Control Of Parallel Manipulator Research Articles

Trajectory tracking control of parallel manipulator actuated with shape memory wire

This study describes the design of a parallel spatial manipulator with four degrees of freedom actuated with shape memory alloy (SMA) wire to validate the use of SMA in complicated mechatronics systems. The manipulator has a closed kinematic structure, which includes a fixed base and a moving square platform (end effector). The four arms of the manipulator are SMA wires fastened between the fixed base and the end effector. SMA wire-based actuators replace bulky conventional revolute actuators. This work spotlights the development of an actuator model, dimensional analysis, and design of cascade control strategies of various PID and sliding mode controller in their integral and fractional order configurations. Experimental evaluation of the actuator is performed through trajectory tracking to quantify the different controller configurations. The experimental results indicate that the parallel manipulator associated with SMA wire actuators is the best alternative to conventional motion stages for highly precise micro-positioning and tracking applications in the fields of 3D printing, intricate surgical operations, the medical and pharmaceutical industries, and flight and gaming simulators.

A new fast nonlinear model predictive control of parallel manipulators: Design and experiments

High-speed parallel manipulators are characterized by fast sampling rates and challenges owing to the presence of constraints, high nonlinearities, uncertainties, and fast dynamics. The development of a reliable nonlinear model predictive control (NMPC) approach for this type of robotic systems is challenging because of the complex dynamics that involves high computational burden. To address this control problem, this paper proposes a new fast NMPC strategy applied to high-speed parallel robots. Based on (i) a parameterization technique, (ii) a fast gradient solver, (iii) a proportional integral derivative (PID) control term, (iv) a nonlinear dynamic model, and (v) an artificial neural network (ANN) model, two fast NMPC frameworks were developed to reduce the computational cost of the classical NMPC and address online implementation. In this study, we focus on improving the performance of the standard predictive control strategy outside of the range of its classical applicability by developing a fast NMPC controller for high-speed parallel kinematic manipulators (PKMs). Numerical simulations and real-time experimental results were presented and discussed to validate the relevance of the proposed controllers. Experiments were conducted on a four-degree-of-freedom (4-DOF) PKM called VELOCE developed in our laboratory. The results show that the proposed solution outperforms the original scheme in terms of real-time tracking performance.

Dynamic Modeling and Adaptive Robust Synchronous Control of Parallel Robotic Manipulator for Industrial Application

Control of parallel manipulators is very hard due to their complex dynamic formulations. If part of the complexity is resulting from uncertainties, an effective manner for coping with these problems is adaptive robust control. In this paper, we proposed three types of adaptive robust synchronous controllers to solve the trajectory tracking problem for a redundantly actuated parallel manipulator. The inverse kinematic of the parallel manipulator was firstly developed, and the dynamic formulation was further derived by mean of the principle of virtual work. Furthermore, linear parameterization regression matrix was determined by virtue of command function “equationsToMatrix” in MATLAB. Secondly, the three adaptive robust synchronous controllers (i.e., sliding mode control, high gain control, and high frequency control) are developed, by incorporating the camera sensor technique into adaptive robust synchronous control architecture. The stability of the proposed controllers was proved by utilizing Lyapunov theory. A sequence of simulation tests were implemented to prove the performance of the controllers presented in this paper. The three proposed controllers can theoretically guarantee the errors including trajectory tracking errors, synchronization errors, and cross-coupling errors asymptotically converge to zero for a given trajectory, and the estimated unknown parameters can also approximately converge to their actual values in the presence of unmodeled dynamics and external uncertainties. Moreover, all the simulation comparative results were presented to illustrate that the adaptive robust synchronous high-frequency controller possess a much superior comprehensive performance than two other controllers.

