Cooperating Robot Manipulators Research Articles

Erratum to: “On position/force tracking control problem of cooperative robot manipulators using adaptive fuzzy backstepping approach” [ISA Trans. 70 (2017) 432-446

Erratum to: “On position/force tracking control problem of cooperative robot manipulators using adaptive fuzzy backstepping approach” [ISA Trans. 70 (2017) 432-446

Adaptive robust synchronized control for cooperative robotic manipulators with uncertain base coordinate system

In this paper, cooperative robotic manipulators under uncertain base coordinate are investigated. The coordinate uncertainties result in biases of cooperative robotic dynamics, which involve horizontal and vertical translational errors in the task space and rotational errors in the joint space. To the best of our knowledge, uncertainties in the base coordinate system of cooperative robotic manipulators have drawn little attention in existing literature. To solve this problem, this paper presents an adaptive robust controller for the synchronized control of two cooperative robotic manipulators. An adaptive neural network associated with base coordinate parameter adaption law is proposed to estimate the cooperative system parameters given unknown system dynamics and base coordinate uncertainties. A synchronization-factor-based robust slide mode controller is then derived to stabilize the target position and internal force between the cooperative manipulators. Mathematical proof and numerical experiments under various conditions are conducted. The results demonstrate the satisfactory and effective convergences of both the cooperative robotic trajectory and internal force despite of uncertainties in the base coordinate system.

Adaptive Tracking Control of Cooperative Robot Manipulators With Markovian Switched Couplings

Many cooperative robotic systems have not only modeling heterogeneity and uncertainty but also switched couplings, causing control difficulties. Here, we develop a neural network adaptive control framework for cooperative robot manipulators with unknown Euler–Lagrange dynamics and Markovian switched couplings. Second-order Markovian switching networks are used for modeling such cooperative robotic systems, which admit a hybrid neural network control with a desired tracking performance. The hybrid neural network control scheme contains a distributed adaptive controller and a hybrid adaptation law, enabling learning in the closed-loop system. The position and velocity tracking errors are shown to be practically uniformly exponentially stable in the mean-square sense, respectively, guaranteeing the second-order practical tracking. The results also suggest that the neural weight evolves with practical convergence to the ideal, showing the effect of network structure on the adaptation capacity.

Collision detection and avoidance method for two cooperative robot manipulators

The paper examines a collisions detection and avoidance problem for two cooperative robot manipulators. The proposed collision detection method is based on the division of workspace into small discrete volume spaces. Each of the discrete volumes have the status “occupied” or “free”. The control system generates restriction signals when the motion along the calculated path will bring the manipulator into occupied volume spaces. A step-by-step algorithm of the collision detection system is given.

Optimal Scheduling and Model Predictive Control for Trajectory Planning of Cooperative Robot Manipulators

Abstract A hierarchical control approach for cooperative pick-and-place tasks in a narrow shared workspace is proposed. A scenario with two robot arms performing pick-and-place tasks with moving objects while ensuring collision-free planning and execution of their respective trajectories is specifically addressed. To this end, we consider a hierarchical architecture with two-layer optimization-based control policies involving task scheduling in the top layer and path planning, along with the motion constraints, at the bottom one. On the one hand, for task allocation, a distance minimization algorithm is introduced, leading to an integer optimization problem with linear constraints and a bilinear cost function. On the other hand, we invoke model-based collision-free minimum-time planning of robot trajectories. Hereby, inverse robot dynamics and time scaling appear to be useful tools. The former accounts for the compensation of nonlinear robot dynamics, while the latter converts the trajectory planning to a fixed-time optimization problem, thus enabling synchronous robot task executions.

On position/force tracking control problem of cooperative robot manipulators using adaptive fuzzy backstepping approach

In this paper, the position and force tracking control problem of cooperative robot manipulator system handling a common rigid object with unknown dynamical models and unknown external disturbances is investigated. The universal approximation properties of fuzzy logic systems are employed to estimate the unknown system dynamics. On the other hand, by defining new state variables based on the integral and differential of position and orientation errors of the grasped object, the error system of coordinated robot manipulators is constructed. Subsequently by defining the appropriate change of coordinates and using the backstepping design strategy, an adaptive fuzzy backstepping position tracking control scheme is proposed for multi-robot manipulator systems. By utilizing the properties of internal forces, extra terms are also added to the control signals to consider the force tracking problem. Moreover, it is shown that the proposed adaptive fuzzy backstepping position/force control approach ensures all the signals of the closed loop system uniformly ultimately bounded and tracking errors of both positions and forces can converge to small desired values by proper selection of the design parameters. Finally, the theoretic achievements are tested on the two three-link planar robot manipulators cooperatively handling a common object to illustrate the effectiveness of the proposed approach.

