Showing papers on "Parallel manipulator published in 2015"

Robust Trajectory Tracking of a Delta Robot Through Adaptive Active Disturbance Rejection Control

Abstract: This paper describes the adaptive control design to solve the trajectory tracking problem of a Delta robot with uncertain dynamical model. This robot is a fully actuated, parallel closed-chain device. The output-based adaptive control was designed within the active disturbance rejection framework. An adaptive nonparametric representation for the uncertain section of the robot model was obtained using an adaptive least mean squares procedure. The adaptive algorithm was designed without considering the velocity measurements of the robot joints. Therefore, a simultaneous observer–identifier scheme was the core of the control design. A set of experimental tests were developed to prove the performance of the algorithm presented in this paper. Some reference trajectories were proposed which were successfully tracked by the robot. In all the experiments, the adaptive scheme showed a better performance than the regular proportional-integral-derivative (PID) controller with feed-forward actions as well as a nonadaptive active disturbance rejection controller. A set of numerical simulations was developed to show that even under five times faster reference trajectories, the adaptive controller showed better results than the PID controller.

A Versatile Tension Distribution Algorithm for $n$ -DOF Parallel Robots Driven by $n+2$ Cables

Abstract: Redundancy resolution of redundantly actuated cable-driven parallel robots (CDPRs) requires the computation of feasible and continuous cable tension distributions along a trajectory. This paper focuses on n -DOF CDPRs driven by n + 2 cables, since, for n = 6, these redundantly actuated CDPRs are relevant in many applications. The set of feasible cable tensions of n -DOF ( n + 2)-cable CDPRs is a 2-D convex polygon. An algorithm that determines the vertices of this polygon in a clockwise or counterclockwise order is first introduced. This algorithm is efficient and can deal with infeasibility. It is then pointed out that straightforward modifications of this algorithm allow the determination of various (optimal) cable tension distributions. A self-contained and versatile tension distribution algorithm is thereby obtained. Moreover, the worst-case maximum number of iterations of this algorithm is established. Based on this result, its computational cost is analyzed in detail, showing that the algorithm is efficient and real-time compatible even in the worst case. Finally, experiments on two six-degree-of-freedom eight-cable CDPR prototypes are reported.

Minimum-Time Trajectory Planning and Control of a Pick-and-Place Five-Bar Parallel Robot

Abstract: This paper presents trajectory planning optimization and real-time control of a special five-bar parallel robot. Planning is based on a cubic spline stochastic approach that minimizes trajectory time and selects the best combination of working mode regions to circumvent all parallel singularities, allowing the size of the workspace to be increased. Identification of the dynamic model of the robot and its actuators allows a precise implementation of the trajectory planning and real-time control approach. The optimization algorithm achieves a fast trajectory and a controller that operates with an error of less than 0.7° for both actuated joints of the robot.

Design and Development of a High-Speed and High-Rotation Robot With Four Identical Arms and a Single Platform

Abstract: In this paper, a novel parallel kinematic mechanism (PKM) with Schonflies motion has been proposed under the guidance of a graphical type synthesis method. This PKM is composed of four identical arms and a single platform and has high rotational capability. The single-platform structure used in the proposed PKM can reduce structural complexity, increase dynamic response. In addition, the composite parallelogram structure in each arm brings in better limb stiffness. Based on the proposed concept, optimal design is carried out to make the PKM realize its high rotational potential. In this process, an input transmission index (ITI) and an output transmission index (OTI) (the two indices can be used to numerically evaluate motion and force transmission performance of PKMs, respectively) are taken as the performance evaluation criteria. On this basis, some other indices are defined and the corresponding performance atlases are also plotted to investigate the potential workspace. Consequently, dimensional parameters of the discussed PKM are derived on the precondition that the rotational capability should reach at least ±90 deg, and the workspace has also been identified. Based on these foundations, a parallel robot X4 has been developed which can realize high-speed pick-and-place manipulation in industrial lines.

