Kinematics, dynamics and construction of a planarly actuated parallel robot

Kinematic and dynamic analysis of a parallel robot consisting of three planarly actuated links, is presented in this paper. Coordinated motion of three planar motors, connected to three fixed-length links, produces a six-degrees-of-freedom motion of an output link. Its extremely simple design along with much larger work volume than the commonly used parallel robots make this high performance-to-simplicity ratio robot very attractive. Experimental model verifies the unique combination of large work volume and high accuracy of this robot.     

Structural design and kinematics of a new parallel reconfigurable robot

Reconfigurable robots can be defined as a group of robots that can have different geometries, thus obtaining different structures derived from the basic one, having different degrees of freedom and workspaces. Thanks to the optimum dexterity they offer, the user can accomplish a large variety of industrial tasks, using a structurally optimized robot leading towards better energy control and efficiency especially in case of batch size production lines where the task (for the robot) may vary periodically. Reconfigurable systems are a challenge for numerous scientists, due to the advantage of dealing with changes and uncertainties on the ever-changing manufacturing market. One of the main problems of reconfigurable robots is the proper structural geometry determination, so that the resulting structure is able to perform a variety of tasks. This paper presents the structural design of an innovative parallel robot with six degrees of freedom and its proposed configurations with five, four, three and two degrees of freedom. The kinematic analysis and the workspace representations of all the presented configurations of the parallel robot, called Recrob, are also presented.     

Dynamics of a six degrees-of-freedom parallel robot actuated by three two-wheel carts

This paper deals with a new, six degrees-of-freedom parallel manipulator comprising a platform, three links and three two-wheel carts supporting the links. The wheels are independently driven, allowing the manipulator a workspace which is limited only by the lengths of the links and the size of the plane on which the carts move. The direct and inverse dynamic problems of the manipulator are solved. It is shown that the Jacobian associated with the direct problem becomes identically singular when used to solve the inverse problem, and hence must be redefined; and that once redefined, it losses its standard structure and cannot be used to solve the direct problem. Three solution methods to the inverse problem are presented and are shown to lead to indistinguishable results.     

Type-2 fuzzy control for a flexible-joint robot using voltage control strategy

Type-1 fuzzy sets cannot fully handle the uncertainties. To overcome the problem, type-2 fuzzy sets have been proposed. The novelty of this paper is using interval type-2 fuzzy logic controller (IT2FLC) to control a flexible-joint robot with voltage control strategy. In order to take into account the whole robotic system including the dynamics of actuators and the robot manipulator, the voltages of motors are used as inputs of the system. To highlight the capabilities of the control system, a flexible joint robot which is highly nonlinear, heavily coupled and uncertain is used. In addition, to improve the control performance, the parameters of the primary membership functions of IT2FLC are optimized using particle swarm optimization (PSO). A comparative study between the proposed IT2FLC and type-1 fuzzy logic controller (T1FLC) is presented to better assess their respective performance in presence of external disturbance and unmodelled dynamics. Stability analysis is presented and the effectiveness of the proposed control approach is demonstrated by simulations using a two-link flexible-joint robot driven by permanent magnet direct current motors. Simulation results show the superiority of the IT2FLC over the T1FLC in terms of accuracy, robustness and interpretability.     

Experiences and results from designing and developing a 6 DoF underwater parallel robot

REMO I Robot is a novel application of a parallel structure as an underwater robot of 6 DoF. Compared to other underwater robots, navigation of REMO I Robot is performed by the capability of its parallel structure to modify its geometric structure (thruster and front ring) and to displace by itself. This kinematic property of the parallel platform allows vectorial formation of thrusting forces to take place. Remo I Robot has just one single thruster in its rear ring, therefore the vectorial navigation gives maneuverability, flexibility, and holonomic capabilities for its navigation and positioning. The latter is important for intervention and manipulation tasks. That is why it gives a solid alternative when compared to traditional submarine robots such as shown in the simulation results and experiments performed using a real prototype. In conclusion, this paper proposes a conceptual frame for the development of underwater parallel robots. Moreover, it also points out the experience acquired from the development of the underwater Remo I Robot.     