Dynamic Modelling of 3-RUS Spatial Parallel Robot Manipulator

Parallel manipulators are characterized as having closed-loop kinematic chains. Parallel robots have received increasing attention due to their inherent advantages over conventional serial mechanism, such as high rigidity, high load capacity, high velocity, and high precision. A definite advantage of parallel robots is the fact that, in most cases, actuators can be placed on the truss, thus achieving a limited weight for the moving parts, which makes it possible for parallel robots to move at a high speed. These advantages avoid the drawbacks on serial ones and make the mobile platforms of the parallel manipulators carry out higher performances. Therefore, parallel manipulators have been applied to the industrial manufacturing, flight simulation, medical resuscitation, and so on. The basis for model-based control of parallel manipulators is an efficient formulation of the motion equations. In this paper a formulation of the motion equations in redundant coordinates is presented for parallel manipulators. The fully coupled non-linear equations of motion of 3-RUS spatial parallel manipulator having 3 DOF with Revolute-Universal-Spherical joints are obtained by using the Lagrange equations with multipliers for constrained multibody systems.

Corrigendum to “Trajectory Tracking Control of Parallel Manipulator Based on Udwadia-Kalaba Approach”

Corrigendum to “Trajectory Tracking Control of Parallel Manipulator Based on Udwadia-Kalaba Approach”

SYNTHESIS AND CONTROL 3-DOF PLANAR PARTLY DECOUPLED PARALLEL MANIPULATOR

This paper deals with a new planar parallel manipulator, kinetic energy of this mechanism, designing controller. The translation movements are decoupled from rotation. The control algorithm of parallel robot satisfying partial decoupling between translation and orientation degrees of freedom is synthesized. Simulation result of control algorithm in desired trajectory of end-effector of robot is shown. Here parallel manipulator control algorithm while intersecting singular zones is considered.

An iterative tuning approach for feedforward control of parallel manipulators by considering joint couplings

Feedforward control is an effective way to improve the joint tracking accuracy of robotic systems. This paper presents an iterative approach for feedforward controller parameter tuning of parallel manipulators that considers joint couplings (cross-talk). Based upon a compound control strategy, increments of the feedforward tuning parameters are iteratively updated by minimizing the sum of squares of joint tracking errors at each step. A plant-free identification Jacobian is formulated using the measured data associated with a number of sequential statuses within each iteration cycle. Experiments on the 3-DOF parallel mechanism within a 5-DOF hybrid robot verify parameter convergence and the extrapolation capability of the proposed approach. Compared to otherwise similar feedforward control not considering joint couplings, the root mean square of joint tracking errors was reduced by up to 22% when the mechanism moved at high speed along a path in the neighborhood of the reference configuration.

Trajectory Tracking Control of Parallel Manipulator Based on Udwadia-Kalaba Approach

There have been many approaches for achieving the trajectory tracking control of parallel manipulator. However, these approaches are complex for calculating Lagrangian multipliers. In this paper, unlike the former approaches, a new approach of trajectory tracking control which is based on Udwadia-Kalaba approach is presented. Using this methodology, we can obtain a concise and explicit equation of motion and consider holonomic and nonholonomic constraint whether it is ideal or nonideal simultaneously. The most important difference is that we divide constraints into structural constraints and performance constraints in this paper. Structural constraints are used to establish dynamic model without regard for trajectory control. And performance constraints are used to represent the desired trajectory. For the parallel manipulator, a nonlinear dynamics system, its constraint forces are obtained by second-order constraints. And the numerical simulation in MATLAB shows the parallel manipulator’s movement meets the requirement; tracking trajectory is exact and perfect. Through this paper, we can see that the method can simplify calculation availably.

Zeroing dynamics based motion control scheme for parallel manipulators

Zeroing dynamics (ZD), as a powerful method proposed for time-varying problems solving, has found successful applications in motion control of serial manipulators. Compared with serial manipulators, parallel manipulators possess some attractive advantages such as high carrying capacity and high operation accuracy. However, the inherent differences between parallel and serial manipulators set great difficulties on the applications of ZD to the control of parallel manipulators. Making progress along this direction, the first ZD based motion controller of parallel manipulators is proposed and the design procedure of the ZD based scheme is presented. As a typical application, the proposed scheme is utilised to control a Stewart platform for tracking a quatrefoil-shaped path, which illustrates the effectiveness of the ZD based scheme.

