Rajiv V. Dubey

A weighted least-norm solution based scheme for avoiding joint limits for redundant joint manipulators

It is proposed to use weighted least-norm solution to avoid joint limits for redundant joint manipulators. A comparison is made with the gradient projection method for avoiding joint limits. While the gradient projection method provides the optimal direction for the joint velocity vector within the null space, its magnitude is not unique and is adjusted by a scalar coefficient chosen by trial and error. It is shown in this paper that one fixed value of the scalar coefficient is not suitable even in a small workspace. The proposed manipulation scheme automatically chooses an appropriate magnitude of the self-motion throughout the workspace. This scheme, unlike the gradient projection method, guarantees joint limit avoidance, and also minimizes unnecessary self-motion. It was implemented and tested for real-time control of a seven-degree-of-freedom (7-DOF) Robotics Research Corporation (RRC) manipulator. >

Compensatory movements of transradial prosthesis users during common tasks

BACKGROUND Recent studies have documented motions of the upper limbs of healthy subjects during activities of daily living. The aim of this study was to investigate compensatory motions of the upper extremity and torso during tasks for transradial prosthesis users and to determine if bracing simulates prosthesis use. METHODS Seven transradial myoelectric prosthesis users and 10 non-amputee volunteers performed four common tasks. Bracing was used to simulate the use of a transradial prosthesis by the non-amputee subjects. Range of motion of the glenohumeral (shoulder) joint, elbow joint and torso were calculated from optical motion analysis data. The motions between the non-braced, braced and transradial prosthesis user groups were statistically compared. Degree of asymmetry between the affected and unaffected arm was computed for the bilateral tasks. FINDINGS Myoelectric transradial prosthesis users compensate for lack of wrist and forearm movement differently depending on the task. Compensatory motion in torso bending occurs while opening a door. For the box lift task, prosthesis users rely more on the sound arm and torso bending. While drinking from a cup, decreasing flexion of the glenohumeral joint and increasing elbow flexion was shown while using a prosthesis. While turning a steering wheel, prosthesis users are similar to non-amputee subjects. INTERPRETATION By looking at the compensatory motions caused by limiting forearm and wrist movement, a greater understanding of the problems with transradial prosthetic design can be developed. Although bracing intact subjects showed similar mechanisms of compensation in most tasks, the magnitude of compensation was greater for prosthesis users.

Efficient gradient projection optimization for manipulators with multiple degrees of redundancy

An efficient gradient projection optimization scheme is presented for manipulators with multiple degrees of redundancy. This is an extension of the gradient projection scheme presented by R.B. Dubey et al. (Proc. IEEE Int. Conf. on Robotics and Automation, p.28-36, 1989) for manipulators with one degree of redundancy. The feasibility and effectiveness of this scheme are tested through simulations of the seven-degree-of-freedom NASA Laboratory Telerobotic Manipulator (LTM). Only the position of the LTM end effector is controlled, which requires only three degrees of freedom. The remaining joints, except for the wrist roll joint, which does not contribute to the end-effector linear velocity, provide three degrees of redundancy.<<ETX>>

An efficient gradient projection optimization scheme for a seven-degree-of-freedom redundant robot with spherical wrist

A computationally effective kinematic control scheme is presented for a seven-degree-of-freedom redundant robot with spherical wrist. This scheme uses a gradient projection optimization method, which eliminates the need to determine the generalized inverse of the Jacobian when solving for joint velocities for given Cartesian end-effector velocities. Closed-form solutions are obtained for joint velocities using this approach. The application of this scheme to the seven-degree-of-freedom manipulator at the Center for Engineering Systems Advanced Research (CESAR) is described.<<ETX>>

Real-time implementation of an optimization scheme for seven-degree-of-freedom redundant manipulators

A computationally efficient kinematic optimal control scheme for seven-degree-of-freedom (7-DOF) manipulators is presented. This scheme uses the gradient projection optimization method in the framework of resolved motion rate control and does not require calculation of the pseudoinverse of the Jacobian. An efficient formulation for determining joint velocities for given Cartesian components of linear and angular end-effector velocities is obtained. This control scheme is well suited for real-time implementation, which is essential if the end-effector trajectory is continuously modified based on sensory feedback. Implementation of this scheme on a Motorola 6820 VME bus-based controller of the 7-DOF manipulator is described. A comparison of computational complexity with previously available schemes is presented. >

