JPH01224617A - Distance detecting device - Google Patents

Abstract

PURPOSE:To expand the distance measurement range and to improve the distance measurement accuracy by receiving reflected light from a subject at a distance of a base line from a projecting means and comparing the signal obtained from the reflected light with a specific level. CONSTITUTION:The projecting means 29 projects luminous flux on the subject and its reflected light is photodetected by a photodetecting means 30 which is arranged at the distance of the base line from the means 29 to generates a photoelectrically converted signal corresponding to the photodetection position. An arithmetic means 31 receives the signal to calculate the subject distance and a comparing means 33 compares this signal with the specific level. A selecting means 34 selects the output of the means 31 or the signal output of a signal generating means 32 corresponding to the specific distance according to the comparison result. Namely, when the signal exceeds the specific level, the output of the means 31 is selected and when not, the output of the means 32 is selected.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a distance detection device, and more specifically, to a distance detection device, and more specifically, a distance detection device that detects light reflected by a subject of light projected from a light projecting element toward a subject by a certain normal length. The present invention relates to a so-called active type distance detection device that measures the distance to a subject by detecting it with a light receiving element.

[Prior Art] An active type distance detection device that detects the distance to the subject by projecting light toward the subject and receiving the reflected light is already well known from Japanese Patent Application Laid-Open No. 59-99420. be. In recent years, active type distance detection devices have been under pressure to improve their performance in order to accommodate telephoto shooting using longer focal length lenses and close-up shooting using close-up shots. That is, there is a demand for improvement in distance measurement accuracy so that telephoto shooting can be carried out in good focus at longer distances, and for an expansion of the 1111 distance range so that shooting can be done at closer distances.

In order to meet such demands, problems encountered in conventional distance detection devices will be described in detail below.

In the conventional active type distance detection device, as shown in FIG. 11, pulsed light emitted by a light projecting element 39 is focused by a light projecting lens 26 and irradiated onto a subject 28, and the reflected light is received. An image is formed on the semiconductor device detection device (hereinafter abbreviated as PSD) 1 by the lens 27 . P.S.
The DI is arranged with its center aligned with the optical axis of the light receiving lens 27. In other words, if the center of gravity of the image point formed by the reflected light from the object in (2) coincides with the center of the PSD, the baseline length is L1, the deviation from the optical axis of the image point is x1, the focal length of the light receiving lens 27 is f4, If the subject distance is a, then x-f J ·L/a (1) is obtained. The total photocurrent is Iφ, the total length of PSDI is 2tI, -1
-I2=Iφ (4). As can be seen from the above equations (2) and (3), the photocurrents Il and I2 contain distance information 1/a, so the distance measurement calculation is performed using the photocurrents I, I2, and the calculation is Distance information a can be obtained from the result.

Now, there have traditionally been various types of distance measurement calculations, but here are some typical examples:
The distance calculation circuit shown in the figure is used to calculate I2/(work 1+12). Calculation output I at this time. becomes . Substituting the above equations (2) and (3) into equation (5) gives -1)/
The calculation (1, +1.) must be performed. By substituting the above equations (2) and (3) into this equation (7), we get the reciprocal of the subject pressure fia and the above calculation output ■ o
The relationship is as shown in the graph shown in Figure 15. ■vTgn
(I2/■1) This can be done by using an arithmetic circuit as shown in FIG.
In (I2/11) is calculated. The calculation output V at this time. is V ”V IIn (12/11)”””(9)
It becomes T. Substituting the above equations (2) and (3) into equation (9) gives the following equation. Therefore, the calculation output V. is the reciprocal of the subject distance (1
When differentiated by /a), we get: That is, (t/f L) 2> (1/a) 2...
112), the slope is 2f, L/
It is equal to the straight line of l, and under other distance conditions, the slope will be larger. In the normal distance measurement range, the area where the above condition (12) applies is set, so
A graph showing the relationship between the reciprocal of the object distance a and the above calculation output Vo is shown in FIG.

Note that detailed explanations of the circuits shown in FIGS. 12, 14, and 16 and their operations are disclosed in Japanese Patent Application No. 62-310689 (see Japanese Patent Application Laid-Open No. 1988-1990) previously filed by the applicant. Therefore, the same reference numerals as those of the constituent members explained in FIGS. 1, 7, and 8 of the accompanying drawings of the above-mentioned application will be given, and the explanation thereof will be omitted.

