阅读说明：本技术 预加载力工具 (Pre-load force tool ) 是由 C.迈尔斯 P.米尔纳 R.萨卢姆 于 2018-04-04 设计创作，主要内容包括：本发明涉及用于指示在涡轮分子泵转子轴承上的轴承预加载力的轴承预加载力计量器。所述计量器包括：壳体；指示器,其用于指示轴承预加载力；以及致动器,其通过构件联接到叶轮接合表面,该构件被构造成在致动器和叶轮接合表面之间提供弹性偏压。本发明还涉及轴承预加载工具以及用于测量在涡轮分子泵上的轴承预加载力的方法。(The invention relates to a bearing preload force gauge for indicating a bearing preload force on a turbomolecular pump rotor bearing. The meter includes: a housing; an indicator for indicating a bearing preload force; and an actuator coupled to the impeller-engaging surface by a member configured to provide a resilient bias between the actuator and the impeller-engaging surface. The invention also relates to a bearing preload tool and a method for measuring bearing preload force on a turbomolecular pump.)

1. A bearing preload force gauge for indicating a bearing preload force on a turbomolecular pump rotor bearing, the gauge comprising: a housing; an indicator for indicating the bearing preload force; and an actuator coupled to the impeller engagement surface by a member configured to provide a resilient bias between the actuator and the impeller engagement surface.

2. A counter according to claim 1 wherein, in use, the bearing preload force is indicated by: coupling the impeller engagement surface with a pump impeller and moving the actuator relative to the engagement surface against the action of the resilient biasing member to overcome the bearing preload force.

3. A counter according to claim 1 or 2 wherein the actuator, the resilient biasing member and an impeller locating member comprising the impeller engaging surface are movable in a reciprocating motion relative to the housing.

4. A counter according to claims 1 to 3, wherein the indicator provides an indication as to whether the bearing preload force is within or outside a predetermined preferred range when the bearing preload force is overcome.

5. A gauge according to claim 4, wherein the indicator provides a first indication as to whether the bearing preload force is within the predetermined preferred range when the bearing preload force is overcome.

6. A gauge according to claim 5, wherein the indicator provides a second indication as to whether the bearing preload force is outside the predetermined preferred range when the bearing preload force is overcome, the second indication being different from the first indication.

7. A gauge according to claims 4-6, wherein when the bearing preload force is overcome, the indicator indicates whether the bearing preload force is above or below the predetermined preferred range if the bearing preload force is outside the predetermined preferred range.

8. A counter according to any preceding claim, wherein the indication provided by the indicator is visual.

9. A counter according to any preceding claim, wherein the indicator comprises a marker coupled to the housing or actuator and a marker identifier, wherein in use the marker and identifier are moveable relative to each other to indicate the bearing preload force.

10. A counter according to claim 9, wherein a marker indicates a lower limit of a predetermined preferred preload force range and a marker indicates an upper limit of the predetermined preferred preload force range.

11. A counter according to claim 9 or 10, comprising indicia indicating when the bearing preload force is within a predetermined preferred range.

12. A counter according to claim 9, 10 or 11, wherein the indicia comprises a stepped upper surface on the housing, and wherein a first step indicates a lower limit of a predetermined preferred preload force range and a second step indicates an upper limit of the predetermined preferred preload force range.

13. A counter according to claim 12, wherein the first and second steps each comprise a secondary marker indicating the predetermined preferred preload force range.

14. A counter according to any preceding claim, wherein the resilient member comprises a spring, preferably a compression spring, preferably a helical compression spring.

15. A counter according to any preceding claim wherein overcoming the bearing preload force is accompanied by an audible signal.

16. A meter according to any preceding claim, further comprising a preload adjuster for altering a bearing preload force on a rotor bearing of the turbomolecular pump.

17. A preload force tool for a turbomolecular pump comprising a rotor bearing under an adjustable preload force, the tool comprising a preload force gauge and a preload force regulator.

