Patent Description:
Vacuum cleaners are often used in workshops to make sure waste particles are not dispersed into the air or distributed over the surfaces of the workshops. Some vacuum cleaners are rated to maintain a specific airflow velocity in order to remove potentially harmful particles for the user.

For example, an H class vacuum cleaner is rated for collection of dust hazardous to health and the airflow velocity is maintained above <NUM>/s in the suction hose.

This means that the vacuum cleaner must detect the airflow velocity to ensure it is compliant with the relevant safety regulations. One known method of determining the air velocity in a vacuum cleaner is with differential pressure sensors (as disclosed in <CIT>). However, pressure sensors are expensive, sensitive to shocks, and susceptible to failure. This means that the vacuum cleaner must be repaired before being safe to use in a hazardous environment.

Examples of the present disclosure aim to address the aforementioned problems.

According to an aspect of the present disclosure there is a method of determining an airflow parameter in a vacuum cleaner comprising a motor-fan assembly comprising: receiving one or more signals relating to one or more operational parameters of the motor; determining a torque of a rotatable shaft of the motor based on the one or more operational parameters; and determining an airflow parameter based on the determined torque of the rotatable shaft of the motor.

Optionally, the receiving one or more signals relating to one or more operational parameters comprises receiving one or more signals relating to one or more operational electrical parameters of the motor-fan assembly during operation of the motor-fan assembly.

Optionally, the receiving one or more signals comprises receiving a signal relating to the voltage.

Optionally, the receiving one or more signals comprises receiving a signal relating to the current.

Optionally, the method comprises determining the power based on the received signals relating to the current and the voltage.

Optionally, the determining the torque is based on the determined power.

Optionally, the method comprises determining the rotational speed of the motor.

Optionally, the determining the speed is based on a received signal from a motor rotational speed sensor and / or the motor.

Optionally, the method comprises determining one or more other operational parameters of the motor-fan assembly in dependence of the received one or more signals and / or stored parameter information of the motor-fan assembly.

Optionally, the determining one or more other operational parameters of the motor-fan assembly comprises determining an efficiency of the motor-fan assembly.

Optionally, the determining the efficiency of the motor-fan assembly comprises receiving a stored efficiency parameter for the motor-fan assembly.

Optionally, the determining the efficiency of the motor-fan assembly comprises determining the efficiency parameter for one or more actuating variables of the motor-fan assembly.

Optionally, the determining the airflow parameter is based on the determined torque and the determined efficiency of the motor-fan assembly.

Optionally, the functional relationship between the airflow and the torque is predetermined.

Optionally, the method comprises determining that the airflow parameter is below a first threshold value.

Optionally, the method comprises issuing an alert to a user in dependence of the determining that the airflow parameter is below the first threshold value.

Optionally, the method comprises initiating a filter cleaning procedure in dependence of the determining that the airflow parameter is below the first threshold value.

Optionally, the filter cleaning procedure comprises reversing the motor-fan assembly such that the direction of airflow reverses through a filter.

Optionally, the method comprises that the airflow parameter is above a second threshold value.

Optionally, the method comprises modifying the operational electrical parameters to reduce the airflow flow parameter below the second threshold value.

Optionally, the airflow parameter is air velocity.

In another aspect of the present disclosure there is provided a vacuum cleaner comprising: a motor-fan assembly; at least one sensor for measuring one or more operational parameters of the motor during operation of the motor-fan assembly; a controller configured to receiving signals from the at least one sensors, wherein the controller is configured to: determine a torque of a rotatable shaft of the motor based on the one or more operational parameters; and determine an airflow parameter based on the determined torque of the rotatable shaft of the motor.

In yet another aspect of the present disclosure there is provided a controller for a vacuum cleaner, the controller comprising: at least one communication port configured to receiving signals from the at least one sensors, wherein the controller is configured to: determine a torque of a rotatable shaft of the motor based on the one or more operational parameters; and determine an airflow parameter based on the determined torque of the rotatable shaft of the motor.

