Static Model-Based Grasping Force Control of Parallel Grasping Robots With Partial Cartesian Force Measurement

This article presents a static model-based approach for grasping force control of a class of low-inertia kinematically redundant parallel and hybrid parallel robots with remotely operated gripper. Although these robots are originally studied with kinematic redundancy, they can also be considered to be redundantly actuated or nonredundant depending on the interactions with the environment. Three different static models are then developed according to the types of redundancy and velocity Jacobians, which are demonstrated through a planar and a spatial parallel robots. The possibility of implementing these models for grasping force control is analyzed. Moreover, we show that the Cartesian force and moment included in the closed force control loop do not need to be measured directly by multidegree-of-freedom force/torque sensors, but can be calculated based on the grasping force that is acting on each jaw of the gripper, which is easily measured using a load cell. A combined position and grasping force control scheme is proposed and experiments are conducted to verify the effectiveness of the nonredundant static model. The proposed approach is readily applied to other kinematically redundant parallel grasping robots.