JPH04225113A - Distance detecting apparatus - Google Patents

Abstract

PURPOSE:To provide a multi-beam type distance detecting apparatus which can accurately separate signal components and can detect the accurate distance to an object. CONSTITUTION:Light projecting elements Pj1-Pj3 sequentially emit light on objects SB1-SB3 in a time-division mode. In synchronization with the emission of the light from the. light projecting element Pj1, a switching circuit SW2 is connected to photodetector RV1, and a switching circuit, SW1 is connected to a photodetector RV2. Only a disturbance-light component is inputted into the switching circuit SW1. The disturbance light component and a signal light component are inputted into the switching circuit SW2. A current mirror circuit is formed of a transistor TR1 and a transistor TR2. Therefore, only the same current based on the disturbance light component flows through the transistors TR1 and TR2. Thus, only the current based on the signal light component is inputted into a current/voltage converting circuit IV1.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance detection device.

0002

2. Description of the Related Art A so-called multi-beam type distance detection device used in an autofocus camera and the like has been known (for example, see Japanese Patent Laid-Open No. 62-223734).

[0003] This multi-beam distance detection device is
Since the distance to the object is measured using a plurality of light projecting elements, it is effective in preventing so-called hollow spots.

0004

[Problem to be solved by the invention] In a normal distance measuring range, most of the light detected by the light receiving element is ambient light;
This makes it difficult to accurately separate signal components.
It was difficult to detect the exact distance to the object.

SUMMARY OF THE INVENTION An object of the present invention is to provide a multi-beam distance detection device that can accurately separate signal components and detect accurate distances to objects.

[0006]

[Means for Solving the Problems] A distance detection device according to the present invention includes a light projecting element that generates a plurality of irradiation lights that irradiate an object at different timings, and an object that is irradiated with each of the irradiation lights. a plurality of light receiving elements that receive the reflected light and generate a photoelectric conversion signal, a first selection circuit that selects the light receiving element that does not receive the reflected light, and a first selection circuit that selects the light receiving element that receives the reflected light. A second selection circuit to select, and a first current output from the light receiving element selected by the first selection circuit flowing through the primary side, and a second current output from the light receiving element selected by the second selection circuit. A current mirror circuit that flows a third current that is the same as the current on the primary side to the secondary side, a difference detection circuit that detects a difference current between the second current and the third current, and the difference detection circuit. and a distance detection circuit that detects the distance to the target object based on the differential signal detected by.

[0007]

Embodiments Hereinafter, embodiments of the distance detecting device according to the present invention will be described with reference to the explanatory diagram shown in FIG.

[0008] The light projecting elements PJ1, PJ2 and PJ3 are as follows:
Object (subject for autofocus cameras) SB1, S
It generates irradiation light to irradiate B2 and SB3, and is constructed using light emitting diodes. These light projecting elements PJ1, PJ2 and PJ3 are PJ1-PJ2
-PJ3-PJ1-PJ2...... The light is emitted cyclically and sequentially.

[0009] The timing circuit TM1 includes a light emitting element PJ1.
, PJ2, and PJ3, and switches switching circuits SW1 and SW2, which will be described later, in synchronization with the above-mentioned light emission timing.

[0010] The light receiving elements RV1, RV2 and RV3 are
Objects SB1, SB2 and SB3 irradiated by the irradiation light generated from the light projecting elements PJ1, PJ2 and PJ3
It generates a photoelectric conversion signal by receiving the reflected light from each, and is constructed using a position-sensitive device. Position sensitive...
The device generates a current from both ends of the device depending on the light receiving position in the longitudinal direction. These light receiving elements RV1
, RV2 and RV3 are installed close to each other and have the same photoelectric conversion characteristics. Note that most of the light detected by these light receiving elements RV1, RV2, and RV3 is ambient light, and the proportion of signal light based on the irradiated light from light emitting elements PJ1, PJ2, and PJ3 is very small compared to the ambient light. It is small.

Switching circuit SW1 (first selection circuit)
The switching circuit SW2 (second selection circuit) performs a switching operation in conjunction with the timing signal from the timing circuit TM1. The switching operation is synchronized with the light emission timing of the light projecting elements PJ1, PJ2, and PJ3. At the light emission timing of the light projecting element PJ1, the switching circuit SW2 is connected to the light receiving element RV1, and the switching circuit SW1 is connected to the light receiving element RV2. At the light emission timing of the light projecting element PJ2, the switching circuit SW2 is connected to the light receiving element RV2, and the switching circuit SW1 is connected to the light receiving element RV3. At the light emission timing of the light projecting element PJ3, the switching circuit SW2 is connected to the light receiving element RV3, and the switching circuit SW1 is connected to the light receiving element RV1. That is, the switching circuit SW1 selects the light receiving element that does not receive the reflected light from the object based on each irradiation light,
The switching circuit SW2 selects the light-receiving element that is receiving the reflected light from the object based on each irradiation light. In other words, only the first current based on the disturbance light component flows through the switching circuit SW1, and the second current based on the disturbance light component and the signal light component flows through the switching circuit SW2. Since the light receiving elements RV1, RV2, and RV3 are installed close to each other, the disturbance light components input to the switching circuit SW1 and the switching circuit SW2 can be considered to be the same.

