This application is a Section 371 National Stage Application of International Application No. PCT/GB2013/052673, filed Oct. 14, 2013, which is incorporated by reference in its entirety and published as WO 2014/068277 A1 on May 8, 2014 and which claims priority of British Application No. 1219518.6, filed Oct. 30, 2012.
The invention relates to a vacuum pump.
The use of a turbomolecular pumping mechanism in a vacuum pump is known hereto. A turbomolecular pumping mechanism is typically used for generating high or ultra high vacuums having a pressure of between about 10−3 to 10−10 mbar. In order to generate such high vacuums, the rotor blades are rotated at high rotational speeds by a drive shaft for example between about 20,000 and 90,000 revolutions per minute. A turbomolecular pumping mechanism requires precision manufacturing techniques and close tolerances in order to achieve such high speeds and vacuums.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the background.
The present invention provides an improved vacuum pump.
The present invention provides a vacuum pump comprising a turbomolecular pumping mechanism and an orientation sensor for sensing an orientation of the vacuum pump.
The orientation sensor in a preferred example is an accelerometer, and in this case, the accelerometer may be additionally arranged to sense impacts imparted to the pump for determining a condition of the pump which is sensitive to such impacts.
Other preferred and/or optional aspects of the invention are defined in the accompanying claims.
The Summary is provided to introduce a selection of concepts in a simplified form that are further described in the Detail Description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
In order that the invention may be well understood, some embodiments thereof, which are given by way of example only, will now be described with reference to the accompanying drawings in which:
Referring to
A turbomolecular pumping mechanism is typically used for generating high or ultra high vacuums having a pressure of between about 10−3 to 10−8 mbar. In order to generate such high vacuums, the rotor blades are rotated at high rotational speeds by drive shaft 15 for example between about 20,000 and 90,000 revolutions per minute. The drive shaft 15 is supported for rotation at its lower end portion by lubricated bearings 18, 20 and at its upper end portion by a magnetic bearing (not shown). Bearings other than magnetic type bearings may replace the bearings at the upper end portion.
A motor (not shown) rotates the drive shaft 15. A motor drive 22 comprising an inverter and a variable power controller provides the necessary electrical signals for driving the motor. The drive 22 can be located adjacent or in contact with the pump housing 24 or located remotely and connected to the motor by a cable 26, as shown in broken lines.
A lubrication circuit, or supply, is established for supplying lubricant to relatively moving surfaces of the vacuum pump which in the example shown comprises at least the bearing 20 for supplying lubricant between relatively moving inner and outer races of the bearing to allow friction reduced rotation of the roller bearing members. The lubrication circuit is described in more detail below with reference to
Operation of the turbomolecular pumping mechanism 14 and efficient pumping of gas from an enclosure is dependent on the proper functioning of the lubrication supply and the lubrication supply is dependent upon on the orientation of the vacuum pump. Other operative characteristics of the vacuum pump such as the loading on, or forces associated with, for example the bearings, the pumping mechanism or the drive shaft are affected by the orientation of the pump. The effect of the orientation of the pump may reduce performance of the pump from the rated or optimum levels or in more severe circumstances may cause failure of the pump, whether quickly or over time.
Operation of the pump is dependent on its orientation, on the lubrication system and other operative characteristics as described above but also the performance of the pump is dependent on its orientation during storage or transportation particularly over sustained periods. For example, transportation or storage in an undesirable orientation may cause damage to the pump or otherwise deteriorate its performance when in use.
In the embodiment shown in
The orientation sensor is preferably one that senses gravitational force ‘g’ as shown in
Referring to
Referring to
The amount by which the pump is tilted towards the
Of course, other parts, components or functionality of the vacuum pump are affected by its orientation as discussed above. For example, the bearing 18 is configured for use in an upright orientation and use in the horizontal orientation causes a change in loading on the bearings which can reduce its lifetime before requiring maintenance or before failure.
Referring to
The performance of the pump and duration prior to failure is reduced the closer the orientation of the pump is towards inverted and therefore the sensor may be configured to sense an angle of orientation intermediate the horizontal orientation and the inverted orientation.
