JPS61277009A - Range finder - Google Patents

Abstract

PURPOSE:To make it possible to measure a short distance and the distance of an object with high reflectivity by a simple signal processing circuit, by measuring a distance on the basis of a light receiving signal after the level of pulse light reflected from the object and received reached a predetermined value or less. CONSTITUTION:When a light emitting element is allowed to emit light and light receiving signal quantity is larger than a certain reference value, the range finding operation result thereof is not used and pulse light is again emitted to compare light receiving signal quantity with the reference value and the range finding operation result at the time when said signal quantity became smaller than the reference value is used. By this method, an accurate range finding result is obtained with respect to a short distance subject with high reflectivity. If the signal quantity obtained by first light emission is less than the reference value, the range finding operation result at that time is used to enable range finding. A light receiving signal AC1 is compared with the reference value determined by reference voltage VR in a comparator 18 and,when said signal AC1 is less than the reference value, said comparator 18 issues output. As a result, a sampling signal SP is outputted to a lens control circuit 17 from an AF control circuit 19 and the lens control circuit 17 takes in the output from a differential amplifier (subtractor) 16 as a range finding signal to control a lens system.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a distance measuring device that performs active distance measuring using an infrared light emitting diode or the like in a camera or the like.

(Prior art) One of the distance measuring methods for conventional autofocus cameras is to install a light emitting element and a light receiving element within the camera body at a predetermined distance (baseline length), and emit pulsed infrared light from the light emitting element toward the subject. An active distance measuring method is known in which a beam is emitted and the reflected beam from the subject is used to determine the distance to the subject by triangulation from the baseline length and viewing angle. - Fig. 6 shows the principle of the active ranging method, in which a narrow beam of infrared rays is projected from an infrared light emitting diode 1 driven by an infrared control pulse to a subject 3 through a projection lens 2@. The infrared light beam reflected by the subject 3 is received as a spot light on the optical position detector 5 through the light receiving lens 4. The photocurrent output from the output terminal of the optical position detector 5 is set to 11 depending on the imaging position of the infrared spot light.
Assuming .degree.I2, the sum of the amount of received light signals (11+12) is inversely proportional to the square of the subject distance and proportional to the reflectance of the subject.

Therefore, if the amount of light emitted is increased so that distance measurement can be carried out over a long distance, the amount of light received will become extremely large in the case of a close-distance object with a high reflectance, making it impossible to perform signal arithmetic processing. For example, the output when converting the received light signal under the conditions that the subject distance is 10 m and the subject reflectance is 20% is iom
If the voltage is V, the converted output will reach as much as 10 V under conditions where the subject distance is 1 m and the subject reflectance is 100%.

Therefore, it is necessary to widen the dynamic range of the light-receiving signal processing circuit, and conventional methods have been to increase the power supply voltage or to increase the dynamic range of the semiconductor device detector used as the light-receiving element, as in Japanese Patent Laid-Open No. 57-44809. The light emitting element is pulse-modulated by the sum signal of two outputs, and the output of the light emitting element is feedback-controlled so that the sum signal is always constant regardless of the subject distance.
As in the above publication, a method has been proposed in which a light emitting driving means is provided to gradually increase the output of the light emitting element, and distance measurement is performed by detecting when the sum of two outputs of the light receiving means has reached a predetermined value. .

However, the above method requires a booster circuit, which increases the cost, and requires a light emission output control circuit, which makes the signal processing circuit complicated.

(Purpose and Structure of the Invention) The present invention has been made in view of the above points, and aims to enable distance measurement of short-distance, high-reflectance objects using a simple signal processing circuit, and achieves this purpose. In order to do this, the distance measurement is performed based on the light reception signal after the level of the pulsed light reflected from the object and received becomes below a predetermined value.

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

There are light emitting circuits used in the active distance measuring method according to the present invention as shown in FIGS. 5(a), 5(b), and 5(c).
A capacitor C is connected in parallel with . (A) is an example using a booster circuit 7, (B) and (C) are examples using a resistor R and a battery 8. In both cases, when a pulse control signal is applied to terminal A, the switching transistor 9 is turned on and off. Then, the infrared light emitting diode 6 is pulse-driven and emits light.

When the values of the capacitor C and resistor R of these light emitting circuits are appropriately selected and pulsed light is emitted continuously, the light emitting power becomes gradually smaller as shown in FIG. 2, which will be described later, and the light receiving signal 11.
12 will naturally become smaller as well.

FIG. 1 shows an embodiment of a distance measuring device according to the present invention, and in the figure, 5 indicates infrared light emitted from an infrared light emitting diode 6 as a light emitting element toward a subject, reflected by the subject, and returned. Receive the beam and generate photocurrent according to the receiving position ■1. (2) An optical position detector that outputs 2; 9 is a switching transistor that drives an infrared light emitting diode 6;

In FIG. 1, reference numerals 10 and 11 refer to photocurrent 11.1 output from the optical position detector 5. (2) This is an I/V converter that converts only the 2nd exchange voltage into voltage, and both of them are composed of C, R1, and R2 for cutting the DC component, and a voltage conversion circuit consisting of an operational amplifier.

12, 13 Amplifiers that amplify the outputs of the LtI/V converters 10 and 11, 14.15 a logarithmic converter that logarithmically converts the received light images @A C2 and A C1 amplified by the amplifiers 12 and 13, and 16 a logarithmic converter that logarithmically converts the received light images @A C2 and A C1 amplified by the amplifiers 12 and 13. A subtracter 17 that calculates the difference between the converters 14 and 15 is a lens control circuit that moves the lens system based on a voltage corresponding to the object distance output from the subtracter 16.

