| 摘要 |
1293760 Machine tool control systems NATIONAL RESEARCH DEVELOPMENT CORP 12 May 1970 [12 May 1969] 23998/69 Heading G3R A servo-control system for a machine tool (e.g. a lathe), using the thermo-electric voltage V TW developed between a cutting tool and a workpiece to control cutting speed, is generally as described in Specification 1293759 but the claims are directed primarily to the arrangement for detecting the accumulation of swarf between a workpiece and the machine frame. Due to the thermo-electric e. m.f. V TW generated, a thermo-electric current flows from the thermo-electric junction between workpiece 21 and cutting tool 23, through an insulated toolholder 22, R26, the machine frame (indicated as earth point), R25, brush 20, slip ring 18, spindle 17, chuck 19, and into workpiece 21 completing the circuit. Swarf which simultaneously touches the workpiece and frame, substantially short circuits R25 causing an increase in thermoelectric current and consequently an increase in voltage V T H across R26. In addition an input voltage V SR to an amplifier 10 substantially disappears, V TH increasing correspondingly so that the sum V SR + V TH = V TW does not change and amplifier 10 output is unaffected. A swarf threshold circuit 27 compares V TH with a reference level from a pot 28 and when V TH is excessive operates a switch circuit 30 which lights a lamp 32 to attract the lathe operator. At the same time an override signal is sent to a threshold 4 which causes the opening of a switch 2 and closing of a switch 15. Thereby the lathe spindle speed is reduced to a low steady value, being governed by the setting of a potentiometer 16 instead of a potentiometer 1. A peak charge circuit (including a capacitor and diode not shown) has an output which is an average of peak excursions of the signal in the outer feedback loop, and allows rapid decrease in cutting speed providing additional compensation for attenuations of the outer loop control signal caused by swarf. |
