JP3121076B2 - Distance measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance measuring apparatus, and more particularly to a distance measuring apparatus applied to distance detection used for a device such as a camera which requires distance measuring.

[0002]

2. Description of the Related Art FIG. 9 shows an example of a conventional distance measuring apparatus using a PSD (optical position detecting element). This distance measuring device is an IRED that projects pulsed light on a subject 1 to be measured.
The object distance is obtained by detecting the position of a light source 2 such as an (infrared light emitting diode) and the position of an incident spot where a reflected light spot of pulse light from the light source 2 by the subject 1 is formed.

In FIG. 1, infrared light projected from an IRED 2 via a light projecting lens 3 is reflected by a subject 1 and is incident on a PSD 5 via a light receiving lens 4.
Here, the distance between the light projecting lens 3 and the light receiving lens 4 is S, the distance between the light projecting lens 3 and the subject 1 is l,
When the distance of D5 is f and the incident position of infrared light is x,
As shown in the drawing, the relational expression expressed by Equation 1 is established with the intersection of the optical axis of the light receiving lens 4 and the PSD 5 as the origin.

[0004]

(Equation 1)

[0005] In principle, the PSD 5 has a signal light current i _P
Is generated, and signal currents i _A and i _B depending on the incident position x are output from the two output terminals. And, P on the IRED2 side
Assuming that the distance from the SD end to the origin is a, the relational expression of Expression 2 is established.

[0006]

(Equation 2) Here, t represents the length of PSD5. Further, the relational expression of Expression 4 is established from the relational expression of Expression 3.

[0007]

(Equation 3)

[0008]

(Equation 4) Therefore, the subject distance l can be obtained by performing the ratio operation based on the relational expression of the above equation (4).

Incidentally, in addition to the pulse light from the light source 2, external light is also incident on the PSD 5. Therefore, the photocurrent component due to the reflected light of the pulse light is superimposed on the steady photocurrent due to the external light. Therefore, the detection circuit at the subsequent stage of the PSD 5 must have a function of separating and extracting only the photocurrent component due to the reflected light of the pulse light. Such a stationary light removing method is disclosed in Japanese Patent Application Laid-Open No. 1-240812, and there is a stationary light current extracting method. Hereinafter, the steady-state photocurrent extraction method and the fact that an output depending on the subject distance l is obtained using the detection circuit shown in FIG. 9 will be described.

First, the output current i (i _A ) from the PSD 5
Is amplified by a preamplifier 7A and an amplification transistor 8A via an input terminal 6A. This amplification transistor 8
A is connected to current sources 9A and 10A, a compression diode 11A and a buffer 12A. The hold amplifier 13A has an inverting input terminal for the amplifying transistor 8A, a non-inverting input terminal for a compression diode 14A and a current source 15A, and an output terminal for a hold transistor 16A, a hold resistor 17A, and a hold capacitor 1A.
8A are connected as shown.

The output of the compression diode 11A is connected to the transistors 21 and 22 constituting the ratio calculation circuit 20 together with the current source 19 via the buffer 12A. The compression diodes 11A and 14A have the same characteristics, and the current sources 9A and 15A are set to the same current value. Further, the hold amplifier 13A
Is determined such that the output voltages of the compression diodes 11A and 14A, that is, the input voltages of the inverting input terminal and the non-inverting input terminal of the hold amplifier 13A become equal.

In the detecting circuit shown in FIG.
Each of the components denoted by B to 18B has the same and similar configuration as the components denoted by reference numerals 6A to 18A described above, so that the reference numeral A of the same component is replaced with B. The description of the configuration and operation is omitted.
Next, the operation of the circuit having such a configuration will be described.

First, a steady light storing operation for storing a steady light current component is performed. In FIG. 9, the hold signal T ₁ and hold amplifier 13A, a current source 10A is turned on, IRED2, except the ratio calculation circuit 20, the entire circuit starts operating. In this state, the output current i
Hold amplifier 13A is activated for storage is equal to the steady photocurrent I _P, which in the hold capacitor 18A.

[0014] constant photocurrent I _P is amplified by a preamplifier 7A, compression diode 11A lowers the output voltage by the current, also decreases the potential of the inverting input terminal of the hold amplifier 13A. Then, since the output voltage of the hold amplifier 13A rises, the base potential of the hold transistor 16A rises, and the steady-state photocurrent I _P flows to the ground as a collector current via the hold resistor 17A. That is, the steady photocurrent I _P always flows to the ground by such a feedback action without being amplified.

