Incremental kinesthetic teaching of end-effector and null-space motion primitives

2015 ◽  
Author(s):  
Matteo Saveriano ◽  
Sang-ik An ◽  
Dongheui Lee
Keyword(s):  
Null Space ◽  
End Effector ◽  
Motion Primitives ◽  
Space Motion

scholarly journals An Efficient Stochastic Constrained Path Planner for Redundant Manipulators

2021 ◽  
Vol 11 (22) ◽  
pp. 10636
Author(s):  
Arturo Gil Gil Aparicio ◽  
Jaime Valls Valls Miro
Keyword(s):  
Null Space ◽  
Redundant Actuation ◽  
Redundant Manipulators ◽  
Optimal Solutions ◽  
Task Space ◽  
Efficient Manner ◽  
End Effector ◽  
Space Motion ◽  
Manipulability Measure ◽  
Path Planner

This brief proposes a novel stochastic method that exploits the particular kinematics of mechanisms with redundant actuation and a well-known manipulability measure to track the desired end-effector task-space motion in an efficient manner. Whilst closed-form optimal solutions to maximise manipulability along a desired trajectory have been proposed in the literature, the solvers become unfeasible in the presence of obstacles. A manageable alternative to functional motion planning is thus proposed that exploits the inherent characteristics of null-space configurations to construct a generic solution able to improve manipulability along a task-space trajectory in the presence of obstacles. The proposed Stochastic Constrained Optimization (SCO) solution remains close to optimal whilst exhibiting computational tractability, being an attractive proposition for implementation on real robots, as shown with results in challenging simulation scenarios, as well as with a real 7R Sawyer manipulator, during surface conditioning tasks.

Cooperation and Null-Space Control of Networked Omni-Directional Mobile Manipulators

2020 ◽  
Author(s):  
Michael John Chua ◽  
Yen-Chen Liu
Keyword(s):  
Degrees Of Freedom ◽  
Null Space ◽  
Kinematic Model ◽  
Mobile Manipulator ◽  
Main Task ◽  
Mobile Manipulators ◽  
Robot Arm ◽  
Task Space ◽  
End Effector ◽  
Mobile Base

Abstract This paper presents cooperation and null-space control for networked mobile manipulators with high degrees of freedom (DOFs). First, kinematic model and Euler-Lagrange dynamic model of the mobile manipulator, which has an articulated robot arm mounted on a mobile base with omni-directional wheels, have been presented. Then, the dynamic decoupling has been considered so that the task-space and the null-space can be controlled separately to accomplish different missions. The motion of the end-effector is controlled in the task-space, and the force control is implemented to make sure the cooperation of the mobile manipulators, as well as the transportation tasks. Also, the null-space control for the manipulator has been combined into the decoupling control. For the mobile base, it is controlled in the null-space to track the velocity of the end-effector, avoid other agents, avoid the obstacles, and move in a defined range based on the length of the manipulator without affecting the main task. Numerical simulations have been addressed to demonstrate the proposed methods.

scholarly journals A singularity handling algorithm based on operational space control for six-degree-of-freedom anthropomorphic manipulators

2019 ◽  
Vol 16 (3) ◽  
pp. 172988141985891
Author(s):  
Zhi-Hao Kang ◽  
Ching-An Cheng ◽  
Han-Pang Huang
Keyword(s):  
Null Space ◽  
Singularity Analysis ◽  
Degree Of Freedom ◽  
Control Input ◽  
Real Time Control ◽  
Time Control ◽  
Operational Space ◽  
Industrial Manipulators ◽  
Space Motion ◽  
Six Degree Of Freedom

In this article, we analyze the singularities of six-degree-of-freedom anthropomorphic manipulators and design a singularity handling algorithm that can smoothly go through singular regions. We show that the boundary singularity and the internal singularity points of six-degree-of-freedom anthropomorphic manipulators can be identified through a singularity analysis, although they do not possess the nice kinematic decoupling property as six-degree-of-freedom industrial manipulators. Based on this discovery, our algorithm adopts a switching strategy to handle these two cases. For boundary singularities, the algorithm modifies the control input to fold the manipulator back from the singular straight posture. For internal singularities, the algorithm controls the manipulator with null space motion. We show that this strategy allows a manipulator to move within singular regions and back to non-singular regions, so the usable workspace is increased compared with conventional approaches. The proposed algorithm is validated in simulations and real-time control experiments.