Geometry Selection of a Redundantly Actuated Cable-Suspended Parallel Robot

Abstract: This paper is dedicated to the geometry selection of a redundantly actuated cable-suspended parallel robot intended to manipulate heavy payloads over a wide workspace. Cable-suspended refers here to cable-driven parallel robots in a crane-like setting, where all the cable drawing points are located on top of the base frame, gravity being used to keep the cables taut. Geometry selection consists of determining the relative positions of the cable drawing points on the base frame and of the cable attachment points on the mobile platform together with the cable arrangement between these two sets of points. An original performance index is introduced. It is defined as the maximum acceptable distance between the mobile platform geometric center and the center of mass of the set consisting of the platform and a payload. This performance index is of particular interest in heavy payload handling applications. Used within a two-phase geometry selection strategy, it yields a new cable-suspended robot geometry having a very large workspace to footprint ratio and able to handle heavy payloads. A large-dimension redundantly actuated cable-suspended robot was built in order to demonstrate these capabilities.

Localization, obstacle avoidance planning and control of a cooperative cable parallel robot for multiple mobile cranes

Abstract: This paper addresses the cooperative problems in terms of localization, obstacle avoidance planning and automatic leveling control for a cable parallel robot for multiple mobile cranes (CPRMCs). The design model of the CPRMCs is elaborated on. The three-dimensional grid map method is utilized to plot the environment map based on the operation environment model. By combining the relative localization method with the absolute localization method, a cooperative localization scheme of the CPRMCs is developed, and an improved localization algorithm is designed on the basis of multilateration method. Then, according to the grid-based artificial potential field method, a global path planning of the CPRMCs is performed. Considering the possible collision of the single mobile crane, the sensor technology is applied to the cooperative obstacle avoidance. In addition, a four-point collaborative leveling method is adopted for automatic leveling control of the platform of the CPRMCs. Finally, the effectiveness of the CPRMCs system is verified through simulations. Cable parallel robots for multiple mobile cranes are designed.Localization analysis of the robots are reported.Obstacle avoidance planning and automatic leveling control are performed.Illustrative simulation studies highlight the performance of the robots.

Optimal control of hydraulically driven parallel robot platform based on firefly algorithm

Abstract: A new cascade load force control design for a parallel robot platform is proposed. A parameter search for a proposed cascade controller is difficult because there is no methodology to set the parameters and the search space is broad. A parameter search based on firefly algorithm (FA) is suggested to effectively search the parameters of the cascade controller. We used unified mathematical model of hydraulic actuator of parallel robot platform. These equations are readily applicable to various types of proportional valves, and they unify the cases of critical center, overlapped and underlapped valves. These unified model equations are useful for nonlinear controller design. The optimal results are compared to those obtained from other metaheuristic algorithms: GA, PSO and CS. A comparative study is also made between proposed optimal tuned cascade control using FA and well-tuned PID controller. Simulation results show the advantages of the proposed optimal tuned cascade controller using FA to solve a formulated tracking problem.

A parallel manipulator for mobile manipulating UAVs

Abstract: Manipulating objects using arms mounted to unmanned aerial vehicles (UAVs) is attractive because UAVs may access many locations that are otherwise inaccessible to traditional mobile manipulation platforms such as ground vehicles. Most previous efforts seeking to coordinate the combined manipulator-UAV system have focused on using a manipulator to extend the UAV's reach and assume that both the UAV and manipulator can reliably reach commanded goal poses. This work accepts the reality that state of the art UAV positioning precision is not of a high enough quality to reliably perform simple tasks such as grasping objects. A 6 degree of freedom parallel manipulator is used to robustly maintain precise end-effector positions despite host UAV perturbations. A description of a unique parallel manipulator that allows for very little moving mass, and is easily stowed below a quadrotor UAV is presented along with flight test results and an analytical comparison to a serial manipulator.

Three-Stage Design Analysis and Multicriteria Optimization of a Parallel Ankle Rehabilitation Robot Using Genetic Algorithm

Abstract: This paper describes the design analysis and optimization of a novel 3-degrees of freedom (DOF) wearable parallel robot developed for ankle rehabilitation treatments. To address the challenges arising from the use of a parallel mechanism, flexible actuators, and the constraints imposed by the ankle rehabilitation treatment, a complete robot design analysis is performed. Three design stages of the robot, namely, kinematic design, actuation design, and structural design are identified and investigated, and, in the process, six important performance objectives are identified which are vital to achieve design goals. Initially, the optimization is performed by considering only a single objective. Further analysis revealed that some of these objectives are conflicting, and hence these are required to be simultaneously optimized. To investigate a further improvement in the optimal values of design objectives, a preference-based approach and evolutionary-algorithm-based nondominated sorting algorithm (NSGA II) are adapted to the present design optimization problem. Results from NSGA II are compared with the results obtained from the single objective optimization and preference-based optimization approaches. It is found that NSGA II is able to provide better design solutions and is adequate to optimize all of the objective functions concurrently. Finally, a fuzzy-based ranking method has been devised and implemented in order to select the final design solution from the set of nondominated solutions obtained through NSGA II. The proposed design analysis of parallel robots together with the multiobjective optimization and subsequent fuzzy-based ranking can be generalized with modest efforts for the development of all of the classes of parallel robots.

