Missing or broken wafer sensor

Details Missing or broken wafer sensor Missing or broken wafer sensor

1982-05-24

1985-04-23

Heyman, John S.

Electrical pulse counters, pulse dividers, or shift registers: c

Systems

Comparing counts

377 8, 377 24, 340674, G01B 1104, G04F 1004

Patent

active

045134308

ABSTRACT:
Apparatus for sensing a missing or broken wafer in an automated wafer transfer system. The apparatus includes means for moving a wafer transfer mechanism from a first position along a prescribed path. A counter coupled to an oscillator is enabled when the wafer transfer mechanism and a wafer are moved away from the first position. A photosensor senses the presence of the wafer at a second position along the prescribed path and inhibits the counter. The count stored in the counter is compared with a predetermined count corresponding to the time required for movement of an unbroken wafer to the second position. If the counts do not agree, a missing or broken wafer is indicated and corrective action is taken.

REFERENCES:
patent: 3952944 (1976-04-01), Koyanagi et al.
patent: 4063820 (1977-12-01), Borgese
patent: 4246577 (1981-01-01), Shima et al.
patent: 4268843 (1981-05-01), Brown et al.
patent: 4311427 (1982-01-01), Coad et al.

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