Patent Description:
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 <NUM>, as illustrated in <FIG>, usually comprise a thermopile <NUM>, which is a plurality of thermocouples connected in series with the hot junctions <NUM>, i.e. the detecting junctions <NUM>, connected to an infrared absorbing material (absorber) <NUM>, such as a very thin membrane (or window) <NUM>. The small thermal mass of the absorber <NUM> means that it quickly responds to changes in surface temperature, TOB, of the object <NUM> that is being measured.

The cold junctions <NUM> of the thermopile <NUM> are usually located in an isothermal block <NUM> so that they are all at the same temperature, the reference temperature of the sensor, TREF, as measured by a thermistor <NUM> internal to the sensor.

When an object <NUM> to be measured is positioned in front of the sensor's IR absorbing surface <NUM>, the IR absorbing surface <NUM> will undergo either a net gain or net loss of heat in the form of thermal (infrared) radiation depending on whether the absorbing surface <NUM> is at a higher or lower temperature respectively than that of the object <NUM> being measured.

As the surface temperature (TOB) of the object <NUM> rises in comparison to the sensor <NUM>, the hot junction <NUM> will begin to absorb infrared radiation and become hotter than the reference temperature (TREF). This causes a voltage to be generated in the thermopile <NUM> corresponding to the temperature change of the surface of the object (TOB). The temperature, TOB, measured by the infrared sensor is compensated by the temperature TREF, measured by the internal thermistor <NUM>, 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 <NUM>.

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; 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 sensor's 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.

<CIT> describes a method of measuring the absorptivity or emissivity factor of a sample at ambient temperature in which a thermopile is maintained at a constant temperature substantially above ambient temperature and the sample is exposed to radiation exclusively from the thermopile.

<CIT> describes a turbomolecular pump in which a radiation temperature measuring apparatus has a radiation thermometer for measuring a temperature of a component of the pump.

<CIT> describes a coke oven using a pyrometer with a window cleanliness monitor.

<CIT> describes the use of a thermopile to measure the temperature of a rotor of an electrical machine.

According to one aspect of the present invention there is provided a method of testing the operational status of an infrared sensor system, the system comprising an infrared sensor comprising a thermopile having a plurality of thermocouples connected in series with hot junctions connected to an infrared sensor absorber window and a heater, located proximate to the infrared sensor, for heating the infrared sensor, 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; said method comprising the steps of directing the infrared sensor at the vacuum pump rotor surface, the vacuum pump rotor surface having an emissivity E; raising the temperature of the heater to heat the infrared sensor without significantly heating the vacuum pump rotor surface; measuring the voltage generated, VG, by heating the infrared sensor; comparing the voltage generated by the infrared sensor with an expected voltage, VE; and, if VG does not substantially equal VE, determining that the infrared system is not at ideal operational status due to contamination of the window or, if VG substantially equals VE, determining that the infrared system is at ideal operational status The infrared sensor system may be located in a turbomolecular pump.

The method may be initialised when the pump is at room temperature or the method may be initialised when the pump is at a steady state of operation.

The infrared sensor may be located integral with a motor connected to the vacuum pump rotor and which provides the heater, and the temperature of the heater may be raised by applying a DC current to at least one motor winding to raise the temperature of the motor without causing significant rotation of the motor.

According to a further aspect of the present invention there is provided a vacuum pump, in particular a turbomolecular pump, comprising a vacuum pump rotor and an infrared sensor system comprising an infrared sensor directed at a vacuum pump rotor surface, the infrared sensor comprising a thermopile having a plurality of thermocouples connected in series with hot junctions connected to an infrared sensor absorber window, a heater, located proximate to the infrared sensor, for heating the infrared sensor, and a controller arranged to test the operational status of an infrared sensor system by raising the temperature of the heater to heat the infrared sensor without significantly heating the vacuum pump rotor surface, measuring the voltage generated VG by the infrared sensor, comparing the voltage generated by the infrared sensor with an expected voltage VE, and, if VG does not substantially equal VE, determining that the infrared system is not at ideal operational status due to contamination of the window or, if VG substantially equals VE, determining that the infrared system is at ideal operational status.

