POWER CONTROL METHOD FOR A MOTOR OF AN AIR-MOVING DEVICE

Abstract

A method to control an input power of a motor of an air-moving device that includes performing a measurement process to determine a first value of an operating parameter of the motor. The operating parameter is an operating pressure of the motor or an airflow rate through the motor. The method includes performing a determination process to determine a value of the inlet restriction of the air-moving device, based on the first value of the operating parameter of the motor and a first pre-determined relationship between values of the operating parameter of the motor and values of an inlet restriction of the air-moving device. The method also includes controlling, based on the determined value of the inlet restriction, the input power of the motor.

Claims

1. A method to control an input power of a motor of an air-moving device, the method comprising: performing a measurement process to determine a first value of an operating parameter of the motor, wherein the operating parameter is an operating pressure of the motor or an airflow rate through the motor; performing a determination process to determine, based on the first value of the operating parameter of the motor and a first pre-determined relationship between values of the operating parameter of the motor and values of an inlet restriction of the air-moving device, a value of the inlet restriction of the air-moving device; and controlling, based on the determined value of the inlet restriction, the input power of the motor.

2. The method of claim 1, wherein the operating parameter is the operating pressure and the measurement process comprises determining the first value of the operating parameter of the motor based on: an ambient pressure measurement; and a motor-inlet pressure measurement during operation of the motor.

3. The method of claim 2, wherein the ambient pressure measurement and the motor-inlet pressure measurement are measured at different times by a single pressure sensor.

4. The method of claim 1, wherein the measurement process comprises determining the first value of the operating parameter of the motor based on: a first pressure measurement of a pressure at a first position in a motor assembly in which the motor is located; and a second pressure measurement of a pressure at a second position in the motor assembly; wherein the second position is downstream of the first position.

5. The method of claim 1, wherein the first pre-determined relationship relates values of the operating parameter of the motor and values of one or more further parameters to values of the inlet restriction of the air-moving device, and wherein the determination process comprises: determining the value of the inlet restriction based on one or more respective further parameter values of the one or more parameters.

6. The method of claim 5, wherein the one or more further parameters comprise one or more of: an ambient pressure; an ambient temperature; a motor input power; and a build tolerance of the air-moving device.

7. The method of claim 5, wherein the determination process comprises: determining a first normalised value of the operating parameter by normalising the first value of the operating parameter by use of one or more respective values of the one or more further parameters; and determining the value of the inlet restriction of the air-moving device based on the normalised operating parameter.

8. The method of claim 5, wherein the one or more further parameters comprise a value of a filter loading of a filter of the air-moving device.

9. The method of claim 8, wherein the determination process comprises determining the value of the filter loading.

10. The method of claim 9, wherein the determining the value of the filter loading comprises: performing a second measurement process comprising determining a first value of a second operating parameter of the air-moving device, the first value being a value of the second operating parameter when the air-moving device is operating with a first inlet restriction condition; and performing a second determination process to determine the value of the filter loading, the determination process comprising determining, based on the first value of the second operating parameter and a second pre-determined relationship relating, for the air-moving device when operating with the first inlet restriction condition, values of the second operating parameter to values of the filter loading, the value of the filter loading.

11. The method of claim 10, wherein the second operating parameter is: the operating pressure of the motor of the air-moving device; a speed of the motor of the air-moving device; or an airflow rate through the motor of the air-moving device.

12. The method of claim 10, wherein the determining the first value of the second operating parameter comprises: determining a plurality of values of the second operating parameter; determining a distribution of the plurality of values of the second operating parameter; determining a first property of the distribution; and determining, based on the first property of the distribution, the first value of the second operating parameter.

13. The method of claim 12, wherein the first property of the distribution is a minimum value in the distribution.

14. The method of claim 1, wherein the controlling comprises adjusting the motor input power according to a set profile relating motor input power values to inlet restriction values.

15. The method of claim 14, wherein the set profile is a continuous profile.

16. The method of claim 14, wherein the set profile comprises a plurality of discrete power levels, each of the power levels corresponding to a respective range of values of inlet restriction.

17. The method of claim 1, comprising, during operation of the air-moving device, performing the measurement process, the determination process and the controlling a plurality of times.

18. A set of machine-readable instructions which when executed by a processor of an air-moving device cause the air-moving device to perform the method according to claim 1.

19. An air-moving device comprising: a processor; and a storage comprising a set of machine-readable instructions which when executed by the processor cause the processor to perform the method according to claim 1.

20. The air-moving device of claim 19, wherein the air-moving device is a vacuum cleaner.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The present invention will now be described, by way of example only, with reference to the following figures, in which:

[0046] FIG. 1 shows a schematic representation of an example motor assembly of an air-moving device;

[0047] FIG. 2 shows an example of an air-moving device;

[0048] FIG. 3 is a flow chart representation of a method to control an input power of a motor of an air-moving device;

[0049] FIG. 4 shows an example of a plot of values of an operating pressure and values of an inlet restriction in an air-moving device;

[0050] FIG. 5 shows further examples of plots of values of the operating pressure and values of the inlet restriction;

[0051] FIGS. 6A to 6C show, schematically, example power control profiles for an air-moving device;

[0052] FIG. 7 is a flow chart representation of a method to determine a value of a filter loading of an air-moving device;

[0053] FIG. 8 illustrates, schematically, aspects of an example method of determining the value of the filter loading;

[0054] FIG. 9 illustrates, schematically, further aspects of the example method shown in FIG. 8;

[0055] FIG. 10 illustrates, schematically, further aspects of the example method shown in FIGS. 8 and 9;

[0056] FIGS. 11A and 11B illustrate yet further aspects of the example method shown in FIGS. 8 to 10;

[0057] FIG. 12 shows a schematic representation of another example motor assembly of an air-moving device;

[0058] FIG. 13 shows a schematic representation of another example motor assembly of an air-moving device;

[0059] FIG. 14 shows a schematic representation of certain components of a motor assembly of an air-moving device according to an example; and

[0060] FIG. 15 shows a schematic representation of certain components of an example motor assembly of an air-moving device according to another example.

