GB2553374A

GB2553374A - Temperature sensor for a high speed rotating machine

Info

Publication number: GB2553374A
Application number: GB1615124.3A
Authority: GB
Inventors: Haslett Brent; Grantham Andrew; Alexander Haylock James
Original assignee: Edwards Ltd
Current assignee: Edwards Ltd
Priority date: 2016-09-06
Filing date: 2016-09-06
Publication date: 2018-03-07
Anticipated expiration: 2036-09-06
Also published as: CN109642826B; SG11201901869SA; GB201615124D0; TW201816371A; EP3510369A1; KR20190044074A; JP2019529949A; GB2553374B; US20190226914A1; US10837836B2; TWI766879B; WO2018046913A1; KR102464713B1; CN109642826A; JP7273712B2

Abstract

An infrared temperature sensor system measures the emissivity of a surface, such as a rotor 101. An IR sensor 2 is positioned near or integral to a heating means, such as a heater (14, fig 2) or a motor 26. The IR sensor 2 is directed at the surface of an object such as a rotor shaft 100 and the temperature of the sensor 2 is raised by the heating means 26 without significantly heating the object surface 101. The voltage generated by the sensor 2 is compared with an expected voltage and determines whether the IR system is working at ideal operational status. This measurement can also enable calculating the emissivity of the surface 101 depending on an expected emissivity and the ratio of expected and generated voltages. The system is intended for use in a turbo-molecular vacuum pump rotor 100 to monitor potential thermal expansion of rotor blades 9 and therefore prevent failure.

Description

(54) Title of the Invention: Temperature sensor for a high speed rotating machine

Abstract Title: Infrared temperature sensor system for measuring the emissivity of a surface such as a rotating machine rotor (57) An infrared temperature sensor system measures the emissivity of a surface, such as a rotor 101. An IR sensor 2 is positioned near or integral to a heating means, such as a heater (14, fig 2) or a motor 26. The IR sensor 2 is directed at the surface of an object such as a rotor shaft 100 and the temperature of the sensor 2 is raised by the heating means 26 without significantly heating the object surface 101. The voltage generated by the sensor 2 is compared with an expected voltage and determines whether the IR system is working at ideal operational status. This measurement can also enable calculating the emissivity of the surface 101 depending on an expected emissivity and the ratio of expected and generated voltages. The system is intended for use in a turbo-molecular vacuum pump rotor 100 to monitor potential thermal expansion of rotor blades 9 and therefore prevent failure.

Figure 3

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Tob

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TEMPERATURE SENSOR FOR A HIGH SPEED ROTATING MACHINE

FIELD OF THE INVENTION

The present invention relates to an infrared sensor system configured to measure the temperature of a rotating machine rotor, in particular a high speed rotating machine rotor such as a turbomolecular vacuum pump rotor and a motor comprising the infrared sensor system. The invention also relates to a method of testing the operational efficacy of an infrared sensor system; and a controller configured to operate said method. The invention further relates to a method of calibrating the emissivity of a surface to be monitored by an infrared sensor, and a controller configured to operate said method.

BACKGROUND

Many rotating machines utilize infrared sensors to detect the temperature of thermally sensitive moving parts. Contacting sensors are difficult to position against the moving parts and so a contactless sensor, such as an infrared sensor is an ideal solution.

Known infrared sensors 2, as illustrated in Figure 1, usually comprise a thermopile 4, which is a plurality of thermocouples connected in series with the hot junctions 6, i.e. the detecting junctions 6, connected to an infrared absorbing material (absorber) 8, such as a very thin membrane 8. The small thermal mass of the absorber 8 means that it quickly responds to changes in temperature, Tob, of the object 101 that it is measuring.

The cold junctions 10 of the thermopile 4 are usually located in an isothermal block 12 so that they are all at the same temperature (the reference temperature, Tref).

-2When an object to be measured 101 is in front of the sensors’ IR absorbing surface 8, the IR absorbing surface 8 wili undergo either a net gain or loss of heat in the form of thermal (infrared) radiation depending on whether it is at a higher or lower temperature than the object being measured respectively.

