuit γ in the transmitting section and in the amplifier 8, waveform conversion circuit 9, etc. in the receiving section, resulting in high measurement accuracy.

In order to eliminate these drawbacks, the present invention provides a reflecting mirror facing the light-receiving element, and combines the reflected signal light from a stationary or moving reflecting object with a part of the transmitted signal light. The object of the present invention is to provide a distance measuring device that measures the distance to a reflecting object with high precision using the relationship between the modulation frequency and the amplitude change of the synthesized received signal light obtained by sweeping the cass modulation frequency. .

FIGS. 2 and 3 are conceptual diagrams explaining the invention in detail.

FIG. 2 shows a basic configuration diagram of the optical system, in which a light emitting element 2, a light receiving element 3, a stationary or moving reflecting object 5, and a reflecting mirror 10 are arranged at 90 degrees from each other with the beam splitter 1 at the center. The positional relationship forms an angle of °,
A combined signal light consisting of the reflected signal light from the reflecting object 5 and the reference signal light obtained by reflecting a part of the transmitted signal light emitted from the emitting element 2 by the reflecting mirror 10 enters the light receiving element 3. .

FIG. 3a shows the vector change with respect to the modulation frequency change of the composite signal light when the reflecting object is stationary. The amplitude Rs of the received signal light moves on the circumference α in the figure as the modulation frequency changes.

Figure 3 shows the relationship between the change in modulation frequency and the change in amplitude Ps.The change in waveform is sinusoidal, and the maximum and minimum values of the amplitude are respectively at point A in Figure 3a. , corresponds to point B.

The modulation frequency difference △f that gives such a change in A-B is:
It becomes like the first equation.

That is, it can be seen that the distance to the stationary reflecting object can be found from the maximum and minimum values of the amplitude change of the combined received signal light from equation (1).

Note that C is the speed of light.

In the above, we have explained the case where the reflecting object is stationary, but even in the case of a moving reflecting object, the maximum time change in the moving distance of the reflecting object is about Oms, whereas the sweep time of the modulation frequency is can be 100 μs at most, and as shown in FIG. 4, the time change in the distance is gradual compared to the sweep time ΔT, so the distance can be considered to be constant within one frequency sweep time.

Figure 4a shows the time change of the distance, and the two arbitrary points P and Q are enlarged to show the time change of the distance, the time change of the sweep of the modulation frequency f, and the reception width Rs. Figures 4b and 4c show the relationship with time changes.

At this time, the reception double width R changes due to the sweep of the modulation frequency.
Difference in frequencies △f1p△f that gives the maximum and minimum values of s
2, the instantaneous distance L1.2 to the moving reflecting object can be obtained from equation (1). L2 can be obtained respectively.

FIG. 5 is a block diagram showing an embodiment of the present invention based on the above measurement principle.

In FIG. 5, numerals 1 to 10 are the same as those in FIGS. 1 and 2, and a drive circuit 7 is used to modulate the light emitting element 2 in proportion to the signal from the frequency sweep oscillator 11 to emit modulated light.

At that time, the combined signal light of the reflected signal light from the stationary or moving reflecting object 5 and the reference signal light reflected by the reflecting mirror 10 is received by the light receiving element 3, amplified by the amplifier 8, and then transmitted to the detector 12. Detect.

Thereafter, the detected signal is input to the limiter amplifier 13 and then to the gate circuit 14.

The gate circuit 14 generates an ON/OFF switching signal for the maximum/minimum value of the amplitude change of the received signal as the modulation frequency is swept, and the frequency meter 15 measures the modulation frequency at the time of ON/OFF switching. Read it with

At this time, the frequency sweep oscillator 11 is automatically repeatedly swept, and the ON signal output from the gate circuit 14 is
After storing the modulation frequencies read by the frequency meter 15 in the respective temporary registers based on the OFF switching signal,
The distance to the reflective object 5 is automatically displayed on the display circuit 17 by the arithmetic circuit 16 which determines the frequency difference between the two and calculates the distance using equation (1).

