Energy efficiency of cable-driven parallel robots

Cable-driven parallel robots, hereinafter referred to as cable robots, use cables to manipulate a mobile platform with 6 DOF. Cable robots have a low moved mass, as the winches with the servo drives are fixed to the machine frame and light weight synthetic fiber cables can be used. Therefore, cable robots are assumed to have a good energy efficiency. To analyze the energy efficiency in detail, we establish an energy consumption model for a cable robot and parametrize it for the cable robot IPAnema 3. Losses in the mechanical parts like winches as well as electrical losses in the servo amplifier and recuperation effects are taken into account. The analysis of the energy consumption shows that the mechanical losses are dominant. The losses occur especially during movement of the robot while the energy needed for statically balancing the load is quite low. We can experimentally determine a maximum winch efficiency of 85%. For dimensioning the drive, one has to add approximately one third of the torque to account for the friction in the mechanics. In a fully-constrained cable robot, the energy consumption can be influenced by the internal tension in a range of 20%. We also compare the energy efficiency of the cable robot with an industrial robot. The comparison shows, that both robots consume almost the same amount of energy.