FR2812041A1 - Cooling of a vacuum pump used in the semiconductor industry, uses proximity sensor to control the cooling of the stator in maintain the optimum play between stator and rotor - Google Patents

Abstract

The pump includes a proximity sensor (16) disposed in the stator (1) and adapted to detect the play (E) at the neighborhood of a control zone (17) between the stator and the rotor (4). The control zone is in or at the neighborhood of the critical zone (117) where the contact is most probable between the rotor and the stator during one evolution of temperature of the rotor and/or the stator. The signal produced by the sensor is used for controlling the cooling circuit of the stator, in order to maintain the play at a value greater to the minimum admissible value.

Description

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  VACUUM PUMP COOLING PRINCIPLE

  The present invention relates to dry vacuum pumps intended for producing a high vacuum, for use in particular in the semiconductor industry for lowering the

  pressure in the process chambers from the atmosphere.

  These dry vacuum pumps include at least one mobile rotor rotating in a stator with an appropriate clearance between the

rotor and stator.

  The temperature of the body of a vacuum pump must be controlled, on the one hand to avoid seizures due to thermal expansion, on the other hand to maintain the gases pumped at appropriate temperatures avoiding their transformation into the form of

solid deposit in the pump.

  Cooling of dry vacuum pumps is often achieved by forced convection with air or water as the coolant. The coolant flows through the stator of the vacuum pump, while the rotor is cooled by thermal conduction from the rotor to the stator. As a result, the rotor is generally warmer than the stator, and the temperature variations of the stator differ from those of the rotor.

  during discontinuous operations of the vacuum pump.

  In this respect, it should be noted that the operation of the vacuum pump is generally not constant, and that it must follow the necessary variations in the atmosphere in the process chambers to carry out the various stages of a process.

  semiconductor processing company.

  This results in temperature differences, varying in the

time, between the rotor and the stator.

  Up to now, the temperature of vacuum pumps has been controlled by housing, in the rotor, one or more temperature sensors, the signals of which are used to control the operation of the cooling system, and in particular the flow

coolant.

  However, such a control method is not entirely satisfactory, because of its insufficient precision, and because of the delays likely to occur between the heating of the rotor and the subsequent heating of the zone close to the

temperature sensors.

  This relative imprecision, and these delays, make it necessary to keep a relatively large clearance between the rotor and the stator of the vacuum pumps, clearance likely to affect the performance of

the vacuum pump.

  The problem proposed by the present invention is to design a new structure making it possible to appreciate more quickly and more precisely the temperature differences between the rotor and the stator of a vacuum pump, in order to maintain more precisely and permanently the clearance between the rotor and the stator

  within a predetermined authorized variation range.

  Consequently, according to the invention, it is possible to reduce the permanent play between the rotor and the stator of a vacuum pump, without risking damage by contact between the rotor and

  the stator during operation.

  Thus, the invention aims to effectively and permanently prevent the clearance between the rotor and the stator from becoming

  less than a minimum necessary.

  Also, the invention aims to reduce the production cost of vacuum pumps, by minimizing the number of sensors necessary to ensure satisfactory temperature regulation.

of the pump.

  Also, the invention aims to reduce defects and rejects in the mass production of vacuum pumps, and

  simultaneously increase the reliability of the vacuum pump.

  To achieve these and other objects, a dry vacuum pump according to the invention comprises at least one rotor mobile in rotation in a stator with an appropriate clearance between the rotor and the stator; at least one proximity sensor is disposed in the stator and is adapted to detect the play in the vicinity of a control zone between the stator and the rotor; the control zone is in or near the critical zone where contact is most likely between the rotor and the stator during an evolution of

  rotor and / or stator temperature.

  It will be noted that this structure makes it possible to adapt the temperature of the stator to that of the rotor, both in steady state and during the transient stages of operation, by ensuring the fastest possible cooling of the stator and therefore of the rotor, but simultaneously without risking that cooling the

rotor becomes too fast.

  It will be noted in particular that too rapid cooling of the stator, in the presence of significant heating of the rotor, would be liable to excessively reduce the clearance between the rotor and the stator, and to lead to contact between the rotor and the stator

  and destruction of the vacuum pump.

  The invention more effectively ensures the absence of contact between the rotor and the stator under all conditions of

vacuum pump operation.

  According to an advantageous embodiment: - the vacuum pump comprises an elongated rotor, having a length greater than its diameter, the proximity sensor is arranged to sense the axial play between a portion of the first axial end of the rotor and the portion corresponding stator, - the rotor is held in the stator by a first bearing at the first end and by a second bearing at the second end, the first bearing ensuring radial retention of the rotor by allowing its axial displacement, the second bearing ensuring radial maintenance

  and a simultaneous axial holding of the rotor in the stator.

