PUMP ASSEMBLY, METHOD AND COMPUTER PROGRAM

Abstract

A pump assembly method and computer program are disclosed. The pump assembly comprises: a pump, an associated motor controller and an accelerometer mounted on the pump. The motor controller is configured to control power supplied to drive the pump and to receive data output from the accelerometer, the motor controller comprising processing circuitry configured to process the data received from the accelerometer to determine accelerations experienced at the pump due to the pump operation. These accelerations can be used to determine a condition of the pump.

Claims

1. A pump assembly comprising: a pump, an associated motor controller and an accelerometer mounted on said pump; said motor controller being configured to control power supplied to drive said pump; and to receive data output from said accelerometer, said motor controller comprising processing circuitry configured to process said data received from said accelerometer to determine accelerations experienced at said pump due to said pump operation, said processing circuitry being operable to process data received from said accelerometer in conjunction with motor controller data so as to separate acceleration data generated by said pump operation and other signals.

2-38. (canceled)

39. The pump assembly according to claim 1, wherein said processing circuitry is configured to synchronise sampling of data signals output from said accelerometer with at least one type of said motor controller data.

40. The pump assembly according to claim 1, wherein said processing circuitry is operable to correlate said data received from said accelerometer with said motor controller data.

41. The pump assembly according to claim 1, wherein said motor controller data comprises motor control data indicative of motor control signals generated by said motor controller.

42. The pump assembly according to claim 39, wherein said motor controller comprises at least one sensor, said motor controller data comprising data received from said at least one sensor, and wherein said at least one sensor is for sensing at least one of current output to drive said pump, voltage output to drive said pump, temperature and power; and wherein said pump comprises a rotor and said at least one sensor is for sensing rotor speed or rotor angular position.

43. The pump assembly according to claim 1, wherein said pump comprises a rotor, and said processing circuitry is operable to determine at least one of rotor angular position and rotor speed from said motor controller data.

44. The pump assembly according to claim 42, said processing circuitry being operable to generate rotor condition data from said data received from said accelerometer and at least one of said rotor angular position data and said rotor speed.

45. The pump assembly according to claim 1, wherein said processing circuitry is configured to convert sampled data from said accelerometer to the frequency domain.

46. The pump assembly according to claim 1, wherein said processing circuitry comprises comparison circuitry for comparing data output by said accelerometer and processed by said processing circuitry with at least one threshold value to generate at least one warning signal.

47. The pump assembly according to claim 46, further comprising output circuitry for outputting warning indications, said output circuitry being configured to be triggered by said at least one warning signal.

48. The pump assembly according to claim 1, said pump further comprising a power source for providing power to said accelerometer, said pump comprising a data store for storing data received from said accelerometer.

49. The pump assembly according to claim 1, wherein said accelerometer is mounted on said pump; and said motor controller being separate from said pump and being configured to receive data from said accelerometer via at least one of a wired and a wireless connection.

50. The pump assembly according to claim 1, wherein said pump comprises a pump mechanism and a pump housing, and said motor controller is mounted within a housing that is rigidly connected to said pump housing, said accelerometer being mounted within said motor controller housing.

51. The pump assembly according to claim 1, said pump comprising a compressor or a vacuum pump; wherein said vacuum pump comprising at least one of a turbo-molecular pump, a dry pump, and a rotary vane pump

52. A method of analysing data received from an accelerometer mounted on a pump comprising: receiving data output from said accelerometer; receiving motor controller data from a motor controller for controlling a drive motor of said pump; and processing said acceleration data in conjunction with said motor controller data to determine accelerations experienced at said pump due to operation of said pump, wherein said step of receiving data output from said accelerometer comprises sampling data signals output from said accelerometer, said sampling being synchronised with at least one type of said motor controller data.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which:

[0054] FIG. 1 shows a vacuum pump with motor controller and accelerometer according to a first embodiment;

[0055] FIG. 2 shows a vacuum pump with accelerometer and remote motor controller according to a second embodiment;

[0056] FIG. 3 shows the driving voltages and current for a vacuum pump motor, and FIG. 4 shows variations in the current supplied to the vacuum pump motor;

[0057] FIG. 5 schematically shows a vacuum pump and motor controller according to a third embodiment; and

[0058] FIG. 6 shows a flow diagram illustrating steps performed in the method according to an embodiment.

