An exoskeleton haptic interface is developed for functional training in virtual environments. A composite control scheme enables a variety of tasks to be implemented, and a ¿Qt¿ graphics library is used to generate the virtual environment for the haptic interface at the hand and graphical user interfaces for input and telemetry. Inter-process communications convert telemetry from the exoskeleton into motion commands for objects in the virtual environment. A second haptic interface at the upper arm is used to control the elbow orbit self-motion of the arm during tasks. Preliminary results are reviewed for a wall-painting task in which the virtual wall stiffness and viscosity are generated using an admittance controller.

A control methodology is developed for modulating shoulder impedance in an arm exoskeleton during physical therapy. Setting the remote center of compliance at the shoulder will allow the exoskeleton to enact resistance training protocols that strengthen the rotator cuff and other joint musculature supporting the shoulder complex. The rotational kinematics for the shoulder are first derived, and then the torques applied at the shoulder are estimated using force sensors placed at the hand and elbow interfaces. Impedance and admittance control schemes are both developed for realizing isolateral strengthening exercises, and some preliminary experimental results are presented for implementation on an arm exoskeleton currently under development.

A haptic interface is generated for a powered arm curl machine for modulating resistance "on-the-fly" during strength training and rehabilitation. Force signals from a load cell are input to an impedance loop based on the desired resistance law, which then outputs position commands to a servomotor. The kinematics between the actuator drive and arm curl angle are derived, and the admittance control implementation used for realizing the resistance laws is described. Preliminary experimental results are presented for viscous and inertial control laws.

Cameras are often used for visual servoing or realtime mapping of the external environment in both autonomous and teleoperated tasks with a dexterous manipulator. Nominal operations will likely produce manipulator configurations that occlude the line-of-sight from the camera to a target of interest. In this paper, a technique is developed that treats the camera line-of-sight as a virtual obstacle in order to prevent camera occlusion. The approach is based on using virtual point charges to represent obstacles and using the self-motion of the arm to avoid collisions. The approach is demonstrated on the Ranger Dexterous Manipulator.

The problem of estimating external forces exerted on a robotic manipulator with harmonic drive gearing without a force-torque sensor is considered. Manipulator dynamics together with motor current feedback is used to estimate external joint torques, which are transformed into estimated external end effector forces using knowledge of the manipulator's kinematics. Adaptive control is used to tune the parameters of the robot's modeled dynamics, while adaptive radial basis function (RBF) "neural" networks are used to learn the friction model. Compliance control is implemented on a two degree of freedom manipulator based on the force estimates. Results are compared to compliance control using a six-axis force-torque sensor mounted on the manipulator

Force-reflecting master arms are explored for use as haptic displays in physical therapy interventions over the internet. Rehabilitation tasks can be constructed in which both the patient and therapist can interact with a common object from distant locations. Each haptic master exerts "forces" on a virtual object which, in response, generates desired velocities for the master arm to track. A novel cooperative control architecture based on wave variables is implemented to counter the destabilizing effect of internet time-delay. The control scheme is validated experimentally using a pair of InMotion2 robots in a virtual beam manipulation task between remote sites.

This paper describes the development of a tendon-driven, multi-fingered dexterous robot hand for space operations. This hand can achieve cylindrical grasps while producing a holding strength necessary for grasping several crew aids, tools (CATs) and interfaces. The design is based on grasping requirements for 242 CATs and interfaces found in the extravehicular activity (EVA) Tools and Equipment Reference Book. The results of this study show that over 50% of the required grasps are cylindrical, and that it may be possible for a three-fingered hand to achieve over 90% of these grasps. Further tests are implemented to show that tendon tensions agree with the predicted kinematic model.

The design of a four-axis wrist with a skewed pitch axis is described. The skew-axis design increases the joint travel over traditional gimballed configurations while the excess degree of freedom can be used to avoid singularities. A generalized inverse kinematics procedure locally minimizes the joint velocities for a given tool orientation while steering the wrist away from singular regions and mechanical hard stops. The singularity surfaces are mapped in 3D-space, and simulations are used to illustrate the operation of the wrist. Hardware integration and testing of the wrist on the new dexterous manipulator for the Ranger Telerobotic Shuttle Experiment are also discussed.

