JPH0578767B2 - - 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 light projection type distance detection device using a semiconductor position detection element.

[Prior Art] A light projection type that measures a distance by projecting pulsed light onto a subject and receiving the reflected light from the subject by a light receiving section placed a predetermined baseline length away from the projecting section. Various distance measurement methods have been proposed.

The method is as follows: (1) Multiple light-receiving elements are provided in the light-receiving section, the structure is configured so that the reflected light from a subject at a specific distance enters only the specific light-receiving element, and the light-receiving element on which the reflected light enters is detected. (2) Semiconductor position detection device (hereinafter referred to as PSD)
There is a system in which a light-receiving element that outputs a signal corresponding to the position of the incident spot light is placed in the light-receiving section, and the output signal is calculated and processed to obtain distance information.

[Problems to be solved by the invention] Examples of the problems mentioned in (1) above include, for example,
As disclosed in Publication No. 29110, it is necessary to connect a detection circuit that detects the change in photocurrent due to pulsed light to each of the multiple light receiving elements, making it difficult to match these detection circuits. In addition, since the light receiving section is quantized, there is a drawback that the division of distance to the subject is limited.

Furthermore, the method shown in (2) above has the disadvantage that the means for obtaining distance information is the absolute amount of change due to pulsed light, and the detection accuracy is low due to the large influence of circuit noise.

[Means and operations for solving the problem] As shown in FIG. 1, this distance detecting device continuously projects pulsed light from a pulsed light projecting means 1A toward a subject 3A. By receiving the pulsed light reflected by the light receiving means 5A, the object 3 is detected as an output of the light receiving means 5A.
The first and second electric signals corresponding to the distance to A are first and second integrating means 101 and 10, respectively.
Send to 3.

The output of the first integrating means 101 is held by the holding means 102 after a predetermined time T has elapsed, and then supplied to one input terminal of the comparing means. On the other hand, the output of the second integrating means 103 is immediately supplied to the other input terminal of the comparing means, and this comparing means compares the magnitude of the two outputs.

If these two outputs become equal at time t from the start of integration, then this time t becomes
The magnitude of the first and second electrical signals and the predetermined time T
Moreover, this time t has a value corresponding to the distance to the subject.

On the other hand, if the amount of movement of the photographic lens corresponding to this time t is set in advance and the lens is moved according to the actually measured time t, an autofocus device can be obtained.

[Example] FIG. 2 is a schematic diagram for explaining the principle of triangulation applied to the distance detecting device of the present invention, in which an infrared light emitting diode 1 emits pulsed light and a projection lens 2 When the pulsed light projected by the object 3 is irradiated onto the object 3, it is reflected by the object 3,
An image is formed on a semiconductor position detection element (hereinafter referred to as PSD) 5 by an imaging lens 4 located at a position apart from the light emitting diode 1 by a base line length S. The image position on the PSD 5 has a correlation with the position of the subject 3 based on the principle of triangulation.

Here, the above-mentioned PSD 5 uses the same principle as a photodiode, as is well-known, and extracts the photocurrent generated by the photoelectric effect of the PN junction from both ends of the resistive layer through a uniform resistive layer, thereby adjusting the incident position of the light. 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 FIGS. 2 and 3, regarding the image formation position on the PSD 5,
If x is the distance from the center of the imaging lens 4 that coincides with the optical axis, then this distance x is determined by the base length S, the distance l to the subject 3, and the imaging lens 4.
The distance f between the PSDs 5 is expressed as in the following equation (1).

x=S・f/l...(1) Also, from both terminals 5a ₁ and 5a ₂ of the PSD 5, changes in photocurrent i ₁ and
i ₂ is starting to flow out, and further common terminal 5
A current of (i ₁ + i ₂ ) flows from a ₃ . The changes in photocurrent i ₁ and i ₂ are
The distance d between the terminals 5a ₁ and 5a ₂ of the PSD 5 and the distance x have the following relationship.

i ₁ :i ₂ =(d/2+x):(d/2-x)...(2) When this equation (2) is transformed, it becomes the following equation.