The bias current of the amplifying transistor 8A is supplied by the current source 9A. When the IRED 2 does not emit light, no current flows at points A and B in the figure. Such stationary light storage operation, the hold signal T ₁ is performed continuously for a predetermined time, the charges corresponding to the stationary light component is charged in the hold capacitor 18A, it is held. The time during which the steady light storage operation is performed is referred to as a stable time.

Next, at the same time as the emission signal T ₂ causes the IRED ₂ to emit light, the hold amplifier 13 A stops its function according to the hold signal T ₁ . Here, the hold capacitor 18A holds a charge for removing steady light. Therefore, the signal current i is amplified by the preamplifier 7A and the amplifying transistor 8A while the steady light current _IP is removed, and the signal current flows through the compression diode 19. Also at the time of emission of IRED2, current source 10A is turned off by the hold signal T _1. Therefore, the output voltage V of the compression diode 11A is represented by the relational expression of Expression 5.

[0017]

(Equation 5)

Here, V _T ; heat voltage I _S ; reverse saturation current K; gain by preamplifier 7A and amplifying transistor 8A.

As described above, the output current of the PSD 5 becomes a voltage compressed by the compression diode. Hereinafter, the ratio calculation circuit 20 for obtaining the above-described ratio i _A / i _A + i _B using the compression signal will be described. . I _OUT and I _Z in the figure are represented by the relational expressions shown in Expressions 6 and 7.

[0020]

(Equation 6)

[0021]

(Equation 7) Therefore, the relational expression of Expression 8 is established.

[0022]

(Equation 8) Here, since I _Z = I ₀ −I _OUT from Equation 6, the following relational expressions of Equations 9, 10 and 11 are obtained.

[0023]

(Equation 9)

[0024]

(Equation 10)

[0025]

[Equation 11] By substituting the relational expression of Equation 4 into this, the relational expression of Equation 12 is obtained.

[0026]

(Equation 12) As described above, an output depending on the subject distance 1 can be obtained.

[0027]

As described above, the conventional circuit for extracting steady light requires a hold capacitor. However, first, since the capacitor has a characteristic that its charge voltage leaks with time, a relatively long time is required, for example, by performing a plurality of distance-measuring light projections after holding a steady-state photocurrent component. In this case, the draw-out current gradually decreases, resulting in a problem such as giving an error to the distance measurement result. This is remarkable especially under bright high brightness of external light.

Second, due to the holding error due to the dielectric absorption of the property of the capacitor itself,
The error current ΔI _P due to dielectric absorption is superimposed again, and adversely affects the distance measurement accuracy.

Third, a tantalum capacitor of about 0.47 μF to 1 μF is currently used as an element that can be used due to the above-mentioned hold characteristics. They are large and costly. Further, since the capacitor is externally attached to the IC chip, an extra pin is required for the IC, which causes problems in cost and space.

The present invention has been made in view of the above problems, and does not cause a problem such as giving an error to a distance measurement result.
It is an object of the present invention to provide a distance measuring device which does not adversely affect distance measuring accuracy and has no problem in cost and space.

[0031]

That is, the present invention provides a light projecting means for projecting a light beam on a distance measuring object, a light receiving means for receiving reflected light of the light beam from the distance measuring object, and a photocurrent corresponding to a light receiving position. And a distance calculating means for calculating a distance to the object to be measured based on the output of the position detecting means. Before projecting light, the steady-state photocurrent output by the position detection means is converted into a digital value of the steady-state light by digital conversion.
Digital storage means for storing Te, the digital storage means
Set the extraction current according to the steady light digital value stored in
And pull current setting means for constant, when the light projection of said light beam by said light projecting means, the photocurrent output by the position detecting means, which is set by the pull-out current setting means argument
A distance measuring device comprising: a current extracting means for extracting a drawing current.

[0032]

According to the distance measuring apparatus of the present invention, the reflected light of the light beam from the distance measuring object projected by the light projecting means is received,
A photocurrent corresponding to the light receiving position is detected by the position detecting means.
Also, before the light beam is projected, the steady-state photocurrent output by the position detecting means is converted into a digital signal, and the
Stored as a value . This stored steady light digital value
Is set by the extraction current setting means.
You. Then, at the time of projecting the light beam, the extraction current setting step is performed based on the photocurrent output by the position detection means.
The extraction current set in the stage is extracted. Based on the output from the position detector the withdrawal collector <br/> stream is withdrawn, the distance to the distance measuring object is calculated.