Optimal design of a 3-PUPU parallel robot with compliant hinges for micromanipulation in a cubic workspace

In recent years, nanotechnology has been developing rapidly due to its potential applications in various fields that new materials and products are produced. In this paper, a novel macro/micro 3-DOF parallel platform is proposed for micro positioning applications. The kinematics model of the dual parallel mechanism system is established by the stiffness model with individual wide-range flexure hinge and the vector-loop equation. The inverse solutions and parasitic rotations of the moving platform are obtained and analyzed, which are based on a parallel mechanism with real parameters. The reachable and usable workspace of the macro motion and micro motion of the mechanism are plotted and analyzed. Finally, based on the analysis of parasitic rotations and usable workspace of micro motion, an optimization for the parallel manipulator is presented. The investigations of this paper will provide suggestions to improve the structure and control algorithm optimization for the dual parallel mechanism in order to achieve the features of both larger workspace and higher motion precision.     

Dynamic modeling and robust control of a 3-PRC translational parallel kinematic machine

The dynamic modeling and robust control for a three-prismatic-revolute-cylindrical (3-PRC) parallel kinematic machine (PKM) with translational motion have been investigated in this paper. By introducing a mass distribution factor, the simplified dynamic equations have been derived via the virtual work principle and validated on a virtual prototype with the ADAMS software package. Based upon the established model, three dynamics controllers have been attempted on the 3-PRC PKM. The intuitive co-simulations with the combination of MATLAB/Simulink and ADAMS show that the control performance of neither inverse dynamics control nor robust inverse dynamics control is satisfactory in the presence of parametric uncertainties in PKM dynamics. On the contrary, the controller based on the passivity-based robust control scheme is more suitable for tracking control of the PKM in terms of both control performances and controller design procedures. The results presented in the paper provide a sound base for both the mechanical system design and control system design of a 3-PRC PKM.     

Decoupling control for spatial six-degree-of-freedom electro-hydraulic parallel robot

This paper presents a decoupling controller equipped with cross-coupling pre-compensation for an electro-hydraulic parallel robot, in order to weaken system dynamic coupling effects usually ignored on the design of advanced controllers and improve system control performance. The mathematical model of the electro-hydraulic parallel robot is built using the Kane method and a hydromechanics approach, and the kinematical model is established with a closed-form solution and the Newton-Raphson method. The feedback linearization theory is applied to reduce coupling effects stemmed from system dynamics of the parallel robot via incorporating force-velocity control with cross-coupling pre-compensations. The control performance involving stability, accuracy, and robustness of the proposed controller for spatial 6-DOF parallel robot is analyzed in theory and experiment. The experimental results illustrate that the proposed controller can highly improve the control performance by weakening system dynamic coupling effects of the electro-hydraulic parallel robot, especially for trajectory tracking performance.     

一种新的六自由度并联机器人分散控制方法

结合六自由度并联机器人机构的特点.提出一种新的分散控制方法.首先依据机构特点指出了关节空间内惯性矩阵块对角占优特性,从而将耦合强烈的邻近支路加以整体考虑,即分散控制3个两输入两输出子系统;然后将惯性矩阵的逆分解为块对角矩阵与耦合矩阵之和,从而得到每个子系统的动力学方程;最后针对子系统负载随机构运动而变化的特点引入线性变参数(LPV)控制方法,降低了使用线性定常控制器的保守性.仿真结果表明了所提出方法的有效性.     

A parallel processing architecture for sensor-based control of intelligent mobile robots

Parallel processing plays an important role in sensor-based control of intelligent mobile robots. This paper describes the design and implementation of a parallel processing architecture used for real-time, sensor-based control of mobile robots. This architecture takes the form of a network of sensing and control nodes, based on a novel module that we call Locally Intelligent Control Agent (LICA). It is a hybrid control architecture containing low-level feedback control loops and high-level decision making components. All the sensing, planning, and control tasks for intelligent control of a mobile robot are distributed across such a network, and operate in parallel. It has been used successfully in many experiments to perform planning and navigation tasks in real-time. Such a generic architecture can be readily applied to many diverse applications.     