As the surface temperature (Tob) of the object 101 rises in comparison to the sensor 2, the hot junction 6 will begin to absorb infrared radiation and become hotter than the reference temperature (Tref). This causes a voltage to be generated in the thermopile in proportion to the temperature of the surface of the object (Tob). The temperature Tob measured by the infrared sensor is compensated by an internal thermistor temperature Tref (not shown) and an accurate reading of the object surface temperature is obtained.

Turbomolecular pumps are used in many applications where high vacuum, i.e. low pressures, are required. For example, the semiconductor industry uses turbomolecular pumps for many processing steps in order to maintain the low pressures required to increase the yield of low defect devices.

In operation, turbomolecular pump rotors rotate at high rotational speeds. The tolerance, or distance, between the tip of the rotor blade and the inner wall of the pump casing must be as small as possible in order for the pump to achieve the required pumping performance. If the pump operates above a desired temperature the resulting expansion of the rotor blades can be such that a catastrophic failure can occur due to the rotor blades colliding with stationary parts of the internal mechanism, such as the stator blades. Therefore careful control and monitoring of the internal pump temperature is required. This is often achieved using an infrared temperature sensor.

Many processing steps utilized by the semiconductor industry produce corrosive and/or condensable by-products that are conveyed away from a processing chamber and through vacuum pump systems including turbomolecular pumps. These processes can coat, or corrode, any temperature sensors employed;

-3 or coat the surface of the rotor being monitored thereby modifying the surface emissivity, to the extent that it interferes with, in particular, an infrared sensors ability to provide accurate readings.

Thus the temperature sensor may fail to detect a dangerous temperature rise within the pump.

It is an object of the present invention to overcome, or at least reduce the effect of, these issues.

SUMMARY

In a first aspect, the present invention provides method of testing the operational status of an infrared sensor system comprising an infrared sensor; and a heater located proximate to the infrared sensor for heating the infrared sensor; said method comprising the steps of: directing the infrared sensor at the surface of object external to the infrared sensor with an emissivity E; raising the temperature of the heater to heat the infrared sensor without significantly heating the object surface; measuring the voltage generated Vg by the infrared sensor directed at the surface; and comparing the voltage generated by the infrared sensor with an expected generated voltage Ve.

In a second aspect the present invention provides an infrared sensor system for measuring the thermal radiation emitted from the surface of a rotor, comprising an infrared sensor and a heater, located proximate to the infrared sensor, for heating the infrared sensor.

Other preferred and/or optional aspects of the invention are defined in the accompanying claims.

-4BRIEF DESCRIPTION OF THE DRAWINGS

In order that the present invention may be well understood, embodiments thereof, which are given by way of example only, will now be described with reference to the accompanying drawings, in which:

Figure 1 is a schematic section of a known infrared sensor.

Figure 2 is a schematic section of an infrared sensor system according to a second aspect of the invention.

Figure 3 is a cross section of turbomolecular pump comprising an infrared sensor system according to a further aspect of the present invention.

Figure 4 is partial cross section of turbomolecular pump comprising an infrared sensor system according to a further aspect of the present invention

DESCRIPTION OF THE EMBODIMENTS

Referring first to Figure 2, a schematic section of an infrared sensor system 20 according to the present invention is illustrated.

The sensor system 20 comprises an infrared sensor 2 with substantially the same features as that of a standard infrared sensor 2, as illustrated in Figure 1, with the additional feature of a heater 14, located proximate to the sensor, and a controller 16 connected to both the infrared sensor and the heater device.

The controller 16 is configured to operate the infrared sensor system 20 according to the invention.

The heater 14 must be located proximate to, which includes integral with, the infrared sensor 2 such that when the controller 16 operates the heater 14 it heats the infrared sensor 2 without substantially heating the surface 101 at which the infrared system is directed. In the illustrated example in figure 2, the surface is that of a vacuum pump rotor 101. The heater 14 can be separate to, or integral

- 5 with the infrared sensor 2; it may be any suitable type of heater 14, for example a resistive heater.

