Closed-loop Manipulators Research Articles

Application of hybrid robotic systems in crop harvesting: Kinematic and dynamic analysis

Harvesting of agricultural crops, especially when the ripe products have to be picked one by one, has always been a major concern of farmers and growers. Consequently, the use of robots and the mechanization of harvesting operations have been considered as the effective means of tackling such challenges. In the present research, the use of hybrid robots (which combine open-loop and closed-loop manipulators) has been proposed for this purpose; because these robots help reduce the size of the workforce and thus slash the harvesting costs, and they also boost the speed and accuracy of harvesting operations. However, using this type of robots without paying attention to some important factors (e.g., using motors of optimal power at the actuated joints of a robot and choosing appropriate lengths for robot links) can have a substantial adverse effect on the manufacturing cost, working space and the effective functioning of such robots. So the main focus of this paper is on the kinematic and dynamic analysis of hybrid robotic systems. The main advantage of this research over similar works is the generality by which it describes the mechanical behavior of these robots; so that by using the recursive algorithms presented in this paper, all kinds of robots in the hybrid class can be analyzed. However, due to the complexity in the analysis of such systems, a hybrid robot consisting of three closed loops and one open loop was considered in this paper as a sample case study, so that we could explain, visually and graphically, all the steps involved in deriving its motion equations. The simulation results for this robotic system demonstrate the efficacy of the proposed method in the kinematic and dynamic analysis of hybrid robots, as efficient and functional crop harvesting equipment.

The effects of mode shapes on the temporal response of flexible closed-loop linkages under the impulse excitation

In this paper, by relying on the Timoshenko beam theory and the assumed modes method, we have presented a dynamic modeling of the closed-loop flexible linkages in the non-impact and impact stages. The dynamic equations for the suspension stage are obtained by employing the effective, but less used, Gibbs-Appell formulation, and the governing equations for the impact stage are derived by means of the Newton’s impact method. Although the motion equations have been extracted for an n-link mechanism in general, the simulations are performed for two closed-loop manipulators consisting of four elastic links. In order to model the flexibility of the links, the two mentioned manipulators are respectively simulated with the mode shapes associated with the clamped–clamped (C–C) and clamped-free (C-F) boundary conditions. In fact, the primary goal of this research is to investigate the effects of the mode shapes on the temporal response of these types of mechanical systems. Lastly, a criterion based on the mechanical energy conservation law is presented for validating the obtained results.

Compensator-critic structure-based event-triggered decentralized tracking control of modular robot manipulators: theory and experimental verification

This paper presents a novel compensator-critic structure-based event-triggered decentralized tracking control of modular robot manipulators (MRMs). On the basis of subsystem dynamics under joint torque feedback (JTF) technique, the proposed tracking error fusion function, which includes position error and velocity error, is utilized to construct performance index function. By analyzing the dynamic uncertainties, a local dynamic information-based robust controller is designed to engage the model uncertainty compensation. Based on adaptive dynamic programming (ADP) algorithm and the event-triggered mechanism, the decentralized tracking control is obtained by solving the event-triggered Hamilton–Jacobi–Bellman equation (HJBE) with the critic neural network (NN). The tracking error of the closed-loop manipulators system is proved to be ultimately uniformly bounded (UUB) using the Lyapunov stability theorem. Finally, experimental results illustrate the effectiveness of the developed control method.

Kinematic Analysis of an Under-actuated, Closed-loop Front-end Assembly of a Dragline Manipulator

Dragline excavators are closed-loop mining manipulators that operate using a rigid multilink framework and rope and rigging system, which constitute its front-end assembly. The arrangements of dragline front-end assembly provide the necessary motion of the dragline bucket within its operating radius. The assembly resembles a five-link closed kinematic chain that has two independent generalized coordinates of drag and hoist ropes and one dependent generalized coordinate of dump rope. Previous models failed to represent the actual closed loop of dragline front-end assembly, nor did they describe the maneuverability of dragline ropes under imposed geometric constraints. Therefore, a three degrees of freedom kinematic model of the dragline front-end is developed using the concept of generalized speeds. It contains all relevant configuration and kinematic constraint conditions to perform complete digging and swinging cycles. The model also uses three inputs of hoist and drag ropes linear and a rotational displacement of swinging along their trajectories. The inverse kinematics is resolved using a feedforward displacement algorithm coupled with the Newton-Raphson method to accurately estimate the trajectories of the ropes. The trajectories are solved only during the digging phase and the singularity was eliminated using Baumgarte′s stabilization technique (BST), with appropriate inequality constraint equations. It is shown that the feedforward displacement algorithm can produce accurate trajectories without the need to manually solve the inverse kinematics from the geometry. The research findings are well in agreement with the dragline real operational limits and they contribute to the efficiency and the reduction in machine downtime due to better control strategies of the dragline cycles.

