Null torque‐based dynamic control for kinematically redundant manipulators

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Abstract
For the dynamic control of kinematically redundant manipulators, conventional approaches to local torque minimization have induced physically unachievable joint torques that may exceed the torque limits in the tracing motion of a long end‐effector trajectory. This article presents a new control method for redundant manipulators, named the “Null Torque‐Based Dynamic Control” (NTDC), which can guarantee stability for joint torques. The proposed method resolves the redundancyat the torque level.The command torque induced by the proposed method is composed of two terms: (1) theminimum‐norm torque, which locally minimizes torque loadings at the joints; and (2) thenull torque, which is intermittently added to the minimum‐norm torque according to a kinematic criterion to globally reduce excessively large torque requirements. In particular, the concept of null torque is based on the property offull row‐rank minorsfor a Jacobian matrix—theaspectthat is a function of a manipulator's configuration. The simulation results illustrate that the proposed method is effective for torque optimization when compared with conventional methods.

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