In this way, the distance measurement calculation output for the reciprocal of the object distance is expressed by a single characteristic line, but the signal light intensity from the object is a very weak photocurrent of about several tens of pA to several tens of nA. In reality, there is some uncertainty due to the influence of so-called randomly generated circuit noise such as in the photocurrent detection circuit. For example, the straight line g1 shown in FIG. 13 is the noise width A surrounded by the curves g and g shown in FIG.
Since it is a band-shaped area with a diagonal line of 1, the calculation output will be a value that will fall within a certain range with probability, and the correspondence with the reciprocal of the distance will not be determined one-to-one, so the graph will be a single line. It won't form a line. Therefore, as shown in FIG. 18, the subject pressures 1iIfa 1 and a2 may output the same calculation output, so they cannot be completely distinguished. Therefore, the distance measurement accuracy of the distance measurement device can be expressed by the amount 1/a - 1/a2 when the subject distances a1 and a2 are at the limit where they can be completely distinguished. The smaller this value is, the higher the distance detection ability of the distance measuring device is, and the more distant the object distance can be identified.

FIG. 19 is a graph when the slope of the distance measurement calculation output straight line (hereinafter abbreviated as calculation straight line) with respect to the reciprocal of the object distance a is changed. As is clear from comparing Fig. 18 and Fig. 19, if the same photocurrent detection circuit is used, the noise width A1 generated by it is the same, so the distance measurement accuracy increases in proportion to the magnitude of the slope. I know it will get better. In order to increase the slope of the calculation straight line, as can be seen from equation (6), the base line length may be increased, the focal length fj of the light receiving lens may be increased, or the total length 2t of the PSD may be decreased.

Figures 20 (A) to (E) show the relationship among the base line length, the focal length f of the light receiving lens, and the total length 2t of the PSD. Figure 20 (A) shows the relationship in the conventional device. In contrast, by increasing the base line length in FIG. 20(B), the focal length f of the light receiving lens 27 is increased in FIG. 20(C).
By increasing J and, in FIG. 20(D), by decreasing the total length 2t of PSDI, the slope of the calculation straight line is increased.

[Problems to be Solved by the Invention] However, when trying to improve the distance measurement accuracy by increasing the slope of the calculation straight line in this way, as shown in Fig. 20 (B), (C), and (D), As can be seen, a problem occurs in that the closest distance measurement limit becomes far away. In this type of distance measuring device, all of the reflected light from the subject needs to be imaged on the light receiving section of the PSD, so the closest measurable limit distance alI11□ is aIIlin = 'J - L/''... ...(13), and when compared with the above equation (6), this means nothing more than doubling the slope of the calculation straight line.

In other words, improving distance measurement accuracy and shortening the ΔI11 possible distance limit are contradictory.

Therefore, in order to solve the above problem, we changed the configuration of Fig. 20 (D) to the center of PSDI from the center of gravity of the image forming point by the reflected light from the subject in (2) as shown in Fig. 20 (E). It is conceivable that the light projecting element 39 is shifted along the longitudinal direction in a direction opposite to a certain position. If this shift amount is ΔX, the closest possible limit of a1 distance is afflIo wrinkles fjeL/(t+Δx) −・・−・
-(14), and the nearest limit can be shortened by the shift amount by ΔX.

Now, if the total length of PSDI is shortened from 2t to t'-2t/k (k is a constant), the slope of the calculation straight line will double, and the distance measurement accuracy will be doubled. Furthermore, f −L/(t' +
If the shift amount ΔX is determined so as to satisfy the formula Δx)1wfj−L/l, the distance measurement range can be expanded without increasing the closest possible limit of the al11 distance. The same can be considered when changing the focal length f and base line length of the light receiving lens.

In addition, since the space inside the camera is generally very narrow, it is advantageous to reduce the total length of the PSDI in terms of space.
Using SDI means using PSD, which has a high yield, and can also bring out cost benefits. Furthermore, noise caused by background light can also be reduced by reducing the light receiving area of the PSD. Therefore, the center position of PSD is
The above-mentioned contradictory problem can be solved by arranging the light emitting element at a position shifted in the opposite direction from the center of gravity of the image forming point formed by the reflected light from the subject.

However, in reality, shifting causes other problems in combination with the characteristics of the signal detection circuit. Next, this will be explained in detail.

As shown in FIG. 21, signal photocurrents 1, 1 . The signal photocurrents I,1. I, 2 is detected superimposed on the bias current II, so Bl' [32 Therefore, the photocurrent considering the bias current ■lb'' 2b is 1 +b-1p1+I n□ ......・(1
5) I2b""' p2+■82 ・・・・・・・・・
...(16). When the photocurrent 'lb'' 2b is input to the distance calculation circuit shown in FIG. ,, Ip2 is the above (2).

As shown in equation (3), it is expressed as r, 1 + I, 2 = Iφ・−”−(20).
This is the total photocurrent obtained by photoelectrically converting the total amount of received reflected light that decreases as the power increases and reaches 0 at flash. Therefore, distance calculation output! . becomes. Therefore, when the subject is close and Iφ> I Bt + I B2, Io(■φ)I
Bl + ■B2) When the subject is far away and ■φ is IBl''B2. From the above equations (22) and (23), ilN distance calculation output Io
has a linear relationship proportional to the reciprocal of the distance when the object is relatively close, and when the object is ψ, the bias current IBl'pl' p2 superimposed on the signal photocurrent II converges to the value determined by B2 . 22nd
The figure is a graph of this situation, and the bias current lB
1''B2 is not superimposed on the signal photoelectric signal, that is, the reciprocal of the object distance a and the distance measurement calculation output I.

