Showing papers on "Parallel manipulator published in 1994"

Coordinating locomotion and manipulation of a mobile manipulator

Abstract: A mobile manipulator in this study is a manipulator mounted on a mobile platform. Assuming the end point of the manipulator is guided, e.g., by a human operator to follow an arbitrary trajectory, it is desirable that the mobile platform is able to move as to position the manipulator in certain preferred configurations. Since the motion of the manipulator is unknown a priori, the platform has to use the measured joint position information of the manipulator for its own motion planning. This paper presents a control algorithm for the platform so that the manipulator is always positioned at the preferred configurations measured by its manipulability. Simulation results are presented to illustrate the efficacy of the algorithm. The algorithm is also implemented and verified on a real mobile manipulator system. The use of the resulting algorithm in a number of applications is also discussed. >

The agile eye: a high-performance three-degree-of-freedom camera-orienting device

Abstract: This paper presents some results obtained in the development of a three-degree-of-freedom camera-orienting device. The agile eye, as it is referred to, is capable of an orientation workspace larger than that of the human eye. The miniature camera mounted on the end-effector can be pointed within a cone of 140 degrees opening with plus or minus 30 degrees in torsion. The mechanical architecture of the orienting device is based on a spherical three-degree-of-freedom parallel manipulator which leads to high-performance dynamics. A kinematic optimization has been performed in order to determine the dimensional parameters of the prototype which would provide the best overall accuracy. A complete dynamical model of the manipulator has also been derived and programmed, and simulation results have guided the mechanical design. Finally, a prototype has been built and experimented with. >

A Time-Domain Inverse Dynamic Tracking Control of a Single-Link Flexible Manipulator

Abstract: A manipulator system with a large workspace volume and high payload capacity has greater link flexibility than do typical industrial robots and teleoperators. If link flexibility is significant, position control of the manipulator’s end-effector exhibits nonminimum-phase, noncollocated, and flexible-structure system control problems. This paper addresses inverse dynamic trajectory planning issues of a single-link flexible manipulator. The inverse dynamic equation of a single-link flexible manipulator was solved in the time-domain. By dividing the inverse system equation into its causal part and anticausal part, the inverse dynamic method calculates the feed-forward torque and the trajectories of all state variables that do not excite structural vibrations for a given end-point trajectory. Through simulation and experiment with a single-link manipulator, the effectiveness of the inverse dynamic method in producing fast and vibration-free motion has been demonstrated.

Direct-drive manipulator for pen-based force display

Abstract: A pen-based direct-drive manipulator enables precision manipulation and force display of a control point within three degrees of freedom. The control point exhibits substantially no backlash, very low friction and very low inertia making it useful as a force display. The manipulator also has a very high force generation bandwidth allowing high frequency force components to be displayed. A parallel actuator structure controls motion over two degrees of freedom in a horizontal plane. The parallel structure is a redundant structure including three chains in parallel coupled at the control point. The redundant structure provides a uniform force capability throughout the manipulator workspace. A pair of rotational actuators rotate the parallel structure about an axis to approximate a linear motion along a third axis. The rotational actuators provide a third degree of freedom for the control point. Motion about the third axis is substantially decouple from motion about the horizontal plane.

Visual compliance: task-directed visual servo control

Abstract: This paper introduces visual compliance, a new vision-based control scheme that lends itself to task-level specification of manipulation goals. Visual compliance is effected by a hybrid vision/position control structure. Specifically, the two degrees of freedom parallel to the image plane of a supervisory camera are controlled using visual feedback, and the remaining degree of freedom (perpendicular to the camera image plane) is controlled using position feedback provided by the robot joint encoders. With visual compliance, the motion of the end effector is constrained so that the tool center of the end effector maintains "contact" with a specified projection ray of the imaging system. This type of constrained motion can be exploited for grasping, parts mating, and assembly. The authors begin by deriving the projection equations for the vision system. They then derive equations used to position the manipulator prior to the execution of visual compliant motion. Following this, the authors derive the hybrid Jacobian matrix that is used to effect visual compliance. Experimental results are given for a number of scenarios, including grasping using visual compliance. >

Calibration of a parallel robot using multiple kinematic closed loops

Abstract: A method is presented for autonomous kinematic calibration of a 3-DOF redundant parallel robot. Multiple closed loops are used in a least squares optimization method. Ill-conditioning, column scaling of the gradient matrix, and observability indices for the best pose set of robot calibration configurations are discussed. Experimental results are presented and compared with the results using an external calibration device. >