Development of a novel soft parallel robot equipped with polymeric artificial muscles

Abstract: This paper presents the design, analysis and fabrication of a novel low-cost soft parallel robot for biomedical applications, including bio-micromanipulation devices. The robot consists of two active flexible polymer actuator-based links, which are connected to two rigid links by means of flexible joints. A mathematical model is established between the input voltage to the polymer actuators and the robot's end effector position. The robot has two degrees-of-freedom, making it suitable for handling planar micromanipulation tasks. Moreover, a number of robots can be configured to operate in a cooperative manner for increasing micromanipulation dexterity. Finally, the experimental results demonstrate two main motion modes of the robot.

Analysis and Design of a Reconfigurable 3-DoF Parallel Manipulator for Multimodal Tasks

Abstract: This paper presents the design of a reconfigurable 3-DoF parallel kinematics manipulator. The main feature of the device is the ability to change the mobility of its moving platform from pure translation to pure rotation. The manipulator kinematics is conceived so that, when a particular configuration of the manipulator is reached, the transition between the two working modes is possible by changing the configuration of a metamorphic universal joint, which is used to connect the legs of the manipulator with the moving platform. The mechanical design of the joint, which is in fact a lockable spherical joint, is illustrated. With the joint integrated into the robot architecture, an instantaneous overconstrained kinematics is exploited to manage the phase of reconfiguration of the whole mechatronic device. A kineto-static analysis provides information about the influence of geometric parameters on its functional design. The manipulator shows simple kinematics and statics models, as well as good kinematic and static performances. Eventually, the versatility of the manipulator is shown by proposing some advanced manufacturing applications in which it could find use.

Dual-Space Control of Extremely Fast Parallel Manipulators: Payload Changes and the 100G Experiment

Abstract: In this paper, three control schemes are proposed and experimentally compared on the R4 redundantly actuated parallel manipulator for applications with very high accelerations. First, a proportional-integral-differential (PID) in operational space is proposed to adequately take into consideration the actuation redundancy. Because of its lack of performance, a dual-space feedforward control scheme based on the dynamic model of R4 is proposed. The improvements obtained with this controller allowed the implementation of an experiment, which consisted in the tracking of a trajectory with a maximum acceleration of more than 100G. However, such a controller may have loss of performance in case of any operational change (such as different payloads). Therefore, a dual-space adaptive control scheme is proposed. The stability analysis of the R4 parallel robot when controlled by the proposed dual-space adaptive controller is provided. The objective of this paper is to show that the proposed dual-space adaptive controller not only maintains its good performance independently of the operational conditions but also has a better performance than both the PID and the dual-space feedforward controllers, even when the latter is best configured for the given case (which confirms its applicability in an industrial environment).

Trajectory tracking and vibration suppression of a 3-PRR parallel manipulator with flexible links

Abstract: To achieve high speed, flexible planar parallel manipulators (PPM) are typically designed with lightweight linkages, but hence suffer from unwanted structural vibration, diminishing positioning accuracy. To achieve high positioning accuracy, this paper addresses the vibration suppression of a PPM with three flexible linkages actuated by linear ultrasonic motors (LUSM). Based on the extended Hamilton’s principle, a rigid–flexible dynamic model of a proposed PPM is developed using the substructure approach and the assumed mode method (AMM). The assumed mode shapes of the flexible linkages are verified through the experimental modal tests. Then, two control algorithms are designed for tracking control of the end effector and vibration attenuation of the flexible linkages. The first approach is a two-timescale control based on singular perturbation principles, implemented as a joint motion control without additional actuators. The second approach is a dual-stage control method. In this control approach, a variable structural control (VSC) method is applied to realize motion tracking of the moving platform, while the strain and strain rate feedback control (SSRF) is developed to suppress the undesired vibration of the flexible linkages, using multiple distributed collocated lead zirconate titanate (PZT) transducers. Stability analysis of the two algorithms is investigated based on Lyapunov approach. Simulation results of these two approaches show that the dual-stage control method provides better vibration attenuation, and hence, faster settling time of the PPM is achieved.

