6-DOF Parallel Manipulator Research Articles

A methodology to achieve the set of operation modes of reconfigurable parallel manipulators

The demand for increasingly more versatile machinery has boosted the development of the so-called reconfigurable mechanisms. In this paper, the authors present a general methodology to assess the multioperational capacity of a 6-DOF parallel manipulator basing on the possible motion patterns having Lie group structure that the manipulator owns. This ability of having different operation modes enables the manipulator to adapt to diverse tasks. To show the potential of the methodology, this approach has been applied to the 6-DOF 3-CPCR which is capable of generating multiple motion patterns. In addition to carrying out the complete theoretical study in which all the different operation modes are obtained, and validating the procedure with GIM software designed for kinematic analysis and design of mechanisms, a demonstration prototype of the 3-CPCR parallel manipulator has been also built.

Dimensional Synthesis of Kinematic Dexterity and Workspace for 3-DOF Parallel Manipulator

Dimensional Synthesis of Kinematic Dexterity and Workspace for 3-DOF Parallel Manipulator

Type synthesis and kinematics analysis of parallel manipulators with equivalent composite universal joints

Several novel parallel manipulators (PMs) with equivalent composite universal joints Ue are synthesized and their kinematics is studied systematically in this paper. First, the 12 novel PMs with Ue are synthesized, and their degrees of freedom are calculated. Second, the structure and merits of the composite limb with Ue for constructing the PMs with Ue are analyzed; the unified formulas are derived for solving the sub-Jacobian matrix, the sub-Hessian matrix, the angular velocity and the angular acceleration of the composite limb with Ue. Third, the formulas are derived for solving the Jacobian matrix and output velocity, the Hessian matrix and output acceleration of the moving platforms of the 10 novel PMs with Ue. Finally, a 5-DoF PM with 2Ue in the 12 synthesized PMs with Ue is illustrated for solving the kinematics of the PMs with Ue; its reachable workspace is constructed for representing merits of the PMs with Ue. The theoretical kinematics solutions are verified by the simulation solution of the simulation mechanism of the 5-DoF PM with 2Ue.

A Human-Guided Vision-Based Measurement System for Multi-Station Robotic Motion Platform Based on V-Rep

SUMMARYIn the manufacturing process of sophisticated and individualized large components, classical solutions to build large machine tools cannot meet the demand. A hybrid robot, which is made up of a 3 degree-of-freedom (3-DOF) parallel manipulator and a 2-DOF serial manipulator, has been developed as a plug-and-play robotized module that can be rapidly located in multi-stations where machining operations can be performed in situ. However, processing towards high absolute accuracy has become a huge challenge due to the movement of robot platform. In this paper, a human-guided vision system is proposed and integrated in the robot system to improve the accuracy of the end-effector of a robot. A handheld manipulator is utilized as a tool for human–robot interaction in the large-scale unstructured circumstances without intelligence. With 6-DOF, humans are able to manipulate the robot (end-effector) so as to guide the camera to see target markers mounted on the machining datum. Simulation is operated on the virtual control platform V-Rep, showing a high robust and real-time performance on mapping human manipulation to the end-effector of robot. And then, a vision-based pose estimation method on a target marker is proposed to define the position and orientation of machining datum, and a compensation method is applied to reduce pose errors on the entire machining trajectory. The algorithms are tested on V-Rep, and the results show that the absolute pose error reduces greatly with the proposed methods, and the system is immune to the motion deviation of the robot platform.

Modelling and simulation of 3DOF parallel manipulator using artificial neural network

Parallel Robot (PR) has shown its ability to be precise in its movement. Actuators move simultaneously to achieve the required target, on top of that its payload is much greater than what a serial robot can withstand. To determine workspace of the robot with known angles Forward kinematics has to be introduced which, bring a lot of difficulty as it requires the solution of multiple coupled nonlinear algebraic equations. Those equations bring multiple valid solutions. Those solutions could lead to different locations. As it is not going to make the pick and place for PR will be easier. This paper will discuss a numerical method that calculates the Forward Kinematics for PR. This method uses Artificial Neural Network which relay on training with a certain number of iterations. The set of data to be used in the training can be obtained from PR simulation. This method will serve to know workspace around PR as it will help it to pick the target object.

