End-effector Of Manipulator Research Articles

A meta-heuristic proposal for inverse kinematics solution of 7-DOF serial robotic manipulator: quantum behaved particle swarm algorithm

In this study, a quantum behaved particle swarm algorithm has used for inverse kinematic solution of a 7-degree-of-freedom serial manipulator and the results have been compared with other swarm techniques such as firefly algorithm (FA), particle swarm optimization (PSO) and artificial bee colony (ABC). Firstly, the DH parameters of the robot manipulator are created and transformation matrices are revealed. Afterward, the position equations are derived from these matrices. The position of the end effector of the robotic manipulator in the work space is estimated using Quantum PSO and other swarm algorithms. For this reason, a fitness function which name is Euclidian has been determined. This function calculates the difference between the actual position and the estimated position of the manipulator end effector. In this study, the algorithms have tested with two different scenarios. In the first scenario, values for a single position were obtained while values for a hundred different positions were obtained in the second scenario. In fact, the second scenario confirms the quality of the QPSO in the inverse kinematic solution by verifying the first scenario. According to the results obtained; Quantum behaved PSO has yielded results that are much more efficient than standard PSO, ABC and FA. The advantages of the improved algorithm are the short computation time, fewer iterations and the number of particles.

Model-based force/position control of cooperative manipulation systems

ABSTRACTThis paper presents a centralized force/position controller for a heavy object manipulation in a multi-manipulator cooperative system. System dynamics of cooperative manipulating tasks comes from complex interaction of the object with robot manipulators and the environment. In this paper, focussing on the interaction effects in the system as well as by noting the role of imposed kinematics and force constraints, manipulator coordination and minimizing internal forces a pre-designed impedance behaviour between manipulator end effectors and the object is developed. The stability of the feedback system is then presented through passivity theorem and simulation results are finally provided with three manipulators handling the object supporting the relevance of the theoretical results.

Simultaneous Planning Method Considering Both Overall Configuration and End Pose for Hyper-Redundant Manipulators

Featured by extreme flexibility, hyper-redundant manipulators are gradually developed and applied to perform detection and maintenance tasks in confined on-orbit environments. However, its configuration planning is very challenging due to a large number of degrees of freedom. This paper proposes a simultaneous planning method considering both overall configuration and end pose for hyper-redundant manipulators. First, the end effector and intermediate universal joints of the hyper-redundant manipulator are selected as the follow-up controlled points. The corresponding active control points are freely set near the follow-up controlled points. Then, the Euclidean distance between the active control point and the follow-up controlled point is calculated. Combined with gradient projection method, the calculated Euclidean distance is taken as the objective function to be optimized. By adjusting the active control point and the scale factor of gradient projection method, the adjustment of follow-up controlled points (i.e. overall configuration and end pose) can be realized. What is more, this method can optimize its overall configuration to adjust the follow-up controlled points close to or far from the active control point to achieve other planning goals (i.e. obstacle avoidance, singularity avoidance and so on). Therefore, this method satisfies the requirements of simultaneous planning considering both overall configuration and end pose for hyper-redundant manipulators. Finally, the proposed simultaneous planning method is executed in physical experiment system. Results verify the effectiveness of the proposed method.

Design and Implementation of Admittance Control for a Dual-Arm Robot under Space Limitation

Aimed at the situation lack of suitable industrial robots with speed requirement and space limitation, a novel simple structured and high speed dual-arm robot is designed. The robot control system has been achieved by using high speed controller, real-time bus EtherCAT and integrating the sensor system via Ethernet interface. Kinematic and dynamic analysis are the basis of its kinematic control and trajectory planning. This paper presents a force-free control method for direct teaching of the robot and adopts a Cartesian admittance control algorithm to realize human-machine interaction. The admittance control is conducted by utilizing six-dimensional force/torque sensor fixed to the end-effector of manipulator. To evaluate the performance of the proposed controller and control algorithm, a point-to-point teaching task is conducted.

Simulation and Analysis of Pose Setting Test of Space Redocking Manipulator End-effector Based on Parallel Mechanism

Simulation and Analysis of Pose Setting Test of Space Redocking Manipulator End-effector Based on Parallel Mechanism

Collective Behavior of Reconfigurable Magnetic Droplets via Dynamic Self-Assembly.