In another aspect of the present disclosure there is provided a method of controlling a power tool comprising a motor comprising: receiving one or more signals relating to one or more operational parameters of the motor; determining a torque of a rotatable shaft of the motor based on the one or more operational parameters; determining that the torque of the rotatable shaft of the motor exceeds or drops below a threshold value; and issuing a control signal to the power tool in dependence of the determined torque exceeding or dropping below the threshold value. The power tool may be a rotary power tool such as a drill or hammer drill.

Various other aspects and further examples are also described in the following detailed description and in the attached claims with reference to the accompanying drawings, in which:.

<FIG> shows a side view of a vacuum device <NUM> according to an example. In some examples, the vacuum device <NUM> is a vacuum device <NUM> arranged to be used on a construction site or in a tool shop e.g. a workshop vacuum device <NUM>. In some examples, the vacuum device <NUM> is a wet-dry vacuum cleaner. However, in other examples the vacuum device <NUM> is any other type of vacuum device <NUM> such as an upright vacuum cleaner, a stickvac, a handheld vacuum cleaner, a canister vacuum cleaner, or any other type of vacuum cleaner.

The vacuum device <NUM> comprises a housing <NUM>. The housing <NUM> comprises a lower housing portion <NUM> and an upper lid portion <NUM>. The upper lid portion <NUM> is securable to the lower housing portion <NUM> with one or more latches (not shown). The upper lid portion <NUM> can be separated from the lower housing portion <NUM> to empty the vacuum device <NUM>. Furthermore, the upper lid portion <NUM> can be removed from the lower housing portion <NUM> to conduct maintenance and cleaning of the vacuum device <NUM>.

The lower housing portion <NUM> comprises a collection chamber <NUM> for receiving, dirt, debris and / or liquid entrained in the dirty airflow. In some examples, the collection chamber <NUM> may possess any dimensions and shapes suitable for receiving debris and / or liquid.

In the example as shown in <FIG>, the lower housing portion <NUM> and the collection chamber <NUM> are generally cylindrical. In another example, the collection chamber <NUM> may possesses a generally frustoconical shape. Additionally or alternatively, the collection chamber <NUM> may include one or more curved side walls <NUM>. In other examples, the vacuum device <NUM> can comprise any suitable shape. For example, the vacuum device <NUM> can be an elongate shape whereby the length of the housing <NUM> is greater than the height of the housing <NUM>.

Optionally, (although not shown in <FIG>), an interior surface of a base <NUM> of the lower housing portion <NUM> and the collection chamber <NUM> may be generally concave. For example, the bottom of the lower housing portion <NUM> and the collection chamber <NUM> may possess a slightly upward curve to, e.g., prevent the collection chamber <NUM> from sagging when filled with a predetermined amount of debris and / or liquid.

The vacuum device <NUM> comprises a motor-fan assembly <NUM> mounted within the housing <NUM>. The motor-fan assembly <NUM> comprises a motor <NUM> and a fan <NUM> is mounted on a rotatable motor shaft <NUM> (as shown in <FIG>). The motor-fan assembly <NUM> is arranged to generate a negative pressure and create an airflow.

In the examples as shown in <FIG>, the fan <NUM> is mounted directly to the rotatable motor shaft <NUM> of the motor <NUM>. However, in other examples, the rotatable motor shaft <NUM> can be coupled to a gearbox (not shown) configured to transmit rotation to a drive shaft (not shown) and the fan <NUM> is mounted on the drive shaft. In this way, the gearbox can step up or step down the rotational speed of the drive shaft with respect to the rotational speed of the rotatable motor shaft <NUM>.

The generated airflow air is configured to move along an airflow path between a dirty air inlet <NUM> and a clean air exhaust outlet <NUM>. In some examples, the clean air exhaust outlet <NUM> is a plurality of holes in the housing <NUM> e.g. the upper lid portion <NUM>. In other examples, the clean air exhaust outlet <NUM> can be any hole, slot, or orifice in the housing <NUM> to let the clean air exhaust out of the vacuum device <NUM>. The collection chamber <NUM> is positioned along the airflow path and arranged to capture debris, dirt and / or liquid droplets entrained in the dirty airflow. The captured dirt, debris, liquid droplets etc (and other debris) collects at the bottom of the collection chamber <NUM>.

