پلت فرم کنترل میکروارتعاشات برای تجهیزات با فناوری پیشرفته در معرض حرکت زمین ناشی از ترافیک

This paper investigates the possibility of using a microvibration control platform to isolate a batch of high tech equipment from the floor of a building subject to nearby traffic-induced ground motion. The governing equation of motion of the coupled platform–building system is derived in the absolute coordinate to facilitate the feedback control and performance evaluation of the platform based on the BBN vibration criteria with the absolute velocity being targeted. A hybrid control system composed of passive mounts and active hydraulic actuators with a sub-optimal control algorithm is designed to actively control the platform. Hydraulic actuator dynamics are also considered in the modelling of the control system to avoid possible instability of the platform. The performance of actively controlled platform is assessed through comparisons with the cases of the building without control, the building with passively controlled platform, and the building with passive base isolator. Simulation results indicate that passively controlled platform and passive base isolator can be effective in reducing microvibration of high tech equipment if their parameters are properly selected. The actively controlled platform is superior to the passively controlled platform and passive base isolator because of its high performance and robustness.

High tech equipment, such as that used for the production of semiconductors, integrated circuits, optical microscopes, and laser research systems, requires the building floor, on which the high tech equipment is installed, with extremely limited vibrations. For instance, the Bolt Beranek and Newman (BBN) vibration criteria [1] and [2] for high tech equipment take the form of a set of one-third octave band velocity spectra labelled with vibration criterion curves from VC-A to VC-E, which correspond to the allowable root mean square (rms) velocity descending from 50 to 3 μm/s within a frequency range between 8 and 80 Hz. This stringent microscale velocity restriction makes the control of microvibration of high tech equipment inside a building subject to traffic-induced ground motion different from the control of seismic response of building structures. Using passive mounts (spring-damper systems) to isolate individual high tech equipment from floor vibration is a very common practice. However, microvibration reduction level using passive mounts is always limited due to the nature of passive control, and sometime there may be potential problems with static stability of equipment if passive mounts are too soft. To overcome this problem, hybrid control by coupling active actuators with passive mounts has recently been investigated by taking floor vibration as a direct base excitation [3], [4] and [5]. Dynamic interaction between the hybrid control and the building, however, is not considered. Though this treatment may be adequate for a large building with limited amount of high tech equipment, it may not be sufficient and economic for a large building with a great amount of high tech equipment as evidenced in many modern high tech facilities. Recently, Yang and Agrawal [6] carried out an extensive theoretical study on the possible use of various protective systems for microvibration control of high tech facilities under horizontal traffic-induced ground motion in consideration of dynamic interaction between control and building. The protective systems they investigated included passive building base isolation, hybrid building base isolation, passive floor isolation, hybrid floor isolation, passive energy dissipation system, and active control system. They concluded that hybrid floor isolation could be the most effective and practical means in satisfying the design specification for microvibration of high tech equipment. Since the governing equation of motion of the building with protective systems was established in terms of relative motion to the ground in their investigation, the controller was designed based on the drift and relative velocity of the floor. The use of relative velocity as feedback to control the absolute velocity of the floor may not be consistent. This paper aims to investigate the possibility of using a microvibration control platform to isolate a batch of high tech equipment from the floor of a building subject to nearby traffic-induced horizontal ground motion. The governing equation of motion of the coupled platform–building system is derived in the absolute coordinate to facilitate the feedback control and performance evaluation of the platform based on the BBN vibration criteria with the absolute velocity being targeted. A hybrid control system composed of passive mounts and actively controlled hydraulic actuators with a sub-optimal control algorithm is designed to actively control the platform. Hydraulic actuator dynamics are also considered in the modelling of the control system to avoid possible instability of the platform. The performance of actively controlled platform is assessed through comparisons with the cases of the building without control, the building with passively controlled platform, and the building with passive base isolator.

Using an actively controlled platform to isolate a batch of high tech equipment from the floor of a building subject to train-induced horizontal ground motion has been investigated. The actively controlled platform is installed on the building floor through passive mounts and actively controlled hydraulic actuators with sub-optimal control algorithms. The governing equation of motion of the coupled platform–building system, including actuator dynamics, has been established in the absolute coordinate to facilitate the feedback control and the performance evaluation of the platform based on the BBN vibration criteria. Extensive computer simulations were carried out on a three-storey high tech facility to assess the control performance of actively controlled platform. The simulation results show that passive building base isolation can reduce the microvibration of all types of high tech equipment to the allowable level specified in the BBN vibration criteria only when the frequency of the base isolator storey is less than 0.6 Hz. Such a low frequency requirement may be difficult to be implemented in practice or it may cause excessive drift of the building. The passively controlled platform can be effective in reducing the microvibration of all types of high tech equipment to the allowable level when the platform frequency is below 1.6 Hz. The actively controlled platform can, however, achieve high control performance within a wide range of platform frequency and damping ratio. It is superior to the passively controlled platform and the passive building base isolation in terms of its high performance and robustness. The computation results also demonstrated that the coupling effect depended on the stiffness of the building storey and the natural frequency of the platform. In general, the smaller is the stiffness of the building storey or the larger is the natural frequency of the platform, the greater is the coupling effect. It should be pointed out that the above conclusions were drawn from the given building and platform only. More investigations are needed in order to have a full understanding of the concerned subject.