Resolved Motion Rate Control Research Articles

Pressure Cutoff Control of Hydrostatically Driven Hydraulic Excavator.

This paper first presents a system concept of a hydrostatically driven hydraulic excavator. In this system, pumps and actuators are connected each other. Then, the speed of actuators is controlled by the pump flow rate. Herein, a hydraulic excavator has 7 actuators and 4 pumps, and connection/disconnection of each pump and actuator are controlled by 3x4 directional control valves. Microcomputers execute the following controls : maximum pressure limiting (pressure cutoff control), pump absorption power control for prevention of engine stop and suitable power distribution to pumps, transient vibration damping, maximum acceleration limiting and resolved motion rate control of the excavator's arm. Furthermere, in this paper, we report the experimental study of pressure cutoff control which is a basic function for energy saving in a hydrostatically driven hydraulic excavator.

Operator-in-the-loop simulation of a redundant manipulator under teleoperation

For an interactive simulation of 7 degree-of freedom redundant manipulator under teleoperation, this paper describes an iterative form of resolved-motion rate control in which the constraint Jacobian is constructed on-line in real time and used in the pseudoinverse method as the manipulator is teleoperated. The manipulator's tasks may involve trajectory following in free space and frequent contact with the environment through pick-and-put operation. The operator's command is interpreted as a series of increments in Cartesian space, and then the constraint Jacobian is developed between two successive increments by viewing the predecessor as the initial configuration and the successor as the target configuration. The pseudoinverse of the constraint Jacobian then generates necessary changes in joint variables and subsequently joint torque. The Jacobian constructed in this way enables us to treat both free motion and environmental contact in the same way. The simulator is built on a two-processor IRIS workstation, with one processor for graphics and the other for dynamics and control analysis. This simulator has a potential for training the teleoperator, developing operational scenarios through visualization of the simulation, and testing the design of operator-machine interface.

Jacobian control for space manipulator

Parlaktuna, O., Cook, G.E., Strauss, A.M. and Fernandez, K., Jacobian control for space manipulator, Robotics and Autonomous Systems, 11 (1993) 35–44. To control robot or teleoperated manipulators in space, the motion of the satellite (which is actually the base of the manipulator) which will move due to the force exerted by the moving manipulator, must be considered. Most of the algorithms developed to control a robot manipulator assume that the manipulator is connected to a fixed base. Since the satellite moves due to the motion of the robot manipulator, the control schemes developed for fixed-base manipulators cannot be used for space robots and telerobots. In this paper, using a modified resolved motion rate control and angular momentum conservation law, a generalized Jacobian matrix is derived to control the space manipulator. It is shown that a manipulator controlled in this manner follows a prescribed path independent of the motion of the satellite.

Practical Control Method for Antenna and Manipulator Mounted on Free-Flying Robot in Space.

This paper deals with practical simultaneous control of a manipulator and an antenna mounted on a free-flying robot in space. An extended generalized Jacobian matrix and resolved motion rate control are used to establish the control method for antenna positioning and the capture of a target by the manipulator. Moreover, a method revising the angular velocity references to the robot system is introduced to improve the control performances. Computer simulation in which a robot system having a base, 2-DOF manipulator, and one link antenna is used suggest that the proposed method is useful and practical.

Ｓｔｅｗａｒｔ Ｐｌａｔｆｏｒｍ型パラレルリンクマニピュレータのＦｏｒｗａｒｄ Ｋｉｎｅｍａｔｉｃｓ計算アルゴリズム

This paper proposes a method to calculate the forward kinematics of a Stewart Plaftorm type of parallel link manipulators. The Stewart Platform consists of a base platform, a moving platform, and linear actuators connecting the both platforms. First we introduce a virtual parallel link mechanism, having the same kinematic structure as the original parallel mechanism. We assume that the moving platform of the virtual mechanism is directly driven by actuators and the limbs connecting both platforms have no actuators. A trajectory tracking control system is designed for this virtual mechanism based on the resolved motion rate control, so that the displacements of limbs are controlled by the actuators driving the moving platform. We calculate the forward kinematics by numerical simulation of the control system ; the position and orientation of the moving platform of the virtual mechanism is a solution for given displacements of limbs, when the tracking error of limbs converges to zero. The method is effective for a time varying displacements of limbs as long as the displacements are differentiable about time. The position and orientation of the moving platform is obtained without error, once the tracking error converges to zero. The simulation results illustrate the method.

２リンク柔軟マニピュレータの制御実験

This paper is concerned with some control experiments of two-link flexible mainpulator by using a hardware experimental system. A torque servo actuator (TSA) has been developped, which is insalled on each articular joint to achieve a fine torque control. To realize stable control of structurally flexible manipulators, three control methods, i. e., extended local PD-control, pseudo resolved motion rate control and pseudo resolved acceleration control, are examined through the experimental system. The effectiveness of TSA and the control methods are successfully demonstrated.