A hyper-redundant manipulator

Abstract: "Hyper-redundant" manipulators have a very large number of actuatable degrees of freedom. The benefits of hyper-redundant robots include the ability to avoid obstacles, increased robustness with respect to mechanical failure, and the ability to perform new forms of robot locomotion and grasping. The authors examine hyper-redundant manipulator design criteria and the physical implementation of one particular design: a variable geometry truss. >

Inverse dynamics of a parallel manipulator

Abstract: Presented is an analysis of the kinematics and the inverse dynamics of a proposed three degree of freedom (dof) parallel manipulator resembling the Stewart platform in a general form. In the kinematic analysis, the inverse kinematics, velocity, and acceleration analyses are performed, respectively, using vector analysis and general homogeneous transformations. An algorithm to solve the inverse dynamics of the proposed parallel manipulator is then presented using a Lagrangian technique. In this case, it is found that one should introduce and subsequently eliminate Lagrange multipliers to arrive at the governing equations. Numerical examples are finally carried out to examine the validity of the approach and the accuracy of the numerical technique employed. The trajectory of motion of the manipulator is also performed using a cubic spline. © 1994 John Wiley & Sons, Inc.

Control and coordination of locomotion and manipulation of a wheeled mobile manipulator

Abstract: In this thesis, we investigate modeling, control, and coordination of mobile manipulators. A mobile manipulator in this study consists of a robotic manipulator and a mobile platform, with the manipulator being mounted atop the mobile platform. A mobile manipulator combines the dextrous manipulation capability offered by fixed-base manipulators and the mobility offered by mobile platforms. While mobile manipulators offer a tremendous potential for flexible material handling and other tasks, at the same time they bring about a number of challenging issues rather than simply increase the structural complexity. First, combining a manipulator and a platform creates redundancy. Second, a wheeled mobile platform is subject to nonholonomic constraints. Third, there exists dynamic interaction between the manipulator and the mobile platform. Fourth, manipulators and mobile platforms have different bandwidths. Mobile platforms typically have slower dynamic response than manipulators. The objective of the thesis is to develop control algorithms that effectively coordinate manipulation and mobility of mobile manipulators. We begin with deriving the motion equations of mobile manipulators. The derivation presented here makes use of the existing motion equations of manipulators and mobile platforms, and introduces the velocity and acceleration dependent terms that account for the dynamic interaction between manipulators and mobile platforms. Since nonholonomic constraints play a critical role in control of mobile manipulators, we then study the control properties of nonholonomic dynamic systems, including feedback linearization and internal dynamics. Based on the newly proposed concept of preferred operating region, we develop a set of coordination algorithms for mobile manipulators. While the manipulator performs manipulation tasks, the mobile platform is controlled to always bring the configuration of the manipulator into a preferred operating region. The control algorithms for two types of tasks--dragging motion and following motion--are discussed in detail. The effects of the dynamic interaction are also investigated. To verify the efficacy of the coordination algorithms, we conduct numerical simulations with representative task trajectories. Additionally, the control algorithms for the dragging motion and following motion have been implemented on an experimental mobile manipulator. The results from the simulation and experiment are presented to support the proposed control algorithms.

Trajectory Verification in the Workspace for Parallel Manipulators

Abstract: We present a fast algorithm for solving the problem of the ver ification of a trajectory for a 6-DOF parallel manipulator with respect to its workspace: i.e., given two different postures for the end effector, is the straight line joining these two postures in the parameters space fully inside the workspace? This al gorithm is based on the analysis of the algebraic inequalities describing the constraints on the workspace and provides a technique for computing those parts of the trajectory that lie outside the workspace. This method is exact if the orientation of the end effector is kept constant along the trajectory and approximate if the orientation is allowed to vary.

Modeling and compensation of the dynamic interaction of a mobile manipulator

Abstract: A mobile manipulator composed of a manipulator and a mobile platform has a much larger workspace than a fixed-base manipulator. While the on-board manipulator reaches out and performs manipulation tasks, the role of the mobile platform is to position the manipulator in a preferred configuration. In this paper, we study the effect of the dynamic interaction between the manipulator and the mobile platform of a mobile manipulator on the task performance. We consider the task that the end point of the manipulator tracks a desired trajectory in a fixed reference frame. The effect of the dynamic interaction on the tracking performance is examined by comparing four different cases: (1) without any compensation of the dynamic interaction at all; (2) with the mobile platform compensating the dynamic interaction caused by the manipulator; (3) with the manipulator compensating the dynamic interaction caused by the mobile platform; and (4) with full compensation of the dynamic interaction with each other. >

