US Patent 7958970 Acceleration sensor calibrated hoist positioning

A hoist positioning system includes an accelerometer attached to a hoist, a control unit for processing signals from the accelerometer and comparing the processed signals with reference data to determine a position of the hoist, a drive system for moving the hoist up and down, and a relay that is switched ON and OFF by a control signal from the control unit. When the relay is switched ON, power is supplied to the drive system from a high-voltage power source and the hoist is driven up or down. When the relay is switched OFF, power from the high-voltage power source to the drive system is cut off and the hoist stops moving up or down.