[0033]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the concept as a first embodiment of the distance measuring apparatus according to the present invention. The light received by the light receiving unit 23 is supplied to the comparison and determination unit 25 after being detected by the photocurrent detection unit 24. The digital value bit set clear unit 26 sets or clears each bit of the digital value based on the output from the comparison determination unit 25, and outputs the digital value to the digital value storage unit 27. The steady-state photocurrent extracting unit 28 extracts the steady light from the photocurrent detecting unit 24 according to the value of the digital value storage unit 27.

In this configuration, when the light reflected from the object to be measured is received by the light receiving section 23, the light receiving section 2
3 is detected by the photocurrent detector 24. Then, the detection output is compared with a predetermined level in the comparison / determination section 25 to make a determination. Based on the output result of the comparison / determination unit 25, each bit set clear unit 2 of the digital value
Reference numeral 6 sets or clears each bit of the digital value in the digital value storage unit 27. The steady-state photocurrent extracting unit 28 extracts a steady-state current corresponding to the output stored in the digital value storage unit 27 from the photocurrent detecting unit 24. Thus, for each bit, the comparison determination is repeated over the full bits of the digital value, the digital value is determined, and the steady photocurrent is extracted. FIG. 2 is an electric circuit diagram showing a second embodiment of the distance measuring apparatus according to the present invention.

This distance measuring device, as shown in FIG.
A light projecting circuit section 29 for projecting a light pulse to the object to be measured; a photocurrent detecting circuit section 31 for receiving reflected light from the object to be measured by the PSD 30 to detect and amplify a signal pulse light current component;
A and 31B, an arithmetic output circuit unit 32 for obtaining distance information of the subject from the photocurrent superimposed on the bias current, a count circuit unit 33 for A / D converting the output of the arithmetic output circuit unit 32, A control circuit section 34 for sending a control signal to the circuit section; and stationary photocurrent extraction circuit sections 35A and 35A.
B.

The photocurrent detection circuits 31A, 31B,
Since the circuit components 35A and 35B use the same components and have the same configuration, only the circuit portions 31A and 35A will be described.
For the circuits B and 35B, the circuit portions 31A,
The reference number A of 35A will be replaced with B, and a repeated description will be omitted. This is the same in the drawings and each part.

In FIG. 2, the IRED of the light emitting circuit 29
36 is driven by a constant current by a constant current drive circuit including a transistor 37, resistors 38 and 39 and an operational amplifier 40. When on / off of the constant current drive circuit is controlled, the base of the transistor 41 is connected to the terminal T ₆ of the control circuit section 34 via the resistor 42. Therefore, on / off control of infrared light projected from the IRED 36 with a pulse waveform shown in FIG.
Performed by the output signal of the terminal T ₆ of the control circuit section 34 (see FIG. 7).

The photocurrent detection circuit section 31A includes an operational amplifier 4
3A, a preamplifier circuit section including a transistor 44A, and a current mirror circuit including transistors 45A and 46A. Anode 30 of PSD 30
Signal pulse photocurrent I ₁ obtained from the A is supplied to the operational amplifier 43A constituting the preamplifier circuit section. The operational amplifier 43A has its output terminal connected to its base and its non-inverting input terminal connected to the reference power supply _Vref so that feedback is applied by the transistor 44A. Therefore, the base input resistance of the transistor 44A is equivalently reduced to about several tens of kΩ.

As shown in FIGS. 3 to 5, the steady-state photocurrent extraction circuit unit 35A includes a current weighting circuit unit, a flip-flop that turns on and off each weight corresponding to each weight, a comparator, It comprises a digital circuit for turning on and off the output of the flip-flop based on the output of the comparator.

The weighting circuit of FIG. 3 will be described.
This weighting circuit is a four-stage circuit with reference numerals 64, 65, 66 and 67. Since each circuit configuration is the same in each stage, for simplicity, only the circuit 64 will be described, and the circuits 65 to 67 will be omitted.

First, the current source 100 is a current source that outputs a constant current of 5 μA. And from this current source 100,
By the current mirror circuit constituted by the transistors 103 to 108, the collector current of the transistor 105 is 5 μA and the collector current of the transistor 106 is 5 / A.
2 μA, 5/2 ^{2 to} the collector current of transistor 107
μA, and 5 /
2 ³ μA respectively flow. These collector currents are turned on and off by the transistors 109, 110, 111, and 112, respectively.
5, it is determined whether the current is taken out as the collector current of 116.

