Control of Rolling Contacts in Multi-Arm Manipulation

When multiple arms are used to manipulate a large object, it is beneficial and sometimes necessary to maintain and control contacts between the object and the effector (the contacting surface of an arm) through force closure. Rolling and/or sliding can occur at these contacts, and the system is characterized by holonomic as well as nonholonomic (including unilateral) constraints. In this paper, the control of planar rolling contacts is investigated. Multi-arm manipulation systems are typically redundant. In our approach, a minimal set of inputs is employed to control the trajectory of the system while the surplus inputs control the contact condition. The trajectory includes the gross motion of the object as well as the rolling motion at the contacts. A nonlinear feedback scheme for simultaneous control of motion as well as contact conditions is presented. A new algorithm which adapts a two-effector grasp with rolling contacts to external loads and the trajectory is developed. Simulations and experimental results are used to illustrate the salient features in control and planning

Stable Prehensile Pushing: In-Hand Manipulation with Alternating Sticking Contacts

This paper presents an approach to in-hand manipulation planning that exploits the mechanics of alternating sticking contact. Particularly, we consider the problem of manipulating a grasped object using external pushes for which the pusher sticks to the object. Given the physical properties of the object, frictional coefficients at contacts and a desired regrasp on the object, we propose a sampling-based planning framework that builds a pushing strategy concatenating different feasible stable pushes to achieve the desired regrasp. An efficient dynamics formulation allows us to plan in-hand manipulations 100-1000 times faster than our previous work which builds upon a complementarity formulation. Experimental observations for the generated plans show that the object precisely moves in the grasp as expected by the planner. Video Summary -- youtu.be/qOTKRJMx6HoComment: IEEE International Conference on Robotics and Automation 201

Dynamic Control of 3-D Rolling Contacts in Two-Arm Manipulation

When two or more arms are used to manipulate a large object, it is preferable not to have a rigid grasp in order to gain more dexterity in manipulation. It may therefore be necessary to control contact motion between the object and the effector(s) on one or more arms. This paper addresses the dynamic control of two arms cooperatively manipulating a large object with rolling contacts. In the framework presented here, the motion of the object as well as the loci of the contact point either on the surface of each effector or on the object can be directly controlled. The velocity and acceleration equations for three-dimensional rolling contacts are derived in order to obtain a dynamic model of the system. A nonlinear feedback control algorithm that decouples and linearizes the system is developed. This is used to demonstrate the control of rolling motion along each arm and the adaptation of grasps to varying loads

Multi-Arm Manipulation of Large Objects With Rolling Contacts

The problem of manipulating objects which are relatively larger than the size of the manipulators is investigated. Large objects without special features such as handles can not be grasped easily by the conventional end effectors such as parallel-jaw grippers or multi-fingered hands. This work focuses on the manipulation of large objects in the plane and analyzes the contact interactions. The flat surface effectors of planar three link manipulators interact with the object. The dynamics of the object and the manipulators are included in the equations of motion that govern the planar manipulation system. The contacts between the link surface and the object can be characterized by rolling, sliding, and separation. This study focuses on rolling which is explicitly included in the dynamic model of the system. Contact separation is avoided by enforcing the unilateral constraint that each manipulator must push at the contact point. Sliding is avoided by constraining the applied force to fall within the contact friction cone. The dynamic coordination between multiple manipulators is achieved by simultaneously regulating the motion of the object and the critical contact force. Control algorithms are developed that employ nonlinear feedback to linearize and decouple the system. A motion and force planner is developed which incorporates the unilateral constraints into the system. The motion planner also specifies the rolling motion for each contact. Rolling enables the system to avoid slipping by repositioning the contact points such that forces are applied along the surface normals. The calculations of the rolling motion planner are based on the dynamics of the object, the measured external disturbance forces, and desired critical contact force. Extensions of the analysis are investigated by relaxing certain key assumptions. Results from simulation and experimentation are presented to verify the efficacy of the theory and to provide insight into the issues of practical implementation

Dexterous Manipulation Graphs

We propose the Dexterous Manipulation Graph as a tool to address in-hand manipulation and reposition an object inside a robot's end-effector. This graph is used to plan a sequence of manipulation primitives so to bring the object to the desired end pose. This sequence of primitives is translated into motions of the robot to move the object held by the end-effector. We use a dual arm robot with parallel grippers to test our method on a real system and show successful planning and execution of in-hand manipulation

Dynamics and Control of Whole Arm Grasps

In this paper we consider the dynamics and control of whole arm grasping systems. We develop a control scheme that employs a minimal set of inputs to control the trajectory of the system while using the surplus inputs to control the interaction forces in order to maintain the unilateral constraints at both rolling and sliding contacts. Since the number of surplus inputs is less than the number of output force variables, we propose a controller that controls the critical contact force components. We emphasize the dynamic models and algorithms for computing contact forces, which are crucial to the development of the control algorithms. Finally, we show how compliant contact models and a previously developed integrated simulation approach [14] are used to overcome the difficulties with uniqueness and existence of solutions. A planar whole arm manipulation system is used as an example to illustrate the basic ideas