In addition, in this invention, since the light intensity of the combined received signal differs when the distance to the reflecting object differs, the maximum value of the reception width,
Although the minimum value changes relatively, the relationship between the modulation frequencies that give the maximum and minimum amplitude does not change and there is no problem.

Further, if the reflectance of the reflective object changes while it is moving, a measurement error will occur, but this error can be compensated for by repeatedly performing sweeps.

As described above, according to the present invention, it is only necessary to sweep the frequency of the modulated light emitted from the light emitting element and find the difference in the modulation frequency that gives the maximum and minimum values of the received amplitude change at that time, and the device is simple. Moreover, it operates stably.

Further, according to the present invention, since phase fluctuations occurring in the electronic circuit portion can be removed, measurement accuracy can be increased.

Although the device according to the present invention has been described above with reference to the case where it is stationary, it goes without saying that the present invention is not limited to this and can be applied to cases where the device according to the present invention is mounted on a moving body to measure distance. stomach.

As described above, in the distance measuring device according to the present invention, the combined signal light of the reflected signal light from a stationary or moving reflecting object and the reference signal light extracted from a part of the transmitted signal light is combined into one signal light.
The optical system is configured to receive light with individual light receiving elements, and the method measures the amplitude change of the composite signal light caused by sweeping the modulation frequency.
It is possible to provide a means for measuring distance simply and inexpensively, which has a simple configuration both optically and electronically, and has high measurement accuracy.

[Brief explanation of drawings]

Figure 1 is a block diagram of a conventional device that measures distance from the phase difference of sinusoidally modulated light, Figure 2 is a basic configuration diagram of an optical system according to the present invention, and Figure 3a is a change in modulation frequency of combined received signal light. Figure 3b is a characteristic diagram showing the relationship between reception double width and modulation frequency, Figure 4a is a conceptual diagram showing changes in distance over time, and Figures 4b and 4c are vector diagrams at points P and 9, respectively. FIG. 5 is an enlarged view showing the relationship between the time change of distance, the time change of frequency sweep, and the time change of reception amplitude. FIG. 2 is a light emitting element, 3
is a light receiving element, 4 is an oscillator, 5 is a stationary or moving reflective object, 6 is a phase measuring device, 7 is a drive circuit, 8 is an amplifier, 9 is a waveform conversion circuit, 10 is a reflecting mirror, 11 is a frequency sweep Oscillator, 12 is a detector, 13 is a limiter amplifier, 14
is a gate circuit, 15 is a frequency meter, 16 is an arithmetic circuit, 17
is a display circuit. In addition, the same reference numerals are attached to the same or similar parts in the figures.

Claims (1)

[Claims] 1. Emits the modulated light toward a stationary or moving object,
In a measuring device that measures the distance to the object based on the positional difference between the signal light reflected from the object and the transmitted signal light, the light emitting element emits the transmitted signal light based on the modulated signal generated by the frequency sweep oscillator; A reflecting mirror that reflects a part of the transmitted signal light emitted from the emitting element as a reference signal light and makes it enter the light receiving element, and a light receiving element that combines the reflected signal light from the object and the reference signal light and receives the light is a beam splitter. an optical system configured such that the reflecting mirror and the light-receiving element are opposed to each other with the center at the center, and the light-emitting element is perpendicular to the reflecting mirror and the light-receiving element, and the frequency of the modulation signal supplied to the light-emitting element is swept. A frequency sweep oscillator, a frequency meter that detects the modulation frequency difference corresponding to one cycle of the amplitude change of the composite received signal obtained by photo-electrical conversion with the photodetector, and a frequency sweep oscillator that detects the modulation frequency difference detected by the frequency meter to the object. What is claimed is: 1. A distance measuring device comprising: a signal processing system comprising an arithmetic circuit that converts into a distance; and a display circuit that displays an output from the arithmetic circuit.