Rodrigo S. Jamisola

Failure-tolerant path planning for kinematically redundant manipulators anticipating locked-joint failures

This work considers kinematic failure tolerance when obstacles are present in the environment. It 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 simply-connected, obstacle-free surface with no internal local minimum or maximum 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. The technique is illustrated on a seven degree-of-freedom commercially available redundant robot. Although developed and illustrated for a single degree of redundancy, it is possible to extend the algorithm to higher degrees of redundancy

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.

Compliant motion using a mobile manipulator: an operational space formulation approach to aircraft canopy polishing

The operational space formulation provides a framework for the analysis and control of robotic systems with respect to interactions with their environments. In this paper, we discuss its implementation on a mobile manipulator programmed to polish an aircraft canopy with a curved surface of unknown geometry. The polishing task requires the robot to apply a specified normal force on the canopy surface while simultaneously performing a compliant motion keeping the surface of the grinding tool tangentially in contact with the workpiece. A human operator controls the mobile base via a joystick to guide the polishing tool to desired areas on the canopy surface, effectively increasing the mobile manipulators reachable workspace. The results demonstrate the efficacy of compliant motion and force regulation based on the operational space formulation for robots performing tasks in unknown environments with robustness towards base motion disturbances. The mobile manipulator consists of a PUMA 560 arm mounted on top of a Nomad XR4000 mobile base. Implementation issues are discussed and experimental results are shown.

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 self-motion manifold. This method guarantees completion of critical tasks in the event of a single locked-joint failure in the presence of obstacles.

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

This work considers kinematic failure tolerance when obstacles are present hi 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 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.

Guaranteeing task prioritization for redundant robots given maximum number of tasks and singularities

This paper evaluates the effectiveness of a proposed task-prioritization scheme for redundant robots. The scheme has an advantage of a non-inverse computation of the projection matrix. This feature is important because the projection matrix for redundant robots is singular all the time, except when the Jacobian is zero. The evaluation is based on how task prioritization is managed through singularities, despite carrying out maximum load of task requirements. In particular, the redundant robot should be able to: (1) utilize the lost degree of freedom in the world space for the newly prioritized singularity-escape task in the null space, (2) set this new task as the highest-priority task in the null space, and (3) maintain the hierarchy of task prioritization of the previously assigned tasks. To proceed with the evaluation, we first established the maximum number of prioritized tasks that a given redundant robot can accommodate. Then we assigned this maximum number of tasks on the robot, forced it to assume a singular configuration, and evaluated its task prioritization performance. This scenario is very useful when singularity cannot be avoided during task execution, e.g., avoiding obstacles in the null space such that the robot is forced to assume a singular configuration while fully loaded with prioritized tasks.

Integration of Torque Controlled Arm with Velocity Controlled Base for Mobile Manipulation

A mobile manipulation system often involves combining more than one robot together, typically a manipulator arm and a mobile base. To implement force and motion control with dynamic compensation, a torque-controlled system is necessary. However, a torque-controlled robot is not always available. In fact, most commercially available mobile bases are velocity-controlled. This paper presents a method for combining a torque-controlled arm and a velocity-controlled base, while performing a force and motion task. The operational space formulation using a consistent set of integrated arm-base robot dynamics is employed in a mobile manipulation task of polishing an aircraft canopy. The torque controlled arm compensates for the dynamics introduced by the mobile base. The added mobility of the base enables the arm to cover the entire workspace.