Reconfiguration Analysis of a 3-DOF Parallel Mechanism

This paper deals with the reconfiguration analysis of a 3-DOF (degrees-of-freedom) parallel manipulator (PM) which belongs to the cylindrical parallel mechanisms family. The PM is composed of a base and a moving platform shaped as equilateral triangles connected by three serial kinematic chains (legs). Two legs are composed of two universal (U) joints connected by a prismatic (P) joint. The third leg is composed of a revolute (R) joint connected to the base, a prismatic joint and universal joint in sequence. A set of constraint equations of the 1-RPU−2-UPU PM is derived and solved in terms of the Euler parameter quaternion (a.k.a. Euler-Rodrigues quaternion) representing the orientation of the moving platform and of the Cartesian coordinates of the reference point on the moving platform. It is found that the PM may undergo either the 3-DOF PPR or the 3-DOF planar operation mode only when the base and the moving platform are identical. The transition configuration between the operation modes is also identified.

End-effector positioning due to joint clearances: A comparison among three planar 2-DOF parallel manipulators

This paper develops a model for studying the effect of joint clearances on the end-effector’s loci for planar parallel manipulators with 2 degree-of-freedom (DOF). The condition for developing end-effector loci equations with respect to the joint clearance relies on the fact that at least one point of contact is always presented in each joints. The motivation of this work lies in the fact that the proposed procedure allows the study of parallel manipulators that can be considered as design concepts for developing an x-y cutting table for a textile industry. Numerical simulations enable to compare three 2-DOF planar parallel manipulators architectures: i) 2-RRR, ii) 2-RPR, and iii) 2-RPR. A Monte Carlo simulation allows us to find the area of possible end-effector locations for a specific value of clearance. Also, the equations allow us to find the largest distance from the desired location to the one obtained considering clearance. Findings shed some lights on establishing which parallel manipulator is less affected to joint clearance.

Sensorless full body active compliance in a 6 DOF parallel manipulator

• Interpretation of the torque data at actuated joints allowing it to comply to a force at any point of the manipulator. • 3-layer cascaded impedance control which maintains the accuracy of trajectory tracking while making the manipulator inherently compliant. • Comparison of the dynamic performances depending on the choice of topology of the manipulator. • Exhaustive verification of the data using well calibrated tools such as Vicon ® and Bertec ® . Parallel manipulators are being used extensively to cater to the needs of a multitude of industrial automation applications. Due to its kinematic accuracy and structural stiffness , parallel manipulators have proven considerable advantage over their serial counterparts. In modern applications, humans train, collaborate and interact with the manipulators in order to maximize the productivity and the quality of the final product. The critical factor in this human-robot interaction is safety and the ability of the mechanism to comply with human intentions. It thus becomes a necessity for the manipulator to detect external disturbances and interactions, and be able to react accordingly. In this research, a methodology for sensor-less full body active compliance is proposed on a 6-DOF RSS (Rotary-Spherical-Spherical) parallel manipulator. By using the proposed approach, the manipulator can detect and comply with the external forces on any part of its body without using any explicit force/torque sensor at the joint or the end-effector. This is done by utilizing the estimated joint torque based on the actuator current feedback only. A three-layer cascaded impedance controller for active compliance and reaction to various human interactions are reported. The proposed design and unique methodology for compliance exhibits an effective and inexpensive yet reliable alternative to be used in safe human-robot interactions and force controlled manufacturing applications.

Multiobjective Optimization of 6-DOF Parallel Manipulator for Desired Total Orientation Workspace

A desired total orientation workspace for a parallel manipulator is usually an essential requirement in a practical application. At present, for the multiobjective optimization method of 6-DOF parallel manipulator for desired total orientation workspace, it is needed to predefine maximal and minimal lengths of the legs to serve as the constraint, and then the numerical method is used to solve the length of the legs and judge whether the solved maximal and minimal leg lengths meet the constraint. Predefining maximal and minimal length of the legs limits of the optimal range, the numerical method has heavy calculation burden and low calculating accuracy. In this paper, a hybrid method for solving the maximal and minimal lengths of the legs of 6-DOF parallel manipulator with desired total orientation workspace is proposed, and the actuator stroke length is calculated according to the maximal and minimal leg lengths. By judging whether the actuator stroke length can be solved to serve as the constraint, without the predefined maximal and minimal leg lengths to serve as the constraint, the optimal range is enlarged. Aiming at the physical size of the parallel manipulator and the proposed desired workspace condition index (DWCI), the optimization of the geometric parameters of the parallel manipulator is conducted based on the multiobjective optimization algorithm (NSGA-II), which is subject to the actuator stroke length. Stewart platform is set as the example; the geometric parameters of the platform whose workspace contains the desired total orientation workspace are optimized and the hybrid method is proved to be more accurate and efficient compared to the traditional numerical method. This method provides the optimization guidance for engineering designers to design the parallel manipulator for desired total orientation workspace.