18. The method of claim 17, wherein the meter is according to any one of claims 1 to 15.

19. A method for measuring bearing preload force on a turbomolecular pump rotor bearing, the method comprising the steps of:

a) providing a turbomolecular pump comprising a rotor bearing having a preload force applied to the rotor bearing;

b) providing a preload force gauge, the preload force gauge comprising: a housing; an indicator for indicating the bearing preload force; and an actuator coupled to the impeller engagement surface by a means for providing a resilient bias;

c) coupling the impeller engagement surface with the impeller;

d) moving the actuator relative to the impeller-engaging surface against the resilient bias to overcome the bearing preload force on the rotor bearing; and

e) reading an indication of the bearing preload force from the indicator when the bearing preload force is overcome.

20. The method of claim 19, wherein the bearing preload force gauge is the bearing preload force gauge of any of claims 1-16.

21. The method according to claim 19 or 20, further comprising the steps of: preferably, the bearing preload force is adjusted and optionally re-measured using the gauge without removing the gauge from the turbomolecular pump.

Technical Field

The present invention relates to force gauges, and more particularly to force gauges for measuring bearing preload forces in turbomolecular pumps. The invention also provides a bearing preload tool comprising a bearing preload force gauge and a bearing preload force adjuster, and a method for measuring a bearing preload force.

Background

Vacuum pumps typically include an impeller in the form of a rotor mounted on a shaft for rotation relative to a surrounding stator. The rotor shaft is supported by a bearing arrangement comprising two bearings located at or intermediate respective ends of the shaft. Typically, the upper inlet side bearing may be in the form of a passive magnetic bearing and the lower outlet side bearing in the form of a rolling bearing.

To improve rolling bearing performance, a bearing preload force may be applied for normal operating conditions, i.e., the rotor shaft assembly will be axially biased in one direction. Typically, the bearing preload force is generated by an upper passive magnetic bearing. Typically, the rotor shaft is biased towards the pump inlet.

Generally, the total stop (gross stop) is characterized by a limit of axial movement between positive and negative preload. The total stop can act on the outer ring of the rolling bearing or on a damping assembly possibly coupled to the outer ring of the bearing.

The inner race of the rolling bearing is typically coupled to the turbine rotor shaft. When a sufficiently large force (which is opposite to the force of the magnetic bearings) is applied to the rotor, the rotor shaft assembly will be forced to change position axially in the opposite direction, which is referred to as a negative preload. The transition from positive to negative preload is typically accompanied by an audible noise, such as a click or click.

During maintenance, it may be necessary to measure and adjust the bearing preload after the rolling bearing is replaced. This is preferred to ensure that the bearing operates within acceptable preload limits.

Many methods have been used to measure the preload force including the use of force sensors, load sensors or weights with carriers (carriers). However, force sensors or load sensors with their instrumentation have proven prohibitively expensive for field use. However, at the low end of the price range, the use of weights has proven to be too complex and cumbersome for practical use. Furthermore, it relies on the experience and feel of the operator, which adds additional expense in operator training. For these reasons, there is a need for an inexpensive, simple, and accurate method for measuring bearing preload forces.

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

Disclosure of Invention

Accordingly, in a first aspect, the present invention provides a bearing preload force gauge for indicating a bearing preload force on a turbomolecular pump rotor bearing.

The meter may include: a housing; an indicator for indicating a bearing preload force; and an actuator coupled to the impeller-engaging surface by a member configured to provide a resilient bias between the actuator and the impeller-engaging surface. Typically, the impeller engagement surface may be located at a distal end of an impeller locating member (e.g., an impeller engagement spike). Typically, the impeller locating member will be configured such that, in use, the impeller engagement surface engages and is movable with the impeller shaft or a surface coupled to and directly movable with the impeller shaft. Thus, the force transmitted to the engagement surface may be transmitted to the impeller, and/or movement of the engagement surface may move the impeller.

Typically, at rest and/or during use, the impeller locating member may extend in front of the housing so as to extend through the turbomolecular pump housing to the impeller.

The impeller locating member may also include a surface for engaging a resilient biasing member, such as an upper surface of a protrusion (e.g., a radially extending circumferential flange on the shaft of the locating member).

