Orientation Of End-effector Research Articles

Position Error Sensitivity Analysis for Polishing Robot

t is the goal of this paper to describe an error analysis methodology for polishing robot on a manufacturing floor. With the generalized errors considered in the model, the end-effector position and orientation errors are calculated as a function of the generalized error. The analysis is to determine which physical errors significantly influence the end-effector error. The method and computer program have been applied to the performance evaluation of a robotic manipulator to be used in a polishing robot. This methodology can be applied to estimate calibration error and give the severity value to help the designer to select the polishing robot parameters.

Error Modelling for Master Slave Surgical Robot System

The Position and orientation accuracy of robot manipulator has long become a major issue to be considered in its advanced application. A linear error model that described the end-effector position and orientation errors of the master salve surgical robot system due to kinematics parameters errors has been presented. A computer program to perform the accuracy analysis has been developed in MATLAB. This methodology and software are applied to the accuracy analysis of a master-slave surgical robot system. The position error in its workspace cross section (XOZ) has been plotted as 3D surface graph and discussed.

A LEARNING METHOD TO DETERMINE HOW TO APPROACH AN UNKNOWN OBJECT TO BE GRASPED

We present a learning algorithm to determine the appropriate approaching pose to grasp a novel object. Our method focuses on the computation of valid end-effector orientations in order to make contact with the object at a given point. The system achieves this goal by generalizing from positive examples provided by a human operator during an offline training session. The technique is feature-based since it extracts salient attributes of the object to be grasped rather than relying on the availability of models or trying to build one. To compute the desired orientation, the robot performs three steps at run time. Using a multi-class Support Vector Machine (SVM), it first classifies the novel object into one of the object classes defined during training. Next, it determines its orientation, and, finally, based on the classification and orientation, it extracts the most similar example from the training data and uses it to grasp the object. The method has been implemented on a full-scale humanoid robotic torso equipped with multi-fingered hands and extensive results corroborate both its effectiveness and real-time performance.

Pose Accuracy Analysis of Robot Manipulators Based on Kinematics

The pose accuracy of robot manipulators has long become a major issue to be considered in its advanced application. An efficient methodology to generate the end-effector position and orientation error model of robotic manipulator has been proposed based on the differential transformation matrix theory. According to this methodology, a linear error model that described the end-effector position and orientation errors due to robot kinematics parameters errors has been presented. A computer program to generate the error model and perform the accuracy analysis on any serial link manipulator has been developed in MATLAB. This methodology and software are applied to the accuracy analysis of a Phantom Desktop manipulator. The positioning error of the manipulator in its workspace cross section (XOZ) has been plotted as 3D surface graph and discussed.

Optimal Paint Gun Orientation in Spray Paint Applications—Experimental Results

In this paper, we present the experimental results of a new spray paint algorithm presented in previous publications. Both theory and simulations indicate that the proposed method allows a robotic manipulator to paint a given surface using substantially lower joint torques than with conventional approaches. In this paper, we confirm this by implementing the algorithm on an ABB robot and we find that the joint torques needed to follow the trajectory are substantially lower than for the conventional approach. The approach presented is based on the observation that a small error in the orientation of the end effector does not affect the quality of the paint job. It is far more important to maintain constant velocity for the entire trajectory. We thus propose to allow a small error in the specification of the end-effector orientation, and we show how this allows us to obtain a higher constant speed throughout the trajectory. In addition, to improve the uniformity of the paint coating we are also able perform the paint job in less time.

Toward the Development of a Hand-Held Surgical Robot for Laparoscopy

Minimally invasive surgery (MIS), which typically involves endoscopic camera and laparoscopic instruments may seem to be the ideal surgical procedure for its apparent benefits. However, in comparison to open surgeries, the spatial and mechanical tool limitations posed on surgeons are so high that often MIS is foregone for complex cases and even when it is possible, the procedure requires a high dexterity, caliber, and experience from the surgeon. Particularly, suturing procedure through MIS is known to be extremely challenging. We are working toward the development of a robotic hand-held surgical device for laparoscopic interventions that enhances the surgeons' dexterity. The instrument produces two independent DOFs, which is sufficient for enabling MIS suturing procedure in vivo. The end-effector's orientation is controlled by an intuitive and ergonomic controller and its position is controlled directly by the surgeon. Different control modes, handles, and end-effector kinematics are primarily evaluated using a virtual reality simulator before choosing the best combination. A proof-of-concept prototype of the device has been developed.

