JPH02184788A - Range-finding sensor - Google Patents

Abstract

PURPOSE:To accomplish stable range-finding by switching a 1st optical path that light from a light emitting part is reflected by a reflecting body and made incident on a light receiving part and a 2nd optical path that the light from the light emitting part is directly made incident on the light receiving part time sequentially and obtaining a phase difference. CONSTITUTION:An optical path switching mirror 31 disposed in front of the light emitting part 1 is controlled to be turned under the control of a timing circuit 6. By setting the mirror 31 in a direction A nearly in parallel with the light from the light emitting part 1, the light from the light emitting part 1 is projected to the reflecting object 8 and the reflected light therefrom passes through a half mirror 32 and is made incident on the light receiving part 2, thereby obtaining the 1st optical path. By setting the mirror 31 in a direction B at the angle of about 45 deg., the light from the light emitting part 1 is reflected by the mirror 31 and made incident on the light receiving part 2 by reflecting all the light as reference light without projecting the light to the outside, thereby obtaining the 2nd optical path. The range- finding light and the reference light are thus received in the same light receiving part 2 time sequentially. An output from the circuit 6 is inputted in a distance arithmetic operation part 5, which discriminates whether the output from a phase comparison part 4 is caused by the range-finding light or by the reference light and outputs the range-finding signal in accordance with the difference of the output from the comparison part 4.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a light receiving means for receiving reflected light from a detected object of a light beam projected from a light projecting means onto a detection area;
The present invention relates to a distance measuring sensor that measures the distance to a detected object within a detection area based on the output of a light receiving means.

[Prior Art] FIG. 5 is a block diagram showing a conventional example of this type of distance measuring sensor. The output light from the light emitting unit 1 is intensity-modulated at a frequency of 10, and the light emitted from the light emitting unit 1 is illuminated by a reflecting object 8 using a light projection optical system. Emits light to. Then, the reflected light from the reflective object 8 is made incident on the light receiving section 2a by the light receiving optical system.

At this time, as shown in FIG. 6, there is a difference between the reference light waveform emitted from the light emitter 1 and the ranging light waveform received by the light receiver 2a, depending on the distance l to the reflecting object 8. , resulting in a phase shift θd. Expressing this relationship as a formula, It-cθd/4 yr to (m)
-■ However, 1: Distance to the reflecting object [Zeng] C: Speed of light (+e/5ec) If the phase difference θd (set) is measured, the distance l to the reflecting object can be determined. In the configuration shown in FIG. 5, in order to correct phase fluctuations due to changes in the light emitting part 1, the light receiving part 2, and the circuit system over time and changes in temperature and humidity, a part of the light from the light emitting part 1 is transferred to a half mirror 32, 33 to the light receiving section 2b, and signal processing is performed using the same circuit system as the light receiving circuit system for the ranging light, that is, by comparing the relative phases of the reference light and the ranging light, It is configured to cancel absolute phase fluctuations in the light emitting section 1, the light receiving section 2a, and the circuit system.

On the other hand, the modulation frequency f0 is greatly influenced by the ranging resolution. Now, in order to achieve the distance measurement resolution Δl1=10 (n+m) at the phase resolution Δθd=2π/1000, from the formula ■, r o =CΔθd/4πΔl...■To
= 15 (MHz). In order to accurately perform phase comparison of such high frequencies, in the configuration shown in FIG. It is mixed with the local oscillation frequency, converted to a lower frequency by frequency conversion, and then phase comparison is performed. Then, the result of the phase comparison by the phase comparator 4 is integrated by an integrator 7 with a predetermined time constant, and a voltage corresponding to the distance l is output.

[Problems to be Solved by the Invention] As mentioned above, in conventional distance measuring sensors, in order to avoid canceling the absolute phase fluctuations of the light emitting part, the light receiving part, and the circuit system,
A light receiving circuit system for the reference light system is provided.

The light receiving circuit system of the reference light system is the same circuit composed of the same circuit elements as the light receiving circuit system of the ranging light system, and ideally it is expected to produce exactly the same absolute phase fluctuation. It is. However, in reality, there are various variations due to variations in individual circuit elements, circuit wiring, arrangement, etc., and there is a problem in that relative phase errors occur due to these variations.

The present invention has been made in view of these points, and its purpose is to eliminate variations in the absolute phase fluctuation characteristics of individual circuit elements and circuit blocks.
The object of the present invention is to provide a distance measurement sensor capable of stable distance measurement.

[Means for Solving the Problems] In the present invention, in order to solve the above problems, the first
As shown in the figure, a first optical path in which light from the light emitting unit 1 is reflected by a reflective object 8 and incident on the light receiving unit 2;
an optical path switching device 3 for time-sequential switching between a second optical path and a second optical path for directing the light from the light source to the light receiving section 2; and a phase comparator section for determining the phase difference between the light emission phase of the light emitting section 1 and the light reception phase of the light receiving section 2. 4, and a distance calculation section 5 that generates a distance signal according to the difference in the output of the phase comparison section 4 when selecting the first optical path and when selecting the second optical path. .

