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This paper describes a control strategy of a proportional-integral-derivative (PID) controller based on stability analysis considering passivity in null space motion of redundant manipulator. Control spaces of redundant manipulator are divided into work space and null space. In the proposed approach, a disturbance observer is employed in work space, which is called work space observer. On the other hand, null space uses PID controller which is passive controller. Using gamma-dissipative property, the PID controller can compensate null space without deteriorating the motion stability. This means that the proposed approach makes it possible to realize stable and dexterous null space motion effectively. The validity of the proposed approach is verified by simulations and experiments of 4-link redundant manipulator.