Operator Performance with Alternative Manual Control Modes in Teleoperation

Recent experiments conducted at the Jet Propulsion Laboratory (JPL) comparing alternative manual control modes using the JPL Advanced Teleoperator (ATOP) System are described in this paper. Of particular interest were control modes that provide force reflection to the operator. The task selected for the experiment is a portion of the Solar Maximum Satellite Repair (SMSR) procedure we developed to demonstrate the repair of the Solar Maximum Satellite with teleoperators. SMSR had been successfully performed by NASA astronauts in 1984 and it was selected as a task to demonstrate the ATOP system capability for space applications. The seven manual control modes evaluated in the experiment are combinations of manual position or resolved motion rate control with alternative control schemes for force reflection and remote manipulator compliance. Performance measures used were task completion times, average force and torque exerted during the execution of the task, and cumulative force and torque exerted. The results were statistically analyzed and they show that, in general, force reflection significantly improves operator performance and indicate that a specific force-reflecting scheme may yield the best performance among the control modes we tested. Also, our experiment showed that, for the selected task, the position control modes were preferable to the rate control modes and slave manipulator compliance reduced task interaction forces and torques.

Practical inverse kinematics of a kinematically redundant robot using a neural network

In solving inverse kinematics problems, traditional methods such as RMRC (resolved motion rate control) and the IKM (inverse kinematic method) are mostly complicated and time-consuming. Using a neural network, however, a practical algorithm for obtaining accurate joint angles in a much shorter time is possible. The neural network approach assumes a transfer function between inputs and outputs and trains the network to satisfy the representative input-output pairs in the least squares sense. First, a test of the appropriateness of the neural network method is performed for the case of a planar two degrees of freedom (DOF) robot. Then the neural network method is employed to find three joint angles of a planar 3-DOF robot maximizing local manipulability. In this algorithm, the proximal redundant joint angle is determined from a neural network and then the remaining joint angles are determined from analytical functions. The results from this method compare favourably with those from the other two traditional...

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.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Weighted selection of image features for resolved rate visual feedback control

The authors develop methodologies for the automatic selection of image features to be used to visually control the relative position and orientation (pose) between the end-effector of an eye-in-hand robot and a workpiece. A resolved motion rate control scheme is used to update the robot's pose based on the position of three features in the camera's image. The selection of these three features depends on a blend of image recognition and control criteria. The image recognition criteria include feature robustness, completeness, cost of feature extraction, and feature uniqueness. The control criteria include system observability, controllability, and sensitivity. A weighted criteria function is used to select the combination of image features that provides the best control of the end-effector of a general six-degrees-of-freedom manipulator. Both computer simulations and laboratory experiments on a PUMA robot arm were conducted to verify the performance of the feature-selection criteria.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Adaptive image feature prediction and control for visual tracking with a hand-eye coordinated camera

An adaptive method for visually tracking a known moving object with a single mobile camera is described. The method differs from previous methods of motion estimation in that both the camera and the object are moving. The objective is to predict the location of features of the object on the image plane based on past observations and past control inputs and then to determine an optimal control input that will move the camera so that the image features align with their desired positions. A resolved motion rate control structure is used to control the relative position and orientation between the camera and the object. A geometric model of the camera is used to determine the linear differential transformation from image features to camera position and orientation. To adjust for modeling errors and system nonlinearities, a self-tuning adaptive controller is used to update the transformation and compute the optimal control. Computer simulations were conducted to verify the performance of the adaptive feature prediction and control.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Theoretical and Experimental Study on In-Orbit Capture Operation With Satellite Mounted Manipulator

This paper treats both theoretical and experimental study on a control problem of a space free-flying space manipulator. The authors' main target is to develop a new control method for trajectory tracking or target capturing, considering the dynamical interaction between the manipulator arm and the base vehicle in space micro-gravity environment. In the theoretical study, the Generalized Jacobian Matrix (GJM) concept is introduced. By means of this new matrix, the conventional control methods for ground-fixed manipulators is directly applicable for space manipulators. In the experimental study, a laboratory model of robot satellite supported on air bearings is developed in order to simulate the flee-flying behavior of mechanical links in micro-gravity environment. The model comprises a base satellite and a two-link manipulator arm. An on-line Resolved Motion Rate Control scheme with vision feedback is developed for experimenting capture operations, utilizing the GJM. The manipulator can properly chase and capture both a standing target and a moving target in spite of complex satellite/manipulator dynamical interaction. The experimental results confirm the validity of the GJM concept and the proposed control method.

