The mathematics of coordinated control of prosthetic arms and manipulators.

Consideration of dynamics is critical in the analysis, design, and control of robot systems. This article presents an extensive study of the dynamic properties of several important classes of robot...

Inertial properties in robotic manipulation: an object-level framework

This paper extends the theory of hybrid position/force control to the case of multiarm cooperating robots. Cooperation between n robot arms is achieved by controlling each arm such that the burden of actuation is shared between the arms in a non-conflicting way as they control the position of and force on a designated point on an object. The object which may or may not be in contact with a rigid environment, is assumed to be held rigidly by n robot end-effectors. Natural and artificial position and force constraints are defined for a point on the object and two selection matrices are obtained to control the arms. The position control loops are designed based on each manipulator's Cartesian space dynamic equations. In the position control subspace, a feature is provided which allows the robot arms to exert additional forces/torques to achieve compression, tension, or torsion in the object without affecting the execution of the motion trajectories. In the force control subspace, a method is introduced to minimize the total force/torque magnitude square while realizing the net desired force/ torque on the environment.

Hybrid position/Force control of multi-arm cooperating robots

The dynamic control module of the Dynamic and Strategic Control of Cooperating Manipulators (DASCCOM) project for aerospace robotics is presented. The cooperative manipulation problem is analyzed from a systems perspective, and the desirable features of a control system for cooperative manipulation are discussed. A control policy is developed that enforces a controlled impedance not of the individual arm endpoints, but of the manipulated object itself. A parallel implementation for a multiprocessor system is presented. The controller fully compensates for the system dynamics and directly controls the object internal forces. Most importantly, it presents a simple, powerful, intuitive interface to higher level strategic control modules. Experimental results from a dual two-link-arm robotic system show the effectiveness of the object impedance controller compared to other strategies, both for free-motion slews and environmental contact. >

Object impedance control for cooperative manipulation: theory and experimental results

This paper presents a new methodology for the analysis and control of internal forces and center-of-mass (CoM) behavior, which are produced during multicontact interactions between humanoid robots and the environment. The approach leverages the virtual-linkage model that provides a physical representation of the internal and CoM resultant forces with respect to reaction forces on the supporting surfaces. A grasp/contact matrix describing the complex interactions between contact forces and CoM behavior is developed. Based on this model, a new torque-based approach for the control of internal forces is suggested and illustrated on the Asimo humanoid robot. The new controller is integrated into the framework for whole-body-prioritized multitasking, thus enabling the unified control of CoM maneuvers, operational tasks, and internal-force behavior. The grasp/contact matrix is also proposed to analyze and plan internal force and CoM control policies that comply with frictional properties of the links in contact.

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Compliant Control of Multicontact and Center-of-Mass Behaviors in Humanoid Robots

A computer control structure has been designed and implemented to enable two robot arms to function in a coordinated manner. One algorithm has been derived and implemented but not tested for a closed-loop configuration. Errors for the open-loop operation are given in the report.

Coordinated control of two robot arms

Computing manipulator joint velocities and accelerations, given the end-effector Cartesian rates (velocities and accelerations), is complicated by the singular positions the manipulator can assume along a trajectory. At such configurations the Jacobi matrix that relates Cartesian end-effector rates to joint rates cannot be inverted. Geometric approaches in solving for joint rates yield expressions that are indeterminate at such configurations. It is shown that exact solutions for the joint rates can be obtained in most singularity situations if the system of differential kinematic relations is properly partitioned. A solution methodology is developed and illustrated by an example. >

Solving for manipulator joint rates in singular positions

A single-link flexible manipulator with a rotary actuator at one end and a mass at the other is modeled using the Lagrangian method coupled with an assumed modes vibration model. A SIMO state space model is developed by linearizing the equations of motion and simplified by neglecting natural damping. Laplace domain pole-zero plots between torque input and tip position show nonminimum phase behavior. Nonminimum phase behavior causes difficulty for both conventional and artificial neural network (ANN) inverse-model control. The most promising ANN method for the control of flexible manipulators does not appear to converge to a solution when the system is lightly damped. To overcome this limitation, a modified cost function is proposed. Simulations show that the ANN is able to converge to a solution even in the case of no damping. The modified approach fails, however, for beams exceeding some critical length measure. Identification of the critical length and proposals for extending the result are discussed.

C.O. Alford

Papers

Coordinated control of two robot arms

Solving for manipulator joint rates in singular positions

Artificial neural network control of a nonminimum phase, single-flexible-link