Patent GB-861973-A (GB)
Title: Improvements in or relating to acceleration control systems
Inventor: YEOMANS KENNETH ALFRED
IPC: B66B1/16
Filed: 1958-03-06
Abstract: 861,973. Control of D.C. motors; controllers. EXPRESS LIFT CO. Ltd. March 6, 1959 [March 6, 1958], No. 7240/58. Class 38 (3). [Also in Group XXXV] An electric lift motor 1 is supplied from a Ward Leonard generator 3, the field winding 6 of which is fed from a magnetic amplifier 5 controlled automatically in accordance with a desired motor torque, such torque being influenced to maintain a predetermined relationship between signals respectively dependent upon the acceleration and speed of the load, the arrangement being such that any change in the acceleration of the motor is effected at a predetermined constant rate. A tachometer generator 8 provides a signal proportional to the speed of the motor, an accelerometer 9 produces a signal proportional to the acceleration, and potentiometers 10, 11 provide signals which are functions of the position of the lift. Initially, a small speedsignal is fed through a change-over switch 19 to a selector circuit 15, and a circuit 16 provides a pattern acceleration signal, proportional to the square root of the speed, which is compared with the signal from the accelerometer 9. The error signal is supplied to the amplifier 5, whereby the acceleration increases at a uniform rate. When the speed-signal V exceeds a constant signal Va, the latter is selected by the circuit 15 so that the acceleration is held at a constant value. At a further point, the signal Vm - V from a circuit 20 becomes smaller than the signal Va (Vm representing the maximum speed) and is therefore selected in place of the latter. The pattern acceleration signal is now proportional to the square root of Vm - V and decreases linearly to zero, that condition being reached when the motor is operating at maximum speed. When the lift reaches a predetermined position, an inductor relay causes the change-over switch 14 to move to its alternative position so that a reversing circuit 17 and a further selector circuit 18 are rendered effective. At the same time, switches 19 and 21 are changed-over. A pattern retardation signal proportional to the square root of Vm - V is supplied by the circuit 18, this signal increasing at a uniform rate until it exceeds a signal fed to the circuit 18 from a divider circuit 22. This second retardation signal, which is a function of the square of the speed, and the position of the lift, becomes the new pattern signal for controlling the retardation. When a signal cv, derived from the potentiometer 11, becomes equal to the signal V, obtained from the tachometer generator 8, a relay 27 operates a change-over switch 12 and the motor is now controlled in accordance with the error signal ev - V which is fed to the amplifier 5 so that the lift reaches a stopping position at zero speed and zero acceleration. The second pattern retardation signal may be provided in a simpler form which allows easier computation, Figs. 7, 8 (not shown). In another arrangement, the relay 27 is dispensed with, and the motion of the lift controlled by signals becoming smallest in magnitude, and therefore selected in turn as the final position is approached, Fig. 9 (not shown). The speed of the lift may be controlled down to a creep speed, instead of to rest, it being unnecessary to provide a change-over switch 12 for selecting a pattern speed signal towards the end of the wind, Fig. 6 (not shown). The system may be used for controlling motors other than lift motors, and control signals other than electric signals may be provided.