TW202305244A - Holweck drag pump - Google Patents

Abstract

The present invention provides a Holweck drag pump comprising a non-ferromagnetic helically grooved surface for conveying a gaseous medium, said surface being provided by a rotor shaft-facing surface of a motor stator of the Holweck drag pump or by an outer surface of a rotor shaft, preferably by a rotor shaft-facing surface of a motor stator of the Holweck drag pump or motor stator-facing outer surface of a rotor shaft. The present invention also provides a permanent magnet motor for use in a vacuum pump, and a vacuum pump comprising such a Holweck drag pump and/or permanent magnet motor.

Description

Holvik trailed pump

The present invention relates to a Holweck drag pump and in particular a Holweck drag pump having a non-metallic helically grooved surface for conveying a gaseous medium. The invention further relates to a permanent magnet motor for use in a vacuum pump and a vacuum pump comprising the permanent magnet motor and/or the Holvik drag pump.

Vacuum pumps (including, for example, a turbomolecular pump mechanism) are known to include a housing providing an inlet and an outlet. The housing may house one or more pump mechanisms. A turbomolecular pump mechanism may form one of these mechanisms and generally includes at least one rotor having a plurality of annular arrays of axially spaced inclined rotor blades. Typically, the vanes are evenly spaced within each array and extend radially outward from a rotor shaft. The stator of the pump surrounds the rotor and comprises at least one annular array of inclined stator blades alternating with the array of rotor blades in an axial direction. Each pair of adjacent rotor blade arrays and stator blade arrays is referred to herein as a level. A turbomolecular pump mechanism may include a plurality of such stages.

Typically, a motor is disposed within the housing to rotate the rotor shaft during operation of the pump. The motor can be an induction motor or a permanent magnet motor. As the rotor rotates, the rotor blades impinge on incoming molecules of the gaseous medium. This impact converts the mechanical energy of the blades into the momentum of gas molecules, which are guided through the pump towards the pump outlet.

A vacuum pump may typically comprise a turbomolecular pump stage followed by at least one molecular drag stage, such as a Holvik drag pump or Siegbahn pump. The Hallvik molecular drag stage is known to include a gap (referred to herein as a channel) between a rotating cylinder and the like arranged adjacent to a stator, wherein the stator or cylinder has a helical groove or a thread. The impact of the gas molecules on the rotating rotor imparts a stimulating velocity to it causing displacement of the gaseous medium along the channel.

To increase the efficiency of the molecular drag stage and thereby increase the overall compression ratio of the vacuum pump, several concentric molecular drag stage channels may be provided around the rotor axis. Therefore, it is desirable to provide a plurality of channels in the molecular drag stage. Typically, one of the limiting factors in the number of molecular drag channels that can be included in a vacuum pump is the total available size of the pump. A vacuum pump is usually part of a larger system with a room set aside to accommodate the vacuum pump. Accordingly, it would be desirable to provide vacuum pumps of reduced size.

Due to the concentric arrangement of the molecular drag stage channels, when the vacuum pump is in use, the direction of gas flow through is opposite between adjacent channels. Therefore, for practicality, usually only an odd number of molecular drag stages are used so that the outlet of the final channel is located away from the turbomolecular pump mechanism in which the pump outlet can be easily located. Therefore, the design freedom of current Holvik molecular drag pumps is somewhat restricted, which reduces the efficiency of the pumping system.

There is a constant need to improve the Holvik molecular drag stage, which is more efficient, simpler and cheaper to manufacture, increases the compression ratio of vacuum pumps, and offers a high degree of design freedom.

The present invention at least partially addresses these and other problems of the prior art.

Thus, in a first aspect, the present invention provides a Holvik drag pump comprising a non-ferromagnetic helically grooved surface for conveying a gaseous medium. The surface is provided by a rotor shaft facing surface of a motor stator of the Holvik drag pump or an outer surface of a rotor shaft. Preferably, the surface is provided by a rotor shaft facing surface of a motor stator of the Holvik drag pump or an outer motor stator facing surface of a rotor shaft.

Preferably, the surface provides the innermost and/or last channel of the Holvik drag pump. The last innermost and/or last channel may be directly fluidly connected to an outlet of the Holvik drag pump.

The motor stator is preferably configured to generate an electromagnetic drive field for transmitting a torque to the rotor. The motor stator may have a core comprising windings preferably arranged around a central magnetic, in particular soft magnetic and/or metallic material. Typically, the windings are metallic. Preferably, the Holvik drag pump comprises a motor stator surrounding a rotor shaft with substantially no ferromagnetic material between a rotor shaft facing surface of the coil wound core of the motor stator and a metal of the rotor shaft between surfaces.

