RCC characteristics of planar/spherical three degree-of-freedom parallel mechanisms with joint compliances

A three degree-of-freedom (DOF) planar parallel manipulator has been extens ively studied as the fundamental example of parallel manipulators. In this work, we explicitly show that this mechanism possesses a completely decoupl ed compliance characteristic at the object space, which is the important op erational requirement for a RCC device. As the first condition to have a RC C point, this mechanism should maintain symmetric configurations. As the se cond condition, the same magnitude of revolute joint compliance should be s ymmetrically placed at the same joint location of each chain. We also inves tigate the compliance characteristics of a spherical 3 DOF mechanism which has a similar kinematic structure to the planar mechanism through simulatio n. It turns out that the spherical mechanism also has a RCC point at the in tersection point of all nine joint axes in its symmetric configuration. Fur ther, more general output compliance model is derived for those mechanisms with redundant joint compliances, It is expected that these two parallel me chanisms not only can be used as excellent 3 DOF RCC devices, but also can be integrated into the design of a new six DOF RCC device. [S1050-0472(00)0 1101-6].