JPH0435006B2 - - Google Patents

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 object is used to determine the distance to the object by triangulation from the baseline length and viewing angle.

FIG. 6 shows the principle of the active distance measuring method, in which a narrow beam of infrared rays is projected onto a subject 3 through a projection lens 2 from an infrared light emitting diode 1 driven by an infrared control pulse. The infrared light beam reflected by the subject 3 is transmitted to the light receiving lens 4.
The light is received as a spot light on the optical position detector 5 through the light. Depending on the imaging position of the infrared spot light, the photocurrent output from the output terminal of the optical position detector 5 is I ₁ ,
Assuming I ₂ , the sum of the received light signal amounts (I ₁ +I ₂ ) 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 calculation processing. For example, if the output when the received light signal is converted is 10 mV when the subject distance is 10 m and the subject reflectance is 20%, then the converted output will be 10 V when the subject distance is 1 m and the subject reflectance is 100%. It also reaches.

Therefore, it is necessary to widen the dynamic range of the light-receiving signal processing circuit, and in the past, for this purpose, the power supply voltage was boosted, or the two outputs of a semiconductor position detector used as a light-receiving element were Pulse modulation is applied to the light emitting element by the sum signal of A method has been proposed in which a light emitting drive means for gradually increasing the output of the element is provided, 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, resulting in high cost, and requires a light emission output control circuit, resulting in a complicated signal processing circuit.

(Object and Structure of the Invention) The present invention has been made in view of the above points, and an object of the present invention is to enable distance measurement of short-distance, high-reflectance objects using a simple signal processing circuit. In order to achieve this, a light projecting means for continuously emitting pulses of the spot light projected onto the object to be measured; a light receiving means for receiving the spot light reflected by the object to be measured and outputting a pair of light reception signals; In the distance measuring device comprising a distance measuring calculation circuit that calculates a distance measuring signal based on the pair of light reception signals, the light emitting means includes a reducing means for decreasing the output of the spot light emitted in continuous pulses over time. means for comparing the level of the received light signal of the pair of light received signals with a larger output and a preset reference value; and a control circuit that controls the distance measurement calculation circuit to calculate and obtain a distance measurement signal based on either or both of the pair of light reception signals when the signal becomes below and the pair of light reception signals thereafter. It is something that

(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. . A is an example using the booster circuit 7, B and C are resistors R
In both cases, when a pulsed control signal is applied to the terminal A, the switching transistor 9 is turned on and off, and the infrared light emitting diode 6 is pulse-driven to emit light.

If 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 will gradually decrease as shown in Figure 2, which will be described later, and the light emitting signals I ₁ and I ₂ will naturally also gradually decrease. It's getting smaller.

FIG. 1 shows an embodiment of the distance measuring device according to the present invention, and in the figure, reference numeral 5 indicates infrared light emitted from an infrared light emitting diode 6 as a light emitting element toward a subject, and returning after being reflected by the subject. receive the beam,
An optical position detector 9 outputs photocurrents I ₁ and I ₂ according to the light receiving position, and 9 is a switching transistor that drives the infrared light emitting diode 6.

In FIG. 1, 10 and 11 are I/V converters that convert only the alternating current components of the photocurrents I ₁ and I ₂ output from the optical position detector 5 into voltage, and both are I/V converters for cutting the direct current component and It consists of R ₁ , R ₂ and a voltage conversion circuit consisting of an operational amplifier. 1
2 and 13 are amplifiers that amplify the outputs of the I/V converters 10 and 11, 14 and 15 are logarithmic converters that logarithmically convert the received light signals AC ₂ and AC ₁ amplified by the amplifiers 12 and 13, and 16 are two Logarithmic converter 14 and 1
A subtracter 17 that calculates the difference between the subtractor 16 and 5 is a lens control circuit that moves the lens system based on the voltage output from the subtracter 16 that corresponds to the subject distance.