Adaptive Terminal Sliding Mode Control of a Redundantly-Actuated Cable-Driven Parallel Manipulator: CoGiRo

Abstract: This paper presents an extended adaptive control scheme via terminal sliding mode (TSM) for cable-driven parallel manipulators (CDPM). Compared with linear hyperplane-based sliding mode control, TSM is able to guarantee high-precision and robust tracking performances which arise from its main feature of finite-time convergence. This motivates applying TSM to robotic manipulators in general and, as presented in this paper, to CDPM in particular. The scheme presented in this paper extends early developed TSM control schemes which are based on partial knowledge of system dynamics. Instead, making use of the property that the dynamic models of mechanical manipulators are linear in inertial parameters, an adaptive control law is synthesised based on an appropriate choice of Lyapunov function which guarantees finite-time convergence to neighborhood of sliding mode. A key challenge of the control of CDPM is that cable tensions must be admissible, i.e. lying in a non-negative range of admissible values. As long as cable tensions are admissible, the overall dynamics of CDPM can be easily written in either actuator space or operational space which in turn facilitates control system design. The extended adaptive control scheme has been applied to a large redundantly actuated CDPR prototype, CoGiRo. Simulation results show the effectiveness of the proposed control method.

Dynamic Modeling of Cable-Driven Parallel Manipulators With Distributed Mass Flexible Cables

Abstract: A cable-driven parallel manipulator is an economic way to achieve manipulation over large workspace. However, unavoidable vibration in long cables can dramatically degenerate the positioning performance of manipulators. In this paper, dynamic models of large cable-driven parallel manipulators (CDPMs) are addressed where each cable is considered with distributed mass and can change in length during operation. The dynamic equation of a cable deployed or retrieved is derived using Hamilton's principle. The dynamic model of the system is characterized by partial differential equations with algebraic constraints. By properly selecting the independent unknowns, we solve the model using assumed-mode method.

Dynamics of Parallel Robots: From Rigid Bodies to Flexible Elements

Abstract: This book starts with a short recapitulation on basic concepts, common to any types of robots (serial, tree structure, parallel, etc.), that are also necessary for computation of the dynamic models of parallel robots. Then, as dynamics requires the use of geometry and kinematics, the general equations of geometric and kinematic models of parallel robots are given. After, it is explained that parallel robot dynamic models can be obtained by decomposing the real robot into two virtual systems: a tree-structure robot (equivalent to the robot legs for which all joints would be actuated) plus a free body corresponding to the platform. Thus, the dynamics of rigid tree-structure robots is analyzed and algorithms to obtain their dynamic models in the most compact form are given. The dynamic model of the real rigid parallel robot is obtained by closing the loops through the use of the Lagrange multipliers. The problem of the dynamic model degeneracy near singularities is treated and optimal trajectory planning for crossing singularities is proposed. Lastly, the approach is extended to flexible parallel robots and the algorithms for computing their symbolic model in the most compact form are given. All theoretical developments are validated through experiments

A Reconfigurable Cable-Driven Parallel Robot for Sandblasting and Painting of Large Structures

Abstract: The research work presented in this paper introduces a Reconfigurable Cable Driven Parallel Robot (RCDPR) to be employed in industrial operations on large structures. Compared to classic Cable-Driven Parallel Robots (CDPR), which have a fixed architecture, RCDPR can modify their geometric parameters to adapt their own characteristics. In this paper, a RCDPR is intended to paint and sandblast a large tubular structure. To reconfigure the CDPR from one side of the structure to another one, one or several cables are disconnected from their current anchor points and moved to new ones. This procedure is repeated until all the sides of the structure are sandblasted and painted. The analysed design procedure aims at defining the positions of the minimum number of anchor points required to complete the task at hand. The robot size is minimized as well.