When the bases of the transistors 109 to 112 become H (high level), the transistor 105
To 108 are all supplied by transistors 109 to 112,
The collector current of each of the transistors 3 to 116 is 0
become. Conversely, when the bases of the transistors 109 to 112 become L (low level), the transistors 105 to
The collector current of 8 is provided as the emitter current of the transistors 113 to 116. Therefore, the collector currents of the transistors 113 to 116 flow. As described above, by controlling the bases of the transistors 109 to 112 to H and L, it is possible to control the flowing current.

The transistors 101, 102, 11
7, 118, 119 and 120 constitute a PNP current mirror. The collector current of the transistor 119 is the minimum unit current of the weighting circuit 64, 5 /
2 ³ Half of μA, ie 5/2 ⁴ μA current to the next stage,
In this case, it is output to the weighting circuit 65.

The next-stage weighting circuit 65 and below (66, 6
7) also has a similar circuit configuration. With this configuration, the current having the weight represented by the relational expression of Expression 13 can be extracted.

[0046]

(Equation 13)

The control circuit 34 sets the terminal T ₁ before projecting light.
A clock signal is output. At this time, the anode 30A of the PSD 30, the steady-state current due to external light which is amplified through the photocurrent detection circuit 31A I _PO · β _N is flows compression diode 52. At this time, the potential of the compression diode 52 is represented by the relational expression of Expression 14.

[0048]

[Equation 14] Where V _T : thermal voltage I _S : reverse saturation current

[0049] The potential via a buffer circuit BUF _2, transmitted to the stationary light current sink circuit section 35A, by the comparator in this steady photocurrent withdrawal circuit unit 35A, is compared with a reference voltage V _ref2. The reference voltage V _ref2 is equal to V _ref
It is set to a value slightly higher than that (about 0.4 V). 6 and 7 are timing charts of signals supplied from the control circuit unit 34. Hereinafter, FIGS. 6 and 7
This will be described with reference to the timing chart of FIG.

First, the control circuit 34 outputs a reset pulse from the terminal T ₁ and outputs the steady photocurrent extraction circuit 35 A
Flip-flops FF, FF0-FF15, F0
Clear F15. As a result, all the weights of the current weighting circuit are turned off, and the current is not discharged from the transistor 102 to GND (ground).

Next, when the clock from the terminal T ₂ is input one 1, Q output of flip-flop FF15 is H, same-off
The inverted output of Q of the flip-flop FF15 becomes L, and the output of the NOR gate NOR15 becomes L.

[0052]

As a result, the most significant bit of the current weighting circuit is turned on, and a current of 5 μA is supplied to the transistor 102.
Is discharged to GND. At this time, the compression diode 5
The current flowing into 2 is represented by the relational expression of Formula 16.

[0054]

(Equation 16) In this case, the anode potential of the compression diode 52 becomes
It becomes like the relational expression of 7.

[0055]

[Equation 17]

Here, if I _PO > 5 μA and
If the relational expression represented by 8 holds, H is output from the output of the comparator CP in the steady-state photocurrent extraction circuit unit 35A, and L is output otherwise.

[0057]

(Equation 18)

This output is supplied to the flip-flop FF by the clock output from the terminal T ₂ of the control circuit section 34.
15 is latched and stored. As a result, if I _PO > 5 μA, the collectors of the transistors 104 and 113 to 116
A current of 5 μA is discharged to GND from the wiring connected to .

Further, when one clock is inputted from the terminal T ₂ , the Q output of the flip-flop FF 14 becomes H,
Output becomes L represented by 5, the output of Roh Agate NOR14 becomes L. Then, the ON (most significant -1) bits of the current weighting circuit, a current of 2.5μA are tiger
Transistors 104, 113-116
Is discharged to GND from the wiring . At this time, the current flowing into the compression diode 52 is represented by the relational expression of Expression 19.

[0060]

[Equation 19] Then, the anode potential of the compression diode 52 becomes
It becomes like the relational expression.

[0061]

(Equation 20)

[0062] Here, the Q output of the flip-flop F15 is the Q output of the flip-flop F15 previously stored H, the value by L, and F15Q = 0 when the F15Q = 1, L When the H Become. If the relational expression of Expression 21 is satisfied, the output of the comparator CP inside the steady-state photocurrent extraction circuit unit 35A outputs L, and otherwise outputs H.

