Patent GB-1514125-A (GB)
Title: Levelling apparatus for ac powered elevator
IPC: B66B1/16
Filed: 1976-04-15
Abstract: 1514125 Lift levelling apparatus HITACHI Ltd 15 April 1976 [21 April 1975] 15617/76 Heading B8L A levelling apparatus for an a.c. powered elevator comprises an a.c. induction motor having units SCR1 and SCR2 controlling the motoring and braking torques thereof, a level error detecting means PH, PS for detecting dislocation in either direction of the floor level of an elevator car c from a target floor level whilst loading and unloading thereat, and means for actuating the units SCR1 and SCR2 in response to an output from the error detecting means PH, PS to control the torque produced by the motor to remove said dislocation. The induction motor comprises mechanically coupled high and low speed induction motors IM1, IM2, the high speed motor being controlled through the first thyristor device SCR1 for producing starting and accelerating torque whilst the low speed motor is controlled through the second thyristor device SCR2 for producing decelerating torque, the two motors being connected to a tachometer generator TG, an electrically controlled brake B and a sheave S over which the elevator car rope R passes. The thyristor units SCR1 and SCR2 are controlled to speed up or slow down the car c in either direction, in response to a signal from a phase shifter APS which is determined by the difference between the actual speed of the car c as indicated by the tachometer TG and a desired speed determined by a speed pattern generator PTN. For normal running of the elevator car possible only when the car gates are closed, a signal, e.g. "up", from a controller CTL causes closing of contacts u1, u2 to energize the motor and de-energization of the brake B, a normal running speed pattern signal being fed from the generating unit PTN to the phase shifter for comparison, as a target floor is approached, a first position detector PH signals the controller CTL causing the generating unit PTN to generate a reducing running speed signal appropriately controlling the motors IM1, IM2 until the car c reaches the target floor and the detector PH generates a stop signal causing the brake B to be applied. When a level error of the car floor exceeds a pre-determined setting in either up or down direction, whilst the elevation car gates are open, a second position detecting unit Ps signals the controller CTL which signals the speed pattern generator PTN from which a level correction speed pattern signal is sent to the phase shifter APS. The controller also closes the appropriate "up" and "down" contacts U1, U2 or D1, D2 and de-energizes the brake B. The thyristor units SCR1, SCR2 control the motor torque in response to comparison between the actual speed and the correction speed pattern signals until the level error of the car c becomes less than another predetermined setting where the detecting unit PS applies a normal level attainment signal to the controller CTL which then generates a signal for decelerating and stopping the car c and applying the brake. The second position detecting unit PS comprises two vertically spaced detecting elements mounted on the car for co-operation with a shielding plate fixed on the elevation shaft.