x=d/2(i ₁ −i ₂ )/i ₁ +i ₂ ...(3) Equation (4) is derived from equations (1) and (3).

i ₁ /i ₁ +i ₂ =Sf/ld+1/2 ...(4) As is clear from equation (4), S, f, and d are all known values, so i ₁ /(i ₁ +i ₂ ) The signal changes depending on the distance l to the object. That is, this i ₁ /(i ₁ +i ₂ ) signal indicates the position of the subject, and an autofocus device is realized by controlling the amount of movement of the photographing lens based on the output of this signal.

FIG. 4 is an electrical circuit diagram of a distance detection device showing one embodiment of the present invention.

As shown in FIG. 4, an infrared light emitting diode 1
Its cathode is grounded, and its anode is connected to the collector of a PNP switching transistor 46 and to the inverting input terminal of an operational amplifier 45. A reference voltage Vref2 is connected to a non-inverting input terminal of the operational amplifier 45, and an output terminal of the operational amplifier 45 is connected to the base of the transistor 46. The emitter of the transistor 46 is connected to a terminal that supplies an operating voltage. The output of the oscillation circuit 44 is frequency-divided by the frequency dividing circuit 43, and this frequency-divided pulse is applied to the control terminal of the operational amplifier 45. That is, the transistor 46 is turned on and off in response to this frequency-divided pulse, and in response, pulsed projection light is projected from the infrared light emitting diode 1 onto the subject.

PSD that receives the reflected light from the above light emitting diode 1
The first output end 5a ₁ and the third output end 5a ₃ of 5 are as follows:
They are connected to the inverting input terminals of head amplifiers 6 and 22 that convert the photocurrent of the PSD into voltage, respectively, and
The head amplifiers 6 and 22 are connected to their respective output terminals via feedback resistors 7 and 21, respectively. The second output terminal 5a ₂ of the above PSD 5 is the reference voltage
It is connected to the terminal that supplies Vref, and also to the non-inverting input terminals of the head amplifiers 6 and 22, and also to the non-inverting input terminals of the operational amplifiers 15 and 30, the resistors 9 and 24, and the resistor 10. 25 at one end of each.

The output ends of the head amplifiers 6 and 22 are connected to the resistors 9 and 24 via capacitors 8 and 23, respectively.
and the respective non-inverting input terminals of operational amplifiers 12 and 27 forming a non-inverting amplifier circuit. The inverting input ends of these operational amplifiers 12 and 27 are connected to the other ends of the resistors 10 and 25, respectively, and are also connected to their output ends via resistors 11 and 26, respectively.

The output ends of the operational amplifiers 12 and 27 are connected to the input ends of the analog switches 16 and 32, respectively, and the resistors 13 and 28 are connected to the input ends of the analog switches 16 and 32, respectively.
are connected to the inverting input terminals of the operational amplifiers 15 and 30, respectively. The above operational amplifier 1
The respective inverting input terminals of 5 and 30 are connected to a resistor 14, respectively.
and 29 to their own output terminals, and are also connected to the input terminals of the analog switches 17 and 31, respectively. Opamps 15 and 3 above
0 means that the gain is limited to "-1" by resistors 13 and 14 and 28 and 29, respectively.

The respective output terminals of the analog switches 16 and 32 are connected to the inverting input terminals of the operational amplifiers 20 and 35, respectively, via terminals 48 and 49 and resistors 18 and 33, respectively. are connected to their respective output ends.
The inverting input terminals of the operational amplifiers 20 and 35 are
They are connected to their own output terminals via capacitors 19 and 34, respectively, and further connected to an inverting input terminal and a non-inverting input terminal of a comparator 36, respectively. Here, the operational amplifiers 20 and 35 form an integrating circuit by a resistor 18 and a capacitor 19, and a resistor 33 and a capacitor 34, respectively. The non-inverting input terminals of these operational amplifiers 20 and 35 are connected to the reference voltage Vref.

