Electrical pulse counters – pulse dividers – or shift registers: c – Systems – Comparing counts
Patent
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.
Malhotra Rajender
Vora Mahasukh
Cole Stanley Z.
Heyman John S.
McClellan William R.
Ohralik K.
Varian Associates Inc.
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