Dynamic self-assembly represents an effective approach to form energy-dissipative structures by introducing interactions among multiple building blocks with a continuous energy supply. Time-dependent magnetic fields are treated as convenient energy inputs to construct such a dynamic self-assembled system. The induced interactions can be further tuned by modulating the input field, resulting in a diversity of assembled patterns. However, formation of a functional dynamic pattern with controllability remains a challenge. Herein, we report the formation and pattern control of dynamically self-assembled magnetic droplets at an air-liquid interface, energized by a precessing magnetic field. The formation process involves the assembly of magnetic microparticles into particle chains inside droplets, and then highly ordered patterns are generated by balancing the induced interactions among droplets. By modulating the input field, the interactions and collective behaviors are adjusted and the pattern can be reversibly tuned, i.e., expand and shrink, in a controlled manner. Furthermore, the assembled droplets are able to be steered in two-dimensional as an entity by applying a magnetic field gradient. Utilizing dynamic pattern control and steerability of the assembled structure, cargoes are successfully trapped, transported, and released in a noncontact fashion, indicating that the dynamically assembled droplets can act as a reconfigurable untethered robotic end-effector for manipulation.

Application of a planar air-bearing microgravity simulator for demonstration of operations required for an orbital capture with a manipulator

Microgravity is the aspect of space environment that is important for robotic technologies. One possible approach to simulate microgravity conditions on Earth is to use planar air-bearing microgravity simulators. In this study we have assessed the possible application of such simulator for demonstration of operations required for the orbital capture manoeuvre. In our experiments we have used mock-up of satellite equipped with a manipulator and a set of cold-gas thrusters. Results of two sets of experiments are presented. In both sets the manipulator end-effector followed a straight-line trajectory. In the first set the satellite mock-up was commanded to hold fixed position and orientation, while in the second set the satellite mock-up was commanded to follow a pre-defined trajectory. Performed experiments show that the accuracy of the planar air-bearing microgravity simulator is sufficient to use this facility to validate control algorithms and control strategies. Presented analysis also shows that changes of the satellite-manipulator system parameters caused by the consumption of air and nitrogen from gas canisters located on the satellite mock-up have negligible influence on the dynamic behaviour of the system.

An improved artificial potential field method of trajectory planning and obstacle avoidance for redundant manipulators

In this article, we present an improved artificial potential field method of trajectory planning and obstacle avoidance for redundant manipulators. Specifically, we not only focused on the position for the manipulator end-effectors but also considered their posture in the course of trajectory planning and obstacle avoidance. We introduced boundaries for Cartesian space components to optimize the attractive field function. Moreover, the manipulator achieved a reasonable speed to move to the target pose, regardless of the difference between the initial pose and target pose. We proved the stability using Lyapunov stability theory by introducing velocity feedforward, when the manipulator moved along a continuous trajectory. Considering the shape of the manipulator joints and obstacles, we set up the collision detection model by projecting the obstacles to link coordinates. In this case, establishing the repulsive field between the nearest points on every joint and obstacles with the closest distance was sufficient for achieving obstacle avoidance for redundant manipulators. The simulation results based on a nine-degree-of-freedom hyper-redundant manipulator, which was designed and made in our laboratory, fully substantiated the efficacy and superiority of the proposed method.

Hot-line assembly strategy for connection fittings in 110kV intelligent substation

PurposeThe purpose of this paper is to provide a safe control strategy for aloft hot-line assembly of connection fittings in 110kV intelligent substations, which is significant to research on hot-line working robots.Design/methodology/approachThis paper addresses challenges of the task and establish the contact models of connection fittings. By using this control strategy, neither high precision vision positioning nor preset global reference coordinate system is required. Visual computing only needs to provide an approximately position for the manipulator end-effector, after which the connection fittings assembly task could be completed with the posture of the manipulator adjusted following the guidance by force-position control. The authors also analyze the influence of the intervention of manipulators on the very non-uniform electric field during the operation.FindingsThis strategy will be particularly useful for the hot-line assembly of connection fittings in 110kV intelligent substations as well as some assembly tasks where uncertain target position and complex contact surface such as cylindrical hole is involved.Practical implicationsThis assembly strategy is tested in energized simulated experimental system. The experiment results show that the robot can replace the manual operation to complete the assembly task safely and efficiently.Originality/valueThis assembly strategy is able to achieve the assembly task of connection fittings. Unlike other peg-in-hole assembly strategy, it does not require high stability of manipulator or plane contact surface around the hole.

