Process and apparatus for the automatic inspection of patterns
First Claim
1. A process for the automatic inspection of patterns on printed circuits boards comprising positioning two cameras (3,4) each facing a corresponding printed circuit board (10,11), illuminating the printed circuits on said boards, one of the boards carrying a standard reference printed circuit, and the other a printed circuit to be inspected, providing said cameras with a strip of photodiodes lying in a plane parallel to said printed circuit boards, and effecting a comparison between said standard reference printed circuit and the printed circuit to be inspected by simultaneously:
- a. scanning corresponding areas of the printed circuits of each board by synchronized relative translation of either the cameras or the boards, said relative translation and said scanning of the strips of photodiodes being co-ordinated to cause each board to be entirely explored,b. effecting synchronized cyclic scanning of the photodiodes of said strips of photodiodes, and converting the analog signals delivered by the photodiodes into digital data and by comparing said digital data by a logic circuit providing a fault signal if comparison shows a difference between the boards, said analog signals derived from the cameras being converted into first digital data signals by comparison with a minimum voltage threshold, said first data signals corresponding to light being sensed by the photodiodes after passing through the boards or through holes in the boards, the absence of said first signals corresponding to the absence of light because of the printed circuit pattern, said analog signals which are produced by the sensed light passing through the holes being additionally converted into second digital data signals by comparison with a maximum voltage threshold.
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Accused Products
Abstract
An object pattern to be inspected, such as a printed circuit board, and a reference pattern are scanned synchronously by respective cameras. The outputs of the cameras are compared and a fault signal is produced when the outputs do not coincide.
61 Citations
10 Claims
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1. A process for the automatic inspection of patterns on printed circuits boards comprising positioning two cameras (3,4) each facing a corresponding printed circuit board (10,11), illuminating the printed circuits on said boards, one of the boards carrying a standard reference printed circuit, and the other a printed circuit to be inspected, providing said cameras with a strip of photodiodes lying in a plane parallel to said printed circuit boards, and effecting a comparison between said standard reference printed circuit and the printed circuit to be inspected by simultaneously:
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a. scanning corresponding areas of the printed circuits of each board by synchronized relative translation of either the cameras or the boards, said relative translation and said scanning of the strips of photodiodes being co-ordinated to cause each board to be entirely explored, b. effecting synchronized cyclic scanning of the photodiodes of said strips of photodiodes, and converting the analog signals delivered by the photodiodes into digital data and by comparing said digital data by a logic circuit providing a fault signal if comparison shows a difference between the boards, said analog signals derived from the cameras being converted into first digital data signals by comparison with a minimum voltage threshold, said first data signals corresponding to light being sensed by the photodiodes after passing through the boards or through holes in the boards, the absence of said first signals corresponding to the absence of light because of the printed circuit pattern, said analog signals which are produced by the sensed light passing through the holes being additionally converted into second digital data signals by comparison with a maximum voltage threshold. - View Dependent Claims (2, 3, 4)
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- 5. Apparatus for automatic inspection of patterns on printed circuit boards, said apparatus comprising a bench, a frame, means supporting said frame on said bench for displacement in the plane of the X and Y coordinates, said frame having two windows, a first board with a standard printed circuit thereon mounted on said frame at one of said windows, a second board with a printed circuit thereon to be inspected mounted on said frame at the other of said windows, two cameras equipped with a strip of photodiodes mounted on said bench, said cameras facing respective printed circuit boards for scanning corresponding areas of the printed circuits of each board, the displacement of said frame by the displacement means in the X-Y plane being coordinated with a cyclic scanning of the photodiodes of the strip to enable the cameras to scan synchronously the entire printed circuits on the boards, two light source means for illuminating said boards, and logic circuit means connected to said cameras for synchronously processing analog signals from the photodiodes thereof and for producing a logic signal when there is a fault in the printed circuit being inspected, said logic circuit means comprising means for converting the analog signals from the photodiodes of the cameras into first digital data signals by comparison with a minimum voltage threshold, said signals corresponding to light being sensed by the photodiodes after passing through the boards or through holes in the boards, the absence of said first signals corresponding to the absence of light because of the printed circuit pattern, means for converting those analog signals which are produced by passage of light through the holes into second digital data signals by comparison with a maximum voltage threshold, means for receiving the first and second digital data signals from each camera to produce a third digital data signal and means for comparing the third digital data signals from the two cameras to produce said logic signal indicative of a difference between said third signals signifying the presence of the fault in the printed circuit of the inspected board.
- 8. Apparatus according to claim 12 wherein each camera has an internal logic, one of said cameras imposing its clock pulse rate on the other by an electronic synchronization generating read enable signal (VAL) derived from a clock pulse by a counter corresponding to the number of photodiodes per strip of scanning area, said pulse being introduced in said cameras.
Specification