Nonholonomic Wheeled Mobile Manipulator Research Articles

Output feedback tracking control for nonholonomic wheeled mobile manipulator systems with full-output constraints

An output feedback trajectory tracking control scheme for nonholonomic mobile manipulator robot systems with full-output constraints is presented in this article. Different from the previous methods, the kinematic model of the system is transformed into a special chained form by a rotation-like matrix. A globally exponentially stable speed observer with generalized dynamic scaling function is constructed to obtain the velocity estimation of the system. The output feedback tracking constrained controller is successfully constructed by Barrier Lyapunov function, backstepping and the excellent observer, which considering the system dynamics and the full-output constraints is achieved with only measurable outputs.

Robust Adaptive Sliding Mode Control for Mobile Manipulators

This paper proposes a robust adaptive sliding mode control for the trajectory tracking of a nonholonomic wheeled mobile manipulator in task space coordinate. The proposed algorithm is robust adaptive control strategy where parametric uncertainties and disturbances are compensated by adaptive update technique. The adaptive law is designed based on the Lyapunov method. Simulations results are given to illustrate the effectiveness of the proposed robust adaptive based controller in comparison with a robust sliding mode based controller.

Maximum Allowable Load of Mobile Manipulator in the Presence of Obstacle Using Non-Linear Open and Closed Loop Optimal Control

In this paper, a new method which is a combination of open and closed loop optimal control is developed to find maximum load carrying capacity of nonholonomic wheeled mobile manipulator (WMM) in the presence of environmental obstacles. At first level, open loop control method is used to solve path planning problem and design an optimal trajectory with maximum dynamic load carrying capacity between initial and final point. Optimality conditions are obtained for carrying the maximum payload between two points in an environment including obstacles. The main contribution at first level is applying obstacle avoidance in the objective function that leads to a two-point boundary value problem. At second level, a nonlinear closed loop optimal controller is designed to perform optimal trajectory in real-time conditions. The main contribution at second level is applying the nonlinear Hamilton–Jacobi–Bellman equation to design an optimal nonlinear state feedback controller. Numerical procedure in both levels, that is time consuming, is performed off line and resulted control law is simply applied in real-time conditions. The other contribution of this paper is the combination of these levels; it makes sure that the achieved trajectory and maximum load is applicable. To show the effectiveness of the method, simulations are performed for a planar WMM and a spatial WMM named Scout as well as experimental results for Scout robot.

Dynamic modeling of nonholonomic wheeled mobile manipulators with elastic joints using recursive Gibbs–Appell formulation

This paper focuses on the study of dynamic modeling of nonholonomic wheeled mobile robotic manipulators, which consist of a serial manipulator with elastic joints and an autonomous wheeled mobile platform. To avoid computing the Lagrange multipliers associated with the nonholonomic constraints, the approach of Gibbs-Appell (G-A) formulation in recursive form is adopted. For modeling the system completely and precisely, dynamic interactions between the manipulator and the mobile platform, as well as both nonholonomic constraints associated with the no-slipping and the no-skidding conditions, are included. Based on developed formulation, an algorithm is proposed that recursively and systematically derives the equation of motion. In this algorithm, in order to improve the computational complexity, all mathematical operations are done by only 3×3 and 3×1 matrices. Also, all dynamic expressions of a link are expressed in the same link local coordinate system. Finally, two computational simulations for mobile manipulators with rigid and elastic joints are presented to indicate the capability of this algorithm in generating the equation of motion of mobile robotic manipulators with high degree of freedom.

Adaptive control of mobile manipulators subject to external force and uncertainties

This paper addresses the trajectory tracking control of a non-holonomic wheeled mobile manipulator subjected to uncertainties and external force. The proposed algorithm is robust adaptive control strategy where external force and uncertainties are compensated by adaptive update techniques. The proposed algorithm makes the robot follow simultaneously desired end-effector and platform trajectories in task space without violating the non-holonomic constraints. The system stability and the convergence of tracking errors are rigorously proved using a Lyapunov theory. Simulation results are given to illustrate the effectiveness of the proposed robust adaptive control law in comparison with a classical Computed Torque Controller (CTC).