The relationship is not linear, and an area A2 is created in which one distance measurement calculation output value corresponds to two object distances, resulting in a problem in which distance measurement is impossible.

Such a problem of nonlinearity of the distance measurement calculation output straight line is caused not only by the bias current ratio but also by noise randomly generated in the Al distance circuit. The influence of noise is shown in FIG. 18 above.

As shown in FIG. 19, the distance tends to increase as the subject distance increases. This will be considered next using mathematical formulas.

If the noise generated in the distance measuring circuit is INl"N2, the above equations (15) and (1B) are expressed as
4) I2b= 192"In2"lN2...
...(25). When this is input to the subsequent distance calculation circuit and a distance calculation is performed, for example, as shown in equation (5) above, the output is . Ha = ・・・・
...(26)(Ipt +'p2) + (Io1+
In2) + (INI+IN2). However, the photocurrent Ipl''p2 is as described in (18) above.

It is expressed by equations (19) and (20).

becomes. Therefore, when the subject is close, ■φ>1131'
'132''Nl'' When N2, lo(Iφ> 1 # JB2 t 'N'+
t Engineering N2) 1 ΔX f, -L 1 = −−−+ (−) (−) ... Song (2
7) 2 21 21 a. Also, if the subject is far away, ■φ<1. □”I32''Nl・
lN2(') when Io (Iφ<'B1+'a2t'N1+'N2)
becomes.

This is illustrated in FIGS. 23(A) and 23(B).

Figure 23 (A) shows the center of gravity position and PS of the image formed by the reflected light from the subject in (■) so as not to be affected by the bias current.
The center of D is the same.

Therefore, at long distances where the magnitude of the noise is larger than the signal photocurrent, the noise width A3 is equal to the curve g5 and g
8, a problem similar to the problem of nonlinearity of the 1111j distance calculation output described above occurs due to noise.

To solve this problem, if the bias current IBl'■ is made larger than the noise current INl''N2, the curve g
Since the area is surrounded by 7 and 98, the noise width A4 can be suppressed. However, if the bias current is made too large, the above equation (27) becomes 71!1, and the distance calculation output is influenced by the total photocurrent Iφ obtained by photoelectrically converting the total amount of incident light.

This total photocurrent ■φ is a function of the reflectance of the subject, so even if the subject distance is the same, the calculated output will be a different value depending on the reflectance of the subject, as shown in Figure 23 (B). .

The present invention has been made in view of the above circumstances, and it solves the problem of nonlinearity of the distance measurement calculation output caused by the bias current ratio, the arrangement of the light receiving optical system, or noise, and expands the all distance range compared to the conventional one. It is an object of the present invention to provide a distance detection device that also improves 1llJ distance accuracy.

[Means and effects for solving the problem] As shown in a conceptual diagram in FIG. a light receiving means 30 which is arranged at a position separated by a baseline length and receives reflected light from the subject and generates a photoelectric conversion signal according to the light receiving position; and a calculation means which receives the photoelectric conversion signal and calculates the subject distance. 31, signal generating means 32 for generating a signal corresponding to a predetermined distance, comparing means 33 for comparing the photoelectric conversion signal with a predetermined level, and when the result of the comparison exceeds the predetermined level, the operator stage 31, and select means 34 which selects the output of signal generating means 32 if the output does not exceed a predetermined level.

[Example] Hereinafter, the present invention will be specifically described with reference to the drawings.

Figures 2 (A) and (B) show the arrangement of a distance measuring optical system that can be used by applying the present invention, with an IRED68 as the light emitting element and a PSDI as the light receiving element.
are used, and a ray of light that enters through the principal point of the light-receiving lens 27 enters the light-receiving element 1 in parallel to the projection optical axis projected from the light-emitting element 68 toward the subject by the light-emitting lens 26. The intersection point P1 is the center of gravity of the image point formed by the reflected light from the subject (2). As shown in FIGS. 2(A) and 2(B), the positional relationship between the light emitting element 68 and the light receiving element 1 is such that the center P2 of the light receiving element 1 (PSD)
It is assumed that the point P1 is shifted by a distance ΔX in the direction opposite to the light projecting element 68 along the base line length direction. By arranging the optical system in this manner, it is possible to expand the range of distance measurement and improve the accuracy of distance measurement compared to the conventional system.

