Turbomolecular vacuum pump and method for determining timing of preventive maintenance thereof

Abstract

To predict the need for vacuum pump rotor replacement due to the risk of creep in turbomolecular vacuum pumps. [Solution] The system includes a temperature sensor (23) configured to measure the temperature of the rotor (3), and a creep maintenance counter (24), the creep maintenance counter (24) having a memory in which a creep value of the rotor and a correspondence table providing a time-dependent value of the creep of the rotor (3) as a function of the temperature and rotational speed of the rotor (3) are stored, the creep maintenance counter (24) determines an increment of the creep of the rotor over a predetermined period of time based on the temperature of the rotor, the rotational speed of the rotor, the creep value of the rotor, and the correspondence table, increments the creep value of the rotor by the determined creep increment, and determines information representing the remaining period until preventive maintenance for the creep of the rotor based on the incremented creep value.

Description

[Technical field]

[0001] The present invention relates to a turbomolecular vacuum pump and, likewise, to a method for determining a preventive maintenance timing for determining information representative of the time remaining until the time when preventive maintenance against rotor creep of a turbomolecular vacuum pump must be performed. [Background technology]

[0002] To generate a high vacuum in the chamber, it is necessary to use a turbomolecular vacuum pump therein, which has a stator with a rotor that rotates at high speed, for example at a rotational speed of 30,000 revolutions per minute or more.

[0003] In certain processes using turbomolecular vacuum pumps, such as in the manufacturing of semiconductors and LEDs, a layer of deposits can form inside the vacuum pump. Such deposits can limit the clearance between the stator and the rotor and cause the rotor to seize. It is therefore known to heat the stator in order to avoid condensation of reaction products, inhibit the formation of deposits inside the vacuum pump and extend its service life. Summary of the Invention [Problem to be solved by the invention]

[0004] Besides limiting deposit formation, other considerations may require an increase in the operating temperature of the rotor, in particular the temperature of the vacuum pump, for example to increase the flow rate of the pumped gas or to enable the pumping of heavier gases.

[0005] However, to maintain the mechanical strength of the rotor, the rotor temperature must not exceed a certain upper threshold. In particular, the mechanical strength of the rotor against centrifugal forces decreases with increasing temperature. At high temperatures, irreversible deformation (creep) of the rotor occurs, and there is a risk that the stator will come into contact with the most expanded part of the rotor.

[0006] Furthermore, rotor creep is not linear with increasing temperature. The higher the operating temperature of a vacuum pump, the more frequently maintenance work will be required. For example, a rotor kept at a temperature of 130°C can operate for five years, whereas a rotor heated to 140°C will have to be replaced after only two years, all other operating conditions being the same.

[0007] Furthermore, usefully increasing the rotational speed of the rotor of the vacuum pump, for example to reduce pressure further, can also affect rotor creep and therefore the period between maintenance operations. Such variations in operating point can occur throughout the life of the vacuum pump, making it difficult to predict when maintenance will be required.

[0008] One of the objects of the present invention is to propose a turbomolecular vacuum pump which at least partially overcomes the drawbacks of the prior art, in particular to predict the need for rotor replacement of the vacuum pump due to the risk of creep. [Means for solving the problem]

[0009] To that end, the subject of the present invention is a turbomolecular vacuum pump having a stator, a rotor arranged to rotate in the stator, and a motor arranged to drive the rotation of the rotor, the turbomolecular vacuum pump further comprising: a temperature sensor configured to measure the temperature of the rotor; a creep maintenance counter having a stored memory; - the value of rotor creep; a correspondence table providing values ​​of rotor creep over time as a function of rotor temperature and rotational speed, The creep maintenance counter includes: determining an increment of creep of the rotor over a predetermined period of time based on the rotor temperature measured by the temperature sensor, the rotor rotational speed, the rotor creep value, and a correspondence table; - incrementing the rotor creep value by the determined creep increment; - determining information representative of the remaining time until preventive maintenance for creep of the rotor based on the incremented creep value.

[0010] Said creep maintenance counter makes it possible to obtain very accurate information representing the remaining time until preventive maintenance against rotor creep is required, taking into account the relatively complex conditions of use of the vacuum pump, i.e. conditions of temperature and rotational speed variations over the useful life of the vacuum pump. By adding (counting) successive increments of creep resulting from different periods spent at different temperature and rotational speed values, the creep maintenance counter makes it possible to access a relatively realistic value for the current creep and the remaining period until preventive maintenance for rotor creep is required.

[0011] The vacuum pump may further comprise one or more of the features described below, either alone or in combination. The creep maintenance counter may be configured to determine information representative of the remaining time until preventive maintenance for rotor creep at least once a day, e.g. at least once an hour, e.g. at least once a minute, and / or at least once a month, e.g. once a week, and / or at least once a year. The creep maintenance counter can be configured so that the correspondence table can be updated with measured values ​​of the deformation of the rotor obtained from maintenance work on the vacuum pump.

[0012] The creep maintenance counter may be configured to communicate information representing the remaining time until preventive maintenance for rotor creep is performed to an output device such as a vacuum pump communication bus or a human machine interface, or to a central device connected to multiple vacuum pumps. The creep maintenance counter can be configured to store in a memory and make readable information representative of a determined remaining period until preventive maintenance against rotor creep is performed.

[0013] The temperature sensor is, for example, an infrared sensor. The temperature sensor may be configured to measure the temperature of a bottom of the sleeve of the rotor located at the discharge of the vacuum pump. The temperature sensor may also be located on the underside of the rotor sleeve.

[0014] The rotor may be made, for example, of aluminum or coated aluminum, such as nickel-plated aluminum. The turbomolecular vacuum pump may comprise a heating device configured to heat the stator.

[0015] The turbomolecular vacuum pump may also have the following configuration: a deposition thickness determination device configured to determine the thickness of a deposition in a vacuum pump; a deposit maintenance counter configured to determine information representative of the remaining time until preventive maintenance of a deposit of a vacuum pump based on the determined value of the deposit thickness. Since the setpoint of the operating temperature control of the vacuum pump influences the thickness of deposits in the vacuum pump in a particular operation, a deposit maintenance counter can make it possible to assist the user in selecting the operating temperature, on the one hand, the time remaining until preventive maintenance of the vacuum pump against deposits, and on the other hand, the time remaining until preventive maintenance against creep. The deposition thickness determining device may be a physical size measurement sensor such as a capacitive deposition sensor.

[0016] According to another embodiment, the deposition thickness determination apparatus includes a memory, the memory including: the value of the deposit thickness, a correspondence table providing values ​​of deposit thickness over time as a function of the operating temperature control of the vacuum pump; and The deposition thickness determination device is - determining an increment in thickness of the deposit over a predetermined period of time based on the operating temperature control of the vacuum pump, the deposit thickness value, and the correspondence table; - configured to increment the value of the thickness of the deposit by the determined thickness increment of the deposit.

[0017] A correspondence table (or correlation law) of a "virtual" deposition thickness determination device (or a model of the evolution of the deposit) is derived, for example, from a linear relationship providing the growth rate of the deposit as a function of the temperature. The correspondence table (or correlation law) (or model of the evolution of the deposit) of the "virtual" deposit thickness determination device results from a linear relationship that provides the deposit growth rate as a function of temperature. The correspondence table (or correlation law), (or model of deposit evolution) can also provide values ​​of deposit thickness over time by taking into account values ​​of other parameters, such as the pressure of the gas at the time of discharge and / or the operating time of the vacuum pump at a given motor torque. The deposition thickness determining device may be configured to update the correspondence table with measured values ​​of the deposition thickness obtained from maintenance work on the vacuum pump.

[0018] Another subject of the invention is a method for determining information representative of the time remaining until preventive maintenance for rotor creep of a turbomolecular vacuum pump as defined above, characterized in that said method comprises the following steps: - determining an increment of rotor creep over a predetermined period of time based on the rotor temperature measured by the temperature sensor, the rotor rotational speed, the rotor creep value and a correspondence table; - incrementing the rotor creep value by the determined creep increment; - determining information representative of the remaining time until preventive maintenance for said creep of the rotor is performed based on said incremented creep value.

[0019] The time when preventive maintenance for rotor creep should be performed may be a percentage of the maximum allowable creep. According to one example embodiment, the time remaining until preventive maintenance for rotor creep is determined based on a model of creep aging, taking into account the rotor rotational speed and rotor temperature that allow for the determination of an increment for creep. According to one example embodiment, the creep aging model is a state function with two variables: temperature and rotational speed. According to one example embodiment, the method further comprises determining information representative of the time remaining until preventive maintenance of the deposits in the vacuum pump based on the determined thickness of the deposits in the vacuum pump.

[0020] The time when preventive maintenance of vacuum pump deposits is required is the percentage of the maximum allowable deposit thickness at which the vacuum pump becomes unreliable, for example 80% of the minimum clearance between the rotor and stator. To this end, for example, the deposit maintenance counter is configured to determine the remaining time until the maximum allowable deposit thickness is reached based on the determined deposit thickness value and a deposit aging model that takes into account that the operating temperature control of the vacuum pump does not change. The model for the aging of the deposits is, for example, a linear relationship that provides the growth rate of the deposits as a function of temperature.

[0021] According to one embodiment of determining the deposit thickness, a deposit thickness increment over a predetermined period of time is determined based on the operating temperature control of the vacuum pump, the deposit thickness value and a correspondence table, and the deposit thickness value is incremented by the determined deposit thickness increment.

[0022] Other advantages and features of the present invention will become apparent from the following description of particular, but non-limiting, embodiments of the invention and from the accompanying drawings, in which: [Brief description of the drawings]

[0023] [Figure 1] 1 is an axial cross-sectional view of a turbomolecular vacuum pump according to an embodiment of the present invention; [Diagram 2] 2 is a flow chart illustrating example components of the vacuum pump of FIG. 1. [Diagram 3] 1 is a graph of a first set of curves (or charts) showing creep (F) (y-axis) in %) as a function of time (T) (years) (x-axis) at different rotational speeds when the rotor is at a first temperature of 150°C, with rotational speeds of 45K rpm (thick solid line), 40K rpm (medium solid line), and 35K rpm (thin solid line). [Figure 4] FIG. 4 is a graph of a second set of curves similar to FIG. 3 giving the creep (F) (%) (y-axis) as a function of time (T) (years) (x-axis) for different rotor rotational speeds, when the rotor is at a second temperature of 140° C., at rotational speeds of 45 Krpm (thick dashed line), 40 Krpm (plain dashed line), and 35 Krpm (thin dashed line). [Diagram 5] FIG. 4 is a graph of a third set of curves similar to FIG. 3 giving the creep (F) (%) (y-axis) as a function of time (T) (years) (x-axis) for different rotor rotational speeds, when the rotor is at a third temperature of 130° C., the rotational speeds being 45 Krpm (thick dashed line), 40 Krpm (medium dashed line), and 35 Krpm (thin dashed line). [Figure 6] The first, second and third sets of curves from Figures 3, 4 and 5 are plotted on the same graph. [Figure 7] A three-dimensional graphical representation with the creep rate (VF) (in % / year) on the y-axis as a function of rotor temperature (T°) (in °C) and rotor speed (in Krpm) to illustrate the determination by linear regression extrapolation of the creep rate for a given rotor temperature and rotational speed. [Figure 8]A three-dimensional graphical representation of creep rate (VF) (in % / year) on the y-axis as a function of rotor temperature (T°) (in °C) and rotor speed (in Krpm) to illustrate the polynomial extrapolation method for determining creep rate for a measured rotor temperature and a given rotational speed. [Figure 9] 1 is a graph of creep (F) (%) on the y-axis as a function of time (T) (years) for an example of determining the remaining time until preventive maintenance for rotor creep at a given point in time. [Figure 10] 4 is a flow chart illustrating another example of components of the vacuum pump of FIG. 1. [Figure 11] 1 is a graph of deposit thickness (mm) on the Y-axis as a function of time (T) (years) for an example of determining the remaining time until preventive maintenance for deposits in a vacuum pump at a given point in time. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] In the following figures, identical elements are given the same reference numbers. The following embodiments are illustrative. Although one or more embodiments are referred to in this specification, this does not necessarily mean that each reference relates to the same embodiment or that a feature applies only to one embodiment. In addition, individual features of different embodiments can be combined or substituted to provide other embodiments. An "upstream" element is understood to mean an element that comes before another element with respect to the circulation direction of the gas. In contrast, a "downstream" element is understood to mean an element that comes after another element with respect to the circulation direction of the gas being pumped.

[0025] 1 is a diagram showing an example of one embodiment of a turbomolecular vacuum pump 1 of the present invention. The turbomolecular vacuum pump 1 has a stator 2 in which a rotor 3 is configured to rotate at a high shaft rotation speed of, for example, 30,000 revolutions per minute or more. In the embodiment of FIG. 1, the turbomolecular vacuum pump 1 is of the so-called hybrid type, which comprises a turbomolecular stage 4 and a molecular stage 5 located downstream of the turbomolecular stage 4 in the direction of circulation of the pumped gas (indicated by the arrow F1 in FIG. 1). The gas to be pumped enters the turbomolecular vacuum pump 1 at an inlet 6, passes first through a turbomolecular stage 4, then through a molecular stage 5 and is discharged towards an outlet 7. In operation, the outlet 7 is connected to the primary pump.

[0026] An inlet flange 8, for example an annular flange, surrounds the inlet 6 and connects the inlet to the chamber of the vacuum pump 1 that is to be depressurized. In the turbomolecular stage 4, the rotor 3 has at least two stages of blades 9 and the stator 2 has at least one stage of vanes 10. The blades 9 and vanes 10 of each stage are axially successive along the rotation axis II of the rotor 3 in the turbomolecular stage 4. The rotor 3 has, for example, four or more stages of blades 9, for example four to twelve stages of blades 9 (seven stages in the example shown in FIG. 1).

[0027] The blades 9 of each stage of the rotor 3 have angled blades extending substantially radially from a hub 11 of the rotor 3 which is secured, for example by screws, to a drive shaft 12 of the vacuum pump 1. The blades are evenly spaced around the circumference of the hub 11. Each stage of vanes 10 of the stator 2 comprises a ring having substantially radially extending inclined vanes evenly distributed around its inner circumference. The vanes 10 of one stage of the stator 2 engage between the blades of the blades 9 of two successive stages of the rotor 3 . The blades 9 of the rotor 3 and the vanes 10 of the stator 2 are angled to direct the molecules of the pumped gas towards the molecular stage 5 .

[0028] Here, in the molecular stage 5, the rotor 3 further comprises, downstream of at least two stages of blades 9, a sleeve 13, called the Holweck sleeve, formed by a smooth cylinder which rotates through a helical groove 14 of the stator 2. The helical groove 14 of the stator 2 makes it possible to compress the gas to be pumped and direct it towards the outlet 7. The rotor 3 further has an inner bowl 15 coaxial with the axis of rotation II, which is formed below the sleeve 13 and projects below the rotor 3 facing a bell housing 17 of the stator 2. During operation, the rotor 3 rotates within the stator 2 without contact between the inner bowl 15 and the bell housing 17.

[0029] The rotor 3 may be an integral type (monoblock) or may be an assembly of multiple parts. For example, it is made of aluminum (or aluminum alloy) and / or nickel. In particular, to improve corrosion resistance, it may be coated with nickel or the like. For example, it is made of nickel-plated aluminum. The rotor 3 is driven in rotation within the stator 2 by an internal motor 16 of the vacuum pump 1. The motor 16 is located, for example, within a bell housing 17 of the stator 2, the bell housing itself being located below the internal bowl 15 of the rotor 3, with the drive shaft 12 passing through the bell housing 17 of the stator 2.

[0030] The rotor 3 supports its drive shaft 12 and is guided laterally and axially by magnetic or mechanical bearings 18 located within the stator 2. For example, there is a first bearing 18 that supports and guides a first end of the drive shaft 12 at the bottom of a bell housing 17 of the stator 2, and a second bearing 18 that supports and guides a second end of the drive shaft 12 and is located at the top of the bell housing 17.

[0031] Other electrical and electronic components may be located within the bell housing 17 of the stator 2, such as position sensors. The vacuum pump 1 may also comprise a cooling device arranged for cooling the bell housing 17, for example arranged within the bell housing 17 or in thermal contact with the bell housing 17, such as the hydraulic circuit, in order to continuously cool the elements it contains, in particular the bearings 18, the motor 16 and other electrical or electronic components, to enable them to function.

[0032] The vacuum pump 1 may comprise a purge device 20 configured to inject a purge gas into the gap between the bell housing 17 of the stator 2 and the internal bowl 15 of the rotor 3. The purge gas is preferably air or nitrogen, but may also be other neutral gases such as helium or argon. The purge device is for example configured to inject the purge gas into at least one bearing 18 arranged in the stator 2 which supports and guides the drive shaft 12 of the rotor 3, such that the flow of the purge gas passes through the at least one bearing 18 before leaving the bell housing 17 of the stator 2 and circulating in the gap. The circulation of the purge gas is indicated diagrammatically by the arrows f2 in FIG. 1.

[0033] The vacuum pump 1 may comprise a heating device 21, for example arranged to heat the stator 2 so that the temperature of the rotor 3 is maintained at a value between 120°C and 150°C. This heating device 21 may comprise an external resistive heating belt or a radiant element arranged in the gas flow path of the vacuum pump 1 and is configured, for example, to heat a bushing 22 of the stator 2 in which the spiral groove 14 is formed.

[0034] The turbomolecular vacuum pump 1 further comprises a temperature sensor 23 arranged to measure the temperature of the rotor 3, and a creep maintenance counter 24 (see FIG. 2). The temperature sensor 23 is, for example, an infrared sensor. Since the infrared sensor is a non-contact type, it can measure the temperature of the rotating rotor 3 in a temperature range of 50° C. or more and 250° C. or less with high accuracy. The temperature sensor 23 can be configured to measure the temperature of the sleeve 13 of the rotor 3 (cylindrical part) and can be configured to target the position of the rotor 3 that is most subjected to mechanical stress, in particular at the bottom, i.e. the part located on the side of the outlet 7 of the vacuum pump 1.

[0035] The temperature sensor 23 is for example located behind (below) the sleeve 13 of the rotor 3, between the stator 2 and the inner bowl 15 of the rotor 3 (see FIG. 1). In this way, the temperature sensor 23 is not located in the path through which the gas is pumped and is therefore less susceptible to corrosive attack from the pumped gas and can benefit from the protection provided by the purge gas.

[0036] The creep maintenance counter 24 comprises, for example, a controller or microcontroller or microprocessor or computer and a memory. The creep maintenance counter 24 can be implemented on an electronic circuit board housed in the stator 2 of the vacuum pump 1. The creep maintenance counter 24 comprises a memory in which the rotor creep value and a correspondence table giving the value of the creep of the rotor 3 over time as a function of the rotor temperature and rotational speed.

[0037] The correspondence table (or correlation law) is shown in Figures 3, 4 and 5 as a set of curves (charts) of creep as a function of time for different temperatures of the rotor 3 and for different rotational speeds of the rotor.

[0038] The first set of curves in FIG. 3 shows the creep of the rotor 3 over time when the first temperature of the rotor 3 is 150° C. and the rotation speed of the rotor 3 is different. It should be noted that the creep increases faster over time as the rotation speed of the rotor 3 increases. For example, if the temperature of the rotor 3 is 150° C. and the rotation speed is 45 Krpm, the creep after 6 months is 0.2%, but if the rotation speed is reduced to 40 Krpm at the same temperature, this creep value is reached after more than two years, and if the rotation speed is reduced to 35 Krpm, this creep value is not reached even after three years.

[0039] The same trend can be observed in the second set of curves in Figure 4 and the third set in Figure 5. They show the creep of rotor 3 over time for different rotational speeds of rotor 3, with the temperature of rotor 3 decreasing to 140°C in Figure 4 and 130°C in Figure 5. Note that, as in Figure 3, creep increases more rapidly with increasing rotor 3 rotational speed, but not as quickly at lower temperatures. For example, for a rotational speed of 45 Krpm, the creep of 0.2% (thick solid line in Figure 3) obtained after 6 months at a rotor temperature of 150°C is reached after about 8 months at a rotor temperature of 140°C (thick dashed line in Figure 4) and after more than a year at a rotor temperature of 130°C (thick dashed line in Figure 5).

[0040] It will be appreciated that creep increases more rapidly over time as rotational speed and temperature increase, as can be seen more clearly in Figure 6, where for a given creep level (first horizontal dotted line), the inflection points / slope of the first, second and third sets of creep curves of Figures 3, 4 and 5 are indicated by double headed arrows on the same graph. The creep of aluminum (or aluminum alloys) as a function of temperature is well known in the field of metallurgy, which makes it easy to create a correspondence table containing information for rotors 3 made from aluminum.

[0041] This correspondence table can also include simulation results of the rotor 3 obtained by changing the temperature and rotation speed in more complex ways. Since the sleeve 13 of the rotor 3 is cylindrical, a deformation model can be obtained by modeling the deformation of the diameter of the sleeve 13 of the rotor 3.

[0042] The creep maintenance counter 24 may likewise be configured to update the correspondence table with measurements of the deformation of the rotor 3 resulting from maintenance work on the vacuum pump 1. This may involve, for example, measuring the diameter of the sleeve 13 of the rotor 3 during maintenance and comparing this with the factory diameter value to determine the creep. This update allows the deformation model to be refined. The creep maintenance counter 24 is configured to determine the increment of creep of the rotor 3 over a predetermined period of time based on the temperature of the rotor 3 measured by the temperature sensor 23, the rotational speed of the rotor 3, the creep value of the rotor 3, and a correspondence table.

[0043] The initial value of rotor creep (at the time of shipment from the factory or at the time of maintenance) can be considered to be zero. The creep maintenance counter 24 may receive information regarding the rotational speed of the rotor 3, for example from a speed sensor of the vacuum pump 1, for example from a speed controller 25 of the motor 16 (see FIG. 2).

[0044] The rotational speed of the vacuum pump 1 is typically maintained at a constant nominal speed, which varies for each vacuum pump 1, from 20,000 rpm for the largest vacuum pump to 100,000 rpm for the smallest vacuum pump. Depending on the requirements, the user can switch to one or more speed settings, e.g. up to 10% higher than the nominal speed or up to 10% lower than the nominal speed. The creep increment of the rotor 3 is determined periodically, for example every minute, every hour, every two hours, every day, etc. Performing the creep increment calculation periodically makes it possible to take into account the fact that creep increase is not linear.

[0045] The creep maintenance counter 24 may determine a new increment value for the creep of the rotor 3 at the end of each predetermined time period, or may maintain the same increment value as previously determined if the temperature and rotational speed have not changed after the predetermined time period. Therefore, for example, in FIG. 3, if we consider that the "current" creep value of rotor 3 is 0.1%, the temperature of rotor 3 is 150°C, the rotational speed of rotor 3 is 40Krpm, and the predetermined period is one month, then using the correspondence table it can be determined that the increment in creep over this predetermined period is 0.01%. If the measured rotor 3 temperature or rotor 3 rotational speed is not a value in the correspondence table, the creep of the rotor 3 can be determined by extrapolation, for example by linear regression or polynomial extrapolation.

[0046] This is shown in the examples of FIGS. 7 is a graph showing another representation of the correspondence table, showing the values ​​of the rotor 3 creep increment as a function of time for multiple rotor 3 temperature / rotation speed pairs (9 in this example) and the extrapolated values ​​by linear regression connecting these points. In this example, the rotor 3 creep increment is determined for temperatures and rotation speeds different from the values ​​in the correspondence table, so two extrapolations are required. Figure 8 shows the same example with values ​​extrapolated by polynomial extrapolation, which is more accurate.

[0047] The creep maintenance counter 24 is similarly configured to increment the rotor creep value by the determined creep increment and determine information representing the remaining time until rotor creep preventive maintenance based on the incremented creep value. The point at which preventive maintenance of the rotor with respect to creep needs to be performed is, for example, a percentage of the maximum allowable creep, for example 0.2%, above which the rotor 3 is unreliable.

[0048] To this end, for example, the creep maintenance counter 24 is configured to determine the remaining time until the maximum allowable creep is reached based on the creep increment value and a creep aging model, the rotational speed of the rotor 3 and the temperature of the rotor 3 enabling the creep increment to be determined, i.e. enabling the "current" creep value to be determined. The model of creep change over time is a state function having two variables, for example temperature and rotational speed, and is of the following type, for example: dCreep / dT = nonlinear function (T°, rotation speed, creep)

[0049] The graph in Figure 9 shows an example of creep over time. In this curve, the creep time t 0 The increment in creep up to is shown by the solid line. Also, the remaining time D R is the time Tf when the creep reaches the maximum creep value (0.2% in this case) and the "current" creep F from the extrapolation curve of the change model (dashed line). 0 The last time t 0 It is also clear that there is a time difference between

[0050] The information representative of the remaining time until preventive maintenance for rotor creep can be determined at a first frequency, for example hourly or daily, i.e. at least once a day, for example at least every hour, for example at least every minute. This short-term determination makes it possible to assist the user in adjusting the input parameters, in particular the rotational speed, less frequently than the period of the thermal inertia of the vacuum pump 1 (approximately one hour). In particular, if the user changes the input parameters, it is possible to quickly see the impact of the new adjustment on the useful life of the vacuum pump 1 or the remaining time until the next maintenance operation.

[0051] The information representative of the remaining time until preventive maintenance for rotor creep can be determined at least once a month, such as weekly or monthly, with a secondary frequency of weekly or monthly. This medium-term determination makes it possible to assist the user in planning the maintenance stages.

[0052] Information representative of the remaining time until preventive maintenance for rotor creep can be determined at a third frequency, i.e., once a year. This long-term determination makes it possible to plan rotor or vacuum pump replacement.

[0053] The creep maintenance counter 24 may be configured to store information in its memory representative of the remaining time until preventive maintenance against creep of the rotor, for example at least until the next estimate, or may periodically accumulate the storage of this information. The information representative of the remaining time until preventive maintenance against creep of the rotor may likewise be readable by an external reader. The creep maintenance counter 24 may be configured to communicate information representing the remaining time until preventive maintenance of the rotor for creep to an output device 26, e.g. for display, such as a communication bus or a human-machine interface of the vacuum pump 1, or to a central controller, e.g. connected to a number of vacuum pumps and shared by, e.g., a group of vacuum pumps.

[0054] A user wishing to increase the temperature of the vacuum pump 1, for example during an operational phase known as hot cleaning, can easily know how to adjust the rotational speed of the rotor 3, and in particular how to reduce the rotational speed, if he does not want to reduce the service life of the vacuum pump 1.

[0055] Similarly, a user wishing to increase the pumping speed, for example to reduce the limiting vacuum pressure, may consider adjusting the operating temperature control of the vacuum pump 1 (and thus the rotor 3), in particular lowering the temperature, in order to avoid increasing the rotational speed of the vacuum pump 1 and therefore shortening the life of the vacuum pump 1.

[0056] It will be appreciated that the creep maintenance counter 24 makes it possible to obtain very accurately information representative of the remaining period until preventive maintenance of the rotor against creep, taking into account the relatively complex use of the vacuum pump 1, i.e. changes in temperature and rotational speed use over the useful life of the vacuum pump 1. In this manner, the creep maintenance counter 24 adds (counts) successive increments of creep resulting from different times spent at different temperature and rotational speed values, thereby making it possible to access a relatively realistic value for the current creep and the time remaining until rotor creep preventive maintenance.

[0057] In certain processes using turbomolecular vacuum pumps 1, such as semiconductor and LED manufacturing processes, a layer of deposits may form inside the vacuum pump 1. Such deposits may limit the clearance between the stator 2 and the rotor 3 and cause seizure of the rotor 3. To avoid condensation of reaction products, inhibit the formation of deposits inside the vacuum pump 1 and extend its service life, it is known to heat the stator. This is because the growth rate of the deposits depends mainly on the operating temperature control of the vacuum pump 1. The higher the operating temperature control of the vacuum pump 1, the slower the growth of the deposits. However, the more the rotor 3 is heated, the faster the creep.

[0058] It will therefore be appreciated that the user has a trade-off to make when choosing to control the operating temperature of the vacuum pump 1 between, on the one hand, prioritizing the pre-maintenance period for creep of the rotor 3 and, on the other hand, prioritizing the pre-maintenance period for deposits of the vacuum pump 1. It is therefore advantageous for the user to provide a deposit maintenance counter 28 in parallel with the creep maintenance counter 24. Therefore, according to one example embodiment, the turbomolecular vacuum pump 1 further comprises a deposition thickness determination device 27 configured to determine the thickness of the deposit in the vacuum pump 1, and a deposit maintenance counter 28 (see FIG. 10).

[0059] The deposition thickness determination device 27 may be configured to determine the thickness of the deposition at the discharge of the vacuum pump 1, for example downstream of the sleeve 13 and upstream of the discharge port 7 of the vacuum pump 1 where the pressure is highest. The deposition thickness determining device 27 (see FIG. 10) may be a physical size measurement sensor such as a capacitive deposition sensor.

[0060] According to another embodiment, the deposition thickness determination device 27 is a "virtual sensor", i.e. it is capable of providing the deposit thickness after a given time as a function of the previous deposit thickness value and the deposit thickness increment determined based on the deposit evolution model. To this end, the deposition thickness determination device 27 includes, for example, a controller, a microcontroller, a microprocessor, or a computer, and a memory. The deposition thickness determination device 27 is configured to determine a deposition thickness increment in a given period of time based on the operating temperature control of the vacuum pump 1, the deposition thickness value, and a deposition change model (or correspondence table).

[0061] More specifically, the deposition thickness determination device 27 has a memory in which are stored values ​​of the thickness of the deposit and a correspondence table (or correlation law), (or a model of the evolution of the deposit), providing values ​​of the thickness of the deposit over time as a function of the operating temperature control of the vacuum pump 1, e.g. the set temperature of the heating device 21. The correspondence table is specific to the method in which the turbomolecular vacuum pump 1 is used, e.g. semiconductor or LED manufacturing. This correspondence table (or correlation law), (or model of deposit evolution) can also provide values ​​of deposit thickness over time by taking into account values ​​of other parameters such as the gas pressure at the discharge of the vacuum pump 1 and / or the operating time of the vacuum pump 1 at a given motor torque.

