Adjustable manipulability of closed-chain mechanisms through joint freezing and joint unactuation

This paper presents the adjustment of the manipulability of a closed-chain mechanism using joint freezing/releasing and joint unactuation/actuation, leading to the improved task adaptability. A closed-chain mechanism under consideration consists of multiple redundant subchains and individual joints can be put into frozen, actuated or unactuated mode, as needed. First, the joint freezing and joint unactuation allowed for a closed-chain mechanism are examined, which limits the possible combinations of joint modes. Second, the kinematics of a closed-chain mechanism is formulated, taking into account joint freezing and joint unactuation. Third, the manipulability ellipsoids of a closed-chain mechanism with/without joint freezing and/or joint unactuation are defined and compared. Finally, the wide range of the manipulability of a closed-chain mechanism due to the changes of joint modes is exemplified