FIG. 3 is a processing circuit of a distance detection device showing a first embodiment of the present invention. This processing circuit includes photocurrent detection circuits 80 and 80A that remove and amplify background photocurrent components from the first photocurrent (1) and second photocurrent (2) output from the PSDI, respectively, and detect these. Photocurrent detection circuit 80
．． The forward voltage obtained by energizing the diode 13 with the sum of the output current of 81 of 80A and the photocurrent detection circuit 80.80A is compared with a predetermined level, and when it exceeds the predetermined level, the "H" level A comparison means 82 outputs an "L" level when the output is below the output logic signal of the comparison means 82; It consists of a selection means 83 that selects and outputs the output of a signal generation means 84, which will be described later, and a signal generation means 84 that outputs a signal corresponding to a predetermined distance.

In the photocurrent detection circuit 80, the operational amplifier 3 applies feedback to the transistor 2 that amplifies the photocurrent 11 of the PSDI, and as a result, the base input resistance of the transistor 2 is equivalently reduced to about several ohms. , photocurrent 11 can flow into the base of transistor 2 without affecting the signal current division ratio of PSDI.

The photocurrent It is multiplied by β in this transistor 2, and is outputted as a collector current of transistor 9 via transistors 8 and 9 forming the next current mirror circuit.

The background light component is generated by operational amplifier 5. Capacitor 7° is removed by a background light removal circuit formed by transistor 4. Since the reference voltage V rel is applied to the non-inverting input terminal of the operational amplifier 5 and the output of the operational amplifier 3 is applied to the inverting input terminal, when the background photocurrent flows into the base of the transistor 2, the output voltage of the operational amplifier 3 As the voltage decreases, the inverting input terminal of the operational amplifier 5 becomes lower than the non-inverting input terminal, and the output terminal of the operational amplifier 5 becomes 'H' level.Then, as the transistor 4 increasingly passes current, the base of the transistor 2 becomes low. The background photocurrent that flows in and goes to zero is discharged to the ground via the transistor 4. As a result, the base input current to the transistor 2 decreases, and the potential at the inverting input terminal of the operational amplifier 5 increases. Through a feedback loop, the background photocurrent component Ct is all discharged to the ground by the transistor 4. On the other hand, since the signal photocurrent component has a high frequency, the above-mentioned foot check is not applied by the capacitor 7, and the base of the transistor 2 flows into.

In this way, only the signal photocurrent flows into the base of the transistor 2, is amplified, and is output to the calculation means 81 as the collector current of the transistor 8. In addition, the second PSDI
The photocurrent I2 is also processed in the same manner by a photocurrent detection circuit 80A configured similarly to the photocurrent detection circuit 80, and then outputted to the calculation means 81.

This calculation means 81 is the distance calculation circuit shown in FIG. 12 with diodes 85 and 86 added thereto. The diode 85 receives the signal photocurrent β11 from the photocurrent detection circuit 80, and the diode 86 receives the signal photocurrent β11 from the photocurrent detection circuit 80.
Signal photocurrent β from 0A! 2 are respectively supplied, the diode 13 of the comparison means 82 receives the signal photocurrent 11.
A current that is β times the sum of and 12 will flow.

The saturation current of the diode 13 of the comparison means 82 is Is, and the reference voltage applied to the cathode of the diode 13 is Vr.
If el'2, then the potential V of the anode of the diode 13
13 represents the magnitude of the signal photocurrent. This potential V13
, a reference voltage Vrer of a predetermined level is set by the comparator 19 to be slightly higher than the reference voltage Vrcf'2.
It is compared with 3. Therefore, when ■■+■2 is smaller than the predetermined level, the output of the comparator 19 is "L" level, and when 11+12 is larger than the predetermined level, the output is "H" level.

The signal generating means 84 is a constant current source 89 here. Here, the constant current value of the constant current source 89 is set to be approximately equal to the theoretical value of the circuit output of the calculation means 82 corresponding to the country of the object distance, or when the slope of the calculation straight line of the calculation means 82 is positive, It is set to be smaller than the value, and larger if negative.

The output of the signal generating means 84 is supplied to the selecting means 83 together with the outputs from the calculating means 81 and the comparing means 82. "H" of the output of the comparator 19 of the comparison means 82,
According to “L”, the transistor 92 turns off and on,
Since the transistor 93 turns on and off, the output terminal out
When the magnitude of the signal photocurrent (1+12) is larger than a predetermined level, the output from the calculation means 81 is output, and when it is smaller, the output from the signal generation means 84 is output.

FIGS. 4A, 4B, and 4C are diagrams showing the output characteristics of the first embodiment. That is, (A),
CB) and (C) are the values of the output of the signal generating means 84, respectively, and FIGS. When the output is approximately equal to the theoretical value of 82. Figure 4 (
C) is a case where the slope of the output straight line of the output of the calculation means 82 is positive, so it is set smaller than the theoretical value.

In this way, the distance measurement calculation output is switched from the output of the calculation means 82 to the output of the signal generation means 84 before the nonlinearity of the distance measurement calculation output caused by the bias current and the arrangement of the light receiving optical system or noise occurs. Therefore, the above problem is fundamentally solved.