DETAILED DESCRIPTION OF THE INVENTION

[0061] FIG. 1 shows an example schematic representation of a motor assembly 100 of an air-moving device. The motor assembly 100 comprises set of coils 102, a shaft 104 with magnets (not shown) mounted thereon, bearings 106 and an impeller 108. The motor assembly 100 comprises motor air inlets 110, and air outlets/diffuser 112. The motor assembly comprises a circuit board 114 on which are mounted sensor an ambient temperature sensor 116 and a first pressure sensor 118. The motor assembly 100 comprises a housing 124 in which the other components are housed. The motor assembly 100 further comprises a pre-motor filter 126 for filtering air which is drawn into the motor in use.

[0062] FIG. 2 shows an example air-moving device 200 comprising the motor assembly 100. The air-moving device 200 is a vacuum cleaner. The vacuum cleaner 200 comprises an inlet tube 202 with a tool 204 attached to a distal end of the inlet tube 202. The tool 204 is for engaging with a surface to be cleaned by the vacuum cleaner and comprises an air inlet (not shown) to the vacuum cleaner 200. The tool 204 may be active, comprising one or more mechanically-operated components, e.g. a rotating brush bar, to assist with cleaning tasks. Alternatively, the tool 204 may be passive and not comprise any such mechanically-operated components. A passive tool may nevertheless comprise elements such as bristles or the like to assist with cleaning tasks. In examples, the inlet tube 202 or a portion thereof may be removable. A tool, such as a passive tool, may be attached to the device 200 when the inlet tube 202 or the portion thereof is removed. The vacuum cleaner 200 also comprises a dirt-separating chamber 206, which may, for example, be a cyclone chamber. The vacuum cleaner 200 further comprises a processor 208 and a storage 210 for storing machine-readable instructions for execution by the processor 208 to control operation of components of the vacuum cleaner 200 including the motor 100. The machine-readable instructions when executed may cause the processor 208 to carry out any of the example methods described herein.

[0063] In use, the motor of the motor assembly 100 draws air through the air inlet to the air-moving device 200, through the air-moving device 200, and out of an exhaust. Air is drawn through the device 200 along an airflow path 128 which passes through the inlet tube 202, through the dirt-separating chamber 206, through the motor assembly 100 and exits the device 200 through an exhaust.

[0064] Returning to FIG. 1, when the motor is in use in the air-moving device 200, an electric current is passed through the coils 102, in a manner which causes the generation of a varying magnetic field. This varying magnetic field is configured to act on the magnets on the shaft 104 to cause the shaft 104 to rotate about its longitudinal axis. This in turn rotates the impeller 108. Air, driven by the impeller 108, is drawn into the air-moving device 200 and along the airflow path 128. The airflow path 128 enters the motor assembly 100, passing through the pre-motor filter 126, which removes particulate matter from the air, and into the housing 124 through the air inlets 110. The airflow path 128 continues through the motor to the impeller 108 and, after passing over the impeller 108, exits the motor assembly 100 through the air outlets 112.

[0065] FIG. 3 shows a flow chart representation of an example method 300 to control an input power of a motor of an air-moving device, such as a vacuum cleaner.

[0066] The method 300 comprises, at block 302, performing a measurement process to determine a first value of an operating parameter of the motor. The operating parameter may be an operating pressure or an airflow rate.

[0067] The operating pressure of the motor is an air pressure relating to the motor when the motor is in operation, i.e. when the motor is running. The operating pressure may relate to an air pressure at one or more locations along the airflow path 128. The operating pressure may be a differential air pressure. The operating pressure may, for example, be a pressure difference between an upstream and a downstream location, in the motor assembly, along the airflow path 128.

[0068] In another example, the operating pressure is a difference between a first pressure measured when the motor is not running and a second pressure measured when the motor is running. The first pressure and the second pressure may be measured at the same location. A value of an operating pressure may, for example, be obtained by determining a difference between an ambient pressure measurement, taken when the motor is not running, e.g. before start-up of the air-moving device 200, and a pressure measurement taken during operation of the motor. In some examples described herein, such an operating pressure is referred to as delta-P. The pressure measurement taken during operation of the motor may, for example, be taken at the air inlet 110. Alternatively, the measurement may be taken at an air outlet from the motor. In some examples, the pressure measurements used to obtain a value of an operating pressure may be taken by the same pressure sensor. This allows for a value of the operating pressure to be obtained using a single pressure sensor, which may be cost- and space-efficient.

[0069] The airflow rate is a rate at which, in use, air, being drawn by the operation of the motor, flows through the motor.

[0070] Examples of methods of obtaining operating pressure measurements and airflow rate measurements will be described in more detail below.

[0071] At block 304, the method 300 comprises performing a determination process to determine, based on the first value of the operating parameter of the motor and a first pre-determined relationship between values of the operating parameter of the motor and values of an inlet restriction of the air-moving device 200, a value of the inlet restriction of the air-moving device 200.

[0072] Values of the inlet restriction of the air-moving device 200 define a level of restriction acting on the air inlet through which air flows into the device 200. The level of inlet restriction may vary based on various factors such as obstructions blocking the flow of air into the device 200. For example, the inlet restriction may vary depending on a type of surface the vacuum cleaner 200 is being used to clean. For instance, a carpeted surface or similar may place a greater restriction on the flow of air into the vacuum cleaner 200 than a smooth surface such as a wood or tile surface. The value of the inlet restriction may also vary depending on a type of tool attached to the vacuum cleaner 200. Different tools may, for example, have different geometries and thus restrict the flow of airflow into the vacuum cleaner 200 by different amounts. For example, different tools may have different air inlet diameters. Further, certain tools may include elements which obstruct the flow of air-flow into the device 200, such as bristles for cleaning carpet, while other tools may not include such elements.