An Avoidance Control Strategy for Joint-Position Limits of Dual-Arm Robots

The joint position constraints of two cooperative robotic manipulators is a critical issue, especially when both manipulators grasp and move the same object. When two robots cooperate to move a grasped object from one point to another one, following a desired path, the general solution adopted in the literature is to use the kinematic redundant motions possessed by a single manipulator, in order to avoid joint constraints. However, this method requires a number of redundant motions at least equals to the number of joint constraints to satisfy. The study proposed in this paper is focused on developing a joint position limits avoidance strategy, which is able to satisfy all joint limits even when the number of redundant motions are no longer sufficient to ensure them with a classical approach. This is achieved by means of a supervisory control system, which allows to locally and temporary change the desired end-effectors motion, when the redundant motions are not available. The supervisory control sacrifices the path following task in order to ensure joint position limits avoidance, while preserving at the same time the relative end-effector motion, such that the stability of the grasped object is still ensured. The proposed strategy has been implemented on a commercial robot, namely Baxter, which possesses two anthropomorphic arms having one degree of redundancy. The obtained results prove the effectiveness of the proposed supervisor controller, which can be easily extended and applied in manufacturing scenario. Whereas path following can be temporary sacrificed (e.g., the grasped object can be moved from one point to another in different ways), the joint constraints must be strictly preserved for safety reasons.

Launches and Captures of the Space “Frisbees”: Dynamics Modelling and Simulation

The current paper presents a concept of the non-conventional method of handling/transfer of the space objects/payloads, using single and multiple cooperative robotic manipulators with extremely flexible arms. Practical cases may involve launch only (as in the case of the ejection of the spacecraft), capture only (as in the case of the capture of the dysfunctional spacecraft or debris) or launch and capture, combined together (as in the case of a payload transfer from one platform to another). This method is seen as having numerous advantages over the traditional methods, employing propulsive systems on the payloads. These include: simplicity,reliability, re-usability, ability to handle passive payloads, and small power requirements. In this study, various operational scenarios of the launches and captures of the payloads are considered and designed in detail. In particular, we demonstrate the feasibility of the launch of the outgoing rotating payloads (called "frisbees") using a highly elastic robotic arm, capable of transferring its potential energy of the pre-deformed shape into the kinetic energy of the payload. Using the co-rotational FEM, we firstly simulate pre-launch phases, coiling the elastic elements in different shapes, for example, "U", "S" or even more complex shapes, and then propose and simulate the scenarios of ejecting the payloads utilising the kinetic energy of the elastic members (playing role of catapults). We also demonstrate the feasibility of the ejection of the payloads with required dynamic parameters, using cooperative robotic manipulator arms, performing coordinated throwing manoeuvres. This is done in compliance with the kinematics of the system and dynamics laws. The cases of the ejection of the payload is simulated using fully non-linear formulation, employing so-called co-rotational FEM,which enables to deal with large deformations, large rotations and large translations of the simulated elastic robotic arms. Numerical simulation allows to observe, to analyse and to suppress the transient strains and stresses in the flexible arms. In the cases of the payload capture, the co-rotational FEM method is used to simulate the process of de-spin, slowing and stopping the spinning object. This is also supplemented with the analysis of the strains and stresses on the members of the robotic arm manipulators. Various study cases are illustrated with the animations of the representative cases in Virtual Reality.