Robust sliding-mode control applied to a 5-link biped robot

In this paper the application of robust control to a 5-link biped robotic model is investigated through the sliding mode approach, and compared to pure computed torque control. The biped consists of five links, namely the torso and two links in each leg. These links are connected via four (two hip and two knee) rotating joints which are considered to be friction-free and driven by independent d.c. motors. The locomotion of the biped is assumed to be constrained on the sagittal plane. The paper provides a full derivation of the biped dynamic model (single-leg support phase, biped-in-the-air phase) and an outline of the computed torque and sliding mode control algorithms. The simulation results were derived with two sets of parameters (one of which corresponds to a human-sized biped) and several degrees of parametric uncertainty (from 10% to 200%). In all cases the results obtained through the sliding mode control were much better than those obtained with the computed torque control. This superiority was shown to become stronger as the degree of uncertainty and the size of the biped increases.     

高精度轨迹跟踪的6-PRRS并联机器人自抗扰控制研究

针对6-PRRS并联机器人控制系统的非线性、耦合等特性,采用分散控制策略。在关节空间设计强鲁棒性的自抗扰控制器对其进行控制．该自抗扰控制器由非线性跟踪微分器、扩张状态观测器、非线性PD和扰动补偿4部分组成．具有模型补偿功能的扩张状态观测器可以获得系统的状态估计和未知外扰的实时作用量,使系统性能得到有效补偿．该控制器以离散的形式进行设计,易于工程实现．仿真结果证明了所提出的控制策略具有强鲁棒性,跟踪性能良好．     

Position tracking of a 3-PSP parallel robot using dynamic growing interval type-2 fuzzy neural control

Parallel robots have complicated structures as well as complex dynamic and kinematic equations, rendering model-based control approaches as ineffective due to their high computational cost and low accuracy. Here, we propose a model-free dynamic-growing control architecture for parallel robots that combines the merits of self-organizing systems with those of interval type-2 fuzzy neural systems. The proposed approach is then applied experimentally to position control of a 3-PSP (Prismatic–Spherical–Prismatic) parallel robot. The proposed rule-base construction is different from most conventional self-organizing approaches by omitting the node pruning process while adding nodes more conservatively. This helps preserve valuable historical rules for when they are needed. The use of interval type-2 fuzzy logic structure also better enables coping with uncertainties in parameters, dynamics of the robot model and uncertainties in rule space. Finally, the adaptation structure allows learning and further adapts the rule base to changing environment. Multiple simulation and experimental studies confirm that the proposed approach leads to fewer rules, lower computational cost and higher accuracy when compared with two competing type-1 and type-2 fuzzy neural controllers.     

Control of underactuated robot manipulators using switching computed torque method: GA based approach

A new concept for controlling of underactuated robot manipulators is presented by using switching computed torque method. One fundamental feature of the present approach is to use the partly stable controllers (PSCs) in order to fulfill the ultimate control objective. Dynamic model of an underactuated robot system is directly analyzed to synthesize partly stable, computed torque controllers without performing rigorous linearizations or any other deformation methods to the original nonlinear system. Here, we use genetic algorithms (GAs) to employ the optimum control action for a given time frame with the available set of elemental controllers, depending on which links or state variables are controlled, i.e. the selection of optimum switching sequence of the control actions. Two underactuated robot manipulators are taken into consideration so as to illustrate the design procedure. Simulation results show the effectiveness of the proposed method. This basic concept has led authors to explore a vast research area on controlling underactuated manipulators.     

