Pumps – Condition responsive control of pump drive motor – Responsive to pump or pump fluid temperature
Reexamination Certificate
1999-10-04
2002-07-09
Freay, Charles G. (Department: 3746)
Pumps
Condition responsive control of pump drive motor
Responsive to pump or pump fluid temperature
C417S423400, C417S228000, C415S118000
Reexamination Certificate
active
06416290
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a turbomolecular pump, and more specifically, to a turbomolecular pump in which a temperature of a rotor blade can be detected, thereby making it possible to prevent an abnormal increase in the temperature of the rotor blade, as well as to prevent the deposition thereon of generated products, to increase pressure upon baking, to provide an alarm of the extraordinary operation of the rotor blades, and to improve the exhaustion performance.
BACKGROUND ART
A turbomolecular pump is a vacuum pump in which rotor blades rotating at high speed and having blades at plural stages, which are divided in a circumferential direction, impart a certain momentum to a gas molecule impinging upon the surface thereof, to transport the gas. This type of pump is also used as a part of semiconductor manufacturing equipment.
Conventionally, when a turbomolecular pump is used to discharge an active gas or the like, a reaction with the active gas may cause generated products to be solidified or adhered. These generated products described above were in a state liable to solidify or adhere particularly when the temperature was low around the exhaust port. Therefore, as shown in
FIG. 12
, a temperature sensor
21
(e.g., thermistor) is embedded in a base portion
13
, and is managed so that a temperature of the base portion
13
is kept constant in response to signals of the temperature sensor
21
(hereinafter referred to as TMS: Temperature Management System).
Degassing (hereinafter referred to as baking) from the turbomolecular pump, a piece of semiconductor manufacturing equipment and from a pipe connected therewith are carried out under such a state that they are heated to a certain temperature for a certain time period before the turbomolecular pump is operated. Thereafter, when the temperature is returned to an ordinary temperature, the degree of vacuum at a portion of an inlet port of the turbomolecular pump and an inside of a chamber may be increased (a so-called utmost pressure will be increased).
In addition, as shown in
FIG. 12
, the conventional turbomolecular pump includes a motor M driven by a motor driver
8
that is equipped with an r.p.m. sensor
2
for detecting an r.p.m. of the motor M, a motor current sensor
3
for detecting a current of the motor M, and an axial electromagnet current sensor
4
for detecting a current of an axial electromagnet causing the rotor blade to magnetically float.
An r.p.m. comparator
7
is connected to the r.p.m. sensor
2
, and outputs a difference between an output of the r.p.m. sensor
2
and a set r.p.m. to the motor driver
8
via a set r.p.m. adjuster
11
. With such an arrangement, the r.p.m. of the motor pump can be controlled.
Meanwhile, if the temperature of the rotor blade exceeds a long-term allowable heat-resistant temperature (e.g., 150° C. when a material of the rotor blade is aluminum alloy), there is a concern that the strength of the rotor blade may particularly be lowered because of damage caused by heat generation, resulting in breaking the turbomolecular pump in the worst case.
Generally, when an output of the motor driver
8
is large (a maximum level of the current is made large, and is rated at 500 W, for example), this large output (because of output allowances) allows the r.p.m. not to be reduced even when a gas load is made larger. However, on the other hand, heat generation at the rotor blade becomes larger, with the result that the rotor blades deteriorate or are lowered in their strength due to the heat generation.
To cope with this, the output of the motor driver
8
was typically lowered to, e.g., 400 W to be set, and if the gas load exceeds an allowable value, the r.p.m. of the rotor blades is slightly lowered from the allowable rating. As a result, deterioration of the rotor blades caused by heat generation could be prevented.
In addition, an allowable flow rate is experimentally calculated, and determined so that the temperature of the rotor blade may be set within the allowable value even when the turbomolecular pump is operated for a certain time period.
In addition, in order to prevent an abnormal increase in the temperature of the rotor blade, a temperature sensor
23
(e.g., thermistor) is disposed in the vicinity of the motor M. When the temperature sensor
23
senses a certain level or more in the temperature, the turbomolecular pump is caused to stop immediately.
However, the conventional apparatus does not monitor the temperature of the rotor blade, and there are such disadvantages as will be described below. That is, the higher a set temperature of the TMS that is set, the smaller the deposition of generated products, so that the set temperature is preferably set as high as possible. If the set temperature is set as high, however, the temperature is elevated around the rotor blade, and heat radiation is prevented at the rotor blade. This results in a higher temperature of the rotor blade, a shorter lifetime of the rotor blade, a breakage, etc. Accordingly, there is a limit on increasing the set temperature of the TMS.
Further, similarly, if baking is carried out at a higher temperature, the utmost pressure is further improved, so that baking is preferably carried out at a temperature as high as possible. When baking is carried out at an excessively high temperature, however, the temperature of the rotor blade is elevated, and the heat generation may cause the lifetime of the rotor blade to be shortened.
In addition, even in the case where the temperature of the rotor blade is lower than an allowable heat-resistive temperature (within a sufficient allowance), if the turbomolecular pump is used under a reduced driver-output, the r.p.m. of the rotor blade is lowered (e.g., from normal 35,000 rpm to 33,000 rpm) with an increase of the gas load, thereby causing the exhaustion or exhaust performance to be deteriorated. The exhaustion performance in this case means that the exhaustion speed is lowered or an exhaust port pressure is increased. In other words, the higher the r.p.m. of the rotor blade is, the more the exhaustion performance is enhanced.
Moreover, if the gas load abruptly changes, the r.p.m. of the rotor blade is likely to fluctuate as the driver output is low, and therefore the exhaustion speed and the inlet port pressure may not be stabilized.
Further, there is a fear that even with the reduced driver output, the rotor blade may be gradually heated to have a high temperature as a long time elapses. In any event, there has been a need for measuring the temperature of the rotor blade to prevent deterioration of the rotor blade caused by the heat generation.
The present invention has been made in view of such conventional problems, and an object of the invention is to provide a turbomolecular pump in which a temperature of a rotor blade, etc., can be measured.
Another object of the invention as set forth in claim
6
is to provide a turbomolecular pump in which deposition of generated products can be prevented more effectively than in the conventional pump.
Still another object of the invention is to provide a turbomolecular pump with an improvement in an utmost pressure by increasing the utmost pressure when baking is performed.
Yet another object of the invention is to protect a turbomolecular pump.
Still yet another object of the invention is to provide a turbomolecular pump in which the exhaustion performance is exerted to the maximum extent for reducing losses when a temperature of a rotor blade is within an allowable value, a variation in an r.p.m. of a motor pump is lowered to maintain an exhaustion speed and an inlet port pressure at constant levels even though the gas load varies, and deterioration of the rotor blade caused by heat generation can be prevented when the temperature of the rotor blade exceeds the maximum allowable value.
Another object of the invention is to provide a turbomolecular pump which is forcibly cooled around rotor blade to thereby improve the exhaustion performance (allowable gas flow rate, allowable inlet port pressure).
Adams & Wilks
Freay Charles G.
Seiko Instruments Inc.
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