A gap, specifically a radially extending gap, is located between the motor stator and the rotor shaft. Preferably, the gap extends along the motor stator in an axial direction, ie in a direction parallel to the axis of rotation of the rotor. The electromagnetic drive field extends across the gap to transmit drive torque to the rotor shaft.

The inventors have found that, particularly on the motor stator, the use of a ferromagnetic helically grooved surface can be disadvantageous. In use, such a ferromagnetic surface may be present in the electromagnetic drive field generated by the motor of the Holvik drag pump. The presence of a ferromagnetic surface can disrupt the electromagnetic drive field by creating parasitic eddy currents, and thus can reduce the efficiency of the motor. Furthermore, the parasitic eddy currents induced in the surface can lead to a local temperature increase and thermal expansion of the surface when present in an electromagnetic field. Thermal expansion of the surface is undesirable because increased tolerance must be provided, which in turn reduces the efficiency of the motor.

Advantageously, the non-ferromagnetic helically grooved surface can be present in and minimally disturb the electromagnetic drive field generated by the motor of the Holvik drag pump. The non-ferromagnetic helically grooved surface provides additional pump capacity for the Holvik drag pump. Therefore, providing such a non-ferromagnetic surface can improve pumping performance without negatively affecting motor efficiency.

For purposes of the present invention, a helical groove surface may be a substantially concave helical groove defined in a surface. For the avoidance of doubt, the or each helical groove may be bounded by one or more corresponding male helical threads formed on the surface. Preferably, all grooves are non-ferromagnetic. Preferably, the groove(s) are monolithic. The relative thickness of the trench(s) can be selected depending on the intended use.

The helically grooved surface may comprise one or more helically grooves, eg, from about 1 to about 15 helically grooves. The helical groove(s) may be a substantially constant pitch helix, or alternatively may be a variable pitch helix. The helical groove(s) may have a substantially rectangular, trapezoidal, semicircular or other cross-sectional convex profile. The cross-sectional profile and/or size of the helical groove(s) may be uniform or may vary along the length of the helical groove(s).

Advantageously, since the surface comprising the helical groove is non-ferromagnetic, a high degree of design freedom is available for the configuration of the helical groove. Providing the helical groove in a non-ferromagnetic surface results in negligible disruption of the electromagnetic drive field of the motor compared to a helical groove on a ferromagnetic surface. Thus, the present invention increases the freedom of design of the helical groove surface while allowing efficient operation of the pump.

Preferably, the at least one helical groove extends axially from a first end of the surface of the motor stator to a second end or a distance along the length of the motor stator of the rotor shaft.

In an embodiment, the Holvik drag pump may include a conduit defining an axial passage extending through the Holvik drag pump. The axial passage may extend from an opening in a base of the pump to an opening axially beyond a pump inlet. The rotor shaft and motor stator may extend around the conduit. The conduit may be coaxial with the axis of rotation of the rotor shaft.

Preferably, the conduit defining the axial channel may be located radially inward of the surface of the non-ferromagnetic helical groove. Preferably, the duct defining the axial channel may be located within the rotor shaft.

Advantageously, the axial channel through the Holvik drag pump may provide a central path for connectors, a mounting shaft, a power supply and/or other components through the Holvik drag pump, As discussed in more detail with respect to embodiments of another aspect defined herein. This can assist in providing uniform airflow, especially when the inlet of the Holvik drag pump is connected to an outlet of a turbomolecular pump mechanism.

In another aspect, the invention provides a permanent magnet motor for use in a vacuum pump. The permanent magnet motor includes a rotor shaft of the vacuum pump and a motor stator. A rotor shaft-facing surface of the motor stator and a motor stator-facing surface of the rotor shaft form a channel of a Holvik drag pump. One of the surfaces is non-ferromagnetic and provides helical grooves for conveying a gaseous medium.

Preferably, the vacuum pump including the permanent magnet motor may include a Holvik drag pump mechanism. More preferably, the channel of the Holvik drag pump of the permanent magnet motor is fluidly connectable to the Holvik drag pump mechanism.

Preferably, the surface provides the innermost and/or last channel of the Holvik drag pump. The last innermost and/or last channel may be fluidly connected to an outlet of the Holvik drag pump.

