Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1993-01-08
1995-03-21
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
356 301, G01N 2186
Patent
active
053998707
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a laser sensor equipped in a robot performing arc welding, sealing and the like, more particularly to a position detecting method and its apparatus for detecting an object position in an operation of welding, sealing and the like by use of this sensor.
BACKGROUND ART
Conventionally, an arc welding robot, a sealing robot and the like are equipped with a laser sensor for detecting a welding position or a sealing position etc.
This laser sensor is comprised as shown in FIG. 1. In FIG. 1, a detecting unit 10 includes a laser oscillator 11, a swing mirror (i.e. galvanometer) 12 that causes a laser beam emitted from the laser oscillator 11 to scan, and an optical system 13 that converges a reflection beam reflected back on an objective so as to form an image on a light receiving element 14. A control unit 20 includes a laser actuating unit 21 for actuating the laser oscillator 11 to generate a laser beam, a mirror scanning unit 22 that causes the swing mirror 12 to pivot about its axis, and a signal detecting unit 23 for detecting a position of a received beam according to the position detected by the light receiving element 14.
The laser oscillator 11 is actuated by the laser actuating unit 21 to emit a laser beam. The mirror scanning unit 22 cooperates with the laser actuating unit 21 to cause the swing mirror 12 to perform a scanning so that the laser beam emitted from the laser oscillator 11 is directed toward a predetermined point on the object 30. The laser beam reflected back on the object 30 is converged by the optical system 13 to form an image on the light receiving element 14 in accordance with the reflected position on the object 30. This light receiving element is normally constituted of a PSD (Position Sensitive Detector) of non-split & integration type element, or a CCD (Charged Coupled Device) of split type element.
In the case where a PSD is used as a light receiving element, a beam received on a light receiving surface as shown in FIG. 2, i.e., an image of a reflected beam, is converted into a photoelectric current, and then outputted from electrodes on both sides of the element. A light receiving position x.sub.a is determined based on the values of two electric currents outputted from the electrodes on both sides of the light receiving element.
To be more specific, given that a distance from the center of the light receiving element to the respective electrode is L; a distance from the center of the light receiving element to the light receiving position is x.sub.a ; and further, the two electric current values are I.sub.1 and I.sub.2, the distance x.sub.a can be obtained by the following equation 1.
On the basis of thus obtained position x.sub.a on the light receiving element, a position of the object 30 with respect to the sensor is calculated as will be described later.
In the case where a CCD is used as the light receiving element, a beam received on a light receiving surface, i.e., an image of a reflected beam, is converted into a photoelectron and then stored into its cell. Electric charges stored in respective cells are outputted one after another from an outermost end at predetermined intervals. In the case of a CCD, the larger the quantity of the light received by a cell, the larger the amount of the electric charge stored by the cell. Accordingly, a position that has received the largest quantity of light reflected can be identified by detecting the position of the cell that gives the largest output. Thus, on the basis of such a position, the position of the object 30 with respect to the sensor can be calculated.
FIG. 3 is a view illustrating a method for determining a coordinate position (X, Y) of the object 30 with respect to the sensor on the basis of the position x.sub.a detected by the light receiving element 14. In this method, assume that a sensor origin (0, 0) is located on a straight line passing the center of the optical system 13 and the center of the light receiving element 14 (this straight line is hereinafter referre
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P. Cielo, et al., Improvement of subpixel resolution in triangulation ranging by astigmatic spot projection and wide-aperture line array imaging, Optics & Laser Technology, vol. 20, No. 1, Feb. 1988, pp. 19-24.
Iwamoto Takashi
Naito Yasuo
Nihei Ryo
Torii Nobitoshi
Wakio Hiroshi
Fanuc Ltd.
Nelms David C.
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