As shown in <FIG>, the upper lid portion <NUM> houses a motor-fan assembly <NUM> configured to generate an airflow. The motor-fan assembly <NUM> in some examples is electrically connected to a power source <NUM> (as shown in <FIG>). In some examples, the power source <NUM> is an AC power source e.g. a mains power supply. In some other examples the power source <NUM> is a DC power source e.g. a battery. In some examples, the power source <NUM> is a mains power supply. In some examples, the motor-fan assembly <NUM> is additionally or alternatively electrically connected to a battery (not shown).

In some examples, the vacuum device <NUM> comprises one or more filters <NUM> which is mounted to the upper lid portion <NUM>. The filter <NUM> is positioned such that the filter <NUM> is positioned on the airflow path between the dirty air inlet <NUM> and the clean air exhaust outlet <NUM>.

In some examples, the filter <NUM> is optionally removably mounted on a safety valve <NUM>. The safety valve <NUM> is arranged to prevent liquid from overflowing form the collection chamber <NUM> into the upper lid portion <NUM> when the vacuum device <NUM> is operated in a "wet mode". The safety valve <NUM> is known and will not be discussed any further. In order to prepare the wet-dry vacuum device <NUM> for wet mode operation, the filter <NUM> is removed from the safety valve <NUM>. The arrangement of the vacuum device <NUM> as shown in <FIG> is with the filter <NUM> and the vacuum device <NUM> is operable in a "dry mode".

Referring back to <FIG> again, the upper lid portion <NUM> comprises one or more electrical and electronic components of the vacuum device <NUM>. Whilst <FIG> shows the one or more electrical and electronic components mounted in the upper lid portion <NUM>, the one or more electrical and electronic components can be mounted anywhere within the housing <NUM>.

In some examples, the vacuum device <NUM> comprises a control panel <NUM> having one or more actuators <NUM> (e.g., a control knob) operable to control the operational parameters of the device. For example, the control panel <NUM> is configured to control the power (ON/OFF) with a main ON/OFF switch (not shown) and the fan speed of the motor-fan assembly <NUM> with a fan control speed dial (not shown). The control panel <NUM> may optionally further include one or more power outlets <NUM> or other power connections (not shown). In this way, a power tool (not shown) can be connected by a power cord and receive electrical power from the vacuum device <NUM>. The electrical components may be controlled via a circuit board or a controller <NUM> mounted in the housing <NUM>.

In another example, the controller <NUM> is mounted within the housing <NUM> of the motor <NUM> e.g. inside the motor can housing (not shown). In this way, the motor <NUM> and the controller <NUM> are a unitary component.

In some other examples, the controller <NUM> is mounted to the interior surface of the control panel <NUM> on the upper lid portion <NUM>. In some other examples, the controller <NUM> is mounted in any other location within the housing <NUM>. The controller <NUM> may be implemented on hardware, firmware or software operating on one or more processors or computers. A single processor can operate the different functionalities or separate individual processors, or separate groups of processors can operate each functionality.

Turning to <FIG>, the controller <NUM> will be discussed in further detail. <FIG> shows a schematic diagram of the controller <NUM> and the vacuum device <NUM>.

The controller <NUM> is configured to control the motor-fan assembly <NUM> to change the torque on the rotatable motor shaft <NUM> and the airflow speed generated by the fan <NUM> as discussed hereinafter.

The controller <NUM> is connected to one or more sensors configured to detect one or more operating electrical parameters of the motor <NUM>. In some examples, the controller <NUM> is connected to a voltage sensor <NUM> and a current sensor <NUM> for respectively detecting the voltage across the motor <NUM> and the current through the motor <NUM>. In some examples, the voltage sensor <NUM> and the current sensor <NUM> are mounted within the housing of the motor <NUM> e.g. inside the motor can housing. In this way, the motor <NUM> and the voltage sensor <NUM> and the current sensor <NUM> are a unitary component.

The controller <NUM> is configured to receive at least one signal relating to one or more operational parameters of the motor <NUM> during operation of the motor-fan assembly <NUM> as show in step <NUM> of <FIG> shows a flow diagram of a control process implemented in the controller <NUM>.