Preferably, a rotor shaft-facing surface of a motor stator has helical grooves for conveying a gaseous medium and is non-ferromagnetic. The motor stator facing surface of the rotor shaft may be substantially smooth. For the purposes of the present invention, substantially smooth may define one of the surfaces without helical grooves. Advantageously, balancing the rotor can be easier if the rotor has a smooth (eg, featureless) surface and the helical groove is on a stator.

As explained with respect to the previous aspects, the motor stator is preferably configured to generate an electromagnetic drive field for transmitting a torque onto the rotor. The motor stator may have a core comprising windings preferably arranged around a central magnetic, in particular soft magnetic and/or metallic material. Typically, the windings are metallic. Preferably, substantially no ferromagnetic material is located between the rotor shaft facing surface of the coil wound core of the motor stator and the metallic surface of the rotor shaft.

A gap, specifically a radially extending gap, is located between the motor stator and the rotor shaft. Preferably, the gap extends along the motor stator in an axial direction, ie in a direction parallel to the axis of rotation of the rotor. The electromagnetic drive field extends across the gap to transmit drive torque to the rotor shaft.

Typically, the rotor shaft is radially surrounded by the motor stator and the rotor shaft and motor stator are radially separated by a gap. Preferably, the gap extends through the motor in an axial direction, ie in the direction of the axis of rotation of the rotor shaft.

As discussed above, the inventors have discovered that employing a ferromagnetic helically grooved surface especially on the motor stator can be disadvantageous due to disruption of the electromagnetic drive field of the motor and formation of parasitic eddy currents in the surface.

Advantageously, the non-ferromagnetic helically grooved surface can be present in and minimally disturb the electromagnetic drive field generated by the permanent magnet motor. We have found that the gas compression provided by the channel of the Holvik drag pump is suitable to overcome any increased gas friction between the rotor shaft facing surface of the motor stator and the motor stator facing surface of the rotor shaft . Therefore, providing such a non-ferromagnetic helical grooved surface can improve pumping performance with little impact on the efficiency of the motor. Such a motor can efficiently provide drive torque to the rotor shaft while increasing the compression ratio of the pump.

Advantageously, because the surface comprising the helical groove is non-ferromagnetic, a high degree of design freedom is available for the configuration of the helical groove. Providing the helical groove in a non-ferromagnetic surface results in negligible disruption of the electromagnetic drive field of the motor compared to a helical groove in a ferromagnetic surface. Thus, the present invention increases the freedom of design of the helical groove surface while allowing efficient operation of the pump.

Preferably, the at least one helical groove extends axially from a first end of the surface of the motor stator to a second end or a distance along the length of the motor stator of the rotor shaft.

The following features are applicable to the Holvik drag pump and/or permanent magnet motor according to any of the foregoing aspects or embodiments.

Preferably, the non-ferromagnetic surface has a magnetic permeability of less than about 1.0×10 ⁻⁴ H/m, preferably less than about 1.260×10 ⁻⁶ H/m. Additionally or alternatively, the non-ferromagnetic surface may have a relative magnetic permeability of less than about 10, preferably less than about 1.05.

The non-ferromagnetic surface may have a resistivity of less than about 2.0×10 ⁻⁸ Ω·m, preferably less than about 6.9×10 ⁻⁷ Ω·m.

Preferably, the helically grooved surface is provided by injection moulding, an insert, co-molding and/or coating attached to a rotor or stator.

Preferably, the helically grooved surface can be manufactured by injection moulding, extrusion, additive manufacturing and/or machining. A further finishing step may be performed, for example a machining step. Optimally, the helically grooved surface may be injection molded, followed by a machining step.

In embodiments where the helically grooved surface is provided by an insert, the insert may be coupled to one of a vacuum pump by a clamp, an interference fit, a snap fit, and/or one or more gaskets. Motor stator or rotor shaft. Advantageously, such an insert is separable from the Holvik drag pump or permanent magnet motor and thus replaceable. Additionally, this insert can be retrofitted to an existing Holvik drag pump or permanent magnet motor. The insert can include a substantially tubular member configured to be inserted into a gap between the motor stator and rotor shaft. Preferably, the insert can be configured to couple to the motor stator and a radially inward surface thereof can define the helical groove non-metallic surface.

The insert can be monolithic or preferably comprises segments configured to provide the non-ferromagnetic surface when assembled in situ, for example within the Holvik drag pump or permanent magnet motor. Advantageously, providing the insert as a plurality of interconnectable segments enables easier assembly of the insert. Furthermore, it also enables the insert to be retrofitted to existing Holvik drag pumps or permanent magnet motors.

