Abstract
This paper discusses coupling of two 2R open kinematic chains with their second joints unactuated in the horizontal plane. When they are not coupled, they can operate as independent underactutaed manipulators and when they are coupled, they can operate as a single 5R parallel manipulator which has the same number of actuators as its degrees of freedom. In the horizontal plane, they cannot make use of gravity for motion generation. In parallel mechanisms, uncertainty and stationary-uncertainty singularities exist in general. If the two open kinematic chains form such a singular configuration when they touch with each other, they can exert force with each other and therefore can be coupled easily. In addition, at a stationary-uncertainty singular configuration, they can escape from it after they are coupled simply by controlling their joint velocities. We propose a coupling mechanism without actuation, which can be a smooth free joint when coupling is achieved. The two open kinematic chains can reach an uncertainty singular configuration if they touch with each other at certain initial configurations. This paper analyzes this motion and show such initial configurations. We experimentally verify the proposed coupling.
