JP2007502932A - Reduced exhaust pump pulsation - Google Patents

Abstract

The vacuum pump has a stator that houses first and second shafts, and the first and second shafts rotate counterclockwise within the stator. Each shaft supports a plurality of rotor elements such that the rotor element of the first shaft meshes with the rotor element of the second shaft. The pump further has a pump inlet for receiving the fluid to be pumped and a pump outlet for discharging the pumped fluid. Each of the intermeshing rotor elements located near the pump outlet has a plurality of protrusions extending from the center of rotation, and these protrusions are arranged rotationally asymmetric about the center of rotation of the rotor element.
[Selection] Figure 3

Description

The present invention relates to the final design of vacuum pumps, in particular dry pumps and multistage dry pumps.
Dry pumps are widely used in the semiconductor manufacturing industry, for example, to create a clean, low pressure (often vacuum) environment within a process chamber where wafers can be manufactured. The pump mechanism of the dry pump is provided in various forms, one of which typically has one or more rotors that are housed by a stator. The rotor is suitably shaped to draw gas from the process chamber into the pump inlet and exhaust pumped gas from the pump outlet. The rotor often has a large number of rotor elements arranged continuously along the rotation axis of a common rotating shaft.

  An example of the dry pump mechanism is a roots type mechanism. In a roots-type mechanism, each root-type rotor element has two or more substantially sized and shaped lobes, each lobe extending radially or radially from the rotational axis of the rotating shaft. The lobes are arranged in a rotationally symmetrical state around the rotational axis of the shaft. Within the first stage of the pump (ie, the stage located near the pump inlet), the number of lobes provided on the rotor element may be small. For example, two lobes are typically used in the first stage of the pump. The rotors that make a pair are in close contact with each other, but they should be arranged in a state where they do not touch each other. Each rotor element is arranged at an angle with respect to the opposing rotor element to form a step so that when the two rotor shafts rotate, the lobes of one rotor element pass through the space between the other lobes. It is supposed to be.

  Another mechanism is called the Northey or “claw” type mechanism. In this mechanism, instead of the lobes described above for the Roots stage, pickles or claw shapes are used that are rotationally symmetrical around the axis of rotation of the rotating shaft.

  A third mechanism that operates on substantially the same principle as the root and claw mechanisms is sometimes referred to as a ball and socket type device. In this device, the rotors are aligned in parallel in pairs. The first rotor has one or more rotor elements, each rotor element being generally circular, but cut around the circle and equally spaced radially around the axis of rotation of the shaft It has a cross section with a number of sockets. The second rotor has correspondingly one or more rotor elements, each rotor element having a generally circular cross section, with protrusions extending from the periphery thereof, the protrusions being It is shaped and positioned to mate with the socket of the rotor element immediately adjacent to one rotor. Each pair of rotor elements that cooperate with each other is referred to as a stage.

  In each of the above examples, periodic pressure fluctuations occur when the two rotors rotate at a stable rotational speed. Each stage of the rotor element captures gas slag between the rotor and the stator and discharges some of it to the pump outlet. Since the shafts rotate in opposite directions at a constant speed, the rotor elements are also rotationally symmetric, so that trapped gas emissions occur regularly. Thus, a pulsation having a constant cycle occurs. If these rotor elements are located in the final or exhaust stage of the pump, this periodic pulsation may be transmitted through the connecting pipe between the pump and the containment and this is audible in the ambient environment. There is a case. Such pulsations can cause various problems, for example, the pulsations can greatly distract those who are working in an environment where such periodic pulses must be heard over a long period of time. . Also, if the pulse reaches the harmonic frequency of the components in the containment, these components can be excited and vibrate vigorously, resulting in excessive noise.

  Conventionally, this noise problem has been addressed by introducing a stage with a number of lobe-rotating rotor elements in the final stage of the pump adjacent to the exhaust (outlet). This multiple lobe rotor element has more lobes than the previous stage rotor element and helps to reduce the magnitude of the pulses produced by the previous stage of the pump mechanism.

  Nevertheless, in use, this stage produces its own periodic beat or beat at a higher frequency than the other stages. This may excite the ducts used to direct the exhaust gas to the appropriate vent space, and this may cause the above mentioned noise problems.