The output terminal of the comparator 36 is connected to the counter 4
The counter 41 is connected to a terminal for stopping the count of 1, and the counter 41 is activated to stop the count at the rising edge of the output of the comparator 36. The first output terminal 4 of this counter 41
7 is connected to the first input terminals of AND gates 39 and 40, and this first output terminal 47
counts the output pulses of the frequency dividing circuit 43, and changes from H level to L level after a predetermined time.

The second output terminal of the counter 41 is connected to the input terminal of an encoder 42 that divides the time from the start of counting of the counter 41 until the counting stops when the comparator 36 rises and outputs the divided time into several regions. has been done. Further, the second input terminal of this counter 41 is connected to the frequency dividing circuit 4.
The inverter 38 is connected to the output end of the inverter 38
It is connected to the second input terminal of the AND gate 39 via. The output terminal of this AND gate 39 is connected to the control terminal of the analog switch 31. Furthermore, the output terminal of the frequency divider circuit 43 is connected to the second input terminal of the AND gate 40 and also to the control terminal of the analog switch 17, and is also connected to the control terminal of the analog switch 16 via the inverter 37. connected to the terminal. The output terminals of the AND gates 39 and 40 are connected to analog switches 31 and 3, respectively.
It is connected to the control terminal of 2.

Next, the operation of this embodiment will be explained.

In the initial state, the oscillation circuit 44, the frequency dividing circuit 43, the counter 41, and the encoder 42 are reset, the capacitors 19 and 34 are discharged by an analog switch (not shown), and the outputs of the operational amplifiers 20 and 35 are It has the same potential as the reference voltage Vref. In this state, when a distance measurement start signal (not shown) is input by shutter release, etc., all resets are canceled and
The discharge analog switches for the capacitors 19 and 34 are also turned off.

At the same time, the pulsed light from the infrared light emitting diode 1 starts to be emitted in synchronization with the output pulse of the frequency dividing circuit 43, and the PSD photocurrent due to the reflected light from the subject is transmitted from the terminal 5a ₁ as a current i ₁ and from the terminal 5a ₃ . are supplied as currents (i ₁ +i ₂ ) to head amplifiers 6 and 22, respectively, and are converted into voltages by these head amplifiers 6 and 22 and output as voltage signals. Each voltage signal is passed through a high-pass filter (each capacitor 8
(composed of a resistor 9, a capacitor 23, and a resistor 24), and is amplified by operational amplifiers 12 and 27, which are non-inverting amplifiers. These op amps 1
The outputs of 2 and 27 are V ₁ = A(i ₁ ) and V ₂ = A
It is expressed as (i ₁ +i ₂ ) (A is a constant), and the output waveform is as shown in FIG. 5A. Here, when the infrared light emitting diode 1 is turned on, it is the (-) side, and when it is turned off, it is the (+) side. Also, as mentioned above, the gains of operational amplifiers 15 and 30 are "-1", so
The output waveforms of these operational amplifiers 15 and 30 are inverted waveforms of the waveforms shown in FIG. 5A (see FIG. 5B).

The analog switch 16 is controlled to be conductive when the light emitting diode 1 is turned on, and the analog switch 17 is controlled to be conductive when the light is turned off (see FIG. 5C and D). The voltage waveform is synchronously detected and becomes a signal waveform only on the (-) side with respect to Vref, as shown in FIG. 5E. A similar voltage waveform is obtained at the terminal 49, but since this signal system obtains the photocurrent of the PSD 5 from the common electrode _5a3 , the output of the operational amplifier 27 is out of phase with respect to the output of the operational amplifier 12. is shifted by 180 degrees. Therefore, the analog switch 32 is controlled to be conductive when the light emitting diode 1 is turned off, and the analog switch 31 is controlled to be conductive when the light emitting diode 1 is turned on, so that a signal in phase with the output signal at the terminal 48 is obtained. It is configured.

