A new parallelogram linkage configuration for gravity compensation using torsional springs

All articulated robots suffer from the adverse effects of gravity loading, namely, increased actuator size and degraded performance. It is pointed out that parallelogram linkage manipulators are uniquely suited for counterbalancing technique due to the decoupled nature of gravity terms in their dynamic equations. The authors present a novel parallelogram linkage configuration where the two actuated degrees-of-freedom in the vertical plane are gravity compensated using torsional springs. They show that the robot design is thus improved in two ways: the peak torques required to be output by the actuators are reduced, thereby allowing smaller motors to be selected; and by ensuring that the equilibrium position for all robot joints assumes a safe configuration on power-off, i.e. a position where the robot links do not collide with one another or with other objects, the need for fail-safe brakes is eliminated. A three-degree-of-freedom direct drive robot using the proposed configuration is under development at the Centre for Artificial Intelligence and Robotics to demonstrate the feasibility of these concepts