GB899233A - An automatic device for indicating the peak-to-valley voltage from an electrical feeler device measuring the profile of a workpiece - Google Patents

Abstract

899,233. Checking dimensions. PERTHEN, J. March 16, 1959 [March 14, 1958], No. 8988/59. Class 40 (1). [Also in Group XXXVI] The difference between the maximum and minimum values of the cross-section of a workpiece is evaluated by a feeder which impresses corresponding low-frequency modulations on a carrier and a measuring circuit attached thereto comprising a phase-sensitive detector, means for eliminating the D.C. component due to the standard value of the cross-section and a valvevoltmeter circuit responsive to the low-frequency modulations to indicate the desired difference. In Fig. 1, a transducer 2 is fed with A.C. from a source 3, and fluctuations in the position of the edge of the rotating workpiece 1 cause the A.C. to be modulated. This modulated signal is passed from a bridge 4 to a phasesensitive. demodulator 6, the output of which goes to the measuring circuit via a capacitor C1 to block the signal representing the average value and pass only alternating signals representing fluctuations. The difference between the extreme values of the signal is measured by allowing opposite half-cycles to charge up capacitors C3 and C4 through oppositely-connected rectifiers G3 and G4, and indicating on a voltmeter J the difference between the voltages on the capacitors. Switch S1 cancels the reading, and this may be ganged with the switch for starting rotation of the workpiece (say through 1“ revolutions). In a modification (Figs. 2 and 3, not shown) one or both of the capacitors C3 and C4 is initially charged to a high potential and then, by moving a switch, is allowed to discharge through the rectifier until its voltage equals that to be measured. All these switches may be ganged with that controlling rotation of the workpiece. So that one side of the indicating meter can be earthed, the balanced signal can be modulated or interrupted (Fig. 4) in a further valve V6 and the output demodulated (if desired) by the rectifier system D3, D4 and C10 (or an equivalent mean value rectifier). The modulation can also be effected mechanically. In Fig. 5 the output of the measuring circuit is used to reject workpieces whose deviations fall outside a predetermined limit. By assuming that every workpiece has some deviations, which are usually small enough to be acceptable, it is ensured that no specimen is accepted as " good " by reason of failure of the testing apparatus. The signal from V6 passes through a heptode V7 before being demodulated by D7 and D8, and is then applied to the grid of V8. This valve will not conduct unless there is a signal on its grid, and the positive half-cycles of this signal allow anode current to flow through an electromagnet 10 to operate a sorting flap 11 and a red or green lamp 13 or 14. If the modulated signal exceeds a certain amplitude its negative half-cycle from D5 will exceed a preset positive potential from a potentiometer U1- V5, and will cut off the heptode V7 at its second control grid. Thus no signal will pass to V8 and the electromagnet will not be energized. The instrument can be modified to indicate deviations of thickness in the longitudinal direction of the workpiece (Fig. 6, not shown). A resistor across the operating switch S1 (Fig. 1) will set the datum point for measurement, and a further resistor in series with the lead to G3 and G4 will attenuate the signal to cater for large deviations.