JPS61226607A - Range finder - Google Patents

Abstract

PURPOSE:To improve the distance measuring accuracy by making constant the sum of two light outputs without being influenced by the distance up to the object and the reflecting ratio of the object. CONSTITUTION:An infrared emission beam light pulse-modulated from an infrared emission diode 1 is emitted toward an object 3, and the reflecting beam light is photo-detected by a light position detecting device 5. Photodetecting circuits 6 and 7 output voltages V1 and V2 corresponding to electric currents I1 and I2, at a light emitting control circuit 10, first, a subtracter 10a calculates the difference between V1+V2 and a reference voltage V0, an integrator 10b integrates the difference Vr. By integrating in a such a way, the parameter only of photodetecting circuits 6 and 7 is related to the output of the light position detecting device 5, a photodetecting element, from the theorem of the final value, and therefore, the parameter is not related to the distance up to the object and the reflecting ratio of the object. Thus, the range of the amplifier at the photodetecting circuit can be made narrow and a logarithm compression goes to be unnecessary.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a distance measuring device that can accurately measure distances over relatively long distances regardless of the reflectance of a subject.

(Prior Art) Autofocus cameras and autofocus video cameras have been developed in recent years, making photography much easier.
Bokeh image detection method that detects the sharpness of the subject image, left and right 2
Double image matching detection method that detects the overlap of two objects to be measured, or upper and lower image matching detection method, which uses the reflected light of the light beam emitted towards the object to be measured to calculate the distance using the triangulation method from the baseline length and viewing angle. Various methods are known, such as the ray distance formula, for determining .

FIG. 4 shows the principle of distance measurement using the ray distance method, in which a narrow infrared beam is projected onto a subject 3 through a projection lens 2 from an infrared light emitting diode I driven by a red light control pulse. The infrared light beam reflected from the subject 3 is received as a spot light on the optical position detector 5 through the light receiving lens 4. Optical position detector 51, Fig. 3 (
As shown in b), two electrodes P1. Charging output terminals 5a, 5b and common electrode terminal 5C connected to P2 respectively
The position d of the infrared spot light on the detector 5 is the distance from the light emitting lens 2 to the subject 3, the focal length of the light receiving lens 4 is f, the light emitting, the light receiving lens 2, The distance between the optical axes of 4 (called the baseline length) is S
Then, the imaging position of the infrared spot light is subject 3.
You can see that it changes depending on the distance. On the other hand, light
The magnitude of the photocurrents I, I2 outputted from the output terminals 5a, 5b of the position detector 5 changes depending on the imaging position of the infrared spot light, and is expressed by the following relational expression.

Here, C is the length of the light receiving surface of the optical position detector 5.

This relationship is illustrated in Figure 5 (b), which shows 1'2
It can be seen that /I is approximately proportional to 1/L.

As can be seen from the above formula, I2/11 is the base line length S, the focal length f of the light receiving lens 4, and the light receiving surface length 2C of the optical position detector 5.
Therefore, distance measurement is possible regardless of the strength of the spot light due to differences in the reflectance of the subject or deterioration of the infrared light emitting diode 1 over time. Furthermore, as can be seen from FIG. 3(b), the smaller the distance to the subject, the larger the output value and the larger the change, allowing for highly accurate distance measurement.

In this way, the optical distance measurement method can realize a compact and highly reliable distance measurement system because distance measurement is performed purely electrically and no mechanical mechanism or operation is required. In the distance measuring system as shown in FIG. 4, when the amount of light from the infrared light emitting diode 1 is constant, the received light IQ of the optical position detector 5 is expressed by the following equation.

Here, γ is the reflectance of the subject (5 to 100%). Now, even if the distance to the subject is 1 to 10 m, the received light IQ varies over a very wide range of 1 to 103, so the front-stage amplification of the optical position detector 5 must be logarithmically compressed.

Therefore, the distance measurement output becomes 9°I2/11, which is not simply proportional to 1//shi, so in order to continuously move the shooting lens like a video camera, a conversion is necessary to calculate the extension amount from the distance measurement output. There is a problem that the conversion circuit for this becomes complicated.

