John Fasoulas

Feedback control for object manipulation by a pair of soft tip fingers

This paper discusses the problem of stable grasping and object manipulation by a pair of robot fingers when fingertips are covered with soft compressible material and fingers are allowed to incline their last link against the object surface. The area contact between the fingertips and the rigid object surface leads to nonholonomic constraints even for the planar case; however, the variational principle can be applied and the equation of motion is derived as a set of nonlinear differential equations with extra terms of Langrange multipliers incorporating the constraints. The proposed feedback controller is a linear combination of simple feedback control signals each designed for realizing grasp stabilization, regulation of object rotation and regulation of object position respectively. The controller is shown to achieve asymptotic convergence to the desired state at a stable grasping configuration. Simulation results are presented confirming the theoretical findings.

Grasping control of rolling manipulations with deformable fingertips

This paper deals with the problem of stable grasping in rolling manipulations with soft deformable fingertips in two-dimensional space and without the effect of gravity. Two rolling distance models for the soft-area contact motion and their effect on contact kinematics are considered. The modeling of contact forces in soft-area contacts is discussed and an analysis of a stable grasp is made. A simple feedback controller for stabilizing the grasp is proposed and tested in simulation. The control law is based on the objects equilibrium conditions and is designed so that it drives the system at rest by achieving a desired value for the normal contact forces and appropriate tangential forces to balance the moments created by the contact offset.

Stable pinching by a pair of robot fingers with soft tips under the effect of gravity

This paper analyses lumped-parameter dynamics of a pair of robot fingers with soft and deformable tips pinching a rigid object under the effect of a gravity force. The dynamics of the system in which area contacts between the finger-tips and the surfaces of the object arise are compared with those of a pair of rigid robot fingers with rigid contacts with an object, with or without effect of the gravity. It is then shown that there exists a sensory feedback from measurement of finger joint angles and the rotational angle of the object to command inputs to joint actuators, and this feedback connection from sensing to action realizes secure grasping of the object in a dynamic sense and regulation of the object posture. It is further shown that there are various types of other feedback connections from sensing to action, which can be used in combination of feedback signals for stable grasping and posture control of the object for realizing sophisticated object manipulation.

ACTIVE CONTROL OF ROLLING MANOEUVRES OF A ROBOTIC FINGER WITH HEMISPHERICAL TIP

In this paper we are concerned with the problem of sensory motor coordination of a robotic finger in order to evoke rolling maneuvers in a force-positioning task on a flat rigid surface. We use two different approaches to modeling the reaction of the soft fingertip with the contacted surface. Firstly, we assume that the environment imposes a purely kinematic rolling constraint on the end-effector motion in the tangent direction of the contacted surface. This implies no energy transfer or dissipation between the fingertip and the environment due to frictional forces. On the other hand, we assume that it is feasible for the fingertip to slip in which case pure rolling motion could be disturbed. The two different models are subsequently used to show by simulation that control laws, which have been designed on a rolling constraint dynamic model for frictional forces, fail to perform rolling in various environments. An extra control input that uses a reference rolling trajectory that is state dependent is proposed, which, if superimposed on a conventional force-position control law, can achieve rolling even on a surface with low friction characteristics. The proposed feedback signal does not utilize the modeling information in the control formulation, and thus permits easy implementation. Finally, the total controller is shown to achieve asymptotic convergence to the desired force-positioning task by simultaneously evoking pure rolling motion for the fingertip.

Object stable grasping control by dual robotic fingers with soft rolling contacts

The control of object stable grasping and pose regulation by two robotic fingers with soft rolling contacts is considered. The motion of the dual fingers is confined to the horizontal plane and is not affected by the gravity force. A simple feedback control law is proposed with the task to achieve a desired normal contact force and appropriate tangential forces to ensure a dynamically stable grasp. The nonlinear asymptotic stability of the closed loop system is proved. Simulation results for two 3-DOF fingers manipulating a rectangular object from an initial state to a final stable grasp configuration demonstrate the effectiveness of the controller.

Stable grasping control under gravity by dual robotic fingers with soft rolling contacts

In this paper dealing with the problem of stable grasping of a rigid and rectangular object with two robotic fingers with soft tips, we consider the case of rolling fingertips under a soft contact motion model which leads to non-holonomic constraints even for the planar case while taking into consideration the gravity effect. The analytical hand-object system kinematics and dynamics are derived and a feedback controller is proposed. The controller compensates finger gravity and superimposes control signals that realize a stable grasp configuration and compensate for the object gravity forces while driving the object at the upright position. The controller is shown to achieve asymptotic convergence to the desired upright object position at a stable grasp configuration. Simulation results are presented confirming the theoretical findings.

Dynamics, Contact Motion and Control of Dual Arm Object Manipulation With Soft Rolling Fingertips

In this paper a detailed derivation is made of the kinematics and dynamics of a pair of robotic fingers manipulating a rectangular object with soft fingertips that are allowed to roll along the object surface. The whole system is confined to the horizontal plane. Two contact motion models for the soft area contact are considered and it is shown that they significantly affect contact mode and type of finger rolling constraints. A discussion on contact forces and a grasp analysis at object’s equilibrium is made. Last, simple feedback control solutions that have been proposed for stabilizing the grasping and regulating the object’s posture are presented.Copyright