[0073] In some examples, it may not be possible or practical to directly measure a value of inlet restriction of the air-moving device 200. Accordingly, according to examples described herein, values of the operating parameter of the motor are measured and used to determine values of the inlet restriction of the device 200. The first pre-determined relationship may be defined in terms of a curve relating values of the operating parameter of the motor and values of an inlet restriction of the air-moving device 200.

[0074] The pre-determined relationship between values of the operating parameter and values of the inlet restriction may be obtained, for example, by a calibration process. This calibration process may involve, for example, operating the device 200 under known operating conditions, including a known value of inlet restriction, and measuring values of the operating parameter. This may be done by operating the device 200 with orifice plates having orifices of differing diameters restricting airflow into the device 200. The value of inlet restriction of the device in operation may then be defined in terms of the diameter of the orifice which would provide an equivalent level of restriction to airflow into the device 200. As an example, the vacuum cleaner 200 when being used to clean a carpeted surface may be operating under a high level of inlet restriction which may be equivalent to operating in known conditions with an orifice plate having an orifice of small diameter restricting airflow into the vacuum cleaner 200. Conversely, the vacuum cleaner 200 when cleaning a wood surface may be operating under a lower level of inlet restriction, equivalent to that presented by an orifice of larger diameter.

[0075] The first pre-determined relationship may relate values of the operating parameter of the motor and values of one or more further parameters to values of the inlet restriction of the air-moving device. The value of the inlet restriction may then be determined based on a first value of the operating parameter and respective values of the one or more further parameters. The further parameters may be parameters of the air-moving device 200 which influence the value of the operating pressure which is measured for a given value of the inlet restriction.

[0076] For example, different values for parameters such as the ambient pressure, ambient temperature, motor input power, filter loading of a filter of the motor, and build tolerance of the air-moving device may result in different values of the operating parameter for the same value of inlet restriction.

[0077] Ambient pressure and ambient temperature form part of the external conditions under which the device 200 is operating. In some examples, ambient pressure may be measured prior to start-up of the motor by the first pressure sensor 118. Ambient temperature may be measured by the temperature sensor 116. Motor input power is the power which is supplied to drive the motor.

[0078] The motor input power may be controlled by the processor 208 and supply a DC or AC power, for example from a battery (not shown) of the device 200 or from a mains supply. The motor input power may control the suction power of the air-moving device.

[0079] The filter loading may be a level of loading of a filter which filters particulate matter from the airflow which passes through the motor. For example, the filter loading may be a level of loading of the pre-motor filter 126. Alternatively, the filter loading may be a level of loading a post-motor filter or may take into account a level of loading of a plurality of filters, e.g. a pre-motor filter and a post-motor filter. The level of loading of the filter may define how much dirt has been collected by the filter. In examples, this may be expressed in terms of the amount of dirt the filter may collect before it is deemed in need of replacing or cleaning. For example, a filter loading of 100% may represent that the filter has collected an amount of dirt such that it is deemed in need of replacing or cleaning. A filter loading level of 0% may represent that the filter has collected no dirt, e.g. because it has been fully cleaned or newly replaced. Typically, the level of filter loading may increase steadily during use of the device 200 as air passes through the device and dirt is filtered from the air.

[0080] The build tolerance of the air-moving device 200 may account for the variability in operation between different devices. For example, various operating parameters of the device may be measured during a calibration process following assembly of the device. The build tolerance of a particular device may be expressed as a percentage of a total allowable tolerance. In one example, at an end of a production line for a device, an orifice plate having an orifice of a given diameter is connected to an inlet of the device, wherein the device is known to have clean filters, i.e. the filter loading value is 0%. The ambient temperature and pressure are measured. The device is operated at a given power level and the operating parameter, e.g. delta-P, is measured. With values of the input power, ambient temperature, ambient pressure, filter loading, being measured or otherwise known, the measured delta-P is indicative of the build tolerance factor. This process may be repeated at multiple power levels and at different orifice diameters.

[0081] The first pre-determined relationship may in some examples define a multi-dimensional look-up table mapping values of the operating parameter and values of one or more further parameters to values of the inlet restriction. In one example, the first pre-determined relationship defines a six-dimensional look-up table which maps respective values of build tolerance, ambient pressure, ambient temperature, motor input power, filter loading and operating parameter. e.g. the operating pressure, to a value of the inlet restriction.

[0082] In another example, a look-up table of lower dimensionality may be used in which normalised values of the operating parameter are mapped to values of the inlet restriction. The normalised values of the operating parameter may be obtained by normalising values of the operating parameter with respect to one or more further parameters, such as those mentioned above. For example, a five-dimensional look-up table may be defined which maps respective values of build tolerance, ambient pressure, ambient temperature, motor input power, and a value of the operating pressure to a normalised value of the operating pressure.

[0083] A further, two-dimensional, look-up table may then be used to obtain a value of the inlet restriction from the normalised value of the operating pressure and a value of the filter loading. The lower dimensionality of the look-up table in this example means that the calculation is simpler. However, the accuracy of the determined inlet restriction value is highly dependent on the accuracy of the normalisation process. In contrast, using a look-up table of higher dimensionality without performing a normalisation process means that the calculation may be more computationally expensive but the accuracy of the output is not dependent on the accuracy of any normalisation process.

