Computational feasibility study of failure-tolerant path planning, A

Includes bibliographical references (page 239).This work considers the computational costs associated with the implementation of a failure-tolerant path planning algorithm proposed in [1]. The algorithm makes the following assumptions: a manipulator is redundant relative to its task, only a single joint failure occurs at any given time, the manipulator is capable of detecting a joint failure and immediately locks the failed joint, and the environment is static and known. The algorithm is evaluated on a three degree-of-freedom planar manipulator for a total of eleven thousand different scenarios, randomly varying the robot's start and goal positions and the number and locations of obstacles in the environment. Statistical data are presented related to the computation time required by the different steps of the algorithm as a function of the complexity of the environment

Identifying mass, center of mass, and moment of inertia through natural oscillations for full-dynamics control of robot manipulators

Inclusion of the dynamics parameters information into the robot control is critical in achieving robustness in the robots performance. These dynamics parameters are mass, center of mass, and moment of inertia. Integrating the correct values of these parameters in the dynamics model helps achieve full-dynamics force and motion control of robot manipulators. Such type of control is necessary for a manipulator to behave robustly, especially when it is required to interact with an unstructured environment. However, the greatest challenge remains on how to identify these parameters accurately. The absence of a generic method to identify dynamics parameters of a multi-body system makes full-dynamics control hard to achieve. One successful full-dynamics control of a mobile manipulator used a simplified symbolic mathematical model (whose lumped inertias are independent) to identify its dynamics parameters. Despite its success, its major limitation is its requirement of a simplified symbolic mathematical model which can become very computationally expensive especially with higher degrees of freedom robots. In addition, only the lumped inertias, and not the individual inertias, were identified in that previous successful implementation. This work has improved on the mentioned previous work and has identified the individual dynamics parameters without the need of a symbolic dynamics model, thus, avoiding the computationally expensive process in deriving it. In addition, individual dynamics parameters were treated separately. Two experimental procedures are presented: mass and center of mass identification, and inertia identification. In both cases the experimental methods are optimization computations with well-defined objective functions. For the mass and center of mass identification experiment, the correct parameters are identified when the minimum natural frequency of oscillation, min2, is achieved. In the inertia identification experiment, the correct parameters are identified when the square of the natural frequency of oscillations become equal to the proportional gain, 2 = kp. The experimental methods are analyzed and theorems are presented that support the claims presented in this work. These theorems can be used as tools for verification to check the accuracy of a given manipulator dynamics model. In addition, the experimental procedure presented in this work is unique because, to the best of our knowledge, it is only in this work where known dynamics parameters are derived experimentally to verify the accuracy of the proposed experimental procedure. In addition to the dynamics identification procedures, optimization methods using metaheuristic computations are presented in this work, namely, probabilistic artificial neural network, simulated annealing, and modified genetic algorithm. These optimization computations are used in finding the minimum-norm-residual solution to linear systems of equations. By demonstrating a set of input parameters, the objective function and the expected results, solutions are computed for determined, overdetermined, and underdetermined linear systems. This work presented an overview and provide the basic understanding on implementing metaheuristic optimization techniques. In addition, this work has presented a genetic algorithm with a modified approach in terms of reproduction and mutation. Experimental results for randomly generated matrices with increasing matrix sizes are presented and analyzed

Optimization of failure-tolerant workspaces for redundant manipulators

For a redundant manipulator a region in its workspace that is guaranteed failure tolerant, called the failure-tolerant workspace, promises completion of critical tasks placed within it. By judiciously choosing a set of artificial joint limits which constrain the acceptable robot configurations prior to a failure, a failure-tolerant workspace can possibly exist even for manipulators with a single degree of redundancy. This work identifies the candidate boundaries of failure-tolerant workspaces, and presents justification on their validity and competeness. Based on the identified boundaries, optimization results for a 3-degree-of-freedom (dof) planar manipulator, as well as for a 4-dof planar manipulator, are presented. It assumed that the manipulator has the ability to lock a joint that has failed, and that the manipulator\u27s workspace dimension remains the same before and after a joint failure

Full dynamics identification of multi-link inverted pendulum: Analysis and implementation