On-line multi-criteria based collision-free posture generation of redundant manipulator in constrained workspace

Robotica ◽  
2002 ◽  
Vol 20 (6) ◽  
pp. 625-636 ◽  
Author(s):  
Jin-Liang Chen ◽  
Jing-Sin Liu ◽  
Wan-Chi Lee ◽  
Tzu-Chen Liang
Keyword(s):  
Null Space ◽  
Large Degree ◽  
Redundancy Resolution ◽  
Secondary Tasks ◽  
End Effector ◽  
Robotic Arms ◽  
Tracking Motion ◽  
On Line ◽  
Joint Limits ◽  
Joint Velocity

The manipulator with a large degree of redundancy is useful for realizing multiple tasks such as maneuvering the robotic arms in the constrained workspace, e.g. the task of maneuvering the end-effector of the manipulator along a pre-specified path into a window. This paper presents an on-line technique based on a posture generation rule to compute a null-space joint velocity vector in a singularity-robust redundancy resolution method. This rule suggests that the end of each link has to track an implicit trajectory that is indirectly resulted from the constraint imposed on tracking motion of the end-effector. A proper posture can be determined by sequentially optimizing an objective function integrating multiple criteria of the orientation of each link from the end-effector toward the base link as the secondary task for redundancy resolution, by assuming one end of the link is clamped. The criteria flexibly incorporate obstacle avoidance, joint limits, preference of posture in tracking, and connection of posture to realize a compromise between the primary and secondary tasks. Furthermore, computational demanding of the posture is reduced due to the sequential link-by-link computation feature. Simulations show the effectiveness and flexibility of the proposed method in generating proper postures for the collision avoidance and the joint limits as a singularity-robust null-space projection vector in maneuvering redundant robots within constrained workspaces.

Null space velocity control with dynamically consistent pseudo-inverse

Robotica ◽  
2000 ◽  
Vol 18 (5) ◽  
pp. 513-518 ◽  
Author(s):  
Bojan Nemec ◽  
Leon Zlajpah
Keyword(s):  
Physical Meaning ◽  
Null Space ◽  
Space Velocity ◽  
Velocity Control ◽  
Redundant Manipulator ◽  
Projection Technique ◽  
Space Motion ◽  
Pseudo Inverse ◽  
Globally Stable ◽  
Good Behaviour

Null space velocity control is essential for achieving good behaviour of a redundant manipulator. Using the dynamically consistent pseudo-inverse, the task and null space motion and forces are decoupled. The paper presents a globally stable null space velocity controller and the gradient projection technique in conjunction with the dynamically consistent pseudo-inverse. The physical meaning and influence of the compensation terms in null the space velocity controller are explained. The performance of the proposed null space controller is tested on 4. d.o.f planar redundant manipulator interacting with the environment.

Force Compensating Trajectories for Redundant Robots: Experimental Results

2009 ◽  
Vol 21 (1) ◽  
pp. 104-112
Author(s):  
Daniela Vassileva ◽  
◽  
George Boiadjiev ◽  
Haruhisa Kawasaki ◽  
Tetsuya Mouri ◽  
...  
Keyword(s):  
Configuration Space ◽  
Null Space ◽  
End Effector ◽  
New Approach ◽  
Working Zone ◽  
Redundant Robots ◽  
Control Schemes ◽  
Position And Orientation ◽  
Pseudo Inverse ◽  
Eigenvectors And Eigenvalues

We proposed a new approach for redundant robots trajectories planning, based on the Null space (or Kernel) features. The Null space (Kernel) exists only in the case of redundant robots and it describes these joints motion which do not affect the robot end-effector motion in the sense of both position and orientation. Based on this “hidden motion” realized in the configuration space, which does not affect the motion in the working zone, we can control independently the robot end-effector position and orientation motions, or just maintain its state while some external force is applied to it. The proposed control strategy is simple, no additional penalty functions are used to restraint the end-effector motion as in the case of the conventional methods. No pseudo inverse kinematics calculations are required; the desired trajectories are generated directly in the configuration space. No complicated control schemes are introduced, the proposed method is based on solving algebraic systems of equations and finding eigenvectors and eigenvalues. In the paper the results from simulations and experiments based on the proposed method are presented and discussed.

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