In operation, the infrared sensor system controller 16 is able to run an operational status check according to the first aspect of the invention.

By this method the operational status of the infrared sensor system 20 can be determined when the vacuum pump rotor 101 is either at room temperature,

i.e. before the pump (not shown) has been started, or during a steady state operation, when for example the pump is running at operational speed and no gas is passing through the inlet.

When the vacuum pump is at steady state, such as when it is nonoperational and at room temperature, the net exchange of heat between the infrared sensor 2 and rotor surface 101 will be zero because they will be at substantially the same temperature.

Then, when the heater 14 heats both hot 6 and cold 10 terminals of the infrared sensor thermopile 4 equally, and the infrared sensor absorber window 8 is clean, there will be a net heat loss to the rotor surface 101 which will now be at a lower temperature than the infrared sensor 2. Thus a negative voltage Vg will still be generated in the thermopile which will match the expected voltage generated Ve. Thus the controller 16 will indicate that the operational status of the infrared system 20 is ideal.

However, if the sensor absorber window 8 is coated with grease or other debris the rate of heat loss from the window 8 will be lower than expected, due to the insulation from the debris and heat reflection back to the sensor. Thus the Voltage generated Vg will not substantially equal the expected voltage generated Ve and the controller 16 will indicate that the system 20 requires servicing.

-6The controller 16 is also configured to operate the system 20 according to a further aspect of the invention to provide a method of measuring the initial emissivity, Ei, of a surface, with an expected emissivity of, Ee.

It is particularly advantageous to apply a high emissivity coating to the surface of rotors 101 which are to have their temperatures measured by infrared sensors 2. High emissivity coatings ensure that an accurate temperature readings can be obtained as they ensure that no heat from the infrared sensor 2 is reflected away from the surface 101 and that all thermal radiation generated by the surface of the rotor 101 is directed to the infrared sensor. It has been found particularly advantageous to apply a carbon fiber reinforced epoxy sleeve to rotors, such as that of turbomolecular pumps to overcome issues with loss of coatings over time.

However, if the surface of the sleeve 101 becomes coated with grease during initial manufacturing of the pump the initial emissivity, Ei, of the sleeve will be lower than expected, Ee, leading to inaccurate readings for the rest of the pumps operation.

Therefore by using the infrared sensor system 20 it is possible to calibrate the initial emissivity of the surface after production, i.e. before use, so that accurate readings can be obtained. The method comprises the steps of raising the temperature of the heater 14 to heat the infrared sensor without significantly heating the surface 101; measuring the voltage generated, Vg, by the infrared sensor 2 directed at the surface 101; comparing the voltage generated, Vg, by the infrared sensor 2 with an expected voltage, Ve; and calculating the initial emissivity of the surface, Ei according to the equation Ei = Ee(Vg/Ve).

If the emissivity of the surface is as expected then the voltage generated Vg during the test will substantially match that of the expected voltage generated Ve. If however the surface of rotor sleeve 101 is not as expected, less heat will be absorbed by the surface 101 during the test and the voltage generated will be

-7proportionally different, thus giving the initial emissivity of the sleeve surface. If the emissivity measurement is within a predetermined acceptable range, for example 0.9 to 0.97, then the calculated initial emissivity Ei is used by the controller 16 to calibrate future temperature readings whilst the pump is operational. If the initial emissivity measured falls outside the predetermined acceptable range, the pump will need to be serviced and the sleeve replaced.

Referring now to Figures 3 and 4, a cross section of a turbomolecular pump 1 comprising a motor 26 according to a further aspect of the present invention is illustrated. The pump 1 comprises a housing 19 with, at an upper end thereof, an inlet 3 for receiving gas and, at a lower end thereof, an outlet 5 for exhausting the gas conveyed through the pump 1 in use. The rotor also comprises, proximate to the outlet 5, a series of molecular drag, or Holweck, stages 13 which lower the pressure requirements of the pump backing the turbomolecular pump.

Within the casing 19 there is provided a rotor 100, which comprises a number of radially outwardly extending rotor blade stages 9. The casing 19 defines a stator component comprising a series of stator blades stages 11 extending radially inwardly and located between each of the rotor blade stages 9 in a manner well known to those skilled in the art of turbomolecular pump design.