[0062] The pressure of the gas at the time of discharge can be measured directly by a pressure sensor in the vacuum pump 1 or indirectly, for example by measuring the temperature of a heating element arranged close to the discharge opening 7 . The operating time of the vacuum pump 1 at a given motor torque can be estimated by the time that the motor torque (measured by the current supplied to the motor 16) exceeds a given threshold.

[0063] The deposition thickness determination device 27 may be configured to update the correspondence table based on measurements of the thickness of the deposit obtained during maintenance work on the vacuum pump 1. The initial value of the deposit thickness (at the time of delivery from the factory or at the time of maintenance) can be considered as zero. The increase in thickness of the deposit is determined periodically, for example, every minute, every hour, every two hours, or every day.

[0064] At the end of each predetermined period, the deposition thickness determination device 27 may determine a new deposition thickness increment or may maintain the same increment value as previously determined if the operating temperature control of the vacuum pump 1 has not changed after the predetermined period. The deposition thickness determination device 27 is similarly configured to increment the deposition thickness value by the determined deposition thickness increment.

[0065] The deposit maintenance counter 28 comprises, for example, a controller or microcontroller or microprocessor or computer and a memory. The deposit maintenance counter 28 may be mounted on an electronic circuit board housed in the stator 2 of the vacuum pump 1. This is, for example, the same processing device as the creep maintenance counter 24 and / or the "virtual" deposit thickness determination device 27. The deposit maintenance counter 28 is configured to determine information representing the remaining time until preventive maintenance of the deposit vacuum pump based on the deposit thickness value determined by the deposit thickness determination device 27 (physical size measurement sensor or virtual sensor).

[0066] The time when preventive maintenance of the vacuum pump against deposits needs to be carried out is, for example, when the ratio of the deposit thickness to the maximum allowable deposit thickness, at which the vacuum pump 1 becomes unreliable, reaches, for example, 80% of the minimum clearance between the rotor 3 and the stator 2. To that end, for example, the deposit maintenance counter 28 is configured to determine the remaining time until the permissible maximum deposit thickness value is reached based on the determined deposit thickness value and a model of the deposit's change over time, taking into account that the operating temperature control of the vacuum pump 1 remains unchanged.

[0067] This model of the deposition evolution is specific to the process, such as semiconductor or LED manufacturing, in which the turbomolecular vacuum pump 1 is used, and is the same as the correspondence table used, for example, by the “virtual” deposition thickness determination device 27 . A model of the evolution of the deposit over time is, for example, a linear relationship providing the deposit growth rate as a function of temperature.

[0068] The graph in FIG. 11 shows an example of the change in thickness of the deposit over time. In this curve, the thickness of the deposit changes from the start of the vacuum pump 1 to the time t 0 The thickness of the deposit as determined by the deposit maintenance counter 28 during the period from is shown by a solid line. The change is not linear, because the temperature of the vacuum pump 1 changes during use. Also, the remaining time D R is the time t when the sediment thickness calculated from the extrapolated curve of the change model (dashed line) reaches the maximum deposition value (2 mm in this case). F and the time t when the "current" deposition (0.61 mm in this case) was last determined. 0 It is also clear that there is a time difference between

[0069] Information representative of the time remaining until preventive maintenance of the deposit vacuum pump may be determined, for example, every minute or hour, or at least every 24 hours, every week or month, or at least once a year.

[0070] The deposit maintenance counter 28 may be configured to store information indicative of the time remaining until preventive maintenance of the deposit vacuum pump in a memory, for example at least until the next estimation, or may be configured to periodically accumulate the storage of this information. The information indicative of the time remaining until preventive maintenance of the deposit vacuum pump may likewise be readable by an external reader. The deposit maintenance counter 28 may be configured to transmit information representing the remaining time until preventive maintenance of the vacuum pump for deposits to an output device 26, such as a communication bus for a display or a human machine interface of the vacuum pump 1, or may be configured to transmit information to an output device 26 connected to multiple vacuum pumps, such as a central unit shared by a group of vacuum pumps, for example.

[0071] The user may then adjust the operating temperature control setpoint of the vacuum pump 1 so that, for example, the time remaining until preventive maintenance of the vacuum pump for deposits corresponds to the time remaining until preventive maintenance for creep. Alternatively, the user may adjust the operating temperature control setpoint of the vacuum pump 1 so that, for example, the time remaining until preventive maintenance of the vacuum pump for deposits is a fraction of the time remaining until preventive maintenance for creep, for example, one-third or one-quarter. It is therefore possible to schedule three or four preventative maintenance operations on the vacuum pump for deposits before performing preventative maintenance on the rotor for creep. [Explanation of symbols]

[0072] 1. Turbomolecular vacuum pump 2 Stator 3 Rotor 4 Turbomolecular Stages 5. Molecular Stage 6 Intake port 7 Outlet 9 Blades 10 Vane 11 Drive shaft 16 Motor 21 Heating device 23 Temperature Sensor 24 Creep Maintenance Counter 25 Speed ​​Controller 26 Output Devices 27 Deposition thickness determination device

Claims

1. 1. A turbomolecular vacuum pump (1) having a stator (2), a rotor (3) configured to rotate within the stator (2), and a motor (16) configured to drive the rotation of the rotor (3), a temperature sensor (23) configured to measure the temperature of the rotor (3), and a creep maintenance counter (24); the creep maintenance counter (24) having a memory in which is stored a creep value of the rotor (3) and a correspondence table providing a creep value of the rotor (3) over time as a function of temperature and rotational speed of the rotor (3); The creep maintenance counter (24) - determining an increment of the creep of the rotor (3) over a given period of time based on the temperature of the rotor (3) measured by the temperature sensor (23), the rotational speed of the rotor (3), the creep value of the rotor and the correspondence table; incrementing the creep value of the rotor by the determined creep increment; - determining information representative of the remaining time until preventive maintenance for said creep of said rotor is performed based on said incremental value of said creep.

2. 2. The turbomolecular vacuum pump according to claim 1, wherein the creep maintenance counter (24) is configured to determine, once every predetermined period, information representative of the remaining period until preventive maintenance for the creep of the rotor is performed.

3. 2. The turbomolecular vacuum pump according to claim 1, wherein the creep maintenance counter (24) is configured to update the correspondence table using measured values ​​of deformation of the rotor (3) collected during the maintenance work of the vacuum pump (1).

4. 2. The turbomolecular vacuum pump according to claim 1, characterized in that the creep maintenance counter (24) is configured to communicate information representative of the remaining period until preventive maintenance for the creep of the rotor to an output device (26) of a communication bus or a human machine interface of the vacuum pump (1) or of a central unit connected to a plurality of the vacuum pumps.

5. 2. The turbomolecular vacuum pump according to claim 1, wherein the creep maintenance counter (24) is configured to store in the memory and read out information representing the remaining period until the preventive maintenance for the creep of the rotor is performed.

6. 2. The turbomolecular vacuum pump according to claim 1, characterized in that the temperature sensor (23) is an infrared sensor.

7. 2. The turbomolecular vacuum pump of claim 1, characterized in that the temperature sensor (23) is configured to measure the temperature of a bottom of the sleeve (13) of the rotor (3) located at the discharge port (7) of the vacuum pump (1).

8. 2. The turbomolecular vacuum pump according to claim 1, characterized in that the temperature sensor (23) is arranged behind the sleeve (13) of the rotor (3).

9. 2. A turbomolecular vacuum pump according to claim 1, characterized in that the rotor (3) is made of aluminium or of coated aluminium, for example nickel-plated aluminium.

10. 2. The turbomolecular vacuum pump according to claim 1, further comprising a heating device (21) arranged to heat the stator (2).

11. 11. A deposition thickness determination device (27) according to claim 10, configured to determine the thickness of a deposition in the vacuum pump (1), 13. A turbomolecular vacuum pump comprising: a deposit maintenance counter (28) configured to determine information representative of the remaining time until preventive maintenance of a deposit of the vacuum pump based on the determined value of the deposit thickness.

12. 12. The turbomolecular vacuum pump of claim 11, wherein the deposition thickness determination device (27) has a memory, the memory including: the value of the thickness of the deposit, a correspondence table providing values ​​of the thickness of the deposit over time as a function of the operating temperature control of the vacuum pump (1), The deposition thickness determination device (27) - determining the thickness increment of the deposit over a given period of time based on the operating temperature control of the vacuum pump (1), the value of the deposit thickness and the correspondence table; a turbomolecular vacuum pump, characterized in that it increments the value of the thickness of the deposit by the determined thickness increment of the deposit.

13. 2. A method for determining a preventive maintenance timing for a turbomolecular vacuum pump (1) according to claim 1, for determining information representative of a period remaining until preventive maintenance of the rotor against creep, the method comprising the steps of: - determining an increment of creep of the rotor (3) over a predetermined period of time based on the temperature of the rotor (3) measured by the temperature sensor (23), the rotational speed of the rotor (3), the creep value of the rotor and the correspondence table; - incrementing the creep value of the rotor by the determined creep increment; - determining information representative of the remaining time until preventive maintenance of said rotor for said creep based on said incremented creep value.

14. 14. A method for determining when to perform preventive maintenance on the rotor as claimed in claim 13, wherein the time when preventive maintenance should be performed on the rotor for the creep is a percentage of a maximum allowable creep.

15. 14. A method for determining a time for preventive maintenance according to claim 13, characterized in that the time remaining until preventive maintenance of the rotor for creep is determined on the basis of a model of the evolution of the creep over time, taking into account the rotational speed of the rotor (3) and the temperature of the rotor (3) which allow the determination of an increment for creep.

16. 16. A method for determining a preventive maintenance timing according to claim 15, wherein the model of creep aging is a state function having two variables, the temperature and the rotational speed.

17. 14. A method for determining a time for preventive maintenance according to claim 13, characterized in that it comprises a step of determining information representative of the remaining time until preventive maintenance of the deposit of the vacuum pump (1) based on the determined value of the thickness of the deposit in the vacuum pump (1).

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