Experiments with Force Control of Redundant Robots in Unstructured Environment Using Minimal Null-space Formulation

2001 ◽  
Vol 5 (5) ◽  
pp. 263-268
Author(s):  
Bojan Nemec ◽  
◽  
Leon Zlajpah Institute Jozef Stefan
Keyword(s):  
Force Control ◽  
Null Space ◽  
Robot Arm ◽  
End Effector ◽  
Redundant Robots ◽  
Unstructured Environment ◽  
Space Formulation ◽  
Null Space Approach ◽  
Selection Of ◽  
Space Approach

The paper describes the implementation of the force control for redundant robots in an unstructured environment. We assume that the obstacles are not known in advance. Hence, the robot arm has to be compliant with the environment while tracking the desired position and force at the end effector. Using the minimal null space approach the appropriate impedance controller, which decouples the end effector and the null space spaces was derived. The control algorithm enables the selection of dynamic characteristics in both subspaces independently.The proposed method was verified with the simulation and with experiments on a 4 D.O.F planar redundant robot.

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 Compliant behaviour of redundant robot arm - experiments with null-space

2015 ◽  
Vol 12 (1) ◽  
pp. 81-98
Author(s):  
Petar Petrovic ◽  
Nikola Lukic ◽  
Ivan Danilov
Keyword(s):  
Stiffness Matrix ◽  
Jacobian Matrix ◽  
Null Space ◽  
Joint Space ◽  
Robot Arm ◽  
Kinematic Redundancy ◽  
Redundant Robot ◽  
Redundant Robots ◽  
Compliant Behavior ◽  
Congruent Transformation

This paper presents theoretical and experimental aspects of Jacobian nullspace use in kinematically redundant robots for achieving kinetostatically consistent control of their compliant behavior. When the stiffness of the robot endpoint is dominantly influenced by the compliance of the robot joints, generalized stiffness matrix can be mapped into joint space using appropriate congruent transformation. Actuation stiffness matrix achieved by this transformation is generally nondiagonal. Off-diagonal elements of the actuation matrix can be generated by redundant actuation only (polyarticular actuators), but such kind of actuation is very difficult to realize practically in technical systems. The approach of solving this problem which is proposed in this paper is based on the use of kinematic redundancy and nullspace of the Jacobian matrix. Evaluation of the developed analytical model was done numerically by a minimal redundant robot with one redundant d.o.f. and experimentally by a 7 d.o.f. Yaskawa SIA 10F robot arm.

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.

scholarly journals A Fuzzy Backstepping Control of a Mobile Manipulator with Torque Limits Avoidance

1970 ◽  
Vol 5 (2) ◽  
pp. 127-133
Author(s):  
Mohamed Boukattaya ◽  
Tarak Damak ◽  
Mohamed Jallouli
Keyword(s):  
Control Algorithm ◽  
Null Space ◽  
Joint Torque ◽  
Mobile Manipulator ◽  
Redundancy Resolution ◽  
Task Space ◽  
End Effector ◽  
Simulation Results ◽  
Pseudo Inverse ◽  
Selection Of

In this paper, we present a dynamic redundancy resolution technique for mobile manipulator subject to joint torque limits. First, the dynamic model of the mobile manipulator in feasible motion space is given. Next, a control algorithm is proposed which completely decouples the motion of the system into the end-effector motion in the task space and an internal motion in the null space and controls them in prioritized basis with priority given to the primary task space and enables the selection of characteristics in both subspaces separately. A special attention is given to the joints torque limits avoidance where a new weighted pseudo-inverse of the Jacobian that accounts for both inertia and torque limits is proposed to solve problems inherent to torque limits of the system. Simulation results are given to illustrate the coordination of two subsystems in executing the desired trajectory without violating the joint torque limits.

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