[0084] In another example, the first pre-determined relationship may be represented using multi-dimensional curve fits or an artificial neural network. Such representations may in some examples be more efficient than a look-up table in terms of the amount of memory required.

[0085] An example of a first pre-determined relationship relating normalised values of the operating pressure to the values of inlet restriction is shown in FIG. 4. This example is for the motor of a vacuum cleaner.

[0086] In the example of FIG. 4, the operating pressure, shown on the y-axis, is a delta-P value defining a difference between an ambient pressure of the motor prior to start-up and a pressure at a motor inlet during operation. Delta-P is in units of kPa. The values of the inlet restriction are in terms of orifice diameter, in millimetres. A first curve 402 mapping values of normalised delta-P to values of inlet restriction has been obtained by a suitable calibration process involving operating the vacuum cleaner under known conditions with inlet restriction provided by orifices of various diameter. Corresponding values of the diameter of the orifice and delta-P have been measured. The first curve 402 has been obtained by normalising values of delta-P with respect to values of build tolerance, ambient pressure, ambient temperature and motor input power. The first curve 402 uniquely maps a normalised value of the operating pressure to a value of the inlet restriction. However, as will be described with reference to FIG. 5, the normalised value of the operating pressure does not take into account a value of the filter loading of the motor. Accordingly, different values of the filter loading will result in a different mapping between values of normalised operating pressure and values of the inlet restriction.

[0087] FIG. 5 shows a set of curves 402, 504, 506 relating normalised values of the operating pressure to values of the inlet restriction. Each curve corresponds to a different value of filter loading. The first curve 402 of FIG. 4 is also shown in FIG. 5 and corresponds to a value of filter loading of 0%. A second curve 504 corresponds to a value of filter loading of 50%. A third curve 506 corresponds to a value of filter loading of 100%. To determine the value of the inlet restriction, using the set of curves 402, 504, 506, one of the curves 402, 504, 506 may be selected based on a given value of the filter loading. The normalised value of the operating pressure then uniquely determines a value of the inlet restriction for the known value of the filter loading. In some examples, the method 300 involves determining the value of the filter loading. An example of a method for determining the value of the filter loading is described in detail below.

[0088] Returning to FIG. 3, at block 306, the method 300 comprises controlling, based on the determined value of the inlet restriction, the input power of the motor. The controlling may comprise adjusting the motor input power according to a set profile relating motor input power values to inlet restriction values. For example, a set profile may be defined which maps determined values of the inlet restriction to values of the input power. The set profile may be used to determine a desired input power from a determined value of the inlet restriction. The input power to the motor may then be adjusted to the determined desired input power.

[0089] In some examples, the set profile comprises a plurality of discrete power levels, with each of the power levels corresponding to a range of values of inlet restriction. The number of discrete power levels may be, for example, two or three or more. In other examples, the set profile may be a continuous profile. For example, the power profile may comprise a curve relating a range of values of inlet restriction to values of input power.

[0090] Examples of such profiles are shown in FIGS. 6A-C. In FIGS. 6A-C, values of motor input power are shown on the y-axis. Values of inlet restriction are on the x-axis and are defined in terms of an orifice diameter, in same manner as in FIGS. 4 and 5.

[0091] A first example power profile is shown in FIG. 6A. In FIG. 6A, the set profile comprises two discrete power levels: a first power level 602 and a second power level 604. The first power level 602 corresponds to a first, higher, power P1 and the second power level 604 corresponds to a second, lower, power level P2. A range of low values of orifice diameter map to the first power level 602 while higher values of orifice diameter map to the second power level 604. Accordingly, when the inlet restriction of the air-moving device is highly restricted, i.e. the value of the orifice diameter is low, the method determines that the first, higher, input power P1 should be used. This allows the suction power of the device to be increased when the airflow into the device is highly restricted. When the level of inlet restriction is lower, i.e. the value of the orifice diameter is higher, the method determines that the second, lower, input power P2 should be used. Using a lower power at lower levels of restriction may, when it is practical to do so, allow the device to operate with lower power consumption while still providing adequate suction power. This may allow for less energy to be used by the device 200 and, for example, for a battery-powered device to operate for a longer period before the battery becomes depleted.

[0092] A power profile may also define transition points between different power levels. The transition points may differ depending on whether the transition is a transition from a lower to a higher power level or a transition from a higher to a lower power level. For example, a transition up from a lower to a higher level may occur at a lower orifice diameter than a transition down from a higher to a lower power level. This may help prevent the power level transitioning between power levels more often than is desired, for example when there are small changes in the determined orifice diameter value around a boundary between power levels.

[0093] FIG. 6A shows examples of such transition points represented by dotted arrows 606a, 606b. As can be seen from FIG. 6A, a first transition 606a from the lower power level 604 to the higher power level 602 occurs at a lower orifice diameter value than a second transition 606b from the higher power level 602 to the lower power level 604.

[0094] FIG. 6B shows a second example power profile. This second example power profile comprises three discrete power levels 608, 610, 612, compared with the two discrete power levels of the first example power profile of FIG. 6A. As with the example of FIG. 6A, different transition points, represented by dotted arrows, are defined between the power levels 608, 610, 612, depending on whether the transition is an up transition or a down transition.

[0095] FIG. 6C shows a third example power profile. The power profile of FIG. 6C is continuous. That is, there are no transition points between discrete power level wherein the power level is discontinuous for varying orifice diameter. The power profile of FIG. 6C comprises a first section 614 corresponding to low orifice diameters and a second section 616 corresponding to higher orifice diameters. The first section 614 in this example is flat and maps a range of values of orifice diameter to a single, high, power value. The second section 616 defines a curve which maps increasing orifice diameter values to decreasing values of power.