A Real-Time Algorithm for Determining the Optimal Paint Gun Orientation in Spray Paint Applications

In this paper, we present a method for increasing the speed at which a standard industrial manipulator can paint a surface. The approach is based on the observation that a small error in the orientation of the end effector does not affect the quality of the paint job. It is far more important to maintain constant velocity throughout the trajectory. We consider the freedom in the end-effector orientation as functional redundancy and represent the restriction on the orientation error as barrier functions or linear matrix inequalities. In doing this, we cast the problem of finding the optimal orientation at every time step into a convex optimization problem that can be solved very efficiently and in real time. We show that the approach allows the end effector to maintain a higher constant velocity throughout the trajectory guaranteeing uniform paint coating and substantially reducing the time needed to paint the object.

1A2-A20 複数のマニピュレータによる線状柔軟物体のハンドリング

A wire also called Deformable Linear Object(DLO) has a shape of simple line or spline. But has an uncertainty properties of deformation. We can see even the natural status of the wire has a different shapes caused by the internal stress and contact conditions. Especially extern condition determines the shape of the wire. We believe handling motion planning and strategies of DLO, we are considering the electric wire, can automate industrial application. Our interest is not a topological shape of wire, but the manipulation and assembly applications by multiple manipulators. As the first step, wire handling motion planning of manipulator can constraint the end effector's orientation and the gripping strategies of deformable linear object will be shown. Simulation result showed the performance and the effectiveness of our approaches.

Application of the Rotation Matrix Natural Invariants to Impedance Control of Rotational Parallel Robots

Force control of parallel robots with rotational degrees of freedom through impedance algorithms is considerably influenced by the representation method of the end-effector orientation. Using the natural invariants of the rotation matrix and the angular velocity vector in the impedance control law has some theoretical advantages, which derive from the Euclidean-geometric meaning of these entities. These benefits are particularly evident in case of robotic architectures with three rotational degrees of freedom (serial or parallel wrists with spherical motion). The behaviour of a 3-CPU parallel robot controlled by an impedance algorithm based on this concepts is assessed through multibody simulations, and the results confirm the effectiveness of the proposed approach.

Accuracy Analysis of a Pointing Mechanism for Communication Applications

In this paper, a detailed accuracy analysis for the orientation of an innovative open-chain pointing mechanism is carried out, employing methods for indirect measurements. The particular shape of the mechanism exhibits the advantage of high structural stiffness and different pointing accuracy in comparison with a standard orthogonal axes gimbal. With the aim of finding out advantages and drawbacks as regard the accuracy of the proposed pointing mechanism, an accuracy analysis is performed through three different methods of uncertainty expression and propagation based on the probability theory or the theory of evidence. The proposed pointing mechanism, in comparison with the standard orthogonal axes gimbal, exhibits a considerable lower uncertainty for two of the three Euler angles that are used for the end-effector orientation expression and a higher uncertainty for the third Euler angle. Thus, the proposed mechanism could be particularly suited for pointing directional antennas, allowing the employment of high-data-rate communication systems. This result is strengthened by the fact that the accuracy analysis was performed with different uncertainty expression and propagation methods, which take into account only random effects or both random and systematic effects.

Decoupled and Homokinetic Transmission of Rotational Motion via Constant-Velocity Joints in Closed-Chain Orientational Manipulators

This paper presents novel 2DOF and 3DOF closed-chain orientational manipulators, whose end-effector motion is actuated in a decoupled and homokinetic way by frame-located motors via holonomic transmissions based on constant-velocity couplings. The functioning of these couplings is investigated and the conditions applying for homokinetic transmission to be preserved during simultaneous motor drive are revealed and implemented. As a result, decoupled and configuration-independent relations between the motor rates and the time-derivatives of the variables describing the end-effector orientation are achieved. The attainment of analogous relations between the motor speeds and the components of the end-effector angular velocity is conversely proven to be unfeasible. The problem of singularities is furthermore examined, showing that input-output homokinesis is not a sufficient condition for a globally uniform kinetostatic behavior of the mechanism, which may, indeed, possibly reach uncertainty singular configurations. The connecting chains of the most typical constant-velocity couplings are analyzed, in order to obtain analytical expressions for the functions on which such singularities depend. The influence of design parameters is accordingly inspected. The results are valuable for the type and dimension synthesis of closed-chain wrists free from direct kinematic singularities, and characterized by simple kinematics and regular input-output kinetostatic relations.

