Optical distance sensor using a laser beam and processing means

Details Optical distance sensor using a laser beam and processing means Optical distance sensor using a laser beam and processing means

1990-12-11

1992-09-29

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Optical or pre-photocell system

2502016, 356 1, G01N 2186, G01C 300

Patent

active

051516080

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to an optical distance sensor, and more particularly, to a distance sensor which is capable of accurately measuring a distance from a workpiece by the use of a laser beam and which is simple in construction.


BACKGROUND ART

Conventionally, in order to obtain distance information employed for robot control, etc., it has been known to use an optical distance sensor for measuring a distance from a workpiece. This kind of sensor, mounted to, e.g., a welding torch of an arc welding robot, is arranged to project a laser beam onto a workpiece through a mirror which is angularly moved to cause the laser beam to scan the workpiece, and derive a distance between the torch and the workpiece by means of a triangulation method on the basis of an angular movement position of the mirror and an incident position of the laser beam, reflected by the workpiece surface, on a light receiving section of the sensor.
During the distance measurement, a measuring error occurs, if arc light is incident upon the light receiving section. To obviate this, conventionally, a pulsative laser beam (laser pulses) is generated, and contribution of the arc light is removed on the basis of outputs of the light receiving section which are respectively generated when each laser pulse is turned on and turned off. In order to generate the laser pulses, however, a laser-beam demodulator, which is operated in synchronism with a laser-beam modulator, or the like, is required in addition to the laser-beam modulator. Further, the distance sensor of this kind is complicated in circuit arrangement, and is high in cost.
Moreover, since the light receiving section of the conventional distance sensor is composed of a semiconductor position-detection element (hereinafter referred to as PSD) consisting of semiconductor membranes of three uniformly contiguous layers, generally, the light-receiving-element output is extremely small, i.e., in the order of several tens of nA. Thus, an amplifier circuit is inevitably required. Further, this sensor is poor in measurement stability, and makes it difficult to perform steady high-speed scanning. When the strength of the laser beam is so increased as to increase the light-receiving-section output, the human body, particularly, eyes are adversely affected by the laser beam. In case that a laser beam (higher-order reflected light including secondary reflected light) reflected by the workpiece twice or more is incident upon the light receiving section, in addition to a laser beam (primary reflected light) reflected once by the workpiece, an output, which corresponds to an imaginary light receiving position of the composed incident light of the primary reflected light and the higher-order reflected light, is outputted from the conventional light receiving section composed of the PSD. As a result, a measuring error occurs.


DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide an optical distance sensor which is excellent in measuring accuracy and which is simple in construction.
In order to achieve the above-mentioned object, according to the present invention, there is provided an optical distance sensor which comprises a light emitting section for projecting light toward a subject, and a light receiving section for receiving light reflected from the subject, and which is arranged to measure a distance from the subject in accordance with a light receiving position on the light receiving section. The distance sensor comprises the light receiving section having a group of light receiving elements each of which is arranged to generate an output corresponding to an incident light quantity, scanning means for periodically scanning the light receiving section to successively send the outputs from the group of light receiving elements, and peak detection means for detecting a peak of the outputs from the group of light receiving elements.
Preferably, the distance sensor includes a filter disposed in front of the light receiving section for permitting li

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patent: 5015868 (1991-05-01), Park

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