JPH0578766B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a distance detection device, and more particularly, to a distance detection device using a light beam projection method that applies the principle of triangulation in an automatic focusing device for a camera. .

[Prior Art] Conventionally, various distance detection devices using a light beam projection method have been proposed, which measure a distance by projecting pulsed light onto a subject and receiving the reflected light at a light-receiving element that is separated by a baseline length from a light-emitting element. However, a major technical problem that must be solved when this distance detection device is put into practical use is the problem of processing noise generated from fluorescent lights and the like. This is due to the pulsating light component caused by fluorescent lights, etc.
This is because there is not a large difference in the frequencies of the signal components caused by the pulsed light, and it is difficult to detect only the signal components caused by the pulsed light. As a conventional example of solving this problem, a distance detection device disclosed in Japanese Patent Application Laid-Open No. 14906/1980 detects the point in time when the rate of change of pulsating light becomes the minimum, and emits pulsed light in response to this detection signal. How to project is shown.

[Problems to be Solved by the Invention] By the way, this distance detection device has a plurality of light receiving element groups and is configured such that reflected light from an object at a specific distance is mainly input to a specific light receiving element. Distance information can be obtained by detecting the light receiving element on which the reflected light is incident. In this case, as shown in FIG. 10, the value obtained by photoelectrically converting the output of the light receiving element when pulsed light is projected is the sum of the peak values of the pulsed light component P and the pulsating light component R, or the pulsed light component P Since the peak value of the pulsating light component R is subtracted from , distance information can be obtained by detecting a light receiving element whose voltage exceeds the determination voltage.

On the other hand, the distance detection device uses a semiconductor position detection element (hereinafter referred to as PSD) as a light receiving element.
Some distance detection devices obtain distance information by calculating and processing the output signal corresponding to the position of the incident spot light of this PSD.In such distance detection devices, the pulsed light component detected by the PSD Although the size of the pulsed light component corresponds to the distance to the subject, it is clear from the conventional example mentioned above that the size of the pulsed light component itself is determined (output of pulsating light + output of pulsed light component). Therefore, it was difficult.

The present invention has been made with attention to such problems, and even if external light contains pulsating light components, it is possible to easily separate and extract only the signal components caused by pulsed light that are related to distance information, and accurately. An object of the present invention is to provide a distance detection device capable of detecting distance.

[Means and effects for solving the problem] As shown in FIG. is received by the light receiving means 3, and the first and second signals corresponding to the distance to the subject 1 are outputted from the light receiving means 3 to the first signal change detection circuit 4 and the second signal, respectively. The signal is sent to the change detection circuit 5. These first and second signal change detection circuits 4 and 5
Under normal conditions, the first and second signals are shifted in phase by approximately 90 degrees with respect to the pulsating light frequency based on the commercial frequency, and when projecting pulsed light, the phase shift is almost eliminated, or when receiving light in normal conditions. It has a function of holding the output of the means 3. The output of the first signal change detection circuit 4 is compared with the reference voltage V _ref in the comparing means 6, and when the two match, the pulsed light projecting means 2 is controlled to emit pulsed light by the output of the comparing means 6. At the same time, the outputs of the first and second signal change detection circuits 4 and 5 are led to a distance calculation means 7, where a distance information signal is detected.

[Example] FIG. 2 is a schematic diagram for explaining the principle of triangulation applied to the distance detection device of the present invention, in which light is emitted by an infrared light emitting diode 11 and projected from a projection lens 12. When the pulsed light is irradiated onto the subject 1, it is reflected by the subject 1, and an image is formed on the PSD 14 by the imaging lens 13 located at a distance from the light emitting diode 11 by the base line length S.
The image formation position on the PSD 14 has a correlation with the position of the subject 1 based on the principle of triangulation. As is well known, a PSD uses the same principle as a photodiode and can determine the incident position of light by extracting the photocurrent generated by the photoelectric effect of a PN junction from both ends of the same layer through a uniform resistance layer. By calculating the ratio of the photocurrents i ₁ and i ₂ at both ends, the imaging position of the reflected light can be determined. That is, as shown in Figures 2 and 3, the PSD14
Regarding the above imaging position, if x is the distance from the center that coincides with the optical axis of the imaging lens 13, then this distance x is determined by the base length s, the distance l to the subject 1, and the imaging lens 13. It is expressed by the distance f between the PSD 14 and the PSD 14, and x=s·f/l (1). In addition, the reference voltage V _ref is connected to the center terminal 14a ₀ .
The PSD 14 to which is applied has both terminals 14a ₁ and 14a ₂
In response to the reception of the pulsed light, photocurrent changes i ₁ and i 2 flow respectively, and these photocurrent changes i ₁ and _{i 2 flow} across both terminals 14 of the PSD 14 .
The distance t between a ₁ and 14a ₂ and the distance x have the following relationship.

i ₁ :i ₂ =(t/2+x):(t/2-x)...(2) Therefore, by calculating i ₁ /i ₂ in the distance measurement calculation circuit 15, this i ₁ /i ₂ From equations (1) and (2) above, is the position of subject 1, that is, the distance l to subject 1.
If the amount of movement of the photographic lens (not shown) of the camera is controlled by the output of the distance measurement calculation circuit 15, an automatic focus adjustment device can be realized.