DETAILED DESCRIPTION

[0059] Before discussing the embodiments in any more detail, first an overview will be provided.

[0060] An acceleration sensor (accelerometer) is embedded in a pump or in its associated motor controller electronics and the acceleration signal is processed within processing circuitry within the motor controller electronics allowing accelerations due to the operation of the pump to be analysed and the condition of the pump determined. Locating the processing circuitry within the motor controller electronics, provides a location that is suitable for such circuitry and allows easy access to the motor control signals, allowing the motor control signals and acceleration signals to be correlated providing improved information on the operation and condition of the pump. The sampling of the acceleration signal may for example be synchronised with the other control processors in the motor controller and specifically with the PWM of the output voltage.

[0061] FIG. 1 schematically shows a turbomolecular pump 1 connected to a vacuum system 6. Firmly mounted to the vacuum pump 1 is motor controller 2 which generates control signals for controlling the motor driving the vacuum pump rotor. Motor controller 2 has an accelerometer 5 within it and as the motor controller is rigidly attached to the vacuum pump 1, accelerations experienced by the vacuum pump due, for example, to operation of the vacuum pump will be felt by the accelerometer 5 and signals indicative of the accelerations experienced will be generated. These are output to processing circuitry 7 which analyses the signals in conjunction with information received the motor controller to determine both operation and condition of the vacuum pump.

[0062] Mounting the accelerometer within the motor controller means that it is in a position that is designed to be suitable for electronic circuitry as it is where the control circuitry of the motor controller is also located and it is also at a location that is convenient for receiving signals indicative of the driving and operation of the vacuum pump. Thus the acceleration signals and the motor control signals may be analysed in combination allowing more detailed and accurate analysis of the pump's operation.

[0063] FIG. 2 shows an alternative embodiment where the motor controller 3 is mounted remotely from the vacuum pump. This may be preferable where the vacuum pump generates a lot of vibrations or operates at a high temperature making it an unsuitable location for electronic circuitry. In such a situation, the accelerometer 5 is mounted within the vacuum pump housing perhaps on the vacuum pump cartridge and in this way senses accelerations experienced at the vacuum pump.

[0064] In this embodiment there is a communication link 4 between the motor controller 3 and the pump 1 to provide drive control signals to the vacuum pump motor. This link is also be used to transmit acceleration signals from the accelerometer 5 to the motor controller 3 such that these signals are received at the motor controller and can be processed by processing circuitry 7. Once again, processing circuitry 7 will process the signals from the accelerometer in conjunction with the signals from the motor controller allowing detailed analysis of operation of the vacuum pump to be performed.

[0065] In this regard, the combination of motor controller or drive and acceleration signals can be used so that accelerations experienced at particular frequencies can be related to operation of particular elements of the pump such as the bearings or the rotor and can be used to diagnose faults with these elements. Alternatively, the combination can be used to reduce noise in the signals received from the accelerometer and increase accuracy in that way.

[0066] Although the pumps shown in FIGS. 1 and 2 are vacuum pumps it would be clear to a skilled person that the motor controller, accelerometer, processing circuitry and motor controller electronics shown in these embodiment could be used in a similar way with any sort of pump or compressor that is driven by a motor.

