GB1456366A - Linear displacement devices - Google Patents

Abstract

1456366 Photo-electric control of displacement HAWKER SIDDELEY DYNAMICS Ltd 14 Dec 1973 [14 Dec 1972] 46618/72 Heading G1A [Also in Division H2] In an actuator having a jack which is linearly moved by a rotary electric motor, the jack displacement is photo-electrically measured by a MoirÚ fringe system which also produces pulses to drive the motor. In Fig. 1 the rotor 12 of the motor drives a jack which carries a grating 14. Moire fringes are produced 90 degrees out of phase at detector systems. 15, and are used to measure displacement, speed and direction at counters 23-25. The detector signals are also applied, amplified, to the field coils 13 of the motor, which is of the brushless D.C. type. The pitch of grating 14 is such that the detector pulses occur at the desired frequency relative to the motor rotation, though provided the frequency is a whole number multiple or submultiple of the desired value it can be electronically divided or multiplied to give the desired result. The measuring system can be combined with logic controls to drive the jack to a given position. Fig. 2 shows a recirculating ball screw jack, whose rotor 12 is keyed to the nut 26 and is driven by coils 13. The jack 27 carries the grating 14 which is optically sensed at 20. The jack can be used to position a gimballed rocket motor, this motor's cryogenic fuel being supplied to cool the actuator via pipes 30. If helium is used, the actuator can be superconducting 2À1‹K and 36mm pressure. The screw jack and balls can be stainless steel lubricated by an electro-plated metal, e.g. gold or lead, or by molybdenum or tungsten disulphide or niobium disellenide. The windings 13 can be copper (600‹K-80‹K) or aluminium (330‹K-4‹K) or Nb 3 Sn, NbTi, V 3 Ga on stainless steel (superconductive).