Shockproof Experimental Study of Automated Stocker System in the High-Tech Factory ()
1. Introduction
1.1. Background and Motivation of the Study
The Science Park is the country’s economic arteries (Hsiao, Pei-Fang, 2005) [1]. Because Taiwan is located on circum-Pacific seismic belt, one of the highly frequent seismic areas, the amount of investment in high-tech industrial equipments is usually really extremely; a single process equipment may cost over 3 million US dollars. Therefore, in the high-tech industries, from the stand points on operating and cost in business, equipment for seismic assessment should be given high priority [2]. To prevent potential serious damage caused by earthquake, the main process equipment and production lines are required to improve seismic design in the structure of the system. In order to ensure that Taiwan’s high-tech Industry obtain satisfactory shockproof process equipment in dealing with earthquakes, the plants are requested to research and develop sustainable technology [3]. Therefore, the various high-tech industries are actively involved in issues of shockproof.
1.2. Literature Review
Different from traditional architecture, the special demand for the constructional structure of the high-tech factories not only requires stringent structural seismic safety, but also provides substantial prevention from micro vibration harm in the clean room of manufacturing environment [4].
With the high-tech industry continuing to rise, the increasing demands in manufacturing process are also facing new challenges in display industry. The most obvious changes are the increasing size of the glass panel, a single equipment size increasingly became larger and its function more complex. The facts in various equipment manufacturing process, complex construction and enormous numbers can cause impact on the baseline assessments of the equipment seismic demand (Chen, Chang-Liang, 2008) [5].
The Automated Material Handling System, AMHS, is the central system to reach manufacture process automation. The clean room stocker is one of important components in display factory. The automation Stocker System was shown in Figure 1, Lin, Kun-Bin (2007) [6].
The system is able to use stocker space efficiently by using computer online system to realize automated control manufacture, and continue to check the expired or overdue inventorial products. It can prevent poor inventory and improve management efficiency, as well, shorten producing time and reduce the operating cost. The AMHS application has become the main-stream in display factory.
Due to the nature of aluminum extrusion materials which is light weight, high stiffness, and simplicity to assemble, the aluminum extrusion materials have been generally used on cover and the internal structure for the AMHS in the clean room. This experiment aims to explore what the stocker’s situation of the overall structure is, using aluminum extrusion materials, when earthquakes occur.
Following generations of evolution, the size of glass panel and the storage system are relatively enlarged. In the large stocker system, a full load of Cassettes weights about 600 kg; its length and width are 4 m, and height up to 7 m.
When an earthquake occurs, due to the overall cassette mass ratio is more than the shed bit, the whole stocker with low stiffness tends to have shaken violently which causes fraction of the glass panel as cassette edges slide off and collide. Another issue is that the automated stocker system is high precise equipment. If the shed bit is excessively deformed, it will affect the accuracy of the operation of the mechanical arm. When the situation is critical, the system is required to stop and be examined. When the duration is extended, the problems in production line are consequently followed.
The stocker overall structure is low stiffness; therefore, it tends to shake violently. Consequently, seismic force convey upwards to the top of the stocker structure and
amplifies its effects. This study will examine and test the reinforcement measures: method 1, the team installed the bracing to improve the overall stiffness of the Stocker which will inhibit displacement issue, but it can be expected that acceleration will increase and enlarge. Method 2, the team installed a damper, the function of the damper is to increase the damping (or impedance) of the structure, and to reduce the vibration of external forces by earthquake or wind.
The main principle of the damper is to use the characteristics of the material itself to achieve the effect of energy conversion. The dampers in the market include fluid viscous damper (FVD), viscoelastic dampers (VE Damper) and Viscous Elastic Material (VEM), and the characteristics and speed of the force have proportional relationship. Usually, it will not excessively increase the overall stiffness of the structure. Therefore, the low stiffness Stocker sample with installation of the damper is expected to reduce the absolute acceleration and displacement of the stocker at the same time.
1.3. Study Aim
In this study, the AMHS took the high-tech factory as the research background; the main purposes are to explore the original machine tests because there is no reliable information for the equipment for high-tech industry. We need to understand both how to improve and reinforce the seismic strategies and technical content, in order to modify the failing mechanism in equipment during earthquake. To strengthen seismic retrofit to the failing mechanism, the study tested common stocker system to investigate the seismic capacity and failing modes. The stocker was designed by original manufacturer and was used in the high-tech factory.
The team completed 2 kinds of reinforcement tests to investigate the seismic behavior: 1) the installation of bracing to improve the overall stiffness; 2) the installation of the viscous dampers to improve the overall damping ratio. This pilot study used the stocker with the shake table experiments in the National Earthquake Engineering Research Center. It is expected to enhance the seismic capacity of the original designed stocker. The experimental results can be discussed to give concrete proposals for the best reinforcement and to upgrade the seismic capacity.
2. The Original Machine Tests of the Stocker System
This pilot study used the D6000 type stocker with the shake table experiments in the National Earthquake Engineering Research Center. The original machine tests for testing single stocker system, D6000 type, were to investigate the seismic capacity and failing modes. The D6000 type stocker was designed and manufactured in Japan and was used in the high-tech factories. The stocker for storing is an important equipment for storing a large number of both semi-finished and finished products.
2.1. Micro-Vibration Measurement for the High-Tech Factory
In order to accurately simulate the effect upon Stocker by seismic forces at its location, the National Center for Research Earthquake Engineering was commissioned to conduct the micro vibration measurement. The micro vibration measurement sensors were Model VSE15D speed type micro vibration meter, made by Tokyo SOKUSHIN Co., LTD. The micro vibration meter has both the horizontal and vertical radial velocity measurement; the duration of measurement was 250 seconds, with a sampling frequency of 200 Hz. The layout of micro-vibration sensors in the high-tech factory was shown in Figure 2. The sensors installed on each floor, e.g. placed at escape ladders, and are distant from the process equipments to avoid the influence of vibration by the process equipments themselves. The micro-vibration sensors in the stocker installed at top-layer. It helps to understand the factory structure and floor frequency by the measurement. Then, the team used the measurement result to translate and meet the panel site’s potential designed response spectra.
The result of micro-vibration measurement for this high-tech factory, showed that the structure’s frequency of X direction is 1.22 Hz; the structure’s Y direction is 1.04 Hz (as Figure 2). For the stocker system with cassettes, the natural frequency of X direction is 4.53 Hz; the natural frequency of Y direction is 4.9 Hz. For the high-tech factory, the stick model can be built based on the micro-vibration measurement results. The team chose the closest stations to the panel site that is the 0304 seismic wave, Chiahsien earthquake in Taiwan, from CHY099 Shanhua elementary measure station.
Figure 3 shows the inputted signals following the research of all the shake table tests, respectively, the X is shock waves GX (NS), Y is shock waves GY (EW), and Z is axial shock waves GZ (V). The time history showed at Figure 3. For simulation of the ground surface acceleration, the team established the response spectrum of artificial acceleration, the tri-axial duration history shown in Figure 4. The response spectrum met the Taiwanese official code Seismic Design Specifications and Commentary of Buildings. Furthermore, the team simulated the seismic waves of actual floor to investigate the seismic behavior of equipment in the high-tech factory.