[0067] FIG. 3 shows the voltage of a three phase voltage supply supplied to drive a motor of a vacuum pump using pulse switch modulation. It also shows how the current varies with these voltages. As can be appreciated, the switching of the drive voltage will generate noise signals within associated electronic circuitry due to inductive effects. When sampling current to determine current provided by this driving voltage, sample points which occur towards the mid-point of the current value which is a point that is relatively remote from a voltage switching point should be used. Thus, these waveforms provide two opportunities to sample the current, which coincide with the start and centre of the PWM cycle. Similarly, when sampling signals from the accelerometer, sample points remote from the voltage switching points should be used and thus, a knowledge of the drive signals from the motor controller allows the data from the accelerometer to be sampled in a way that reduces noise in the signals sampled and thereby allows for an increased accuracy.

[0068] FIG. 4 shows current ripple for one PWM period. These ripples occur in a generally sinusoidal signal produced by the PWM voltage and might be at 20 kHz with a few of these cycles in each motor rotation. As noted with respect to FIG. 3, when sampling signals from the accelerometer, it may be advantageous to sample signals towards the mid-point of changes in a current or voltage value and thus, sampling towards the mid-point of each ripple would reduce the noise in the signal due to fluctuating voltages and currents. In this way, combining signals from the motor controller circuitry with accelerometer processing can help improve the accuracy of the acceleration data that is then analysed.

[0069] FIG. 5 shows a diagram of a pump 1 having motor 20 and motor controller 3. Motor controller 3 transmits control signals to motor 20 to control the driving the motor of the vacuum pump. Motor controller 3 has control circuitry 17 for generating the motor control signals and power supply 15 for providing the power to drive motor 20. In this embodiment, there is an ammeter 16 for measuring the current supplied to the motor and this transmits signals to processing circuitry 7. Accelerometer 5 mounted on the vacuum pump cartridge also transmits signals to processing circuitry 7 as does motor controller circuitry 17. Processing circuitry 7 will process these received signals to determine the condition of the vacuum pump. In this regard, it may comprise comparison circuitry 9 which compares values of monitored signals with threshold values and where thresholds are reached, it will output a warning signal to warning indicator 11 and/or to output 12. In this embodiment, warning indicator 11 comprises warning lights which are illuminated in response to the warning signal. There is a green light indicating operation is detected as being satisfactory and an orange light indicating that servicing may be required shortly and a red light indicating that the pump should not be operated.

[0070] Processing circuitry 7 may process the signals in a number of ways and may include a frequency domain convertor for converting the signals from amplitude versus time to amplitude versus frequency. This allows the peak values of acceleration amplitude at specific frequencies to be determined and these may indicate particular faults within the vacuum pump.

[0071] For example where the rotor speed is known, then accelerations detected at a frequency corresponding to this speed may indicate problems with the rotor while accelerations at a frequency corresponding to a factor of this speed may indicate bearing wear. Furthermore, where the angular position of the rotor is known then accelerations related to that position may indicate an unbalanced rotor. This can be useful when balancing the rotor using balancing screws, when the vacuum pump is being made ready for use or as an indicator that servicing is required.

[0072] The presence of an accelerometer and processing circuitry which can coordinate with the motor controller circuitry is particularly useful during pump final test and avoids the need of temporarily fitting testing circuitry to every pump that is built and tested. Tests performed involve performing a FFT (Fast Fourier Transform); results input to the threshold comparison circuitry 9 which uses a pass/fail envelope indicate whether the pump is suitable for use or not. The accelerometer may also be used in pre and post service testing where, for example, the field bearings have been changed to check that the pump has not been compromised by the field service operation and that the rotor is still in the correct position.

[0073] In addition, during normal operation, any deterioration in the pump condition may be determined from increases in acceleration values at particular frequencies and warning signals can be generated. For example, it may be used to automatically identify when the bearings need changing or to provide some early warning system that they will need replacements soon.

[0074] In addition or as an alternative to illuminating warning signals, the signals collected during analysis may also be sent to output 12, where they may be transmitted to the operator or customer to help fault finding. Where there is data logging of vacuum pump operation, the accelerometer may also provide its data to that onboard data logging system and this may be useful in recording the pump running history. This can be advantageous in identifying where particular use of the pumps may have caused damage to the pump. In effect, it may be useful for detecting abuse events where the pump has been misused.