Recurrent fuzzy wavelet neural networks based on robust adaptive sliding mode control for industrial robot manipulators

A robust adaptive control method is proposed in this paper based on recurrent fuzzy wavelet neural networks (RFWNNs) system for industrial robot manipulators (IRMs) to improve high accuracy of the tracking control. The RFWNNs consist of four layers, and second layer has the feedback connections. Wavelet basis function is used as fuzzy membership function. In general, it is not easy to adopt a model-based method to achieve this control object due to the uncertainties of the IRM, such as unknown dynamic, disturbances and parameter variations. To solve this problem, all the parameters of the RFWNNs system are tuned online by an adaptive learning algorithm, and online adaptive control laws are determined by Lyapunov stability theorem. In addition, the robust controller is designed to deal with the approximation error, optimal parameter vectors and higher-order terms in Taylor series. Therefore, with the proposed control, the desired tracking performance, stability and robustness of the closed-loop manipulators system are guaranteed. The simulations and experimental performed on a three-link IRMs are provided in comparison with fuzzy wavelet neural network and robust neural fuzzy network to demonstrate the effectiveness and robustness of the proposed RFWNNs methodology.

Robust adaptive sliding mode control for industrial robot manipulator using fuzzy wavelet neural networks

In this paper, a robust adaptive control method based on Dynamic Structure Fuzzy Wavelet Neural Networks (FWNNs) system is presented for trajectory tracking control of industrial robot manipulators (IRM) with uncertainties and disturbances via adaptive sliding mode control (SMC). Four layer FWNNs in the Dynamic structure FWNNs is constructed on the basis of fuzzy rules which associates with wavelet function in the consequent part, to compensate for structured and unstructured uncertainties and model complex processes. However, it is difficult to design a suitable control scheme to achieve the required approximation errors, such as friction forces, external disturbances error and parameter variations. To deal with the mentioned problems, all the parameters of the Dynamic structure FWNNs system are tuned on-line by an adaptive learning algorithm, and adaptive robust control laws are determined by Lyapunov stability theorem. By using Dynamic structure FWNNs, this control system could achieve desired tracking performance, the stability and robustness of the closed-loop manipulators system are guaranteed. In addition, the simulations and experimental performed on a three-link IRM are provided in comparison with wavelet network control (WNC) and adaptive Fuzzy control (AFC) to demonstrate the effectiveness and robustness of the proposed Dynamic structure FWNNs methodology.

Target Tracking Manipulation Theories for Combined Force and Position Control in Open and Closed Loop Manipulators

This paper presents a new manipulation theory for controlling compliant motions of a robotic manipulator. In previous closed loop control methods, both direct kinematics and inverse kinematics of a manipulator must be resolved to convert feedback force and position data from Cartesian space to joint space. However, in many cases, the solution of direct kinematics in a parallel manipulator or the solution of inverse kinematics in a serial manipulator is not easily available. In this study, the force and position data are packed into one set of “motion feedback,” by replacing the force errors with virtual motion quantities, or one set of “force feedback,” by replacing motion errors with virtual force quantities. The joint torques are adjusted based on this combined feedback package. Since only Jacobian of direct kinematics or Jacobian of inverse kinematics is used, the computational complexity is reduced significantly, and the control scheme is more stable at or near singular manipulator configurations. Furthermore, the complexities and oddities associated with hybrid control, such as nonuniformity of the space matrix and incompatibility of simultaneous position and force control in the same direction are circumvented. The applications of this theory are demonstrated in simulation experiments with both serial and parallel manipulators.

