Robot Manipulator Control

Teleoperation with kinematically redundant robot manipulators with sub-task objectives

“…In (1) and (2), F H (t) ∈ R n represents the unmeasurable user input force applied to the master system, and F E (t) ∈ R n represents the unmeasurable input force from the environment. The subsequent development utilizes the property that the inertia matrices are positive definite, symmetric and satisfy the following inequalities [19] …”

Grasping with a soft glove: intrinsic impedance control in pneumatic actuators

“…To see this, we note that, in the simplest setting where a rigid single degree-of-freedom actuator enters into contact with an elastic object with intrinsic stiffness k e , the interaction force simply reads k e Dx, where Dx is the indentation. This force can attain large values and can even destabilize a controller designed only to regulate the position of the end effector [1]. Embedding soft linkages in underactuated grippers can mitigate this issue by partially delegating the stabilization of the grasping task to the mechanical response of the gripper itself: see [2] for a recent design of an underactuated compliant grasper exploiting this principle; however, there are clear limitations to this approach, which requires partial or complete knowledge of the environment.…”

“…By choosing k p (k e , the interaction force can be greatly reduced and the overall closed-loop stability is preserved, albeit at the expense of an error in tracking the position of the end effector. This approach has since been extended and widely used to control the motion of robotic arms and fingers and, simultaneously, the force exerted on the grasped object, as reviewed for example in [1]. In modern implementations, a combination of position and force controllers is therefore used to divide the control task into subtasks normal and tangential to the contact surface [1]; examples of real experimental realizations of this class of controllers are presented in [4][5][6].…”

“…Although techniques for the controlled motion of manipulators in the absence of obstacles or interacting with known objects are well established, both the stability of the system while in contact with objects of unknown stiffness and the safety of the manipulator and the object being held still pose significant challenges [1]. To see this, we note that, in the simplest setting where a rigid single degree-of-freedom actuator enters into contact with an elastic object with intrinsic stiffness k e , the interaction force simply reads k e Dx, where Dx is the indentation.…”

“…Attempts to imitate this performance in artificial systems such as robotic grippers has highlighted the intrinsic difficulties associated with this task. These difficulties include the ability to get a good grasp on objects with different shapes while controlling the interaction force to achieve robust grasping without damaging the object (or the gripper itself) and simultaneously predicting the mechanical response of the unknown grasped objects [1].…”