The actuator, the resilient member, and the impeller locating member including the impeller engaging surface may be in a sliding arrangement relative to the housing. That is, one or more portions are in sliding contact with the housing. Typically, the actuator, the resilient member and the impeller positioning member comprising the impeller engaging surface will be arranged to move in a reciprocating motion along the longitudinal axis of the gauge and/or relative to the housing. In use, the longitudinal axis of the gauge may be substantially aligned with the axis of the rotor shaft of the turbomolecular pump.

The housing of the meter may be configured to couple with the housing of the turbomolecular pump in order to keep the meter substantially fixed relative thereto during use.

The housing of the gauge may further comprise means for adjusting the bearing preload force. Typically, the means for adjusting the bearing preload force will be configured to adjust the position of the inner race of the passive magnetic bearing relative to the outer race thereof. Preferably, the bearing preload force can be measured and adjusted without removing the meter from the turbomolecular pump.

The gauge may be arranged such that, in use, the bearing preload force is indicated by coupling the impeller engagement surface with the pump impeller and moving the actuator relative to (generally towards) the engagement surface against the resilient bias. The gauge may be configured such that the restoring (reaction) force provided by the resilient member increases as the actuator moves towards the engagement surface. Typically, the restoring (reaction) force of the resilient member increases until the bearing preload force is overcome (i.e., the bearing preload force changes from positive to negative). Typically, the bearing preload force is indicated when the actuator has moved sufficiently to overcome the bearing preload force.

Advantageously, the bearing preload gauge of the present invention can be used in any orientation. Thus, the meter is particularly useful in the measurement of multi-stage turbomolecular pumps where the rotor shaft and preload force may be in a non-vertical (e.g., horizontal) direction.

The gauge according to the invention is particularly useful in the measurement of the bearing preload force in turbomolecular pumps: the turbomolecular pump has an upper inlet-side passive magnetic bearing and a lower outlet-side rolling bearing, and/or wherein the bearing preload force is positive (i.e. in the direction of the pump inlet). They provide an inexpensive, accurate and easy to use solution to measure bearing preload forces in turbomolecular pumps.

The resilient member is configured to provide a resilient bias between the actuator and the impeller-engaging surface. That is, it resiliently resists movement of the actuator relative to the impeller engagement surface. Typically, the resilient member resiliently resists movement of the actuator towards the impeller-engaging surface (i.e. they are biased apart). Typically, the resilient member is a spring, preferably a compression spring, preferably a helical compression spring. Preferably, the spring is substantially linear. The spring rate of the spring may be selected such that a preferred range of preload forces is achieved within the compression range of the spring.

Preferably, the gauge is configured such that when the bearing preload force is overcome, the bearing preload force indicator provides an indication as to whether the bearing preload force is within or outside of a predetermined preferred range. Preferably, when the bearing preload force is overcome, the bearing preload force indicator provides an indication that the bearing preload force is within a predetermined range if the bearing preload force is within the predetermined preferred range.

Additionally or alternatively, when the bearing preload force is overcome, the bearing preload force indicator may provide an indication that the bearing preload force is outside the predetermined preferred range if the bearing preload force is outside the predetermined preferred range, preferably providing an indication that is different from the indication provided when within the predetermined preferred range.

Preferably, when the bearing preload force is overcome, the indicator indicates whether the bearing preload force is above or below a predetermined preferred range if the bearing preload force is outside the predetermined preferred range.

Typically, the indication provided by the indicator is visual. The marker (indium) may be selected from the group comprising: a structure formed in or on a surface of the actuator or housing, printed indicia, or a combination thereof. The indication may include primary and secondary markers.

Advantageously, the indicator of the present invention may not include a scale or digital output that must be read and interpreted. Preferably, the user is able to discern directly from the indicator whether the bearing preload force is within a predetermined preferred range, i.e., without having to refer to a secondary source to determine whether the bearing preload force is acceptable for that particular turbomolecular pump. The meter will typically be constructed for a particular turbomolecular pump model with a particular pump geometry and predetermined preferred bearing preload forces and ranges.