Force Compensating Trajectories for Redundant Robots: Experimental Results

We proposed a new approach for redundant robots trajectories planning, based on the Null space (or Kernel) features. The Null space (Kernel) exists only in the case of redundant robots and it describes these joints motion which do not affect the robot end-effector motion in the sense of both position and orientation. Based on this “hidden motion” realized in the configuration space, which does not affect the motion in the working zone, we can control independently the robot end-effector position and orientation motions, or just maintain its state while some external force is applied to it. The proposed control strategy is simple, no additional penalty functions are used to restraint the end-effector motion as in the case of the conventional methods. No pseudo inverse kinematics calculations are required; the desired trajectories are generated directly in the configuration space. No complicated control schemes are introduced, the proposed method is based on solving algebraic systems of equations and finding eigenvectors and eigenvalues. In the paper the results from simulations and experiments based on the proposed method are presented and discussed.

Vehicle Simulation System: Controls and Virtual-reality-based Dynamics Simulation

This paper introduces a cable-suspended robot, the vehicle simulation system, designed for pilot and driver training. The main idea of this work is to make a system that will provide realistic simulations of vehicle motion using virtual reality and a motion platform. A method to produce inertial forces acting on the vehicle user is proposed. A detailed description of the robot's dynamics constraints is provided, accompanied with a numerical solution. Using the developed mathematical model, the robot workspace is analyzed, as well as the influence of the end-effector orientation angle ranges on the available workspace. Adequate robot platform motion is provided through four control systems in a form of a cascade control with a fuzzy logic controller in outer loops. The cable robot is non-linear and difficult from a classical control point of view, since it requires a local linearization of the dynamics equations. A fuzzy logic control concept has been applied in order to control the end-effector position, velocity and acceleration and it turns out to be convenient in simulation, allied with inner-loop classical control. As the system is under-constrained, with nine unknown cable tensions and six dynamics equations, an optimization method is used. The control complexity is increased by the requirement, specific to cable robots, of maintaining positive cable tensions. The system simulations are done using a virtual reality environment and results are presented accompanied with the discussion.

Real-Time Direct Position Analysis of Parallel Spherical Wrists by Using Extra Sensors

The paper presents an algorithm for the real-time evaluation of the actual end-effector orientation of general parallel spherical wrists. Conceptually, the method relies on evidence that the pose of a rigid body is defined once the location of at least two linearly independent vectors attached to the body is known. The location of these vectors of the wrist end-effector is determined by the solution of the direct position analysis of some properly chosen kinematic chains (legs) of the manipulator. In order to accomplish this analysis, extra sensors, which measure suitable non-actuated variables of the chosen legs, need to be placed in addition to the ones normally embedded in the servomotors, i.e., the sensors which measure the actuated variables. From a mathematical point of view, the algorithm is built on the polar decomposition of a matrix and has inherent least square features. Thus, together with measurement redundancy, i.e., more sensors (extra sensors) than the mechanism degrees of freedom, the method also makes it possible to minimize the influence of both round-off and measurement errors on the estimation of the location of the wrist end-effector. The method is general but, in order to prove its effectiveness, without loss of generality it has been customized to the solution of the 3(UPS)-S fully parallel wrist architecture (where U, P and S are for universal, prismatic and spherical joint, respectively). Comparison of the proposed method, in both its general and specialized form, with others from the literature is provided.

Trajectory coordination planning and control for robot manipulators in automated material handling and processing

Motion coordination planning and control play a crucial role in robot application to Cartesian task operations with taking into account kinematics and dynamics constraints. This paper presents a unified approach to coordination planning and control for robot position and orientation trajectories in Cartesian space. The concept of generalised robot pose is defined as the robot configuration consisting of position and orientation, in which the orientation is described by a vector equivalent to the rotational angular displacement. The robot pose ruled surface is formed as a three-dimensional motion locus of its configuration vector. The unified treatment of the end-effector positions and orientations is based on the robot pose ruled surface concept and used in trajectory interpolations. The coordination planning of pose trajectories for the robot end effector is accomplished by generating and optimising the pose ruled surface under the constraints of kinematics and dynamics performances. The coordination control is implemented through controlling the motion laws of two end points of the orientation vector and calculating the coordinates of instantaneous corresponding points. The simulation experiment using PUMA 560 robot in arc welding and surface finishing processes are carried out to verify the feasibility of the proposed approach and demonstrate the capabilities of generation and control models.