The infrared sensor may be located proximate to the motor windings.

The motor windings may be encapsulated in a potting material and the infrared sensor may be mounted in said potting material. The heater may be provided by the motor.

The infrared sensor may be 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. Alternatively, the surface which the infrared sensor is directed at may be a carbon fibre reinforced sleeve.

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:.

Referring first to <FIG>, a schematic representation of an infrared sensor system <NUM>, according to the present invention, is illustrated.

The sensor system <NUM> comprises an infrared sensor <NUM> with substantially the same features as that of a standard infrared sensor <NUM>, as illustrated in <FIG> and described above. The sensor system <NUM> additionally comprises a heater <NUM>, located proximate to the sensor <NUM>, and a controller <NUM> connected to both the infrared sensor <NUM> and the heater device <NUM>.

The controller <NUM> is configured to operate the infrared sensor system <NUM> according to a method of the invention.

The heater <NUM> must be located proximate to the infrared sensor <NUM> such that when the controller <NUM> operates the heater <NUM>, the heater <NUM> heats the infrared sensor <NUM> without substantially heating a surface <NUM> of the object <NUM> at which the infrared system is directed. In the example illustrated in <FIG>, the surface <NUM> is that of a vacuum pump rotor, object <NUM>. The heater <NUM> of the sensor system <NUM> can be separate to, or integral with the infrared sensor <NUM>; it may be any suitable type of heater <NUM>, for example a resistive heater.

In operation, the infrared sensor system controller <NUM> is able to run an operational status check according to the first aspect, namely a method, of the invention as will now be described.

By this method, the operational status of the infrared sensor system <NUM> can be determined when the surface <NUM> of the vacuum pump rotor <NUM> 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 an inlet thereof. When the vacuum pump is in one of these two conditional states (off or at steady state), the net exchange of heat between the infrared sensor <NUM> and rotor surface <NUM> will be zero because they will each be at substantially the same temperature.

Then, when the heater <NUM> heats both hot <NUM> and cold <NUM> junctions/terminals of the infrared sensor thermopile <NUM> equally, and the infrared sensor absorber window <NUM> is clean and free from residue, there will be a net heat loss to the rotor surface <NUM> as it will now be at a lower temperature than the infrared sensor <NUM>. Thus, a negative voltage VG will be generated in the thermopile <NUM> which will match the expected voltage generated VE. Thus the controller <NUM> will indicate that the operational status of the infrared system <NUM> is ideal.

By "ideal" we mean that the status of the sensor is such that it is considered to be functioning as expected and that no maintenance thereof is required at the present time.

However, if the sensor absorber window <NUM> is coated with grease or other debris the rate of heat loss from the window <NUM> will be lower than expected, due to the insulating effect of the debris and heat reflection back to the thermopile <NUM>. Thus the voltage generated VG will not substantially equal the expected voltage generated VE and the controller <NUM> will, thus, indicate that the operational status is not ideal and that the system <NUM> requires servicing.

The controller <NUM> may also be configured to operate the system <NUM> according to a further aspect to provide a method of measuring the initial emissivity, EI, of a surface, and comparing this with an expected emissivity EE.

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

However, if the surface <NUM> of the coated rotor <NUM> or a surface <NUM>' of the sleeve <NUM> becomes coated with grease during initial manufacturing of the pump the initial emissivity, EI, of the coated surface or sleeve will be lower than expected, EE, leading to inaccurate readings for the rest of the pump's operational life.

Therefore, by using the infrared sensor system <NUM>, it is possible to calibrate the initial emissivity EI of the surface <NUM>, <NUM>' after production, i.e. before use, so that accurate readings can be obtained thereafter. This second method comprises the steps of raising the temperature of the heater <NUM> to heat the infrared sensor <NUM> without significantly heating the surface <NUM>, <NUM>'; measuring the voltage generated, VG, by the infrared sensor <NUM> directed at the surface <NUM>, <NUM>'; comparing the voltage generated, VG, by the infrared sensor <NUM> with an expected voltage, VE; and calculating the initial <NUM>, EI according to the equation EI = EE(VG/VE).