As discussed above in relation to the horizontal orientation, other parts, components or functionality of the vacuum pump are affected in an inverted orientation, in the same or different ways.
Referring to
The orientation of the pump during use affects short and long term pump performance. Additionally, storage or transportation of the pump in an impermissible orientation affects subsequent performance of the pump particularly if a pump is maintained in an impermissible orientation for sustained periods. It is normally the case that a pump is transported or stored without connection to electrical power and therefore if orientation during transportation or storage is to be determined the vacuum pump comprises an electrical power supply arranged for supplying power to the sensor. A suitable power supply would be a battery.
The orientation sensor is arranged to output a signal 46 indicative of the orientation of the vacuum pump for input to a control unit 48. The control unit 48 is responsive to the signal 46 and may be arranged for example to control operation of the vacuum pump dependent on the sensed orientation or compile data corresponding to the sensed orientation.
In
The drive 22 may also be configured for supplying data to the control unit 48 relating to operation of the pump. For example, operation in an impermissible orientation may reduce the period which the pump can be operated before maintenance is required. Therefore the drive may supply data relating to the speed of rotation of the pump over time for use by the control unit 48 for determining a next maintenance event.
The processing unit 50 can write to and read from a store or memory 52 for storing the sensed orientations of the pump. The sensed orientations which are stored may be associated with a duration in which the pump is orientated in each orientation according to an input from a timer unit 54. For example, if the pump is used in a horizontal orientation, the memory stores the orientation ‘horizontal’ for a period of 100 hours operation. This compilation of use can be used to determine maintenance periods for a customer or checking post sale use of a pump.
The processor unit 50 is arranged to read compiled data from the memory 52 for displaying information to a user on a display 56. Such information may include a warning regarding operation of a pump in an impermissible orientation or the hours of use remaining in any given orientation. The processor unit is also arranged to output data from the memory to a transceiver 58 for transmission to a remote location 60.
The remote location may be a pump supplier to enable the pump supplier to monitor in which orientation the pump is being operated. This information allows the supplier for example to time maintenance periods dependent on real time pump usage or to anticipate the occurrence of faults. The supplier can also transmit control signals to the transceiver for controlling operation of the vacuum pump drive 22 if for example the pump is being operated in an impermissible orientation.
The vacuum pump 10 described above comprises an orientation sensor for sensing orientation of the pump. The orientation of the pump can affect the operational lifetime of the pump prior to requiring maintenance. In addition to orientation, a vacuum pump may receive impacts which affect its operational lifetime. In one of the examples described above, the sensor 28 is an accelerometer. An accelerometer may be configured additionally to sense impacts imparted to a pump. Particularly, although not exclusively, a back-up bearing of a pump may be sensitive to impacts and require maintenance or replacement after a certain amount of use. The following description describes the use of an accelerometer in a turbomolecular pump for sensing use of a back-up bearing in addition to use of the accelerometer to determine pump orientation.
Referring to
A first bearing assembly 112 controls movement of the rotor and drive shaft in the direction R during rotation of the drive shaft about rotational axis A. Direction R is principally movement in the radial direction although it has a small element in the axial direction, since the drive shaft is angularly displaced about a lower bearing assembly 117 discussed in more detail below. In the embodiment shown the vacuum pumping mechanism is a turbomolecular pumping mechanism which is rotated at rotational speeds of between about 20,000 and 90,000 revolutions per minute, and in order to reduce friction between the first bearing assembly and the rotating parts of the pump, the first bearing assembly 112 is a non-contact bearing assembly which controls radial movement without contacting the rotor or the drive shaft. An example of a non-contact bearing is a magnetic bearing assembly in which opposite generally annular magnetic poles 113, 115 are located on the rotating part and the fixed part respectively. In this example, movement of the rotating magnetic pole on the drive shaft towards the fixed magnetic pole causes an increased magnetic force to be applied to the rotating magnetic pole in a radial direction of the drive shaft thereby bringing the drive shaft back into correct alignment. This arrangement is low friction and therefore suitable for such high speed pumps, but as the bearing is non-contact it allows some radial movement of the rotor and the drive shaft, particularly if the vacuum pump receives an external impact or knock.