The rotor 100 is supported for rotation at its uppermost and lowermost ends with bearings 17 and 15 respectively. The lowermost bearings 15 comprise a ball type bearing arrangement and the uppermost bearings 17 comprise a passive magnetic bearing arrangement. The uppermost part of the rotor may also be protected by a set of ball type, thrust bearings (not shown) to prevent the rotor from colliding with the stationary parts of the pump in the event of a passive magnetic bearings 17 failure.

The rotor 100 is connected to a motor 26. In the example shown the motor is a synchronous two-pole, three-phase brushless 24 volt DC motor contained in a stator 28. The motor 26 comprises three sets of motor coil windings 44 that are

-8evenly distributed around the motor stator. The motor coil windings 44 are contained in a potting material, such as an epoxy resin with good thermal conductivity. A motor shaft is connected to the rotor 100 for rotation thereof.

In normal use, commutation of the motor rotor 100 is controlled using an external controller 16 which, depending on the location of the poles of the magnets, turns on each of the three motor windings 44 in sequence to rotate the motor shaft and thus the pump rotor 100.

The motor 26 also comprises an integral infrared sensor system 20 comprising an infrared sensor 2. The sensor is shown as being contained within the coil winding potting material 44, but may also be located in and/or on the motor stator housing 28. The infrared sensor 2 is, as described above, a non-contacting surface temperature measuring sensor comprising a thermopile for measuring the temperature Tob of an object device surface (in this example a rotor) by monitoring its infrared radiation emissions and a thermistor for monitoring the temperature Tref of the infrared sensor casing for the purposes of temperature compensation.

In normal use, the infrared sensor 2 monitors the infrared radiation emitted from a target area 101, on the rotor 100, as shown in Figure 3 (or 102 in Figure 4). The temperature Tob measured by the infrared sensor is compensated by an internal thermistor temperature Tref and an accurate reading of the temperature of the rotor surface 101 is obtained. During normal use of the turbomolecular pump 1, if the gas load being pumped or the backing pressure at the outlet 5 remains above the levels for which the pump is designed, the rotor temperature will rise. The infrared sensor 2 passes a signal to the controller 16 indicative of the object rotor temperature and, if above a predetermined temperature, an alarm is raised and/or the pump is slowed down to prevent damage or pump failure.

In order to improve the rotor temperature reading obtained by the infrared sensor the target scanning area 101, 102 on the rotor may have a high emissivity coating applied, such as described in US5350275, or preferably a carbon fiber

-9reinforced epoxy sleeve 101. The target scanning area is ideally on the rotor shaft, but it is also suitable to position the infrared sensor in the motor such that the object target surface 102 for the infrared sensor is a stator blade or drag pump mechanism.

Previously attempted locations for the infrared sensor have been within the pump casing 19, or embedded in the base portion of the pump as disclosed in EP 1348940. However, these sensors were affected by corrosion and/or process deposition thus unable to provide consistently reliable temperature measurements.

The embodiment illustrated in Figures 3 and 4 provides a further advantage over the infrared system 20 described above by providing a motor 26 with an integral infrared sensor 2 to provide a device in which the operational status of the sensor 2 can be checked and tested. In this example, it is the motor 26 which acts as the heater device 14 and the method comprises the steps applying a direct current to at least one motor winding to raise the temperature of the motor without causing significant rotation of the motor, to heat the infrared sensor without significantly heating the object surface; and then measuring the voltage generated Vg by the infrared sensor directed at the surface to compare with an expected generated voltage Ve.

The operational status of the sensor 2 inside the pump 1 is ideally tested while the pump 1 is at room temperature. The pump controller 16, or an operative, first passes a direct current through at least one of the motor coil windings 44, preferably at a higher current than the usual operating current of the coil windings 44, until a predetermined temperature rise is measured by the sensor’s thermistor. Passing a current through at least one of the motor coil windings 44, or any number of them simultaneously means that the pump windings themselves heat up but the rotor 100, without a commutation signal, does not rotate. Some minor rotation might initially occur, but it will be substantially lower than the rated rotational frequency of the pump 1. Without the commutation signal the pump is unable to rotate at full speed and thus no, or little, heat is generated in the rotor 100 due to gas compression.

