Comparison of object-level grasp controllers for dynamic dexterous manipulation

Abstract

Object-level control of a dexterous robot hand provides an intuitive high-level interface to solve fine manipulation tasks. In the past, many algorithms were proposed based on a weighted pseudoinverse of the grasp map. In a different approach, Stramigioli introduced a virtual-object based controller -called an Intrinsically Passive Controller (IPC). These controllers are reviewed and compared. A new controller that is similar to the IPC but using a virtual frame rather than a virtual object is subsequently proposed. The controllers are compared with respect to their object force distribution, the extendability to N fingers, the ease of specifying the object-level impedance and grasp forces, the dimensionality of the coupling springs, the internal controller dynamics, and the computational effort. Controllers for robotic hands usually implement only stiffness controllers and do not program the damping. We address how to choose and implement damping as a function of the desired object-level stiffness and the effective hand-object inertia. The evaluation reveals the dynamic effects of fast motions, which should not be neglected for the design of grasp controllers in practice. The application of the controllers to the torque-controlled DLR Hand II is employed to compare their effectiveness in experiments.

A static intrinsically passive controller to enhance grasp stability of object-based mapping between human and robotic hands

“…The basis for this control was the virtual object frame which was defined by the positions of the fingertips. This control approach has been later defined as static-Intrinsically Passive Controller (s-IPC) in [10] to remark that the dynamic introduced by the virtual object in the IPC controller is not considered in this case.…”

“…In the following, the main equations necessary for the s-IPC definition are reported. Further details can be found in [9] and [10].…”

“…Details on the derivation of the damping term D(θ) can be found in [10]. In conclusion, the input for the s-IPC controller can be considered the desired position of the object frame H ho,des and the desired contact stiffness defined by l i,des .…”

“…The considered controller is the static Intrinsically Passive Controller (s-IPC) that has been presented in [9], [10]. This solution provides an intuitive control law for object-level manipulation that does not require robust contact detection/tracking.…”

Coordinated multi-arm motion planning: Reaching for moving objects in the face of uncertainty

“…It allows for highly complex manipulation of heavy or large objects that would otherwise be infeasible for singlearm systems. Most effort in the field of multi-arm control has focused primarily on devising strategies for coordinated and stable manipulation of static objects that are already partially or fully grasped by the multi-arm system [1,23,5,21,33,7]. Seldom work has focused on developing reaching strategies that a multi-arm system can use to reach and grab moving objects.…”