US Patent 10201393 Constant force spring with active bias

A compensated constant force spring device includes a bracket, a drum rotatably supported by the bracket, and a constant force spring wound on the drum. A motor is fixed to the bracket and provides a compensating force to the drum. The motor may be located in an interior volume of the drum. A control module may coupled to the motor to control the compensating force. A position sensor may be coupled to the control module. The compensating force may be responsive to a signal from the position sensor. The constant force spring may support a load and counterbalance gravitational forces on the load. The compensating force may be adjusted when the load approaches an end of a range of travel.