FIG. 4 is an electrical circuit diagram of a distance detection device showing one embodiment of the present invention. In FIG. 4, the infrared light emitting diode 11 is connected to a timing generation circuit 21.
It is connected to the. The timing generation circuit 21 is a distance measurement start signal generation switch 2 such as a release switch.
2 is turned on, by a pulse from the pulse generation circuit 23 or by the distance measurement start signal generation switch 2.
The light emitting diode 11 is made to emit light after a certain period of time from the time when the light emitting diode 2 is turned on. Provided at a position apart from the light emitting diode 11 by a baseline length.
On the output side of the PSD 14, first and second photoelectric conversion circuits 24 and 25, which are first and second signal change detection circuits 4 and 5 (see FIG. 1), are provided.
In the first photoelectric conversion circuit 24, the inverting input terminal of the operational amplifier 27 is connected to the center terminal 14a ₀ of the PSD 14 and also connected to the terminal 28 to which the reference voltage V _ref is applied, and the non-inverting input terminal is connected to the PSD 1
4 is connected to one input terminal 14a _{1 of}
It is connected to the collector of the NPN transistor 29. The base of transistor 29 is operational amplifier 2
7 and the base of the NPN transistor 30. The emitters of transistors 29 and 30 are grounded. transistor 30
The collectors of the transistors 31 and 32 are connected to the bases of the PNP transistors 31 and 32 and the collectors of the transistor 31, and the emitters of the transistors 31 and 32 are connected to the power supply voltage +V terminal. transistor 3
The collector of No. 2 is connected to the non-inverting input terminal of the operational amplifier 33, and the inverting input terminal of the operational amplifier 33 is connected to the reference voltage terminal 28. operational amplifier 3
The output terminal of 3 is connected via an analog switch 34 controlled by the timing generation circuit 21.
It is connected to the base of the NPN transistor 35. The collector of this transistor 35 is connected to the collector of the transistor 32, and its emitter is grounded. A capacitor 36 for external light storage is connected between the base and emitter of this transistor 35, and a capacitor 36 for external light storage is connected between the collector and emitter.
Logarithmic compression diodes 37 and 38 are connected in series in the forward direction. The second photoelectric conversion circuit 25 also has the same circuit configuration as the first photoelectric conversion circuit 24 with respect to the other terminal _14a2 of the PSD 14, so illustration thereof is omitted.

The output terminal 24A of the first photoelectric conversion circuit 24 on the anode side of the logarithmic compression diode 37 is connected to the non-inverting input terminal of the comparator 40, and the inverting input terminal of the comparator 40 is connected to the reference voltage terminal 28. This comparator 40 sends a drive output to the pulse generation circuit 23 when the voltage at the output terminal 24A of the first photoelectric conversion circuit 24 matches the reference voltage _Vref . The output terminal 24A of the first photoelectric conversion circuit 24 is connected to the inverting input terminal of the operational amplifier 45 via the resistor 41, and the output terminal 25A of the second photoelectric conversion circuit 25 is connected to the non-inverting input terminal of the operational amplifier 45 via the resistor 44. connected to the end. A resistor 42 is connected between the inverting input terminal and the output terminal of the operational amplifier 45.
A resistor 43 is connected between the non-inverting input terminal of the operational amplifier 45 and the reference voltage terminal 28. These resistors 41 to 44 and operational amplifier 45
constitutes a differential amplification circuit which is the distance calculation means 7 (see FIG. 1), and is configured to produce an output difference between the two photoelectric conversion circuits 24 and 25 at its output terminal 46.

Next, the operation of the distance detecting device will be explained. Even in a state where pulsed light is not projected, the PSD 14 receives external light, and in response to this external light, the terminals 14a ₁ ,
A photocurrent i flows through _14a2 . photoelectric conversion circuit 24,
25 are similar, so if we consider the photoelectric conversion circuit 24 now, when a photocurrent i flows to the collector of the transistor 29, the same current i flows to the collector of the transistor 30, and furthermore, when the photocurrent i flows to the collector of the transistor 30,
Since transistors 1 and 32 form a current mirror circuit, current i also flows through the collector of transistor 32.