A Supervisory Sliding Mode Control Approach for Cooperative Robotic System of Systems

This paper deals with the formulation of a supervisory sliding mode (SM) control approach oriented to deal with the interesting class of system of systems of robotic nature. This class of systems is characterized by the fact of being inherently distributed, cooperative, and, possibly, heterogeneous. In this paper, we propose a modular and composable approach relying on basic modules featuring a multilevel functional architecture, including a supervisor and a couple of hybrid position/force control schemes associated with a couple of cooperative robotic manipulators. In principle, the overall robotic system we are referring to can be viewed as a collection of basic modules of that type. In this paper, we focus on the design of the basic module. The hybrid position/force control schemes therein included are based on position and force controllers. The proposed position and force controllers are of SM type, to assure suitable robustness to perform a satisfactory trajectory tracking even in presence of unavoidable modeling uncertainties and external disturbances. The verification and the validation of our proposal have been performed by simulating the supervisor and the hybrid control scheme applied to one of the two robotic manipulators while experimentally testing the position control on the other arm. The experimental part of the tests has been carried out on a COMAU SMART3-S2 anthropomorphic industrial robotic manipulator.

Two Cooperating Manipulators with Fractional Controllers

This paper analyzes the dynamic performance of two cooperative robot manipulators. It is studied the implementation of fractional-order algorithms in the position/force control of two cooperating robotic manipulators holding an object. The simulations reveal that fractional algorithms lead to performances superior to classical integer-order controllers.

Two-time scale control and observer design for trajectory tracking of two cooperating robot manipulators moving a flexible beam

In this paper, we present two-time scale control design for trajectory tracking of two cooperating planar rigid robots moving a flexible beam, which does not require vibration measurement for the beam. First, the kinematics and dynamics of the robots and the object are derived. Then, using the relations between different forces acting on the object by the manipulators’ end-effectors, dynamics equations of the robots and the object are combined. The resulting equations show that the coupled dynamics including beam vibration and the rigid motion take place in two different time domains. By applying two-time scale control theory on the combined dynamics, a composite control scheme is elaborated which makes the beam orientation and its center of mass position track a desired trajectory while suppressing the beam vibration. For the controller algorithm, first a slow controller is utilized for the slow (rigid) subsystem and then a fast stabilizing controller is considered for the fast (flexible) subsystem. To avoid requiring measurement of beam vibration for the fast control law, a linear observer is also designed. The simulation results show the efficiency of the proposed control scheme.

A fault tolerance framework for cooperative robotic manipulators

The problem of fault tolerance in cooperative manipulators rigidly connected to an undeformable load is addressed in this paper. Four categories of faults are considered: free-swinging joint faults (FSJFs), locked joint faults (LJFs), incorrectly measured joint position faults (JPFs), and incorrectly measured joint velocity faults (JVFs). Free-swinging and locked joint faults are detected via artificial neural networks (ANNs). Incorrectly measured joint position and velocity faults are detected by considering the kinematic constraints of the cooperative system. When a fault is detected, the control system is reconfigured according to the nature of the isolated fault and the task is resumed to the largest extent possible. The fault tolerance framework is applied to an actual system composed of two cooperative robotic manipulators. The results presented demonstrate the feasibility and performance of the methodology.

Micro/Macro or Link-Integrated Micro-actuator Manipulation—A Kinematics and Dynamics Perspective

Smart (active) materials based actuators, hereinafter called micro-actuators, have been shown to be well suited for the elimination of high harmonics in joint and/or end-effector motions of robot manipulators and in the reduction of actuator dynamic response requirements. Low harmonic joint and end-effector motions, as well as low actuator dynamic response requirements, are essential for a robot manipulator to achieve high operating speed and precision with minimal vibration and control problems. Micro-actuators may be positioned at the end-effector to obtain a micro- and macro-robot manipulation configuration. Alternatively, micro-actuators may be integrated into the structure of the links to vary their kinematics parameters, such as their lengths during the motion. In this paper, the kinematics and dynamics consequences of each of the aforementioned alternative are studied for manipulators with serial and closed-loop chains. It is shown that for robot manipulators constructed with closed-loop chains, the high harmonic components of all joint motions can be eliminated only when micro-actuators are integrated into the structure of the closed-loop chain links. The latter configuration is also shown to have dynamics advantage over micro- and macro-manipulator configuration by reducing the potential vibration and control problems at high operating speeds. The conclusions reached in this study also apply to closed-loop chains of parallel and cooperating robot manipulators.