- 10 By heating the motor 26 to a predetermined temperature, the sensor 2 and controller 16 should detect a difference between the motor 26 and sensor 2 temperature Tref and the object rotor 101 surface temperature Tob that would not normally be present at room temperature. If the sensor’s operational efficacy has not been affected by process by-products the Tref should be greater than Tob by a known value; that is, the voltage generated by the sensor Vg should not differ from the expected generated voltage Ve. If, however, the sensor is coated or has been corroded in any way, or the rotor surface 101 has been coated such that its emissivity has been altered then the sensor 2 will not be able to measure the rotor surface temperature accurately so the voltages Vg generated (i.e. the temperature difference measured) will not be as expected.

The predetermined temperature rise can be achieved by either passing the direct current through at least one of the motor windings, as described above, for a set period of time, or until the sensors thermistor detects that the predetermined temperature rise has been achieved.

For example, in tests, passing a current of 15 Amps through two motor windings coils provides a temperature rise from 25 °C to 35 °C in 3 minutes. If the temperature rise measured is not as expected, for example the above described temperature rise of at least 25 °C , the operator, or controller 16 will detect an issue with the infrared sensor 2, or emissivity of the surface 101, and generate an alarm signal to service the pump.

During production when it is known that the sensor is operating correctly, a rise in object temperature when one is not expected can be attributed to a lower than ideal emissivity from the IR target. In this instance, the unexpected rise will allow the true emissivity of the rotor surface to be calculated, effecting calibration of the IR system once the pump is fully assembled.

- 11 It is of course possible, according to another aspect of the invention to provide a turbomolecular pump 1 comprising the infrared system 20 comprising the infrared sensor 2 and proximate 16 heating device which can also be operated as described above.

Claims

1. A method of measuring the initial emissivity, Ei, of a surface, with an expected emissivity of ,Ee, using an infrared temperature sensor system comprising an infrared temperature sensor directed at the surface and a heater located proximate to the infrared sensor for heating the sensor, the method comprising the steps of:

i. raising the temperature of the heater to heat the infrared sensor without significantly heating the surface;

ii. measuring the voltage generated, Vg, by the infrared sensor directed at the surface;

iii. comparing the voltage generated by the infrared sensor with an expected voltage, Ve; and iv. calculating the initial emissivity of the surface, Ei according to the equation Ei = Ee(Vg/Ve)

2. A method of testing the operational status of an infrared sensor system comprising an infrared sensor; and a heater located proximate to the infrared sensor for heating the infrared sensor; said method comprising the steps of:

i. directing the infrared sensor at the surface of object external to the infrared sensor with an emissivity E;

ii. raising the temperature of the heater to heat the infrared sensor without significantly heating the object surface;

iii. measuring the voltage generated Vg by the infrared sensor directed at the surface; and iv. comparing the voltage generated by the infrared sensor with an expected voltage Ve.

3. A method of testing the operational status of an infrared sensor system comprising an infrared sensor; and a heater located proximate to the

- 13 infrared sensor for heating the infrared sensor according to Claim 2;

wherein said method comprises the additional step of:

v. if Vg does not substantially equal Ve determining that the infrared system is not at ideal operational status.

A method of testing the operational status of an infrared sensor system comprising an infrared sensor; and a heater located proximate to the infrared sensor for heating the infrared sensor according to Claim 2; wherein said method comprises the additional step of:

v. if Vg substantially equals Ve determining that the infrared system is at ideal operational status.

A method of testing the operational status of an infrared sensor system comprising an infrared sensor; and a heater located proximate to the infrared sensor for heating the infrared sensor according to Claims 2 to

4; wherein said infrared sensor system is located in a rotating machine and the infrared sensor is directed to measure the thermal radiation emitted from the rotating surface of the rotating machine.