On the other hand, 18 is a comparator that compares the light reception signal AC ₁ from the amplifier 13 with the reference voltage _VR , and 19 is a release switch S that is turned on when the release button is pressed.
The AF turns on the switching transistor 9 to cause the infrared light emitting diode 6 to emit pulsed light, and outputs the sampling signal SP to the lens control circuit 17 based on the output of the comparator 18.
It is a control circuit. In this case, two received light signals
Of AC ₁ and AC ₂ , AC ₁ was used because AC ₁ is much larger than AC ₂ when the subject is close.

In the distance measuring device configured as above,
When the infrared light emitting diode 6 emits light, the light emitting power becomes as shown in FIG. 2B. The infrared light beam reflected by the subject is received by the optical position detector 5, but the photocurrent output from the optical position detector 5
I ₁ and I ₂ gradually attenuate as shown in C and D of the same figure. At this time, when the received light signals AC ₁ and AC ₂ outputted from the amplifiers 12 and 13 are observed, if the subject is close and has a high reflectance, the amount of received light signals is too large and the signals are distorted as shown in Figure 2 E and F. This will cause the distance measurement calculation result to be incorrect. However, when pulsed light is emitted continuously, the amount of received light signal gradually decreases as the emitted light power decreases, and the signal distortion disappears after a certain point (as shown by diagonal lines in E and F in FIG. 2). 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 received light signal amount is larger than a certain 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 pulsed again and the received light signal amount is calculated. By comparing the distance measurement with a reference value and using the distance measurement calculation result when the value becomes smaller than the reference value, accurate distance measurement results can be obtained even for a close-distance, high-reflectance subject. If the signal amount obtained by the first light emission is below the reference value,
Naturally, 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 falls below 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 1
7 takes in the output from the subtracter 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.

The difference between this embodiment and the embodiment shown in Fig. 1 is that the I/V
Circuit configuration of converters 10 and 11 and amplifier 12
and the logarithmic converter 14 and between the amplifier 13 and the logarithmic converter ₁₅ , respectively.
This is because integrators 20 and 21 that integrate AC ₁ are connected. In this embodiment, analog switches are provided in the integrators 20 and 21 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 integral value of the analog switch intermittently turned on and off by the signal SW from the AF control circuit 19 is added.

FIG. 4 is a diagram similar to FIG. 2 in this embodiment, and the signals after the received light signal AC ₁ becomes less than the reference value determined by the reference voltage V _R are shown with diagonal lines in C and D of FIG. The signal of the portion indicated by is integrated by integrators 21 and 20, and the distance is measured using the integrated value. AF control circuit 19 is comparator 1
A sampling signal SP is output to the lens control circuit 17 based on the output of control.

(Effects of the Invention) As explained above, the present invention provides a distance measuring device that performs active distance measurement using a light emitting element connected in parallel with a capacitor. The structure is configured to calculate and obtain a distance measurement signal based on a pair of received light signals when the level of It becomes possible to measure the distance of subjects.

[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.
Waveform diagrams of the light emission and light reception signals in the embodiment shown in the figure, Figure 5 A, B, and C are different examples of the light emitting circuit used in the distance measuring device according to the present invention, and Figure 6 explains the principle of active distance measurement. It is a diagram. 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, 18 ... Comparator, 19 ... AF control circuit, 20, 21 ... Integrator.

Claims (1)

[Scope of Claims] 1. Light projecting means for continuously emitting pulsed spot light onto the object to be measured, and light receiving means for receiving the spot light reflected by the object to be measured and outputting a pair of light reception signals. and a distance measurement calculation circuit that calculates a distance measurement signal based on the pair of light reception signals, and the reduction means for reducing the output of the continuously pulsed spot light over time. The light projecting means is provided with a comparing means for comparing the level of the received light signal of the pair of light receiving signals with a larger output with a preset reference value; a control circuit that controls the distance measurement calculation circuit to calculate and obtain a distance measurement signal based on either or both of the pair of light reception signals when the light reception signal becomes below the reference value and the pair of light reception signals thereafter; A distance measuring device characterized by being provided with. 2. The distance measurement calculation circuit is configured to calculate and obtain a distance measurement signal based on an integral value obtained by integrating the pair of light reception signals when the level of the light reception signal with the larger output becomes equal to or less than the reference value. The distance measuring device according to claim 1, further comprising a control circuit for controlling the distance measuring device.