This work presents a method of identifying the full dynamics parameters of multi-link inverted pendulum, together with its analysis and implementation. It is assumed that each link has an actuated joint whose axis of rotation is different from its center of mass. Thus its driving torque is influenced by gravitational force. This work will utilize the actual force of gravity for the inverted pendulum to achieve a natural oscillation. The oscillatory motion of the pendulum allows the system to be converted into an optimization problem through the minimization of its frequency of oscillation. The correct dynamics parameters are already found when the minimum frequency of oscillation is achieved. The proposed method is analyzed and a theorem is presented that supports the claims presented in this work. And lastly, implementation results are shown

Experimental identification of manipulator dynamics through the minimization of its natural oscillations

This work presents amethod of identifying the dynamics parameters of rigid-body manipulators through the minimization of its natural oscillations. It is assumed that each link has an actuated joint that is different from its center of mass, such that its driving torque is influenced by gravitational force. In this earlier results of our study, it is assumed that the inertias can be expressed in terms of the mass and center of mass. This work utilizes the actual force of gravity for the manipulator link to achieve natural oscillation. The oscillatory motion allows the system to be converted into an optimization problem through the minimization of the frequency of oscillation. The correct dynamics parameters are found when the minimum frequency of oscillation is achieved. The proposed method is analyzed and a theorem is presented that supports the claims presented in this work together with implementation results

A Path Planning Strategy for Kinematically Redundant Manipulators Anticipating Joint Failures in the Presence of Obstacles

This work considers the failure tolerant operation of a kinematically redundant manipulator in an environment containing obstacles. In particular, the article addresses the problem of planning a collision-free path for a manipulator operating in a static environment such that the manipulator can reach its desired goal despite a single locked-joint failure and the presence of obstacles in the environment. A method is presented that searches for a continuous obstacle-free space between the starting configuration and the desired final end-effector position which is characterized in the joint space by the goal selfmotion manifold. This method guarantees completion of critical tasks in the event of a single locked-joint failure in the presence of obstacles

Relative task prioritization for dual-arm with multiple, conflicting tasks: Derivation and experiments

This paper presents new formulations in task-prioritization for dual-arms with multiple, conflicting tasks and experimental validations. An essential part of the proposed method is the use of relative Jacobian that treats the dual-arm as an equivalent single arm. As a result, three formulations are derived. The first formulation, called relative task prioritization, expresses a task prioritization at the acceleration level for a dual-arm, with multiple tasks, that is controlled as a single manipulator. The second formulation is an impedance control equation that allows direct control of the relative motion and impedance between two end-effectors. Our third formulation is a control law that combines relative task prioritization, impedance control, and time-delay estimation, which contributes to the ease of implementation of our proposed method. In the physical implementation, one arm draws a circle on a plate attached to the other arm in parallel with three subtasks. Then, intentional conflict among subtasks is induced. The experimental results show that when such conflict occurs, the higher priority task is guaranteed an immediate execution without influence from the lower priority task. © 2013 IEEE

Failure-tolerant path planning for the PA-10 robot operating amongst obstacles

Includes bibliographical references (page 5000).This work considers kinematic failure tolerance when obstacles are present in the environment. An example is given using a fully spatial redundant robot, the seven degree-of-freedom Mitsubishi PA-10. This article addresses the issue of finding a collision-free path such that a redundant robot can successfully move from a start to a goal position and/or orientation in the workspace despite any single locked-joint failure at any time. An algorithm is presented that searches for a continuous obstacle-free monotonic surface in the configuration space that guarantees the existence of a solution. The method discussed is based on the following assumptions: a robot is redundant relative to its task, only a single locked-joint failure occurs at any given time, the robot is capable of detecting a joint failure and immediately locks the failed joint, and the environment is static and known

Relative Impedance Control for Dual-Arm Robots Performing Asymmetric Bimanual Tasks

This paper presents a method of implementing impedance control (with inertia, damping, and stiffness terms) on a dual-arm system by using the relative Jacobian technique. The proposed method significantly simplifies the control implementation because the dual arm is treated as a single manipulator, whose end-effector motion is defined by the relative motion between the two end effectors. As a result, task description becomes simpler and more intuitive when specifying the desired impedance and the desired trajectories. This is the basis for the relative impedance control. In addition, the use of time-delay estimation enhances ease of implementation of our proposed method to a physical system, which would have been otherwise a very tedious and complicated process. © 2013 IEEE.