In embodiments where the helical groove surface is provided by a co-mold and/or insert, the co-mold and/or insert may provide the added benefit of isolating the magnetic core of the motor stator. During operation of the motor, a gaseous medium can be conveyed through the gap of the motor. The gaseous medium can carry particulate matter which can degrade the windings which are not insured. Therefore, providing the helically grooved surface as a co-mold and/or insert prevents particle contamination from damaging the magnetic core during operation of the vacuum pump. Therefore, the magnetic core does not require frequent maintenance and replacement.

In embodiments where the helically grooved surface is provided by a coating, the coating may preferably be attached to a stator, more preferably to the motor stator of the permanent magnet motor.

Preferably, the spiral grooved surface is integrally formed with the rotor or stator.

Preferably, the non-ferromagnetic surface comprises polymeric, ceramic or composite materials. Optimally, the non-ferromagnetic surface comprises a polymeric material. Preferred polymers are selected from the group consisting of thermoplastics or thermosets. In particular, thermoplastics classified as high performance thermoplastics are preferred due to their mechanical and thermal properties. Suitable thermoplastic polymers include polyetheretherketone (PEEK), polytetrafluoroethylene (PTFE), polyamide, polyphenylene sulfide (PPS) and their derivatives and copolymers. PEEK is especially good. A suitable thermosetting polymer may be a cured epoxy resin.

Advantageously, these materials reduce magnetic fields that interfere with the motor. Furthermore, it is relatively mechanically rigid, thermally stable and has a low cost. It is also injection moldable and is easily machined and/or injection molded for direct production.

The polymeric material may additionally comprise one or more from the group consisting of antistatic agents, antioxidants, mold release agents, flame retardants, lubricants, colorants, flow enhancers, fillers (including nanofillers) ), light stabilizers and UV absorbers, pigments, anti-weathering agents, and plasticizers.

Additionally or alternatively, the polymeric material may comprise one or more reinforcing elements, such as glass fibers, carbon fibers or particles.

Preferably, the non-ferromagnetic surface is monolithic. In particular, the non-ferromagnetic surface is substantially provided by a single monolithic material. Advantageously, this simplifies the manufacture of the non-metallic surface. For example, the non-ferromagnetic surface or the body comprising the non-ferromagnetic surface can be injection molded to provide a relatively low cost, fast and uniformly reproducible manufacturing method.

The body including the non-metallic surface optionally includes a through-bore fluidly connected to an outlet of the Holvik drag pump mechanism. Therefore, the delivery direction of the gaseous medium through the Holvik channel can be substantially towards or away from the outlet of the Holvik drag pump mechanism.

In some embodiments, the permanent magnet motor may include a conduit defining an axial passage extending through the motor. The axial channel may extend from an opening in a base of the motor to axially beyond an opening at an end opposite the base. Preferably, the duct is delimited within the rotor shaft. The axial channel may be coaxial with the axis of rotation of the rotor shaft. Advantageously, the axial passage through the motor can provide a central path for connectors, a mounting shaft, a power supply, and/or other components, as in embodiments relative to another aspect defined herein discuss.

In another aspect, the present invention provides a vacuum pump comprising a permanent magnet motor and/or a Holvik drag pump according to any preceding aspect or embodiment.

Preferably, the Holvik drag pump mechanism includes at least one further channel arranged concentrically around the rotor shaft. More preferably, the Holvik drag pump mechanism includes from about 2 to about 8 additional channels, wherein the channels are concentrically arranged about the rotor shaft.

When the Holvik drag pump mechanism is in operation, in the subsequent channel the gaseous medium can be pumped in the opposite direction. The directions may be substantially parallel to the axis of rotation of the rotor shaft. In prior art vacuum pumps, having an even number of stages complicates the design by allowing the gaseous medium to exit the last stage within the pump mechanism to require additional channels or drillings to facilitate movement of the gaseous medium to the outlet of the vacuum pump. Therefore, generally there can be only an odd number of molecular drag stages, so that the last molecular drag stage terminates close to the outlet of the vacuum pump, thereby limiting the freedom of design of the vacuum pump.

Advantageously, in a pump according to the invention, the final channel of the Holvik drag pump mechanism may be provided by the non-ferromagnetic helical grooved surface. The extra channel, preferably adjacent to the rotor shaft, can increase the compression ratio of the pump and allow a more efficient use of space to provide the extra channel.

