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

A three degree-of-freedom planar parallel manipulator has been extensively studied as the fundamental example of parallel manipulators. In this work, we explicitly show that this mechanism possesses a completely decoupled compliance characteristic at the object space, which is the important operational requirement for RCC devices. As a first condition to have a RCC point, this mechanism should maintain symmetric configurations. As the second condition, the same magnitude of joint compliance should be symmetrically placed at the same joint location of each chain. An alternative planar configuration with more adjustable feature of compliance is introduced. We also investigate the compliance characteristics of a spherical 3-degree-of-freedom mechanism which has a similar kinematic structure as the planar mechanism. It turns out that the spherical mechanism also has a RCC point at the intersection point of all of nine joint axes in its symmetric configuration. It is expected that these two parallel mechanisms not only can be used as excellent three degree-of-freedom RCC devices, but also can be integrated into the design of a new six degree-of-freedom RCC device