Movement of the drive shaft 106 is shown in the normal condition in
A back-up bearing assembly 114 limits radial movement of the rotor and drive shaft for example to prevent clashing between the rotating parts of the pump and the stationary parts of the pump. Clashing causes damage to the pumping mechanism and can be hazardous, particular as the rotor blades 104 are rotating at speeds of up to 90,000 rpm. The back-up bearing assembly 114 is arranged to limit radial movement by contact with the rotor or the drive shaft. One example of a back-up bearing assembly shown in
As shown in
A force may be imparted to the vacuum pump if it is knocked, for example, by a user while in use or when it is being installed or transported. In some vacuum pumping applications, the vacuum pump is required to be easily transported from one location to another, for example, within devices such as accelerators for cancer treatment in different locations in a hospital. It is convenient therefore to mount the vacuum pump on a transporter such as a trolley or other mobile, or wheeled, unit, however transporting the vacuum pump in this way renders it more susceptible to knocks due to accidental collisions or transport over uneven surfaces. The force required to bring the back-up bearing into use varies dependent on characteristics of the vacuum pump, for example the controlling magnetic force which can be generated by the first bearing assembly. A typical force which is sufficient to cause operation of the back-up bearing assembly is 10 to 100 N applied to the vacuum pump generally in the radial and/or axial direction, although the exact range of forces will depend on the structure and arrangement of the pump and may be higher or even lower.
A sensor 116 is arranged for sensing when radial movement of the rotor or drive shaft is limited by the back-up bearing assembly. In the arrangement shown, the sensor is fixed relative to a pump housing 118, for example, to an outer surface of the pump housing and senses the force applied to the pump housing. The sensor may be an accelerometer for sensing acceleration of the pump housing resulting from the applied force. It is determined prior to operation that an acceleration of ‘x’ meters per second per second causes implementation of the back-up bearing assembly and therefore a contact event is determined to have occurred when the sensor senses an acceleration equal to or greater than ‘x’.
In other arrangements the sensor may comprise means for detecting contact between the rotor or drive shaft and the back-up bearing assembly. One such arrangement may comprise an electrical circuit which is closed on contact. Another arrangement may comprise a proximity switch. Yet another arrangement may comprise means for detecting relative movement of the inner and outer races of the back-up bearing assembly. All sensor arrangements for determining the occurrence of a contact event are included within the scope of the present invention.
The accelerometer arrangement may be preferred in some embodiments because it is capable of sensing a magnitude of an impact in addition to sensing an impact per se. If a sensor is arranged to sense a magnitude of a force imparted to the vacuum pump, the sensed magnitude can be associated with the damage caused to the back-up bearing assembly. For example, a back-up bearing assembly may fail after 500 stronger impacts or 1000 weaker impacts. As explained in more detail below, replacement of a back-up bearing assembly is triggered when the number of sensed impacts exceeds a predetermined value, for example 10,000 impacts. A strong impact may be equivalent to two weaker impacts in the example above and therefore if a strong impact is sensed the total number of impacts recorded is increased by two even though only a single impact has been sensed. The arrangement may have two values representative of strong or weak impacts and add one to the count if a weak impact is sensed or two to the count if a strong impact is sensed. The strength of impacts could of course be divided into more than two different strengths for greater accuracy.
In another arrangement, the total aggregate force applied to the vacuum pump can be measured or the total acceleration experienced by the vacuum pump. For example, if an impact with a force of 50 N causes a single impact and 10,000 such impacts means that replacement of the back-up bearing is necessary, the total force applied to the vacuum pump is 500,000 N. Accordingly, when the total sensed force exceeds 500,000 N replacement is triggered.
Referring particularly to
Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are described as example forms of implementing the claims.
Number | Date | Country | Kind |
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1219518.6 | Oct 2012 | GB | national |
Filing Document | Filing Date | Country | Kind |
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PCT/GB2013/052673 | 10/14/2013 | WO | 00 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO2014/068277 | 5/8/2014 | WO | A |
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Number | Date | Country | |
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20150275902 A1 | Oct 2015 | US |