Virtual prototyping of electro-hydraulic parallel manipulator control systems

Virtual prototyping of electro-hydraulic parallel manipulator control systems

A Systematic Approach for the Jacobian Analysis of Parallel Manipulators with Two End-Effectors

Parallel manipulators with two end-effectors (PM2Es) enable the design of gripping robots with high dynamic performance. The gripping action is enabled by internal, relative degrees of freedom (DoFs) between the two end-effectors. Many standard methods for the analysis and control of parallel manipulators rely on a Jacobian, where a complete Jacobian analysis includes constraint relations. These constraint relations have not been consistently included in previous analyses of PM2Es, while they are specifically relevant for PM2Es because constraints play an important role in the static force analysis of a PM2E. This is because wrenches applied by the actuators can be transferred to the end-effectors through internal constraints, an effect which is not captured by kinematic relations alone. This paper presents a systematic approach to perform the Jacobian analysis of PM2Es, which is based on screw theory, and that takes all constraint relations into account. The approach is applied to a PM2E with three legs and one internal closed-loop chain. An example mechanism was built to experimentally validate the resulting Jacobian analysis using a static force analysis.

Tracking control of parallel manipulator with 3-DOF

A parallel three degrees of freedom (3-DOF) manipulator known as Maryland manipulator is considered in this paper. The manipulator model considered in this paper is more practical because the offset lengths are not taken zero. The trajectory tracking control of the Maryland manipulator is done using linear–quadratic regulator (LQR) based proportional–integral–derivative (PID) controller. Three sequential trajectories are used to provide complete dynamic analysis of the manipulator. The manipulator considered here is more practical because the offset lengths are not taken zero unlike previous research articles. The motivation behind using PID controller is its simplicity and effectiveness. The manipulator is a highly coupled and nonlinear system so the correct determination of control signal is very important to achieve good tracking performance. The process for selecting the PID parameters is discussed in detail and the simulations results are used to show the efficacy of the controller.

A switching inverse dynamics controller for parallel manipulators around drive singular configurations

Despite many advantages, parallel manipulators are known to possess drive singularities where the control of one or more degrees of freedom is lost. Around these singular configurations, the required actuator forces grow unbounded. Previous efforts in the literature put forward singularity-consistent trajectory planning and singularityrobust modification of the dynamic equations as a solution to this problem. However, this previous method is applicable only for the open-loop operation of the manipulator, whereas initial configuration errors, external disturbances, and modeling errors should necessarily be taken into account in a closed-loop sense in real-life applications. With this aim, a switching inverse dynamics controller is proposed in this study for the trajectory tracking control of parallel manipulators as they pass through drive singular configurations. Simulations of the application of the developed controller result in good tracking performance, even in the presence of modeling errors, while the actuator efforts remain bounded and continuous in the neighborhood of the singularity.

Experimental system for the optimization of the parallel manipulator control

This paper presents the results of an experimental system design for the optimization of parallel manipulator control based on an optimal configuration. The experimental system is an open design for various different configurations and controllers to support parallel manipulator research and applications. Traditional PID control and self-tuning fuzzy PID control algorithm are applied for motion control of parallel manipulator. The quality system standard will be analyzed and compared with simulation results. The system can be a useful tool for research and training.

Operating dexterity optimization and analysis of a 3-DOF parallel manipulator for a tunnel segment assembly system

This study focuses on the operating dexterity and multi-objective optimization of a 3-DOF parallel manipulator for the segment assembly system in shield tunneling machines. Operating dexterity, including kinematic and dynamic dexterity, is defined for the manipulator. This work has been done by considering motion transmissibility and acceleration. Multi-objective optimization for the parallel manipulator has been conducted by Isight software with the objective of achieving operating dexterity. Optimal performance evaluation in terms of the dexterity and isotropy of the parallel manipulator was carried out. The optimum region for the manipulator was established based on range of the performance indices of operating dexterity. The results indicate that motion transmission and acceleration performance improved after optimization. The method provides a reference for the design, performance evaluation, and control of parallel manipulators.