Furthermore, since the amount of light emitted from the infrared light emitting diode is constant, there is also the problem that a constant amount of power is always consumed.

(Object and Structure of the Invention) The present invention has been made in view of the above-mentioned points, and aims to provide a distance measuring device that can measure a long distance regardless of the reflectance of the subject, and achieves this object. In order to do this, the reflected light of the spot light projected onto the subject is received by a light receiving means, and the light receiving means outputs the reflected light according to the amount of light received and the light receiving position.
An integrator was provided to integrate the difference between the sum of the two optical outputs and a reference value, and the light intensity of the spot light was controlled based on the integrated output.

(Example) The present invention will be explained below based on the drawings.

FIG. 1 is a block diagram showing a distance measuring device according to the present invention in combination with a lens control device, where A surrounded by broken lines is the distance measuring system and B is the lens control system.

1 to 5 constituting the distance measuring system A are the same as shown in FIG. 6.7 amplifies the output current 11.12 from the optical position detector 5 and generates a proportional voltage v1. The light receiving circuit that outputs v2, color 81, is a subtraction circuit and an addition circuit that subtracts the outputs V1 and ■2 of the light receiving circuits 6 and 7, respectively, but the adding circuit 9 outputs v10 and ■2.
Perform operation 2. Reference numeral 10 denotes a light emission control circuit that controls the light emission state (light emission time and light emission interval) of the infrared light emitting diode 1 based on the output of the adder circuit 9.

On the other hand, 11 constituting the lens control system B is a subtraction circuit that takes the difference between the position signal of the focusing lens 15 and the output of the subtraction circuit 8, and 12 is a distance measuring circuit that measures the distance by comparing the output of the subtraction circuit 11 with two predetermined values. A window comparator that determines whether the value is within the focal depth of the focusing lens; 13, a motor drive circuit that drives the motor 14 for moving the focusing lens based on the output of the window comparator 12; 15, the focusing lens; 16, This is a potentiometer that outputs a position signal according to the position of the focusing lens 15.

FIG. 2 is a specific block diagram of the light emission control circuit 10 of the range finder shown in FIG.
10b is an integrator that integrates the output of the subtracter 10a, and 10c is pulse modulated based on the output of the integrator 10b. This is a pulse modulation circuit.

Next, the operation of the distance measuring device according to the present invention will be explained.

An infrared light emitting diode 1 emits a pulse-modulated infrared beam toward a subject 3, and an optical position detector 5 receives the reflected beam from the subject 3. As a result, from the optical position detector 5, two currents 11. I2 outputs.

The light receiving circuit 6°7 receives these currents ■1. A voltage V1゜■2 corresponding to 2 is output, the subtraction circuit 8 calculates Vl-V2, the addition circuit 9 calculates V1+V2, Vl-V2 is given to the lens control system B, and V1+V2 is given to the light emission control circuit 10.
given to.

In the light emission control circuit 10, as shown in FIG. 2, the subtracter 10a first calculates the difference between v1+V2 and the reference voltage V0,
The difference Vr is integrated by an integrator 10b. By integrating in this way, according to the final value theorem, only the parameters of the light receiving circuits 6 and 7 are involved in the output of the optical position detector 5, which is a light receiving element, so it is independent of the distance to the subject and the reflectance of the subject. . On the other hand, if the output of the subtracter 10a is simply amplified without being integrated, a constant value cannot be obtained because the parameter related to the reflectance of the object will be involved in the output of the optical position detector 5. In the pulse modulation circuit 10c, the output ■ of the integrator 10b. Infrared light emitting diode based on 1
The amount of light emitted is controlled by controlling the peak value of the current flowing through the optical position detector 5, so that the amount of light received by the optical position detector 5 becomes constant.

By integrating the difference between the light output and the reference value in the light emission control circuit 10 in this way, the light output becomes independent of the distance to the subject and the reflectance of the subject, making it possible to narrow the range of the amplifier in the light receiving circuit. This eliminates the need for logarithmic compression.

FIG. 3 shows an example of the light emission control circuit 10.