Transistor TR1 and transistor T
A current mirror circuit is constructed with R2. That is,
Transistor TR1 on the primary side and transistor T on the secondary side
R2 has the same characteristics, and the first current flowing through the transistor TR1 and the third current flowing through the transistor TR2 are the same. A differential current between the second current flowing through the switching circuit SW2 and the third current flowing through the transistor TR2 is extracted from the transistor TR2.

The current-voltage conversion circuit IV1 constitutes a difference detection circuit, and converts the differential current output from the transistor TR2 into a current-voltage state.

The connection of one terminal of the light receiving elements RV1, RV2 and RV3 is as described above, and the same applies to the other terminal, which is connected to a circuit having the same structure as the circuit surrounded by the dotted line in FIG. , the output thereof is input to a distance detection circuit DT1, which will be described later.

The distance detection circuit DT1 detects the distance to the object based on the difference signal from the current-voltage conversion circuit IV1 and the difference signal based on the output from the other terminal of the light receiving elements RV1, RV2, and RV3. It is. For example, in the case of an autofocus camera, the lens position is controlled in conjunction with the distance detection operation.

Next, the operation of the embodiment will be explained.

In response to a timing signal from the timing circuit TM1, the light projecting element PJ1 emits light, and the switching circuit SW2 is connected to the light receiving element RV1, and the switching circuit SW1 is connected to the light receiving element RV2. The irradiated light from the light projecting element PJ1 is detected only by the light receiving element RV1 and not by the light receiving element RV2. Therefore, only the disturbance light component is input to the switching circuit SW1, and the disturbance light component and the signal light component are input to the switching circuit SW2. Since the light receiving elements RV1 and RV2 are installed close to each other, the current based on the disturbance light component is the same in the switching circuit SW1 and the switching circuit SW2. The first current that has passed through the switching circuit SW1 flows directly to the transistor TR1, and the second current that has passed through the switching circuit SW2 flows directly to the transistor TR2.
A third current flows through, and the remaining differential current is input to the current-voltage conversion circuit IV1. Since the transistor TR1 and the transistor TR2 constitute a current mirror circuit, the first current flowing through the transistor TR1 and the third current flowing through the transistor TR2 are the same current. Since the first current flowing through the transistor TR1 is only a current based on the disturbance light component, the third current flowing through the transistor TR2 is also only a current based on the disturbance light component. Therefore, the second current flowing through the switching circuit SW2 and the transistor TR2
The difference current between the third current and the third current flowing therein is only the current based on the signal light component. The difference current, that is, the current based on the signal component, is converted into a current-voltage by a current-voltage conversion circuit IV1, and the voltage-converted difference signal is input to a distance detection circuit DT1.

Similarly, at the light emission timing of the light emission element PJ2, a signal light component based on the irradiation light from the light emission element PJ2 is input to the distance detection circuit DT1, and at the light emission timing of the light emission element PJ3, a signal light component based on the irradiation light from the light emission element PJ2 is inputted to the distance detection circuit DT1. A signal light component based on the irradiation light is input to the distance detection circuit DT1.

[0019]

Effects of the Invention The distance detection device according to the present invention can accurately separate signal components, and therefore can accurately detect the distance to an object.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an embodiment of a distance detection device according to the present invention.

[Explanation of symbols]

PJ1, PJ2, PJ3...Light emitter RV1, RV2, RV3...Light receiving element SW1...Switching element (first selection circuit) SW2...
...Switching elements (second selection circuit) TR1, TR2...
...Current mirror circuit IV1...Current voltage conversion circuit (difference detection circuit) DT1...Distance detection circuit

Claims (1)

[Claims] 1. A light projecting element that generates a plurality of irradiation lights that irradiate a target object at different timings, and a plurality of light projecting elements that generate photoelectric conversion signals by receiving reflected light from the target object irradiated with each of the irradiation lights. a first selection circuit that selects the light receiving element that does not receive the reflected light;
A second selector for selecting the light receiving element receiving the reflected light.
A selection circuit and a first current outputted from the light receiving element selected by the first selection circuit are passed through the primary side, and the second current outputted from the light receiving element selected by the second selection circuit is supplied to the primary side. A current mirror circuit that flows a third current that is the same as the current on the secondary side to the secondary side, a difference detection circuit that detects a difference current between the second current and the third current, and a difference detected by the difference detection circuit. A distance detection device that includes a distance detection circuit that detects the distance to an object based on a signal.