Preferably, the vacuum pump further comprises at least one stage of a turbomolecular pump mechanism fluidly connected to the Holvik drag pump mechanism. Preferably, the vacuum pump comprises about 2 or more turbomolecular pump stages fluidly connected to the Holvik drag pump mechanism. The at least one turbomolecular pump mechanism may comprise one or more stages. Preferably, each turbomolecular pump mechanism comprises from about 2 to about 8 stages, eg 5 stages.

Preferably, the at least one turbomolecular pump mechanism (or stage) is fluidly arranged upstream of the Holvik drag pump mechanism (or stage). During operation of the vacuum pump, a gaseous medium can be conveyed from an outlet of the turbomolecular pump stage to an inlet of the Holvik drag pump mechanism.

Preferably, the at least one turbomolecular pump stage and the Holvik drag pump mechanism can be arranged on a single drive shaft. Preferably, the at least one turbomolecular pump stage and the Holvik drag pump mechanism are drivable by the same motor during operation of the vacuum pump. For example, the at least one turbomolecular pump stage and the Holvik drag pump mechanism may be driven by a permanent magnet motor as set forth in the preceding aspect.

Preferably, the vacuum pump may be a turbomolecular pump manufactured by Edwards Ltd.

Preferably, the vacuum pump may comprise a conduit defining an axial passage extending through the vacuum pump. The conduit may extend from an opening in a base of the pump to an opening axially beyond the pump inlet. The rotor shaft and motor stator may extend around the conduit. Preferably, the axial channel is coaxial with the axis of rotation of the drive shaft.

Preferably, the conduit defining the axial channel may be located radially inward of the surface of the non-ferromagnetic helical groove. Preferably, the conduit defining the axial channel is located within the drive shaft.

The vacuum pump can further include a plate configured to shield the inlet of the turbomolecular pump mechanism (ie, the pump inlet). The plate can be configured to block the pump inlet by a controllable amount. Thereby, the board can control the conduction of an inlet of the vacuum pump. The vacuum pump may further include a shaft for mounting the plate. The shaft may be hollow and extend around the channel. The plate may include the conduit extending through a hole in a central portion. The plate can be a valve plate.

Preferably, the conduit defining the axial channel may be located within the single drive shaft of the turbomolecular pump stage and the Holvik drag pump mechanism.

Preferably, the conduit extends axially through the entire vacuum pump, including both the Holvik drag pump mechanism and the turbomolecular pump mechanism. Providing such a "hollow" vacuum pump enables the use of a poppet valve at the pump inlet (which may be the inlet of the turbomolecular pump). Advantageously, this can be used for pressure control and/or isolation.

During use, the pump inlet can be fluidly connected to a vacuum chamber. For many processes performed in a vacuum chamber, a substrate may be mounted within the chamber, such as semiconductor etching processes. To achieve a high quality result, these processes require uniform gas flow across a substrate. Mounting the base plate above the pump inlet can help provide uniform airflow across the base plate. However, in prior art systems, the support member to some extent and more importantly, the power and control supplied to the substrate can interfere with the airflow and reduce the uniformity of airflow across the substrate. The conduit of the present invention enables a substrate mounting shaft to be fed through the vacuum pump. Additionally or alternatively, the conduit may enable connectors, power supplies, control wiring and/or cooling supplies to be fed through the vacuum pump so that they are centrally aligned below the substrate. This enables uniformity of gas flow around the substrate during operation.

Additionally, the valve plate blocking the pump inlet by a controllable amount provides rapid pressure control and reduces particulate generation and dropout. In addition, it can provide symmetrical flow around the plate and can reduce non-uniformity in airflow across a wafer mounted in the chamber. It should be noted that although the plate may be a flat circular configuration, it may also have other forms, such as a conical form. In general, it is advantageous if the plate has a circular cross-section, since this improves the uniformity of the air flow.

A hollow pump with a plate at least partially shielding the pump inlet can provide efficient and rapid control of the inlet conduction to the pump and thus the pressure in the chamber and a more uniform airflow over the base plate, wherein the axial direction of the plate Movement provides entry conduction control.

The panel can at least partially block the access. Movement of the plate can cause the inlet conductance to vary as the gas flows around the edge of the plate. In some cases, the plate may extend beyond the pump inlet in all axial positions. In other cases, the plate may extend beyond the inlet in some axial positions. Axial movement can be defined as movement substantially parallel to the rotor shaft of the pump. The plate can be mounted on a shaft. Preferably, the shaft may be hollow and may extend around the conduit defining the channel.