Typically, the indicator comprises a marker coupled to the housing or the actuator and a corresponding marker identifier, wherein, in use, the marker and the identifier are moveable relative to each other to indicate the bearing preload force. The tag identifier may be coupled to the other of the housing or the actuator. Typically, one of the marker and the identifier will remain fixed relative to the meter housing and/or the turbomolecular pump housing during use. Typically, the indicia will be formed on one of the housing or actuator and the indicia identifier will be formed on the other of the housing or actuator.

A flag may indicate a lower limit of the preferred preload force range and a flag may indicate an upper limit of the preferred preload force range. These markers may be single markers or separate, and as such, they may be the same or different.

Additionally or alternatively, the indicator may include indicia identifying when the bearing preload force is within a predetermined preferred preload force range. In an embodiment, the indicator includes a first indicia indicating a lower limit of the preferred preload force range, a second indicia identifying the preferred preload force range, and a third indicia indicating an upper limit of the preferred preload force range.

In an embodiment, the indicia may be in the form of a series of steps formed in an upper portion of the gauge housing. Typically, a first upper step indicates a lower limit of the preferred preload force range and a second (typically adjacent) lower step indicates an upper limit of the preferred preload force range.

Additionally, the first step and the second step may each include a secondary marking indicating a preferred preload force range. For example, a first secondary mark may be present on the first step indicating that it is outside of a predetermined preferred range above the step. Additionally or alternatively, the second step may include a second secondary marking different from the first marking indicating that it is within the predetermined preferred range above the second step but below the first step. Optionally, the third lower step may include a secondary marker indicating that it is outside of the predetermined preferred range below the second step.

The secondary mark of the second step may be textual (writen) or symbolic and may generally indicate a positive result, such as "go", "pass", green, or tick. Additionally or alternatively, the secondary indicia of the first and/or optional third steps may be textual or symbolic and may generally indicate a negative result, such as "no pass", "fail", red or cross.

Additionally or alternatively, the marker identifier may be in the form of a printed marking, protrusion or indentation on the outer surface of the actuator which, in use, moves with the actuator relative to the step. Thus, when the force applied to the actuator overcomes the bearing preload force, the position of the identifier relative to the indicia indicates whether the bearing preload force is within a predetermined preferred range.

Alternatively, the indicia identifier may comprise a portion of the housing of the gauge, or a mark, protrusion or indentation on the housing of the gauge, and the actuator may comprise a plurality of indicia or a single indicia identifying the upper and lower limits of the preferred preload force range, the actuator being movable relative to the housing.

Typically, overcoming the bearing preload force is accompanied by an audible signal, such as a click. In use, a user can use the audible signal to determine when the bearing preload force has been overcome and thus when to obtain a measurement from the indicator. Additionally or alternatively, a user may be able to feel when the bearing preload force has been overcome since further movement of the actuator will require a smaller force increase.

In an embodiment, the gauge may further comprise a preload regulator for modifying a bearing preload force on the rotor of the turbomolecular pump.

Additionally, the present invention also provides a preload force tool for a turbomolecular pump configured such that the bearing preload force is adjustable, the tool comprising a preload force indicator and a preload force regulator. The bearing preload force gauge may comprise any of the features disclosed in other aspects of the invention.

Typically, the turbomolecular pump will include a passive magnetic bearing that applies a bearing preload force, and the bearing preload adjuster will be configured to adjust the magnitude of the bearing preload force applied by the magnetic bearing. The bearing preload adjuster may be capable of moving an inner race relative to an outer race of the magnetic bearing.

Preferably, the tool can be used to measure and adjust the bearing preload force without decoupling the tool from the turbomolecular pump.

The housing, actuator, and impeller locating member may each be formed using additive manufacturing (e.g., 3D printing). Typically, they will be made of a polymer. The spring will typically comprise spring steel or another suitable alloy.

The housing, actuator and impeller positioning member of the present invention may each be made of a material selected from the group consisting of: polymers, composites, and metals or alloys.

Polymers are particularly preferred and may be selected from the group comprising: an elastomer, a thermoplastic material, or a thermoset material. Thermoplastic materials are preferred. Typically, the polymer is selected from the group comprising: polyolefins (such as polyethylene and polypropylene); polyvinyl chloride and polyethylene terephthalate; and derivatives and copolymers thereof.

The polymer may additionally comprise one or more from the group comprising: antistatic agents, antioxidants, mold release agents, flame retardants, lubricants, colorants, flow enhancers, fillers (including nanofillers), light and ultraviolet light absorbers, pigments, weathering agents, and plasticizers.

In a further aspect, the present invention provides a bearing preload force gauge for indicating a bearing preload force on a turbomolecular pump rotor bearing, the gauge comprising: a housing; an indicator for indicating a bearing preload force; and an actuator coupled to the impeller positioning member by a member configured to provide a resilient bias between the actuator and the impeller positioning member, wherein one or more of the housing, the indicator, the actuator, and the impeller positioning member are additive manufactured.

In all aspects and embodiments of the present invention, the predetermined preferred range of bearing preload forces may be between about 5N and about 50N, preferably between about 8N and about 10.5N. Typically, the span of the range is no greater than 1.5N, preferably 1N, on either side of the preferred bearing preload force of the turbomolecular pump. Typically, the predetermined preferred bearing preload force is between about 8N and about 10.5N, with an example of about 9.3N.

The spring (resilient member) will be selected so that the return (reaction) force can be equal to the force required to overcome the bearing preload force in the compression range of the spring. The gauge may be changed to accommodate different preload forces for different turbomolecular pumps by selecting an alternative spring having an alternative spring rate, or by altering the arrangement of the indicator (e.g., the spacing between portions of the indicator that indicate the upper and lower limits of a predetermined preferred bearing preload force), or a combination thereof. The configuration of the resilient member (spring) and the indicator will be selected such that, in use, if the bearing preload force is within a predetermined preferred range, the indicator indicates that this is the case, whereas if the bearing preload force is outside the predetermined range, the same indicator indicates that this is the case.

Preferably, the distance on the indicator between the mark indicating the lower end of the predetermined preferred bearing preload force range and the mark indicating the upper end of the predetermined preferred bearing preload force range will be greater than 1 mm, preferably from about 1 mm to about 20 mm, for example 2 mm.

In all aspects and embodiments of the present invention, the bearing preload force gauge and/or the preload force tool is typically substantially free of electronics, preferably electronics. Typically, the gauge and/or the tool, and in particular the indicator, is entirely mechanical.

In a further aspect of the invention, a method of measuring a bearing preload force of a turbomolecular pump is provided.

The method may comprise the steps of: providing a turbomolecular pump comprising a rotor bearing having a preload force applied thereto; providing a preload force gauge, the preload force gauge comprising: a housing; an indicator for indicating a bearing preload force; and an actuator coupled to the impeller-engaging surface by a member configured to provide a resilient bias between the actuator and the impeller-engaging surface; coupling an impeller engagement surface to an impeller; moving the actuator relative to the engagement surface against the resilient bias to overcome a bearing preload force on the bearing; and reading an indication of the bearing preload force from the indicator when the bearing preload force is overcome.

A meter according to any other aspect or embodiment of the invention may be used in the method.

Drawings

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

FIG. 1 shows a cross-sectional view of a bearing preload force gauge;

FIG. 2 shows a cross-sectional view of the bearing preload force gauge in place;

FIG. 3 illustrates a bearing preload force gauge;

FIG. 4 shows a schematic view of a bearing preload force gauge illustrating the indicator preferred range;

FIG. 5 shows the bearing preload force gauge at rest;

FIG. 6 shows the bearing preload force gauge in a failed configuration (the preload force is too low);

FIG. 7 shows a bearing preload force gauge in a pass-through configuration;

FIG. 8 shows the bearing preload force gauge in a failed configuration (the preload force is too high);

fig. 9 shows an alternative indicator in a series of configurations.

Detailed Description

The invention provides a bearing preload force gauge for indicating a bearing preload force on a turbomolecular pump rotor bearing.

As illustrated in fig. 1, in an example, the gauge (100) comprises a housing (1), an impeller positioning member (2), an actuator (4), and a resilient member (3) (in the illustrated example a helical compression spring) between the actuator (4) and the impeller positioning member (2).

Referring also to fig. 2, the impeller positioning member (2) is configured to transmit the force applied thereto by the actuator (4) to the impeller (6) of the turbomolecular pump (7). The impeller positioning member (2) includes: a forward portion (8) configured to extend in front of the housing (1) to couple with the pump impeller (7); and a radially extending circumferential flange (9) slidably engaged with an inner wall (10) of the meter housing (1). The circumferential flange (9) may be located substantially centrally along the length of the impeller locating member (2), dividing the forward portion (8) of the locating member from the rear portion (11). The illustrated impeller positioning member (2) further comprises a rearward portion (11) which may be slidably received within the spring (3) and the actuator (4).

The impeller locating member (2) comprises an impeller engaging surface (12) at its tip which, in use, is coupled with the impeller (6), preferably the surface (12) directly engages the impeller (6), preferably the surface directly engages the rotor shaft (13).

The illustrated housing (1) is generally cylindrical with a central passage configured to receive the actuator (4), the resilient member (3) and the impeller locating member (2). The walls of the central channel (formed by the inner walls of the housing (10)) may comprise ribs or channels configured to engage with corresponding protrusions or indentations on the actuator (4) and/or impeller locating member (2) to aid sliding. The channel further comprises shoulders (14, 15, 16) at its proximal (17) and distal (18) ends to retain the actuator (4) and impeller locating member (2) within the housing (1).

The housing (1) further comprises a series of steps (19, 20, 21) on its upper surface (22). These, together with a circumferential indentation (23) on the actuator (4), form an indicator for indicating whether the bearing preload force is within a predetermined preferred range.

As better illustrated in fig. 3 and 4, in an example, the upper step (19) indicates a lower limit of the predetermined preferred bearing preload force range and the second step (20) indicates an upper limit of the predetermined preferred bearing preload force range. In this example, the circumferential indentations (23) on the actuator (4) are the mark identifiers, and the steps form the primary marks. The steps (19, 20) also include secondary indicia "pass" and "no pass" formed in the surface thereof. If the marker identifier (23) is located between the upper step (19) and the second step (20) when the bearing preload force is overcome, this is by (i.e. the bearing preload force is within a predetermined preferred range) as illustrated in figure 4. Alternatively, if the marker identifier is located above the upper first step (19) when the bearing preload force is overcome, this is a failure (the bearing preload force is too low) as illustrated in fig. 4.

As illustrated in fig. 2, the lower end of the doser housing (1) is configured to be coupled with the housing of the turbomolecular pump (24) such that the doser housing (1) remains substantially fixed relative to the pump housing (24) while bearing preload force measurements are taken. The lower (distal) end of the illustrated housing (1) also includes three adjuster drive legs (25, 26, 27) (better illustrated in fig. 5-8). The regulator drive legs (25, 26, 27) not only facilitate stability of the gauge (100) during use, but are configured to allow the gauge (100) to regulate bearing preload forces, typically by facilitating movement of an inner race (28) of a passive magnetic bearing (30) relative to an outer race (29) thereof. The bearing preload force can be increased by rotating the device (100) about its longitudinal axis (a) in one direction, and can be decreased by rotating the device (100) about its longitudinal axis (a) in the opposite direction. Advantageously, the bearing preload force can be measured and adjusted by the same device (100) without decoupling said device (100) from the turbomolecular pump (101). Typically, the bearing preload force is adjusted when the gauge (100) is in a rest configuration.

The actuator (4) includes a rearwardly facing user interface (5) which, in use, can be depressed by an operator's thumb or finger. The actuator (4) further comprises a resilient member (e.g. spring) engaging surface (31) (in the example, a downwardly (forwardly) facing surface (31) of a radially extending circumferential flange (32) at a distal end of the actuator (4)). The actuator (4) is configured to slide in a reciprocating motion within the housing channel (10). The actuator (4) includes an internal passage (33) configured to receive the rearward portion (11) of the impeller locating member (2) in a reciprocating sliding arrangement.

