Force control of redundant robots in unstructured environment

Abstract

In this paper, a method for force control of redundant robots in an unstructured environment is proposed. We assume that the obstacles are not known in advance. Hence, the robot arm has to be compliant with the environment while tracking the desired position and force at the end-effector. First, the dynamic properties of the internal motion of redundant manipulators are considered. The motion is decoupled into the end-effector motion and the internal motion. Next, the dynamic model of a redundant manipulator is derived. Special attention is given to the inertial properties of the system in the space where internal motion is taking place; we define a null-space effective inertia and its inverse. Finally, a control method is proposed which completely decouples the motion of the manipulator into the task-space motion and the internal motion and enables the selection of dynamic characteristics in both subspaces separately. The proposed method is verified with simulation and with experimental results of a four-degrees-of-freedom planar redundant robot.

Combined Torque and Velocity Control of a Redundant Robot System

“…The system is dynamically consistent when torques in the null space do not produce any accelerations in the task space (Khatib [1995]) and when forces in the task space do not produce any accelerations in the null space (Nemec and Žlajpah [2002]). According to Khatib (Khatib [1995]) the system is dynamically consistent only when inertia weighted generalized inverse is used.…”

Experimental Evaluation of Dynamic Redundancy Resolution in a Nonholonomic Wheeled Mobile Manipulator

“…Such a partitioning, defined in terms of a metric endowed by the kinetic energy of a simple me- chanical system, can formally be shown to be orthogonal and decoupled [23]. This was subsequently extended for mobile manipulator systems with holonomic bases [7] and fully actuated manipulators [24]. However, to the best of our knowledge, this has never been extended to and evaluated within experimental NH-WMMs.…”

Set-point navigation of a redundant robot in uncertain environments using finite range sensors

“…Khatib [16] presented a real-time obstacle avoidance approach for general manipulators using the artificial potential field method first outlined by Koditschek and Rimon [17] which could be adapted for redundant robot manipulators. Nemec and Zlajpah [18] devised a force control method for redundant manipulators operating in an unstructured static environment. To compensate for the unknown workspace, Nemec and Zlajpah allowed the manipulator to bump into the obstacle while ensuring that the resulting forces are minimized to prevent damage to the manipulator and the obstacle.…”