Local Analysis of Singular Configurations of Open and Closed Loop Manipulators

The paper gives a general approach to the local analysis of singularconfigurations of both serial and parallel manipulators. For all possiblecases the maximum rank deficiency of the manipulator Jacobian is given andshown never to exceed 4. This is the equivalent to the maximum number oflinear dependent constraint equations for kinematic loops. Singularconfigurations of serial/parallel manipulators are roughly classified withrespect to the active and passive joints. An algorithm is presented whichdetermines the singular motion of a mechanism. This algorithm is purelyalgebraic and involves at maximum three steps. It is based on theinstantaneous screw system of the considered mechanism. It is shown thatfourth order analysis is always sufficient to locally characterize theconfiguration space manifold in singular points. Thus the singular set canlocally be approximated by a hypersurface of maximum degree 4. The approachcan easily be implemented in existing simulation tools Finally theminimum number of joints is given that a serialmanipulator must activate in order to escape from a singular configuration.

A centro-based characterization of singularities in the workspace of planar closed-loop manipulators

The paper presents a centro-based characterization of singularities in planar multi-DOF mechanisms with arbitrary kinematic structure. A multi-DOF mechanism is treated as an assembly of several single DOF link sets and hence the terms like affected link set, active link set and active centro have been defined. Criteria for end-effector dependent and end-effector independent singularities of a closed-loop manipulator with given output link have been established in the paper in terms of centroes. Based on the relative disposition of the centroes, the singularities have been classified into five types and their physical implications have been explained. End-effector dependent singularities are shown to lie on the coupler curve of a larger single DOF mechanism. A simple linkage transformation has been proposed for the study of manipulators with physical limits on joint motion under the general framework of close-loop manipulators. Several examples have been worked out to demonstrate the centro-based method of singularity analysis.

Dynamic studies on closed-loop manipulators constructed from composites — an FEM approach

Today's manufacturing industry needs robots to work at high speeds to satisfy the demand for increased productivity. Many desirable characteristics of fibre-reinforced composite materials such as high strength-to-weight ratios and high stiffness-to-weight ratios make them suitable for high-speed robots. This paper presents a comparative study of the dynamic performance of a closed-loop manipulator constructed from steel, aluminium and two graphite epoxy laminates. A versatile modelling procedure using finite element method is explained for the analysis of dynamic behaviour of a robot. The study shows that the performance of a robot manufactured from composites is superior to robots manufactured from commercial metals such as steel and aluminium.

Gross Motion and Classification of Manipulators with Closed-Loop, Four-Bar Chains

This article presents an extensive study on the gross motion of 2-DOF manipulators with closed-loop, four-bar chains. The investigation is focused on (1) classification, (2) work space and sub-work space, (3) existence of singular circles, (4) number of postures and service angles, and (5) the effects of the orientation of the wrist on the floating link. One may find that closed-loop manipulators are not only lightweight, they can also provide better kinematic properties in view of work space, singularity, postures, and service angles.

Dextrous Workspaces of Manipulators. I. Analytical Criteria

Abstract ABSTRACT A formulation for analysis of dextrous workspaces of manipulators is presented, including mobility-limited joints, full-range dexterity requirements, full-range input requirements, and planar and spatial closed-loop kinematic structures. A terminology for mechanism and manipulator models that permits specification of input, output, and dexterity requirements is proposed and demonstrated to yield broadly applicable conditions necessary for boundaries of dextrous workspaces. Row-rank deficiency of constraint sub-Jacobian matrices is shown to yield necessary conditions for boundaries of accessible output sets and dextrous accessible output sets that characterize the workspace and dextrous workspace, respectively, of both planar and spatial manipulators. Three closed-loop planar manipulators are analyzed in detail and a three-dimensional, closed-loop Stewart platform is formulated to illustrate applicability of necessary conditions

Workspace and Mobility of a Closed- Loop Manipulator

This paper examines the geometry of a group of closed-loop manipulators with structures based on a planar, revolute jointed, five-bar chain. Of primary interest is the influence of the link lengths on the reachable workspace of the manipula tor. Unlike the commonly used open-loop manipulators, the entire workspace for a closed-loop manipulator will not be freely reachable, in general. The issues pertaining to the independent mobility of the driving links are discussed at length. A classification is made based on mobility criteria, and these mechanisms are further categorized into two types depending upon the influence of the link lengths on the ma nipulator's workspace. Based on this analysis, some general guidelines are laid down to assist the designer in making rational choices in selecting manipulator link lengths.