In some embodiments, the plate may be mounted on the end of the drive shaft of the vacuum pump proximate the inlet of the turbomolecular pump. The drive shaft is movable in an axial direction relative to the motor stator. The drive shaft may be mounted to or positioned within the pump via electromagnetic bearings. A current supplied to the electromagnets associated with the bearings can control the axial position of the drive shaft and thereby the axial position of the plate. The pump may include an actuator associated with the drive shaft for varying the axial position of the shaft and the plate.

In alternative embodiments, the pump may include the plate mounted to a mounting shaft separate from the drive shaft. The mounting shaft can be configured not to rotate. The mounting shaft is movable in an axial direction relative to the motor stator. The pump may include an actuator associated with the mounting shaft for varying the axial position of the shaft and the plate.

In some embodiments, the plate may include an O-ring on a surface facing the pump inlet. In alternative embodiments, the plate may not include an O-ring.

The pump can include control circuitry configured to control the axial position of the plate. The control circuitry may include an input configured to receive a signal indicative of a pressure produced by the vacuum pump. The control circuitry can be configured to control the axial position of the plate based on the signal.

An advantage of having a passage through the vacuum pump can be that any connection to a substrate mount, such as a cathode, can pass through the pump and go under the substrate mount near its center. In some embodiments, the end of the conduit near the pump inlet may include mounting features for mounting a substrate mount, such as a cathode. This may allow the substrate to be centrally mounted above the pump inlet without the need for a separate substrate support which itself would disrupt uniform gas flow.

A vacuum pump suitable for use herein is described in WO 2020/012154, which is incorporated herein by reference. In particular, reference is made to Figures 1 to 3, which illustrate a vacuum pump having an axial passage.

Although in the described example the vacuum pump comprises a Holvik pump mechanism and a turbomolecular pump mechanism, other vacuum pumps with a central shaft (such as a Holvik pump alone or in combination with an alternative pump) could also be used. Suitable and may include a passage through the center and an axially movable valve plate.

In another aspect, the present invention provides a Holvik drag pump, permanent magnet motor and/or vacuum pump according to any preceding aspect or embodiment, wherein the non-ferromagnetic helical grooved surface is formed by injection molding, extrusion Compression, additive manufacturing and/or machining programs are available.

The program may optionally include one or more finishing steps. This final processing step may include, for example, a machining step, applying a coating and/or surface treatment.

For the avoidance of doubt, all the above-mentioned aspects and embodiments may be combined with mutatis mutandis.

FIG. 1 is a schematic cross-sectional view of an embodiment of a vacuum pump according to the present invention.

The vacuum pump (1) includes a turbomolecular pump mechanism (2) and a Holvik dragging pump mechanism (3). The turbomolecular pump mechanism (2) is fluidly connected to the Holvik drag pump mechanism (3). The vacuum pump (1) comprises a casing (4) substantially surrounding a turbomolecular pump mechanism (2) and a Holvik dragging pump mechanism (3).

The turbomolecular pump mechanism (2) includes a rotor. The rotor has a plurality of annular arrays (5) of axially spaced inclined rotor blades. The vanes are evenly spaced within each array (5) and extend radially outward from a rotor shaft (6). A stator surrounds the rotor array (5) and includes a plurality of annular arrays (7) of inclined stator blades alternating with the rotor blade array (5) in an axial direction. Each adjacent pair of arrays of rotor and stator blades forms a stage of a turbomolecular pump stage (2).

The vacuum pump (1) further comprises a Holvik drag pump stage (3). The Holvik drag pump mechanism (3) is fluidly connected to the turbomolecular pump mechanism (2). The Holvik drag pump mechanism (3) includes a rotor (8). The rotor (8) is directly connected to the rotor shaft (6). The rotor (8) includes a first cylinder (9) and a second cylinder (10). The first cylinder (9) and the second cylinder (10) are arranged concentrically around the rotor shaft (6) and are connected to the rotor shaft (6).

The Holvik drag pump mechanism (3) further includes a first stator (11). The first stator (11) has a helically grooved surface facing the radially outward surface of the first cylinder (9). The radially outward helical groove surfaces of the first stator (11) and the first cylinder (9) define a first channel of the Holvik drag pump mechanism (3). The radially inward spiral groove surface of the first stator (11) faces the radially outward surface of the second stator (12) to define a second channel of the Holvik drag pump mechanism (3). The radially outward surface of the second cylinder (10) faces the radially inward spiral groove surface of the second stator (12) to define a third channel of the Holvik drag pump mechanism (3). The radially inward surface of the second cylinder (10) faces the radially outward spiral groove surface of the third stator (13) to define a fourth channel of the Holvik drag pump mechanism (3).