FIG. 5 is an outline of a processing circuit of a distance detection device showing a second embodiment of the present invention. This second embodiment differs from the first embodiment in that the calculation means, the signal generation means, and the selection means are integrated, and the output from the signal generation means is outputted via the calculation means. The configuration is the same as the first embodiment.

When the sum of the signal photocurrents ■1 and I2 from PSDI is lower than the reference voltage Vrel'4 corresponding to a predetermined level, the output of the comparator 19 becomes "L" and the transistor 10
0 and 101 are turned off, the output current ■Bl''B2 of the constant current sources 94 and 95 flows to the compression diode 98 and 99 as a bias current.

This bias current IB1''B2 is a signal light current IB1.

■ and noise ■ Since Nl is set larger than N2, the distance measurement calculation output output from the output terminal 102 will be a value determined by the bias current ratio of IBl'' B2,
Noise width is small. Conversely, when 11+■2 is greater than the predetermined level, the output of the comparator 19 becomes H'', so the transistor 00°101 turns on, the bias current II no longer flows through the compression diode 98.99, and the diode Bl' B2 Only the signal current flows through the leads 98 and 99. Therefore, the distance measurement calculation output output from the terminal 102 is the signal light current I,
, I2.

FIG. 6 is an outline of a processing circuit of a distance detection device showing a third embodiment of the present invention. In this third embodiment, in order to handle the Δ-1 distance signal as a voltage signal, the distance calculation circuit shown in FIG. 16 is used as the calculation means, the constant voltage source Vφ is used as the signal generation means, and the selection means analog switch 1
The only difference from the above embodiments is that signals are switched using signals 03, 104 and an inverter 105, so there is no difference in their operation.

FIG. 7 is an outline of a processing circuit of a distance detection device showing a fourth embodiment of the present invention. In this fourth embodiment, the calculation means, signal generation means, and selection means are integrated as in the second embodiment, and the calculation means is handled as a voltage signal in the same manner as in the third embodiment. There is no difference from each of the above embodiments except for the following points. Therefore, their effects are also the same.

FIG. 8 shows a more specific embodiment of the distance measuring circuit section in the distance detecting device of the present invention, and the processing circuit in each of the above embodiments will also be described. Note that FIG. 9 is a timing chart of signals supplied from the control circuit section 25 in FIG. 8 above. This distance detection device includes a light projection circuit section 21 that projects a light pulse onto a distance measurement object, a photocurrent detection circuit section 22 that receives reflected light from the IIIJ distance object and detects a photocurrent, and a photocurrent detection circuit section 22 that detects a photocurrent by receiving reflected light from the IIIJ distance object. An arithmetic output circuit section 23 that obtains distance information of the object from the voltage generated across the compressed diode, a count circuit section 24 that A/D converts the output of the arithmetic output circuit section 23, and a control signal that is sent to each of the above circuit sections. and a control circuit section 25 that sends out.

In FIG. 8, the light emitting element of the light emitting circuit section 21 is
ED (infrared light emitting diode) 68 is a transistor 67
, resistors 66, 69, and an operational amplifier 65. A transistor 70 that controls on/off of this constant current drive circuit
The base of the IRED 68 is connected to the terminal T1 of the control circuit section 25 through resistors 71 and 74, and the on/off control of the infrared light projected from this IRED 68 with the "projection waveform" shown in FIG. , the output signal of the terminal T1 of the control circuit section 25 (the ninth
(see figure).

The photocurrent detection circuit section 22 includes a preamplifier circuit section and a background light removal circuit section. The first photocurrent (1) obtained from one of the anodes of the PSD'1 is preamplified by a circuit consisting of transistors 2.8, 9.4 and operational amplifiers 3.5 of the photocurrent detection circuit section 22. After the background light is removed, it flows into the logarithmic compression diode 11.

The operational amplifier 3 that amplifies the first photoelectric lacquer obtained from one anode of the PSDI has its output terminal connected to the transistor 2 so that feedback is applied by the transistor 2.
The inverting input terminal is connected to the emitter of transistor 2 and the base of transistor 2, and the input impedance of the base of transistor 2 is equivalently lowered to about several hundred ohms, which affects the photocurrent ratio of PSD 11:■2. Without the above signal■
1 is all inputted to the base of the transistor 2 as the base current. The signal amplified by the current amplification factor β of the transistor 2 is supplied to the next stage transistors 8 and 9°9' forming the first current mirror circuit. The collector of the transistor 9 is connected to a constant current source 10 that sinks current and a non-inverting input terminal of an operational amplifier 5 of the background light removal circuit section.

This operational amplifier 5 becomes active when the transistor 6 is turned on by the "H" level of the output signal of the terminal T1 of the control circuit section 25 being applied to the base through the resistor 74.73 during non-light emission, and is connected to its output terminal. The capacitor 7 accumulates a charge corresponding to the brightness of this background light, and a feedback loop composed of the capacitor 7 and the transistor 4 converts the photocurrent component due to the background light of the PSDI and the bias current component of the operational amplifier 3. is discharged to the ground line as the collector current of transistor 4. As a result, the collector current of the transistor 2 has a constant value that corresponds to the constant current value of the constant current source 10, regardless of the magnitude of the background light.

