Turbomolecular vacuum pump and associated method

Abstract

Turbomolecular vacuum pump and associated method. Turbomolecular vacuum pump (1) with a stator (2), a rotor (3) configured to rotate in the stator (2), and a motor (16) configured to rotate the rotor (3), characterized in that the turbomolecular vacuum pump (1) further includes a temperature sensor (23) configured to measure the temperature of the rotor (3), and a creep counter (24) configured to determine an increment of the creep of the rotor (3) over a predetermined time period based on the temperature of the rotor (3) measured by the temperature sensor (23), the rotational speed of the rotor (3), the value of the creep of the rotor, and the correspondence table.to increment the rotor creep value with the specified creep increment and to determine representative information about the remaining time before preventive creep maintenance of the rotor based on the incremented creep value.

Description

Description Title of the invention: Turbomolecular vacuum pump and associated method Technical field of the invention

[0001] The present invention relates to a turbomolecular vacuum pump. The present invention also relates to a method for determining information representative of a remaining time before preventive maintenance of the rotor for creep of the turbomolecular vacuum pump. Technical background

[0002] Generating a high vacuum in an enclosure requires the use of turbomolecular vacuum pumps consisting of a stator in which a rotor is driven into rapid rotation, for example rotation at more than thirty thousand revolutions per minute.

[0003] In some processes in which turbomolecular vacuum pumps are used, such as semiconductor or LED manufacturing processes, a layer of deposit can form in the vacuum pump. These deposits can lead to a clearance restriction between the stator and the rotor, which can cause the rotor to seize. It is known to heat the stator to prevent condensation of reaction products and thus limit the formation of deposits in the vacuum pump and increase its service life.

[0004] In addition to limiting deposit formation, it may be necessary to increase the rotor operating temperature for other reasons. For example, increasing the vacuum pump temperature may be necessary to increase the flow of gas to be pumped or to pump heavier gases.

[0005] However, care must be taken to ensure that the rotor temperature does not exceed a certain upper threshold in order to preserve its mechanical strength. Indeed, the rotor's mechanical resistance to centrifugal forces decreases as the temperature increases. Irreversible deformations of the rotor (or creep) can occur at high temperatures and risk causing the stator to touch the most expanded part of the rotor.

[0006] Furthermore, rotor creep is not linear with increasing temperature. The higher the vacuum pump's operating temperature, the more maintenance frequency must be increased. For example, a rotor whose temperature is maintained at 130°C can operate for five years but a rotor heated to 140°C, under all other identical operating conditions, must be replaced after only two years.

[0007] In addition, increasing the rotation speed of the vacuum pump rotor, useful for example to further lower the pressure, can also have consequences on rotor creep, and therefore on the time between maintenance.

[0008] All these possibilities of variation in the operating point throughout the life of the vacuum pump make it difficult to anticipate a maintenance date. Summary of the invention

[0009] One of the aims of the present invention is to propose a turbomolecular vacuum pump which at least partially resolves a drawback of the state of the art, in particular to anticipate the need to change the rotor of the vacuum pump due to a risk of creep.

[0010] To this end, the invention relates to a turbomolecular vacuum pump comprising a stator, a rotor configured to rotate in the stator and a motor configured to drive the rotor in rotation, characterized in that the turbomolecular vacuum pump further comprises: - a temperature sensor configured to measure the rotor temperature, and - a creep maintenance counter comprising a memory in which the following are recorded: - a value of rotor creep, - a correspondence table giving values ​​of rotor creep over time as a function of temperature and rotor rotation speed, the creep maintenance counter being configured for: - determine an increment of rotor creep over a predetermined period from the rotor temperature measured by the temperature sensor, the rotor rotation speed, the rotor creep value and the correspondence table, - increment the rotor creep value with the determined creep increment, and - determine information representative of a remaining duration before preventive maintenance of the rotor for creep from the incremented creep value.

[0011] The creep maintenance counter provides information representative of the remaining time before preventive maintenance of the rotor for creep in a very precise manner and with regard to use of the vacuum pump which can be relatively complex, i.e. including variations in use of temperature and rotation speed over the lifetime of the vacuum pump. The creep maintenance counter thus adds (counts) the successive increases in creep resulting from the different times spent at different values ​​of temperature and rotation speed, which makes it possible to access a relatively realistic value of the current creep and the time remaining before preventive maintenance of the rotor for creep.

[0012] The vacuum pump may further include one or more of the features described below, taken alone or in combination.

[0013] The creep maintenance counter may be configured to determine information representative of the remaining time before preventive maintenance of the rotor for creep at least once a day, such as at least every hour, such as at least every minute and / or at least once a month, such as every week and / or at least every year.

[0014] The creep maintenance counter can be configured to allow the correspondence table to be updated with rotor deformation measurements from vacuum pump maintenance.

[0015] The creep maintenance counter may be configured to communicate information representative of the remaining time before preventive maintenance of the rotor for creep to an output device, such as a communication bus or a human-machine interface of the vacuum pump or such as a central unit connected to several vacuum pumps.

[0016] The creep maintenance counter can be configured to record information representative of the remaining time before preventive maintenance of the rotor for creep determined in the memory and make it available for reading.

[0017] The temperature sensor is for example an infrared sensor.

[0018] The temperature sensor can be configured to measure the temperature of a lower portion of a rotor skirt located on the side of a discharge port of the vacuum pump.

[0019] The temperature sensor can be arranged behind a rotor skirt.

[0020] The rotor is for example made of aluminum or coated aluminum, such as nickel-plated aluminum.

[0021] The turbomolecular vacuum pump may include a heating device configured to heat the stator.

[0022] The turbomolecular vacuum pump can also include: - a deposit thickness determining device configured to determine the deposit thickness in the vacuum pump, and - a depot maintenance counter configured to determine a information representative of a remaining time before preventive maintenance of the vacuum pump for deposit from the determined deposit thickness value.

[0023] Since the vacuum pump regulation temperature setpoint influences the deposit thickness in the vacuum pump in certain processes, the deposit maintenance counter can help the user in their choice of temperature based on the time remaining before preventive maintenance of the vacuum pump for deposit and the time remaining before preventive maintenance for creep.

[0024] The device for determining a deposit thickness may be a physical quantity measuring sensor, such as a capacitive deposit sensor.

[0025] According to another example, the device for determining a deposit thickness comprises a memory in which the following are recorded: - a deposit thickness value, - a correspondence table giving values ​​of deposit thickness over time as a function of the regulation temperature of the vacuum pump, the device for determining a deposit thickness being configured to: - determine a deposit thickness increment over a predetermined period from the vacuum pump control temperature, the deposit thickness value and the correspondence table, and - increment the deposit thickness value with the determined deposit thickness increment.

[0026] The correspondence table (or law) (or deposit evolution model) of the device for determining a “virtual” deposit thickness is, for example, derived from a linear relationship giving the growth rate of the deposit as a function of temperature.

[0027] The correspondence table (or law) (or deposit evolution model) can also give values ​​of deposit thickness over time by taking into account the values ​​of other parameters, such as the gas pressure at the discharge and / or the operating time of the vacuum pump at a given engine torque.

[0028] The device for determining a deposit thickness can be configured to allow the correspondence table to be updated by deposit thickness measurements from vacuum pump maintenance.

[0029] The invention also relates to a method for determining information representative of a remaining time before preventive maintenance of the rotor for creep of a turbomolecular vacuum pump as described previously, characterized in that it comprises the steps of: - determine an increment of rotor creep over a predetermined period from the rotor temperature measured by the temperature sensor, the rotor rotation speed, the rotor creep value and the correspondence table, - increment the rotor creep value with the determined creep increment, and - determine information representative of a remaining duration before preventive maintenance of the rotor for creep from the incremented creep value.

[0030] The time when preventive maintenance of the rotor for creep is required may be a percentage of maximum allowable creep.

[0031] According to an exemplary embodiment, the remaining time before preventive maintenance of the rotor for creep is determined from a model of the evolution of creep over time and by considering that the rotation speed of the rotor and the temperature of the rotor are those which allowed the determination of the creep increment.

[0032] According to an exemplary embodiment, the creep evolution model over time is a state function with two variables: temperature and rotation speed.

[0033] According to an exemplary embodiment, the method further comprises a step of determining information representative of a remaining time before preventive maintenance of the vacuum pump for deposition from the determination of a deposit thickness value in the vacuum pump.

[0034] The point at which preventive maintenance of the vacuum pump for deposits is necessary is, for example, a percentage of a maximum permissible deposit thickness beyond which the vacuum pump is no longer reliable. This is, for example, 80% of the smallest clearance between the rotor and the stator.

[0035] For this, for example, the deposit maintenance counter is configured to determine the remaining time before the maximum permissible deposit thickness value is reached, based on the determined deposit thickness value and a model of the deposit's evolution over time and assuming that the vacuum pump control temperature is unchanged.

[0036] The model of the evolution of the deposit over time is, for example, a linear relationship giving the growth rate of the deposit as a function of temperature.

[0037] According to an example of determining the deposit thickness, a deposit thickness increment is determined over a predetermined period of time from the control temperature of the vacuum pump, the deposit thickness value and from a correspondence table and the deposit thickness value is incremented with the determined deposit thickness increment.

[0038] Brief description of the figures

[0039] Other advantages and characteristics will appear on reading the following description of a particular embodiment of the invention, but in no way limiting, as well as the appended drawings in which:

[0040] [Fig. 1] Figure 1 shows an axial sectional view of a turbomolecular vacuum pump.

[0041] [Fig. 2] Figure 2 is a flowchart of elements of the vacuum pump of Figure 1.

[0042] [Fig. 3] Figure 3 is a graph of a first network of curves (or abacus) giving the creep (F) (in %), (on the ordinate) as a function of time (T) (in years) (on the abscissa) for different rotor rotation speeds, for a first rotor temperature of 150°C: 45krpm (strong solid lines), 40krpm (normal solid lines), 35krpm (thin solid lines).

[0043] [Fig. 4] Figure 4 is a graph similar to Figure 3, of a second network of curves giving the creep (F) (in %), (on the ordinate) as a function of time (T) (in years) (on the abscissa) for different rotor rotation speeds, for a second rotor temperature of 140°C: 45krpm (strong mixed lines), 40krpm (normal mixed lines), 35krpm (thin mixed lines).

[0044] [Fig. 5] Figure 5 is a graph similar to Figure 3, of a third network of curves giving the creep (F) (in %), (on the ordinate) as a function of time (T) (in years) (on the abscissa) for different rotor rotation speeds, for a third rotor temperature of 130°C: 45krpm (strong broken lines), 40krpm (normal broken lines), 35krpm (thin broken lines).

[0045] [Fig. 6] Figure 6 shows the first, second and third networks of curves from Figures 3, 4 and 5 on the same graph.

[0046] [Fig. 7] Figure 7 is a three-dimensional graphical representation with the creep rate (VF) (in % / year) as an ordinate as a function of rotor temperatures (T°) (in °C) and rotor rotation speeds (in krpm) to illustrate the determination by linear regression extrapolation of the creep rate for a measured rotor temperature and for a given rotation speed.

[0047] [Fig. 8] Figure 8 is a three-dimensional graphical representation with the creep rate (VF) (in % / year) as an ordinate as a function of rotor temperatures (T°) (in °C) and rotor rotation speeds. (in krpm) to illustrate the determination by polynomial extrapolation of the creep velocity for a measured rotor temperature and for a given rotational speed.

[0048] [Fig. 9] Figure 9 is a graph with creep (F) (in %) as a function of time (T) (in years) as the ordinate for an example of determining the remaining time before preventive maintenance of the rotor for creep at a given time.

[0049] [Fig. 10] Figure 10 is a flowchart of other elements of the vacuum pump of Figure 1.

[0050] [Fig. 11] Figure 11 is a graph with the ordinate being a deposit thickness (in mm) versus time (T) (in years) for an example of determining a remaining time before preventive maintenance of the vacuum pump for deposit at a given time.

[0051] In these figures, identical elements have the same reference numbers. Detailed description

[0052] The following embodiments are examples. Although the description refers to one or more embodiments, this does not necessarily mean that each reference relates to the same embodiment, or that the features apply only to a single embodiment. Single features of different embodiments may also be combined or interchanged to provide other embodiments.

[0053] "Upstream" means an element that is placed before another in relation to the direction of gas flow. Conversely, "downstream" means an element placed after another in relation to the direction of gas flow to be pumped.

[0054] Figure 1 illustrates an exemplary embodiment of a turbomolecular vacuum pump.

[0055] The turbomolecular vacuum pump 1 comprises a stator 2 in which a rotor 3 is configured to rotate at high speed in axial rotation, for example rotation at more than thirty thousand revolutions per minute.

[0056] In the embodiment of Figure 1, the turbomolecular vacuum pump 1 is said to be hybrid: it 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 gases (represented by the arrows F1 in Figure 1). The pumped gases enter through the suction port 6, first pass through the turbomolecular stage 4, then the molecular stage 5, to then be evacuated to a discharge port 7 of the turbomolecular vacuum pump 1. In operation, the discharge port 7 is connected to a primary pumping.

[0057] An annular inlet flange 8 surrounds, for example, the suction port 6 to connect the vacuum pump 1 to an enclosure whose pressure is to be lowered.

[0058] In the turbomolecular stage 4, the rotor 3 comprises at least two stages of blades 9 and the stator 2 comprises at least one stage of blades 10. The stages of blades 9 and blades 10 follow one another axially along the axis of rotation 11 of the rotor 3 in the turbomolecular stage 4. The rotor 3 comprises, for example, more than four stages of blades 9, such as, for example, between four and twelve stages of blades 9 (seven in the example illustrated in FIG. 1).

[0059] Each stage of blades 9 of the rotor 3 comprises inclined blades which extend in a substantially radial direction from a hub 11 of the rotor 3 fixed to a drive shaft 12 of the vacuum pump 1, for example by screwing. The blades are distributed regularly around the periphery of the hub 11.

[0060] Each stage of fins 10 of the stator 2 comprises a crown from which extend, in a substantially radial direction, inclined fins, distributed regularly around the inner periphery of the crown. The fins of a stage of fins 10 of the stator 2 engage between the blades of two successive stages of blades 9 of the rotor 3. The blades 9 of the rotor 3 and the fins 10 of the stator 2 are inclined to guide the pumped gas molecules towards the molecular stage 5.

[0061] Here, in the molecular stage 5, the rotor 3 further comprises a skirt 13, called the Holweck skirt, downstream of the at least two blade stages 9, formed by a smooth cylinder, which rotates opposite helical grooves 14 of the stator 2. The helical grooves 14 of the stator 2 make it possible to compress and guide the pumped gases towards the discharge orifice 7.

[0062] The rotor 3 further comprises an internal bowl 15, coaxial with the axis of rotation 11, formed under the skirt 13 and arranged opposite a bell 17 of the stator 2, projecting under the rotor 3. In operation, the rotor 3 rotates in the stator 2 without contact between the internal bowl 15 and the bell 17.

[0063] The rotor 3 can be made from a single piece (monobloc) or it can be an assembly of several parts. It is for example made from aluminum (or aluminum alloy) and / or nickel. It can have a coating, such as nickel, in particular to better resist corrosion. It is for example made from nickel-plated aluminum.

[0064] The rotor 3 is driven in rotation in the stator 2 by an internal motor 16 of the vacuum pump 1. The motor 16 is for example arranged in the bell 17 of the stator 2, itself arranged under the internal bowl 15 of the rotor 3, the drive shaft 12 passing through the bell 17 of the stator 2.

[0065] The rotor 3 is guided laterally and axially by magnetic or mechanical bearings 18 supporting the drive shaft 12 of the rotor 3, located in the stator 2. There are for example first bearings 18 supporting and guiding a first end of the drive shaft 12 in a base of the bell 17 of the stator 2 and second bearings 18 supporting and guiding a second end of the drive shaft 12 arranged at the top of the bell 17.

[0066] Other electrical or electronic components can be received in the bell 17 of the stator 2, such as for example position sensors.

[0067] The vacuum pump 1 may comprise a cooling device configured to cool the bell 17, arranged for example in the bell 17 or in thermal contact with the bell 17, such as a hydraulic circuit, in order to be able to continuously cool the elements that it contains such as in particular the bearings 18, the motor 16 and other electrical or electronic components to enable their operation.

[0068] The vacuum pump 1 may comprise a purge device 20 configured to inject a purge gas into the gap located between the bell 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 another neutral gas such as helium or argon. The purge device is for example configured to inject a purge gas at at least one bearing 18 located in the stator 2, supporting and guiding the drive shaft 12 of the rotor 3 so that the flow of purge gas passes through the at least one bearing 18 before exiting the bell 17 of the stator 2 and circulating in the gap. The circulation of the purge gas is shown diagrammatically by arrows f2 in FIG. 1.

[0069] The vacuum pump 1 may comprise a heating device 21 configured to heat the stator 2 for example so that the temperature of the rotor 3 is controlled at a value between 120°C and 150°C.

[0070] The heating device 21 may comprise an external heating resistive belt or radiative elements arranged in the gas flow path of the vacuum pump 1, for example configured to heat a sleeve 22 of the stator 2 in which the helical grooves 14 are formed.

[0071] The turbomolecular vacuum pump 1 may further comprise a temperature sensor 23 configured to measure the temperature of the rotor 3 and a creep maintenance counter 24 (figure 2).

[0072] The temperature sensor 23 is, for example, an infrared sensor. The infrared sensor is contactless, which makes it possible to measure the temperature of the rotating rotor 3 with high accuracy in the temperature ranges between 50°C and 250°C.

[0073] The temperature sensor 23 can be configured to measure the temperature of the skirt 13 of the rotor 3 (the cylindrical part), in particular in a lower part, that is to say located on the side of the discharge orifice 7 of the vacuum pump 1, so as to target the place of the rotor 3 which is subjected to the most mechanical stress.

[0074] The temperature sensor 23 is for example arranged behind (under) the skirt 13 of the rotor 3, between the stator 2 and the internal bowl 15 of the rotor 3 (figure 1). In this way, the temperature sensor 23 is not arranged in the gas pumping path and therefore is little subject to corrosive attacks from the pumped gases and can benefit from protection by the purge gas.

[0075] 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 mounted on an electronic card housed in the stator 2 of the vacuum pump 1.

[0076] The creep maintenance counter 24 includes a memory in which a rotor creep value is recorded and a correspondence table giving rotor creep values ​​3 over time as a function of the temperature and rotation speed of the rotor.

[0077] The correspondence table (or law) is illustrated by networks of curves (abacus) of creep as a function of time for different temperatures of the rotor 3 and different rotation speeds of the rotor in figures 3, 4 and 5.

[0078] The first network of curves in Figure 3 gives the creep of rotor 3 over time for different rotation speeds of rotor 3 at a first temperature of rotor 3 of 150°C. It can be seen that the creep increases more quickly over time with increasing rotation speed of rotor 3. For example, the creep is 0.2% after six months at a rotor 3 temperature of 150°C for a rotation speed of 45krpm while it reaches this creep value after more than two years for the same temperature with a speed of reduced rotation to 40krpm and does not even reach it after three years at a reduced rotation speed of 35krpm.

[0079] This same trend is observed on the second and third network of curves in Figures 4 and 5 showing the creep of rotor 3 over time for the different rotation speeds of rotor 3 at a rotor 3 temperature lowered to 140°C in Figure 4 and to 130°C in Figure 5. It can be seen, as in Figure 3, that creep increases more rapidly with increasing rotation speed of rotor 3 but less rapidly at lower temperatures. For example, the creep of 0.2% obtained after six months at a rotor temperature of 150°C for a rotation speed of 45krpm (strong continuous lines in Figure 3) is reached after approximately eight months for a rotor 3 temperature of 140°C (strong mixed lines in Figure 4) and after more than a year for a rotor 3 temperature of 130°C (strong broken lines in Figure 5).

[0080] It is understood that creep increases more quickly over time with increasing rotation speed and temperature as is better seen in Figure 6 where the inflection / slope points of the first, second and third networks of creep curves in Figures 3, 4 and 5 are represented by a double arrow on the same graph for a given creep level (first horizontal dotted line).

[0081] The creep of aluminum (or aluminum alloy) as a function of temperature is well known in the field of metallurgy, which makes it easier to fill in the correspondence table for an aluminum rotor 3.

[0082] The correspondence table may also include simulation results of rotor 3 obtained with more complex changes in temperature and rotation speed. Since the skirt 13 of rotor 3 is a cylinder, it is sufficient to model the deformation of the diameter of the skirt 13 of rotor 3 to obtain a model of the deformations.

[0083] The creep maintenance counter 24 can also be configured to allow the correspondence table to be updated by measurements of the deformation of the rotor 3 resulting from maintenance of the vacuum pump 1. For example, this simply involves measuring the diameter of the skirt 13 of the rotor 3 during maintenance and comparing it with the value of the diameter leaving the factory to obtain the creep. These updates can make it possible to improve the deformation model.

[0084] The creep maintenance counter 24 is configured to determine an increment of the creep of the rotor 3 over a predetermined period of time from the temperature of the rotor 3 measured by the temperature sensor 23, the speed of rotor 3 rotation, rotor 3 creep value and correspondence table.

[0085] The initial value of the creep of a rotor (factory or maintenance) can be considered to be zero.

[0086] The creep maintenance counter 24 can, for example, receive information on the rotation speed of the rotor 3 from a speed sensor of the vacuum pump 1, for example from the speed controller 25 of the motor 16 (figure 2).

[0087] The rotation speed of the vacuum pump 1 is generally controlled at a constant nominal speed, the value of which depends on each vacuum pump 1 and can be from 20000 rpm for the largest up to 100000 rpm for the smallest. Depending on the needs, the user may switch to one or more higher speed setpoints, such as up to 10% higher than the nominal speed, or lower ones, such as up to 10% lower than the nominal speed.

[0088] The creep increment of rotor 3 is for example determined periodically, for example every minute or every hour or every two hours or every day. The periodicity of the creep increment calculation makes it possible to take into account the fact that the creep increase is not linear.

[0089] The creep maintenance counter 24 can determine at each expiration of the predetermined duration a new increment of the creep of the rotor 3 or it can maintain the same increment value as that previously determined if the temperature and the rotation speed have not changed at the end of the predetermined duration.

[0090] For example, in Figure 3, considering that the “current” creep value of rotor 3 is 0.1%, that the temperature of rotor 3 is 150°C, the rotation speed of rotor 3 is 40krpm and the predetermined duration is one month, the correspondence table makes it possible to determine that the creep increment over the predetermined duration is 0.01%.

[0091] When the measured rotor 3 temperature or rotor 3 rotational speed are not those of the values ​​in the correspondence table, the rotor 3 creep can be determined by extrapolation, for example by linear regression or by polynomial extrapolation.

[0092] This is illustrated in the examples in Figures 7 and 8.

[0093] Figure 7 is a graph showing another representation of the correspondence table, this time representing the values ​​of the creep increments of rotor 3 as a function of time for several temperature / temperature pairs. rotational speed of rotor 3 (nine in the example) and the values ​​extrapolated by linear regression connecting these points. The creep increment of rotor 3 is to be determined in this example for a temperature and rotational speed distinct from the values ​​in the correspondence table so that two extrapolations are necessary.

[0094] Figure 8 shows a similar example for values ​​extrapolated by polynomial extrapolation. This extrapolation method is more accurate.

[0095] The creep maintenance counter 24 is also configured to increment the rotor creep value with the determined creep increment and to determine information representative of a remaining time before preventive maintenance of the rotor for creep from the incremented creep value.

[0096] The time when preventive maintenance of the rotor for creep is necessary is, for example, a percentage of maximum permissible creep, beyond which the rotor 3 is no longer reliable, for example, 0.2%.

[0097] For this, for example, the creep maintenance counter 24 is configured to determine the time remaining before the maximum permissible creep value is reached, from the incremented creep value and a model of creep evolution over time and considering that the rotation speed of the rotor 3 and the temperature of the rotor 3 are those which have allowed the creep increment to be determined, i.e. which have allowed the “current” creep value to be determined.

[0098] The model of creep evolution over time is for example a state function with two variables, namely temperature and rotation speed, for example of the type dCreep / dt = Non-linear function (T°, rotation_speed, Creep).

[0099] The graph in Figure 9 shows an example of creep evolution over time. This curve shows in solid lines the incremented creep determined by the creep maintenance counter 24 from the start-up of vacuum pump 1 until time to. We also see that the remaining time DR is the difference between the time Tf when creep will reach the maximum creep value (here 0.2%) from the extrapolated curve (dotted) of the evolution model, and the time to of the last determination of the “current” creep Fo.

[0100] The information representative of the remaining time before preventive maintenance of the rotor for creep can be determined with a first frequency, for example hourly or daily, that is to say at least once a day, such as at least every hour, such as at least every minute. This determination at short term helps the user to adjust the input parameters, in particular the rotation speed for a frequency lower than the thermal inertia time of vacuum pump 1 (of the order of an hour). Indeed, if the user modifies an input parameter, he will be able to quickly see the impact of the new setting on the life of vacuum pump 1 or on the time remaining before the next maintenance.

[0101] The information representing the remaining time before preventive maintenance of the rotor for creep can be determined with a second weekly or monthly frequency, i.e. at least once a month, such as every week. This medium-term determination helps the user to plan the maintenance phases.

[0102] Information representing the remaining time before preventive maintenance of the rotor for creep can be determined with a third annual frequency, i.e. at least once a year. This long-term determination makes it possible to plan the replacement of the rotor or the vacuum pump.

[0103] The creep maintenance counter 24 may be configured to record information representative of the remaining time before preventive maintenance of the rotor for creep in its memory, for example at least until the next estimate or it may accumulate the recording of this information periodically. The information representative of the remaining time before preventive maintenance of the rotor for creep may also be made available for reading by an external reader.

[0104] The creep maintenance counter 24 can be configured to communicate the information representative of the remaining time before preventive maintenance of the rotor for creep to an output device 26, such as a communication bus or a human-machine interface of the vacuum pump 1, for example for display, or such as a central unit connected to several vacuum pumps, for example common to a fleet of vacuum pumps.

[0105] The user who wishes to increase the temperature of the vacuum pump 1 , for example during the so-called hot cleaning operating phases, can thus easily see how to adjust the rotation speed of the rotor 3 accordingly, in particular by reducing it, if he does not wish to reduce the service life of the vacuum pump 1 .

[0106] Similarly, the user who wishes to increase the pumping speed to lower the pressure, for example in ultimate vacuum, can increase the rotation speed of the vacuum pump 1, and see how to adjust the regulation temperature of the vacuum pump 1 (and therefore of the rotor 3) accordingly, in particular by reducing it, if he does not wish to reduce the service life of the vacuum pump 1.

[0107] It is understood that the creep maintenance counter 24 makes it possible to obtain information representative of the remaining time before preventive maintenance of the rotor for creep in a very precise manner and with respect to use of the vacuum pump 1 which may be relatively complex, that is to say including variations in use of the temperature and the rotation speed over the lifetime of the vacuum pump 1. The creep maintenance counter 24 thus adds (counts) the successive increases in creep resulting from the different times spent at the different values ​​of temperature and rotation speed, which makes it possible to access a relatively realistic value of the current creep and the remaining time before preventive maintenance of the rotor for creep.

[0108] In some processes in which turbomolecular vacuum pumps 1 are used, such as semiconductor or LED manufacturing processes, a deposit layer may form in the vacuum pump 1 . These deposits may cause a clearance restriction between the stator 2 and the rotor 3 which may cause seizure of the rotor 3. It is known to heat the stator to prevent condensation of reaction products and thus limit the formation of deposits in the vacuum pump 1 and increase its service life. Indeed, the growth rate of the deposit depends mainly on the control temperature of the vacuum pump 1 . The higher the control temperature of the vacuum pump 1 , the slower the growth of the deposit. However, the more the rotor 3 is heated, the faster the creep.It is therefore understood that there is a compromise to be found for the user in the choice of the regulation temperature of the vacuum pump 1 between, on the one hand, favoring the duration before maintenance of the rotor 3 for creep and, on the other hand, favoring the duration before maintenance of the vacuum pump 2 for deposition. It is therefore interesting for the user to have, in parallel with the maintenance counter for creep 24, a maintenance counter for deposition 28.

[0109] Thus, according to an exemplary embodiment, the turbomolecular vacuum pump 1 further comprises a device for determining a deposit thickness 27, configured to determine the deposit thickness in the vacuum pump 1 and a deposit maintenance counter 28 (figure 10).

[0110] The device for determining a deposit thickness 27 can be configured to determine the deposit thickness at the discharge of the vacuum pump 1, for example downstream of the skirt 13 and upstream of the discharge orifice 7 of the vacuum pump 1, where the pressures are highest.

[0111] The device for determining a deposit thickness 27 may be a physical quantity measurement sensor, such as a capacitive deposit sensor (figure 1).

[0112] According to another example, the device for determining a deposit thickness 27 is a “virtual sensor”, that is to say capable of providing a deposit thickness after a predetermined duration as a function of the previous deposit thickness value and a deposit thickness increment determined from a deposit evolution model.

[0113] For this, the device for determining a deposit thickness 27 comprises, for example, a controller or microcontroller or microprocessor or computer, and a memory.

[0114] The device for determining a deposit thickness 27 is configured to determine a deposit thickness increment over a predetermined duration from the regulation temperature of the vacuum pump 1, the deposit thickness value and a deposit evolution model (or correspondence table).

[0115] More precisely, the device for determining a deposit thickness 27 comprises a memory in which are recorded a deposit thickness value and a correspondence table (or law) (or model of evolution of the deposit) giving deposit thickness values ​​over time as a function of the regulation temperature of the vacuum pump 1, for example the temperature setpoint of the heating device 21. This correspondence table is specific to the process, such as the manufacturing of semiconductors or LEDs, for which the turbomolecular vacuum pump 1 is used.

[0116] The correspondence table (or law) (or deposit evolution model) can also give values ​​of deposit thickness over time by taking into account the values ​​of other parameters, such as the gas pressure at the discharge of vacuum pump 1 and / or the operating time of vacuum pump 1 at a given engine torque.

[0117] The discharge gas pressure can be measured directly by a pressure sensor of the vacuum pump 1 or indirectly by, for example, measuring the temperature of a heating element arranged close to the discharge port 7.

[0118] The operating time of the vacuum pump 1 at a given motor torque can be estimated by the duration during which the motor torque (measured by the supply current of the motor 16) is above a given threshold.

[0119] The device for determining a deposit thickness 27 can be configured to allow the correspondence table to be updated by deposit thickness measurements resulting from maintenance of the vacuum pump 1.

[0120] The initial value of deposit thickness (factory or maintenance) can be considered to be zero.

[0121] The deposit thickness increment is for example determined periodically, for example every minute or every hour or every two hours or every day.

[0122] The device for determining a deposit thickness 27 can determine a new deposit thickness increment at each lapse of the predetermined duration or it can maintain the same increment value as that previously determined if the control temperature of the vacuum pump 1 has not changed at the end of the predetermined duration.

[0123] The deposit thickness determining device 27 is also configured to increment the deposit thickness value with the determined deposit thickness increment.

[0124] 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 card housed in the stator 2 of the vacuum pump 1. It is, for example, the same processing unit as that of the creep maintenance counter 24 and / or that of the device for determining a “virtual” deposit thickness 27.

[0125] The deposit maintenance counter 28 is configured to determine information representative of a remaining time before preventive maintenance of the deposit vacuum pump from the deposit thickness value determined by the deposit thickness determination device 27 (physical quantity measurement sensor or virtual sensor).

[0126] The point at which preventive maintenance of the vacuum pump for deposit is necessary is, for example, a percentage of a maximum permissible deposit thickness, beyond which the vacuum pump 1 is no longer reliable, for example, 80% of the smallest clearance between the rotor 3 and the stator 2.

[0127] For this, for example, the deposit maintenance counter 28 is configured to determine the remaining time before the maximum permissible deposit thickness value is reached, from the determined deposit thickness value and a model of the evolution of the deposit over time and assuming that the control temperature of the vacuum pump 1 is unchanged. This deposition evolution model is specific to the process, such as semiconductor or LED manufacturing, for which the turbomolecular vacuum pump 1 is used. It is, for example, the same as the correspondence table used by the device for determining a “virtual” deposition thickness 27.

[0128] The model of the evolution of the deposit over time is, for example, a linear relationship giving the growth rate of the deposit as a function of temperature.

[0129] The graph in Figure 11 shows an example of the evolution of deposit thickness over time. This curve shows in solid lines the deposit thickness determined by the deposit maintenance counter 28 from the start-up of the vacuum pump 1 until time to. This evolution is not linear, in particular due to the variation in temperature during the use of the vacuum pump 1. We also see that the remaining time DR is the difference between the time tf where the deposit thickness will reach the maximum deposit value (here 2 mm) from the extrapolated curve (in dotted lines) of the evolution model, and the time to of the last determination of the “current” deposit (here 0.61 mm).

[0130] The information representing the remaining time before preventive maintenance of the vacuum pump for depot can be determined for example every minute or every hour, or at least every 24 hours, or every week or every month or at least once a year.

[0131] The depot maintenance counter 28 may be configured to record information representative of the remaining time before preventive maintenance of the depot vacuum pump in its memory, for example at least until the next estimate, or it may accumulate the recording of this information periodically. The information representative of the remaining time before preventive maintenance of the depot vacuum pump may also be made available for reading by an external reader.

[0132] The depot maintenance counter 28 can be configured to communicate the information representative of the remaining time before preventive maintenance of the depot vacuum pump to an output device 26, such as a communication bus or a human-machine interface of the vacuum pump 1, for example for display, or such as a central unit connected to several vacuum pumps, for example common to a fleet of vacuum pumps.

[0133] The user can then adjust the regulation temperature setpoint of vacuum pump 1, for example so that the time remaining before maintenance preventive maintenance of the vacuum pump for deposition corresponds to the preventive time before preventive maintenance for creep. Alternatively, the user can adjust the control temperature setpoint of the vacuum pump 1 , for example so that the remaining time before preventive maintenance of the vacuum pump for deposition is a fraction of the preventive time before preventive maintenance for creep, for example a third or a quarter. He can thus plan three or four preventive maintenances of the vacuum pump for deposition before carrying out preventive maintenance of the rotor for creep.

Claims

DEMANDS

1. A turbomolecular vacuum pump (1) comprising a stator (2), a rotor (3) configured to rotate within the stator (2), and a motor (16) configured to drive the rotor (3) in rotation, characterized in that the turbomolecular vacuum pump (1) further comprises a temperature sensor (23) configured to measure the temperature of the rotor (3) and a creep maintenance counter (24) comprising a memory in which a value of the rotor creep and a lookup table giving values ​​of the rotor creep (3) over time as a function of the temperature and the rotational speed of the rotor (3) are stored, the creep maintenance counter (24) being configured to: - determine an increment of rotor creep (3) over a predetermined time period from the rotor temperature (3) measured by the temperature sensor (23), the rotational speed of the rotor (3), the value of the rotor creep and the correlation table, - increment the rotor creep value with the determined creep increment, and - determine information representative of a remaining time before preventive maintenance of the rotor for creep from the incremented creep value.

2. Turbomolecular vacuum pump (1) according to claim 1, characterized in that the creep maintenance counter (24) is configured to determine representative information of the time remaining before preventive maintenance of the creep rotor at least once a day, such as at least every hour, such as at least every minute and / or at least once a month, such as every week, and / or at least every year.

3. Turbomolecular vacuum pump (1) according to any one of the preceding claims, characterized in that the creep maintenance counter (24) is configured to allow updating of the lookup table by rotor deformation measurements (3) from maintenance of the vacuum pump (1).

4. Turbomolecular vacuum pump (1) according to any one of the preceding claims, characterized in that the creep maintenance counter (24) is configured to communicate information representative of the time remaining before preventive maintenance of the rotor for creep to an output device (26) such as a communication bus or a man-machine interface of the vacuum pump (1) or such as a central unit connected to several vacuum pumps.

5. Turbomolecular vacuum pump (1) according to any one of the preceding claims, characterized in that the creep maintenance counter (24) is configured to record information representative of the time remaining before preventive maintenance of the determined creep rotor in memory and make it available for reading.

6. Turbomolecular vacuum pump (1) according to any one of the preceding claims, characterized in that the temperature sensor (23) is an infrared sensor.

7. Turbomolecular vacuum pump (1) according to any one of the preceding claims, characterized in that the temperature sensor (23) is configured to measure the temperature of a lower part of a skirt (13) of the rotor (3) located on the side of a discharge port (7) of the vacuum pump (1).

8. Turbomolecular vacuum pump (1) according to any one of the preceding claims, characterized in that the temperature sensor (23) is arranged behind a skirt (13) of the rotor (3).

9. Turbomolecular vacuum pump (1) according to any one of the preceding claims, characterized in that the rotor (3) is made of aluminium or coated aluminium, such as nickel-plated aluminium.

10. Turbomolecular vacuum pump (1) according to any one of the preceding claims, characterized in that it comprises a heating device (21) configured to heat the stator (2).

11. Turbomolecular vacuum pump (1) according to claim 10, characterized in that it comprises: - a device for determining a deposit thickness (27) configured to determine the deposit thickness in the vacuum pump (1), and - a maintenance counter for deposit (28) configured to determine information representative of a remaining time before preventive maintenance of the vacuum pump for deposit from the determined deposit thickness value.

12. Turbomolecular vacuum pump (1) according to claim 11, characterized in that the device for determining a deposit thickness (27) comprises a memory in which the following are recorded: - a deposit thickness value, - a lookup table giving deposit thickness values ​​over time as a function of a vacuum pump control temperature (1), the deposit thickness determination device (27) being configured for: - determine a deposit thickness increment over a predetermined time period from the vacuum pump control temperature (1), the deposit thickness value and the lookup table, and - increment the deposit thickness value with the determined deposit thickness increment.

13. A method for determining information representative of the remaining time before preventive maintenance of the creep rotor of a turbomolecular vacuum pump (1) according to any one of the preceding claims, characterized in that it comprises the steps of: - determine an increment of rotor creep (3) over a predetermined time period from the rotor temperature (3) measured by the temperature sensor (23), the rotational speed of the rotor (3), the value of the rotor creep and the correlation table, - increment the rotor creep value with the determined creep increment, and - determine information representative of a remaining time before preventive maintenance of the rotor for creep from the incremented creep value.

14. Method according to claim 13, characterized in that the time at which preventive maintenance of the rotor for creep is required is a percentage of a maximum permissible creep.

15. A method according to any one of claims 13 or 14, characterized in that the remaining time before preventive maintenance of the rotor for creep is determined from a model of the evolution of creep over time and considering that the rotational speed of the rotor (3) and the temperature of the rotor (3) are those which enabled the determination of the creep increment.

16. A method according to claim 15, characterized in that the creep evolution model over time is a state function with two variables, namely temperature and rotational speed.

17. A method according to any one of claims 13 to 16, characterized in that it comprises a step of determining information representative of a remaining time before preventive maintenance of the vacuum pump for deposition from the determination of a deposit thickness value in the vacuum pump (1).

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