Acceleration damping of elevator resonant modes and hydraulic elevator pump leakage compensation

An hydraulic elevator system, comprising:

• an elevator car disposed in a hoistway to serve a plurality of floors in a building;
• an hydraulic hoist cylinder connected to said elevator car for vertically positioning said car in said hoistway;
• a positive displacement rotary pump for providing hydraulic fluid to said cylinder;
• a check valve disposed between said pump and said cylinder, said check valve preventing reverse flow of hydraulic fluid from said cylinder when said cylinder is holding said car stationary at a floor landing, said check valve having a sensor for providing a check valve signal indicative of said check valve beginning to open after pressure of fluid provided by said pump is equal to the pressure of fluid on the cylinder side of said check valve;
• an electric motor for driving said pump;
• a motor speed sensor disposed on said motor to provide a motor speed signal indicative of the rotary speed of said motor;
• a controller responsive to said check valve signal for providing a motor speed command signal to effect a car speed profile after said check valve signal indicates said check valve is opening;
• and
• a motor speed control responsive to said motor speed sensor and to said controller for causing said motor to operate at a rotary speed determined by said motor speed command signal;
• characterized by the improvement comprising:
• said controller, when said car is to run, providing a continuously increasing pump leakage speed command signal until said check valve signal indicates that said check valve has begun to open, and thereafter providing a constant pump leakage speed command signal equal to the value thereof when said check valve began to open, said controller being also responsive to said pump leakage speed command signal to provide said motor speed command signal in response thereto, whereby to ramp up said motor speed to the point where the check valve opens and thereafter to compensate for leakage in said pump.