When light is emitted, the operational amplifier 5 becomes non-active because the transistor 6 is turned off. However, due to the charge accumulated in the capacitor 7, the transistor 4 continues to discharge the photocurrent due to the background light to the ground line, so that there is no current from one anode of the PSD1. The pulsed light component obtained by removing the photocurrent due to the background light from the obtained first photocurrent is multiplied by eight in the transistor 2, reflected by the first current mirror circuit 8.9, and injected into the compression diode 11.

Similar to the above description, the second photocurrent I2 obtained from the other anode of PSDI is connected to transistors 2A, 8A,
9A, 4A and op amp: 3A.

Processed with a similar circuit consisting of 5A, diode 11A
detected from the anode of

Transistor 15.18 and transistor 15A,1
8A form a second current mirror circuit, respectively. The constant current of these second current mirror circuits is provided by a third current mirror circuit composed of a transistor 35.36.degree. 37 and a constant current source 38. If the current value of the constant current source 38 is IB, then from the nature of the current mirror circuit, the transistor 35
．． Each collector current of 36.37 is 8.

Since the transistor 36 is connected in series with the transistor 18, the current flowing through the transistor 18 is the constant current IB. By the way, since the resistor 16 and the variable resistor 17 are connected to the emitters of the transistors 15 and 18, which form one second current mirror circuit, respectively, if the variable resistor 17 and the resistor 16 have the same resistance value, then The bias current 181 flowing through the transistor 15 is also equal to the current value IB of the constant current source 38, but as will be described later, the variable resistor 17 is variably adjusted for the purpose of adjusting the signal level output from the signal generating means. Generally, it is 1131” IB.

Since transistor 18A is in series with transistor 35,
Since the current IB2 flowing through the transistors 15A and 18A constituting the other second current mirror circuit is equal to IB, in the end, the current for boat fishing is 2 rather than 1Bl.

That is, it can be set by varying the variable resistor 17.

Constant current source 12 is constant current source 10. Since it is equal to the sum of IOA, the current flowing through the diode 13 is the signal photocurrent β・(11
+12). Therefore, if the total photocurrent ■1+12 is large, the output terminal of the operational amplifier 19 becomes "H" level, so the transistor 14 is turned on and the transistor 35.36 is turned off, so the bias current 'Bl'IB2 is generated in the diode 11.11A. stops flowing. On the other hand, total photocurrent ■
If 1+I2 is small, the output of the operational amplifier 19 is “L”
level, the transistor 14 is turned off and the diode 11. Bias currents ■Bl and IB2 flow through IIA, respectively.

The signal voltage obtained at the anode of the compression diode 11 or 11A in this way is supplied to the bases of the transistors 41 and 42 of the arithmetic output circuit section 23.

The calculation output circuit section 23 includes a transistor 41°42.44
46 and a constant current source 43, forming a logarithmic expansion circuit for obtaining a distance measurement calculation output. The bases of the transistors 41 and 42 forming the differential amplifier are connected to the anodes of the compression diode 11 and IIA either directly or via a buffer amplifier (not shown), and the emitters of the transistors 41 and 42 are commonly connected to the constant current source 43. It is connected. transistor 4
The collector of transistor 2 is connected to the bases of transistors 44 to 46 forming a current mirror circuit and to the collector of transistor 44.

By the way, the current flowing through each of the diodes 11.11A is the photocurrent 11.11A obtained from each anode of the PSDI. It is the sum of I2 and the bias currents In□ and IB□. That is, the above-mentioned current Itb・I 2bg
It's yo.

Therefore, the collector current IC of the transistor 42 is equal to the constant current of the constant current source 43. Then, it becomes. This (31
) The current Ic shown by the equation (21) has a coefficient . It corresponds to the one multiplied by .

By substituting the above equation (30) into this equation (3I), the following is obtained.

Therefore, by measuring the collector current Ie of the transistor 42, the distance to the object can be determined. Due to the nature of the current mirror circuit, this current 1c also flows to the collector of the transistor 46.
The collector current Ic of 6 becomes the calculation output. This arithmetic output circuit section 23 operates so that the following holds true, where the collector current flowing through the transistor 41 is lcl.

Here, the bias current II is the aforementioned Bl'
B2 As in the first photocurrent 11. Superimposed on the second photocurrent I, each compression diode 11. Since it will flow through ILA, the charge of the electron is q.