[0096] As will be understood, various other types of mapping of inlet restriction to input power may be used. For example, a power profile may comprise one or more continuous sections where the power level varies smoothly for varying orifice diameter and/or one or more discontinuous sections wherein a change in orifice diameter corresponds to a transition between one discrete power level and another discrete power level.

[0097] The method 300 may be performed a plurality of times during operation of the air-moving device. For example, the input power of the motor may be controlled continuously based on the determined level of the inlet restriction. For example, the value of the inlet restriction may be determined at regular intervals according to the steps described above and the value of the input power controlled accordingly. As such, the input power may, for example, be constantly be adjusted to be appropriate for the level of inlet restriction with which the device is operating. The input power may accordingly be being constantly adjusted to an appropriate level for the task being performed by the air-moving device.

[0098] As mentioned above, determining the value of the inlet restriction based on the operating parameter of the motor may allow the inlet restriction to be determined reliably and accurately, based on an observable physical parameter, without directly measuring the inlet restriction. The method may also allow the inlet restriction to be determined for use in controlling the input power without the need for additional sensors or processing to directly measure the inlet restriction.

[0099] FIG. 7 shows a flow chart representation of an example method 700 to determine a value of the filter loading of the air-moving device 200. In some examples, the method 700 is performed to determine the value of the filter loading which is used in a method of determining the input power of the motor. For example, the example method 700 may be performed as a part of the example method 300 of FIG. 3.

[0100] The method 700 comprises, at block 702, performing a measurement process comprising determining a first value of a second operating parameter of the air-moving device, the first value being a value of the second operating parameter when the air-moving device is operating with a first inlet restriction condition.

[0101] The second operating parameter may be an operating pressure of the motor of the air-moving device 200. For example, the operating pressure may be delta-P or any of the other types of operating pressure described above. For example, the operating pressure may be a normalised value of the operating pressure, for example, a normalised delta-P value. In some examples, the operating pressure may be the same operating pressure which is used in the method 300 of determining the value of the input power of the motor. This may be efficient since only one type of operating parameter may be needed in order to determine the filter loading and the input power. In other examples, a different type of operating pressure may be used to determine the value of the filter loading compared to the type of operating pressure used in the method of determining the input power of the motor.

[0102] In some examples, the operating parameter may be a speed of the motor of the air-moving device 200. This speed may be measured, for example, by a suitable sensor (not shown in the figures). In other examples, the operating parameter may be an airflow rate. Airflow rate may in some examples be determined based on pressure operating pressure measurements, as will be described below according to an example.

[0103] The first inlet restriction condition may be indicative of a minimum level of an inlet restriction of the air-moving device 200. For example, the first value of the second operating parameter may be a value of the second operating parameter measured when the air-moving device 200 is operating with a minimum level of inlet restriction, or, equivalently, with a maximum equivalent orifice diameter. This minimum level of inlet restriction may correspond to the device 200 operating in free air. That is, the minimum level of inlet restriction may be the level of inlet restriction acting on the device 200 when a tool of the vacuum cleaner is not engaged with a surface, such that there is no external obstruction to the flow of air into the device 200.

[0104] In other examples, the first inlet restriction condition may be a known property of a distribution of inlet restriction values of the device 200. For example, a mean or mode inlet restriction value of the device 200 over a period of operation may be determined. The first value of the second operating parameter may then be a value measured when the device 200 is operating with the mean or mode inlet restriction value.

[0105] The method 700 also comprises, at block 704, performing a determination process to determine the value of the filter loading of the filter of the air-moving device 200. The determination process comprises determining, based on the first value of the second operating parameter and a first pre-determined relationship relating, for the air-moving device 200 when operating with the first inlet restriction condition, values of the second operating parameter to values of the filter loading, the value of the filter loading.

[0106] An example of a determination process for determining a value of a filter loading will now be described with reference to FIG. 8. FIG. 8 shows the set of normalised delta-P curves 402, 504, 506 described above with reference to FIG. 5. FIG. 8 shows a first probability distribution 802 of applicable inlet restriction values of the vacuum cleaner. The first probability distribution 802 represents the probability of the vacuum cleaner having a given level of inlet restriction, in terms of an equivalent orifice diameter, when operating with a first tool attached. This first probability distribution 802 corresponds to a passive tool comprising a relatively wide nozzle and a selectively engageable brush. As can be seen from FIG. 8, in this example, the inlet restriction values of the first probability distribution 802 range from around 13 mm to around 47 mm. The minimum level of inlet restriction in the first probability distribution 802 corresponds to an orifice diameter of around 47 mm.

[0107] FIG. 8 also shows respective projections of the first probability distribution 802 onto two 402, 506 of the normalised delta-P curves. A first projection 804 is a projection of the first probability distribution 802 onto the first curve 402, which, as described above, corresponds to a filter loading of 0%. A second projection 804 is a projection of the first probability distribution 802 the third curve 506, which, as described above, corresponds to a filter loading of 100%.

[0108] The projections 804, 806 define respective probability distributions of the measured normalised value of delta-P for filter loading values of 0% and 100% respectively. In other words, the first projection 804 defines the probability of measuring a given normalised value of delta-P when the device is operating with 0% filter loading. Similarly, the second projection 806 defines the probability of measuring a given normalised value of delta-P when the device is operating with 100% filter loading. Further projections, not shown in FIG. 8, can be defined, defining the probability distributions of normalised delta-P at different values of filter loading, e.g. 25%, 50%, 75%, etc.

[0109] The values of normalised delta-P defined by the curves 402, 504, 506, in general, decrease rapidly for low values of orifice diameter but begin to level off for high values of orifice diameter. This levelling off means that a given value of normalised delta-P, at high values of orifice diameter, may map uniquely to a given one of the curves 402, 504, 506. In examples, this property may be used to determine the level of filter loading from a measured value of normalised delta-P.