  In this case, the first end of the vacuum pump is advantageously located on the suction side of the vacuum pump, and the proximity sensor is arranged in the lower part

stator pressure.

  In practice, the axial clearance between the rotor and the stator in operating conditions can be approximately 0.05 mm, and the proximity sensor is adapted to detect variations in said clearance.

axial of about 0.05 mm.

  According to a first application, the invention applies to a multi-stage pump with two parallel rotors, for example a roots pump, with a proximity sensor facing the end

of one of the two rotors.

  According to another application, the invention can also be applied to a screw pump, with a proximity sensor in the radial position facing the top of the screw thread of one of the rotors. In all cases, the pump can advantageously be associated with a stator cooling device, controlled by the

  image signal of the game provided by the proximity sensor.

  The control consists in varying the cooling capacity of the stator cooling device, under the following conditions: the stator cooling device is inhibited or slowed down when the game image signal is less than a first predetermined threshold, and it is activated when the game image signal is higher than said first threshold

predetermined.

  In an improved embodiment: - the stator cooling device can take a first inhibition state, a second intermediate cooling state, and a third rapid cooling state, - the stator cooling device is in its first state inhibition when the game image signal is less than a first predetermined threshold, - the stator cooling device is in its second intermediate cooling state when the game image signal is between said first predetermined threshold and a second predetermined threshold higher than said first predetermined threshold, - the stator cooling device is in its third state of rapid cooling when the game image signal is

  higher than said second predetermined threshold.

  In practice, it is advantageously possible to provide that the proximity sensor is connected to an input of a control circuit ensuring the comparison of the image signal of the game with the predetermined threshold or thresholds and generating a control signal of a valve for adjusting the flow of coolant in a

  stator cooling system.

  To improve security, it is possible to provide that the control circuit compares the image signal of the game with a third stop threshold lower than said first threshold, and generates a stop signal sent to a power supply circuit of a motor d driving the vacuum pump when the game image signal is lower than said third stop threshold to reduce or interrupt the speed of

rotation of said motor.

  Other objects, characteristics and advantages of the

  present invention will emerge from the following description of modes

  of particular embodiments, made in relation to the attached figures, among which: - Figure 1 is a schematic view in cutaway of a known structure of roots type vacuum pump; - Figure 2 is a cross section of the roots pump of Figure 1; - Figure 3 is a schematic longitudinal section of a roots pump according to the invention, associated with a drive motor of said pump; - Figure 4 is a schematic perspective view of a screw pump according to an embodiment of the invention; and - Figure 5 is a schematic view of a pump according to the present

  invention associated with a controlled cooling system.

  In the embodiments illustrated in the figures, a vacuum pump 100 comprises a vacuum pump body or stator 1, in which one or more pumping chambers 2 or 3 are produced receiving a rotor 4 or 5 driven by a shaft such that

trees 6 and 7.

  The stator 1 comprises a suction inlet 8 and a

discharge outlet 9.

  Figures 1 to 3 illustrate a roots type vacuum pump, with two cooperating parallel rotors 4 and 5, and with several successive stages distributed along the rotor between the suction stage 10 and the discharge stage 11. S acting as a vacuum pump, the suction stage 10 is the low pressure stage,

  while the discharge stage 11 is the high pressure stage.

  As seen in particular in Figure 3, the vacuum pump 100 comprises an elongated rotor 4, having a length L significantly greater than its diameter D. The rotor 4 is held in the stator 1 by a first bearing 12 of first end 13 and by a second bearing 14 of second end 15. The first bearing 12 ensures a radial retention of the rotor 4, opposing the radial movements of the rotor 4 around its axis of rotation II, but allowing the axial displacement of the first end 13 of the rotor 4. On the other hand, the second bearing 14 provides both radial and axial support for the

second end 15 of rotor 4.

  In the advantageous embodiment illustrated in FIG. 3, the first end 13 of the rotor 4 of the vacuum pump 100 is located on the side of the suction stage 10 of the vacuum pump.

empty 100.

  According to the invention, the dry vacuum pump 100 comprises at least one proximity sensor 16, disposed in the stator 1 and adapted to detect the clearance E in the vicinity of a control zone 17 between the stator 1 and the rotor 4. The control zone 17 is chosen in or near the critical zone 117 where contact is most likely between the rotor 4 and the stator 1 during a

  temperature evolution of rotor 4 and / or stator 1.