Sensitivity analysis of flexible joint nonholonomic wheeled mobile manipulator in singular configuration

This paper proposes a method for decreasing jerk and increasing Maximum Allowable Load (MAL) of nonholonomic Wheeled Mobile Manipulator (WMM) considering flexibility of joints in singular conditions. The full dynamic model of nonholonomic WMM contains simultaneous operation of mobile base and manipulator with joint flexibility (in wheels and manipulator) which is presented here. The problem is formulated in terms of the optimal control which leads to a two point boundary value problem. Then Sobol's sensitivity analysis method is applied to determine the optimal values of flexible joint constants subject to the jerk minimization. To illustrate the proposed method, two categories of conditions are considered: conditions containing non-singular configuration and the singular conditions. An example is explained for non-singular condition of nonholonomic WMM in presence of obstacle in which a complex path is generated but there is no singularity in robot configuration. Some examples of occurring singular configuration in final point and moving boundary condition is also presented. The results show that flexibility of the joints near to singular configuration normalizes the sudden movement and jerk implied to actuators. That is why using a rotational spring with a low stiffness coefficient could be helpful to decrease the high jerk and increase the maximum allowable load in mobile robots.

Differential-Flatness-Based Planning and Control of a Wheeled Mobile Manipulator—Theory and Experiment

This paper presents a differential-flatness-based integrated point-to-point trajectory planning and control method for a class of nonholonomic wheeled mobile manipulator (WMM). We demonstrate that its kinematic model possesses a feedback-linearizable description due to the flatness property, which allows for full-state controllability. Trajectory planning can then be simplified and achieved by polynomial fitting method in the flat output space to satisfy the terminal conditions, while control design reduces to a pole-placement problem for a linear system. The method is then deployed on our custom-constructed WMM hardware to evaluate its effectiveness and to highlight various aspects of the hardware implementation.

Robust adaptive control for mobile manipulators

This paper addresses the trajectory tracking control of a nonholonomic wheeled mobile manipulator with parameter uncertainties and disturbances. The proposed algorithm adopts a robust adaptive control strategy where parametric uncertainties are compensated by adaptive update techniques and the disturbances are suppressed. A kinematic controller is first designed to make the robot follow a desired end-effector and platform trajectories in task space coordinates simultaneously. Then, an adaptive control scheme is proposed, which ensures that the trajectories are accurately tracked even in the presence of external disturbances and uncertainties. The system stability and the convergence of tracking errors to zero are rigorously proven using Lyapunov theory. Simulations results are given to illustrate the effectiveness of the proposed robust adaptive control law in comparison with a sliding mode controller.

Analysis and experimental study of non-holonomic mobile manipulator in presence of obstacles for moving boundary condition

In this paper a general formulation as well as experimental studies for finding Maximum Allowable Dynamic Load (MADL) of non-holonomic Wheeled Mobile Manipulator (WMM) in presence of obstacle and moving boundary condition is presented. Full dynamic model of wheeled mobile base and mounted manipulator is considered with respect to the dynamic of non-holonomic constraint and optimality conditions for carrying maximum payload between start point and moving end boundary in an environment including obstacle is derived. Obstacle avoidance is presented in terms of distance between colliding parts. The problem is formulated using Pontryagin’s minimum principle which leads to a two-point boundary value problem. An iterative algorithm is proposed by considering motor restrictions in terms of torque and jerk along the trajectory. The latest term ensures that the resulting trajectory is smooth enough. Also we proposed an algorithm for finding the maximum allowable dynamic load in moving boundary condition. It is a set of points which have no superiority on each other. This can be used for conditions in which robot is cooperating with conveyer belt. Simulation tests on a two-link planner non-holonomic WMM are done. To verify the effectiveness of the algorithm, the proposed approaches are illustrated using simulations and experimental studies of a two-link Scout WMM.

Experimental Evaluation of Dynamic Redundancy Resolution in a Nonholonomic Wheeled Mobile Manipulator

Mobile manipulators derive significant novel capabilities for enhanced interactions with the world by merging mobility with manipulation. However, a careful resolution of the redundancy and active control of the reconfigurability, created by the surplus articulated DOFs and actuation, are the keys to unlocking this potential. Nonholonomic wheeled mobile manipulators, formed by mounting manipulator arms on disc-wheeled mobile bases, are a small but important subclass of mobile manipulators. The primary control challenges arise due to the dynamic-level coupling of the nonholonomy of the wheeled mobile bases with the inherent kinematic and actuation redundancy within the articulated chain. The solution approach in this paper builds upon a dynamically consistent and decoupled partitioning of the articulated system dynamics between the external (task) space and internal (null) space. The independent controllers, developed within each decoupled space, facilitate active internal reconfiguration, in addition to resolving redundancy at the dynamic level. Specifically, two variants of null-space controllers are implemented to improve disturbance rejection and active reconfiguration during performance of end-effector tasks by a primary end-effector impedance mode controller. These algorithms are evaluated within an implementation framework that emphasizes both virtual prototyping and hardware-in-the-loop testing with representative case studies.

