Static balancing of spatial parallel platform mechanisms -: Revisited

This article discusses the development of statically balanced spatial parallel platform mechanisms. A mechanism is statically balanced if its potential energy is constant for all possible configurations. This properly is very important for robotic manipulators with large payloads, since it means that the mechanism is statically stable for arty configuration, i.e., zero actuator torques are required whenever the manipulator is at rest. Furthermore, only inertial forces and moments have to be sustained while the manipulator is moving. The application that motivates this research is the use of parallel platform manipulators as motion bases in commercial Fight simulators, where the weight of the cockpit results in a large static load. We first present a class of spatial parallel platform mechanisms that is suitable for static balancing. The class of mechanisms considered is a generalization of the manipulator described by Streit (1991, "Spatial Manipulator and Six Degree of Freedom Platform Spring Equilibrator Theory," in Second National Conference on Applied Mechanisms and Robotics, VIII.B, pp. 1-1-1-6). Then sufficient conditions on the kinematic parameters that guarantee static balancing are derived for this class. Finally a particular mechanism is studied in more detail to show the practicability of its design. [S1050-0472(00)01401-X].