  This paper presents a unified algorithm for motion and force control for a
six degree-of-freedom spatial manipulator. The motion-force controller performs
trajectory tracking, maneuvering the manipulator's end-effector through desired
position, orientations and rates. When contacting an obstacle or target object,
the force module of the controller restricts the manipulator movements with a
novel force exertion method, which prevents damage to the manipulator, the
end-effector, and the objects during the contact or collision. The core
strategy presented in this paper is to design the linear acceleration for the
end-effector which ensures both trajectory tracking and restriction of any
contact force at the end-effector. The design of the controller is validated
through numerical simulations and digital twin validation.