Novel Design of a 3-RRUU 6-DOF Parallel Manipulator

A novel 3-RRUU 6-DOF parallel manipulator is designed based on the multi-plane design principle, that provides larger workspace, less chance of link interference and simplified kinematic analysis. The link interference detection by pentagon identification and cross-product is demonstrated. Workspace is optimized by different orientations. The Jacobian matrix by global cartesian coordinate system is developed. A transformation matrix could convert that to Jacobian matrix of a new coordinate system.

Adaptive Neural Integral Full-Order Terminal Sliding Mode Control for an Uncertain Nonlinear System

This paper reports the design of a control system for a class of general nonlinear second-order systems. The significant problems of singularity and chattering phenomenon, which limit the use of the conventional terminal sliding mode control (TSMC) in real applications due to the order of the sliding surface, need to be addressed. In addition, the effects of disturbances and uncertainties need to be removed, and the response rates are increased. Therefore, the integral full-order terminal sliding mode (IFOTSM) surface was proposed. To track the specified trajectories with high accuracy, a control approach is developed for the class of general nonlinear second-order systems by utilizing an IFOTSM surface and an adaptive compensator. The unknown dynamic model is derived based on a radial basis function neural network (RBFNN). Consequently, our controller provides good performance with minimum position errors, robustness against uncertainties, and work without a precise dynamic model. The simulated examples were performed to analyze the effectiveness of the control approach for position pathway tracking control of a 2-DOF parallel manipulator.

A Numerical Approach for 3 PRS Parallel Manipulator

This paper presents a numerical approach on kinematic analysis of 3-DOF parallel manipulator (PM). The proposed mechanisms constitute of PRS (Prismatic-Revolute-Spherical) parallel mechanism with two rotations and one translation. The forward and inverse kinematic equations of the PM are derived by position vector method. A total of 48 solutions are obtained for the forward kinematic equations using MATLAB.

Study of 6-DOF Control of the Stewart Platform

In this paper, we present a design system and control of 6-DOF parallel manipulator commonly known as the Stewart platform. It is meant as a practical guideline covering the basic theory of Stewart platforms and the actual realization. The flight simulator design is based on the Stewart platform mechanism and mainly of two platforms and six linear actuators driven by servo motors. The inverse kinematics solution is provided for the actually constructed prototype, given the position and orientation, and find the actuator lengths.

Dynamics analysis and workspace of a novel 4-DoF parallel manipulator with multi-couple constrained wrenches

A novel 4-DoF parallel manipulator with multi-couple constrained wrenches is proposed. Its 3D model is constructed and its characteristics, DoF and two couple-constrained wrenched are analyzed. Its kinematic formulae for solving DoF, the displacement, velocity, acceleration, singularities of moving links are derived and analyzed. Its dynamics formulae for solving the dynamic active forces and the dynamic couple-constrained wrench are derived, and its workspace is constructed. Finally, an analytic example is given to demonstrate the solution of the kinematics and dynamics, and the results of analytical solution are verified using a simulation mechanism. This paper is aimed at laying a solid theoretical and technical foundation of development of the parallel manipulators with multi-couple constrained wrenches.

A New Parallel Manipulator With Multiple Operation Modes

In this work, a new parallel manipulator with multiple operation modes is introduced. The proposed robot is based on a three-degrees-of-freedom (3DOF) parallel manipulator endowed with a three-dof central kinematic chain, where by blocking some specific kinematic pairs, the robot can modify its mobility. Hence, the robot manipulator is able to assume the role of a limited-dof or a nonredundant parallel manipulator. Without loss of generality, the instantaneous kinematics of one member of the family of parallel manipulators generated by the reconfigurable parallel manipulator, the three-RPRRC + RRPRU nonredundant parallel manipulator with decoupled motions, is approached by means of the theory of screws. For the sake of completeness, the finite kinematics of the robot is also investigated. Numerical examples are included with the purpose to clarify the method of kinematic analysis.

