Electricity: electrical systems and devices – Safety and protection of systems and devices
Reexamination Certificate
2000-01-12
2002-07-02
Leja, Ronald W. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
C361S692000, C361S695000
Reexamination Certificate
active
06414828
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to providing improved ventilation for industrial machines, particularly for industrial lasers.
Industrial laser systems are normally enclosed in a protective housing. In the case of excimer lasers used in industrial applications (and more specifically in photolithographic applications), the protective housing has several functions, including: protection against laser radiation; protection against high voltage components; protection against ozone produced by 193 nm. laser radiation; protection against toxic gases released in case of a leak; air cooling of sub modules and electromagnetic shielding.
The cooling air might contain toxic gases, such as fluorine released by small leaks or ozone produced by high voltage components or deep UV laser radiation. Housing panels and doors are normally sealed with rubber or silicon rubber gaskets. The housing and the exhaust fan are designed in such a way that the laser housing may be operated under negative pressure compared to ambient pressure. This means that for a well designed system, ambient air will enter the laser housing through designed air inlets, but the air enclosed by the housing will not return through the air intakes, small gaps and slots into the environment. The exhaust air flow might contain toxic gases, therefore the exhaust of the laser housing should be connected to an industrial ventilation system. Well-designed systems fulfill the industrial safety standards.
Industrial excimer laser systems are typically adjusted during maintenance or service. During maintenance or service, access panels or doors must be opened, which breaks the protective enclosure. Therefore, it is difficult to maintain the desired negative pressure within the laser housing during maintenance or service.
Moreover, conventional ventilation systems do not make the most efficient use of cooling air. This can be a problem when a laser system is used in a clean room environment, because the cost of providing clean room air can be significant.
There are three state-of-the-art approaches to maintaining ventilation safety. The first approach was used in industrial lasers which were manufactured by Lambda Physik beginning in 1988. The laser housing was divided into several smaller compartments. Each compartment was separately ventilated, i.e., each compartment had its own exhaust blower and exhaust duct. Opening a single panel broke the protective enclosure of a single compartment, but the other compartments were still at negative pressure and safe ventilation conditions. Larger laser systems had up to three exhaust ducts. Installation of such systems was cumbersome for industrial users. The amount of exhausted air was quite high, which created problems when a laser was installed in a clean room.
The second approach was followed by a later version of the Lambda industrial laser series. One strong exhaust blower was installed. The location of all air intakes, internal baffles and vanes were designed in such a manner that a sufficient gas flow was provided at all areas where a leak might occur or ozone might be generated. The combination of vanes, baffles, properly located air intakes and a strong exhaust blower could maintain safe ventilation conditions even when the protective housing was opened at one location. The main disadvantage of this design was the large air exhaust rate.
A third solution Is described in U.S. Pat. No. 5,748,656, which teaches that clear plastic panels or curtains are located behind the access doors. Rubber flaps can be used over access holes in the clear plastic panels. These rubber flaps permit a service engineer to reach into the ventilated enclosure without substantial loss of ventilation. Major disadvantages of these panels, curtains and rubber flaps are the restricted access for the service engineers and the risk of flammability. Like the other designs, this design has a high air exhaust rate.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a ventilation system for industrial lasers which provides adequate cooling while using a minimum of cooling gas.
It is a further object of the present invention to provide a ventilation system for industrial lasers which provides adequate ventilation even when the housing of the laser device is open.
It is a feature of the present invention to provide a laser device with one or more sensors.
It is another feature of the present invention to provide a laser device which can automatically perform safety countermeasures.
It is an advantage of the present invention to reduce the cost of operating a laser device.
It is a further advantage of the present invention to increase the safety of workers who are operating, maintaining or servicing laser devices.
An improved ventilation system consists of an exhaust channel, at least one exhaust port, at least one air inlet and at least one blower. The exhaust channel is in fluid communication with internal compartments of a laser housing which require cooling and allows sufficient ventilation of all such compartments.
In a preferred embodiment, blowers with adjustable speed are used to circulate cooling gas. During normal operation the blowers are running at low speed. The amount of cooling gas can be minimized in this way. This is of special advantage if the laser device is installed in a clean room, because the conditioned clean room air is very expensive.
Various sensors can be installed in the device in order to monitor properties such as temperature or the concentrations of halogen, ozone, smoke, etc. Depending on the sensor outputs, the air flow rate can be adjusted automatically in order to maintain optimum ventilation conditions with minimum cooling air consumption. Sensor outputs can also be used to trigger safety countermeasures.
Sufficient ventilation conditions can be maintained even if the housing of the laser device is opened for service or maintenance. In some embodiments, individual blowers are used for different compartments, so even if the blower at one location is not active during service or maintenance, the other blowers create adequate ventilation. For embodiments which use a single blower, ventilation safety can be maintained during maintenance or service by increasing the blower speed.
REFERENCES:
patent: 4573159 (1986-02-01), Aagano et al.
patent: 4823349 (1989-04-01), Koop et al.
patent: 4956846 (1990-09-01), Iehisa
patent: 5084885 (1992-01-01), Iehisa et al.
patent: 5669813 (1997-09-01), Jairazbhoy et al.
patent: 5748656 (1998-05-01), Watson et al.
patent: 6021150 (2000-02-01), Partio et al.
Rebhan Ulrich
Zimmerman Kay
Lambda Physik AG
Leja Ronald W.
Sierra Patent Group Ltd.
Smith Andrew V.
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