[0063]

(Equation 21)

[0064] This output is the clock output from the terminal T ₂ of the same control circuit unit 34, is latched stored in the flip-flop FF 15. As a result, the current represented by the equation (22) is discharged to GND.

[0065]

(Equation 22) Hereinafter, similarly, the current represented by the relational expression of Expression 23 is represented by G
Discharged to ND.

[0066]

(Equation 23) In this way, the steady light component can be discharged to the minimum unit represented by the relational expression of Expression 24.

[0067]

(Equation 24)

By adopting the configuration of the steady-state photocurrent extraction as described above, for example, when the clock is set to 100 kHz, the extraction of the steady-state photocurrent can be completed at a very high speed represented by the equation (25). It is also very effective in reducing the time lag of the camera.

[0069]

(Equation 25)

As described above, the pulse light component obtained by excluding the photocurrent due to the background light from the photocurrent obtained from the anode 30A of the PSD 30 at the time of light projection is multiplied by β _N by the transistor 44A in the photocurrent detection circuit 31A. Then, it is turned back by the transistors 45A and 46A constituting the current mirror circuit, and is injected into the compression diode 52 of the arithmetic output circuit unit 32 as the signal pulse light current β _{NI 1} .

The photocurrent I ₂ obtained from the other anode 30B of the PSD 30 is also equal to the photocurrent detection circuit section 31A.
A photocurrent detection circuit section 31B for the same operation as are processed respectively in a steady current sink circuit section 35B, is supplied as signal pulse photocurrent beta _N I ₂ to the arithmetic output circuit 32.

The operation output circuit section 32 includes transistors 47, 48, 49, 50 and compression diodes 51, 52
, A constant current source 53, and buffer circuits BUF ₁ , BUF ₂
And constitutes a logarithmic expansion circuit for obtaining a distance measurement calculation output.

Transistor 4 Constituting Differential Amplifier
The bases 7 and 48 are connected to the compression diodes 51 and 52, respectively.
Are connected via buffer circuits BUF ₁ and BUF _2, and their emitters are commonly connected to a constant current source 53. The collector of the transistor 48 is connected to transistors 49 and 50 forming a current mirror circuit.
And the collector of the transistor 49.

Incidentally, the compression diodes 51, 52
The currents I _1b and I _2b flowing through the circuit are connected so that the signal pulse photocurrents output from the photocurrent detection circuit units 31A and 31B flow. Therefore, in the arithmetic output circuit section 32, the above-mentioned current I _1b is
Signal pulse photocurrent beta _N I ₂ from 1B, current I _2b is because the optical signal pulse current beta _N I ₁ from the photocurrent detection circuit section 31A, equation number 26 is established.

[0075]

(Equation 26) Therefore, the collector current I _C of the transistor 48 is
Assuming that the constant current of the constant current source 53 is I _E , the constant current is represented by a relational expression of Expression 27.

[0076]

[Equation 27]

Therefore, the collector current I ₁ ′ of the transistor 50, which is the output of the arithmetic output circuit section 32,
Is substituted into the relational expression of Expression 27 to obtain the relational expression of Expression 28.

[0078]

[Equation 28] As shown in FIG. 8, the output current I ₁ ′ of the arithmetic output circuit unit 32 measures a distance measurement range from ∞ to a close distance according to the reciprocal of the subject distance a. For the inclination correction, shift correction, etc. of the distance measurement output with respect to 1 / a, the correction value is E ² P
The data is written in the ROM, and each correction operation is performed.

On the other hand, the count circuit section 33 measures the integrated value I ₁ ′ of the collector current of the transistor 50 of the arithmetic output circuit section 32, and counts a counter mechanism (not shown) built in the control circuit section 34. ) To measure digitally.

The output current I ₁ ′ of the operation output circuit section 32
Is obtained as follows. PSD in synchronization with light emission
30 becomes active, and the output current of the arithmetic output circuit section 32 flows into the capacitor 54 every time light is projected, so that electric charges are accumulated. The operational amplifier 55 is for resetting the capacitor 54, and the base of the control transistor 56 is connected to the terminal T ₃ of the control circuit section 34 via the resistor 62. Therefore, the output signal of the terminal T ₃ (see FIG. 7), the transistor 5
6 is turned on, the potential of the capacitor 54 is set to the reference voltage _Vref , and turned off immediately before the start of light emission to disable the operational amplifier 55. Thereafter, the potential of the capacitor 54 increases due to the current injected into the capacitor 54.