Evolving a multiobjective obstacle avoidance skill of a seven-link manipulator subject to constraints

A remarkable part of the skills of human experts rendering services in hazardous and dynamic factory environments is their ability to continue to perform a job while reacting to adapt their posture to sudden changes in the environment such as upcoming obstacles. Possession of these typical human skills that can be defined in a set of linguistic objectives will help to build flexible and more dexterous robot manipulators for factory automation systems that will meet the challenges of the growing complexity of the modern automated manufacturing environments. In this paper a novel soft-computing-based method is proposed for redundancy resolution of industrial robot manipulators to perform dexterous obstacle avoidance motions subject to the working constraints of the end effector. The new approach is based on evolving redundant rows of the Jacobian matrix of the manipulator and intelligent manipulation of user-defined kinematic functions for redundancy resolution. An evolutionary approach has been adopted to enhance the search efficiency in the objective space of a linguistic multi-objective problem (MOP) for the task of avoiding an obstacle moving towards the manipulator while keeping the end-effector position and orientation vector static. The objective functions of the MOP appear in the weighted sum of objectives in a gradually growing manner. The basic natural phenomena in the process of complex skill acquisition by human beings are reflected in the proposed approach. The effectiveness of the proposed method is demonstrated through experiments carried out using an industrial seven-link manipulator called PA-10, manufactured by the Mitsubishi Heavy Industries Ltd.

Task-Space Tracking Control of Robot Manipulators via Quaternion Feedback

In this paper, we consider the problem of task-space tracking control of robot manipulators. Based on a quaternion representation of the end-effector orientation, we design a class of task-space controllers that ensure asymptotic end-effector position and orientation tracking. To facilitate the control design, we first develop model-based and adaptive full-state feedback controllers. We then present a model-based output feedback controller that eliminates link velocity measurements via a model-based observer. The application of the proposed control strategy to redundant robots is also discussed. Simulation results based on a six-link manipulator system are presented for the output feedback controller.

Tool orientation and motion error in microsurgical parallel manipulator

Positioning error is inherent in normal human hand motion and limits precision in manual microsurgery. A computer-based surgery can reduce human error. This work discuss tool orientation, motion error and computer simulation of a microsurgical end effector based on a parallel spatial manipulator. Among several previously developed parallel manipulators for other applications, the selected architecture for this work is consisting of a moving platform attached to a base through three identical prismatic-revolute-spherical jointed serial linkages. The actuation is conducted through the prismatic joints while the others are passive. These prismatic actuators lie on a common plane and have radial directions of action. A surgical tool of specific length is attached to the moving platform centre. A computer-based simulation is built for the end effector by obtaining the forward and inverse kinematics solutions. The developed relation for tool tip motion with respect to actuators positioning is used to evaluate tool location and orientation. Architectural designs for two arrangements are compared for better design and positioning error.

A generalised approach to point-to-point motion of multi-DOF parallel manipulators illustrated with TMPM

The work presented in this paper describes a novel approach to the computation of the point-to-point motion of multi-degree-of-freedom parallel mechanisms. The common technique for solving for the inverse kinematics of parallel mechanisms is through intense computations and complex vector transformations. One obvious drawback of this method is the fact that the solution method varies with the type of mechanism being used. In this paper, a generalised alternative approach is presented, which avoids the problems encountered in the available techniques, for solving for the inverse kinematics of parallel manipulator systems. The proposed approach uses a fuzzy system as a general black box model to solve for the joint angles of the desired pose when the position and orientation of the parallel manipulator end-effector are given in advance. Since optimal membership functions are difficult to achieve using the experience of system designers, genetic algorithms are used instead and applied to the fuzzy rules set to optimise the search procedure. To verify the proposed scheme, a three degree-of-freedom parallel manipulator is analysed and the simulation results are very encouraging.

Trajectory‐planning through interpolation by overlapping cubic arcs and cubic splines

AbstractA new path‐planning interpolation methodology is presented with which the user may analytically specify the desired path to be followed by any planar industrial robot. The user prescribes a set of nodal points along a general curve to be followed by the chosen working point on the end‐effector of the mechanism. Given these specified points along the path and additional prescribed kinematical requirements, Overlapping Cubic Arcs are fitted in the Cartesian domain and a cubic Spline interpolation curve is fitted in the time‐domain. Further user‐specified information is used to determine how the end‐effector orientation angle should vary along the specified curve. The proposed trajectory‐planning methodology is embodied in a computer‐algorithm (OCAS), which outputs continuous graphs for positions, velocities and accelerations in the time‐domain. If a varying end‐effector orientation angle is specified, the OCAS‐algorithm also generates continuous orientation angle, orientation angular velocity and orientation angular acceleration curves in the time‐domain. The trajectory‐planning capabilities of the OCAS‐algorithm are tested for cases where the prescribed nodal points lie along curves defined by analytically known non‐linear functions, as well as for nodal points specified along a non‐analytical (free‐form) test‐curve. The proposed trajectory‐planner may be implemented as part of kinematic and kinetic simulation software, and it also has the potential application for controlling machine tools in cutting along free‐form curves. Copyright © 2003 John Wiley & Sons, Ltd.