  In practice, the critical zone 117 is constituted by the upstream radial faces 18a and downstream 18b of the rotor 4 in the suction stage 10, in correspondence with the radial upstream faces 19a and downstream 19b of the stator 1 in this same suction stage 10. It is understood that this critical zone 117 is the most sensitive zone of the vacuum pump 100 during relative temperature variations between the rotor 4 and the stator 1: in the case of a lack of cooling of the stator 1, that -this elongates more than the rotor 4, inducing a maximum relative displacement in the suction stage 10, so that the downstream radial face 18b of the rotor 4 can come into contact with the downstream radial face 19b of the stator 1. Similarly, in the event of too intensive cooling of the stator 1, the upstream radial face 18a of the rotor 4 can come into contact with the face

upstream radial 19a of stator 1.

  It is understood that the proximity sensor 16 does not need to be placed exactly in the critical zone 117, but that it can advantageously be placed in the vicinity of this critical zone 117 in a control zone 17 which is for example, as illustrated in FIG. 3, in stator 1 opposite the first

end 13 of rotor 4.

  The first end 13 of the rotor 4 can for example be constituted by an end assembly piece 20 of the rotor 4, retained by an axial screw 21. Thus, the proximity sensor 16 is arranged to sense the axial play E between a upstream radial portion or face 18a of the first end 13 of the rotor 4 and a corresponding upstream radial portion or face 19a of the stator 1, by the fact that it captures the equivalent clearance between itself and the first

end 13 of rotor 4.

  As can be seen in FIG. 3, the rotor 4 of the vacuum pump is coupled to the shaft 22 of a motor 23 from which the

  motor stator 24 and motor rotor 25.

  It can be seen that the proximity sensor 16 is arranged in the

low pressure part of the stator 1.

  In general, according to the invention, an axial clearance E can be provided, the value of which in operating mode is approximately 0.05 mm. Note that the cold clearance can be greater, for example of the order of 0.20 mm. The proximity sensor 16 must be chosen from the types of sensor suitable for detecting variations in such an axial clearance. A proximity sensor 16 of magnetic type, of capacitive type, of optical type, or any other type of sensor can be used within the reach of those skilled in the art. In the embodiment illustrated in Figure 4, the vacuum pump comprises a rotor 104 in the form of a screw, journalled

  in a stator 101 around the axis of rotation I-I.

  The rotation of the rotor 104 drives the gases from a suction inlet 8 to the discharge outlet 9. In this case, the proximity sensor 16 is placed in the radial position in

  look at the top of the thread of the screw forming the rotor 104.

  We will now refer to FIG. 5, schematically illustrating the vacuum pump 100, associated with its motor 23

  drive and a stator cooling device.

  The motor 23 is supplied by a frequency converter 26 which, from a power supply 27, produces at the input terminals 28 of the motor 23 a variable frequency control voltage determining the speed of rotation of the motor 23. The variable speed drive frequency 26 is controlled by a control signal which it receives on a line 29 coming from a control circuit 30. The control circuit 30 comprises an input 31 connected by a line 32 to the proximity sensor 16 from which it receives the image signal of game E (figure 3). The control circuit 30 controls a valve 33 controlling the circulation of a cooling fluid passing through a cooling circuit 34, a portion 35 of which crosses part of the stator of the vacuum pump 100. For this, the control circuit 30 generates on an output 36 connected to the control input 37 of the valve 33 a valve control signal for regulating the flow of coolant in the circuit

stator cooling 34.

  The control circuit 30, receiving the image signal of the set E on its input 31 coming from the proximity sensor 16, ensures the comparison of this image signal of the set E with one or more predetermined thresholds to generate the control signal

  valve available on its output 36 and sent to valve 33.

  In a first embodiment, by a command to close the valve 33, the stator cooling device is inhibited or slowed down when the image signal of the clearance E is less than a first predetermined threshold recorded in the control circuit 30, and by opening valve 33, the stator cooling device is activated when the image signal of the clearance E is greater than said first threshold

predetermined.

  According to an improved embodiment, the control device 30 is programmed so that: - the stator cooling device can take a first inhibition state in which the valve 33 is closed, a second intermediate cooling state in which the valve 33 is partially open, and a third rapid cooling state in which valve 33 is fully open, the stator cooling device is in its first inhibition state when the image signal of the clearance E is less than a first predetermined threshold , the control circuit 30 then sending the valve 33 a complete or almost complete closing order, - the stator cooling device is in its second intermediate cooling state when the image signal of the clearance E is between said first predetermined threshold and a second predetermined threshold higher than said first threshold, the control circuit 30 sending then at valve 33 a partial opening order, - the stator cooling device is in its third state of rapid cooling when the image signal of the clearance E is greater than said second predetermined threshold, the control circuit

  then sending the valve 33 a complete opening signal.

  According to an improved embodiment, it is provided that the control circuit 30 can also act on the frequency converter 26 to control the speed of rotation of the motor 23 driving the vacuum pump 100. In this case, as illustrated in FIG. 5, the control circuit 30 compares the image signal of the set E also to a third stop threshold lower than said first threshold, and generates a stop signal sent by line 29 to the frequency converter 26 constituting the circuit d supply of the motor 23 driving the vacuum pump 100, in order to reduce or interrupt the speed of rotation of said motor 23 when the

  image signal of the game E is less than said third stop threshold.

  The latter provision constitutes an emergency stop system in the event that the slave cooling device is not sufficient to maintain the clearance E within acceptable limits

Operating.

  The present invention is not limited to the embodiments which have been explicitly described, but it includes the various variants and generalizations which are within the scope of

the skilled person.

Claims (7)

CLAIMS i - Dry vacuum pump, comprising at least one rotor (4) movable in rotation in a stator (1) with a suitable clearance (E) between the rotor (4) and the stator (1), characterized in that: - at least one proximity sensor (16) is arranged in the stator (1) and is adapted to detect the clearance (E) in the vicinity of a control zone (17) between the stator (1) and the rotor (4 ), - the control zone (17) is in or near the critical zone where contact is most likely between the rotor (4) and the stator (1) when the temperature of the rotor (4) changes and / or the stator (1).   2 - Vacuum pump according to claim 1, characterized in that: - the vacuum pump (100) comprises a rotor (4) of elongated shape, having a length (L) greater than its diameter (D), - the sensor proximity (16) is arranged to capture the axial clearance (E) between a portion (18a) of first axial end (13) of the rotor (4) and the corresponding portion (19a) of the stator (1), - the rotor ( 4) is held in the stator (1) by a first bearing (12) at the first end (13) and by a second bearing (14) at the second end (15), the first bearing (12) ensuring radial retention of the rotor (4) authorizing its axial displacement, the second bearing (14) ensuring radial support and axial support   rotor (4) in the stator (1).   3 - Vacuum pump according to claim 2, characterized in that the first end (13) of the vacuum pump is located on the side of the suction stage (10) of the vacuum pump (100), and the sensor proximity (16) is arranged in the low pressure part (10) of the stator (1).   4 - Vacuum pump according to one of claims 2 or 3,   characterized in that the axial clearance (E) in operating mode is approximately 0.05 mm, and the proximity sensor (16) is adapted   for detecting variations in said axial clearance (E).   - Vacuum pump according to any one of the claims   1 to 4, characterized in that it forms a multi-roots pump   stepped with two parallel rotors (4, 5), with a sensor of 1! proximity (16) opposite the end of one of the two rotors (4). 6 - Vacuum pump according to claim 1, characterized in that it forms a screw pump (101, 104), with a proximity sensor (16) in the radial position opposite the top of the thread. screw of one of the rotors (104).   7 - vacuum pump according to any one of claims   1 to 6, characterized in that it comprises a stator cooling device (32, 33, 34) controlled by the image signal of the   clearance (E) provided by the proximity sensor (16).   8 - Vacuum pump according to claim 7, characterized in that the stator cooling device (32, 33, 34) is inhibited or slowed down when the game image signal (E) is less than a first predetermined threshold, and is activated when the signal   image of the game (E) is greater than said first predetermined threshold.   9 - Vacuum pump according to claim 7, characterized in that: - the stator cooling device (32, 33, 34) can take a first state of inhibition, a second state of intermediate cooling, and a third state of rapid cooling, - the stator cooling device (32, 33, 34) is in its first inhibition state when the game image signal (E) is less than a first predetermined threshold, - the stator cooling device ( 32, 33, 34) is in its second intermediate cooling state when the game image signal (E) is between said first predetermined threshold and a second predetermined threshold higher than said first predetermined threshold, - the stator cooling device (32 , 33, 34) is in its third state of rapid cooling when the signal   image of the game (E) is greater than said second predetermined threshold.   - Vacuum pump according to one of claims 8 or 9,   characterized in that the proximity sensor (16) is connected to an input (31) of a control circuit (30) ensuring the comparison of the image signal of the game (E) with the predetermined threshold or thresholds and generating a signal control of a valve (33) to regulate the flow of coolant in a circuit stator cooling (34).   11 - Vacuum pump according to claim 10, characterized in that the control circuit (30) compares the image signal of the game (E) to a third stop threshold lower than said first threshold, and generates a stop signal sent to a supply circuit (26) of a motor (23) driving the vacuum pump (100) when the play image signal (E) is lower than said third stop threshold to reduce or interrupt the speed of rotation of said motor (23).