In some examples, the controller <NUM> is configured to receive a plurality of signals relating to one or more operational electrical parameters of the motor <NUM> during operation of the motor-fan assembly <NUM>.

The controller <NUM> then determines one or more operational electrical parameters of the motor-fan assembly <NUM> based on the received signals as shown in step <NUM> of <FIG>. For example, the controller <NUM> determines the voltage and the current respectively from the received signals from the voltage sensor <NUM> and the current sensor <NUM>.

In this way, the controller <NUM> receives a signal from the voltage sensor <NUM> and a signal from the current sensor <NUM> during operation of the motor-fan assembly <NUM>. In some examples, the voltage sensor <NUM> and the current sensor <NUM> periodically send the signals to the controller <NUM>. In other examples, the voltage sensor <NUM> and the current sensor <NUM> constantly send the signals to the controller <NUM>. The voltage sensor <NUM> is configured to send information relating to the voltage across the motor <NUM> during operation to the controller <NUM>. The current sensor <NUM> is configured to send information relating to the current through the vacuum device <NUM> during operation to the controller <NUM>.

In some examples, the controller <NUM> is configured to determine one or more other operational parameters of the motor-fan assembly <NUM> as shown in step <NUM> in <FIG>. The other operational parameters of the motor-fan assembly <NUM> can be any parameters of the motor-fan assembly <NUM> that can affect the functionality of the motor-fan assembly <NUM> during operation.

In some examples, the controller <NUM> is optionally connected to a speed sensor <NUM>. In some examples the speed sensor <NUM> is a hall sensor configured to detect each revolution of the motor <NUM>. In some alternative examples, the speed sensor <NUM> can be an optical sensor or any other suitable sensor configured to detect rotation of the motor <NUM>, the rotatable motor shaft <NUM>, or the fan <NUM> etc. The speed sensor <NUM> is configured to send a signal to the controller <NUM>. The controller <NUM> is configured to determine the rotational speed of the motor <NUM> in dependence of the received signal from the speed sensor <NUM>.

In some examples, the controller <NUM> is not connected to a speed sensor <NUM> and instead, the controller <NUM> receives information from a look-up table stored in memory (not shown) relating to the speed of the motor <NUM>. For example, the controller <NUM> can receive estimated speed information based on the voltage and current signals during operation.

Alternatively the controller <NUM> receives a signal from the motor <NUM> corresponding to the number of times the rotatable motor shaft <NUM> rotates with respect to the poles (not shown). Similarly, the controller <NUM> determines the rotational speed of the rotatable motor shaft <NUM> based on the signal received from the motor <NUM>. In some examples, the controller <NUM> determines the rotation speed of the motor shaft <NUM> based on the voltage, current and model of the motor <NUM> and the vacuum device <NUM>. In this example, the motor <NUM> may be an AC induction motor. In some other examples, the rotation speed and position of the motor shaft <NUM> may be determined by the controller <NUM> via other sensorless algorithms.

For example, the motor <NUM> may be a BLDC (brushless DC) motor, an induction motor, an ASM (asynchronous motor) or any other motor which generates a back EMF. The rotation speed and position of the motor shaft <NUM> may optionally be determined based on back EMF measurements or variation of the motor induction.

Alternatively in some other examples the motor <NUM> may be a brushed DC motor or an AC brushed motor. The rotational speed may be estimated based on the motor model and the measurement of the voltage and current.

In some examples, the controller <NUM> is configured to determine an efficiency parameter or efficiency factor µ of the motor <NUM> as shown in step <NUM> of <FIG>. The controller <NUM> is configured to determine the efficiency factor µ for one or more actuating variables of the motor <NUM> and / or motor-fan assembly <NUM>.

The controller <NUM> is the controller <NUM> receives information from a look-up table stored in memory (not shown) relating to the efficiency of the motor <NUM>. For example, the controller <NUM> determines the phase angle of the motor <NUM> during operation and receives information relating to the efficiency of the motor <NUM> based on the determined phase angle.

