GB652868A - Improvements in or relating to a measuring machine and method of measuring a workpiece - Google Patents

Abstract

652,868. Gauging linear dimensions; electrical. BROWN & SHARPE MFG. CO. May 22, 1947, No. 13772. Convention date, June 20, 1946. [Class 40 (i)] [Also in Group XIX] In a machine for measuring linear dimensions comprising a tailstock 24 and headstock 22, Figs. 1 and 2 (see Group XIX), the axially movable headstock carries an axially adjustable spindle 28 for fine measurements, e.g. up to 0.00001 inches, the position of the spindle relative to the headstock being measured by bonded electrical strain sensitive gauges mounted on a spring plate 108 connected between the spindle and an element 106 which moves with the headstock. Similar gauges are mounted on a plate 36 for indicating the position of the tailstock spindle 30. As shown in Fig. 8, the gauges on plates 36, 108 are connected in Wheatstone bridge circuits R31-4, R131-4 respectively. The tailstock circuit is balanced by a potentiometer 265 adjusted by a knob 266, Fig. 1, on a panel 268. The headstock circuit is balanced by a potentiometer 270 whose scale is varied by a potentiometer 271. The potentiometer 270 is adjusted by a knob 272 on the panel 268 which also rotates a dial 274 on which a scale is so calibrated, that on movement of the potentiometer 270 to eliminate the unbalance in the headstock circuit due to movement of the spindle 28 relative to the element 106, the dial gives an exact indication of the distance moved by the spindle (e.g. in units of 0.00002 inches). The circuits are closed one at a time by a doublethrow switch 278 controlled by a knob 279 on the panel 268 which also connects the circuits to a sensitivity - controlling potentiometer R3 controlled by a knob 260 on a casing 254, Fig. 1. This casing contains an amplifier for the unbalance voltage fed to potentiometer R3 and an oscillator which supplies current to the Wheatstone bridge circuits through a transformer T2, 1 and also supplies current to a transformer T2, 2. The amplified unbalance voltage is fed to a transformer T3, 1, and the outputs of transformers T3, 1 and T2, 2 are fed through a rectifier ring RX to a meter 255, which then indicates the direction of unbalance. In operation, the dial potentiometer 270 is set to zero and the meter pointer is then brought to zero for the headstock circuit by movement of the spindle 28. After subsequent adjustment of the machine to register the dimension of the work-piece to the largest complete thousandth of an inch (see Group XIX), the spindle 28 is adjusted to remove any strain on the plate 36. The headstock circuit is switched in and the potentiometer 270 rotated until the pointer of the meter 256 is again returned to zero when the dial will indicate the distance moved by the spindle 28 from its zero position and thus the remaining fraction of the dimension of the work-piece. The machine may be used for external or internal gauging.