Xiaoping Yun

Effect of motor dynamics on nonlinear feedback robot arm control

A nonlinear feedback robot controller that incorporates the robot manipulator dynamics and the robot joint motor dynamics is proposed. The manipulator dynamics and the motor dynamics are coupled to obtain a third-order-dynamic model, and differential geometry control theory is applied to produce a linearized and decoupled robot controller. The derived robot controller operates in the robot task space, thus eliminating the need for decomposition of motion commands into robot joint space commands. Computer simulations are performed to verify the feasibility of the proposed robot controller. The controller is further experimentally evaluated on the PUMA 560 robot arm. The experiments show that the proposed controller produces good trajectory tracking performances and is robust in the presence of model inaccuracies. Compared with a nonlinear feedback robot controller based on the manipulator dynamics only, the proposed robot controller yields conspicuously improved performance. >

Design of dynamic control of two cooperating robot arms: Closed chain formulation

In this paper the dynamic equation describing two cooperating robot arms which simultaneously are working on the same object is established by considering the whole system as a closed kinematic chain. This formulation has the advantage of automatically handling the coordination and load distribution between the robot arms through the dynamic equation. It can also be generalized to a multi-robot arm system. The control problem is solved as a design problem for a linear system by first applying a nonlinear feedback and nonlinear coordinate transformation to linearize the nonlinear dynamic equation, and then employing the linear optimal control theory to design a robust controller in the task space. This new dynamic control method establishes a direct control response to task space commands facilitating dynamics based task encoding in robotics.

Coordinated control of two robot arms

A new control method is presented for the coordinated control of two robot arms based on exact system linearization by appropriate non-linear feedback. The two arms are assumed to be working on the same object simultaneously. The control method uses a dynamic coordinator acting on relative position and velocity error and/or on relative force-torque errors between the two arms. Simulation results are presented for the coordinated control of two PUMA 560 robot arms using an optimal dynamic coordinator. For completeness, the paper also presents (i) a new revised set of inertia parameters for all six links of PUMA 560 robot arm, (ii) the form of nonlinear feedback and diffeomorphic state transformation which linearizes the control of PUMA 560 working in all six degrees of freedom, and (iii) the reduced numeric form of all dynamic equations for PUMA 560 working in three (positioning) degrees of freedom.

Coordination of two-arm pushing

Dynamic modeling and coordinated control of two-arm pushing operations are studied. The performance of such tasks requires the simultaneous control of the motion trajectory of the grasped object and the interaction force. The control of the interaction force is needed to ensure that the object is not dropped and to avoid excessive pressing. The motion and force control problem is further complicated by the presence of unilateral constraints since the manipulators can only push the object. The control problem is first formulated in the state space. A coordinated control method that utilizes a state feedback to decouple the motion control subsystem and force control subsystem is then presented. The unilateral constraints are satisfied during the entire motion period using a proposed force control planning algorithm. The effectiveness of the control method is verified by simulations.<<ETX>>

Control of multiple arms with rolling constraints

The authors present a unified formulation for the control problem of multiple arm systems which accommodates both holonomic and nonholonomic constraints. Several unique control properties of nonholonomic systems are discussed. Several useful results regarding input-output linearization and the zero dynamics in such systems are proved. The analysis and controller design are discussed for multi-arm systems. Results from computer simulations are presented to demonstrate the control algorithms. Simulation results illustrate that rolling and sliding can be effectively controlled.<<ETX>>

Object handling using two arms without grasping

Two cooperative manipulators equipped with open-palm end effectors are particularly suited to handle large objects. This can be achieved by having one palm push from one end and the other from the opposite end. This article studies modeling and coordinated control of two-arm pushing operations. The performance of such tasks requires simultaneous control of the motion trajectory of the object and the interaction force. Control of the interaction force is essential to avoid dropping or crushing objects. The motion and force control problem is complicated by the presence of unilateral constraints, as the manipulators can only push the object. The control problem is first formulated in the state space. A coordinated control method is then presented that utilizes a state feedback to de couple the motion control subsystem from the force control subsystem. The unilateral constraints are satisfied during the entire motion period by using a proposed force control plan ning algorithm. The effectiveness of the control method is verified by simulations.Two cooperative manipulators equipped with open-palm end effectors are particularly suited to handle large objects. This can be achieved by having one palm push from one end and the other from the opposite end. This article studies modeling and coordinated control of two-arm pushing operations. The performance of such tasks requires simultaneous control of the motion trajectory of the object and the interaction force. Control of the interaction force is essential to avoid dropping or crushing objects. The motion and force control problem is complicated by the presence of unilateral constraints, as the manipulators can only push the object. The control problem is first formulated in the state space. A coordinated control method is then presented that utilizes a state feedback to de couple the motion control subsystem from the force control subsystem. The unilateral constraints are satisfied during the entire motion period by using a proposed force control plan ning algorithm. The effectiveness of the contr...

Robot arm force control through system linearization by nonlinear feedback

Based on a differential geometric feedback linearization technique for nonlinear time-varying systems, a dynamic force control method for robot arms is developed. It uses active force-moment measurements at the robot wrist. The controller design fully incorporates the robot-arm dynamics and is so general that it can be reduced to pure position control, hybrid position/force control, and pure force control. The controller design is independent of the tasks to be performed. Computer simulations show that the controller improves the position error by a factor of ten in cases in which position errors generate force measurements. A theorem on linearization of time-varying system is also presented.<<ETX>>

Experimental study of two robot arms manipulating large objects

In this paper, we present the architecture of an experimental real-time control system called TRACS (two robotic arm coordination system) and experimental results using two PUMA 250 robot arms that perform tasks of manipulating large objects. The system uses an IBM PC-AT as the host computer which is equipped with an AMD29000 high speed floating point coprocessor. It is configured in such a way that the Intel 80286 processor performs all the input-output interface operations (interface to the sensors, arms, and user) while the AMD29000 carries out the real-time computations of feedback control algorithms. Using the system, we have successfully implemented the dynamic control algorithm developed for coordinating two robotic arms. The two arms perform the task of manipulating a large object by means of enveloping grasp. The coordinated control algorithm utilizes the full dynamics of the two arms. The results from two experimental tasks are described in detail, in which the two arms move an object while adapting the grasp configuration to the motion trajectory and to the external disturbance force. >

Control of rolling contacts in multiple robotic manipulation

When multiple arms are used to manipulate a large object, it is productive and sometimes necessary to maintain and control contacts between the object and surfaces of the robot other than those at the end-effector. Hence, the contact surface of the robot is referred to simply as its effector and includes the surface of any link of the manipulator as well as open palm-like effectors at the arms extremity. Such contacts are characterized by holonomic as well as nonholonomic (including unilateral) constraints. In this paper, the control of rolling contact is investigated. Multiarm manipulation systems are typically redundant. In the approach, a minimal set of inputs is employed to control the trajectory of the system while the surplus inputs control the rolling condition at the contacts. A nonlinear feedback scheme for simultaneous force and motion control is presented and a new approach to adaptively adjust a two-effector grasp with rolling contacts is developed. Simulations are used to illustrate the salient features in control and planning.<<ETX>>

Two-handed grasping with two-fingered hands

Force-closure two-handed grasps of rigid objects in the two-dimensional space is studied. The hands considered are either flat-surface palms or grippers with two angular-motion fingers. Presented is a condition which establishes the existence of force-closure grasps without knowledge of the shape of the grasped object and of the exact contact locations on the palms or fingers. Further, an algorithm is developed, which determines force-closure grasps based on the position and orientation of the two hands.<<ETX>>