Redundant robot control for higher flexibility

The joint velocities required to move the robot end-effector with a desired speed depend on the direction of motion. Robots mobility, i.e., its ability to move, is better in the directions requiring lower joint velocities. When the robot is near a singularity configuration, the joint velocities required to attain the end-effector velocity in certain directions are extremely high. Thus arbitrary directional changes become more difficult. Robots flexibility, defined as its ability to change the direction of the end-effector motion, is low in the vicinity of singular configurations. Addition of redundant joints can greatly enhance their flexibility. However, this requires a proper utilization of redundancy. A control scheme is presented to improve the flexibility of redundant robots. The feasibility and effectiveness of this control scheme are demonstrated through simulation.

Control of a 9-DoF Wheelchair-mounted robotic arm system using a P300 Brain Computer Interface: Initial experiments

A wheelchair-mounted robotic arm (WMRA) system was designed and built to meet the needs of mobilityimpaired persons with limitations of upper extremities, and to exceed the capabilities of current devices of this type. The control of this 9-degree-of-freedom system expands upon conventional control methods and combines the 7-DoF robotic arm control with the 2-degree-of-freedom power wheelchair control. The 3- degrees of redundancy are optimized to effectively perform activities of daily living and overcome singularities, joint limits and some workspace limitations. The control system is designed for teleoperated or autonomous coordinated Cartesian control, which offers expandability for future research. A P300 Brain Computer Interface (BCI), the BCI2000, was implemented to control the WMRA system. The control is done by recording and analysing the brain activity through an electrode cap while providing visual stimulation to the user via a visual matrix. The visual matrix contains a symbolic or an alphabetic array corresponding to the motion of the WMRA. By recognizing online and in real-time, which element in the matrix elicited a P300, the BCI system can identify which element the user chose to communicate. The chosen element is then communicated to the controller of the WMRA system. The speed and accuracy of the BCI system was tested. This paper gives details of the WMRAs integration with the BCI2000 and documents the experimental results of the BCI and the WMRA in simulation.

Telemanipulation Assistance Based on Motion Intention Recognition

In telemanipulation systems, assistance through variable position/velocity mapping or virtual fixture can improve manipulation capability and dexterity [3, 5, 6, 7, 8]. Conventionally, such assistance is based on the sensory data of the environment and without knowing user’s motion intention. In this paper, user’s motion intention is combined with real-time environment information for applying appropriate assistance. If the current task is following a path, a virtual fixture is applied. If the task is aligning the end-effector with a target, an attractive force field is produced. Similarly, if the task is avoiding obstacles that block the path, a repulsive force field is generated. In order to successfully recognize user’s motion intention, a Hidden Markov Model (HMM)-based algorithm is developed to classify human actions, such as following a path, aligning target and avoiding obstacles.

Analysis, evaluation and development of wheelchair-mounted robotic arms

This paper focuses on kinematic analysis and evaluation of wheelchair mounted robotic arms (WMRA). It addresses the kinematics of the WMRA with respect to its ability to reach common positions while performing activities of daily living (ADL). A procedure is developed for the kinematic analysis and evaluation of a WMRA. In an effort to evaluate two commercial WMRAs, the procedure for kinematic analysis is applied to each manipulator. Design recommendations and insights with regard to each device are obtained and used to design a new WMRA to overcome the limitations of these devices. This method benefits the researchers by providing a standardized procedure for kinematic analysis of WMRAs that is capable of evaluating independent designs.

Variable position mapping based assistance in teleoperation for nuclear cleanup

Radioactive tank waste remediation and decontamination and decommissioning (D&D) of contaminated Department of Energy (DOE) facilities, and other nuclear cleanup tasks require extensive remote handling technologies. The unstructured nature of these tasks and limitations of the current sensor and computer decision-making technologies prohibit the use of completely autonomous systems for remote manipulation. This paper presents a new methodology in which model-based computer assistance is incorporated into human controlled teleoperator systems. This approach implies a form of assistance function in which the human input is enhanced rather than superseded by the computer. A specific task of cutting a pipe with a saw is chosen as an example to demonstrate the implementation of the assistance functions in D&D size reduction tasks and the results are presented.