Experimental Evaluation of Dynamic Redundancy Resolution in a Nonholonomic Wheeled Mobile Manipulator

Mobile manipulators derive significant novel capabilities for enhanced interactions with the world by merging mobility with manipulation. However, a careful resolution of the redundancy and active control of the reconfigurability, created by the surplus articulated DOFs and actuation, are the keys to unlocking this potential. Nonholonomic wheeled mobile manipulators, formed by mounting manipulator arms on disc-wheeled mobile bases, are a small but important subclass of mobile manipulators. The primary control challenges arise due to the dynamic-level coupling of the nonholonomy of the wheeled mobile bases with the inherent kinematic and actuation redundancy within the articulated chain. The solution approach in this paper builds upon a dynamically consistent and decoupled partitioning of the articulated system dynamics between the external (task) space and internal (null) space. The independent controllers, developed within each decoupled space, facilitate active internal reconfiguration, in addition to resolving redundancy at the dynamic level. Specifically, two variants of null-space controllers are implemented to improve disturbance rejection and active reconfiguration during performance of end-effector tasks by a primary end-effector impedance mode controller. These algorithms are evaluated within an implementation framework that emphasizes both virtual prototyping and hardware-in-the-loop testing with representative case studies.

Point-to-point trajectory planning of wheeled mobile manipulators with stability constraint. Extension of the random-profile approach

We propose a flexible stochastic scheme for point-to-point trajectory planning of nonholonomic wheeled mobile manipulators subjected to move in a structured workspace. The problem is known to be complex, particularly if obstacles are present and if dynamic stability constraint is considered. The proposed method consists of extending to wheeled mobile manipulators the random-profile approach recently applied to wheeled platforms. This versatile method handles constraints on: (i) geometry (obstacle avoidance, bounded joint positions and path curvature); (ii) kinematics (bounded velocities and accelerations); (iii) dynamics (bounded torques, stability condition). It may be applied using various forms of cost functions involving travel time, efforts and power. Solutions are presented for planar and spatial nonholonomic wheeled mobile manipulators undertaking, in a constrained workspace, a point-to-point task defined either in generalized or operational coordinates.

Dynamic redundancy resolution in a nonholonomic wheeled mobile manipulator

SUMMARYWheeled Mobile Manipulators (WMM) possess many advantages over fixed-base counterparts in terms of improved workspace, mobility and robustness. However, the combination of the nonholonomic constraints with the inherent redundancy limits effective exploitation of end-effector payload manipulation capabilities. The dynamic-level redundancy-resolution scheme presented in this paper decomposes the system dynamics into decoupled task-space (end-effector motions/forces) and a dynamically consistent null-space (internal motions/forces) component. This simplifies the subsequent development of a prioritized task-space control (of end-effector interactions) and a decoupled but secondary null-space control (of internal motions) in a hierarchical WMM controller. Various aspects of the ensuing novel capabilities are illustrated using a series of simulation results.

Dynamic Modeling and Tracking Control of a Nonholonomic Wheeled Mobile Manipulator with Dual Arms

This paper presents methodologies for dynamic modeling and trajectory tracking of a nonholonomic wheeled mobile manipulator (WMM) with dual arms. The complete dynamic model of such a manipulator is easily established using the Lagrange's equation and MATHEMATICA. The structural properties of the overall system along with its subsystems are also well investigated and then exploited in further controller synthesis. The derived model is shown valid by reducing it to agree well with the mobile platform model. In order to solve the path tracking control problem of the wheeled mobile manipulator, a novel kinematic control scheme is proposed to deal with the nonholonomic constraints. With the backstepping technique and the filtered-error method, the nonlinear tracking control laws for the mobile manipulator system are constructed based on the Lyapunov stability theory. The proposed control scheme not only achieves simultaneous trajectory and velocity tracking, but also compensates for the dynamic interactions caused by the motions of the mobile platform and the two onboard manipulators. Simulation results are performed to illustrate the efficacy of the proposed control strategy.