[0110] For example, from the first probability distribution 802, it is known that the minimum normalised delta-P values in the probability distributions 804, 806 correspond to the device operating with a known maximum orifice diameter, in this example of around 47 mm. To determine a filter loading value, a minimum value of normalised delta-P during operation of the vacuum cleaner may be measured and mapped to given one of the curves 402, 504, 506 at the known maximum orifice diameter. By determining which of the curves 402, 504, 506, the measured normalised delta-P value maps to, the value of the filter loading can be determined.

[0111] For example, in FIG. 8, the third curve 506 and the probability distribution 806 show that, for a filter loading value of 100%, the minimum value of normalised delta-P, which corresponds to the maximum orifice diameter value of around 47 mm, is around 15.3 kPa. Accordingly, if the minimum normalised value of delta-P of the vacuum cleaner is measured to be around 15.3 kPa, this is indicative that the filter loading is 100%. Similarly, the first curve 402 and the probability distribution 804 show that, for a filter loading value of 0%, the minimum normalised delta-P value, again which corresponds to the maximum orifice diameter value of around 47 mm, is around 11.2 kPa. A measurement for the minimum normalised value of delta-P of around 11.2 kPa is therefore indicative that the value of the filter loading is 0%.

[0112] FIG. 9 illustrates another example of a method of determining a filter loading value. FIG. 9 is similar to FIG. 8 but relates to the vacuum cleaner when operating with a second tool attached. FIG. 9 shows a second probability distribution 902 of inlet restriction values applicable when the vacuum cleaner is in use with the second tool. Similarly to as described above with reference to FIG. 8, FIG. 9 shows projections 904, 906 of the second probability distribution 902 onto the first curve 402 and the third curve 506 respectively. As described above with reference to FIG. 8, the value of the filter loading can be determined by measuring the minimum normalised delta-P value of the vacuum cleaner in use. It can then be determined to which of a plurality of curves, e.g. the curves 402, 504, 506, this minimum value maps. The curve to which the minimum normalised delta-P value maps is indicative of the value of the filter loading.

[0113] From a comparison of the second probability distribution 902 and the first probability distribution 802, it can be seen that the second tool generally provides a higher level of inlet restriction than the first tool. For example, the second tool may, for example, be a passive, crevice tool. In this example, a minimum level of inlet restriction provided by the second tool corresponds to an orifice diameter of around 23 mm, compared to a value of around 47 mm for the first tool. As a consequence, the minimum normalised delta-P value for a given filter loading value is greater when using the second tool than when using the first tool. For example, when using the second tool, the minimum normalised delta-P value at a filter loading of 100% is around 16.5 kPa and the minimum normalised delta-P value at a filter loading of 0% is around 13.2 kPa. FIG. 9 shows this difference 908 in the minimum normalised delta-P value for a filter loading of 0% when using the first tool and when using the second tool by way of an arrow. In some examples, this difference in minimum normalised delta-P values at the same filter loading value may be used to determine when a tool which is attached to the device is changed.

[0114] FIG. 10 shows a plot of filter loading values, on the y-axis, and minimum normalised delta-P values on the x-axis. FIG. 10 shows a first filter loading curve 1002 which corresponds to the first tool and a second filter loading curve 1004 which corresponds to the second tool. FIG. 10 illustrates how a minimum normalised value of delta-P maps to a given filter loading value for the first tool and the second tool. FIG. 10 shows the difference 908 between the minimum normalised delta-P values for the first tool and the second tool at a filter loading value of 0%. As described above, typically values of the filter loading change gradually as the filter gathers more dirt during use of the device. Accordingly, sudden relatively large changes in a determined value of the filter loading may be generally not expected to occur unless an operating condition of the device changes. If such a sudden change is detected, then in some examples, this change may be taken to indicate a change in an operating condition of the device. For example, a detected sudden change in a determined value of the minimum normalised delta-P may be taken to be indicative of a change in the tool which is attached to the vacuum cleaner. For example, if the measured minimum normalised delta-P value changes by the difference 908 over a relatively short period of usage of the device, this may be taken to indicate that the vacuum cleaner has transitioned from an operating state in which the first tool is attached to an operating state in which the second tool is attached. Further, the correct filter loading curve to be used to relate minimum normalised delta-P values to filter loading values can be determined based on the type of tool which is attached to the device, e.g. if it is known which type of tool is attached to the device. For example, after a detected change 908 in the determined minimum normalised delta-P value, the device may move from determining the value of filter loading using the first filter loading curve 1002 to determining the value of filter loading using the second filter loading curve 1004.

[0115] FIGS. 11A and 11B show examples of probability distributions 1102, 1104 of normalised delta-P values when the device 200 is in use with a given tool, e.g. with the first tool. FIG. 11A corresponds to the vacuum cleaner operating with a filter loading value of 0%. FIG. 11B corresponds to the vacuum cleaner operating with a filter loading value of 100%. In an example, to determine such a probability distribution, a fixed number of counters is defined, e.g. 100 counters may be defined. Two one-dimensional arrays are defined, a pressure bin array and a FIFO, first in, first out, array. The FIFO array has a length equal to the fixed number of counters. A value of delta-P is measured and normalised. A counter is added to the pressure bin corresponding to the measured and normalised value. Once all of the counters have been allocated to bins, with the next measurement of normalised delta-P, the oldest allocated counter, which may be the counter in the final position of the FIFO array, is moved to the bin corresponding to the latest measured normalised delta-P value. In this way, a permanent rolling distribution can be maintained. The rolling distribution may be queried at any time and at any frequency. In the example where the minimum value of normalised delta-P is the value which is determined and used to indicate the filter loading value, the lowest populated bin is determined in order to determine the minimum value of normalised delta-P. In some examples, a minimum counter threshold may be set under which counters in a bin are not tallied, such that the lowest populated bin is the lowest bin with at least the threshold number of counters. This may act as a noise filter. In some examples, the distribution may be filtered, e.g. by determining an exponential moving average, to further remove noise. In other examples, the FIFO array may not be defined and, for example, once all of the counters have been allocated, the counters may be removed from the pressure bins and the allocation of counters may start again.