[0081] When the predetermined number of light projecting ends as shown in the timing chart of FIG. 7, the terminal T ₄ is H → L
(From high level to low level), the transistor 57 is turned off via the resistor 63, and the capacitor 58 is discharged by the transistor 58. At the same time, the control circuit unit 3
The counter built in 4 operates and continues counting until the output of the comparator 59 becomes H. Comparator 59
Changes from L to H when the voltage across the capacitor 54 becomes smaller than the reference voltage _Vref . The discharge speed of the capacitor 54 is determined by a current mirror circuit including a constant current source 60 and transistors 61 and 58 connected in series. In this way, an output corresponding to the subject distance can be obtained as a count value of the counter in the control circuit unit 34.

Although the operation output circuit is not limited to this, other circuits and detailed explanation of the operation are disclosed in Japanese Patent Application Laid-Open No. 1-150809 filed earlier by the present applicant. Omitted.

As described above, before emitting the pulse light for distance measurement, the input state to the steady-state photocurrent photocurrent detecting means is compared and determined, and the bit value for each weight of the steady-state photocurrent extracting means is determined. By this, the majority of the steady-state photocurrent is bypassed to GND, and as a result, the digital value is set so that the steady-state light component superimposed on the pulsed photocurrent becomes a value sufficiently smaller than the pulsed photocurrent value. it can.

Further, the distance measurement error due to leakage or dielectric absorption is eliminated, the distance can be detected accurately, and it is only necessary to determine and set each weight bit.
The time required for the setting of about 6 bits is sufficient, and another digital type steady photocurrent extracting device (Japanese Patent Laid-Open No. 2-195203)
It takes much less time to determine each digital value than in the case of (1), and it has good tracking performance for fluctuating stationary light components such as AC background light, and also shortens the time from power-on to ranging. Is done. Further, the number of pins for externally attaching a capacitor can be reduced, so that there are great advantages in cost and space.

[0085]

As described above, according to the present invention, a problem such as giving an error to the distance measurement result does not occur, the distance measurement accuracy is not adversely affected, and there is no problem in cost and space. A distance device can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a concept as a first embodiment according to a distance measuring apparatus of the present invention.

FIG. 2 is an electric circuit diagram showing a second embodiment of the distance measuring apparatus of the present invention.

FIG. 3 is an electric circuit diagram showing a part of the steady-state photocurrent extraction circuit of FIG. 2;

FIG. 4 is an electric circuit diagram showing a part of the steady-state photocurrent extraction circuit of FIG. 2;

FIG. 5 is an electric circuit diagram showing a part of the steady-state photocurrent extraction circuit of FIG. 2;

FIG. 6 is a timing chart of signals supplied from the control circuit unit in FIG. 2;

FIG. 7 is a timing chart of signals supplied from the control circuit unit in FIG. 2;

8 is a diagram illustrating characteristics of a distance measurement calculation output of FIG. 2 and a reciprocal of a subject distance.

FIG. 9 is an electric circuit diagram showing an example of a conventional distance measuring device using a PSD.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Subject, 2 ... Light source (IRED; infrared light emitting diode), 3 ... Light emitting lens, 4 ... Light receiving lens, 5, 30 ... P
SD (optical position detecting element), 23: light receiving section, 24: photocurrent detecting section, 25: comparison / determining section, 26: clearing section of each bit set of digital value, 27: digital value storing section, 28: steady light current extracting Part, 29 ... Light emitting circuit part, 31A, 31B
... Photocurrent detection circuit section, 32 ... Operation output circuit section, 33 ... Count circuit section, 34 ... Control circuit section, 35A, 35B ... Steady state photocurrent extraction circuit section.

Claims (1)

(57) [Claims] 1. A light projecting means for projecting a light beam to a distance measuring object, a position detecting means for receiving reflected light of the light beam from the distance measuring object and outputting a photocurrent according to a light receiving position; A distance calculating means for calculating a distance to the object to be measured based on an output of the position detecting means, wherein the position detecting means is provided before the light beam is projected by the light projecting means. Converts the steady-state photocurrent output by
And digital storage means for storing a stationary light digital value, a steady light digital value stored in said digital memory means
And pull current setting means for setting a pull-out current corresponding, when the light projection of said light beam by said light projecting means, the photocurrent output by said position detecting means, the pull-out current
A distance measuring device comprising: current extracting means for extracting the extraction current set by the setting means .