CN211751892U

CN211751892U - Anti-pollution face mask

Info

Publication number: CN211751892U
Application number: CN201921619383.5U
Authority: CN
Inventors: 苏伟; 陈伟忠; 孔涛
Original assignee: Koninklijke Philips NV
Current assignee: Koninklijke Philips NV
Priority date: 2018-09-27
Filing date: 2019-09-26
Publication date: 2020-10-27
Anticipated expiration: 2029-09-26
Also published as: WO2020064520A1; CN112770815A; JP6944089B1; CN112770815B; CN110947114B; EP3856360B1; JP2021529070A; EP3856360A1; CN110947114A

Abstract

The disclosed embodiments relate to anti-pollution masks. The mask described herein comprises: an air chamber; a filter for filtering air; a fan for drawing air from outside the air chamber into the air chamber interior and/or drawing air from inside the air chamber to the outside; means for determining a rotational speed of the fan; and a controller, characterized in that the controller is adapted to: deriving from the determined fan speed or change in fan speed a first value and a second value, the first value relating to depth of breathing when the mask is worn and the second value relating to rate of breathing when the mask is worn; and determining whether the mask is worn based on the first value and the second value. The mask provides reliable detection of whether it is being worn and requires only a small number of fan rotation signal samples, thus saving power.

Description

Anti-pollution face mask

Technical Field

The present disclosure relates to a contamination mask for providing filtered air to a wearer of a breathing apparatus with fan-assisted airflow.

Background

According to the World Health Organization (WHO), 400 million people die of air pollution every year. This problem stems in part from the outdoor air quality in cities. The worst of these is the indian cities, such as delhi, whose annual pollution levels exceed the recommended level by a factor of 10. It is well known that the annual average contamination level in Beijing is 8.5 times the recommended safety level. However, even in european cities like london, paris and berlin, the pollution level is higher than the WHO recommended level.

Since the problem does not improve significantly in a short time, the only way to solve this problem is to wear a mask that provides cleaner air by filtering. To improve comfort and effectiveness, one or two fans may be added to the mask. These fans are switched on during use and are typically used at a constant voltage. For efficiency and life reasons, these fans are typically electrically commutated brushless DC fans.

The benefit of using a powered mask by the wearer is that it relieves the lungs of slight strain caused by inhaling against the resistance of the filter in a conventional non-powered mask.

In addition, in conventional non-powered masks, inhalation also causes a slight negative pressure within the mask, resulting in leakage of contaminants into the mask, which may prove dangerous if toxic. The powered mask delivers a steady flow of air to the face and may, for example, provide a slight positive pressure, which may be determined by the resistance of the exhalation valve, to ensure that any leaks are outward rather than inward.

There are several advantages if the operation or speed of the fan can be adjusted. This may be used to improve comfort by more appropriate ventilation during inhalation and exhalation sequences, or may be used to improve electrical efficiency. The latter translates into longer battery life or increased ventilation. Both of these aspects require improvements to existing designs.

To adjust the fan speed, the pressure inside the mask may be measured and both the pressure and the pressure change may be used to control the fan.

For example, the pressure within the mask may be measured with a pressure sensor, and the fan speed may be varied based on the sensor measurement. Pressure sensors are very expensive and it is therefore desirable to provide an alternative method of monitoring the pressure within the mask. This pressure information may be used to control a fan within the power mask, but may also be used as part of any other fan-based system that requires pressure information.

The fan operated mask is a battery powered device and it is therefore desirable to reduce power consumption and cost as much as possible. One problem is that the fan may still be on when the mask is not being worn, which may result in unnecessary power consumption. Sensors dedicated to detecting when the mask is worn may be provided, but this may increase the cost of the breathing mask.

When the mask is donned, the user will typically activate a switch to turn on the fan. Switches can increase mask cost, take up space, and are inconvenient to switch on. The automatic electronic turn-on function avoids these disadvantages. However, this also typically requires a dedicated sensor for sensing mask usage.

It is therefore desirable to find a low cost solution for detecting the wearing of a mask, so as to be able to detect the transition from worn to unworn and/or from unworn to worn.

WO2018/215225 discloses a solution in which the rotation speed of the fan is used to represent a pressure measurement. The pressure or pressure variation is determined based on the rotational speed of the fan. Using this pressure information, it can be determined whether the mask is worn.

When a pressure change is detected to fall below a threshold, it is determined that the mask is not being worn and the fan may be turned off.