Alternatively, the controller <NUM> is configured to determine the efficiency of the motor <NUM> during a calibration operation based on operational parameters of the motor <NUM>. In some examples, the phase angle of the motor <NUM> is determined by the controller <NUM>. Alternatively, the information relating to the phase angle (°phase ) of the motor <NUM> is sent from the motor <NUM> to the controller <NUM>.

In some examples, the vacuum device <NUM> is powered by an AC voltage. Since the grid voltage Ugrid follows a sin wave, the controller <NUM> must determine the phase angle of the voltage in order to determine the electrical power Pelec. For example, the phase angle is the angle or the moment of the sin-wave of the voltage where the triac switches (not shown) on. The controller <NUM> is determines the°phase such that the controller <NUM> can control the power and speed of the motor <NUM>.

The controller <NUM> is configured to determine the phase angle for every half of the sine wave of the grid voltage Ugrid in order to determine how much power is delivered to the motor <NUM>. In some examples, the controller <NUM> is configured to determine the phase angle more frequently e.g. every quarter, sixth, eighth, or tenth etc. of the sine wave of the grid voltage Ugrid. Furthermore, the controller <NUM> determines the phase angle because this affects the power of the motor <NUM> and in turn the operation point of the motor <NUM>.

The operation point of the motor <NUM> is specific point within the operation characteristic of the motor-fan assembly <NUM>.

The efficiency factor µ depends on the operation point of the motor-fan assembly <NUM> and therefore the efficiency factor µ depends indirectly on the phase angle. In some examples, the phase angle is calculated by a motor control part (not shown) of the motor <NUM>. In this way, the controller <NUM> can be configured to receive information relating to the phase angle during operation of the motor <NUM>. In some other examples, the controller <NUM> is configured to measure and determine the phase angle.

In some examples, the vacuum device <NUM> optionally undergoes a calibration process. The one or more parameters of the vacuum device <NUM> are determined during the calibration process. An efficiency look-up table corresponding to the determined parameters of the vacuum device <NUM> during calibration are stored in a memory of the controller <NUM>. Alternatively, the look-up table is stored in the memory of the controller <NUM> without performing a calibration process in a factory set up process.

The controller <NUM> is configured to receive sensor information relating to the motor current and the motor voltage and motor speed. Based on the received motor current, motor voltage and motor speed, the controller <NUM> is configured to determine the efficiency of the motor by using the efficiency look-up table. Accordingly, the controller <NUM> is able to determine the efficiency of the motor <NUM> in real time or near real time.

In contrast, in some examples the motor-fan assembly <NUM> is powered by a DC power source <NUM>. In this case, the phase angle is constant and the efficiency factor is also constant.

In some examples, the controller <NUM> is configured to determine the operational electrical parameters of the motor-fan assembly <NUM> as shown in step <NUM> as follows.

The mechanical power Pmec is equal to the electrical power Pelec multiplied by an efficiency factor µ.

The average electrical power Pelec is determined by the product of the current I(i) and voltage U(i) which are sampled discretely at time intervals i. The controller <NUM> is configured to control the frequency of sampling the current and / or the voltage. In some examples, the controller <NUM> receives signals from the voltage sensor <NUM> and the current sensor <NUM> a plurality of times during a half wave of the grid frequency.

In some examples, the nominal power is calculated by the controller <NUM> over the sinus half wave of the grid voltage. The grid frequency is e.g. <NUM> and comprises two half waves and the controller <NUM> is configured to received signals comprising measured voltage values and current values in one halve wave several times. This means that the controller <NUM> can determine a good estimation of the electrical power. With an adequate number k of samples per half-wave the controller <NUM> is configured to update active power calculation by summation and averaging of the instantaneous power each half-cycle of the mains frequency. In some examples, the number k of samples per half-wave is <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or any other suitable number of samples per half-wave needed to provide a good resolution for determining the power.

The mechanical power Pmech is determined by the torque M on the rotatable motor shaft <NUM> multiplied by the angular velocity ω of the rotatable motor shaft <NUM>. As mentioned above, n can be determined from the speed sensor <NUM>.

Accordingly, when equation [<NUM>] is combined with equation [<NUM>], for an AC power source <NUM>: <MAT>.

In contrast, if a DC power source <NUM> is alternatively used, then the efficiency µ may vary. The efficiency µ may be calculated in a similar way as described above except one or more parameters of the DC power source need to be considered e.g. duty cycle. For example, the following equation may be used: <MAT>.

As mentioned above, the controller <NUM> is configured to determine the efficiency factor µ for one or more actuating variables of the motor <NUM> and / or motor-fan assembly <NUM>. The one or more actuating variables may be the phase angle for an AC motor or a duty cycle for a DC brushless motor.

As mentioned above, the controller <NUM> either determines or receives a signal relating to the phase angle of the voltage across the motor <NUM>.

Where Ugrid is the voltage of the mains power source <NUM>, UADC is the voltage across an analog to digital converter (ADC) (not shown) and Uref is the reference voltage used by the ADC. R<NUM> and R<NUM> are the circuit resistances. Accordingly, Ugrid can be simplified to UADC multiplied by a factor A which corresponds to the specific characteristics of the circuit of the vacuum device <NUM>. The factor A can be calculated during factory setting or a calibration process of the vacuum device <NUM>.

Where I is the current through the motor <NUM>, and IADC is the digital value for the current.

Uoff is the offset voltage. The operational amplifier or Opamp (not shown) is configured to operate as a summing amplifier. This means the voltage over the shunt resistor is amplified with a fixed factor and fixed voltage is added to the Opamp output. Accordingly, an offset to the current is added in the circuit hardware. The controller <NUM> is configured to subsequently remove the current offset , VOp is the voltage in the Opamp, Rshunt is the resistance of the shunt in the circuit. Accordingly, I can be simplified to IADC multiplied by a factor B minus an offset factor b which corresponds to the specific characteristics of the circuit of the vacuum device <NUM>. The factors B , b can be calculated during a factory setting or a calibration process of the vacuum device <NUM>.

Rearranging [<NUM>] with [<NUM>] and [<NUM>] the following can be calculated by the controller <NUM>.

In this way using [<NUM>] and [<NUM>], the torque M can be determined by the controller <NUM> as shown in step <NUM> of <FIG>. In some examples, the controller <NUM> is arranged to use the following equation for the AC power source <NUM>: <MAT>.

Alternatively, the controller <NUM> can use the following equation for the DC power source <NUM>: <MAT>.

The velocity of the air vair in the vacuum device <NUM>, can be determined from torque M as a function of M by the controller <NUM> as shown in step <NUM> of <FIG>.

In some examples, the air velocity vair is a linear function of the torque M. In some examples, the linear function varies in dependence on the operation point of the turbine and motor, and so indirect to the phase angle. The linear relationship between air velocity vair and the torque M and be determined by the controller <NUM> during a factory setting or a calibration procedure.

Accordingly, in some examples, since the functional relationship between the torque and the air velocity vair can be predetermined e.g., in a calibration process, the controller <NUM> can determine the air velocity vair indirectly by determining only the torque M. In other words, the step <NUM> can be carried out before operation of the vacuum device <NUM> in a calibration process. Accordingly, the controller <NUM> may save processing power by only determining the torque during operation and then inferring the air velocity vair from the predetermined functional relationship between the torque and the air velocity vair.

Turning now to <FIG>, further operation of the vacuum device <NUM> and the controller <NUM> will now be discussed. <FIG> shows a graph of airflow of a vacuum device <NUM> over time representing different operational scenarios of the vacuum device <NUM>.

<FIG> shows three different scenarios of the vacuum device <NUM>. The three difference operational scenarios <NUM>, <NUM> and <NUM> are respectively labelled "<NUM>", "<NUM>" and "<NUM>" in circles in <FIG>.

Scenario <NUM> represents the vacuum device <NUM> with the motor-fan assembly <NUM> operating at maximum airflow but subsequently suffers a catastrophic failure. <FIG> shows a maximum air velocity <NUM> at which the vacuum device <NUM> is operating. In some examples, the maximum air velocity <NUM> can be the air velocity generated with the maximum operating speed of the fan <NUM>. Alternatively, the maximum air velocity <NUM> can be air velocity generated at the most efficient speed of the fan <NUM> with respect to the other parameters of the motor-fan assembly <NUM> and the other parameters of the vacuum device <NUM>.

