| 摘要 |
887,131. Automatic speed-control systems. WESTINGHOUSE ELECTRIC CORPORATION. April 26, 1960 [May 5, 1959], No. 14530/60. Class 38 (4). [Also in Group XXIII] A machine for lapping semi-conductor wafers comprises top and bottom lap plates 25, 26. Wafers 32 are contained in pockets 30 in work carriers 28 located between the lap plates and formed as planetary gears located between a sun gear 22 and a ring gear 24 driven, at differing speeds, by a shaft 20 driven through belt 18, gear-box 14 and coupling 16 by a squirrel-cage motor 12 within the housing of which is an eddy current coupling. To bring the shaft 20 up to speed slowly when starting the machine so as to minimize the danger of the wafers shattering, a coil 274 for the eddy current coupling can only be energized when a potentiometer 252 controlling excitation to the eddy current coupling has been placed in minimum speed position. A governor generator 288 connected to rotate with the output side of the eddy current coupling provides a tachometer feedback voltage which is rectified and compared with a control voltage resulting from rectifiers 290, 292 connected to the potentiometer 252, the voltage difference being modulated by grid control of the firing of the valve 286, thereby supplying the desired excitation to the coil 274 for the desired lapping speed.
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