In a normal state in which pulsed light is not projected, the analog switch 34 is on, and therefore operates so that the potential at the non-inverting input terminal and the potential at the inverting input terminal of the operational amplifier 33 become the same potential. In other words,
It operates so that the potential of the output terminal 24A of the photoelectric conversion circuit 24 substantially matches the reference voltage _Vref . At this time, the impedance of the compression diodes 37 and 38 is set to be sufficiently larger than the collector-emitter impedance of the transistor 35 so that the collector current of the transistor 32 flows almost directly to the transistor 35. Therefore, PSD1
Even if the value of the photocurrent i of 4 changes greatly due to external light, the photocurrent i flows between the collector and emitter of the transistor 35, and the potential of the output terminal 24A of the photoelectric conversion circuit 24 is approximately equal to the reference voltage V _ref keep it. Similarly, the output terminal 25A of the second photoelectric conversion circuit 25 also becomes approximately the reference voltage V _ref . For this reason, operational amplifier 4
The potential at the output terminal 46 of the differential amplifier circuit including V.sub.5 approximately matches the reference voltage _V.sub.ref .

Next, when distance measurement is performed by projecting pulsed light, when the distance measurement start signal generation switch 22 is turned on, the timing generation circuit 21 causes the light emitting diode 11 to emit light after a certain period of time, and the infrared pulsed light is emitted from the object. is projected towards. At this time, simultaneously with the projection of the pulsed light, the timing generation circuit 21
The analog switch 34 is turned off. Therefore, the voltage between the base and emitter of the transistor 35 becomes the voltage held in the capacitor 36 immediately before the pulsed light is projected, and as a result, the voltage between the base and the emitter of the transistor 35 becomes
The collector current of No. 5 is the current i immediately before the pulsed light is projected.
to be held temporarily.

The pulsed light reflected by the object is received by the PSD 14. If the change in the photocurrent of the PSD 14 after receiving the pulsed light is i ₁ , then the transistor 32
A current i+i ₁ flows through the collector of the transistor 35 , but only the above current i flows through the collector of the transistor 35 , so the difference current i ₁ flows through the logarithmic compression diodes 37 and 38 and is output to the output terminal of the photoelectric conversion circuit 24 . A voltage corresponding to the change is generated at 24A.
This voltage value is approximately kT/ql _o i ₁ (q: electron charge, k: Boltzmann's constant, T: absolute temperature). Similarly, when the PSD 14 receives the pulsed light, the second
The change in the photocurrent flowing into the photoelectric conversion circuit 25 of
When i ₂ , a voltage of kT/ql _o i ₂ is generated at the output terminal 25A of the photoelectric conversion circuit 25. Therefore, the output terminal 46 of the operational amplifier 45 of the differential amplifier circuit has (V _ref +
A voltage of kT/ql _o i ₁ /i ₂ ) is generated, and this change kT/ql _o
i ₁ /i ₂ becomes distance information.

Here, in the case where the background light includes a pulsating light component with a frequency twice the commercial frequency, such as from a fluorescent lamp, the operational amplifier 33, the capacitor 36, and the transistor 35 form a kind of high-pass filter. The cut-off frequency is set to be a value sufficiently higher than the frequency of the pulsating light component, and it acts as a differentiating circuit for the pulsating light component. Therefore, in the state where the analog switch 34 is on before projecting the pulsed light, the photocurrent waveform _R1 of the PSD 14 shown in FIG. 5A is as follows.
The voltage waveform at the output terminal 24A of the photoelectric conversion circuit 24 is the photocurrent waveform of the PSD 14, as shown in FIG. 5B.
A waveform R ₂ is obtained by differentiating R ₁ , and a sine waveform based on the reference voltage V _ref is obtained. When the comparator 40 detects a point where the output of the photoelectric conversion circuit 24 crosses the reference voltage V _ref , the pulse generation circuit 23 sends a pulse to the timing circuit 21 . If the ranging start signal generating switch 22 is turned on at this time, the timing generating circuit 21 causes the light emitting diode 11 to emit light upon receiving a pulse from the pulse generating circuit 23, thereby projecting pulsed light. Since the analog switch 34 is turned off at the same time as this pulsed light is projected, the operational amplifier 33, the capacitor 36 and the transistor 3
The circuit consisting of 5 does not form a high pass filter,
The capacitor 36 holds the output of the operational amplifier 33 immediately before the analog switch 34 is turned off, and sets the voltage at the output terminal 24A to the reference voltage _Vref . Then, when the pulsed light is received by the PSD 14, a change in photocurrent due to the reception of this pulsed light flows through the compression diodes 37 and 38, so that the voltage waveform at the output terminal 24A of the first photoelectric conversion circuit 24 is The pulse waveform P ₀ is as shown by the dotted line in Figure 5B. The pulse waveform P ₀ shown by this dotted line is the change i ₁ in the collector current of the transistor 32 due to the reception of pulsed light.
This is the waveform of the voltage kT/ql _o i ₁ corresponding to . The timing of this pulse waveform P ₀ is the time when the change in the waveform R ₁ of the pulsating light is the least, and the time when the output end 24A has almost reached the reference voltage V _ref .
Further, the output terminal 25 of the second photoelectric conversion circuit 25
Also in A, the voltage kT/ql _o i ₂ due to the reception of the pulsed light is obtained when the differential waveform due to the pulsating light reaches the reference voltage V _ref . Therefore, even if pulsating light is included as background light when projecting pulsed light, the output terminal 46 of the differential amplifier circuit always receives voltage waveforms from the received pulsed light based on the reference voltage V _ref . The distance information voltage (kT/ql _o i ₁ /i ₂ ) can be obtained without being affected by pulsating light.