[0116] FIGS. 11A and 11B show, by way of example, minimum normalised delta-P values 1106 of the distributions 1102, 1104 which are indicative of filter loading values of 0% and 100% respectively. FIGS. 11A and 11B also show by way of example a threshold counter value 1108 below which counters are not tallied for the purposes of determining the lowest populated bin.

[0117] The above example has been described with reference to two particular tools. However, it will be appreciated that various different types of tool may be used with the device 200 and that each of these different tools may have an associated probability distribution of inlet restriction values which may be used in a method of determining a value of the filter loading of the device 200. Moreover, the inlet restriction probability distribution of a given tool may vary depending on the usage. However, providing a given property of the probability distribution, e.g. the minimum level of inlet restriction, does not change, the given property may be used to determine the filter loading regardless of other variations in the overall probability distribution.

[0118] Although in certain examples described above, the minimum value of the second operating parameter is the value used to indicate the value of the level of the filter loading, in other examples other values of the second operating parameter may be used to indicate the filter loading value. For example, a different property other than the minimum of a probability distribution of the second operating parameter, such as an arithmetic mean, mode or other property, may be determined and used as the value of the second operating parameter which indicates the filter loading value.

[0119] Examples of the above-described method may allow for the filter loading value to be determined based on a correspondence between filter loading values and an operating parameter of the motor. This may in some examples allow for the filter loading value to be determined without use of further additional sensors, such as pressure sensors upstream and downstream of the filter.

[0120] The value of the filter loading may be used for various purposes. For example, as described above, in certain examples, determining an inlet restriction value may require correcting for a filter loading value. In another example, the filter loading value may be used to provide an alert. For example, when the filter loading value reaches a given threshold an alert may be issued indicating that the filter should be washed or replaced.

[0121] The method 700 may also be performed a plurality of times, e.g. at regular intervals, during operation of the air-moving device. For example, the filter loading value may be determined at the same regular intervals as the operating parameter which is used to control the input power of the motor. As above, this may be the same operating parameter as the second operating parameter in some examples, e.g. both may be a delta-P.

[0122] FIG. 12 shows another example schematic representation of a motor assembly 1200. The motor assembly 1200 comprises features corresponding to those of the motor assembly 100 described above with reference to FIG. 1, which, where labelled, are labelled with like reference numbers. The pre-motor filter is not shown in FIG. 12, for the sake of clarity.

[0123] The motor assembly 1200 further comprises a second pressure sensor 1220 and wiring 1222 which electrically connects the second pressure sensor 1220 to circuit board 1214. The motor assembly 1200 further comprises an inlet tube 1226 providing a fluid connection, through housing 1224, from the second pressure sensor 1220 to an inlet 1230 of impeller 1208. This allows the second pressure sensor 1220 to take measurements of a pressure at the impeller inlet 1230. As can be seen by the schematic representation of FIG. 12, a cross-sectional area of the motor is narrower at the impeller inlet 1230 than at the motor inlet 1210.

[0124] FIG. 13 shows another example motor assembly 1300. The motor assembly 1300 is the same as the motor assembly 1200 of FIG. 12 with the exception that, in the motor assembly 1300 of FIG. 13, the second pressure sensor 1320 is located on the circuit board 1314. A channel or duct 1322 provides a fluid connection between the second pressure sensor 1320 and the impeller inlet 1330. The channel 1322 allows the second pressure sensor 1320 to take measurements of a pressure at the impeller inlet 1330 without the second pressure sensor being located at the impeller inlet 1330.

[0125] Such a channel may be provided by various means. In one example, the channel 1326 may be formed by a pipe. The pipe may, for example, extend along an exterior surface of the housing 1324 and extend through a hole 1326 in the housing to provide the fluid connection from the second pressure sensor 1320 to the impeller inlet 1330. At an end of the channel 1326 at which the second pressure sensor 1320 is located, an air-tight seal may be formed around the second pressure sensor 1320. The seal may, for example, comprise a circular, e.g. EPDM, foam seal sealing the pipe to a location on the circuit board 1314 at which the second pressure sensor 1320 is located. A similar seal may be formed around the second pressure sensor 1220 of the motor assembly 1200 of FIG. 12.

[0126] In another example the channel may be integral with the housing of the motor assembly. FIG. 14 shows an example schematic representation of such a housing 1424 with a channel 1422 extending through the housing 1424. In such an example, the housing 1424 may be formed by an injection moulding process, with the channel through the housing 1424 formed during the injection moulding, e.g. by the use of removable pins 1430a, 1430b during the injection moulding. In use, in the manner described with reference to FIG. 13, a hole 1426 through the housing 1424 opens into an impeller inlet of the motor. In use, the second pressure sensor is located at an upstream end 1428 of the channel 1422. This provides a fluid connection via the channel 1422 to the second pressure sensor and allows the second pressure configured to take pressure measurements of the pressure at the impeller inlet. This may allow the second pressure sensor to be conveniently located. The second pressure sensor may, for example, be located on a circuit board of the device. Further, forming the channel 1422 integrally with the housing 1424 may be cost effective and convenient.

