JPH0576565B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a projecting distance measuring device that irradiates a target object with a light beam from a projecting means and measures the distance to the target object from the incident angle of reflected light.

(Prior Art) A light projection type distance measuring device that uses the principle of triangulation by arranging a light projecting means and a light receiving means at regular intervals is widely used as an automatic focus adjustment device of a camera.
As shown in Fig. 3, this light projecting type distance measuring device has a light projecting section A at one end of the camera body and two light receiving elements B ₁ and B ₂ connected in antiparallel at the other end. Light receiving part B
At the same time, this light-receiving section B is linked to the camera's focusing mechanism to scan, and the two light-receiving elements
It is configured to detect the point in time when the amounts of light incident on B ₁ and B ₂ become equal, and use this as a focusing signal.

Conventionally, detection of whether the same amount of light has entered the two light receiving elements B ₁ and B ₂ has been carried out by comparing it with a preset reference voltage as shown in Figure 4. The amount of incident light changes significantly depending on the reflectance and distance, and the detection output fluctuates significantly. Especially when measuring long distances, the level difference ΔV between the reference voltage and the detection output is extremely small, so when focusing There was a problem in that the detection output of the sensor did not necessarily cross the reference voltage, resulting in errors in distance measurement.

(Objective) In view of the above-mentioned problems, an object of the present invention is to provide a projection type distance measuring device that can obtain a focusing signal with high distance accuracy regardless of the level of incident light.

(Structure) Therefore, details of the present invention will be described below based on illustrated embodiments.

FIG. 1 shows an embodiment of the present invention, in which reference numeral 1 denotes a distance measuring optical system, which receives pulsed power from a drive circuit 2 and intermittently irradiates a subject with a light beam. Light projecting unit 3, two light receiving elements 4a,
4b are connected in inverse parallel, and the light receiving section 4 moves on a base line in conjunction with the extension and retraction of the photographing lens 5 of the camera body. Reference numeral 7 denotes a synchronous rectifier circuit, which receives a signal from the amplifier circuit 6 and a signal from a reference signal oscillator 8 (described later), and is configured to rectify the received light signal in synchronization with the blinking timing of the light projector 3. There is. Reference numeral 8 denotes the reference signal oscillator described above, which is configured to output a clock signal of a constant frequency to intermittently light up the light projecting section 3, and to output a clock pulse serving as a reference signal for the synchronous rectifier circuit 7. 9 is an integrating circuit with a resistor R
and a capacitor C, which converts the pulsed signal output from the synchronous rectifier circuit 7 into a DC signal. Reference numeral 10 denotes an inverting amplifier that amplifies the output signal from the integrating circuit 9 with an amplification factor of 1 and inverts it. 11 is a comparator, one input terminal of which is connected to the integrating circuit 9, and the other input terminal of which is connected to the output terminal of the inverting amplifier 10.

Next, the operation of the apparatus configured as described above will be explained based on the timing diagram shown in FIG.

When a release button (not shown) on the camera body is pressed, an operating voltage is supplied to the device, and the light projector 3 flashes at a constant frequency to emit a light beam toward the subject S. At the same time, the motor M operates and the light receiving section 4
is moved in one direction and scans over the baseline length. At this point, the object S is not in focus, so the reflected light from the subject S enters only into the light receiving element 4a forming the light receiving section 4. Therefore, the light receiving section 4 outputs an alternating current signal with a large amplitude that alternates in accordance with the blinking cycle of the light projecting section 3. A synchronous rectifier circuit 7 extracts a component related to the irradiation beam from this AC signal, and an integration circuit 9 converts it into a DC signal. This DC signal is sent to the comparator 11
The signal is input directly to one input terminal of , and is inverted by the inverting amplifier 10 and input to the other input terminal.

At this point, since there is a level difference between the signals input to the two terminals of the comparator 11, the comparator 11 is not inverted.

In this way, as the light receiving section 4 is moved in the focusing direction, the reflected light from the subject starts to enter the other light receiving element 4b of the light receiving section 4, so that the output of the light receiving element 4a is transferred to the other light receiving element 4b. The output level of the integrating circuit 9 begins to decrease as it is offset by the output from the integrating circuit 9. As a result, a monotonically decreasing signal is input to one input terminal of the comparator 11, and a monotonically increasing signal formed by inverting the output from the integrating circuit 9 by the inverting amplifier 10 is input to the other input terminal of the comparator 11. When the photographic lens 5 reaches the in-focus point, the levels of the signals input to the two input terminals of the comparator 11 cross and match, so the comparator 11 is reversed and activates an electromagnet (not shown) to rotate the photographic lens 5. stop.

Needless to say, the point at which the two signals input to the comparator 11 intersect is not affected by the level of the signal output from the integrating circuit 9 or its rate of change;
In other words, it is not affected by the amount of light incident on the light receiving section 4.

(Effects) As explained above, according to the present invention, the signals from the two light receiving elements connected in antiparallel and the inverted signal are compared, and when they match, a focusing signal is output. This eliminates the need to set a reference voltage for focusing point detection, making it possible not only to accurately detect the distance of distant objects or objects with low reflectance, but also to prevent the effects of power supply voltage fluctuations. can do.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a device showing an embodiment of the present invention, FIG. 2 is a waveform diagram showing the operation of the same device, and FIG. 3 is an explanatory diagram showing the principle of a floodlight distance measuring device. and FIG. 4 are explanatory diagrams showing focus detection in a conventional light projection type distance measuring device. DESCRIPTION OF SYMBOLS 1... Distance measuring optical system, 3... Light emitter, 4... Light receiving part, 4a, 4b... Light receiving element, 9... Integrating circuit,
10... Inverting amplifier circuit, 11... Comparator.

Claims (1)

[Claims] 1. A light projecting means that intermittently irradiates light at a constant frequency, a light receiving means that moves at a certain baseline length from the light projecting means and is composed of two light receiving elements connected in antiparallel, and a subject. a photographic lens system for photographing the image; a moving means that scans the light receiving element in the base line length direction and moves the photographic lens system in an optical axis direction in conjunction; and synchronously rectifies the signal from the light receiving means at the frequency. circuit means for outputting a direct current signal from the circuit means; inverting means for inverting the output signal from the circuit means; and outputting a focusing signal when the levels of the output signals of the circuit means and the inverting means are compared and match. A floodlight type distance measuring device characterized by: