METHOD FOR MONITORING AN OPERATING STATE OF A PUMPING DEVICE

Abstract

A method is for surveillance of an operating state of a pumping device connected to a process chamber in order to determine a failing operating state of the pumping device. The pumping device includes at least one rough-vacuum pump including a motor for driving the rough-vacuum pump and a variable speed drive to control the rotation speed of the motor, to receive a first input parameter corresponding to a set point frequency and a second input parameter corresponding to a motor current, and to deliver to the motor an output parameter corresponding to a control frequency. A failing operating state is determined when in steady-state operation the difference between the first input parameter and the output parameter is equal to or exceeds 10% of the first input parameter for a predetermined time greater than 3 seconds. The method can be implemented in a pumping device and an installation.

Claims

1-12. (canceled)

13. A method for surveillance of an operating state of a pumping device connected to a process chamber in order to determine a failing operating state of the pumping device, the pumping device comprising at least one rough-vacuum pump comprising: a motor for driving the rough-vacuum pump, and a variable speed drive configured to control the rotation speed of the motor, and configured to receive a first input parameter corresponding to a set point frequency and a second input parameter corresponding to a motor current and configured to deliver to the motor an output parameter corresponding to a control frequency, the method comprising: determining a failing operating state when, in steady-state operation, a difference between the first input parameter and the output parameter is equal to or exceeds 10% of the first input parameter for a predetermined time greater than 3 seconds.

14. The method according to claim 13, wherein the failing operating state is determined when, in steady-state operation, the difference between the first input parameter and the output parameter is equal to or exceeds 4% of the first input parameter for the predetermined time.

15. The method according to claim 13, wherein the predetermined time is greater than 10 seconds.

16. The method according to claim 13, wherein the predetermined time is less than 30 seconds.

17. The method according to claim 13, wherein, on starting the rough-vacuum pump, the variable speed drive is commanded to increase the control frequency progressively until the set point frequency is reached.

18. The method according to claim 13, wherein, in steady-state operation, the set point frequency is constant at least for a time greater than or equal to the predetermined time.

19. The method according to claim 13, wherein, when the control frequency increases and the motor current exceeds an acceleration current threshold, the variable speed drive blocks the increase in the control frequency.

20. The method according to claim 13, wherein, when the variable speed drive is in steady-state operation and the motor current exceeds an operating current threshold, the variable speed drive reduces the control frequency.

21. The method according to claim 13, wherein, when the difference between the first input parameter and the output parameter is equal to or exceeds 90% of the first input parameter for a predetermined time greater than one minute, an alert or an alarm is triggered.

22. A pumping device, comprising: at least one rough-vacuum pump including: a motor for driving the rough-vacuum pump, and a variable speed drive configured to control the rotation speed of the motor, and configured to receive a first input parameter corresponding to a set point frequency and a second input parameter corresponding to a motor current and configured to deliver to the motor an output parameter corresponding to a control frequency; and a surveillance unit configured for surveillance of an operating state of a pumping device in accordance with the method according to claim 13.

23. The pumping device according to claim 22, further comprising a Roots Blower mounted in series with and on an upstream side of the rough-vacuum pump.

24. An installation comprising: a process chamber connected by a pipe to an intake of the pumping device according to claim 22.

Description

[0033] Other advantages and features will become apparent on reading the following description of one particular but nonlimiting embodiment of the invention and from the appended drawings, in which:

[0034] FIG. 1 represents a diagrammatic view of an installation comprising a process chamber connected to a pumping device,

[0035] FIG. 2 shows a diagrammatic view of the pumping device from FIG. 1,

[0036] FIG. 3 shows a diagrammatic view of elements of a rough-vacuum pump of the pumping device from FIG. 2,

[0037] FIG. 4 shows a diagrammatic view of elements of the pumping device from FIG. 2,

[0038] FIG. 5 shows an example of a graph of the motor current as a function of time in corresponding relationship with the evolution with time of the control frequency of a variable speed drive of the pumping device during a starting phase and during steady-state operation, and

[0039] FIG. 6 is a graph showing an example of the evolution of the control frequency of the variable speed drive in steady-state operation with the occurrence of failure of the pumping device.