The signals obtained at terminals 48 and 49 are connected to resistor 18
and 33, the capacitors 19 and 34 are charged, and the operational amplifier 20
The outputs of and 35 increase monotonically as shown in FIG. 5F. Note that the output of the operational amplifier 20 is current i ₁
Therefore, the slope becomes gentle as shown by the symbol 20A, and the output of the operational amplifier 35 becomes the current (i ₁ + i ₂ ).
Therefore, it is charged quickly and the slope becomes steeper as shown by 35A.

On the other hand, the counter 41 is connected to the infrared light emitting diode 1.
After counting a predetermined number of pulses T from the start of light emission, the output level of the first output terminal 47 of the counter 41 is set to become an L level signal. Switches 31 and 32 are turned off and charging of capacitor 34 is stopped. Therefore, the output of the operational amplifier 35 is held after the predetermined pulse T. This situation is shown in FIGS. 6A to 6D. Here, the symbols V _A and V _B represent the operational amplifier 35, respectively.
and 20, FIG. 6B shows the output pulse of the frequency dividing circuit 43, and FIG. 6C shows the output voltage of the output terminal 4.
7, and FIG. 6D shows the output waveform of the comparator 36.

As shown in FIG. 6B, when light emission from the infrared light emitting diode 1 starts in synchronization with the output of the frequency dividing circuit 43, both V _A and V _B begin to increase. On the other hand, when the counter 41 counts the output pulses of the frequency dividing circuit 43 by a predetermined number T, the counter 41
Since the output signal of the output terminal 47 changes from the H level to the L level (see FIG. 6C), the analog switches 31 and 32 are both turned off, and charging of the capacitor 34 is stopped. Therefore, the increase in the voltage of V _A also stops, and V _A maintains its previous state. After that, the output voltage of operational amplifier 20
V _B continues to increase as integration continues,
When the potential becomes the same as V _A , the output of the comparator 36 changes from L level to H level (see FIG. 6D). Then, the counter 41 latches the pulse number t of the frequency dividing circuit 43 at the time of this change from L to H, and latches the pulse number t latched to the encoder 42.
Output.

Here, since the above output voltage V _A = V _B ,
The charge caused by the current (i ₁ +i ₂ ) flowing into the capacitor 34 by the number of pulses T (proportional to time) is equal to the charge caused by the current i ₁ flowing into the capacitor 19 by the number t of pulses. That is, the following equation is obtained.

T(i ₁ +i ₂ )=ti ₁ If this is transformed, it becomes the following equation.

t=(i ₁ +i ₂ )·T/i ₁ (5) On the other hand, if we take the reciprocal of the equation (4) above, we get the following equation.

i ₁ +i ₂ /i ₁ =1/Sf/ld+1/2...(6) Substituting equation (6) into equation (5) yields the following equation.

t=1/Sf/ld+1/2·T (7) As is clear from equation (7), the number of pulses t corresponds to the distance l to the subject.

The encoder 42 divides the number of pulses t into a plurality of predetermined steps according to the distance to the object, and outputs a signal corresponding to each step. For example, if the boundary values of each step are T ₁ , T ₂ , ..., T _o , then t is T<t<T ₁
"1" is output when T ₁ < t < T ₂ , "n" is output when T _o-1 < t < T _o , and each "1" to An autofocus device can be obtained by providing a lens control device that controls the movement of the photographic lens at a position corresponding to "n".

In addition, in the above embodiments, as the light receiving means
We explained the case using PSD, but this
Not limited to PSD, for example, Fig. 7 A, B, Fig. 8 A,
A case where two SPDs (silicon photodiodes) are arranged as shown in B can also be used as a position detection element.

The position detection element 60 shown in FIGS. 7A and 7B consists of two SPDs 61 whose light receiving surfaces have the same triangular shape,
62 so that their slopes face each other. When the subject is infinite (∞) and the light receiving spot is at the center of the light receiving surface, both
The photocurrent flowing through the terminals 61a and 62a of the SPDs 61 and 62 becomes i ₁ =i ₂ , and when the subject is close and the light receiving spot moves toward the terminal 61a, i ₁ >i ₂ . A common electrode 63 is provided on the bottom surface, and a photocurrent (i ₁ +i ₂ ) flows from this electrode 63.

