Optics: measuring and testing – By polarized light examination – With light attenuation
Patent
1989-09-15
1991-09-10
Evans, F. L.
Optics: measuring and testing
By polarized light examination
With light attenuation
29720, G01B 1114, B23P 2100
Patent
active
050468510
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of sensing the position of a reflecting, rounded corner using an electro-optical device.
One example of considerable interest is a corner of the frame section around a window opening in a car body. Attempts are being made to automate the insertion of windscreens and other car windows. A robot picks up the window, using suction cups on a lifting frame, and pushes it into the window opening. Adhesive has already been run round the edge of the window (or possibly the frame section). A plastic trim may be carried on the window or be pre-fitted in the frame section. A significant problem is that a car body on a production line is only positioned within rather loose tolerances, say .+-.40 mm, and yet the window must be positioned correctly, to better than lmm relative to the window opening, before the robot pushes the window in. Misalignment leads to spectacular but costly results.
It is known to determine the position of the window opening using four or more fixed cameras in conjunction with a powerful image analysis computer. Such a system is very expensive, requires elaborate set-up procedures and is too easily upset by deviations from ideal conditions. It is also known to attach simple source-detector sensors to the lifting frame itself (e.g. light emitting and light sensitive diode pairs) and to move the lifting frame in two dimensions until detected edge transitions indicate that the window is in the right position. This system is simple and cheap but very slow. The lifting frame has to be moved about by the robot for about 15s before the correct position is reliably determined.
Electro-optical position sensors such as diode pairs generally sense whether or not an object is present by the presence or absence of diffused light returning from the object. Thus there are many known electro-optical devices used for sensing profiles, generally employing a scanning beam and a sensor which detects back-scattered light (e.g. EP-A2-0 137 517, EP-A1-0 163 347, GB 1 379 769 and GB-A 2 001 753). EP-A1-0 132 200 discloses a device which detects edges and gaps between edges but which again relies upon scattered light. None of these devices is suitable for use when the object is a reflecting, rounded corner.
Other known devices do sense specularly reflected light (e.g. W086/04676 for sensing angle of inclination of a scanned surface, EP-A-0 143 012 for determining spatial coordinates, using a rotating laser beam). These devices are neither intended for nor suitable for sensing the position of a corner.
The object of the present invention is to provide an improved but simple method of sensing the position of a reflecting, rounded corner.
According to the invention there is provided a method of sensing the position of a reflecting, rounded corner using an electro-optical sensing device, characterized in that the device comprises a light source providing a fan beam of light orientated across the corner and a light detector which specifies the position of a reflecting object as a position along a scale referenced to the optical device, the positions of the source and detector being such that a relatively large amount of the light reaching the detector is light reflected from a narrow stripe extending along the corner.
The term "light" is not intended to restrict the invention to use of visible light. Infra-red light could be used for example.
It is greatly preferred in the present invention to use, as stated above, a fan beam of light, in contrast to the scanning beams which are essential in most if not all of the references mentioned above. Such a beam can be generated very simply using static components such as a slit aperture and/or a cylindrical lens whereas a scanning beam requires more complex optics, e.g. a rotating mirror. Nevertheless, a fan beam, can be simulated by a scanning pencil beam and this is used in a non-preferred modification of the method of the invention.
The invention further relates to automatic assembly apparatus for fitting a component to an object having ro
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Internal Report, Colin Morgan, 20th Oct. 1986, "Visit to Kuka. . . "(5 Pages).
Davy McKee (Poole) Limited
Evans F. L.
Hantis K. P.
O'Connell Robert F.
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