FIG. 6 is an electrical circuit diagram of a distance detection device showing another embodiment of the present invention. In the distance detecting device shown in FIG. 6, the first and second photoelectric conversion circuits 5
4 and 55 are constructed as follows. In the first photoelectric conversion circuit 54, the inverting input terminal is connected to one terminal of the PSD 14, and the non-inverting input terminal is connected to the reference voltage terminal 28 together with the center terminal of the PSD 14, and the inverting input terminal and output of the same operational amplifier 56 are connected. A resistor 57 connected between the ends forms a current-to-voltage conversion circuit to convert the photocurrent of the PSD 14 into voltage, and a capacitor 58 connected to the output end of the operational amplifier 56 and the other end of this capacitor 58 and the reference. Two resistors 59 and 60 connected in parallel with the voltage terminal 28 form a high-pass filter. An analog switch 61 controlled by the timing generation circuit 21 is connected in series with the resistor 59, and when the analog switch 61 is on, the high-pass filter has the characteristics shown by the solid line in FIG. analog switch 6
1 is off, the high-pass filter has the characteristics shown by the dotted line in FIG. An operational amplifier 62 whose non-inverting input terminal is connected to one end of the resistor 60, and an inverting input terminal of this operational amplifier 62 and a reference voltage terminal 2.
8. Resistors 63 and 64 connected to the inverting input terminal and output terminal, respectively, form a non-inverting amplifier circuit, and the voltage - connected to the output terminal of the operational amplifier 62 is
A current conversion resistor 65, an operational amplifier 66 whose inverting input terminal is connected to the resistor 65, and whose non-inverting input terminal is connected to the reference voltage terminal 28, and this operational amplifier 66.
A logarithmic conversion circuit is formed by logarithmic compression diodes 67 and 68 connected in series between the inverting input terminal and the output terminal of the . The output terminal of this logarithmic conversion circuit is connected as the output terminal 54A of the first photoelectric conversion circuit 54 to the non-inverting input terminal of the comparator 40 as in the previous embodiment, and is also connected to the resistor 41 of the differential amplifier circuit. ing. Second photoelectric conversion circuit 55
also has the same configuration as the first photoelectric conversion circuit 54, and its output terminal 55A is connected to the resistor 44 of the differential amplifier circuit.
It is connected to the.

To explain the operation of this distance detection device, PSD
The photocurrent detected by 14 is detected by operational amplifier 56.
However, since the analog switch 61 is on before the pulsed light is projected, the capacitor 58 and the resistor 5
The high pass filter consisting of 9 and 60 has a characteristic, and its cutoff frequency c is determined so that its CR time constant falls within a region that has a differential effect on the frequency of the pulsating light. Therefore, in this case as well, when there is a pulsating light component in the background light, this pulsating light is differentiated to obtain a voltage waveform with a 90° phase shift at the output terminal 54A, and this voltage matches the reference voltage _Vref . At this time, pulsed light is projected by the light emitting diode 11, and in synchronization with this, the analog switch 61 is turned off. At this time, the high-pass filter switches to a characteristic determined by the CR time constant of the capacitor 58 and resistor 60, so the cutoff frequency 'c at this time shifts to a lower frequency side than the frequency of the pulsating light. Therefore, the voltage change due to the reception of the pulsed light passes through the high-pass filter consisting of the capacitor 58 and the resistor 60 without causing a phase shift, and the output terminal 54A is outputted as shown in FIG. A voltage waveform is obtained. Similarly to the embodiment, the voltage at the output terminal 54A and the output terminal 55A of the second photoelectric conversion circuit 55 are
The voltage of resistors 41 to 44 and operational amplifier 45
A distance information voltage is obtained at the output terminal 46 of the differential amplifier circuit.