[0075] In some embodiments, there is a battery associated with the accelerometer shown as 18 in FIG. 5. This can be used to power the accelerometer and record acceleration events in data store 19 that are detected when the pump is not operational and is powered down. This can be useful in particular when the pump is being moved between operational locations, to detect events occurring during the move which may damage the pump. It should be noted that although the battery 18 and data store 19 are shown attached to the vacuum pump in FIG. 5, they may also be mounted in the motor controller 3 and connected to the accelerometer 5 by wires.

[0076] FIG. 6 shows a flow diagram illustrating steps performed at processing circuitry within the motor controller by a method according to an embodiment. Data is received at the processing circuitry from an accelerometer mounted on a pump and operable to detect accelerations due to operation of the pump. The processing circuitry is operable to convert the received signals from the time domain to the frequency domain. It then compares the amplitude of accelerations detected at certain frequencies with threshold values. Where the threshold is reached then a warning indicator is output. A log of incidents of the thresholds being exceeded is also kept.

[0077] In one embodiment, analysis of the accelerations at different frequencies can be used to provide information about the condition of the pump and in particular, the contact angle and hence the preload of the rotor. This can be useful particularly after service when changes in the preload may indicate significant impeller temperature changes, which again are indicative of possible faults.

[0078] Examples of the motor controller data that may be combined with the accelerometer data are the rotational frequency measurements which can be used as an input to the final balance process. Phase and magnitude information relating to the rotor position poles from the accelerometer amplitude poles are indicative of the angular position of any unbalance. A plot of the frequency response of the system during coast down or ramp up could also be generated by the processing circuitry and used to detect critical speeds in specific issues like back-up bearing touch or rotor clash in final tests and in pump development. In this regard back-up bearings are provided to limit the movement of the drive shaft away from its normal position.

[0079] The above gives some examples of uses of a pump assembly according to an embodiment. It is particularly applicable to turbomolecular pumps as they have a drive fitted to the pump in a way that provides very tight mechanical coupling between the pump mechanism and the motor control electronics. In turbomolecular pump applications, the motor control electronics and the accelerometer are mounted rigidly to the pump as in FIG. 1. Other embodiments using other pumps such as dry pumps, may use the arrangement of FIG. 2 where the motor control electronics are mounted remotely from the pump to protect them from vibrations.

[0080] As processing circuitry is already present within the motor controller and as low cost accelerometers using MEMS devices are now available, the fitting of an accelerometer and processing device to such pump assemblies is very low cost and can provide much additional data, which may be transmitted to a user using existing serial communication channels.

[0081] Embodiments of the present invention which provide transmission of the collected data either wirelessly or via a communication port to a remote location, provide a way of detecting operation of the pumps which can be useful to determine operation issues such as the noisiness of the pump from this remote position. One of the most common complaints for a pump is that it is noisy but this is difficult to quantify and verify the scale of the issue without having a service personnel visit or having the pump returned. Being able to collect data from an accelerometer remotely will provide a useful indication of the size of this problem.

[0082] Furthermore, periodically pumps require bearing replacements or other service and it is difficult to predict the correct interval for preventative maintenance as these intervals can vary considerably with the customer application. Monitoring the amplitude and frequency of acceleration peaks could be used to provide early warning that maintenance is really required and also of the nature of the maintenance. This could allow service intervals to be safely extended and could provide early warnings in the cases where the bearing has deteriorated more quickly for whatever reason.

[0083] Although illustrative embodiments of the invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the invention is not limited to the precise embodiment and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the invention as defined by the appended claims and their equivalents.

[0084] Although elements have been shown or described as separate embodiments above, portions of each embodiment may be combined with all or part of other embodiments described above.

[0085] 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.