A method of testing the operational status of an infrared sensor system comprising an infrared sensor; and a heater located proximate to the infrared sensor for heating the infrared sensor according to Claims 2 to 4; wherein said infrared sensor system is located in a vacuum pump and directed to measure the thermal radiation emitted from a vacuum pump rotor surface, in particular a turbomolecular pump rotor.

A method of testing the operational status of an infrared sensor system comprising an infrared sensor; and a heater located proximate to the infrared sensor for heating the infrared sensor according to Claim 6; wherein said method is initialised when the pump is at room temperature.

- 14 8. A method of testing the operational status of an infrared sensor system comprising an infrared sensor; and a heater located proximate to the infrared sensor for heating the infrared sensor according to Claim 6; wherein said method is initialised when the pump is at a steady state of operation.

9. A method of testing the operational status of an infrared sensor system, said system comprising an infrared sensor located either proximate to, or integral with, a motor; comprising the steps of:

ii. applying a DC current to at least one motor winding to raise the temperature of the motor without causing significant rotation of the motor, to heat the infrared sensor without significantly heating the object surface;

10. A method of testing the operational status of an infrared sensor system comprising an infrared sensor located either proximate to, or integral with, a motor according to Claim 5; wherein said method comprises the additional step of:

11. A method of testing the operational status of an infrared sensor system comprising an infrared sensor located either proximate to, or integral with, a motor according to Claim 5; wherein said method comprises the additional step of:

- 15 v. if Vg substantially equals Ve, determining that the infrared system is at ideal operational status.

12. A method of testing the operational status of an infrared sensor system

5 comprising an infrared sensor located either proximate to, or integral with, a motor according to Claims 9 to 11; wherein said infrared sensor system and motor are located in a rotating machine and the infrared sensor is directed to measure the thermal radiation emitted from the rotating surface of the rotating machine.

13. A method of testing the operational status of an infrared sensor system comprising an infrared sensor located either proximate to, or integral with, a motor according to Claims 9 to 12; wherein said infrared sensor system and motor are located in a vacuum pump and directed to measure the

15 thermal radiation emitted from a vacuum pump rotor surface, in particular a turbomolecular pump rotor.

14. A method of testing the operational status of an infrared sensor system comprising an infrared sensor located either proximate to, or integral with,

20 a motor according to Claim 13; wherein said method is initialised when the pump is at room temperature.

15. An infrared sensor system for measuring the thermal radiation emitted from the surface of a rotor, comprising an infrared sensor and a heater,

25 located proximate to the infrared sensor, for heating the infrared sensor.

16. An infrared sensor system according to Claim 15, wherein the heater is integral with the infrared sensor.

30 17. An infrared sensor system according to Claims 15 and 16, wherein the heater is a resistive heater.

- 16 18. A vacuum pump, in particular a turbomolecular pump, comprising the infrared system according to Claims 15 to 17 and positioned for measuring the thermal radiation emitted from the surface a rotor of said vacuum pump.

19. A turbomolecular pump, comprising the infrared system according to Claims 15 to 17 and positioned for measuring the thermal radiation emitted from a surface of at least one of a turbomolecular rotor blade, a turbomolecular stator blade, a rotor shaft and a molecular drag pump rotor.

20. A motor for rotating a rotor, comprising the infrared system of claim 15, wherein the infrared sensor is located proximate to the motor windings and positioned to measure the thermal radiation emitted by a surface of the rotor when in a device comprising said rotor.

21. A motor for rotating a rotor according to Claim 20, wherein the motor windings are encapsulated in a potting material and the infrared sensor is mounted in said potting material.

20 22. A turbomolecular vacuum pump, comprising the motor according to Claims

20 and 21, wherein the infrared sensor is directed to measure the thermal radiation emitted from the surface of at least one of a turbomolecular rotor blade, a turbomolecular stator blade, a rotor shaft and a molecular drag pump rotor.

23. A turbomolecular pump according to Claim 22, wherein the surface which the infrared sensor is directed at is a carbon fibre reinforced sleeve.

Intellectual

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Application No: GB1615124.3 Examiner: Eleanor Jones