The Holvik drag pump mechanism (3) further includes a permanent magnet motor (14) configured to provide a drive torque to the rotor shaft (6) during operation of the vacuum pump (1). Rotation of the rotor shaft (6) is configured to rotate the rotor blade array (5) of the turbomolecular pump mechanism (2) and the rotor(s) (8) of the Holvik drag pump mechanism (3). The permanent magnet motor (14) includes a motor stator (15). The motor stator (15) includes a magnet core (16) which includes windings. The winding is a wire wrapped around a laminated soft iron core. The motor stator (15) further comprises a non-ferromagnetic portion defining a helically grooved surface (17) facing the rotor shaft (6). The surface of the rotor shaft (6) and the non-ferromagnetic helical groove surface (17) define a fifth and last channel of the Holvik drag pump mechanism (3).

During operation, the permanent magnet motor (14) applies a driving torque to the rotor shaft (6), which in turn drives the rotor blade array (5) of the turbomolecular pump mechanism (2) and the Holvik drag The rotor (8) of the pump mechanism (3) rotates. The gaseous medium conveyed by the turbomolecular pump mechanism (2) enters the Holvik drag pump mechanism (3). The first and second cylinders (9, 10) impact gas molecules and convert mechanical energy into gas molecular momentum. Thereby, the rotation of the first and second cylinders (9, 10) relative to the spiral groove surfaces of the first, second and third stators (11, 12, 13) transports the gas medium through the Holvik dragging method respectively. The first, second, third and fourth channels of the pump mechanism (3). Finally, the gaseous medium is conveyed through the fifth channel due to the rotation of the rotor shaft (6) relative to the non-ferromagnetic helical grooved surface (17) of the motor stator (15).

In the example shown, the non-ferromagnetic helical groove surface (17) is polymeric, such as epoxy. Advantageously, this protects the magnet core (16) from particle damage during operation of the vacuum pump (1). The non-ferromagnetic helically grooved surface (17) is monolithic.

The fifth channel of the Holvik drag pump mechanism (3) increases the compression ratio of the vacuum pump (1). This increased compression ratio outweighs any increased friction caused by the introduction of the fifth channel of the Holvik drag pump mechanism (3). Furthermore, since it is non-ferromagnetic, it does not substantially negatively affect the performance of the motor.

2 is a schematic cross-sectional view of an alternative embodiment of a vacuum pump according to the present invention. Figures 1 and 2 have many corresponding features which will not be repeated and the same reference numerals will be used for the same.

In this embodiment, the motor stator (15) further includes an insert (18). The insert (18) includes a radially inwardly helical grooved surface (19). The helically grooved surface (19) and the radially outward surface of the rotor shaft (6) define the fifth channel of the Holvik drag pump mechanism (3). Insert (18) is a non-ferromagnetic material. Preferably, the insert is polymeric, such as epoxy, polytetrafluoroethylene or polyether ether ketone.

The insert (18) is coupled to a body of the motor stator (15) by means of securing means, such as an O-ring (20). The insert (18) is removable from the motor stator (15) and replaced when worn. Advantageously, this avoids the need to replace the entire rotor stator. In addition, the insert (18) can be modified according to the existing vacuum pump to increase the compression ratio.

Figure 3 provides a graph comparing the compression ratio and backing pressure of different vacuum pumps. Line (21) shows the compression ratio of a vacuum pump comprising a turbomolecular pump mechanism followed by a Holvik drag pump mechanism at different backing pressures, where the difference between the turbomolecular pump mechanism and the Holvik drag pump mechanism The rotation of the rotor is driven by a permanent magnet motor according to the prior art, ie without a Holvik drag pump channel inside the permanent magnet motor. Line (22) shows the compression ratio of a vacuum pump at different backing pressures, except that the vacuum pump also includes a Holvik drag pump channel in the permanent magnet motor (i.e., the vacuum pump depicted in Figure 1), It is the same as the compression ratio of line (21).

It can be seen that the compression ratio of the line (22) is greater than that of the line (21) for the corresponding pre-stage pressure. Therefore, the additional channel of the Holvik drag pump within the permanent magnet motor increases the overall compression ratio of the vacuum pump.

For the avoidance of doubt, the features of any aspect or embodiment described herein may be combined mutatis mutandis. It should be understood that various modifications may be made to the illustrated embodiments without departing from the spirit and scope of the invention as defined by the appended claims as construed under the patent laws.