Dynamics analysis of a novel 5-DoF parallel manipulator with couple-constrained wrench

SUMMARYA three-dimensional (3D) model of a novel 5-DoF type parallel manipulator with a couple-constrained wrench is constructed and its couple-constrained wrench is analyzed. First, the formulas are derived for solving the displacement, velocity, acceleration of the moving platform and moving links, and a workspace is constructed. Second, the formulas are derived for solving the inertial wrenches of the moving links. Third, a dynamics equation is established by considering the inertial wrenches and friction, and the formulas are derived for solving the dynamically active forces and the dynamically couple-constrained wrench. Finally, a numerical example is given to demonstrate the analytic solution of the kinematics and the dynamics, and the analytical solutions are verified by utilizing a simulation mechanism.

Solution to the motion of a delta manipulator with three degrees of freedom

ABSTRACTBased on the mechanical structure of a Delta manipulator with three degrees of freedom, the kinematic characteristics of the parallel manipulator were analyzed, and the vector relation between the static and moving platforms was given. The inverse kinematic function of the three-degree-of-freedom (3-DOF)parallel manipulator was deduced by the vector equation. The simulated forward kinematic solution in the moving platform was carried out by Pro/E modeling software and virtual prototype simulation software ADAMS, which is proved simple. These research contents provide a valuable reference for the adjustment and operation of 3-DOF Delta manipulator prototypes with respect to its dynamic performance, motion track planning, mechanical structure, system control, etc.

Teleoperation by Using Nonisomorphic Mechanisms in the Master–Slave Configuration for Speed Control

This paper presents modeling, simulation, and control of a novel teleoperated mechanism, where two nonisomorphic manipulators are used in one integrated system, with the purpose of usage in oil and gas industry in the future. Overall integration of the teleoperated system has been done in the master–slave configuration, where a stuart-type 6-DOF parallel manipulator is used as a master robot and a 6-DOF serial manipulator is used as a slave robot. Since the parallel manipulator has a closed-loop structure and serial manipulator is an open-loop structure, their work spaces are of completely different nature in terms of overall shape and size. A novel task-space mapping mechanism has been proposed in this work to integrate these two completely nonidentical manipulators. Damped least-squares (DLS) method is used for overcoming the singularity of proposed task-space mapping matrix. This paper also presents detailed dynamic modeling of the parallel manipulator along with comprehensive analysis of proposed novel control technique. The biggest benefit of using proposed integration mechanism is the fullest access of the complete cartesian task spaces of both the master and slave manipulators. This paper also proposes usage of lag compensator for the improved tracking performance. Multilevel control architecture with local actuator-space and joint-space controllers, for the parallel and serial manipulators, respectively, has also been presented in this work.

Chest compression with 2-DOF parallel manipulator for cardiopulmonary resuscitation

Chest compression process is used for recovering patients who met with a cardiac arrest in emergency situations. Chest compression is the only possibility of rescuing patients during cardiopulmonary resuscitation (CPR). It is hard to achieve the exact chest compression’s depth and rate even by experienced professionals as per the CPR guideline. A 2-DOF 2-RRR translational parallel manipulator was designed for delivering chest compressions. The kinematic analysis is carried out analytically.The workspace of the manipulator is examined in consideration of physical constraints imposed by joints. Finally, the manipulator operates with exact compression depth and rate during CPR.

Stiffness modeling approach for a 3-DOF parallel manipulator with consideration of nonlinear joint stiffness

Considering the nonlinear characteristics of joint, this paper proposes a new comprehensive stiffness analysis method by combining finite element analysis and matrix structural analysis. Based on the force/moment equilibrium equations of a 3-DOF over-constrained parallel manipulator, a method for solving the internal forces of the joints is proposed. By calculating the stiffness of the bearing under the action of joint internal forces, the stiffness matrix of the revolute joint and the composite spherical joint can be derived. The FEA-based identification method for the stiffness matrix of multi-node components is proposed by importing the structural model into the finite element software for virtual experiments. Then, integrating the stiffness matrices of components and joints, the stiffness matrix of the whole manipulator can be derived and the theoretical stiffness computed from the stiffness model is mapped in the workspace. Finally, the stiffness analysis method is verified by experiments in the physical prototype.