In addition to the mirror 31 as shown in FIG. 1, the optical path switch 3 may include an optical shutter 34 as shown in FIG.
35, an optical scanner 37 as shown in FIG. 4, etc. can be used.

[Function] In the present invention, as described above, the optical path switcher 3 allows the light from the light emitting unit 1 to be reflected by the reflective object 8 and enters the light receiving unit 2, and the first optical path to reflect the light from the light emitting unit 1. light receiving section 2
Since the second optical path that is directly incident on the sensor is switched in time series, it is possible to eliminate variations in the light receiving circuit system for the distance measuring light and the light receiving circuit system for the reference light, making it possible to perform stable distance measurement. It is what it is.

[Embodiment 1] FIG. 1 is a block diagram of a first embodiment of the present invention. A light emitting unit 1 is composed of a light emitting element such as a light emitting diode or a semiconductor laser, and the light emitting unit 1 is composed of a light emitting element such as a light emitting diode or a semiconductor laser. generates an optical signal.

The oscillator 12 oscillates the modulation frequency 10 of the optical signal output from the light emitting unit 1 and supplies it to the light emitting circuit 11, and also supplies the mixer 22 with a local oscillation frequency (“.-fc”) of 0 local oscillation frequency. (f·-re) is a signal whose frequency is slightly different from the modulation frequency f0, and re<fo.

The light receiving section 1 is composed of a light receiving element such as a silicon photodiode, and generates a photocurrent depending on the intensity of the received optical signal. The light receiving circuit 21 includes a current-voltage conversion circuit, and converts the photocurrent obtained by the light receiving section 1 into a voltage signal. The output of the light receiving circuit 21 is converted to a local oscillation frequency (f
--re), converted into a low frequency beat signal, and inputted to the phase comparison section 4. Compare the phase difference with the low frequency beat signal.

In this embodiment, an optical path switching mirror 31 is arranged in front of the light emitting section 1 as an optical path switching device 3.

The optical path switching mirror 31 is rotationally controlled under the control of the timing circuit 6. When the optical path switching mirror 31 is set in a direction A that is substantially parallel to the light from the light emitting section 1, the light from the light emitting section 1 is projected onto the reflecting object 8.

The reflected light from the reflective object 8 passes through the half mirror 32 and enters the light receiving section 2 . Furthermore, when the optical path switching mirror 31 is set in direction B at approximately 45 degrees with respect to the light from the light emitting section 1, the light from the light emitting section 1 is reflected by the optical path switching mirror 31, and then reflected by the half mirror 32. It is reflected again and the light receiving part 2
incident on . In this way, in the distance measuring sensor of this embodiment, the light from the light emitting unit 1 is directly projected onto the reflecting object 8, and
Select a first optical path in which the reflected light is received by the light receiving unit 2, and a second optical path in which the light from the light emitting unit 1 is reflected as reference light and directly received by the light receiving unit 2 without emitting the light to the outside. can do. This allows the same light receiving section 2 to receive the ranging light and the reference light in time series. The output rK of the timing circuit 6 is also input to the distance calculation section 5, and the distance calculation section 5 can distinguish whether the output of the phase comparison section 4 is from the distance measurement light or the reference light. Phase comparison unit 4 when receiving distance measuring light and when receiving reference light
A distance signal is output according to the difference between the outputs. With this configuration, the light receiving section and the light receiving circuit, which conventionally required two systems, can be integrated into one system, and it is possible to avoid ranging errors due to variations in absolute phase fluctuation characteristics. .

Next, signal processing of the ranging light and the reference light that are incident in time series will be explained using FIG. 2. No.

Figure 2(a) shows the phase ratio axis output of the phase comparison section 4, the distance signal output from the distance calculation section 5, and the output r of the timing circuit 6, and a part of it is shown with the time axis expanded. The output rK of the timing circuit 6 that controls the optical path switching mirror 31 shown in FIG. 2(b) becomes "Hi+th" level at a certain period, as shown in FIG. 2(b), and at this time, The optical path switching mirror 31 is switched to select the second optical path, and the reference light is introduced into the light receiving section 2. On the other hand, the phase comparator 4 uses the light reception signal obtained from the mixer 22 and the low frequency signal fc from the oscillator 12.
The phase difference between the two is constantly compared and output. Optical path switching mirror 3
1 is the voltage when the first optical path is selected, the voltage when the distance measuring light is incident is Vc, and the voltage when the second optical path is selected, that is, when the reference light is incident, is Vc. voltage to Vr
Then, these outputs are input to the distance calculation unit 5 in time series. The distance calculation section 6 takes in the voltage Vc and the voltage Vr by sampling the output of the phase comparison section 4 in synchronization with the signal "K" from the timing circuit 6, and calculates the distance signal Vj!=Vc-Vr as the difference between them. This distance signal Vl is obtained by constantly measuring and storing the absolute phase fluctuations of individual circuit elements and circuit blocks, and then correcting the measured value, as shown in Figure 2 (a). Even when there is a phase fluctuation as shown, the distance signal V1
gives a stable output.

