GB991782A - Improvements in apparatus for the measurement of torsion and the like - Google Patents

Abstract

991, 782. Photo-electric torque measuring apparatus. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Aug. 17, 1961 [May 20, 1960], No. 17987/60. Heading G1A. In apparatus for measuring the torque of a rotating shaft 1, light beams from sources 5 and 12 are each passed through one of radial gratings 3 and 8, rotating with the shaft, and through one of the stationary radial gratings 2 and 7, gratings 2 and 3 forming a reference pair, to produce two systems of moirÚ fringes detected respectively by photo-cell 6 and 11. The outputs of the two photocells in the form of two series of pulses Fig. 2, are fed to a phase discriminator 13 comprising a bi-stable flip-flop giving a positive output where triggered by a pulse from photo-cell 6 and a negative output when triggered by a pulse from photocell 11 and having its alternating output fed to a damped servomotor 10, responsive to the average valve of the said output only and controlling an arm 9 adjusting grating 7 over a small angle. With no torque applied to the shaft, servomotor 10 adjusts grating 7 so that the pulses from photocell 11 occur midway between there from photocell 6 and phase discrimator 13 gives a symmetrical alternating output having zero average valve. Pointer 14 then indicates zero torque on scale 15. With torque applied to the shaft the pulses from photo-cell 11 tend to lag from their position midway between the reference pulses causing phase discrimator 13 to give a positive average output causing servomotor 10 to adjust grating 7 to the new position of equilibrium, pointer 14 then giving a direct indication of the applied torque. Alternatively the phase discriminator may comprise a circuit giving "on"/"off" conditions and having its output compared with a fixed valve and fed as above to the servomotor. In another embodiment, servomotor 10 may be dispensed with and the output pulses of photo-cell 11 adjusted to the midway equilibrium position by a delay device 16 giving an indication of the torque on a meter. In this embodiment the amount of measureable twist between the two rotating gratings is limited to one grating division, this limitation however can be overcome by including a frequency divide to reduce the number of pulses compared. A single light source may be used between gratings 8 and 2. Specifications 932,471 and 953,050 are referred to.