[0127] In another example, the channel may be formed between an exterior surface of the housing and a mount located against the exterior surface of the housing. FIG. 15 schematically illustrates such an example. In FIG. 15, a mount 1532, e.g. made of rubber, has a groove 1534 therein. The mount 1532 seals in an air-tight manner against an exterior surface of the housing 1524 which has a hole 1526 which, in use, leads to the impeller inlet. A channel 1522 is created by a gap provided by the groove 1534 in the mount 1532 between the mount 1532 and the exterior surface of the housing 1524. In both of the examples of FIG. 14 and FIG. 15, in use, the second pressure sensor is sealed in an air-tight manner to the channel 1422, 1522 at the upstream end 1428, 1528 of the channel 1422, 1522. For example, in the example of FIG. 15, the mount 1532 may be a rubber mount which forms a seal around the second pressure sensor.

[0128] In each of the example motor assemblies 1200, 1300, the first pressure sensor 1218, 1318 is positioned to take pressure measurements at the air inlet 1210, 1310. The pressure measurements taken by the first pressure sensor 1218, 1318 include an ambient pressure p.sub.a which is measured prior to start-up of the motor. Further, the pressure measurements taken by first pressure sensor 1218, 1318 include measurements of a first pressure p.sub.1 taken during running of the motor. The temperature sensor 1216, 1316 is configured to measure an ambient temperature T.sub.a. The second pressure sensor 1220, 1320 is configured to take pressure measurements of a second pressure p.sub.2 at the impeller inlet 1230, 1330 during running of the motor. Each of the ambient pressure p.sub.a, the first pressure p.sub.1 and the second pressure p.sub.2 are absolute pressures.

[0129] In an example, measurements taken by the first pressure sensor 1218, 1318 the second pressure sensor 1220, 1320 and the temperature sensor 1216, 1316 are used to determine a dynamic pressure value. In one example, a dynamic pressure measurement is determined as follows.

[0130] A gauge static pressure p.sub.static in the motor is determined by subtracting the ambient pressure p.sub.a from the first pressure p.sub.1. The first pressure p.sub.1 is typically lower than the ambient pressure p.sub.a because the running of the motor causes a partial vacuum to be generated within the motor housing 1324.

[0131] A gauge total pressure p.sub.total at the impeller inlet is determined by subtracting the second pressure p.sub.2 from the first pressure p.sub.1. The total pressure p.sub.total at the impeller inlet is made up of the static pressure p.sub.static and a dynamic pressure p.sub.dyn. The second pressure p.sub.2 is typically lower than the first pressure p.sub.1 due to the lower cross-sectional area and associated higher air velocity at the impeller inlet 1230, 1330 as compared with at the motor inlet 1210, 1310.

[0132] The dynamic pressure p.sub.dyn at the impeller inlet 1230, 1330 is determined by subtracting the static pressure p.sub.static in the motor from the total pressure p.sub.total at the impeller inlet 1230, 1330. The dynamic pressure p.sub.dyn may also be referred to as an air velocity pressure.

[0133] The dynamic pressure p.sub.dyn, the first pressure p.sub.1 and the temperature T.sub.a are input into a density ratio formula to determine the dynamic pressure value at STP p.sub.dyn@STP. The value of p.sub.dyn@STP is a dynamic pressure value corrected to standard temperature and pressure. Accordingly, the dynamic pressure value is normalised for the ambient conditions in which the motor is operating. This allows, for example, a single look-up curve to be defined relating dynamic pressure values to airflow rates or other parameters. The applicable density ratio for a given motor may depend on a type of the motor. For example, the following density ratio formulae (1) to (3) apply, respectively, for constant power motors, AC series motors, and constant speed motors:

[00001]$\begin{array}{cc}{p}_{\mathrm{dyn}@\mathrm{STP}}={p_{\mathrm{dyn}}\left(\left(\frac{p_1}{101.325}\right)\left(\frac{293}{T_a+273.15}\right)\right)}^{-\left(\frac{2}{3}\right)}& \left(1\right)\end{array}$$\begin{array}{cc}{p}_{\mathrm{dyn}@\mathrm{STP}}={p_{\mathrm{dyn}}\left(\left(\frac{p_1}{101.325}\right)\left(\frac{293}{T_a+273.15}\right)\right)}^{-\left(\frac{5}{6}\right)}& \left(2\right)\end{array}$$\begin{array}{cc}{p}_{\mathrm{dyn}@\mathrm{STP}}={P_{\mathrm{dyn}}\left(\left(\frac{p_1}{101.325}\right)\left(\frac{293}{T_a+273.15}\right)\right)}^{-\left(1\right)}& \left(3\right)\end{array}$

where p.sub.dyn@STP, p.sub.1, and p.sub.dyn are in units of kPa, T.sub.a is in units of degrees Celsius, 101.325 is standard pressure in units of kPa, 293 is standard temperature in units of Kelvin and 273.15 is 0 degrees Celsius in units of Kelvin.

[0134] A determined dynamic pressure value may be mapped to various parameters. For example, the dynamic pressure value may be used as an operating pressure in examples of the methods described above. For example, dynamic pressure values may be mapped to values of inlet restriction and/or filter loading, e.g. in a similar manner to that described above for delta-P values. Additionally, or alternatively, the dynamic pressure value may be mapped to values of airflow rate through the motor. The airflow rate may be used as an operating parameter in example methods described above. The mapping of dynamic pressure values to airflow rate may be determined, for example, by a calibration process. In such a calibration process, the air-moving device may be operated with an airflow rate measuring apparatus, which may comprise a bell mouth, a venturi, or an orifice plate, being used to measure the airflow rate through the device while at the same time measurements are taken which allow dynamic pressure values to be determined which can be corresponded with airflow measurements. Accordingly, when the device is operated after calibration, dynamic pressure values may be determined and mapped to airflow rate values in order to determine the airflow rate through the device in use.

[0135] The above embodiments are to be understood as illustrative examples of the invention. Other embodiments are envisaged. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.