On the other hand, '18 is a comparator that compares the light reception signal AC1 from the amplifier 13 with the reference voltage VR, and 19 is a comparator that conducts the switching transistor 9 by the on operation of the release switch S, which is turned on when the release button 7- is pressed. While causing the light emitting diode 6 to emit pulse light, a sampling signal S is sent to the lens control circuit 17 based on the output of the comparator 18.
This is an AF control circuit that outputs P. In this case, ACl is used among the two light reception signals AC and AC2 because ACl becomes much thicker than Ac1 when the subject is close.

In the distance measuring device configured as described above, when the infrared light emitting diode 6 is made to emit light, the emitted light power becomes as shown in the same figure (b). The infrared light beam reflected by the subject is received by the optical position detector 5, but the photocurrent 11.12 output from the optical position detector 5 is as shown in (c) and (d) in the same figure.
It gradually attenuates as shown in . At this time, the amplifier 12.1
Observing the received light signals AC1 and AC2 output from 3,
If the object is close and has a high reflectance, the amount of received light signal will be too large and the signal will be distorted as shown in FIGS.

However, when pulsed light is emitted continuously, the signal distortion disappears from the point at which the amount of received light signal gradually decreases as the emitted light power decreases (shown with diagonal lines in Figure 2 (E) and (F)). be). Therefore, distance measurement may be performed using the distance measurement calculation result at this time.

In other words, when the light emitting element emits pulse light and the amount of the received light signal is larger than the reference value (shown by the broken line in (e) in Figure 2), the distance measurement calculation result is not used, and the light emitting element is emitted in pulses again to determine the received light signal. By comparing the amount with a reference value and using the distance measurement calculation result when the amount is smaller than the reference value, accurate distance measurement results can be obtained even for objects at short distances and with high reflectance. If the signal amount 1q caused by the first light emission is less than the reference value, distance measurement can be performed using the distance measurement calculation result at that time.

Therefore, the comparator 18 compares the light reception signal AC1 with a reference value determined by the reference voltage VR, and outputs when it is less than the reference value. As a result, the AF control circuit 19 outputs the sampling signal SP to the lens control circuit 17, and the lens control circuit 17 receives the output from the declination device 16 at this time as a ranging signal and controls the lens system.

FIG. 3 shows another embodiment of the distance measuring device according to the present invention, in which the same components as in FIG. 1 are denoted by the same reference numerals and their explanations are omitted. In this embodiment, an infrared pulse is emitted a plurality of times during distance measurement, the received light signal is integrated, and the same distance measurement is performed based on the integrated value.

This embodiment differs from the embodiment shown in FIG. This is because integrators 20 and 21 are connected to integrate the received light signals AC2 and ACl, respectively. In this embodiment, integrators 20 and 21 are provided with analog switches in order to cause the infrared light emitting diode 6 to emit light multiple times, receive reflected light from the subject, and integrate the received light signal. The analog switch is intermittently turned on and off by a signal SW from the AF control circuit 19 to add the integral values.

FIG. 4 is a diagram similar to FIG. 2 in this embodiment, in which the shaded portions in (C) and (D) of the same figure are integrated by integrators 21 and 20, and the received light signal AC
1 becomes less than the reference value determined by the reference voltage VR, the distance is measured using the integral value of the signal. AF control circuit 19
outputs a sampling signal SP to the lens control circuit 17 based on the output of the comparator 18, and the lens control circuit 17 uses the distance measurement value obtained from the integral value logarithmically converted by the logarithmic converter 14.15 at this time. control the lens system.

(Effects of the Invention) As explained above, the present invention provides a distance measuring device that performs active distance measuring using a light emitting element connected in parallel with a capacitor, in which light is emitted for distance measuring until the received light signal becomes equal to or less than a predetermined value. The structure is configured to measure the distance based on the light reception signal received when or after the value falls below a predetermined value, so it can be used to measure short distances without using a booster circuit or complicated signal processing circuit.
Enables distance measurement of objects with high reflectance.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of a distance measuring device according to the present invention, FIG. 2 is a waveform diagram of light emission and light reception signals in the embodiment shown in FIG. 1, and FIG. 3 is a circuit diagram of an embodiment of a distance measuring device according to the present invention. A circuit diagram of another embodiment, FIG. 4 is a waveform diagram of the light emission and light reception signals in the embodiment shown in FIG. 3, and FIGS.
c) is a different example of a light emitting circuit used in the distance measuring device according to the present invention, and FIG. 6 is a diagram illustrating the principle of active distance measuring. 1.6... Infrared light emitting diode, 2... Emitter lens, 3... Subject, 4... Light receiving lens, 5... Optical position detector, 7... Boost circuit, 8...・Battery, 9...
Switching transistor, 10.11-I/V converter, 12.13... Amplifier, 14.15... Logarithmic converter, 16... Subtractor, 17... Lens control circuit, 1
8... Comparator, 19... AF control circuit, 20.21
...Integrator patent applicant Hiroshi Suzuki, agent of Konishiroku Photo Industry Co., Ltd. Patent attorney Procedural amendment dated August 21, 1986

Claims (1)

[Claims] In a distance measuring device that projects a spot light onto an object to be measured, receives the spot light reflected by the object, and measures the distance to the object based on the received light signal, the spot light is converted into pulsed light. A distance measuring device comprising: a distance measuring control circuit that commands a distance measuring operation when the level of the light reception signal becomes equal to or less than a predetermined value.