| dc.description.abstract | In high-tech factories, the equipment is generally characterized by higher natural frequencies and be considered as rigid equipment. To reduce the impact of micro-vibrations, passive isolator is installed underneath. This transforms the system into non-rigid equipment. This study explores the application of skyhook active control to both rigid and non-rigid equipment to form Single-Degree-of-Freedom and Two-Degree-of-Freedom skyhook active isolation systems. This study derives the motion equations and designs skyhook isolation algorithm. It also considers the restraint of isolation stroke to build the stroke limiting control law. Through conducting numerical simulations and performing experimental verification, the feasibility of the proposed algorithms is ensured. In traditional skyhook control theory, control force is calculated by the absolute velocity feedback of isolation platform and skyhook damping coefficient. Moreover, greater skyhook damping coefficient could get smaller absolute acceleration response. To improve the theory, control force is adjusted to be calculated by the relative velocity feedback between isolation platform and ground, along with the ground acceleration integrated and filtered to obtain ground velocity feedforward. This modification not only considers the influence by inherent damping of isolation platform but also enhances the convenience and stability of signal measurement. Parameters of preselected integral filter are introduced and integrated into skyhook active isolation system, so the performance and concern of the stability issue can be ensured during optimization design. The control force is not full-state feedback, so it utilizes continuous-time direct output feedback and parameter iteration to obtain the optimal gain parameter which minimizes the absolute acceleration of equipment. Furthermore, considering the restraint on isolation stroke, the ground velocity gain parameter can be arranged according to gain scheduling to limit the stroke. To understand the characteristics of skyhook active isolation system applied to rigid equipment, the control effect is discussed through various simulation analysis. The characteristic analysis show that the system pole positions can move away from the primary seismic excitation frequencies after applying the control force, thereby reducing the possibility of resonance due to earthquake. The relative velocity gain parameter can raise the damping ratio of isolation platform and make the system highly over-damped. The over-damped system is less likely to be excited by non-seismic forces and highly likely to maintain stationary during peacetime. In frequency response and time history analysis, skyhook active isolation system outperforms passive isolation system in terms of reducing the absolute acceleration of equipment. Regarding the sensitivity analysis of equipment mass variation, the results show that the control force and movement of non-rigid equipment are sensitive to mass variation. The stability analysis confirms that changing the relative velocity gain parameter will change the system poles position. It requires to consider the stability of the system when the relative velocity gain is changed. However, changing the ground velocity gain parameter does not affect stability that verifies the feasibility of the proposed ground velocity gain scheduling. To consider the time delay effect, various time delays are incorporating into the system to calculate the modal damping ratio, the duration of maximum time delay of the system can be analyzed. By designing stroke restraint control law based on the limitation of the stroke, skyhook active isolation system exhibits reduced isolation stroke while retaining partial isolation functionality in time history analysis. Skyhook active isolation system for non-rigid equipment reaches similar conclusions as with rigid equipment in all simulation analyses. To demonstrate the effectiveness and feasibility of proposed algorithms for achieving both isolation and stroke protection, shaking table experiments are conducted on linear servo slider with rigid and non-rigid equipment. The experimental results show that skyhook active isolation system exhibits excellent isolation effects under the seismic waves, especially the stroke is protected by considering the stroke restraint control law.
Keywords: skyhook control, active isolation, base acceleration integral feedforward, direct output feedback, shaking table experiment, stroke restraint, gain scheduling. | en_US |