When pushed in the forward (downward) direction, the actuator (4) pushes the spring against the impeller locating member (2), thereby compressing the spring (3). The impeller positioning member (2) transmits a force to an impeller (6) of a turbomolecular pump (101). By increasing the force applied to the actuator (4), the spring (3) is further compressed and the restoring (reaction) force of the spring increases: also, the force transmitted to the impeller (6) (and rotor bearing) increases. The force applied to the actuator (4) is increased until the force transmitted to the impeller (6) is sufficient to overcome the bearing preload force. At that time, a click will be heard and the indicator read to verify whether the bearing preload force is within its predetermined preferred range.

The release actuator (4) allows the gauge (100) and the turbomolecular pump (101) to return to their respective rest positions.

If the bearing preload force is not within the predetermined preferred range of the turbomolecular pump (101), the bearing preload force can be adjusted and re-measured. This process may be repeated until the bearing preload force is within a predetermined preferred range.

The exemplified device is for use in a nEXT85 ™ chamber available from Edwards Vacuum ™, and is configured to have a predetermined preferred bearing force range of from about 8.3N to about 10.3N. The illustrated spring is LC036G05S available from Lee spring ltd, which has a spring rate of 1.05N/mm. The distance between the uppermost step and the next step was 2 mm. The skilled person will appreciate that the particular spring and indicator arrangement will be selected depending on the preferred bearing preload force range for a particular turbomolecular pump.

The illustrated devices may be hand-held and/or manually actuated. In the case of manual actuation, it is understood that the force required to overcome the bearing preload force is applied to the actuator by the hand of the operator.

The housing, actuator and impeller locating member are additively manufactured by Objet Veroblue RGD 840.

Fig. 5-8 illustrate the device in various configurations. Fig. 5 shows the device (100) in its rest configuration. In this configuration, no force is applied to the actuator (4), the spring (3) is not displaced or compressed, and the actuator (4) and the impeller locating member (2) are in their uppermost position. In this configuration, the circumferential groove (23) of the indicator is well above the top step (19) of the counter housing (1).

Fig. 6 illustrates the device (100) in a configuration where the bearing preload force is too low. The spring (3) is compressed and the actuator (4) has moved downwards (forwards) relative to the housing (1); however, the circumferential groove (23) is above the top step (19) of the meter housing (1), which indicates that the bearing preload force is too low.

Fig. 7 illustrates the device (100) in a configuration in which the bearing preload force is within a predetermined preferred range. The spring (3) is further compressed and the actuator (4) and impeller locating member (2) have moved further downwards (forwards) relative to the housing (1). In this configuration, the circumferential groove (23) is below the top step (19) of the gauge housing but above the second step (20), which illustrates that the bearing preload force is within a predetermined preferred range.

Fig. 8 illustrates the device in a configuration where the bearing preload force is too high. The spring (3) is compressed even further and the actuator (4) and the impeller locating member (2) have moved even further downwards (forwards) relative to the housing (1). In this configuration, the circumferential groove (23) is below the second step (20) of the meter housing (1), which indicates that the bearing preload force is too high.

Fig. 9 illustrates an alternative example of an indicator suitable for use in the present invention in a series of configurations. In this example, the indicator comprises two markings (34, 35) in the form of circumferential grooves formed in the surface of the actuator (4). In use, when the actuator (4) is pushed into the housing (1), the upper groove (34) indicates a lower limit of the predetermined preferred range of bearing preload forces, and the lower groove (35) indicates an upper limit of the predetermined preferred range of bearing preload forces. In this example, the marker identifier (23) is an upper surface of the meter housing (1) that is proximate to the actuator (4).

Thus, in contrast to the previous examples, the markers (34, 35) are located on the actuator (4) and are movable relative to a fixed marker identifier (23) located on the housing (1).

Thus, as illustrated, if both grooves (34, 35) are above the housing (1) when the bearing preload force is overcome during testing, the bearing preload force is too small, whereas if neither groove is above the housing (1), the bearing preload force is too high. In contrast, if the upper groove (34) is above the housing (1) but the lower groove is not above the housing (1) when the bearing preload force is overcome, the bearing preload force is within a predetermined preferred range. In this example, no secondary markers are employed. It will be appreciated that the grooves may be replaced with printed lines or other suitable indicia.

It will be understood that various modifications may be made to the illustrated embodiments without departing from the spirit and scope of the present invention as defined by the appended claims as interpreted according to the patent laws.