A novel concentric multilink spherical joint with parallel robotics applications

Abstract: A new spherical joint mechanism which is well suited to parallel robotics is presented. The concentric multilink spherical (CMS) joint allows two or more struts to be connected together such that they rotate about a single point. This joint can replace the traditional ball or universal (Hooke) joints in Stewart platforms, variable geometry truss manipulators, and other parallel robots. The TETRA2 robot consists of five nodes and six actuated struts. It provides a range of motion of 1m/spl times/0.5m/spl times/0.5m and has lifted a payload of 10 kg at full lateral extension. Simulation of a 48 struct walking robot illustrates the use of CMS joints to design more complex structures. The simulation also demonstrates new algorithms for parallel robot control. >

Development of a hyper-redundant multijoint manipulator for maintenance of nuclear reactors

Abstract: A tendon-driven manipulator, the CT Arm, has a specific tendon traction transmission mechanism, in which a pair of tendons for driving a joint is pulled from base actuators via pulleys mounted on the based-side joints. The mechanism makes the most of the coupled drive function of the tendon tractions and thus enables the lightweight manipulator to exhibit enormous payload capability. By this tendon-driven mechanism, a multijoint manipulator with super-redundant degrees of freedom could be realized, which is suitable to the maintenance of nuclear reactors. In this article, we introduce the CT Arm and discuss the possibility of generating a multijoint maintenance manipulator for nuclear reactors, which must have super-redundant degrees of freedom. A position-coordination approach for a hyper-redundant manipulator to carry tools or inspection equipment passing through a hole to a work location in a nuclear reactor is also proposed. Computer simulation has been used to show the validity of the hyper-redundant...

A “3-2-1” kinematic configuration of a Stewart platform and its application to six degree of freedom pose measurements

Abstract: This paper outlines a simple yet accurate approach to measuring the six degree of freedom position and orientation of a robot end-effector. The mechanism, which will be far less costly than currently available devices, can be used to make both static and dynamic measurements for robot calibration as well as real-time endpoint control. The kinematics of the approach stem from a configuration of the Stewart platform. A “3-2-1” kinematic configuration is proposed which results in a closed-form forward kinematic solution for the Stewart platform. The closed-form algorithm can be computed about 100 times faster than conventional iterative algorithms. A prototype system using six string encoders was built and tested. Issues on error compensation were also studied. The presented approach should be useful for a broad range of applications other than robot metrology where convenient, low-cost, six degree of freedom static and/or dynamic pose measurements are required or preffered.

Instantaneous kinematics and design of a novel redundant parallel manipulator

Abstract: In this paper we study the velocity and acceleration relations of a novel redundant parallel manipulator. Through this study, we derive the Jacobian matrices of the inverse and direct velocity problems. Moreover, we introduce two practical designs that are kinematically equivalent to the ideal manipulator. The proposed manipulator has potential to be used in a wide range of applications from space robotics to highly dexterous flight simulators. >

The (true) Stewart platform has 12 configurations

Abstract: We consider a Stewart platform and show that its forward kinematics has at most 12 solutions. A first geometrical demonstration is provided which uses the concept of circularity and in a second proof we show that this problem is equivalent to find a system of two planar parallel manipulators with each 6 solutions to the forward kinematic problem. A geometrical construction is provided to construct such a system and a Stewart platform with 12 configurations is exhibited. >

Design and control of a simplified Stewart platform for endoscopy

Abstract: Presents the development of a workspace controller for a newly designed platform. The platform is designed to manipulate endoscopic tools and is actuated by tendons to meet the small scale requirements in endoscopy. The tendon actuation provides challenges to the controller design since the number of degrees of freedom equals the number of tendons. In typical tendon-driven systems, the number of tendons is greater than the number of degrees of freedom. This paper presents the kinematic and dynamic analysis of the manipulator and presents a workspace controller for the tendon driven system. Simulation as well as experimental results are presented for the controlled system. The results demonstrate the effectiveness of the controller in tracking a step response and a circular trajectory at 2.0 Hz and greater. The device is similar to the Stewart platform and the basic design can be used in applications where the fall range of motion of the Stewart platform is not required. Applications of the device range between targeting systems, snake-like robots, and endoscopy. >

A Special Type of Singular Stewart-Gough Platform

Abstract: A Stewart-Gough platform, whose base attachment points occupy a particular cubic surface, may exhibit continuous motion while all six prismatic actuators are locked. Line geometric analysis reveals that, during such motion, the six leg axes remain in a specific linear complex, congruence or hyperboloidal ruled surface. Furthermore the pose or direct kinematics of any platform, five of whose leg base attachment points lie in such a cubic surface, is readily obtained and admits no more than four real solutions.