Tip-position/velocity Tracking Control of Manipulator for Hull Derusting and Spray Painting based on Active Disturbance Rejection Control

During sandblasting and spray painting for hull, the tracking performance of the end-effector of manipulator to the outer surface of the hull in uniform velocity is seriously affected by uncertainty of the electrohydraulic actuator and deflection of the manipulator. To effectively improve the tracking performance of the tip-position/velocity, a novel tracking control strategy is proposed, which is based on active disturbance rejection control (ADRC) with extended state observer (ESO) and setting position feedforward control with deflection compensation. First, to reduce tracking error caused by the deflection, the reference positions of two cylinders driving telescopic and luffing motion are calculated with consideration of the deflection influence according to manipulator geometry. And then, ADRC technique is adopted to design the position servo controller of the luffing/telescopic cylinder with the help of the estimate for the uncertainty of the electro-hydraulic system by the ESO. The stability of the whole closed-loop system and the convergence of tracking error are guaranteed theoretically, simultaneously, simulation carried out in Matlab/Simulink environment with physical parameters of a real system demonstrates the effectiveness and superiority of the proposed control strategy compared with existing control schemes. Furthermore, the experimental result is given to show the feasibility and availability of the control method.

Stable and Compliant Motion of Physical Human–Robot Interaction Coupled With a Moving Environment Using Variable Admittance and Adaptive Control

There are an increasing number of applications that require the end-effector of a robotic manipulator to be compliant in response to the intended force exerted by a human operator. In physical human-robot interaction, the stability and compliance are often affected in the presence of both human and an environment, especially during the transition from noncontact to contact. Unlike previous works, the physical human-robot interaction in this letter takes into consideration of the interaction of the human, robot, and a moving environment. To achieve this, this letter proposes a variable admittance control strategy with an adaptive controller to produce a time-varying stiffness interacting with the human and a moving environment simultaneously. The passivity of the system is guaranteed for time-varying admittance with human interaction coupled with a moving environment. Experiments are conducted to demonstrate the capability of the controller.

Human-robot cooperation for robust surface treatment using non-conventional sliding mode control

This work presents a human-robot closely collaborative solution to cooperatively perform surface treatment tasks such as polishing, grinding, deburring, etc. The method considers two force sensors attached to the manipulator end-effector and tool: one sensor is used to properly accomplish the surface treatment task, while the second one is used by the operator to guide the robot tool. The proposed scheme is based on task priority and adaptive non-conventional sliding mode control. The applicability of the proposed approach is substantiated by experimental results using a redundant 7R manipulator: the Sawyer cobot.

GA Based Adaptive Singularity-Robust Path Planning of Space Robot for On-Orbit Detection

As a new on-orbit detection platform, the space robot could ensure stable and reliable operation of spacecraft in complex space environments. The tracking accuracy of the space manipulator end-effector is crucial to the detection precision. In this paper, the Cartesian path planning method of velocity level inverse kinematics based on generalized Jacobian matrix (GJM) is proposed. The GJM will come across singularity issue in path planning, which leads to the infinite or incalculable joint velocity. To solve this issue, firstly, the singular value decomposition (SVD) is used for exposition of the singularity avoidance principle of the damped least squares (DLS) method. After that, the DLS method is improved by introducing an adaptive damping factor which changes with the singularity. Finally, in order to improve the tracking accuracy of the singularity-robust algorithm, the objective function is established, and two adaptive parameters are optimized by genetic algorithm (GA). The simulation of a 6-DOF free-floating space robot is carried out, and the results show that, compared with DLS method, the proposed method could improve the tracking accuracy of space manipulator end-effector.

Learning of operator hand movements via least angle regression to be teached in a manipulator

In this document, a control system is developed to allow a manipulator to learn and plan references from demonstrations given by an operator hand. Data entry is acquired by a sensor and is learned by the generalized learning model with least angle regression to create a desired reference in three dimensional space. A fifth reference profile is employed to smooth the desired reference. Direct and inverse kinematics are gotten to represent the transformation between the three dimensional space and each of the manipulator links. A dynamic model is gotten using Newton–Euler formulation. An evolving proportional derivative (PD) control is applied to get that the manipulator end effector follows the operator hand movements. The monitoring and control systems are implemented in an embedded platform for testing purposes.

Path Planning and Collision Avoidance for a Multi-Arm Space Maneuverable Robot

In this paper, a path planning algorithm for a multi-arm space robot is proposed. The robot is capable of maneuvering on the exterior of a large space station. Based on the maneuver strategy, continuous and smooth trajectories of the manipulator end effectors are first determined via the polynomial interpolation method. Then, the kinematics describing the relation between the end effector and the joint angles as well as the platform are formulated. A Moore–Penrose pseudoinverse solution of the joint trajectories is calculated to describe the motion of the manipulators, particularly, considering the singularity avoidance. In addition, a collision detection algorithm is developed to estimate the security during operation. Constraints are formulated by considering collision avoidance, based on which a collision-free trajectory is optimized through the multiplier-penalty method. The numerical results of a triple-arm space robotic system are given to demonstrate the effectiveness of the proposed algorithms.