Nonlinear control of parallel manipulators for very high accelerations without velocity measurement: stability analysis and experiments on Par2 parallel manipulator

SUMMARYThis paper presents a comparison between control/state estimation methods applied on Par2 parallel manipulator for pick-and-place applications as well as a discussion about the mechanical vibrations issue that may become important when reaching very high accelerations. Real-time experiments were performed first to compare two controllers (a linear Proportional-Derivative controller and a nonlinear/adaptive Dual Mode (DM) controller) complied with the same High-Gain Observer (HGO) to estimate articular velocities, and second to compare three state observers (a Lead-lag-based, an Alpha-beta-gamma (ABG) and an HGO) complied with the same nonlinear DM controller. The stability analysis of the Par2 robot under the control of the proposed DM controller (complied with the HighGO for joint velocity estimation) is also provided. Some small mechanical vibrations were noted when reaching 20 G acceleration, which means that it can become an important issue for higher accelerations. Some suggestions are then made for future investigations to avoid/damp these vibrations.

Motion Control of Parallel Manipulators Using Acceleration Feedback

Acceleration feedback (AF) is applied to restrain the trajectory disturbances in the motion control of parallel manipulators to increase the trajectory tracking accuracy. A dynamic model is formulated in the task space, and the optimal exciting trajectory is calculated for dynamic identification. The acceleration signals can be estimated without acceleration sensors on the basis of the closed-loop constraint equations. Furthermore, the dynamic acceleration feedback (DAF) controller is developed by introducing the AF into the robust dynamics compensation and trajectory tracking, and the stability of the closed-loop system is proven. The DAF controller is implemented on a planar parallel manipulator platform, and the corresponding experimental results are compared with an existing, robust controller.

Robust tracking control of 6-DOF parallel electrical manipulator in Joint-Task space with fast friction estimation

This paper presents a robust tracking controller equipped with a fast friction estimator for a 6-DOF parallel electrical manipulator in the joint-task space. Parallel manipulator control scheme mainly stems from two frameworks: the task space control and the joint space control. The former requires the system states obtained via costly direct measurements or time-consuming forward kinematics. The latter's performance is subject to the inaccurate dynamic model. To minimize their weaknesses, the joint-task space framework is constructed by transforming the dynamics on the task space into the joint space. With this transformation, the desired positional data are used to calculate the nominal value of dynamics. On the other hand, the friction property depends on the uncertain load condition due to the spiral drive way of the electrical cylinders. A fast friction estimator is then designed to estimate the uncertain friction fast and effectively. The robust control scheme is proposed based on the Lyapunov design method to guarantee a practical stability under uncertainties such as inertia, modeling errors, friction, and measurement errors. Experimental results are presented to show the effectiveness of the proposed scheme.

Modeling and trajectory tracking control of 6-DOF RSS type parallel manipulator

SUMMARYIn this study, kinematic analysis of 6-DOF RSS parallel manipulator using Denavit Hartenbeng (D-H) method is investigated. In addition, in order to improve the proposed method, determination of all the active and passive angles, required to obtain Jacobian and complete dynamic model of manipulator, is also achieved. The effects of dynamic models of 6-DOF RSS parallel manipulator with its actuators on trajectory tracking control are studied in detail. Feedback dynamic compensation terms of motor-mechanism coupling system that is needed to compute torque control are obtained through both a single link approximation model and a complete dynamic model. The complete model is derived by taking account of the interaction between the input links and coupler links of the manipulator. Simulations showed that obtaining complete model of manipulator by means of D-H method and using computed control law could improve the quality of trajectory tracking control of parallel manipulator.

Dynamic Model of the 6-DOF Parallel Manipulator Control Using Lagrangian Equation

This paper presents the control of the 6-DOF parallel manipulator using Lagrangian equation. The 6-DOF parallel manipulator are composed of fix base and moveable platform are couple by the actuators. The dynamic equations express by Lagrangian equation, the structure of the 6-DOF parallel manipulator and kinematics and are explains in this paper. The 6-DOF parallel manipulator using Lagrangian equation are accurate and good ability.