[0040] In these figures, identical elements bear the same reference numbers.

[0041] The following embodiments are examples. Although the description refers to one or more embodiments, this does not necessarily mean that each reference concerns the same embodiment or that the features apply only to only one embodiment. Single features of different embodiments may equally be combined or interchanged to provide other embodiments.

[0042] A rough-vacuum pump is defined as a positive displacement vacuum pump which with the aid of two rotors aspirates, transfers and then discharges the gas to be pumped at atmospheric pressure. The rotors are carried by two shafts driven in rotation by a motor of the rough-vacuum pump.

[0043] A Roots Blower is defined as a positive displacement vacuum pump which with the aid of Roots type rotors aspirates, transfers and then discharges the gas to be pumped. This vacuum pump is mounted on the upstream side of and in series with a rough-vacuum pump. The rotors are carried by two shafts driven in rotation by a motor of the Roots Blower.

[0044] By upstream is meant an element that is placed before another relative to the direction of flow of the gas. Acontrario, by downstream is meant an element placed after another relative to the direction or flow of the gas to be pumped, the upstream element being at a lower pressure than the downstream element.

[0045] The installation 1 represented in FIG. 1 includes a process chamber 2 connected by a pipe 3 to the intake 4 of a pumping device 5 for pumping gases coming from the chamber 2 in the flow direction represented by the arrows. This chamber 2 may be a chamber in which any treatment process takes place, for example deposition, etching, ion implantation or heat treatment processes used in the fabrication of microelectronic devices on silicon wafers or in flat screen or photovoltaic substrate fabrication processes.

[0046] The pumping device 5 includes at least one rough-vacuum pump 7 including a pump body inside which two rotors 10 can be driven in rotation by a drive motor M1 of the rough-vacuum pump 7 (FIGS. 2 and 3).

[0047] The rough-vacuum pump 7 is a multistage pump, that is to say includes a plurality of, at least three, for example five, pumping stages T1, T2, T3, T4, T5, mounted in series between an intake and a discharge of the rough-vacuum pump 7 and in which a gas to be pumped can flow.

[0048] Each pumping stage T1-T5 comprises a respective inlet and a respective outlet. The successive pumping stages T1-T5 are connected in series one after the other by respective interstage pipes connecting the outlet of the preceding pumping stage to the inlet of the following pumping stage. The inlet of the first pumping stage T1 communicates with the intake of the vacuum pump 7 and the outlet of the last pumping stage T5 communicates with the discharge 6 of the vacuum pump 2.

[0049] As can be seen better in FIG. 3, each pumping stage T1-T5 comprises at least two rotors 10 driven in rotation in a stator 8 of the pump body. The rotors 10 extend in the pumping stages T1-T5. The shafts of the rotors 10 are driven on the discharge stage T5 side by the motor M1 of the rough-vacuum pump 7 (FIG. 2).

[0050] The rotors 10 feature lobes with identical profiles. The rotors represented are of Roots type (8 or bean shape section). Of course, the invention applies equally to other dry type multistage rough-vacuum pump types, such as the Claw type or spiral type or screw type or in accordance with another principle similar to a positive displacement vacuum pump.

[0051] The rotors 10 are angularly offset and driven to turn synchronously in opposite directions in the central housing 9 of each stage T1-T5. During rotation, the gas aspirated from the inlet is trapped in the volume generated by the rotors 10 and the stator 8 and is then driven by the rotors 10 to the next stage (the direction of flow of the gases is illustrated by the arrows G in FIGS. 2 and 3).

[0052] The rough-vacuum pump 7 is termed dry because in operation the rotors 10 turn inside the stator 8 with no mechanical contact with the stator 8, which allows the total absence of oil in the pumping stages T1-T5.

[0053] The discharge pressure of the rough-vacuum pump 7 is atmospheric pressure.

[0054] The pumping device 5 may include a Roots Blower 11 mounted in series with and on the upstream side of the rough-vacuum pump 7, as can be seen in FIG. 2.

