Apparatus for detecting proper positioning of objects in a holde

Details Apparatus for detecting proper positioning of objects in a holde Apparatus for detecting proper positioning of objects in a holde

1994-03-23

1995-11-14

Westin, Edward P.

Radiant energy

Photocells; circuits and apparatus

With circuit for evaluating a web, strand, strip, or sheet

25055943, 414935, G01N 2186

Patent

active

054669456

ABSTRACT:
The positions of objects in a holder, such as a cassette containing semiconductor wafers, are determined by a system that projects a pair of coplanar light beams through the cassette from one side. A reflector on the opposite side reflects both light beams back though the cassette and onto separate photodetectors on the one side. A computer analyzes signals from the photodetectors as the cassette is moved through the light beams. As the cassette moves the light beams are interrupted by the wafers. The relative widths and timing of pulses in the signals indicate the location of wafers in the cassette and whether a wafer is misaligned.

REFERENCES:
patent: 4786816 (1988-11-01), Ohmori et al.
patent: 4803373 (1989-02-01), Imamura et al.
patent: 4954721 (1990-09-01), Suzuki
patent: 5003188 (1991-03-01), Igari
patent: 5225691 (1993-07-01), Powers et al.
patent: 5308993 (1994-05-01), Holman et al.
patent: 5319216 (1994-06-01), Mokuo et al.

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