In addition, in the above embodiment apparatus, the case where a so-called PSD was used as the light receiving means 3 (see Fig. 1) was explained, but it is not limited to such a so-called PSD, for example, as shown in Figs. like 2
Similarly, when SPDs (silicon photodiodes) are arranged, it can be used as a semiconductor position detection element. The position detection element 60 shown in FIG. 8 is formed by abutting two triangular SPDs 61 and 62, and when the subject is ∞ and the light receiving spot is in the center, the terminals 61a of both SPDs 61 and 62,
The photocurrent flowing through the terminal 62a becomes i ₁ =i ₂ , and when the subject is close and the light receiving spot moves to the terminal 61 a, i ₁ >i ₂ . Further, the position detection element 70 shown in FIG. 9 has a triangular SPD 71 and a rectangular SPD 71.
When the subject is close and the light receiving spot is on the side of terminals 71a and 72a, both photocurrents are i ₁ = i ₂ , and when the subject is ∞ and the light receiving spot is located in the center, i ₁ = i ₂ /2.

[Effects of the Invention] As described above, according to the present invention, even if the external light includes pulsating light from a fluorescent lamp or the like, only the signal component caused by the pulsed light that is related to distance information can be reliably and easily separated and extracted. Thus, a distance information signal with less error can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the basic configuration of the distance detecting device of the present invention, FIG. 2 is a schematic diagram for explaining the principle of triangulation applied to the distance detecting device of the present invention, and FIG. The figure is a schematic side view for explaining an example of a semiconductor position detecting element that can be used in the device of the present invention, FIG. 4 is an electric circuit diagram of a distance detecting device showing an embodiment of the present invention, and FIG. A and B are
FIG. 6 is a signal waveform diagram for explaining the operation of the device shown in FIG. 4, FIG. 6 is an electric circuit diagram of a distance detecting device showing another embodiment of the present invention, and FIG.
8 and 9 are plan views showing other examples of semiconductor position detection elements that can be used in the device of the present invention,
FIG. 10 is a signal waveform diagram for explaining the operation of a conventional distance detection device. 1... Subject, 2... Pulse light projection means, 3...
...light receiving means, 4...first signal change detection circuit,
5... Second signal change detection circuit, 6... Comparison means, 7... Distance calculation means, 11... Infrared light emitting diode (pulsed light projection means), 14... PSD
(semiconductor position detection element, light receiving means), 21...timing generation circuit (pulsed light projection means), 24, 5
4...First photoelectric conversion circuit (first signal change detection circuit), 25, 55...Second photoelectric conversion circuit (second signal change detection circuit), 40...Comparator (comparison means) , 41 to 44... Resistor (distance calculation means), 45... Operational amplifier (distance calculation means),
60, 70... semiconductor position detection element (light receiving means),
61, 62, 71, 72...SPD.

Claims (1)

[Scope of Claims] 1. Pulsed light projection means for projecting pulsed light toward a subject; first and second means for receiving reflected light from the subject onto which the pulsed light is projected, and corresponding to the distance to the subject. a light-receiving means for outputting a signal; and a cut-off frequency is higher than that of a pulsating light frequency such as a fluorescent lamp, and before the pulsed light is projected, the cut-off frequency acts as a differentiating circuit for the input signal, and the pulsed light is projected. At the same time, first and second signal change detection circuits include a high-pass filter whose cutoff frequency is lower than the pulsating light frequency, and detect changes in the first and second signals when the pulsed light is projected. , a comparison means that generates a signal when the output of the first signal change detection circuit matches a predetermined reference voltage and controls the pulsed light projection means; and the first and second signal change detection circuits. A distance detection device comprising: distance calculation means for calculating the distance to a subject based on the output of the circuit and outputting a distance signal. 2 The high-pass filter in the first and second signal change detection circuits are transistors for passing currents according to the first and second signals output from the light receiving means before the pulsed light is projected. , comprising a negative feedback circuit provided with a capacitor for storing the level of the current, and a switching element for cutting off the negative feedback path of the negative feedback circuit. Distance detection device according to item 1. 3. The high-pass filter in the first and second signal change detection circuits includes a capacitor, first and second resistors connected in parallel to the capacitor,
The distance detecting device according to claim 1, further comprising a switching element connected to the first resistor.