Masaru Uchiyama

A symmetric hybrid position/force control scheme for the coordination of two robots

A symmetric scheme-not a master/slave scheme-is proposed for the coordination of two robots to manipulate a single object jointly. The definition of workspace force, velocity, and position vectors as symmetric functions of the joint space force, velocity and position vectors of the two robots is essential to implementing the symmetric scheme. These workspace vectors are derived by first analyzing the statics of the closed kinematic chain consisting of the two robots and the object, and then calculating velocities using the force-velocity duality. The workspace-position vector is defined by integrating the velocities. The derived workspace vectors are used successfully to implement the symmetric scheme.<<ETX>>

Reaction null-space control of flexible structure mounted manipulator systems

A composite control law for end-effector path tracking with a flexible structure mounted manipulator system is proposed, such that no disturbances on the flexible base are induced. The control law is based on the reaction null-space concept introduced earlier to tackle dynamic interaction problems of free-floating robots, or moving base robots in general. The control law is called composite since it ensures base vibration suppression control as well, although independently of the reactionless motion control subtask. The requirement of task independence is essential to avoid the appearance of complex dynamics expressions in the control law, such as nonlinear velocity-dependent coupling terms and dependencies of inertias on the elastic coordinates. We present experimental data from computer simulations and the experimental test bed TREP developed at Tohoku university. The experimental data is shown to agree well with theory.

Hybrid position/Force control for coordination of a two-arm robot

In this paper we discuss the control of cooperating tasks being done by two robotic arms. In order to control those tasks, we extend hybrid position/force control scheme presented thus far by various researchers for a single-arm robot. The point of the extension is formulation of kinematics and statics for a two-arm robot which is new in this paper. We define a unique system of workspace coordinates and, corresponding to the unique workspace, introduce an unique jointspace vector consisting of joint-vectors of the two arms. Using these work and joint spaces, we formulate kinematics and statics. Based upon this formulation, we successfully apply the hybrid scheme to the two-arm robot. A demonstration of the theory working on a real two-arm industrial robot and experimental data of simultaneous control of position and force proves the effectiveness of our method.

Model-based space robot teleoperation of ETS-VII manipulator

In our previous research, we developed space robot teleoperation technology to achieve control from the ground of effective manual manipulations in orbit. To solve the communication time delay in the space robot teleoperation, we propose a mixed force and motion command-based space robot teleoperation system that is a model-based teleoperation. Moreover, we have also developed a compact 6-degree-of-freedom haptic interface as a master device. The important features of our teleoperation system are its robustness against modeling errors and its ability to realize the force exerted by the operator at the remote site. We introduce a new control method, which modified our model-based teleoperation system, to control the real robotic system Engineering Test Satellite VII manipulator. Surface-tracking and peg-in-hole tasks have been performed to confirm the effectiveness of our system. The experimental results obtained with our system including the haptic interface demonstrate its ability to perform these tasks in space without any major problems. We also evaluated different master device approaches for the model-based space teleoperation system. For this purpose, we used two methods, which are a master-slave (MS) approach and a force-joystick approach. Our results show that the MS approach is the best control method for contact tasks in which the directions of motion of the slave arm and of the operators input force are different, as in the surface-tracking task.

Moving Base Robotics and Reaction Management Control

This paper addresses a new paradigm of moving base robotics, for a class of robots which have manipulator systems on a moving base. For such robots, kinematic and dynamic coupling between the manipulator arm and the base degrades positioning accuracy and operational dexterity. Moving base robots are classified into the following four categories: (a) Free Floating Manipulator System, (b) Flexible Structure mounted Manipulator System, (c) Macro-Mini Manipulator System, and (d) Mobile Vehicle mounted Manipulator System. Among them, this paper focuses the Flexible Structure mounted Manipulator System, because this class of system displays inherent dynamic coupling between manipulator operation and base structure flexibility, hence control methods to avoid base vibration are strongly needed. A dynamic analysis for reaction management control using the Reaction Null Space is introduced and applied to yield a reactionless operational path for PTP operation. Force control of this class of system is also addressed.

Reaction null-space based control of flexible structure mounted manipulator systems

The control of a dexterous manipulator mounted on a flexible structure is discussed. Using a concept called reaction null space, the manipulator dynamics is totally decoupled from the base dynamics. As a consequence of the decoupling, feedback control gains can be determined in a straightforward manner. We examine the simultaneous performance of the following two tasks: (1) base vibration suppression and (2) end-point path tracking without base disturbance.

Asymmetric simple exclusion process with open boundaries and Askey–Wilson polynomials

We study the one-dimensional asymmetric simple exclusion process (ASEP) with open boundary conditions. Particles are injected and ejected at both boundaries. It is clarified that the steady state of the model is intimately related to the Askey–Wilson polynomials. The partition function and the n-point functions are obtained in the integral form with four boundary parameters. The thermodynamic current is evaluated to confirm the conjectured phase diagram.

Singularity-consistent parameterization of robot motion and control

The inverse kinematics problem is formulated as a parameterized autonomous dynamical system problem, and respective analysis is carried out. It is shown that a singular point of work space can be mapped either as a critical or a noncritical point of the autonomous system, depending on the direction of approach to the singular point. Making use of the noncritical mapping, a closed-loop kinematic controller with asymptotic stability and velocity limits along degenerate singular or near-singular paths is designed. The authors introduce a specific type of motion along the reference path, the so-called natural motion. This type of motion is obtained in a straightforward manner from the autonomous dynamical system and always satisfies the motion constraint at a singular point. In the vicinity of the singular point, natural motion slows down the end-effector speed and keeps the joint velocity bounded. Thus, no special trajectory replanning will be required. In addition, the singular manifold can be crossed, if necessary. Further on, it is shown that natural motion constitutes an integrable motion component. The remaining, nonintegrable motion component is shown to be helpful in solving a problem related to the critical point mapping of the autonomous system. The authors design a singularity-consistent resolved acceleration controller, which they then apply to singular or near-singular trajectory tracking under torque limits. Finally, the authors compare the main features of the singularity-consistent method and the damped-least-squares method. It is shown that both methods introduce a so-called algorithmic error in the vicinity of a singular point. The direction of this error is, however, different in each method. This is shown to play an important role for system stability.

Dark Solitons in F=1 Spinor Bose–Einstein Condensate

We study dark soliton solutions of a multi-component Gross–Pitaevskii equation for hyperfine spin F =1 spinor Bose–Einstein condensate. The interactions are supposed to be inter-atomic repulsive an...

Stiffness Analysis and Design of a Compact Modified Delta Parallel Mechanism

In our previous work, we developed a compact 6-DOF haptic interface as a master device which achieved an effective manual teleoperation. The haptic interface contains a modified Delta parallel-link positioning mechanism. Parallel mechanisms are usually characterized by a high stiffness, which, however, is reduced by elastic deformations of both parts and bearings. Therefore, to design such a parallel mechanism, we should analyze its structural stiffness, including elastic deformations of both parts and bearings. Then we propose a simple method to analyze structural stiffness in a parallel mechanism using bearings. Our method is based on standard concepts such as static elastic deformations. However, the important aspect of our method is the manner in which we combine these concepts and how we obtain the value of the elasticity coefficient of a rotation axis in a bearing. Finally, we design a modified Delta mechanism, with a well-balanced stiffness, based on our method of stiffness analysis.