  In addition or as an alternative to the solution described above, it is known to use silencers or mufflers to reduce the noise generated at the discharge of the pump. In certain situations, it is not desirable to use a silencer. Some semiconductor manufacturing processes produce dusty or condensable materials that can be used if they accumulate in significant amounts and are exposed to air (eg, pump maintenance). Or during maintenance) may be dangerous. When a silencer or muffler is used in such an environment, it can result in the accumulation of such harmful end products, making maintenance or maintenance problems more difficult.

The present invention seeks to provide a vacuum pump that overcomes some of the above-mentioned problems associated with pulsations at the pump discharge.
According to the present invention, a vacuum pump having a chamber containing first and second meshing rotor elements, wherein the first rotor element and the second rotor element are attached to respective shafts; The rotor element is configured to rotate reversely in the chamber, and at least one of the rotor elements has a plurality of protrusions extending from the rotation center, and the protrusions are arranged rotationally asymmetrically around the rotation center of the rotor element. A vacuum pump is provided.

The protrusions may be in the form of, for example, roots type rotor element lobes, drive rotor element claws or ball socket type device protrusions (or spaces between sockets).
As will be appreciated, each protrusion has a vertex and a sector angle that are radially spaced from the center of rotation. Desirably, the angle between each vertex pair with respect to the center of rotation is different from the equivalent sector angle between adjacent vertex pairs. The sector angles between adjacent vertices are all different from each other. The sector angle is selected randomly. Preferably, each sector angle is different from all others, but this is not a requirement.

  The plurality of protrusions is desirably 3 or more, more preferably 3 to 9. For example, the rotor element has 4, 5, 6 or 7 protrusions. The protrusions may be integrally formed with the rotor element, or alternatively, the protruding components may be formed separately and assembled together, and then the rotor element.

  In use, the rotationally asymmetric rotor element is desirably positioned as the last rotor element of the pump adjacent to the pump exhaust (outlet). The pump may further comprise rotationally symmetric rotor elements that mesh with each other.

  In another aspect, the present invention provides a vacuum or dry pump that includes a rotor having at least one rotationally asymmetric roots rotor element, the rotor element being a plurality of rotationally asymmetric arrangements about a rotational center of the rotor element. Having protrusions.

The present invention is also a vacuum pump having a pump inlet for receiving fluid to be pumped, a pump outlet for discharging pumped fluid, and a stator containing first and second shafts, the first shaft; The second shaft is configured to rotate in reverse in the stator, and each shaft is provided with a plurality of rotor elements, and the rotor element of the first shaft is connected to the rotor element of the second shaft. Each of the rotor elements that are adapted to mesh with each other near the pump outlet has a plurality of protrusions extending from the center of rotation, the protrusions being rotationally asymmetrically disposed about the center of rotation of the rotor element. Provide a vacuum pump.
For illustrative purposes, several embodiments of the rotor element of the present invention will now be described with reference to the drawings.

  FIG. 1 schematically shows an embodiment of a multistage vacuum pump. In the illustrated embodiment, the pump has two parallel aligned rotating shafts 2a, 2b, each supporting a rotor assembly 1a, 1b in the form of a series of rotor elements. The shafts 2a and 2b are mounted in the bearings 3a, 3b, 3c and 3d. The shaft 2b is driven by the drive mechanism 3, and a timing gear device (not shown) connects the two shafts 2a and 2b to each other so that the two shafts rotate in reverse in synchronization. The rotor elements 1a and 1b are housed in a housing unit 4, which constitutes a stator element having a series of chambers each housing a pair of rotor elements 1a and 1b.

  In this embodiment, each of the rotor elements 1a, 1b has a roots profile. The shafts 2a and 2b are separated from each other by a distance shorter than twice the maximum radius of the rotor, and when the shaft 2b rotates, the rotor meshes with each other so that the lobe of the rotor element 1b has a space between the lobes of the rotor element 1a. It has come to pass.

  FIG. 2 shows the axial gas flow path in the pump shown in FIG. A pump inlet 7 provided in the housing 4 is in direct communication with a chamber containing a pair of intermeshed rotor elements 1a, 1b located at the first or first stage of the pump, i.e. closest to the inlet 4, for example Gas received from the process chamber is transported to the first stage of the pump. A channel 6 is provided between adjacent stages to direct pumped gas from one stage outlet to the next stage inlet. A pump outlet 5 is provided in communication with an exhaust stage, ie a pair of intermeshing elements located closest to the outlet 5, so that the pumped gas can be discharged from the pump.