A Family of Hyperbolic-Type Explicit Force Regulators with Active Velocity Damping for Robot Manipulators

This paper addresses the explicit force regulation problem for robot manipulators in interaction tasks. A new family of explicit force-control schemes is presented, which includes a term driven by a large class of saturated-type hyperbolic functions to handle the force error. Also, an active velocity damping term with the purpose of obtaining energy dissipation on the contact surface is incorporated plus compensation for gravity. In order to ensure asymptotic stability of the closed-loop system equilibrium point in Cartesian space, we propose a strict Lyapunov function. A force sensor placed at the end-effector of the robot manipulator is used in order to feed back the measure of the force error in the closed-loop, and an experimental comparison of the performanceL2-norm between 5 explicit force control schemes, which are the classical proportional-derivative (PD), arctangent, and square-root controls and two members of the proposed control family, on a two-degree-of-freedom, direct-drive robot manipulator, is presented.

Trajectory Planning of Redundant Manipulators Moving along Constrained Path and Avoiding Obstacles

An optimum trajectory planning for a planar redundant manipulators is presented by minimizing the power consumption, when its end effector is commanded to move in its prescribed path. The Equations of motion of the robot manipulator are determined using Lagrange formulation. In order to accomplish a desired trajectory, the displacements of the revolute joints are interpolated as polynomial functions of time. The proposed approach generates the trajectory for the manipulator joints and end-effector by minimizing total power consumption by taking the kinematic, dynamic constraints and the obstacles in the workspace in to account. The methodology is illustrated using a planar 3-Degrees of Freedom (DOF) robot using two types of motion planning simulations; point to point motion and continuous path motion planning. Simulation results have been reported for the joint trajectories, end–effector motion for the above two cases. Results of joint trajectories are smooth and efficient.

A Two Link Manipulator End Effector Control

The goal of the paper is to present a regulation and control model of a two link manipulator end effector position. Attention is paid to kinematic and dynamic analysis of the manipulator. Then the simulation model with a control algorithm of its end effector position is proposed. MSC Adams Control Toolkit is used for computer simulation. Finally the results of the simulation are presented in graphical form.

Condition-Based Less-Error Data Selection for Robust and Accurate Mass Measurement in Large-Scale Hydraulic Manipulators

This paper proposes a practical scheme for measuring the mass of an object grasped by the end-effector of a large-scale hydraulic manipulator. Such a measurement system requires high accuracy and robustness considering the nonlinearity and uncertainty in hydraulic pressure-based force measurement during rigorous outdoor work. It is thus difficult to precisely model system behaviors and completely remove error force components (white-box modeling) under such conditions, so our scheme adopts a less-error data selection approach to relatively improving the accuracy and reliability of the measurand (gray-box modeling). It first removes dominant error forces, i.e., gravity and dynamic friction forces, then defines the on-load state by evaluating measurement conditions to omit data in indeterminate conditions, then extracts data during the object-grasp state identified by a grasp motion model and removes high-frequency components by a simple low-pass filter, and finally integrates data from multiple sensors using the posture-based priority and averages all selected data. Evaluation experiments were conducted using an instrumented hydraulic arm. Results indicate that our scheme can precisely measures the mass of the grasped object under various detection conditions with fewer errors.

Dual manipulator system of the field hot-line working robot in 110-kV substations

PurposeThe purpose of this paper is to present a dual manipulator system for aloft hot-line assembly tasks of connection fittings in 110-kv intelligent substation, which is significant to the research on hot-line working robots.Design/methodology/approachThis paper addresses the challenges of the task and presents a dual manipulator system which can overcome these challenges to realize the robotic assembly of connection fittings in narrow space without impacting the safe distance of both phase to phase and phase to ground. Two manipulators share a same global reference coordinate. The mission of Manipulator 1 is to position the fixed part of connection fittings and screw the bolts on it. Visual computing provides the approximately position for the end-effector of Manipulator 2, after which The Manipulator 2 carries the removable part of connection fittings to this position. Then, the assembly task could be completed with the posture of the Manipulator 2 adjusted following the guidance by force-position control.FindingsThe dual manipulator system can position the target under different illumination conditions and complete fast assembly of connect fittings in 110-kV substation. No strong arc discharge or surface erosion phenomenon has been observed.Practical implicationsThis dual manipulator system will be particularly useful for the hot-line assembly of connection fittings in 110-kv intelligent substation, as well as some assembly tasks where uncertain target position and complex contact surface such as cylindrical hole is involved.Originality/valueThis study presents a dual manipulator system used by a field robot working in 110-kv intelligent substation. The system is able to achieve the connection fittings assembly task under energized simulation experimental system. Unlike other peg-in-hole assembly strategy, it does not require high stability of manipulator or plane contact surface around the hole.