The use of telerobots in remote locations allows humans to extend their capabilities to distant and hazardous environments. Although safer for the operator, this extension of capabilities comes at a price. Due to communication across great distances, experiencing time delays of up to several seconds is common. Any time delay in the human/robot interaction can significantly degrade the effectiveness of operator control. This paper will looks at two common instances of human-in-the-loop command of robots: command of vehicle motion and command of a manipulator to perform an assembly task. Results from three studies are summarized to show the degradation in performance caused by varying levels of time delay.

Space and underwater vehicles with robotic arms can severely tax the capability of conventional control systems. Submersible vehicles used in neutral buoyancy simulation are subject to even greater demands since they must simulate the dynamics of spacecraft in orbit as well as function as a remotely-operated underwater vehicle. In this report, the onboard control architecture, human-machine interface, and vehicle/operator communications are described for one such vehicle in operation at the University of Maryland Neutral Buoyancy Research Facility (NBRF). The Ranger Neutral Buoyancy Vehicle (RNBV) exemplifies the high-dimensional, computationally intensive nature of the current fleet of autonomous underwater vehicles while its complement of four manipulators exceeds the capabilities of most remotely operated vehicles in service today. The sensor-based, embedded onboard control system is described, and its implementation using multiple control stations is discussed.

A new paradigm is explored for controlling free-flying robots using a robot-centered coordinate strategy. The use of "dynamic" tool vectors for controlling manipulator motion is key to the development of this new approach. Variable tool vectors allow the arms to function in multiple roles, including camera positioning and self-maneuvering of the vehicle. In addition, these concepts are embodied in a resolved-rate architecture for controlling manipulators in robo-centric operations. The ranger neutral buoyancy vehicle, currently under development at the University of Maryland Space Systems Laboratory, is used to illustrate the application of this approach.

This work describes the experimental application of impedance control to a seven joint revolute manipulator built for neutral buoyancy operation. Compensator design methodologies previously applied to a single joint are extended to the full manipulator and tested in 1 g tasks. The controller was configured to mimic three useful modes at the end-effector: accommodation control, spring-dashpot control, and inertial mode. Simulated parameter errors were negligible even for outer force loop rates as low as 40 Hz. Hard contact tasks typically required damping augmentation of 5-10 times the freespace values to maintain stable contact. Preliminary experiments indicate that this controller can be a useful tool in fulfilling future objectives in space telerobotic operations.

Compares two position-based impedance controllers obtaining desired end-effector impedances during robot interaction with the environment. It is shown that while these two controllers have similar structures, the Adept Controller yields more accurate impedances in the DC region because of the stiffness control properties of the force loop. In addition, adding a force feedforward component to offset the contact force was found to significantly reduce the impedance errors in both controllers. The effect of bandwidth and force feedforward are examined for a planar arm example for a typical set of desired impedance specifications.>

An adaptive controller is developed for adjusting robot arm parameters while manipulating payloads of unknown mass and inertia. The controller is tested experimentally in a master/slave configuration where the adaptive slave arm is commanded via human-operator inputs from a master. Kinematically similar six-joints locked for simplification. After a brief initial adaptive period for the unloaded arm, the slave arm retrieves different-size payloads and maneuvers them about the workspace. Comparisons are then drawn with similar tasks when the adaptation is turned off. Several simplifications of the controller dynamics are addressed and experimentally verified.>

The authors use the concept of sliding surfaces for generating two types of tracking control laws for a free-flying robot engaged in zero-gravity assembly tasks. Suction control, developed elsewhere for controlling manipulators with stationary bases, is used to track workspace trajectories for manipulators mounted on mobile platforms. Zone control is formulated for the purpose of stationkeeping a robot maneuvering unit during payload manipulation. Experimental results are described for tests performed on an air-bearing robot tracking payload trajectories along a glass surface.>

In designing a robot control system for dual arm configurations, the control engineer is faced with two challenges: to derive the equations of motion for a given situation, and to meet certain desired control requirements (for instance, minimum energy). The former may involve closed kinematic chains, such as the case when the two arms are grasping a common object. The latter usually involves nonlinear optimization. These issues are considered in the context of transporting an inertial load using two planar three-link arms. A generalized 'reduction transformation' is applied to the dynamics to remove the singularity in the system equations. A suboptimal minimum energy method is presented to reduce a difficult 12-state, six-control nonlinear optimization to two independent, nonconflicting suboptimizations. A simulation example is provided to illustrate the degree of energy reduction possible using the optimal arm torque distribution that was developed.>