Dynamics and elasto-dynamics optimization of a 2-DOF planar parallel pick-and-place robot with flexible links

Dynamic modeling and analysis of a 2-DOF translational parallel robot with flexible links for high-speed pick-and-place operation is presented in this paper. Optimization is implemented with the goal to improve the dynamic accuracy of the end-effector at high speed. The governing equations of flexible links within the robot are formulated in the floating reference frame using Euler–Lagrange method, leading to a global FEM model being generated using the KED (Kineto-Elasto-Dynamics) technique. The dynamic characteristics of the robot are then investigated by model analysis. A numerical dynamic index is proposed to identity the range of natural frequency when the robot reaches different configurations. The comparisons are made between the optimized and original designs in terms of dynamic stress and response.     

Robust scheme of global parallel force/position regulators for robot manipulators under environment uncertainty

A simple robust scheme of parallel force/position control is proposed in this paper to deal with two problems for non-planar constraint surface and nonlinear mechanical feature of environment： i） uncertainties in environment that are usually not available or difficult to be determined in most practical situations; ii） stability problem or/and integrator windup due to the integration of force error in the force dominance rule in parallel force/position control. It shows that this robust scheme is a good alternative for anti-windup. In the presence of environment uncertainties, global asymptotic stability of the resulting closed-loop system is guaranteed; it environment with complex characteristics. Finally, numerical robot manipulator. also shows robustness of the proposed controller to uncertain simulation verifies results via contact task of a two rigid-links     

Robust scheme of global parallel force/position regulators for robot manipulators under environment uncertainty

A simple robust scheme of parallel force/position control is proposed in this paper to deal with two problems for non-planar constraint surface and nonlinear mechanical feature of environment: i) uncertainties in environment that are usually not available or difficult to be determined in most practical situations; ii) stability problem or/and integrator windup due to the integration of force error in the force dominance rule in parallel force/position control. It shows that this robust scheme is a good alternative for anti-windup. In the presence of environment uncertainties, global asymptotic stability of the resulting closed-loop system is guaranteed; it also shows robustness of the proposed controller to uncertain environment with complex characteristics. Finally, numerical simulation verifies results via contact task of a two rigid-links robot manipulator.     

Robust nonlinear control of a planar 2-DOF parallel manipulator with redundant actuation

A new robust nonlinear controller is presented and applied to a planar 2-DOF parallel manipulator with redundant actuation. The robust nonlinear controller is designed by combining the nonlinear PD (NPD) control with the robust dynamics compensation. The NPD control is used to eliminate the trajectory disturbances, unmodeled dynamics and nonlinear friction, and the robust control is used to restrain the model uncertainties of the parallel manipulator. The proposed controller is proven to guarantee the uniform ultimate boundedness of the closed-loop system by the Lyapunov theory. The trajectory tracking experiment with the robust nonlinear controller is implemented on an actual planar 2-DOF parallel manipulator with redundant actuation. The experimental results are compared with the augmented PD (APD) controller, and the proposed controller shows much better trajectory tracking accuracy.     

Motion control analysis of a parallel robot assisted minimally invasive surgery/microsurgery system (PRAMiSS)

This paper presents motion control architectures for a parallel robot assisted minimally invasive surgery/microsurgery system (PRAMiSS) that enable it to achieve milli/micro-manipulations under the constraint of moving through a fixed penetration point or so-called remote centre-of-motion (RCM) point without any mechanical constraint. Two control structures suitable for minimally invasive surgery operations with submillimeter accuracy and for minimally invasive microsurgery operations with the desired accuracy in micron range are proposed. The control algorithm also applies orientation constraints preventing the tip from orienting around the instrument axis due to the robot movements as well as a minimum displacement constraint to minimise the movements of the parallel micropositioning robot. Experiments were performed and the results are analysed in this paper to verify accuracy and effectiveness of the proposed control algorithm for both cases of minimally invasive surgery and microsurgery operations. The experimental results present good accuracy and performance of the control algorithm. The numerical modelling and graphical simulations were also carried out and the results are also provided that demonstrate the correlation between the experimental results and physical responses.