In the figure, 20 is the reference voltage V. A variable resistor 21 is used to generate the voltage difference between (■1+V2) and vo.
22 is a switch that determines the modulation frequency; 23 is a gate-configured oscillation circuit; 2
4 is a Darlington-connected amplifier circuit. switch 22
When turned on and off at a predetermined period, the infrared light emitting diode 1 is driven by a current pulse-modulated at a frequency determined by the frequency, and emits infrared pulsed light. The light output of the detector 5 (see FIG. 1) is independent of the distance to the object and the reflectance of the object.

In the lens control system B, the subtraction circuit 11
The difference γ between the output (Vl + V2 >) and the position signal Y of the focusing lens 15 output from the potentiometer 16 is determined. If not, the motor 1 is connected via the motor drive circuit 13.
4, the focusing lens 15 is moved back and forth so that it comes within the depth of focus. In this way, automatic focus adjustment of the lens is performed.

The present invention is not limited to the embodiments described above,
Various modifications are possible. For example, as a light receiving means, a photocurrent 11. Although one element that outputs I2, ie, an optical position detector, is used, two separate photoelectric elements that each output an output according to the distance may be used.

In addition, the sum of the two outputs ■1 + ■2 is input to the integrator, but the necessary function is to measure the absolute value of the reflected light from the measurement object, and in this sense, either of the two outputs Either one (■1 or V2>) may be input to the integrator.

(Effects of the Invention) As explained above, the present invention allows a light-receiving means to receive the reflected light from the object of the spot light projected onto the object, and to make contradictory changes depending on the receiving distance and the light-receiving position. In a distance measuring device that outputs two optical outputs and controls the light intensity of the projected spot light so that the sum of the two optical outputs becomes constant,
The difference between the sum of the two light outputs and a predetermined reference value is integrated, and the light intensity of the projection spot is controlled based on this integrated output, so the sum of the two light outputs is the distance to the subject. It becomes easy to keep the distance constant without being affected by the reflectance of the subject or the subject, and the accuracy of distance measurement can be improved.

Roughly speaking, according to the present invention, since the difference between the two light outputs from the light receiving means is inversely proportional to the distance to the subject and also inversely proportional to the amount of extension of the focusing lens, the lens control system that controls the position of the lens is The structure can be simplified.

Furthermore, since the amount of light emitted by the infrared light emitting diode is reduced when a subject with a high reflectance or the subject is close, power consumption and the life of the diode are extended.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of a distance measuring device according to the present invention, FIG. 2 is a block diagram of a light emission control circuit of the distance measuring device shown in FIG. 1, and FIG. 4 is a diagram explaining the principle of the conventional distance measuring method adopted in the present invention, and FIG. 5 (A) is a diagram explaining the principle of the distance measuring method adopted in the present invention. The diagram (b) is a characteristic diagram showing the relationship between the distance and the output current of the optical position detector shown in (a). 1... Infrared light emitting diode, 2... Light projection lens, 3
... Subject, 4... Light receiving lens, 5... Optical position detector, 6.7... Light receiving circuit, 8... Subtraction circuit, 9.
...Addition circuit. 10... Light emission control circuit, 11... Subtraction circuit, 12.
...Window comparator, 13...Motor drive circuit, 14...Motor, 15...Focusing lens, 16...Potentiometer, 10a...Comparator,
10b... Integrator, 10G... Pulse modulation circuit. Patent applicant Konishiroku Photo Industry Co., Ltd. Agent Patent attorney Hiroshi Suzuki Male lineage 5 chart (A) (O) Range L

Claims (2)

[Claims] (1) A distance measuring device that measures the distance to the measurement target by projecting a spot light onto the measurement target, receiving the reflected light from the measurement target with a light receiving unit, and calculating the output of the light receiving unit, In the distance measuring device that feeds back the output of the light receiving means to the light projecting means to control the light projecting means, an integrator for integrating the difference between a reference voltage and the output of the light receiving means is provided in the feedback circuit, and the integrator A distance measuring device characterized in that the output is used to control the light projecting means. (2) The light receiving means generates two outputs that show different changes with respect to changes in the distance to the measurement target, and the distance information is obtained from the relative value of the two outputs, and the distance information is obtained from the relative value of the two outputs.
2. The distance measuring device according to claim 1, wherein the sum of two outputs or one of the two outputs is input to the integrator.