This method works well if the fan speed signal is sampled at a high sampling rate, since a detailed analysis of the signal can then be performed. However, it is preferable to use a lower sampling rate to save power.

In particular, if a low sampling rate is used, it may happen that the mask is closed even if it is still worn. If the system sampling rate is too low, a reliable respiration signal may not be obtained, although power consumption is low. For example, if the sampling rate is too low, short spikes in the respiratory signal during speech may be missed. Thereby possibly generating an erroneous shut down signal.

If the system sampling rate is too high, breathing can be tracked well, but background noise is also included and power consumption is high.

If the user is speaking, the user's breath may be much shallower than normal and therefore may not be detectable. Simply setting different thresholds may not be appropriate because even if the mask is not worn, the mask may be opened based on detection of a slight pressure change that is not a result of breathing.

EP0661071 discloses a device and method for automatic stop-start control in the delivery of Continuous Positive Airway Pressure (CPAP) therapy. When it is determined that the patient is wearing the mask, administration of CPAP therapy is initiated. Conversely, when it is determined that the patient is no longer wearing the mask, administration of CPAP therapy is stopped. In one example, whether the mask is worn may be determined based on an analysis of the current supply to the flow generator.

There remains a need for more accurate breath detection and a way to avoid processing large amounts of sampled fan rotation data.

SUMMERY OF THE UTILITY MODEL

According to an embodiment of one aspect of the present disclosure, there is provided a contamination mask, comprising:

an air chamber;

a filter, such as a filter that directly forms a boundary between the air chamber and the ambient environment outside the air chamber;

a fan for drawing air from outside the air chamber into the inside of the air chamber and/or drawing air from inside the air chamber to the outside;

means for determining a fan speed; and

a controller, the controller adapted to:

deriving a first value and a second value from the determined fan speed or change in fan speed, the first value being related to depth of breathing when the mask is worn and the second value being related to respiratory rate; and is

Determining whether the mask is worn based on the first value and the second value.

The first value is related to the depth of breath at the time the breath is detected, which means that there is a positive correlation between the first value and the depth of breath. The second value is related to the breathing rate at which breathing is detected, which means that there is a positive correlation between the second value and the breathing rate.

More generally, for example, the first value may relate to (i.e., be associated with) a magnitude of the pressure fluctuation across the fan (whether the pressure fluctuation is caused by breathing or not), and for example, the second value may relate to (i.e., be associated with) a rate of the pressure fluctuation (whether the rate of the pressure fluctuation is caused by breathing or not). By "pressure fluctuation rate" is meant the periodic pressure fluctuation rate caused by respiration, not the instantaneous pressure change rate. When the mask is worn and in normal use, the pressure fluctuations are caused by breathing, whereas when the mask is not worn, any detected pressure fluctuations will be caused by other factors.

The present disclosure relates to an anti-pollution mask. This means a device whose main purpose is to filter the ambient air breathed by the user. The mask does not undergo any form of patient treatment. In particular, the pressure levels and flows resulting from the fan operation are only intended to help provide comfort (by affecting the temperature or relative humidity within the air chamber) and/or to help provide airflow through the filter without significant additional respiratory effort by the user. The mask does not provide full breathing assistance compared to a situation where the user does not wear the mask.

In this system, fan speed (for a fan that drives air into and/or expels air from the chamber) may be used as a proxy for the pressure measurement. To measure the fan speed, the fan itself may be used, so that no additional sensors are required. In normal use, the chamber may be closed such that pressure fluctuations within the chamber have an effect on the load condition of the fan and thereby alter the electrical characteristics of the fan. Similarly, the fan electrical characteristics may determine the properties of the chamber, such as the volume of the chamber, and whether the chamber is open or closed.

To detect whether the mask is worn, the fan rotation signal is analyzed to avoid false positives (i.e., the mask is falsely detected as not worn) and false negatives (the mask is falsely detected as worn). This is achieved by taking into account the pressure fluctuation level, which is indicative of the depth of breathing when breathing is detected, and the rate of cyclic pressure fluctuation, which is indicative of the breathing rate when breathing is detected. This allows to detect not only normal breathing (as in the solutions that the applicant has proposed but not disclosed), but also the pressure fluctuations associated during speaking. Thereby enabling reliable detection of respiration at a lower sampling rate.

By determining whether the mask is worn, the mask design achieves power savings without requiring any additional sensors when the mask is not worn. In particular, if no pressure differential across the mask is detected, this is an indication that both sides are at atmospheric pressure and the mask is not being worn. In fact, there is no longer a closed or partially closed chamber, leaving the air chamber open to the atmosphere. If it is detected that the mask is not being worn, the fan may be turned off. A threshold may be set for this detection but erroneous detection results are avoided by additionally taking into account the rate of cyclic pressure fluctuations.