A complete and general solution to the forward kinematics problem of platform-type robotic manipulators

Abstract: In this paper a general method is presented, based on the data of three point positions, velocities and accelerations of the end effector, for solving the forward kinematics problem of any platform-type manipulator, including the 6 DOF Stewart Platform. Numerical examples are included to demonstrate the application of the method. It is shown that the equations for the forward position kinematics are highly-nonlinear, however, closed-form solutions to the forward rate kinematics and the forward acceleration kinematics can be obtained by solving a system of linear equations. The advantages of using additional passive joint encoders is also discussed, to simplify the solution of the position kinematics problem, and obtain a one-to-one relation between the actuated joint variables and the end effector configurations. >

Design and control of a three‐degrees‐of‐freedom, in‐parallel, actuated manipulator

Abstract: The mechanics, design, and control of a 3–degrees-of-freedom, in-parallel, pneumatically actuated manipulator are presented. The manipulator consists of two platforms connected by three serial chains. The kinematic design is such that the three relative degrees of freedom between the two plates allow the manipulator to accomodate uncertainties and sustain impacts while contacting and interacting with unknown environments. In particular, the manipulator is naturally compliant in translation along the approach direction as well as in rotations about axes perpendicular to the approach direction, while it is stiff in other directions. In this article, an overview of the manipulator kinematics, a description of the manipulator system and the associated hardware, and experimental results on the dynamic behavior of a prototype are presented. © 1994 John Wiley & Sons, Inc.

Dynamic load-carrying capacity and inverse dynamics of multiple cooperating robotic manipulators

Abstract: A unified method for computing the dynamic load-carrying capacity (DLCC) and the inverse dynamics of multiple cooperating robotic manipulators is developed in this paper. In this method, the kinematic constraints and the governing dynamic equations of the multi-robot system are formulated in the joint space based on a coordinate partitioning technique and the generalized D'Alembert's principle. This approach not only gives the minimum number of equations but also allows separate computations of the dynamics of the robots and that of the payload. The upper limit of the DLCC at any points on a given trajectory is obtained by solving a small-size linear programming problem. An iterative algorithm for evaluating the maximum allowable DLCC of the trajectory is also developed. After the DLCC is determined, the optimum distribution of actuator torques are computed by using a quadratic programming technique. The proposed method is conceptually straightforward, and it is applicable to wide varieties of multi-robot systems as well as fully parallel robots with redundant actuators. >

Mobility and position analyses of a novel redundant parallel manipulator

Abstract: Presented in this paper is a new platform-type manipulator that is parallel and kinematically redundant. The use of redundancy not only increases the workspace, but also helps in coping with singularities and improves dexterity. A complete kinematic model of the structure is presented in this paper, that is used for its mobility, and its direct and inverse position analyses. >

Inverse kinematics of six-degree of freedom “general” and “special” manipulators using symbolic computation

Abstract: This paper presents an algorithm that solves the inverse kinematics problem of all six degrees of freedom manipulators, “general” or “special”. A manipulator is represented by a chain of characters that symbolizes the position of prismatic and revolute joints in the manipulator and the special geometry that may exist between its joint axes. One form of the loop closure equation is chosen and the Raghavan and Roth method is used to obtain symbolically a square matrix. The determinant of this matrix yields the characteristic polynomial of the manipulator in one of the kinematic variables. As an example of the use of this algorithm we present the solution to the inverse kinematics problem of the GMF Arc Mate welding manipulator. In spite of its geometry, this industrial manipulator has a non-trivial solution to its inverse kinematics problem.

Kinematic feature analysis of parallel manipulator systems

Abstract: This paper presents an in-depth analysis on the kinematic features of parallel manipulators, such as deficiency, singularity, and redundancy. Parallel manipulators under consideration are of a general form, with no restriction on their structure. Three orthogonal instantaneous motion spaces (IMSs) of a parallel manipulator are identified including deficient, uncontrollable, and controllable IMSs. Based on the IMSs, the deficiency and singularity of a parallel manipulator are devised and analyzed and their remedies are devised. Three types of redundancies of a parallel manipulator are introduced including the redundancies in serial chain, joint actuation, and parallelism. The three types of redundancies are shown to overcome the singularity of a parallel manipulator, as well as to improve either its dexterity or load capacity. >

Robust Non-Linear H∞/Adaptive Control of Robot Manipulator Motion

Abstract: In robotics, despite considerable effort to minimize system modelling errors, uncertainties are always present and sometimes significant. In this paper, modelling errors are first represented by a class of bounded disturbances in the input channels (torques) of the robot. A measure of the robot system's ability to reject these disturbances is formulated in an L2 gain sense and a control design is subsequently proposed to achieve optimal disturbance rejection. If more detailed information is available on the plant-model mismatch, then the control design can be modified to incorporate an adaptive scheme (with explicit parameter updating laws) in order to reduce the conservativeness of the original design and to improve robust performance of the overall system.