The Forward Kinematics of Cable-Driven Parallel Robots with Sagging Cables

Abstract: Solving the forward kinematics (FK) of parallel robots is known to be a difficult task and the problem is even more complex for cable driven parallel robot (CDPR): the system of equations that has to be solved is larger than with rigid legs as first the static equations have to be taken into account and, second because the deformation of the cables because of their elasticity and their mass may play a role, while being described by a relatively non algebraic complex model. We consider in this paper any arbitrary CDPR whose cables may present a significant deformation due to their elasticity and own mass and we present for the first time an interval analysis based generic algorithm that allows to calculate in a guaranteed manner all the FK solutions and illustrate its use for a CDPR with 8 cables.

ARACHNIS: Analysis of Robots Actuated by Cables with Handy and Neat Interface Software

Abstract: This paper presents ARACHNIS, a graphical user interface for the analysis and parametric design of Cable Driven Parallel Robots (CDPRs). ARACHNIS takes as inputs the design parameters of the robot, the task specifications, and returns a visualisation of the CDPR Wrench Feasible Workspace (WFW) and Interference-Free Constant Orientation Workspace (IFCOW). The WFW is traced from the capacity margin, a measure of the robustness of the equilibrium of the robot. Interferences between the moving parts of a CDPR are also determined by an existing technique for tracing the interference-free workspace of such robots. Finally, the WFW and the IFCOW of a planar cable-driven parallel robot and of a spatial cable-driven parallel robot are plotted in order to demonstrate the potential of ARACHNIS.

Kinematic Model and Analysis of an Actuation Redundant Parallel Robot With Higher Kinematic Pairs for Jaw Movement

Abstract: A jaw movement robot that can simulate jaw movement and reaction forces in temporomandibular joints (TMJs) of a man will find many applications in dentistry, food science, and biomechanics. The TMJ is the most sophisticated joint in the human body, and its compound movements are not given sufficient consideration when a jaw robot is designed. Based on the biological finding about the mastication system and its motion characteristics, this paper proposes an actuation redundant parallel mechanism for the jaw movement robot and designs the actuation systems and models the TMJ in a higher pair kinematic joint. The prototype of the proposed jaw movement robot is presented, consisting of six prismatic–universal–spherical linkages for muscle groups of mastication and two point contacts for left and right TMJs. This robot has four degrees of freedom but is driven by six actuators. Each prismatic–universal–spherical linkage is made up of a rotary motor, a prismatic joint, a universal joint, and a spherical joint. The closed-form solution to the kinematics is found. This novel robot is evaluated by simulations of kinematics, workspace, and a chewing movement experiment.

Inverse dynamics and control of a 3-DOF planar parallel (U-shaped 3-PPR) manipulator

Abstract: This paper addresses the inverse dynamics of three degrees of freedom (DOF) U-shaped planar parallel manipulator having three legs consisting of prismatic-prismatic-revolute (PPR) joint arrangement in which each leg has one active prismatic joint. This paper also proposes a proportional-derivative (PD) like adaptive sliding mode control combined with a disturbance observer for the motion control of the proposed manipulator. Using this control scheme, the controlled robotic manipulator is transformed into decoupled dynamics, and thus the motion performance is very convenient to quantify. Based on Lyapunov like argument the global asymptotic stability of the proposed closed loop system is proved. Real time experiments performed on the in-house fabricated prototype of the proposed manipulator are provided to substantiate the effectiveness and the improved performance of the proposed controller. The proposed controller performances are also compared with traditional controllers such as proportional integral derivative (PID) controller, sliding mode controller (SMC) and computed torque controller (CTC) Inverse dynamics of a 3-DOF planar parallel robot (3-PPR) is presented.A robust tracking controller with disturbance compensation has been introduced.Effectiveness of the controller has been demonstrated with prototype experiments.A comparative study of the proposed and existing controllers has been performed.

A Survey on Parallel Robots with Delta-like Architecture

Abstract: In the early 1980s, Reymond Clavel invented the Delta robot at the Ecole polytechnique federale de Lausanne. The initial objective was the development of an industrial robot dedicated to high-speed handling tasks of very light objects. Nowadays, the Delta robot is one of the best-known and most widely spread parallel robots. Besides various different designs of the original architecture, e.g. Delta robots with rotary and/or linear actuation, current industrial versions employ additional serial mechanisms in order to obtain rotational degrees of freedom. This paper gives an overview about the different variants of translational three degrees of freedom Delta-like robots and serial-parallel hybrid as well as fully-parallel Delta-like robots with rotational degrees of freedom.