[0055] The Roots Blower 11 is, like the rough-vacuum pump 7, a positive displacement vacuum pump which, with the aid of Roots type rotors, aspirates, transfers and then discharges the gas to be pumped.

[0056] The Roots Blower 11 includes at least one pumping stage B1 in which two rotors are driven in rotation by a motor M2 of the Roots Blower 11. The rotation frequency of the motor M2 is for example set to between 30 Hz and 100 Hz, for example 55 Hz.

[0057] The Roots Blower 11 differs from the rough-vacuum pump 7 mainly in greater dimensions, greater clearance tolerances and the fact that the Roots Blower 11 does not discharge at atmospheric pressure but has to be used mounted in series on the upstream side of a rough-vacuum pump 7.

[0058] The rough-vacuum pump 7 further includes a variable speed drive 12 configured to control the rotation speed of the motor M1 of the rough-vacuum pump 7. The motor M1 is for example an asynchronous motor, for example having a motor power of the order of 5 kW.

[0059] The variable speed drive 12 is configured on the one hand to receive a first input parameter corresponding to a set point frequency C and a second input parameter corresponding to a motor current i and on the other hand to deliver to the motor M1 an output parameter corresponding to a control frequency F (FIG. 4).

[0060] The set point frequency C may be a parameter set by the user, for example by modification of an analogue input signal of the variable speed drive 12 or by means of a manual adjuster knob of the variable speed drive 12. The set point frequency C is for example between 30 Hz and 60 Hz inclusive, for example 60 Hz.

[0061] The motor current i is the current consumed by the motor M1. The motor current i increases if the load on the motor M1 increases and decreases if the load on the motor M1 decreases.

[0062] According to one embodiment, the variable speed drive 12 controls the control frequency F in an open loop, for example by pulse width modulation (PWM).

[0063] The inverter of the variable speed drive 12 controls the motor M1 using a stream of pulses that determines both the voltage and the frequency.

[0064] Open loop control does not use sensors to measure the rotation speed or the angular position of the shaft. This configuration without sensors is economical and relatively simple to implement.

[0065] On starting the rough-vacuum pump 7 (starting phase D, FIG. 5), the variable speed drive 12 is controlled so as to increase the control frequency F progressively during a rise time, for example in accordance with an increasing linear relation or in accordance with a succession of increasing linear relations that can be preprogrammed, until the set point frequency C is reached.

[0066] Then, once the set point frequency C has been reached, the variable speed drive 12 controls the control frequency F so that it is constant and equal to the set point frequency C (steady state operation H).

[0067] An acceleration current threshold S1 may be used to protect the variable speed drive 12 against current surges when the control frequency F increases. A current surge may occur for example if the rise time is too short in the starting phase D.

[0068] If the motor current i exceeds the acceleration current threshold S1 the variable speed drive 12 blocks the increase in the control frequency F until the motor current i decreases and passes again below the acceleration current threshold S1 (see for example the starting overload phases E1 in FIG. 5).

[0069] The acceleration current threshold S1 may be adjustable.

[0070] An operating current threshold S2 is provided to protect the variable speed drive 12 against current surges in steady state operation H where the variable speed drive 12 sets the control frequency F to the set point frequency C.

[0071] If the motor current i exceeds the operating current threshold S2 the variable speed drive 12 reduces the control frequency F until the motor current i decreases and passes again below the operating current threshold S2 (see for example the in-operation overload phases E2 in FIG. 5). This overload situation can arise for example at the time of establishing a vacuum in the process chamber 2 at atmospheric pressure.

[0072] If the value of the motor current i is below the operating current threshold S2 less a few percent the variable speed drive 12 again increases the control frequency F until the set point frequency C is reached.

[0073] The decrease and the increase of the control frequency F under the control of the variable speed drive 12 in steady state operation H may be linear. The operating current threshold 52 may be adjustable. It is for example less than the acceleration current threshold S1.