1: vacuum pump 2: Turbomolecular pump mechanism / turbomolecular pump stage 3: Holvik dragging pump mechanism / Holvik dragging pump stage 4: Shell 5: Rotor blade array 6: Rotor shaft 7: Angular array of stator blades 8: rotor 9: The first cylinder 10: Second cylinder 11: The first stator 12: Second stator 13: The third stator 14:Permanent magnet motor 15: Motor stator 16:Magnet core 17: Non-ferromagnetic spiral grooved surface 18: Insert 19: Spiral grooved surface 20: O-ring 21: line 22: line

Preferred features of the present invention will now be described by way of example with reference to the accompanying drawings, in which:

FIG. 1 shows a schematic cross-sectional view of an embodiment of a vacuum pump according to the present invention.

Figure 2 shows a schematic cross-section of an alternative embodiment of a pump stage according to the invention.

Figure 3 shows a graph comparing the compression ratio and backing pressure of different vacuum pumps.

1: vacuum pump

2: Turbomolecular pump mechanism / turbomolecular pump stage

3: Holvik dragging pump mechanism / Holvik dragging pump stage

4: Shell

5: Rotor blade array

6: Rotor shaft

7: Angular array of stator blades

8: rotor

9: The first cylinder

10: Second cylinder

11: The first stator

12: Second stator

13: The third stator

14:Permanent magnet motor

15: Motor stator

16:Magnet core

17: Non-ferromagnetic spiral grooved surface

Claims (15)

A Holvik drag pump comprising a non-ferromagnetic helically grooved surface for conveying a gaseous medium, the surface being formed by one of the motor stators of the Holvik drag pump facing the rotor shaft surface or An outer surface of a rotor shaft is provided, preferably by a rotor shaft-facing surface of a motor stator of the Holvik drag pump or a motor stator outer surface of a rotor shaft. A permanent magnet motor used in a vacuum pump, the permanent magnet motor includes a rotor shaft of the vacuum pump and a motor stator, wherein a surface of the motor stator facing the rotor shaft and a surface of the rotor shaft facing the motor stator form a Hall A channel of a Ervik drag pump in which one of the surfaces is non-ferromagnetic and provides helical grooves for conveying a gaseous medium. The Holvik drag pump and/or permanent magnet motor of claim 1 or 2, wherein the non-ferromagnetic surface has less than about 1.0×10 ^-4 H/m, preferably less than about 1.260×10 ^-6 H/m m, and/or a relative permeability less than about 10, preferably less than about 1.05. The Holvik drag pump and/or permanent magnet motor of any preceding claim, wherein the non-ferromagnetic surface has less than about 2.0×10 ⁻⁸ Ω·m, preferably less than about 6.9×10 ⁻⁷ Ω·m One resistivity. Holvik drag pumps and/or permanent magnet motors as claimed in claims 1 to 4, wherein the helical groove surface is formed by injection molding, an insert, co-molding and/or attached to a rotor or The coating of the stator is provided. The Holvik drag pump and/or permanent magnet motor of any preceding claim, wherein the helically grooved surface is integrally formed with the rotor or stator. The Holvik drag pump and/or permanent magnet motor of any preceding claim, wherein the non-ferromagnetic helical groove surface comprises a polymeric material. The Holvik drag pump and/or permanent magnet motor according to claim 7, wherein the polymer material is selected from epoxy resin, polytetrafluoroethylene, polyether ether ketone, polyamide or polyphenylene sulfide. The Holvik drag pump and/or permanent magnet motor of claim 7 or 8, wherein the polymeric material includes one or more reinforcing elements. The Holvik drag pump and/or permanent magnet motor of any preceding claim, wherein the helical groove surface is monolithic. A vacuum pump comprising a permanent magnet motor and/or a Holvik drag pump according to any one of claims 1 to 10. The vacuum pump of claim 11, wherein the Holvik drag pump mechanism includes at least one additional channel, preferably from about 2 to about 8 additional channels, wherein the channels are concentrically arranged around the rotor shaft. The vacuum pump of claim 11 or 12, further comprising at least one stage of a turbomolecular pump mechanism fluidically connected to the Holvik drag pump mechanism. The Holvik drag pump, permanent magnet motor and/or vacuum pump of any preceding claim, wherein the non-ferromagnetic helically grooved surface is processed by an injection molding, extrusion, additive manufacturing and/or a machining program to provide. The Holvik drag pump, permanent magnet motor and/or vacuum pump of claim 14, wherein the procedure includes one or more final processing steps.

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