Robot Control near Singularity and Joint Limit Using a Continuous Task Transition Algorithm (original) (raw)
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A continuous task transition algorithm for operational space control framework
2012 9th International Conference on Ubiquitous Robots and Ambient Intelligence (URAI), 2012
As more sophisticated robots are being developed, robots are increasingly expected to execute many types of task sets sequentially or simultaneously. When these multiple task sets are executed, the controllers of the robots should be able to deal dynamically with task changes. Especially during the task transitions, there will be discontinuous behaviors of robots in the absence of careful consideration of control. In this paper, a task transition approach is proposed to provide continuous task transitions and to ensure stable behavior of robots within the operational space control framework. In the proposed approach, the control law is not modified but the control command is composed using intermediate desired values. In this paper, a continuous task transition algorithm is applied for singularity avoidance and for joint limit avoidance purposes during the control of a 6-DOF manipulator to demonstrate its performance.
Manipulator control at kinematic singularities: a dynamically consistent strategy
This paper presents a general strategy for manipulator control at kinematic singularities. When a manipulator is in the neighborhood of singular configurations, it is treated as a redundant mechanism in the subspace orthogonal to the singular directions of the end-effector. Control in this subspace is based on operational forces, while null space joint torques are used to deal with the control in the singular directions. Decoupled behavior is guaranteed by using the dynamically consistent force/torque relationship. Two different types of kinematic singularities are identified and strategies dealing with these singularities are developed. Experimental results of the implementation of this approach on a PUMA 560 manipulator are presented
A general singularity avoidance framework for robot manipulators: task reconstruction method
IEEE International Conference on Robotics and Automation, 2004. Proceedings. ICRA '04. 2004, 2004
There are several kinds of singularity in controlling robotic manipulator. Among those, the kinematic and algorithmic singularity avoidance have been investigated intensively. What seems to be lacking, however, is excessive performance reduction in non-singular region and difficulty in performance tuning. In this paper, we develop a new method to solve kinematic and algorithmic singularities using task reconstruction approach. This new method drives the manipulator singularity-free path, and simultaneously guarantees task performance. And it can be easily extended singularity avoidance of multiple tasks case in task priority based method of redundant manipulators. The advantage and performance of the proposed method is validated by simulation works.
A singularity-free motion control algorithm for robot manipulators—a hybrid system approach
Automatica, 2004
This paper presents the design and implementation of a singularity-free tracking algorithm for robot manipulators using a hybrid system approach. A hybrid robot motion controller is designed to ensure feasible robot motion in the neighborhood of kinematic singularities. The hybrid control system has a two-layered hierarchical structure, a discrete layer and a continuous layer. The robot workspace is partitioned into subspaces based on the singular conÿgurations of the robot. Switching between continuous controllers is involved when the robot travels across the subspaces. With the hybrid controller, the robot can work at the vicinity of singular conÿgurations, but also can go through and stay at the singular conÿgurations. The stability of the hybrid system is investigated using multiple Lyapunov function theory. Experimental results have demonstrated the advantages of the hybrid robot motion control method. ?
Many Faces of Singularities in Robotics
Pomiary Automatyka Robotyka
In this survey paper some issues concerning a singularity concept in robotics are addressed. Singularities are analyzed in the scope of inverse kinematics for serial manipulator, a motion planning task of nonholonomic systems and the optimal control covering a large area of practical robotic systems. An attempt has been made to define the term singularity, which is independent on a specific task. A few classifications of singularities with respect to different criteria are proposed and illustrated on simple examples. Singularities are analyzed from a numerical and physical point of view. Generally, singularities pose some problems in motion planning and/or control of robots. However, as illustrated on the example on force/momenta transformation in serial manipulators, they can also be desirable is some cases. Singularity detection techniques and some methods to cope with them are also provided. The paper is intended to be didactic and to help robotic researchers to get a general vie...
Singularity Robust Manipulator Control using Virtual Joints
2002
A singularity handling method is proposed in this paper. It is done by introducing virtual redundant joints into the Jacobian matrix to maintain the rank of the Jacobian matrix when singularity occurs. These additional joints do not exist physically. Therefore, although mathematically stable, the manipulator still can not perform tasks in the degenerate direction(s). This method is comparatively straight forward to implement and it does not have a singular subspace defined within which a special and different control algorithm is performed, thus it avoids the problem associated with discontinuous control or switching of control. The method was tested on simulation and implemented in real-time on the PUMA 560 robot. 2418 0-7803-7272-7/02/$17.00
A framework for the analysis and control of manipulator systems with respect to the dynamic behavior of their end-effectors is developed. First, issues related to the description of end-effector tasks that involve constrained motion and active force control are discussed. The fundamentals of the operational space formulation are then presented, and the unified approach for motion and force control is developed. The extension of this formulation to redundant manipulator systems is also presented, constructing the end-effector equations of motion and describing their behavior with respect to joint forces. These results are used in the development of a new and systematic approach for dealing with the problems arising at kinematic singularities. At a singular configuration, the manipulator is treated as a mechanism that is redundant with respect to the motion of the end-effector in the subspace of operational space orthogonal to the singular direction.
Robot control in the neighborhood of singular points
IEEE Journal on Robotics and Automation, 1988
In this paper, we propose an alternative method for designing a robot controller in Cartasian coordinates using a timescale transformation. The proposed controller achieves slow poles in the area of poor manipulative ability and fast poles in the area of good manipulative ability. Thus we can properly control the robot in the neighborhood of singular points without reducing the performance outside the neighborhood of these points.
Dynamic task priority approach to avoid kinematic singularity for autonomous manipulation
IEEE/RSJ International Conference on Intelligent Robots and System, 2002
In this paper, we describe an on-line trajectory control scheme for robotic manipulators with dynamic change of the task priority. First, given tasks are reconstructed using a geometric projection on the given index function. Then, the reconstructed tasks are analyzed in the framework of task priority based method. From this analysis, the proposed algorithm is shown to have the property that the task priority is assigned dynamically. Using this algorithm, we easily set the criteria of changing task priority and estimate the performance of the given index function. Considering the measure of manipulability as a index function, the approach is suitable for avoiding kinematic singularities for autonomous operation of, for example, underwater robot. The result shows a good performance near the singular configurations, as shown by simulation results.
Design of a controller for enlarging parallel robots workspace through Type 2 singularity crossing
2014 IEEE International Conference on Robotics and Automation (ICRA), 2014
In order to increase the workspace size of parallel robots (largely reduced by the presence of singularities) several solutions have been proposed. One promising solution consists in the definition of optimal trajectories that ensure the non degeneracy of the dynamic model in the singularity and therefore are able to cross the Type 2 singularities. Those works are based on the computation of the optimal trajectories and assume that the robot can perfectly track the desired trajectory. Nevertheless, this assumption cannot be verified in reality due to modelling errors which largely impact the control law used to follow the desired trajectory. Therefore, if the optimal trajectory is not perfectly tracked, the dynamic model can degenerate near the Type 2 singularities and the robot might stay blocked. In order to solve that problem, this paper proposes a multimodel approach that allows parallel robots to cross the Type 2 singularities without any torque discontinuity. The main idea is to shift near singularities from the full robot dynamic model to another simplified one that can never degenerate. The proposed control law is then coupled with an optimal trajectory planning methodology that makes the singularity crossing more robust to modelling errors. The proposed approach is validated experimentally on a prototype of Five-bar planar parallel mechanism.