Assuming that the absolute temperature is T, the Boltzmann constant is , and the reverse saturation current is Is, the thermal voltage is VT, and for simplicity we assume that there is no background light, the subject distance is sufficiently far and the photocurrent is 1.1. When sufficiently small, the diode 11. 11A anode potential v1. (2) becomes (34). (34)

That is, in this case, the compression diode i1. The potential of the anode of lIA is determined only by the bias current I[31" B2. Therefore, the calculation output Ic at this time
is obtained from the above equation (32).

Next, if the subject is close enough that the photocurrent from the PSDI is 1
1. If I2 is large, it becomes a compression diode, so in this case, the equation (32) above is obtained.

In the conventional distance measuring circuit, IBl''B2 was used, so the calculation output 1c was 1c -■E, but in this embodiment, the bias current was set to be constant and equal to I8 of constant current ?R38. , for the bias current IBL, the transistor 15.18, the resistor 16 with a resistance value R1, and the variable resistor 17 with a resistance value R2, the variable resistor 17 has a distance-output relationship such that: J3 is satisfied so as to satisfy the following relational expression. In this embodiment, a variable resistor is used for adjustment, but adjustment is not necessarily necessary, and a fixed resistor may be used so that the bias current ratio is fixed at a predetermined bias current ratio.

The count circuit section 24 measures a component obtained by removing the background component of the ranging calculation output from the collector current of the transistor 46, and digitally measures the component using a counter mechanism (not shown) built in the control circuit section 25. It is.

The transistor 48 that controls the circuit that stores and holds the background component of the distance measurement calculation output has its base connected to the terminal T2 of the control circuit section 25 via the resistor 75, and the output of the terminal T2 of the control circuit section 25. It is turned on and off by a signal (see FIG. 9). In other words, the transistor 48 is turned on when no light is emitted. When transistor 48 is on, operational amplifier 47. Due to the feedback loop formed by the transistor 50 and the capacitor 49, the collector current Ic given by the above equation (32) flows through the transistor 50, and since the transistor 50 and the transistor 51 form a current mirror circuit, at this time, the transistor 51 Current Ic also flows.

At this time, a charge corresponding to the background light is stored in the capacitor 49, but the current Ic when no light is emitted is 1l-I2
-0, so in this case, as mentioned above, (32)
According to the formula, the amount of charge stored in the capacitor 49 is such that the transistors 50 and 51 discharge the following amount of current to the ground.

In other words, the transistor 51 plays the role of discharging the calculation output when the subject distance is open to the ground. When light is emitted, the transistor 48 is turned off and the operational amplifier 47 becomes inoperable, so the charge held in the capacitor 49 causes the transistor 51 to be turned off.
The amount of discharge current will be maintained.

In this way, a current obtained by subtracting the output when the object distance is ω from the calculation output when the object distance is finite flows through the capacitor 52 each time light is emitted, and charges are accumulated. The operational amplifier 53 is for resetting the capacitor 52, and the base of the transistor 54 for controlling the operational amplifier 53 is connected to the terminal T3 of the control circuit section 25 via a resistor 76.

Therefore, the transistor 54 is turned on by the output signal of the terminal T3 (see FIG. 9) to set the potential of the capacitor 52 to the reference voltage Vref'l, and is turned off immediately before the start of light emission to operate the operational amplifier 53. Make it impossible. Thereafter, the potential of the capacitor 52 increases due to the current injected into the capacitor 52.

When light has been emitted a predetermined number of times, the terminal T4 becomes H-L as shown in the timing chart of FIG.
is discharged. At the same time, a counter built in the control circuit section 25 operates and continues counting until the output of the comparator 62 becomes H. The comparator 62 is connected to the capacitor 5
When the voltage across 2 becomes smaller than the reference voltage Vrcr1,
Changes from L to H. The discharge rate of the capacitor 52 is determined by the constant current source 61, the resistor 58.59, and the transistor 57.60.
determined by The resistor 59 is a variable resistor, and by changing it, an arbitrary discharge speed can be set. In this way, an output corresponding to the subject distance can be obtained as the count value of the counter in the control circuit section 25.

Incidentally, in the distance detecting device described above, the adjustment of the variable resistor 17 is performed in the following procedure.

(B) Two relatively close distances are set at all distances, and the count value when the subject distance is a is set as C1, and the count value when the subject distance is a is set as C2.

(b) (3) Calculate the count value and find it by ω count. This formula (38) is calculated from the 7111J distance value (1/ac) at the two locations, (1/az, C2) to the 41st
(2) This is a calculation formula for finding a straight line 1° as shown in Figure (A) and calculating the JIIJ distance value (2), that is, the coordinates of the intersection point P4 with the vertical axis.

(c) Adjust the variable resistor 17 so that the light receiving section is shielded from light and the count value becomes approximately equal to 'oo.

The above is the method for adjusting the variable resistor 17 in this distance detection device.

