A novel methodology for the design of a gravity-balanced serial-type spatial manipulator is presented. In the design, gravity effects of the system can be completely compensated at any configuration. The gravity balance of the n-DOF manipulator is achieved by the suspensions of only n zero-free-length springs, where each spring is individually fitted between a primary link and its adjacent auxiliary link. No spring has to be installed across the spatial manipulator from a far remote link to ground such that the motion interference among the springs and the links can be prevented. Besides, since the embedded auxiliary links along the primary links of the manipulator form a series of spatial parallelogram revolute-spherical-spherical-revolute modules, the active DOFs of the system remain the same as the primary manipulator and the range of motion of the manipulator will not be hindered. As a result, the n-DOF manipulator can serve the general function of an articulated serial-type manipulator in kinematics. The simulated results of a 6DOF gravity-balanced manipulator modeled on ADAMS shows that the static equilibrium as well as the kinematics of the system can be successfully accomplished by this proposed methodology.
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