Direct design of a velocity controller and load disturbance estimation for a self-balancing industrial manual manipulator

Self-balancing manual manipulators are devices that countervail the weight of a load that must be manually handled and moved by a human operator. Standard manipulators are made of a framework with an electric motor on the top and a spool connected to the motor shaft through a transmission gear. The load is hung by a handling device connected to a metallic rope wound on the spool. The device considered in this paper, in its current layout, is endowed with a load cell that measures the load weight and is controlled in an open loop. A new layout has been designed, which is not including the weighting load cell and is feedback controlled. The load’s counterbalance and movement are obtained by a velocity closed loop control algorithm designed using a direct design method, the Virtual Reference Feedback Tuning (VRFT). VRFT provides controller parameters tuning in a completely automatic way based on a single I/O batch measurement on the plant. Moreover, the elimination of the load weight transducer causes issues to some handling devices that need weight measurements to attach and detach the load. So, a load mass observer has been designed using a gravitational torque estimator, which is an enhanced version of standard disturbance torque observer for electric motors.