If the emissivity of the surface <NUM>, <NUM>' is found to be as expected then the voltage generated VG during the test will substantially match that of the expected voltage generated VE. If, however, the emissivity of surface <NUM>, <NUM>' of the coated rotor <NUM> or the rotor sleeve <NUM> is not as good as expected, the amount of heat absorbed or reflected by the surface <NUM>, <NUM>' during the test will differ and the voltage generated VG will be proportionally different. Thus the initial emissivity EI of the coated surface <NUM> or the sleeve surface <NUM>' can be calculated. If the emissivity measurement is within a predetermined acceptable range, for example <NUM> to <NUM>, then the calculated initial emissivity EI is used by the controller <NUM> 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 <NUM> replaced or coating replenished.

Referring now to <FIG>, a cross section of a turbomolecular pump <NUM>, comprising a motor <NUM> according to a further aspect of the present invention, is illustrated. The pump <NUM> comprises a housing or casing <NUM> with an inlet <NUM> for receiving gas and an outlet <NUM> for exhausting the gas conveyed through the pump <NUM>, in use.

Within the casing <NUM> there is provided a rotor <NUM>, which comprises a number of radially outwardly extending rotor blade stages <NUM>. The casing <NUM> defines a stator component comprising a series of stator blade stages <NUM> extending radially inwardly and located between each of the rotor blade stages <NUM> in a manner well known to those skilled in the art of turbomolecular pump design. The rotor <NUM> also comprises, proximate to the outlet <NUM>, a series of molecular drag, or Holweck, stages <NUM> which lower the inlet pressure requirements of the pump backing the turbomolecular pump.

In this embodiment, the rotor <NUM> is supported for rotation at its uppermost and lowermost (as illustrated) ends with bearings <NUM> and <NUM> respectively. The lowermost bearings <NUM> comprise a ball type bearing arrangement and the uppermost bearings <NUM> 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 failure of the passive magnetic bearings <NUM>.

The rotor <NUM> is connected to a motor <NUM>. In the example shown the motor <NUM> is a synchronous two-pole, three-phase brushless <NUM> Volt DC motor contained in a stator <NUM>. The motor <NUM> comprises three sets of motor coil windings <NUM> that are evenly distributed around the motor stator <NUM>. The motor coil windings <NUM> are contained in a potting material, such as an epoxy resin with good thermal conductivity. A motor shaft <NUM> is connected to the rotor <NUM> for rotation thereof.

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

The motor <NUM> also comprises an integral infrared sensor system <NUM> comprising an infrared sensor <NUM>. The sensor is shown as being contained within the potting material of the coil winding <NUM>, but may also be located in and/or on the motor stator housing <NUM>. The infrared sensor <NUM> is, as described above, a noncontacting surface temperature measuring sensor comprising a thermopile <NUM> for measuring the surface temperature TOB of an object device <NUM> (in this example rotor <NUM>) by monitoring its infrared radiation emissions and a thermistor <NUM> for monitoring the temperature TREF of a casing <NUM> of the infrared sensor <NUM> for the purposes of temperature compensation.

In normal use, the infrared sensor <NUM> monitors the infrared radiation emitted from a target area <NUM>, on the rotor <NUM>, as shown in <FIG> (or <NUM> in <FIG>). 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 <NUM> is obtained. During normal use of the turbomolecular pump <NUM>, if the gas load being pumped or the backing pressure at the outlet <NUM> remains above the levels for which the pump is designed, the rotor temperature will rise. The infrared sensor <NUM> passes a signal to the controller <NUM> indicative of the object rotor temperature TOB 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 <NUM>, the target scanning area <NUM>, <NUM> on the rotor may have a high emissivity coating applied, such as described in <CIT>, or preferably a carbon fibre reinforced epoxy sleeve <NUM>. The target scanning area is ideally on the rotor shaft <NUM>, but it is also suitable to position the infrared sensor in the motor such that the object target surface <NUM> for the infrared sensor is a stator blade <NUM> or drag pump mechanism <NUM> (as illustrated in <FIG>).

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

The embodiments illustrated in <FIG> provide a further advantage over the infrared system <NUM> described above, by providing a motor <NUM> with an integral infrared sensor <NUM>, a device in which the operational status of the sensor <NUM> can be checked and tested is provided. In these examples, it is the motor <NUM> which acts as the heater device <NUM> and the method comprises the steps of applying a direct current to at least one motor winding to raise the temperature of the motor without causing significant rotation of the motor. Thus the infrared sensor <NUM> may be heated without significantly heating the object surface <NUM>. The voltage generated VG by the infrared sensor <NUM> directed at the surface may then be measured and compared with an expected generated voltage VE.

The operational status of the sensor <NUM> inside the pump <NUM> is preferably tested/initialised while the pump <NUM> is at room temperature. The pump controller <NUM>, or an operative, first passes a direct current through at least one of the motor coil windings <NUM>, preferably at a higher current than the usual operating current of the coil windings <NUM>, until a predetermined temperature rise is measured by the sensor's internal thermistor <NUM>. Passing a current through at least one of the motor coil windings <NUM>, or any number of them simultaneously means that the pump windings themselves heat up but the rotor <NUM>, 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 <NUM>. Without the commutation signal the pump <NUM> is unable to rotate at full speed and thus no, or little, heat is generated in the rotor <NUM> due to gas compression.

By heating the motor <NUM> to a predetermined temperature, the sensor <NUM> and controller <NUM> should detect a difference between the motor <NUM> and sensor <NUM> internal reference temperature TREF and the object rotor <NUM> 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 <NUM> has been coated such that its emissivity has been altered then the sensor <NUM> will not be able to measure the rotor surface temperature accurately so the voltages VG generated (i.e. the temperature difference measured) will differ from the expected generated voltage VE.

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

For example, in tests, passing a current of <NUM> Amps through two motor windings coils provides a temperature rise from <NUM> to <NUM> in <NUM> minutes. If the temperature rise measured is not as expected, for example the above described temperature rise of at least <NUM> , the operator, or controller <NUM> will determine that the infrared sensor <NUM>, or emissivity of the surface <NUM> are providing an non-ideal reading, and generate an alarm signal to service the pump.

During production, when it is known that the sensor is operating correctly, an unexpected rise in object temperature TOB can be attributed to a lower than expected emissivity from the target surface <NUM>, <NUM>. In this instance, the unexpected rise allows the true emissivity of the rotor surface to be calculated, affecting calibration of the IR sensor system <NUM> once the pump <NUM> is fully assembled.

Claim 1:
A method of testing the operational status of an infrared sensor system (<NUM>), the system comprising an infrared sensor (<NUM>) comprising a thermopile having a plurality of thermocouples connected in series with hot junctions connected to an infrared sensor absorber window (<NUM>), and a heater (<NUM>), located proximate to the infrared sensor (<NUM>), for heating the infrared sensor (<NUM>), wherein said infrared sensor system (<NUM>) is located in a vacuum pump and directed to measure the thermal radiation emitted from a vacuum pump rotor surface (<NUM>, <NUM>'); said method comprising the steps of:
i. directing the infrared sensor (<NUM>) at the vacuum pump rotor surface (<NUM>, <NUM>'), the vacuum pump rotor surface (<NUM>, <NUM>') having an emissivity E;
ii. raising the temperature of the heater (<NUM>) to heat the infrared sensor (<NUM>) without significantly heating the vacuum pump rotor surface (<NUM>, <NUM>');
iii. measuring the voltage generated, VG, by heating the infrared sensor (<NUM>); and
iv. comparing the voltage generated by the infrared sensor (<NUM>) with an expected voltage, VE, and
v. if VG does not substantially equal VE, determining that the infrared system (<NUM>) requires servicing due to contamination of the window (<NUM>) or, if VG substantially equals VE, determining that the infrared sensor system (<NUM>) is at ideal operational status.