In some examples, the vacuum device <NUM> is designed to operate over a minimum air velocity <NUM> represented by line <NUM>. In some examples, the minimum air velocity <NUM> is predetermined and corresponds to the air velocity to remove hazardous particles from a work environment. In some examples, the predetermined minimum air velocity <NUM> is <NUM>/s.

In some examples, the minimum air velocity <NUM> can be adjusted by the user. For example, the user can select the minimum air velocity <NUM> suited for a particular job. Alternatively, the minimum air velocity <NUM> is fixed and cannot be adjusted by the user. This means that the vacuum device <NUM> can be certified that the vacuum device <NUM> is rated to a particular standard e.g., H Class or M class.

In some examples, the controller <NUM> determines that an airflow parameter or the determined torque of the rotatable motor shaft <NUM> is below a threshold value as shown in step <NUM> in <FIG>. In some examples, the controller <NUM> determines when the airflow parameter is above or below the minimum air velocity <NUM>.

In some examples, the controller <NUM> determines that the vacuum device <NUM> is operating normally when the determined airflow velocity is between the minimum air velocity <NUM> and the maximum air velocity <NUM>. For example, the controller <NUM> determines that the air velocity is at the maximum air velocity <NUM> at the time T1. In this case, the controller <NUM> takes no action based on the determined airflow velocity. Accordingly, the method returns to step <NUM> and controller <NUM> continues determining the airflow velocity.

However, in some examples the vacuum device <NUM> ceases to operate normally. For example, in scenario <NUM> the fan <NUM> breaks, or the dirty air inlet <NUM> becomes blocked. In this case, the determined airflow will suddenly decrease and reduce to zero or below the minimum air velocity <NUM> at time T2. Accordingly, when the controller <NUM> determines that the air velocity has fallen below the minimum air velocity <NUM> in step <NUM>, the controller <NUM> can take one or more actions.

In some examples, the controller <NUM> can issue an alert to the user as shown in step <NUM> <FIG>. The controller <NUM> can display the alert in the form of a visual signal such as an LED (not shown) indicating operational status on the vacuum device <NUM>. Alternatively, the controller <NUM> can issue a display message (not shown) on the control panel <NUM>. Additionally, or alternatively, the controller <NUM> can send a signal to a loudspeaker to issue an audible warning. In this way, the user can receive information warning that the vacuum device <NUM> is not generating sufficient air velocity to remove hazardous particles from the workplace. Once the user receives the alert, the user can perform maintenance on the vacuum device <NUM> to clear the alert.

In some examples, the controller <NUM> is configured to determine the rate of change of the air velocity. The controller <NUM> can determine the type of operating issue with the vacuum device <NUM> depending on the how the air velocity changes over time. For example, in scenario <NUM>, the controller <NUM> is able to determine that there is a blockage or a fan <NUM> failure because the air velocity drops rapidly below the minimum air velocity <NUM> and possibly to <NUM>/s.

In scenario <NUM>, the filter <NUM> becomes blocked over time. At time T3 the controller <NUM> instructs the motor-fan assembly <NUM> to spin up to a fan speed for generating the maximum air velocity <NUM>. Thereafter, the vacuum device <NUM> operates normally. However, after a period of time, the air velocity gradually decreases. Accordingly, the controller <NUM> determines that the air velocity at time T4 is below the maximum air velocity <NUM> despite instructing the motor-fan assembly <NUM> to generate the maximum air velocity <NUM>. The controller <NUM> then determines that the air velocity drops below the minimum air velocity <NUM> at time T5.

The controller <NUM> can then issue an alert as previously discussed in reference to step <NUM>. Since the controller <NUM> has determined the air velocity has been gradually decreasing over time e.g., at T4 and T5, the controller <NUM> determines that the filter <NUM> has become clogged due to a buildup of dirt and debris during operation of the vacuum device <NUM>.

