GB893207A - Apparatus for driving an object along a path or orbit - Google Patents

Abstract

893,207. Automatic positional control systems. NATIONAL RESEARCH DEVELOPMENT CORPORATION. June 11, 1959 [June 13, 1958], No. 18924/58. Class 38 (4). [Also in Groups XXXVIII and XL (c)] In a remote positional control servo system, the object to be positioned (a radar scanner or machine tool element) is driven by the combined outputs of an hydraulic motor which is capable of a high initial acceleration but has a low maximum velocity, and an electric motor capable of a high velocity but providing poor acceleration. The motors are controlled by incremental pulses recorded on a magnetic tape. The shaft 10 carrying a radar aerial is driven by the hydraulic motor Q and, through a sun and planet-wheel system 1 by the electric motor M. Alternatively, Fig. 9 (not shown), the electric motor may have a " stator " driven by the hydraulic motor. The electrical control signal may be applied in parallel to both motors, or the hydraulic motor may close a centrifugal switch, Fig. 4 (not shown), to energize the electric motor only when the hydraulic motor has reached a given velocity, or the signal may be integrated as in Fig. 2, before being applied to the electric motor, or the signals for the two motors may be obtained from separate tracks of a magnetic programme tape, Fig. 8 (not shown). If the scanner is reversible, two centrifugal switches are controlled through oppositely arranged free-wheels so as to control reversing contacts, Fig. 5 (not shown), in the circuit of motor M, which is a 3-phase motor. If the motor M is controlled by integrating the signal to motor Q, the integrated signal may be compared, Fig. 6 (not shown), with the output of a tachometer generator and any unbalance used to control a pair of triodes, Fig. 7 (not shown), which energize forward and reverse relays to run the motor M in the required direction. The position of the shaft may be detected by a disc 12, Fig. 2, carrying a radial diffraction grating which forms moirÚ fringes with a fixed reference grating 16, the fringes being detected by a photo-cell 18. The number of pulses generated by the fringes is compared at 24 with the number of pulses representing increments of movement recorded on a magnetic tape 22 and any error used to energize the driving motors. If the radar scanner is ship-borne the reference grating 17, photo-cell 18, &c. Fig. 3, are mounted on a bracket 14 which can rotate about the shaft 10 and is positioned through a linkage 28, 29, 32 to a directional gyro 33 so that movements of the scanner are made relative to a fixed directional reference instead of having the yaw of the ship superimposed.