Note that the output voltage Vr of the phase comparator 4 when receiving the reference light is:
Since the output rK from the timing circuit 6 is updated sequentially every cycle, it is necessary to set the cycle of the output f of the timing circuit 6 to be sufficiently small for phase fluctuations as shown in FIG. 2(a). It goes without saying that there is.

[Embodiment 2] FIG. 3 is a block diagram of a second embodiment of the present invention. In this embodiment, a half mirror 3 is used as the optical path switch 3.
2, 33 and shutters 34 and 35 are used. As the shutters 34 and 35, optical shutters that can block or transmit light by applying a voltage are used. 1st
The second shutter 34 is arranged in the optical path of the reference light, and the second shutter 35 is arranged in the optical path of the ranging light. The output f from the timing circuit 6 is applied to the first shutter 34 and also to the second shutter 35 via the inverter 36. As a result, one shutter moves in the opposite direction to the other shutter, and the distance measuring light and the reference light can be alternately guided to the light receiving section 2 in a time-series manner.

The operating waveform diagram of this embodiment is the same as that shown in FIG.
The light receiving circuit system is integrated into one system, and even if absolute phase fluctuation occurs in each circuit element or circuit block, it becomes possible to correct the error.

Note that if an optical shutter without mechanical operation, such as a liquid crystal shutter, is used, high-speed operation is possible and the ability to correct phase errors is further improved.

[Embodiment 3] FIG. 4 is a block diagram of a third embodiment of the present invention. In this embodiment, an optical scanner 3 is used as the optical path switch 3.
7 is used. The optical scanner 37 scans the projected beam under the control of the drive circuits i and II, and is capable of measuring the distance and direction to a reflecting object. Then, one end of the optical fiber 39 for receiving the reference light is arranged in the direction of a certain scanning angle, and the other end of the optical fiber 39 is arranged facing the light receiving section 2 . At the scanning angle at which the projected beam enters the optical fiber 39, the projected beam does not become a distance measuring light;
The structure is such that all or part of the light is guided to the light receiving section 2 as a reference light. The timing circuit 6 is connected to the drive circuit 38, and determines the timing at which the optical scanner 37 is scanned at a scanning angle such that light enters the optical fiber 39, and sets the output r to the "High" level at that timing. do.

This allows the optical scanner '37 to be used as the optical path switch 3.

In this embodiment, since the optical scanner 37 used for scanning the distance measuring light is also used as the optical path switch 3 for obtaining the reference light, the number of parts is significantly larger than in other embodiments. This can be expected to reduce costs, making it possible to reduce costs.

[Effects of the Invention] As described above, in the present invention, since the reference light and the ranging light are guided to the same light receiving section in time series by the optical path switch, the light receiving circuit system for the ranging light is It is possible to eliminate variations in the light receiving circuit system of the reference light and the reference light, thereby enabling stable distance measurement and improving the distance measurement accuracy. Furthermore, since the light receiving section and the light receiving circuit are integrated into one system, it is possible to significantly reduce the number of parts and reduce costs. In particular, in the invention set forth in claim 4, since the existing scanning optical system is also used as an optical path switch, there is no need to add new parts, and there is an advantage that the optical system can be configured simply and at low cost.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a first embodiment of the present invention, FIG. 2 is an operation waveform diagram of the same as above, FIG. 3 is a block diagram of a second embodiment of the present invention, and FIG. 4 is a block diagram of a third embodiment of the present invention. FIG. 5 is a block diagram of the embodiment, FIG. 5 is a block diagram of the conventional example, and FIG. 6 is an operation waveform diagram of the same. 1 is a light emitting section, 2 is a light receiving section, 3 is an optical path switch, 4 is a phase comparison section, and 5 is a distance calculation section.

Claims (4)

[Claims] (1) Time-sequential switching between a first optical path in which the light from the light emitting section is reflected by a reflective object and incident on the light receiving section, and a second optical path in which the light from the light emitting section is directly incident on the light receiving section. an optical path switch; a phase comparator for determining the phase difference between the light emission phase of the light emitting section and the light reception phase of the light receiving section;
and a distance calculation section that generates a distance signal according to the output difference of the phase comparison section when selecting an optical path. (2) The distance measuring sensor according to claim 1, wherein the optical path switch is a means for switching the optical path using a reflector. (3) The distance measuring sensor according to claim 1, wherein the optical path switch is a means for switching the optical path using a shutter. (4) The distance measuring sensor according to claim 1, wherein the optical path switch is a means for switching the optical path using a scanning optical system that scans the light from the light emitting section onto a reflective object.