Abstract
This study proposed a novel approach for the offline dynamic parameter identification of parallel kinematics mechanisms in which the friction is significant and varying. Since the friction is significant, it should be incorporated to provide an accurate dynamic model. Furthermore, the varying normal forces as a result of the changing posture of the mechanism lead to varying friction forces, specifically varying static and Coulomb friction forces. By considering this variation, the static and Coulomb friction parameters are identified as coefficients instead of forces. A bound-constrained optimization technique using an iterative global search tool was employed in this work to minimize the residual errors while maintaining the physical feasibility of the solutions. Moreover, the friction was modeled by using the nonlinear Stribeck friction model since a linear friction model was not sufficient, whereas the variation of the friction followed the variation of the normal forces, which were evaluated through the Lagrange multipliers in the constrained dynamic model of the mechanism. The solutions obtained were verified by using some trajectories that were different from those used in the identification.
Highlights
The dynamic parameters of a rigid body system typically consist of the inertial and friction parameters
This study investigated the identification of the dynamic parameters of a parallel kinematics mechanism (PKM) by considering nonlinear, varying friction
Table shows the the estimates estimates of the dynamic dynamic parameters, which consisted of the barycentric inertial parameters and the friction parameters
Summary
The dynamic parameters of a rigid body system typically consist of the inertial and friction parameters. In a system where its inertial parameters are very dominant and its friction parameters are relatively very small, the friction parameters can be neglected in the identification. When the friction is significant, one should incorporate it in the dynamics, and include the friction parameters in the identification. An identification usually estimates the inertial parameters as the so-called barycentric parameters, which consist of the masses, the first moments of inertia, and the moments of inertia relative to the origin of the component frames. The moments of inertia relative to the COM can be obtained from the moments of inertia relative to the component frame by utilizing the Huygens–Steiner theorem, which is commonly called the parallel axis theorem
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