Further, in each of the above embodiments, for convenience of explanation, a PSD was used as the light receiving element, but the light receiving element is not limited to this. For example, a 5PD (silicon photo diode) is used as shown in FIG. A), (B), (
As shown in C), it may be divided into two, 5PD1° and 5PD2, or the like. In other words, in this case, the position where the light intensity of the received light spot image spread over 1' across the two divided SPD 5PD2 is equal to half is the PS
This corresponds to the center position of D. The optical arrangement may be performed taking this into consideration.

[Effects of the Invention] As described above, according to the present invention, (1) the problem of nonlinearity of the distance measurement calculation output caused by the bias current ratio and the arrangement of the light-receiving optical system or noise is solved; There will be no effect.

(2) The range of distance measurement can be expanded compared to conventional devices, and the accuracy of distance measurement can also be improved.

(3) Furthermore, since the area of the light-receiving element used can be small, the cost of the light-receiving element is reduced, yield is improved, and reliability is also improved.

(4) In addition, since there is no need to adjust the distance between the light emitting element and the light receiving element, which had to be adjusted on the order of 10 μm in conventional equipment, productivity is improved and the equipment is inexpensive and highly reliable. Production becomes possible.

(5) In the above-mentioned effect (4), remarkable effects such as great effectiveness can be obtained in distance measuring devices having a large number of light projecting elements and light receiving elements.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram of the distance detection device of the present invention, and FIG. 2 (A
), (B) is a layout diagram of the distance measuring optical system in the distance detecting device of the present invention, FIG. 3 is a circuit diagram of the main part of the processing circuit of the distance detecting device showing the first embodiment of the present invention, Figures 4 (A), (B), and (C) are diagrams showing the relationship between the calculation output and the reciprocal of the subject distance in Figure 3 above, and (A) and (B) are the output signals from the signal generation means. (C) is a diagram showing the case where is set to be approximately equal to the theoretical value of the output of the calculation means when the object distance is approximately 100 degrees, and (C) is a diagram showing the case where it is set smaller than the theoretical value of the output of the calculation means. 6 is a circuit diagram of a main part of a processing circuit of a distance detection device showing a second embodiment of the present invention; FIG. 6 is a circuit diagram of a main part of a processing circuit of a distance detection device showing a third embodiment of the present invention; FIG. 8 is a circuit diagram of a main part of a processing circuit of a distance detecting device according to a fourth embodiment of the present invention; FIG. 8 is a circuit diagram of a distance measuring circuit of a distance detecting device of the present invention; FIG. Timing chart of each signal output from the control circuit section in FIG. 8, FIG. 10(A),
(B) and (C) are plan views showing other examples of light receiving elements in the distance detecting device of the present invention, and FIG. 11 is a schematic diagram for explaining the principle of triangulation used in the present invention. , FIG. 12 is a circuit diagram showing an example of a distance calculation circuit in a conventional distance detection device, FIG. 13 is a characteristic diagram showing the relationship between calculation output and object distance in FIG. 12, and FIG. A circuit diagram showing another example of a distance calculation circuit in a conventional distance detection device, FIG. 15 is a characteristic diagram showing the relationship between calculation output and object distance in FIG. 14, and FIG. 16 is a conventional distance detection circuit. A circuit diagram showing still another example of the distance calculation circuit in the device; FIG. 17 is a characteristic diagram showing the relationship between calculation output and object distance in FIG. 16; FIGS. This is a characteristic line diagram showing the relationship between calculation output and object distance when random noise is superimposed on the photocurrent detection circuit in the detection device. Figure 18 is a graph showing the case where the slope is small, and Figure 19 is a graph showing the case when it is large. , Figure 20 (A), (I3), (C), (D
), (H) explain the principle of triangulation,
(A) is the conventional example, (B) is when the baseline length is doubled, (
C) is (D) when the focal length of the receiving lens is doubled.
(E) is an explanatory diagram showing the case where the total length of the PSD is halved, and (E) is an explanatory diagram showing the case where the center of the PSD is shifted in the direction away from the light projecting means. FIG. 22 is a circuit diagram of the signal light detection and all-input operation circuit for explaining the problems that occur when the arrangement is as follows.
A characteristic diagram showing the relationship between calculation output and object distance when the object distance in FIG. 21 is close to the country, and FIG. Figure 23 (B) is a characteristic diagram showing the relationship between calculation output and object distance when
is a diagram showing the variation of the above diagram corresponding to the reflectance of the subject.

Claims (1)

[Claims] (1) A light projection means for projecting a luminous flux onto a subject; and a light projection means disposed at a position separated from the light projection means by a baseline length, receiving reflected light from the subject and generating a photoelectric conversion signal according to the light receiving position. a light receiving means, a calculation means for calculating a subject distance upon receiving the photoelectric conversion signal, a signal generation means for generating a signal corresponding to a predetermined distance, a comparison means for comparing the photoelectric conversion signal with a predetermined level; Selecting means for selecting the output of the arithmetic means when a predetermined level is exceeded as a result of the comparison by the comparison means, and selecting the output of the signal generating means when the predetermined level is not exceeded. distance detection device.