Inverse kinematics of a class of 7R 6-DOF robots with non-spherical wrist

Mathematical Problems in Engineering

Zhang

Zhao

2017

The 7R 6-DOF robots with hollow nonspherical wrist have been proven more suitable for spray painting applications. However, the inverse kinematics of this kind of robot is still imperfect due to the coupling between position and orientation of the end-effector (EE). In this paper, a new and efficient algorithm for the inverse kinematics of a 7R 6-DOF robot is proposed. The proposed inverse kinematics algorithm is a two-step method. The geometry of the 7R 6-DOF robot is analyzed. A comparison between the 7R 6-DOF robot and the well-known equivalent 6R robot is made. Based on this comparison, a rational transformation between these two kinds of robots is constructed. Then the general inverse kinematics algorithm of the equivalent 6R robot is applied to calculate the approximate solutions of the 7R 6-DOF robot, in the first step. The Damped Least-Squares (DLS) method is employed to derive the exact solutions, in the second step. The accuracy and efficiency of the algorithm are tested on a 7R 6-DOF painting robot. The results show that the proposed algorithm is more advantageous in the case without an approximate solution, such as the initial point of a continuous trajectory.

Section: New Inverse Kinematics Algorithmmentioning

confidence: 99%

Section: Simulationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Inverse Kinematics of a 7R 6‐DOF Robot with Nonspherical Wrist Based on Transformation into the 6R Robot

Mathematical Problems in Engineering

Zhang

Zhao

2017

“…13 The orientation mechanism determines the terminal posture, while the positioning mechanism determines the reachable workspace. Wu et al 14 proposed the concept of "virtual wrist center" for non-orthogonal spraying robots and simplified the reachable workspace analysis. The geometry method is intuitive, simple to operate, and easy to understand with good precision, which is adopted in the following analysis.…”

Section: Introductionmentioning

confidence: 99%

Analysis of flexible supported industrial robot on terminal accuracy

International Journal of Advanced Robotic Systems

Chen

Shao

et al. 2018

To meet comprehensive performance requirements of large workspace, lightweight, and low energy consumption, and flexible supported industrial robots emerge, which are usually composed of a six-degrees-of-rotational-freedom (6R) industrial robot and a flexible support. Flexible support greatly expands the motion range of the attached industrial robot. Flexible supported industrial robots have been adopted in surface coating of large structures such as aircrafts and rockets. However, the rigid-flexible coupling exists in these robot systems. When the industrial robot moves, the reaction force and torque of the robot disturb the flexible support and introduce vibration, which may result in the deterioration of the system's terminal accuracy. This study focuses on both the robot body accuracy and system vibration suppression to improve the terminal accuracy of the flexible supported industrial robot. Firstly, based on kinematics analysis, accuracy of the industrial robot is investigated with the local conditioning index. Then, reaction force and torque ellipsoids are proposed with the deduced dynamic model to evaluate disturbances that the industrial robot applies to the flexible support. Considering these two aspects, the high-quality workspace of the flexible supported industrial robot is established. Numerical simulations show that reaction force and torque are effectively limited in the high-quality workspace, which greatly reduce the vibration energy and improve the terminal accuracy of the system.

“…However, the problem is that these methods are limited to 6R robots. For the 7R 6-DOF robot, Wu et al 9 proposed a two-step method: the approximate analytical solutions are first derived through solving the 7R robot with spherical wrist by introducing a virtual wrist center, and the Levenberg-Marquardt (LM) method is used to calculate the exact solutions. This is an interesting approach, but a complex polynomial system needs to be solved in the first step which is time consuming.…”

Section: Introductionmentioning

confidence: 99%

The inverse kinematics of a 7R 6-degree-of-freedom robot with non-spherical wrist

Advances in Mechanical Engineering

Zhang

Zhao

2017

The 7R 6-degree-of-freedom robots with hollow non-spherical wrist have been proven more suitable to spray painting. However, the inverse kinematics of this robot is still imperfect due to the coupling between position and orientation of the end-effector. In this article, a reliable numerical iterative algorithm for the inverse kinematics of a 7R 6-degree-offreedom robot is proposed. Based on the geometry of the robot, the inverse kinematics is converted into a onedimensional iterative research problem. Since the Jacobian matrix is not utilized, the proposed algorithm possesses good convergence, even for singular configurations. Moreover, the multiple-solution problem in the inverse kinematics is also discussed. By introducing three robot configuration indicators which are prespecified by a user, the correct solution could be chosen from all the possible solutions. In order to verify the accuracy and efficiency of the proposed algorithm, several simulations are implemented on a practical 7R 6-degree-of-freedom painting robot. The result shows that the proposed algorithm is more advantageous for a continuous trajectory.