Accordingly, the controller <NUM> can include information about the type of error with the vacuum device <NUM> in the alert in step <NUM>. Additionally, or alternatively, the controller <NUM> can initiate a filter cleaning procedure based on the determination that the filter <NUM> has become clogged.

In some examples, the controller <NUM> sends a control instruction to the motor-fan assembly <NUM> to reverse the airflow through the filter <NUM> as shown in step <NUM> in <FIG>. The reversed airflow can dislodge the dirt and debris on the filter <NUM>. The air velocity will then return to the maximum air velocity <NUM> and the vacuum device <NUM> can return to normal operation. This automatic filter cleaning process is advantageous because the filter cleaning process only occurs when the filter <NUM> is blocked. This means that the vacuum device <NUM> does not need to carry out a filter cleaning process based on a timer expiring. Accordingly, the user does not experience as much disruption when using the vacuum device <NUM>.

In scenario <NUM>, the motor-fan assembly <NUM> is generating an airflow at an air velocity which is above the maximum air velocity <NUM>. At time T6, the controller <NUM> sends a control signal to the motor-fan assembly <NUM> to spin the motor-fan assembly <NUM> at the maximum air velocity <NUM>. However, at that time there is not much dirt or debris in the air and therefore there is less load on the fan <NUM>. This means that the motor-fan assembly <NUM> is generating an airflow at an air velocity which is above the maximum air velocity <NUM>. The controller <NUM> determines that the air velocity is above maximum air velocity <NUM> and sends a control instruction to reduce the speed of the motor-fan assembly <NUM> as shown at time T7 and step <NUM> as shown in <FIG>. Similarly, the controller <NUM> can determine that the air velocity is below minimum air velocity <NUM> and sends a control instruction to increase the speed of the motor-fan assembly <NUM>. For example, there is an increase amount of dirt or debris in the air and therefore there is more load on the fan <NUM>.

In this way, the controller <NUM> can perform a dynamic control on the motor-fan assembly <NUM> speed to control the air velocity within a predetermined range e.g., between the maximum air velocity <NUM> and the minimum air velocity <NUM>. Alternatively, the controller <NUM> can perform a dynamic control on the motor-fan assembly <NUM> speed to control the air velocity about a predetermined value e.g., the maximum air velocity <NUM>.

In general, the various examples of the disclosure may be implemented in hardware or special purpose circuits, software, logic, or any combination thereof. For example, some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor, or other computing device, although the disclosure is not limited thereto. While various aspects of the disclosure may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques, or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

The examples of this disclosure may be implemented by computer software executable by a data processor, such as in the processor entity, or by hardware, or by a combination of software and hardware. The data processing may be provided by means of one or more data processors. Further in this regard it should be noted that any blocks of the logic flow as in the Figures may represent program steps, or interconnected logic circuits, blocks and functions, or a combination of program steps and logic circuits, blocks, and functions.

Appropriately adapted computer program code product may be used for implementing the examples, when loaded to a computer. The program code product for providing the operation may be stored on and provided by means of a carrier medium such as a carrier disc, card, or tape.

The controller in some examples may comprise a memory. The memory may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory, and removable memory. The data processors may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multi core processor architecture, as non-limiting examples.

Some examples of the disclosure may be implemented as a chipset, in other words a series of integrated circuits communicating among each other. The chipset may comprise microprocessors arranged to run code, application specific integrated circuits (ASICs), or programmable digital signal processors for performing the operations described above.

Examples of the disclosures may be practiced in various components such as integrated circuit modules. The design of integrated circuits can be by and large a highly automated process. Complex and powerful software tools may be available for converting a logic level design into a semiconductor circuit design ready to be etched and formed on a semiconductor substrate.

Claim 1:
A method of determining an airflow parameter for a vacuum cleaner (<NUM>) comprising a motor-fan assembly (<NUM>) comprising:
receiving one or more signals relating to one or more operational parameters of the motor; and characterised by
determining a torque of a rotatable shaft (<NUM>) of the motor based on the one or more operational parameters;
determining an efficiency of the motor-fan assembly; and
determining an airflow parameter based on the determined torque of the rotatable shaft of the motor and the determined efficiency of the motor-fan assembly.