[0074] If the difference between the first input parameter corresponding to the set point frequency C and the output parameter corresponding to the control frequency F is equal to or exceeds 90% of the first input parameter over a long time period greater than one minute, an alert or an alarm is triggered. This may indicate for example binding of the rough-vacuum pump 7 in the starting phase D, the latter not succeeding in starting for example.

[0075] The pumping device 5 further includes a surveillance unit 13 configured for surveillance of an operating state of the pumping device 5 in accordance with a surveillance method described hereinafter.

[0076] The surveillance unit 13 includes one or more microcontrollers or computers with memories and programs adapted for surveillance of an operating state of the pumping device 5. The surveillance unit 13 may be that of the variable speed drive 12 or a remote unit connected to the variable speed drive 12.

[0077] The surveillance unit 13 monitors the control frequency F sent to the motor M1 by the variable speed drive 12 at least in steady state operation H, that is to say when the variable speed drive 12 is not in the starting phase D or in a stopped phase. In steady state operation, the set point frequency C is constant at least during a time period greater than or equal to a predetermined time T, for example three seconds.

[0078] An operating state necessitating maintenance intervention on the rough-vacuum pump 7 in steady state operation H is determined if the difference between the first input parameter corresponding to the set point frequency C and the output parameter corresponding to the control frequency F is equal to or exceeds 10% of the first input parameter for a predetermined time T greater than 3 seconds, for example greater than 10 seconds, the first input parameter being greater than the output parameter. In other words, the operating state necessitates intervention if CF0.1*C, that is to say if F0.9*C (FIG. 5).

[0079] For example, imminent failure of the rough-vacuum pump 7 is determined if the control frequency F sent by the variable speed drive 12 to the motor M1 is less than or equal to 54 Hz for the predetermined time T.

[0080] According to a more restrictive criterion, an operating state necessitating maintenance intervention on the rough-vacuum pump 7 is determined if in steady state operation H the difference between the first input parameter and the output parameter is equal to or exceeds 4% of the first input parameter for the predetermined time T. In other words, the operating state necessitates intervention if CF0.04*C, that is to say if F0.96*C, i.e. earlier than for F0.9*C.

[0081] For example, imminent failure of the rough-vacuum pump 7 is determined if the control frequency F sent by the variable speed drive 12 to the motor M1 is less than 57.6 Hz for the predetermined time T.

[0082] The predetermined time T may be measured by a timer relay or directly by the surveillance unit 13. The predetermined time T may be less than 30 seconds.

[0083] Accordingly, and as can be seen in the example from FIG. 6, it is seen that a drop in the control frequency F of more than 2.4 Hz for more than 13 seconds leads to failure of the rough-vacuum pump 7 in the few seconds that follow the end of the predetermined time T.

[0084] This detection of imminent failure of the pumping device 5 enables prediction of sudden stopping of the pumping device 5 within a time of the order of a few seconds, between 1 second and 2 minutes and here of the order of 10 to 20 seconds, which leaves time to isolate the pumping device 5 from the upstream process chamber 2 and possibly a turbomolecular vacuum pump and to shut off the feeding of the gases.

[0085] In the case of progressive clogging of the rough-vacuum pump 7 that the aim is to diagnose, the load of the rough-vacuum pump 7 fluctuates. In fact, the control frequency F decreases and increases alternately without falling below the alert or alarm threshold. The variable speed drive 12 can then compensate the frequency reductions caused by the current surges for a few seconds or a few minutes. The surveillance method therefore enables detection of this situation in order to enable the user to be able to take measures and to protect the process chamber 2 before the clogging becomes excessive.

[0086] The surveillance unit 13 may for example switch a logic output if imminent failure is determined or switch a relay connected in series with the alert and alarm relays of the rough-vacuum pump 7. These relays can be used to shut isolating valves arranged between the process chamber 2 and the pumping device 5 and/or to shut off the arrival of the gases in the process chamber 2.

[0087] The surveillance method therefore enables simple and robust identification of abnormal behaviour of the pumping device 5 on the one hand with no indication of the treatment process taking place in the process chamber 2 and on the other hand without being impacted by disturbances to or modifications of the treatment process.