Direct Drive Robot

Statically Balanced Direct Drive Robot

The University of California direct-drive robot is of a practical architecture using a four-bar-linkage and is statically balanced without counterweights. Due to the elimination of the gravity forces, smaller actuators and thus smaller amplifiers drive this robot. The motors yield an acceleration of 5g at the endpoint without overheating. High-torque, low-speed, neodymium (NdFeB) magnet AC brushless synchronous motors power the robot. Due to the high magnetic field strength (maximum energy products: 35 MGOe) of the rare earth NdFeB magnets, the motors have a hightorque-to-weight ratio; the peak torque of the base motor is 118 Nm, while those of other motors are 78 and 58 Nm. Pancake-type resolvers are used as position and velocity sensors. Graphite-epoxy composite material is used for the construction of the robot links. The open-architecture controller used in the system lets users access all the control loops: the user has complete freedom in the choice of how to control the robot at all levels.