A Novel Spatial 3-DoF Constant-Force Generator for the Static Balancing of Parallel Robots

A statically-balanced mechanism can remain in indifferent equilibrium at a continuous set of poses while the actuators exert zero work, as the links’ weight is resisted by conservative balancing forces. This can be achieved, for example, by adding counterweights or springs. Studies on gravity balancing frequently target parallel robots, to increase their intrinsic advantages of high stiffness and smaller motor size. Here, it is considered how to balance a 3-DoF kinematic chain for applications on parallel robots, such that the chain generates a constant force on the end-effector. The design does not include counterweights and has most of the auxiliary balancing elements on the fixed base, thus reducing the inertia of moving elements; the motion is transmitted through a lightweight system of gears, pulleys and synchronous belts. The design also leaves greater freedom in the selection of the spring, which (unlike most previous works) may have nonzero free length.