  FIG. 3 shows a Roots-type rotor element forming the exhaust stage of the pump of FIG. Each element has a center of rotation R, and five lobes extend radially or radially from this center of rotation. Each lobe has vertices A1, A2, A3, A4, A5, and the roundness of these vertices is directed around the center of rotation of the rotor element. Sector angles (i.e., interior angles between R of adjacent vertices) are shown.

  By pulling the lobes apart from each other by different rotation angles, the frequency of the pulses at the exhaust becomes irregular. As a result, regular pulses cannot be heard. In contrast, the generated noise spreads over a range of frequencies. Such random noise is unlikely to be enhanced by the pipeline system in the pump system or is likely to excite various frequencies in the duct system, thereby reducing the occurrence of the above-mentioned problems.

  Similar advantages are associated with the configuration of the rotor element for the pump exhaust stage utilizing a ball socket type pumping mechanism as shown in FIG. The ball socket stage consists of a first “ball” rotor element, generally designated 21, and a second “socket” rotor element, generally designated 22. The ball rotor element has a central part 23 of substantially circular cross-section and five protrusions 24a, 24b, 24c, 24d, 24e, which are spaced at unequal angular intervals about the center of rotation R of the central part 23. Are provided in the radial direction. These protrusions may be manufactured separately and then joined to the central part during the next assembly of the rotor. As a modification, these protrusions may be formed as an integral part of the central part. The socket rotor element consists of a single part 25, which is a substantially circular cross-section part, from which five sockets 26a, 26b, 26c, 26d, 26e are cut and thereafter five protrusions 27a. , 27b, 27c, 27d, 27e are provided in a radial direction with unequal angular intervals around the rotation center R of the part 25, so that in use, the protrusions 24a, 24b, 24c, 24d, 24e are sockets during use. 26a, 26b, 26c, 26d, and 26e are engaged with each other and the pumped gas is drawn through the pump.

  The foregoing describes only two embodiments of the invention, but it is to be understood that it does not limit the true scope of the invention as set forth in the claims.

It is a figure which shows one Embodiment of a multistage pump. It is XX arrow sectional drawing of FIG. It is a figure which shows the form of the single stage of the pump of FIG. FIG. 2 shows a single stage variant embodiment of the pump of FIG. 1.

Claims (14)

  A vacuum pump having a chamber containing first and second meshing rotor elements, wherein the first rotor element and the second rotor element are attached to respective shafts, At least one of the rotor elements has a plurality of protrusions extending from a rotation center, and the protrusions are arranged rotationally asymmetrically around the rotation center of the rotor element. Being a vacuum pump.   Each of the protrusions has a vertex and a sector angle that are radially spaced from the rotation center, and an angle between each vertex pair with respect to the rotation center is an equivalent sector angle between adjacent vertex pairs ( 2. A vacuum pump according to claim 1, which is different from equivalent sector angle).   The vacuum pump according to claim 2, wherein the sector angles between adjacent vertices are all different from each other.   The vacuum pump according to claim 3, wherein the sector angle is selected at random.   The vacuum pump according to claim 1, wherein the rotor element has three or more protrusions.   The vacuum pump according to claim 5, wherein the rotor element has 3 to 9 protrusions.   The vacuum pump of claim 6, wherein the rotor element has 4, 5, 6 or 7 of the protrusions.   The vacuum pump according to claim 1, wherein the protrusion is formed as an integral part of the rotor element.   The vacuum pump according to claim 1, wherein both the first rotor element and the second rotor element have the plurality of protrusions.   The vacuum pump of claim 9, wherein each rotor element is a Roots rotor element and the protrusions are lobes of the Roots rotor element.   The vacuum pump according to any one of claims 1 to 8, wherein the rotor element is a ball rotor element of a ball socket stage, and the protrusion is formed of a ball provided on the ball rotor element.   The vacuum pump according to claim 1, wherein the rotor element is located near the outlet of the pump.   The vacuum pump according to claim 1, wherein each shaft is provided with at least one additional rotor element.   A vacuum pump having a pump inlet for receiving fluid to be pumped, a pump outlet for discharging pumped fluid, and a stator containing first and second shafts, the first shaft and the second shaft The shaft is configured to rotate in reverse in the stator, and each of the shafts is provided with a plurality of rotor elements, and the rotor element of the first shaft meshes with the rotor element of the second shaft. Each of the rotor elements that mesh with each other near the pump outlet has a plurality of protrusions extending from a center of rotation, the protrusions being rotationally asymmetric about the center of rotation of the rotor element. Arranged, vacuum pump.

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