Impedance control of redundant manipulators for safe human-robot collaboration

In this paper, the impedance control paradigm is used to design control algorithms for safe human-robot collaboration. In particular, the problem of controlling a redundant robot manipulator in task space, while guaranteeing a compliant behavior for the redundant degrees of freedom, is considered first. The proposed approach allows safe and dependable reaction of the robot during deliberate or accidental physical interaction with a human or the environment, thanks to null-space impedance control. Moreover, the case of control for co-manipulation is considered. In particular, the role of the kinematic redundancy and that of the impedance parameters modulation are investigated. The algorithms are verified through experiments on a 7R KUKA lightweight robot arm

Tracking Control of Redundant Manipulators with Singularity-Free Orientation Representation and Null-Space Compliant Behaviour

This paper presents a suitable solution to control the pose of the end-effector of a redundant robot along a pre-planned trajectory, while addressing an active compliant behaviour in the null-space. The orientation of the robot is expressed through a singularity-free representation form. To accomplish the task, no exteroceptive sensor is needed. While a rigorous stability proof confirms the developed theory, experimental results bolster the performance of the proposed approach

Cooperative impedance control with time-varying stiffness

The focus of much automation research has been to design controllers and robots that safely interact with the environment. One approach is to use impedance control to specify a relationship between a robot\u27s motion and force and control a grasped object\u27s apparent stiffness, damping, and inertia. Conventional impedance control practices have focused on position-based manipulators - which are inherently non-compliant - using constant, task-dependent impedances. In the event of large trajectory tracking errors, this implementation method generates large interaction forces that can damage the workcell. Additionally, these position-based devices require dedicated force/torque sensors to measure and apply forces. In this paper, we present an alternative impedance controller implemented on cooperating torque-based manipulators. Through the use of time-varying impedance parameters, this controller limits the interaction forces to ensure harmless manipulation. Successful completion of transport and insertion tasks demonstrated the effectiveness of the controller

Contact Estimation in Robot Interaction

In the paper, safety issues are examined in a scenario in which a robot manipulator and a human perform the same task in the same workspace. During the task execution, the human should be able to physically interact with the robot, and in this case an estimation algorithm for both interaction forces and a contact point is proposed in order to guarantee safety conditions. The method, starting from residual joint torque estimation, allows both direct and adaptive computation of the contact point and force, based on a principle of equivalence of the contact forces. At the same time, all the unintended contacts must be avoided, and a suitable post-collision strategy is considered to move the robot away from the collision area or else to reduce impact effects. Proper experimental tests have demonstrated the applicability in practice of both the post-impact strategy and the estimation algorithms; furthermore, experiments demonstrate the different behaviour resulting from the adaptation of the contact point as opposed to direct calculation