The position detection element 70 shown in FIG.
A common electrode 73 is placed on the bottom of the SPD72.
When the subject is close and the light receiving spot is on the side of terminals 71a and 72a, both photocurrents become i ₁ = i ₂ , and when the subject is ∞ and the light receiving spot is located at the center of the light receiving surface. , i ₁ =i ₂ /2.

Then, instead of the PSD 5 shown in FIG. 4, the position detection element 60 is used, the terminal 61a is connected to the inverting input terminal of the head amplifier 6, the common electrode 63 is connected to the inverting input terminal of the head amplifier 22,
Furthermore, the terminal 62a may be connected to the reference voltage Vref. In this way, the photocurrent i ₁ is supplied to the head amplifier 6, and the photocurrent (i ₁ +i ₂ ) is supplied to the head amplifier 22, so that the same distance signal as in the previous embodiment (see FIG. 4) can be obtained. Obtainable.

Furthermore, the position detection element 70 is used instead of the PSD 5, the terminal 71a is connected to the inverting input terminal of the head amplifier 6, the terminal 72a is connected to the inverting input terminal of the head amplifier 20, and the common electrode 73 is connected to the reference voltage Vref. Then, a distance signal can be obtained in the same manner as described above. However, with this configuration, since the signals are in phase from the beginning, it is necessary to control the analog switches 31 and 32 in a manner opposite to that of the previous embodiment (see FIG. 4).

In this case, the signal current ratio is 1:1 when the distance to the subject is close, and 1:2 when the distance is ∞.
However, the configuration may be reversed, that is, 1:2 when the object is close and 1:1 when the object is ∞, and the setting of the ratio is not limited to this. That is, if the signal (first electrical signal) connected to the head amplifier 22 is "1", the signal (second electrical signal) connected to the head amplifier 22 is "1".
is 0 in all ranges of distance to the subject.
~1'', it can be implemented. In addition, if the boundary point of the step described above is set at the point where the second electric signal becomes "1", the second electric signal becomes "1".
Only one step can be set when the electrical signal of is >1.

[Effects of the Invention] According to the present invention, since distance information is obtained by integrating photocurrent, the influence of noise is small, and highly accurate distance detection can be performed.In addition, the signal processing system is simple, so the circuit size can be reduced. can be made smaller.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the concept of the present invention, FIG. 2 is a diagram explaining the principle of triangulation used in the present invention, and FIG. 3 is a semiconductor position detection element ( PSD), and FIG. 4 is an electric circuit diagram showing a distance detection device according to an embodiment of the present invention.
Figures 5 and 6 are diagrams explaining the operation of the electric circuit diagram shown in Figure 4, Figures 7A and B, Figure 8A,
B is a position detection element (SPD) used in place of the semiconductor position detection element (PSD) shown in Fig. 4 above.
FIG. 1... Infrared light emitting diode, 1A... Pulse light projecting means, 5... Semiconductor position detection element (PSD), 5A... Light receiving means, 19, 34... Capacitor, 36... Comparator, 36A... Comparing means , 41... Counter, 101... First integrating means, 102... Holding means, 103... Second integrating means, 104... Distance calculation means.

Claims (1)

[Scope of Claims] 1. A light projecting means for projecting pulsed light toward a subject; and receiving reflected light from the subject and outputting first and second electrical signals corresponding to the distance to the subject. a light receiving means; a first integrating means for integrating the first electrical signal; and a second integrating means for integrating the first electrical signal;
a second integrating means for starting the integration of the electric signal; a holding means for holding the first integral output integrated by the first integrating means after a predetermined time T; a comparison means for comparing whether or not the integral output of the second electric signal has a predetermined relationship with the integral output of the electric signal; calculation means for calculating the distance to the subject based on the time t until the comparison means detects that the first integral output and the second integral output have a predetermined relationship; A distance detection device characterized by comprising: