Patent Description:
In process of manufacturing semiconductor devices, liquid crystal panels, LEDs, solar cells, etc., a process gas is introduced into a process chamber to perform a certain type of process, such as etching process or CVD process. The process gas that has been introduced into the process chamber is exhausted by a vacuum pump apparatus. Generally, the vacuum pump apparatus used in these manufacturing processes that require high cleanliness is so-called dry vacuum pump apparatus that does not use oil in gas flow passages. One typical example of such a dry vacuum pump apparatus is a positive-displacement vacuum pump apparatus having a pair of pump rotors in a pump chamber which are rotated in opposite directions to deliver the gas.

The process gas introduced into the process chamber may form solidified by-product through reaction within the chamber as a temperature of the process gas is decreased or increased. When a large amount of solidified by-product accumulates in the vacuum pump apparatus, the solidified by-product may impede the rotation of the pump rotors and may cause the vacuum pump apparatus to suddenly stop. Such an unexpected operation stop of the vacuum pump apparatus can damage products, such as semiconductor devices, which are being manufactured.

The above-described by-product is also deposited in a pipe coupling the process chamber and the vacuum pump apparatus, and in a pipe coupling the vacuum pump apparatus and an abatement device disposed downstream of the vacuum pump apparatus. For this reason, pipe maintenance is conducted regularly. During the pipe maintenance, the vacuum pump apparatus is stopped, and after the pipe maintenance is completed, the vacuum pump apparatus is restarted. However, if a large amount of by-product accumulates in the pump chamber, a resistance to the rotation of the pump rotor is so large that the vacuum pump apparatus cannot restart.

<CIT> discloses a vacuum pump apparatus which includes: a pump casing having a rotor chamber therein; a pump rotor arranged in the rotor chamber; a rotation shaft to which the pump rotor is secured; an electric motor coupled to the rotation shaft; a side cover forming an end surface of the rotor chamber; and a side heater arranged in the side cover.

<CIT> discloses a pump which has a rotor shaft supported in rotation in a main bearing associated with a stator by a rolling bearing. A central housing comprising an axial wall and a radial wall is arranged at an end of the rotor shaft. The stator comprises a rolling bearing support axle projected from the central housing. The rolling bearing is interposed between the rolling bearing support axle and the axial wall of the central housing of the rotor shaft, where the rolling bearing support axle is formed as a single piece with the stator.

<CIT> discloses a vacuum pump provided with a heater for suppressing deposition of products and the like contained in exhaust gas on an inner wall surface of a pump chamber.

<CIT> discloses a vacuum apparatus casing which houses at least one pumping mechanism or at least one abatement device. The casing has internal channelling which defines at least one closed heat transfer pathway. The internal channeling includes first and second annular channels which are inter connected by at least one elongate channel. Heat is conducted through the casing from a first position to a second position via the channels to be rejected from the casing to an external cooling system.

Therefore, a pump-stop method has been proposed in which by-product accumulated in the pump chamber is gradually scraped away by the pump rotors by repeating rotation and stop of the pump rotors when the operation of the vacuum pump apparatus is to be stopped, (the <CIT>). This method can remove the by-product from the pump chamber and can allow the vacuum pump apparatus to restart.

However, this pump-stop method takes a long time (for example, about three hours) to complete and lowers a throughput of manufacturing products, such as semiconductor devices. For this reason, this method may not be accepted by users.

Accordingly, the present invention provides a vacuum pump that can reduce deposition of by-product in a pump chamber caused by a process gas, can prevent an unintended stop of a vacuum pump apparatus, and can ensure restarting of the vacuum pump apparatus. The present invention further provides a method of operating such a vacuum pump.

In accordance with the present invention, a vacuum pump apparatus and a method as set forth in the appended claims is provided. In particular, in an embodiment, there is provided a vacuum pump apparatus comprising: a pump casing having a pump chamber therein; a pump rotor arranged in the pump chamber; a rotation shaft to which the pump rotor is secured; an electric motor coupled to the rotation shaft; a bearing that rotatably supports the rotation shaft; a side cover coupled to the pump casing, the bearing being coupled to the side cover; a heater attached to the side cover and configured to generate heat to cause an axial displacement of the bearing; and a heater controller configured to instruct the heater to generate heat intermittently when the pump rotor is rotating.

In an embodiment, the side cover forms an end surface of the pump chamber.

In an embodiment, the pump casing forms an end surface of the pump chamber.

In an embodiment, the vacuum pump apparatus further includes a bearing housing that holds the bearing, and the bearing housing is held by the side cover.

In an embodiment, the side cover comprises: a side wall forming the end surface of the pump chamber; and a spacer made of the same material as the side wall or made of a material having a larger coefficient of linear expansion than that of the side wall, the heater being arranged in the spacer.

In an embodiment, the side cover comprises: a side wall forming the end surface of the pump chamber, the side wall being made of the same material as the rotation shaft or made of a material having a larger coefficient of linear expansion than that of the rotation shaft; and a spacer holding the bearing, the heater being arranged in the side wall.

In an embodiment, the side cover comprises: a side wall coupled to the pump casing; and a spacer made of the same material as the side wall or made of a material having a larger coefficient of linear expansion than that of the side wall, the heater being arranged in the spacer.

In an embodiment, the side cover comprises: a side wall coupled to the pump casing, the side wall being made of the same material as the rotation shaft or made of a material having a larger coefficient of linear expansion than that of the rotation shaft; and a spacer that holds the bearing, the heater being arranged in the side wall.

In an embodiment, the vacuum pump apparatus further comprises: a first temperature sensor configured to measure a temperature of the pump casing; and a second temperature sensor configured to measure a temperature of the side cover, wherein the heater controller is configured to determine a target temperature based on the temperature of the pump casing, and control the heater such that the temperature of the side cover reaches the target temperature.

In an embodiment, the heater controller is configured to instruct the heater to stop the heat generation or lower the temperature of the heat generation of the heater after the temperature of the side cover reaches the target temperature.

In an embodiment, the vacuum pump apparatus further comprises a displacement sensor configured to measure an axial displacement of the bearing, wherein the heater controller is configured to instruct the heater to stop the heat generation when the axial displacement of the bearing reaches a threshold value.

In an embodiment, the vacuum pump apparatus further comprises a second heater attached to the pump casing.

In an embodiment, the vacuum pump apparatus further comprises a cooler attached to the pump casing.

In an embodiment, there is provided a method of operating a vacuum pump apparatus according to claim <NUM>, comprising: intermittently generating heat by a heater to cause an axial displacement of the bearing when evacuating a process gas by rotating a pump rotor arranged in a pump chamber of a pump casing, the pump rotor being secured to a rotation shaft which is rotatably supported by a bearing, the bearing being coupled to a side cover which is coupled to the pump casing, the heater being attached to the side cover.

In an embodiment, the bearing is held by a bearing housing, and the bearing housing is held by the side cover.

In an embodiment, the method of operating the vacuum pump apparatus further comprises: determining a target temperature based on a temperature of the pump casing; and controlling the heater such that a temperature of the side cover reaches the target temperature.

In an embodiment, the method of operating the vacuum pump apparatus further comprises stopping the heat generation of the heater or lowering a temperature the heat generation of the heater after the temperature of the side cover reaches the target temperature.

In an embodiment, the method of operating the vacuum pump apparatus further comprises stopping the heat generation of the heater when an axial displacement of the bearing reaches a threshold value.

In an embodiment, the method of operating the vacuum pump apparatus further comprises heating the pump casing by a second heater attached to the pump casing.

In an embodiment, the method of operating the vacuum pump apparatus further comprises cooling the pump casing by a cooler attached to the pump casing.

When the heater generates the heat intermittently during the rotation of the pump rotor, the side cover repeats thermal expansion and contraction, which cause the rotation shaft to reciprocate in an axial direction via the bearing coupled to the side cover. As the rotation shaft reciprocates in the axial direction, the pump rotor also reciprocates in the axial direction, so that the rotating pump rotor can scrape off by-product deposited in the pump chamber. As a result, the pump rotor can rotate smoothly.

<FIG> is a cross-sectional view showing an embodiment of a vacuum pump apparatus. The vacuum pump apparatus of the embodiment described below is a positive-displacement vacuum pump apparatus. In particular, the vacuum pump apparatus shown in <FIG> is a so-called dry vacuum pump apparatus that does not use oil in its flow passages for a gas. Since a vaporized oil does not flow to an upstream side, the dry vacuum pump apparatus can be suitably used for a semiconductor-device manufacturing apparatus that requires high cleanliness.

As shown in <FIG>, the vacuum pump apparatus includes a pump casing <NUM> having a pump chamber <NUM> therein, pump rotors 5A to 5E arranged in the pump chamber <NUM>, rotation shafts <NUM> to which the pump rotors 5A to 5E are secured, and electric motor <NUM> coupled to the rotation shaft <NUM>. The pump rotors 5A to 5E and each rotation shaft <NUM> may be an integral structure. Although only one set of pump rotors 5A to 5E and only one rotation shaft <NUM> are depicted in <FIG>, a pair of pump rotors 5A to 5E are arranged in the pump chamber <NUM>, and are secured to a pair of rotation shafts <NUM>, respectively. The electric motor <NUM> is coupled to one of the pair of rotation shafts <NUM>. In one embodiment, a pair of electric motors <NUM> may be coupled to the pair of rotation shafts <NUM>, respectively.

The pump rotors 5A to 5E of the present embodiment are Roots-type pump rotors, while in one embodiment the pump rotors 5A to 5E may be claw-type pump rotors. Further, the pump rotors 5A to 5E may be a combination of Roots-type and claw-type pump rotors. Although the pump rotors 5A to 5E of the present embodiment are multi-stage pump rotors, in one embodiment the pump rotors may be single-stage pump rotors.

The vacuum pump apparatus further includes side covers 10A and 10B located outwardly of the pump casing <NUM> in an axial direction of the rotation shafts <NUM>. The side covers 10A and 10B are provided on both sides of the pump casing <NUM> and are coupled to the pump casing <NUM>. In the present embodiment, the side covers 10A and 10B are fixed to end surfaces of the pump casing <NUM> by not-shown screws.

The pump chamber <NUM> is formed by an inner surface of the pump casing <NUM> and inner surfaces of the side covers 10A and 10B. The pump casing <NUM> has an intake port 2a and an exhaust port 2b. The intake port 2a is coupled to a chamber (not shown) filled with gas to be delivered. In one example, the intake port 2a may be coupled to a process chamber of a semiconductor-device manufacturing apparatus, and the vacuum pump apparatus may be used for evacuating a process gas from the process chamber.

The vacuum pump apparatus further includes a motor housing <NUM> and a gear housing <NUM> which are housing structures located outwardly of the side covers 10A and 10B in the axial direction of the rotation shafts <NUM>. The side cover 10A is located between the pump casing <NUM> and the motor housing <NUM>, and the side cover 10B is located between the pump casing <NUM> and the gear housing <NUM>.

The motor housing <NUM> accommodates a motor rotor 8A and a motor stator 8B of the electric motor <NUM> therein. Inside the gear housing <NUM>, a pair of gears <NUM> that mesh with each other are arranged. In <FIG>, only one gear <NUM> is depicted. The electric motor <NUM> is rotated by a not-shown motor driver, and one rotation shaft <NUM> to which the electric motor <NUM> is coupled rotates the other rotation shaft <NUM> to which the electric motor <NUM> is not coupled in an opposite direction via the gears <NUM>.

In one embodiment, a pair of electric motors <NUM>, which are coupled to the pair of rotation shafts <NUM>, respectively, may be provided. The pair of electric motors <NUM> are synchronously rotated in opposite directions by a not-shown motor driver, so that the pair of rotation shafts <NUM> and the pair of pump rotors 5A to 5E are synchronously rotated in opposite directions. In this case, the role of the gears <NUM> is to prevent loss of the synchronous rotation of the pump rotors <NUM> due to a sudden external cause.

In the embodiment shown in <FIG>, the motor housing <NUM> is arranged outwardly of the side cover 10A, and the gear housing <NUM> is arranged outwardly of the side cover 10B, while configurations of the vacuum pump apparatus are not limited to this embodiment. In one embodiment, the gear housing <NUM> may be arranged outwardly of the side cover 10A, and the motor housing <NUM> may be arranged outwardly of the side cover 10B. Further, in one embodiment, both the motor housing <NUM> and the gear housing <NUM> may be located outwardly of either the side cover 10A or the side cover 10B.

When the pump rotors 5A to 5E are rotated by the electric motor <NUM>, a gas is sucked into the pump casing <NUM> through the intake port 2a. The gas is sequentially compressed by the rotating pump rotors 5A to 5E, delivered to the exhaust port 2b, and discharged from the pump chamber <NUM> through the exhaust port 2b.

Each rotation shaft <NUM> is rotatably supported by bearings <NUM> and <NUM>. The bearing <NUM> is held by a bearing housing <NUM>, and the bearing <NUM> is supported by the side cover 10B. The bearing <NUM> is coupled to the side cover 10A via the bearing housing <NUM>. More specifically, the bearing housing <NUM> is held by the side cover 10A, and positions of the bearing housing <NUM> and the bearing <NUM> are fixed by the side cover 10A. Since an inner race of the bearing <NUM> is fixed to the rotation shaft <NUM>, an axial position of a portion of the rotation shaft <NUM> held by the bearing <NUM> is fixed.

In contrast, the bearing <NUM> is axially movably supported by the side cover 10B. More specifically, an inner race of the bearing <NUM> is fixed to the rotation shaft <NUM>, while an outer race of the bearing <NUM> is not fixed to the side cover 10B, and simply supported by the side cover 10B. Therefore, the bearing <NUM> is axially movable together with the rotation shaft <NUM>.

A bearing housing holding the bearing <NUM> may be disposed between the side cover 10B and the bearing <NUM>. In this case, the bearing housing is fixed to the side cover 10B, but the outer race of the bearing <NUM> is not fixed to the bearing housing, and is simply supported by the bearing housing, so that the bearing <NUM> can move axially together with the rotation shaft <NUM>.

During operation of the vacuum pump apparatus, the gas is compressed by the pump rotors 5A to 5E while the gas is being transferred from the intake port 2a to the exhaust port 2b. Therefore, the rotation shaft <NUM> located in the pump chamber <NUM> thermally expands due to compression heat of the gas. The axial position of the bearing <NUM> is fixed, whereas the bearing <NUM> is movable in the axial direction. Accordingly, the rotation shaft <NUM> thermally expands in the axial direction beginning from the bearing <NUM>, and the bearing <NUM> moves in the axial direction as the rotation shaft <NUM> thermally expands.

<FIG> is an enlarged sectional view showing the side cover 10A, the bearing housing <NUM>, and the bearing <NUM> at the exhaust side. As shown in <FIG>, the pump casing <NUM> has a partition wall <NUM> therein, and the pump rotor 5E is arranged between the partition wall <NUM> and the side cover 10A. In this embodiment, the side cover 10A includes a side wall <NUM> forming an end surface of the pump chamber <NUM> and a spacer <NUM> made of the same material as the side wall <NUM> or made of a material having a larger coefficient of linear expansion than that of the side wall <NUM>. The spacer <NUM> is located between the side wall <NUM> and the bearing housing <NUM>. The bearing housing <NUM> is held by the spacer <NUM>, and the bearing housing <NUM> is coupled to the side wall <NUM> via the spacer <NUM>.

The vacuum pump apparatus has a heater <NUM> attached to the side cover 10A. In this embodiment, the heater <NUM> is arranged in the spacer <NUM> of the side cover 10A. The spacer <NUM> is made of the same material as the side wall <NUM> and the pump casing <NUM>, or made of metal having a coefficient of linear expansion larger than that of the side wall <NUM>. For example, when the side wall <NUM> and the pump casing <NUM> are made of cast iron, the spacer <NUM> is made of cast iron, or stainless steel, aluminum, aluminum alloy, or copper having a larger coefficient of linear expansion than that of cast iron. When the heater <NUM> generates heat, the spacer <NUM> thermally expands, and the bearing housing <NUM> held by the spacer <NUM> moves in the axial direction. In particular, the spacer <NUM> has a shape that surrounds the bearing housing <NUM> and is prone to the thermal expansion in the axial direction.

A process gas treated by the vacuum pump apparatus may form solidified by-product through reaction in the chamber as the temperature of the process gas decreases or increases. Such by-product gradually accumulates in the pump chamber <NUM> as the vacuum pump apparatus operates. <FIG> is a cross-sectional view showing a state in which the pump rotor 5E is moved in the axial direction due to the thermal expansion of the rotation shaft <NUM>. As described above, the high-temperature rotation shaft <NUM> thermally expands in the axial direction, and as a result, the pump rotor 5E is moved in a direction away from the side cover 10A forming the end surface of the pump chamber <NUM>. By-product <NUM> is gradually deposited in a gap between the pump rotor 5E and the side cover 10A. Such by-product <NUM> impedes the rotation of the pump rotor 5E, and may cause an unintended operation stop of the vacuum pump apparatus, or may prevent the vacuum pump apparatus from restarting.

Thus, as shown in <FIG>, the heater <NUM> generates heat that causes the thermal expansion of the spacer <NUM>, which moves the bearing housing <NUM> and the bearing <NUM> in the axial direction, thereby moving the pump rotor 5E toward the side cover 10A. As the rotating pump rotor 5E moves toward the side cover 10A (i.e., toward the end surface of the pump chamber <NUM>), the rotating pump rotor 5E gradually scrapes off the by-product <NUM> deposited in the gap between the pump rotor 5E and the side cover 10A.

The heat generation of the heater <NUM> is stopped when the pump rotor 5E reaches an initial position shown in <FIG>. The initial position of the pump rotor 5E is a position of the pump rotor 5E when the entire vacuum pump apparatus has a room temperature. When the heat generation of the heater <NUM> is stopped, the temperature of the spacer <NUM> gradually decreases and the spacer <NUM> gradually contracts. As the spacer <NUM> contracts, the pump rotor 5E is moved in a direction away from the side cover 10A, and the gap between the pump rotor 5E and the side cover 10A increases as shown in <FIG>. Since the by-product <NUM> gradually accumulates in this gap, the heater <NUM> generates heat again to thermally expand the spacer <NUM>. As shown in <FIG>, as the rotating pump rotor 5E moves toward the side cover 10A (i.e., toward the end surface of the pump chamber <NUM>), the rotating pump rotor 5E gradually scrapes off the by-product <NUM> deposited in the gap between the pump rotor 5E and the side cover 10A.

Similarly, the by-product <NUM> deposited between the partition wall <NUM> and the pump rotor 5E is gradually scraped off by the rotating pump rotor 5E after the heat generation of the heater <NUM> is stopped and when the pump rotor 5E is moved in a direction away from the side cover 10A (i.e., toward the partition wall <NUM>).

In this way, while the vacuum pump apparatus is in operation (i.e., while the process gas is being exhausted or evacuated), the heat generation and stoppage of the heat generation of the heater <NUM> are repeated to cause the rotating pump rotor 5E to reciprocate in the axial direction, so that the rotating pump rotor 5E can scrape off the by-product deposited in the pump chamber <NUM>. With the similar mechanism, the rotating pump rotors 5A to 5D can also scrape off by-product deposited in the pump chamber <NUM>. As a result, the by-product is removed from the pump chamber <NUM>, and the pump rotors 5A to 5E can rotate smoothly.

In a conventional pump, pump rotors do not reciprocate during operation as described above. As a result, a large amount of by-product may be deposited near the pump rotors during operation, and the pump rotors bite the large amount of by-product at a certain moment, causing sudden stop of the pump. According to the present invention, the pump rotors 5A to 5E constantly repeat the reciprocating motion, which makes it possible to create a condition in which almost no by-product is accumulated in the pump chamber <NUM>, particularly near the pump rotors 5A to 5E. As a result, sudden stop of the pump can be prevented.

As shown in <FIG>, the vacuum pump apparatus includes a heater controller <NUM> configured to control the heat generation of the heater <NUM>. The heater controller <NUM> is configured to intermittently instruct the heater <NUM> to generate the heat (i.e., periodically repeat heat generation and stop of the heat generation of the heater <NUM>) while the pump rotors 5A to 5E are rotating. The heater controller <NUM> includes a memory 40a storing programs therein, an arithmetic device 40b configured to perform arithmetic operations according to instructions included in the programs, and a power source 40c configured to supply electric power to the heater <NUM>. The heater controller <NUM> includes at least one computer. The memory 40a includes a main memory, such as a random access memory (RAM), and an auxiliary memory, such as a hard disk drive (HDD) or solid state drive (SSD). Examples of the arithmetic device 40b include a CPU (central processing unit) and a GPU (graphic processing unit). However, the specific configurations of the heater controller <NUM> are not limited to these examples.

The vacuum pump apparatus further includes a first temperature sensor <NUM> configured to measure a temperature of the pump casing <NUM> and a second temperature sensor <NUM> configured to measure a temperature of the side cover 10A. The first temperature sensor <NUM> is fixed to the pump casing <NUM>. The first temperature sensor <NUM> may be fixed to an outer surface of the pump casing <NUM> or may be embedded in the pump casing <NUM>. This first temperature sensor <NUM> is provided to indirectly measure the temperature of the rotation shaft <NUM>. Specifically, the temperature of the rotation shaft <NUM> arranged in the pump casing <NUM> can be estimated from the temperature of the pump casing <NUM> measured by the first temperature sensor <NUM>.

The second temperature sensor <NUM> is fixed to the side cover 10A. The second temperature sensor <NUM> may be fixed to an outer surface of the side cover 10A or may be embedded in the side cover 10A. In the embodiment shown in <FIG>, the second temperature sensor <NUM> is fixed to the spacer <NUM> of the side cover 10A. Therefore, the second temperature sensor <NUM> can measure the temperature of the side cover 10A (more specifically, the temperature of the spacer <NUM>). The second temperature sensor <NUM> may be embedded in the spacer <NUM>.

The heater controller <NUM> is configured to determine a target temperature of the spacer <NUM>, i.e., a target temperature of the side cover 10A, based on the temperature of the pump casing <NUM> measured by the first temperature sensor <NUM>. Since the temperature of the pump casing <NUM> indirectly indicates the temperature of the rotation shaft <NUM>, a degree of thermal expansion of the rotation shaft <NUM> (i.e., an axial movement distance of the pump rotor 5E from its initial position) can be estimated from the temperature of the pump casing <NUM>. Therefore, the heater controller <NUM> can determine the target temperature of the spacer <NUM> required to return the pump rotor 5E, which has been moved by the thermal expansion of the rotation shaft <NUM>, to the initial position.

The heater controller <NUM> determines the target temperature of the spacer <NUM> required to return the pump rotor 5E to its initial position based on the temperature of the pump casing <NUM>, an axial thickness of the spacer <NUM>, and the coefficient of linear expansion of the spacer <NUM>. A relationship between a movement distance of the pump rotor 5E and the temperature of the spacer <NUM> may be obtained by experiment or simulation, and the target temperature of the spacer <NUM> may be determined from the relationship obtained.

The heater controller <NUM> is configured to control the heater <NUM> such that the temperature of the spacer <NUM> reaches the determined target temperature. The temperature of the spacer <NUM> is measured by the second temperature sensor <NUM>, and the spacer <NUM> is heated to the target temperature. As the spacer <NUM> is heated, the bearing housing <NUM>, the bearing <NUM>, the rotation shaft <NUM>, and the pump rotor 5E are moved axially. When the spacer <NUM> is heated to the target temperature, the pump rotor 5E returns to its initial position shown in <FIG>. Thereafter, the heater controller <NUM> instructs the heater <NUM> to stop its heat generation. In one embodiment, the heater controller <NUM> may instruct the heater <NUM> to lower the temperature of its heat generation after the spacer <NUM> is heated to the target temperature. Furthermore, the heater controller <NUM> may instruct the heater <NUM> to stop the heat generation after instructing the heater <NUM> to lower the temperature of the heat generation of the heater <NUM>.

In this manner, the heater controller <NUM> instructs the heater <NUM> to generate heat intermittently, thereby causing the pump rotor 5E to reciprocate between the initial position shown in <FIG> and the thermal expansion position shown in <FIG>. With this operation, the other pump rotors 5A to 5D also reciprocate in the axial direction in the same manner. Since the pump rotors 5A to 5E reciprocate in the pump chamber <NUM> in the axial direction while the pump rotors 5A to 5E are rotating, the pump rotors 5A to 5E can scrape off the by-product deposited in the pump chamber <NUM>.

In one embodiment, as shown in <FIG>, the vacuum pump apparatus includes a displacement sensor <NUM> configured to measure an axial displacement of the bearing <NUM>. The displacement sensor <NUM> is attached to the side wall <NUM> of the side cover 10A and arranged so as to face the bearing housing <NUM> holding the bearing <NUM>. Therefore, the displacement sensor <NUM> measures the axial displacement of the bearing <NUM> by measuring an axial displacement of the bearing housing <NUM>. In one embodiment, the displacement sensor <NUM> may be arranged to directly measure the axial displacement of the bearing <NUM>.

The displacement sensor <NUM> is electrically coupled to the heater controller <NUM>. The heater controller <NUM> is configured to instruct the heater <NUM> to stop the heat generation when the axial displacement of the bearing <NUM> reaches a threshold value. Such controlling of the heat generation of the heater <NUM> based on the axial displacement of the bearing <NUM> can prevent the pump rotor 5E from contacting the inner surface of the side cover 10A (i.e., the end surface of the pump chamber <NUM>).

In one embodiment, as shown in <FIG>, the side cover 10A may be constructed from a single material. More specifically, a part of the side cover 10A forms the end surface of the pump chamber <NUM>, and other part of the side cover 10A holds the bearing housing <NUM>. The side cover 10A is made of the same material as the pump casing <NUM> or made of a material having a larger coefficient of linear expansion than that of the pump casing <NUM>. For example, when the pump casing <NUM> is made of cast iron, the entire side cover 10A is made of cast iron, or made of stainless steel, aluminum, aluminum alloy, or copper having a larger coefficient of linear expansion than that of the pump casing <NUM>. In the embodiment shown in <FIG>, the rotating pump rotors 5A to 5E can scrape off the by-product deposited in the pump chamber <NUM> by repeating the heat generation and stop of the heat generation of the heater <NUM> as well as the previous embodiments.

In one embodiment, the bearing housing <NUM> may be omitted, as shown in <FIG>. In the embodiment shown in <FIG>, the bearing <NUM> is held directly on the side cover 10A. More specifically, the bearing <NUM> is directly held by the spacer <NUM> of the side cover 10A. Further, in one embodiment, as shown in <FIG>, the side cover 10A may be constructed from a single piece of material and the bearing housing <NUM> may not be provided. The embodiment shown in <FIG> is a combination of the embodiment shown in <FIG> and the embodiment shown in <FIG>. The bearing <NUM> is directly held by the side cover 10A. In the embodiments shown in <FIG> and <FIG>, the rotating pump rotors 5A to 5E can scrape off the by-product deposited in the pump chamber <NUM> by repeating the heat generation and stop of the heat generation of the heater <NUM> as well as the previous embodiments.

In one embodiment, as shown in <FIG>, the vacuum pump apparatus may further include a second heater <NUM> attached to the pump casing <NUM> in order to prevent deposition of the by-product in the pump chamber <NUM> due to a decrease in temperature of the process gas. A certain type of process gas may form by-product as a temperature of the process gas rises. When the vacuum pump apparatus is used for evacuating such a process gas, the vacuum pump apparatus may further include a cooler <NUM> attached to the pump casing <NUM>, as shown in <FIG>. The cooler <NUM> may be a water-cooled cooler. The second heater <NUM> shown in <FIG> and the cooler <NUM> shown in <FIG> may be attached to the outer surface of the pump casing <NUM> or may be embedded in the pump casing <NUM>.

According to the embodiments shown in <FIG> and <FIG>, the combination of the axial reciprocation of the pump rotors 5A to 5E by the intermittent operation of the heater <NUM> and the second heater <NUM> or the cooler 51can reliably prevent the deposition of the by-product.

<FIG> is a cross-sectional view showing another embodiment of the vacuum pump apparatus. As shown in <FIG>, in the vacuum pump apparatus of this embodiment, lubricating oil <NUM> for lubricating and cooling the bearing <NUM> is stored at a bottom of the motor housing <NUM>. Configurations and operations of this embodiment, which will not be particularly described, are the same as those of the embodiments described with reference to <FIG>, and redundant descriptions thereof are omitted.

The vacuum pump apparatus of this embodiment includes rotary disks <NUM> configured to supply the lubricating oil <NUM> to the bearing <NUM> and a partition wall <NUM> arranged between the electric motor <NUM> and the bearing housing <NUM>. Each rotary disk <NUM> is coupled to each of the pair of rotation shafts <NUM> and rotates together with each rotation shaft <NUM>. In one embodiment, a rotary disk <NUM> may be coupled to one of the pair of rotation shafts <NUM> and may rotate together with that rotation shaft <NUM> coupled to the rotary disk <NUM>. The rotation of the rotary disk <NUM> splashes up the lubricating oil <NUM> onto the bearing <NUM>.

The partition wall <NUM> is fixed to the inner surface of the motor housing <NUM> and has through-holes (not shown) through which the rotation shafts <NUM> extend. The partition wall <NUM> is configured to separate a space in which the lubricating oil <NUM> is stored from a space in which the electric motor <NUM> is disposed, and is provided to prevent the lubricating oil <NUM> from contacting the electric motor <NUM>.

The lubricating oil <NUM> in the motor housing <NUM> is always in contact with the spacer <NUM> of the side cover 10A. If the heater <NUM> is arranged in the spacer <NUM>, the temperature of the lubricating oil <NUM> rises due to the heat generated by the heater <NUM>, and a sufficient cooling effect for the bearing <NUM> may not be obtained. Therefore, in the embodiment shown in <FIG>, the heater <NUM> is arranged in the side wall <NUM> of the side cover 10A.

The side cover 10A has the side wall <NUM> forming the end surface of the pump chamber <NUM> and the spacer <NUM> holding the bearing <NUM>. The spacer <NUM> is coupled to the side wall <NUM> and is located between the side wall <NUM> and the bearing housing <NUM>. The bearing housing <NUM> is held by the spacer <NUM>, and the bearing housing <NUM> is coupled to the side wall <NUM> via the spacer <NUM>. The bearing <NUM> is coupled to the spacer <NUM> via the bearing housing <NUM>. The spacer <NUM> holds the bearing <NUM> via the bearing housing <NUM>.

The side wall <NUM> is made of the same material as a material of the rotation shaft <NUM> or made of metal having a larger coefficient of linear expansion than that of the rotation shaft <NUM>. For example, when the rotation shaft <NUM> is made of cast iron, the side wall <NUM> is made of cast iron, or stainless steel, aluminum, aluminum alloy, or copper having a larger coefficient of linear expansion than that of cast iron. In one embodiment, the side wall <NUM> may be made of the same material as the material of the pump casing <NUM> and/or the spacer <NUM>, or may be made of metal having a larger coefficient of linear expansion than that of the pump casing <NUM> and/or the spacer <NUM>.

When the heater <NUM> generates heat, the side wall <NUM> thermally expands, and the spacer <NUM> coupled to the side wall <NUM> moves axially. As a result, the bearing housing <NUM> and the bearing <NUM> held by the spacer <NUM> move axially, and the pump rotor 5E moves toward the side cover 10A. When the rotating pump rotor 5E moves toward the side cover 10A (i.e., toward the end surface of the pump chamber <NUM>), the rotating pump rotor 5E can gradually scrape off the by-product deposited in the gap between the pump rotor 5E and the side cover 10A.

When the heat generation of the heater <NUM> is stopped, the temperature of the side wall <NUM> gradually decreases and the side wall <NUM> gradually contracts. As the side wall <NUM> contracts, the pump rotor 5E moves in a direction away from the side cover 10A, and the gap between the pump rotor 5E and the side cover 10A increases. In the embodiment shown in <FIG>, the rotating pump rotors 5A to 5E can scrape off the by-product deposited in the pump chamber <NUM> by repeating the heat generation and stop of the heat generation of the heater <NUM>, as well as the embodiments described with reference to <FIG> and <FIG>.

<FIG> is a cross-sectional view showing still another embodiment of the vacuum pump apparatus. Configurations and operations of this embodiment, which will not be particularly described, are the same as those of the embodiments described with reference to <FIG>, and redundant descriptions thereof are omitted. As shown in <FIG>, the pump casing <NUM> of this embodiment has casing side walls 70A and 70B that form end surfaces of the pump chamber <NUM>. The pump casing <NUM> covers the entire pump chamber <NUM>. The pump chamber <NUM> is formed by the inner surface of the pump casing <NUM>. The side covers 10A, 10B are provided on both sides of the pump casing <NUM> and coupled to the pump casing <NUM>. More specifically, the side wall <NUM> of the side cover 10A is coupled to the casing side wall 70A of the pump casing <NUM>, and the side cover 10B is coupled to the casing side wall 70B of the pump casing <NUM>. The rotation shafts <NUM> extend through the casing side walls 70A and 70B of the pump casing <NUM>.

The side cover 10A includes the side wall <NUM> coupled to the casing side wall 70A of the pump casing <NUM>, and further includes the spacer <NUM> made of the same material as the side wall <NUM> or made of a material having a larger coefficient of linear expansion than that of the side wall <NUM>. The spacer <NUM> is located between the side wall <NUM> and the bearing housing <NUM>. The bearing housing <NUM> is held by the spacer <NUM>, and the bearing housing <NUM> is coupled to the side wall <NUM> via the spacer <NUM>. In this embodiment, the heater <NUM> is arranged in the spacer <NUM> of the side cover 10A. In the embodiment shown in <FIG>, the rotating pump rotors 5A to 5E can scrape off the by-product deposited in the pump chamber <NUM> by repeating the heat generation and stop of the heat generation of the heater <NUM>, as well as the previous embodiments.

<FIG> is a cross-sectional view showing still another embodiment of the vacuum pump apparatus. In the vacuum pump apparatus of this embodiment, lubricating oil <NUM> for lubricating and cooling the bearings <NUM> is stored at the bottom of the motor housing <NUM>, as in the embodiment described with reference to <FIG>. Configurations and operations of this embodiment, which will not be particularly described, are the same as those of the embodiment described with reference to <FIG>, and redundant descriptions thereof will be omitted. As shown in <FIG>, the pump casing <NUM> of this embodiment has casing side walls 70A and 70B that form end surfaces of the pump chamber <NUM>. The pump casing <NUM> covers the entire pump chamber <NUM>. The pump chamber <NUM> is formed by the inner surface of the pump casing <NUM>. The side covers 10A, 10B are provided on both sides of the pump casing <NUM> and coupled to the pump casing <NUM>. More specifically, the side wall <NUM> of the side cover 10A is coupled to the casing side wall 70A of the pump casing <NUM>, and the side cover 10B is coupled to the casing side wall 70B of the pump casing <NUM>. The rotation shafts <NUM> extend through the casing side walls 70A and 70B of the pump casing <NUM>.

The side cover 10A includes the side wall <NUM> coupled to the casing side wall 70A of the pump casing <NUM>, and further includes the spacer <NUM> holding the bearing <NUM>. The side wall <NUM> is made of the same material as a material of the rotation shaft <NUM> or made of metal having a larger coefficient of linear expansion than that of the rotation shaft <NUM>. In this embodiment, the heater <NUM> is arranged in the side wall <NUM> of the side cover 10A. In the embodiment shown in <FIG>, the rotating pump rotors 5A to 5E can scrape off the by-product deposited in the pump chamber <NUM> by repeating the heat generation and stop of the heat generation of the heater <NUM>, as well as the previous embodiments.

Claim 1:
A vacuum pump apparatus comprising:
a pump casing (<NUM>) having a pump chamber (<NUM>) therein;
a pump rotor (5A-5E) arranged in the pump chamber (<NUM>);
a rotation shaft (<NUM>) to which the pump rotor (5A-5E) is secured;
an electric motor (<NUM>) coupled to the rotation shaft (<NUM>);
a bearing (<NUM>, <NUM>) that rotatably supports the rotation shaft (<NUM>);
a side cover (10A, 10B) coupled to the pump casing (<NUM>), the bearing (<NUM>, <NUM>) being coupled to the side cover (10A, 10B); characterized by
a heater (<NUM>), attached to the side cover (10A, 10B), configured to generate heat to cause an axial displacement of the bearing (<NUM>, <NUM>); and
a heater controller (<NUM>) configured to instruct the heater (<NUM>) to generate heat intermittently when the pump rotor (5A-5E) is rotating.