Motion and force control of cooperative robotic manipulators with passive joints

In this paper, robotic systems when two or more underactuated manipulators are working in a cooperative way are studied. The underactuation effects on object to be controlled and on load capacity of the cooperative arms are analyzed. A hybrid control of motion and squeeze force is proposed. For the motion control, a Jacobian matrix that relates the torques in the actuated joints to the resulting force in the load is obtained. In addition, a method to compute the dynamic load-carrying capacity of cooperative manipulators with passive joints is presented. Results of the control system are verified in simulations and in an actual system formed by two cooperative arms.

FRACTIONAL CONTROL OF TWO ARMS WORKING IN COOPERATION

This paper analyzes the performance of two cooperative robot manipulators. It is studied the implementation of fractional-order algorithms in the position/force control of two robots holding an object. The experiments reveal that fractional algorithms lead to performances superior to classical integer-order controllers.

Dynamic loads coordination for multiple cooperating robot manipulators

For the situation of multiple manipulators handling a single object, the dynamic model of the system that mapping directly the dynamics between object space and joint space, is established in terms of object dynamic, individual arm dynamics and joint driving torques. Then the methods are introduced which distribute directly the object dynamic and arm dynamics over the joint space in line with the joint-input based criteria.

Dynamics of cooperating manipulators for fixtureless assembly and robust control based on fuzzy logic

This article presents the modeling of the dynamics of two cooperating robot manipulators performing assembly tasks such as the peg-in-hole job while coordinating the payload along the desired trajectory. The system has uncertainty due to unknown mass and moment of inertia of the manipulators and the payload, and has disturbances due to coupling forces between manipulators and due to frictional forces during the assembly process. To control the uncertain system, a robust control algorithm with computed torque control is proposed. The robust control algorithm includes fuzzy logic that has two functions: one is to regulate the magnitude of the input torque of the manipulators to not go beyond the torque saturation. The other function is to reduce trajectory tracking errors. To validate the proposed control algorithm, a numerical example using dual 3 degree-of-freedom manipulators is shown. ©1999 John Wiley & Sons, Inc.

A study on the control of two-cooperating robot manipulators for fixtureless assembly

This paper proposes the modeling of the dynamics of two cooperating robot manipulators performing the assembly job such as peg-in-hole while coordinating the payload along the desired path. The mass and moment of inertia of the manipulators and the payload are assumed to be unknown. To control the uncertain system, a robust control algorithm based on the computed torque control is proposed. Usually, the robust controller requires high input torques such that it may face input saturation in actual application. In this reason, the robust control algorithm includes fuzzy logic such that the magnitude of the input torque of the manipulators is controlled not to go over the hardware saturation while keeping path tracking errors bounded. A numerical example using dual three degree-of-freedom manipulators is shown.

Determining the collision-free joint space graph for two cooperating robot manipulators

The problem of path planning for two planar robot manipulators that cooperate in carrying a rectangular object from an initial position and orientation to a destination position and orientation in a 2-D environment is investigated. The two robot arms, the carried object, and the straight line connecting the two robot bases are modeled as a 6-link closed chain. The problem of path planning for the chain is solved by two major algorithms: a collision-free feasible-configuration-finding algorithm and a collision-free path-finding algorithm. The former maps the free space in the Cartesian world space to the robot's joint space in which all the collision-free feasible configuratiions (CFFCs) for the 6-link closed chain are found. The latter builds a connection graph representing the CFFCs and the transitions between any two groups of CFFCs at adjacent joint intervals. A graph search method is employed to find a collision-free path for each joint of both manipulators. >

Simulation of cooperating robot manipulators on a mobile platform

The dynamic equations of motion are presented for two or more cooperating manipulators on a freely moving mobile platform. The system of cooperating robot manipulators forms a closed kinematic chain where the force of interaction must be included in the formulation of robot and platform dynamics. The formulation includes the full dynamic interactions from arms to platform and arm tip to arm tip, and the possible translation and rotation of the platform. The equations of motion are shown to be identical in structure to the fixed-platform cooperative manipulator dynamics. The structure of the closed-chain dynamics, allows the use of any solution for the open topological tree of base and manipulator links. The number of degrees of freedom (DOF) of the system is sufficiently large to make recursive dynamic calculation methods potentially more efficient than closed-form solutions. A complete simulation with two 6-DOF manipulators of a free-floating platform is presented along a with a multiple-arm controller to position the common load. >