Resolved motion rate control of space manipulators with generalized Jacobian matrix

The authors establish a control method for space manipulators taking dynamical interaction between the manipulator arm and the base satellite into account. The kinematics of free-flying multibody systems is investigated by introducing the momentum conservation law into the formulation and a novel Jacobian matrix in generalized form for space robotic arms is derived. The authors develop a control method for space manipulators based on the resolved motion control concept. The proposed method is widely applicable in solving not only free-flying manipulation problems but also attitude-control problems. The validity of the method is demonstrated by computer simulations with a realistic model of a robot satellite.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

一般化ヤコビ行列を用いた宇宙用ロボットマニピュレータの分解速度制御

In recent years, space has attracted special interest as a new application field of robotics. A robotic teleoperator system installed with space manipulators will play an important role in future space projects, such as constructing space structures or servicing satellites. However, in space environment, the lack of a fixed base arises many problems in controlling space robotic systems. In general, any motion of the manipulator arm will induce reaction forces and moments which disturb position and attitude of the supporting base satellite. To establish a control method for space manipulators taking dynamical interaction between the manipulator arm and the base satellite into account, the authors investigate the kinematics of free-flying multi-jointed link systems by introducing the momentum conservation law into the formulation and derive a new Jacobian matrix in generalized form for space robotic arms. By means of the new matrix, they develop a control method for space manipulators based on the resolved motion rate control concept. The proposed method is widely applicable for not only free-flying manipulation problems but also attitude control problems. The validity of the method is demonstrated by computer simulations with a realistic model of robot satellite.

Control of Kinematically Redundant Robots Using {1}-Inverses

Resolved motion rate control of kinematically redundant manipulators using the simplest of the generalized inverses, the {1}-inverse, is investigated. For the case of a planar articulated coordinate redundant robot with an arbitrary number of axes, closed-form equations for the joint rates are developed. The structure of these equations is such that the redundant joint velocities can be arbitrarily specified. Simple constraints are presented which ensure that closed trajectories in gripper configuration space generate closed trajectories in joint space. A strategy for controlling the redundant joint rates that is applicable to obstacle avoidance is examined and illustrated with examples.

Resolved Motion Adaptive Control for Mechanical Manipulators

This paper presents the development of a resolved motion adaptive control which adopts the ideas of “resolved motion rate control” [8] and “resolved motion acceleration control” [10] to control a manipulator in Cartesian coordinates for various loading conditions. The proposed adaptive control is performed at the hand level and is based on the linearized perturbation system along a desired hand trajectory. The controlled system is characterized by feedforward and feedback components which can be computed separately and simultaneously. The feedforward component resolves the specified positions, velocities, and accelerations of the hand into a set of values of joint positions, velocities, and accelerations from which the nominal joint torques are computed using the Newton-Euler equations of motion to compensate all the interaction forces among the various joints. The feedback component consisting of recursive least square identification scheme and an optimal adaptive self-tuning controller for the linearized system computes the perturbation torques which reduce the manipulator hand position and velocity errors along the nominal hand trajectory. The feasibility of implementing the proposed adaptive control using present day low-cost microprocessors is explored.

Resolved motion rate control of a materials-handling machine

Resolved motion rate control - a technique developed for controlling robotic manipulators - is applied here to an industrial vehicle used for the handling of materials. An on-board microprocessor is used to compute trigono metrical transformations necessary to achieve co-ordinated movement of servo-valves which control the hydraulic cylinders. It is shown that, by this method, the operator's task is significantly eased, bringing potential benefits in speed of operation and safety.

An evaluation of control modes in high gain manipulator systems

The performance of replica master and resolved motion rate control of a large manipulator is evaluated for two tasks. The first task simulates removing parts from a conveyor and stacking them on a pallet. The second task simulates stowing palletized cargo in a container. Related experiments are discussed and the results correlated to this work. Results show the bilateral master to have a distinct performance advantage over resolved motion rate control. The advantage is not as large as reported for small manipulators, however.

The LEMMA concept: A new manipulator

The LEMMA is a proposed conceptual design of a remote teleoperator manipulator arm with 6 degrees of freedom, exclusive of the end-effector. The bevel gear arrangement in 4 of the 6 degrees of freedom, together with the concentric-tubular arm configuration, requires a unique and a novel drive mechanism. This differential drive assembly, housed in the shoulder, is a self-compensating device and simplifies the matrix solution for the resolved motion rate control system needed to guide the arm in its performances. The article will describe the need for the 6 degrees of freedom as established by the work envelope, the functioning of the differential shoulder drive, the arm and joint configuration, and the anticipated degree of accuracy.

Resolved Motion Rate Control of Manipulators and Human Prostheses

The kinematics of remote manipulators and human prostheses is analyzed for the purpose of deriving resolved motion rate control. That is, the operator is enabled to call for the desired hand motion directly along axes relevant to the task environment. The approach suggests solutions to problems of coordination, motion under task constraints, and appreciation of forces encountered by the controlled hand.