Modeling and feed-forward control design of flexible multibody systems with environment contact
Light-weight machine designs are becoming more and more important. This is due to increasing demands for energy efficiency and higher working speeds. However, this often yields undesirable elastic vibrations. If these machines have to perform large working motion, they must be modeled using the method of flexible multibody system dynamics. Also in many practical applications the contact between machines and their environment is becoming increasingly more important. Therefore, this project is aimed at modeling, inversion-based feed-forward control and trajectory control of flexible multibody systems with environment contact. In the first project phase a unified approach was developed for feed-forward control of flexible multibody systems with kinematic loops, permanently closed contacts and trajectory tracking. Thereby, a model inversion method based on so-called servo-constraints has been proven to be most suitable. Based on these encouraging results of the first funding period, the models and methods should be further developed in the second funding period such that an efficient usage in real applications is possible. Besides mythological improvements and numerical tests, selected experimental investigations should also be performed. Therewith the practical applicability of the developed models and methods will be demonstrated. A first goal of the second funding period is the improvement of the numerical efficiency of the boundary value solver for the model inversion. Thus, also for larger problems, a fast feed-forward control computation should become possible. For midsize problems computation times in the magnitude of the real time of the predefined trajectory are sought. The second goal is the improvement of the model accuracy, especially concerning friction modeling as well as an extension to opening and closing of the contact. This yields in both cases non-smooth models, and thus the developed solver of the inverse models must be modified. A third focal point is the combination of the feed-forward control with additional feedback control. Thus, also external disturbances in the elastic coordinates can be controlled. Such disturbances can be vibrations which are caused by friction at the contact point or vibrations excited when the contact closes. This project seeks to establish an output feedback control approach for the control task. Thereby, using strain gauges the curvature of the flexible bodies is measured. These are then compared with desired curvatures which are determined in the inverse model and feed back to the joint actuators. Further, the possibility of combing such a control concept with contact force measurements should be investigated. Final points of the second project phase are numerical and experimental validation of the develop methods using an existing flexible parallel kinematics.