For example, the first value is the maximum swing of fan speed within the sampling window, and the controller is adapted to set the first threshold to the first value. This swing represents the degree of pressure fluctuation and, therefore, for breathing, is related to the depth of breathing.

The sampling window is selected to be sufficient to acquire at least one full breath cycle, for example 6 seconds, to acquire the full breath cycle at the lowest breath rate of 10 breaths/min. The data sampling rate within the window may be chosen as low as possible to save power and data processing. The sampling rate may be fixed so that the fastest breathing rate can be coped with. For example, for the fastest breath rate of 30 breaths/min, the sampling rate may be 2Hz (4 times the maximum breath rate).

However, an alternative is to sample the fan speed at a rate dependent on the second value when detecting a breath. This allows the lowest sampling rate to be maintained to save power,

for example, the first threshold value depends on the average fan speed. Thus, the change in fan speed caused by breathing may depend on the fan speed itself. A given breathing pattern may result in greater variations in fan speed as the fan is driven to a faster speed.

The average fan speed may be obtained from measurements of previous samples or may be known from a drive signal applied to the fan from a controller. Both of these options are intended to be included within the scope of the present disclosure.

For example, the second value is a frequency based on the time between successive maxima and minima of the fan speed. For breathing, i.e. half of the breathing cycle.

The controller may then be adapted to determine that breathing is detected and thus that the mask is worn when the first value exceeds the threshold and the second value is within a predetermined range. Therefore, in order to detect breathing, it is necessary to detect a specific depth of breathing and a specific range of breathing rates.

For example, the predetermined range is 12-30 cycles/minute, corresponding to a typical range of breathing rates.

The controller may be adapted to apply the following time periods: during this time period, breathing must not be continuously detected before it can be determined that the mask is not being worn. This reduces the risk of switching off the fan by mistake.

The filter, for example, directly forms a boundary between the air chamber and the ambient environment outside the air chamber. This provides a compact arrangement, avoiding the need for convection transport channels. This means that the user can inhale through the filter. The filter may have multiple layers. For example, the outer layer may form the body of the mask (e.g., a fabric layer), while the inner layer may be used to remove finer contaminants. The inner layer may then be removable for cleaning or replacement, but it is believed that the two layers together constitute a filter, as air is able to pass through the structure and the structure performs a filtering function.

Thus, the filter preferably comprises the outer wall of the air chamber and optionally one or more further filter layers. This provides a particularly compact arrangement and enables a large filtering area to be achieved, as the mask body performs the filtering function. Thus, when a user inhales, ambient air is provided directly to the user through the filter.

Maximum pressure used in air chambers, e.g. below 4cm H₂O, e.g. less than 2cm H₂O, e.g. below 1cmH₂O, higher than the pressure outside the air chamber. If a fan is used to provide increased pressure within the air chamber (e.g., flow into the air chamber during inhalation), only a small increase in pressure need be provided, e.g., to assist the user in inhaling.

The fan may be used only to draw air from inside the air chamber to the outside. In this way, the supply of fresh filtered air to the air chamber can be facilitated even during exhalation, thereby improving user comfort. In this case, the pressure within the air chamber may be always lower than the external (atmospheric) pressure, so that fresh air is always supplied to the face.

In one example, the fan is driven by an electronically commutated brushless motor, and the means for determining the speed of rotation comprises an internal sensor of the motor. Internal sensors have been provided in such motors to effect rotation of the motor. The motor may even have an output port on which the internal sensor output is provided. Thus, there is a port carrying a signal suitable for determining the rotational speed.

Alternatively, the means for determining the rotational speed may comprise a circuit for detecting a ripple of the power supply to the motor driving the fan. This ripple originates from the closing current through the motor coil, resulting in an induced variation of the supply voltage due to the limited impedance of the input voltage source.

The fan may be a two-wire fan and the circuitry for detecting the fluctuations comprises a high pass filter. The additional circuit requirements for motors that do not already have the proper fan speed output can be kept to a minimum.

The mask may also include an outlet valve for controllably venting the air chamber from the exterior. The outlet valve may comprise a passive pressure regulating check valve or an actively driven electrically controllable valve. This can be used to make the mask more comfortable. During inspiration, unfiltered air is prevented from being inhaled by closing the valve (actively or passively). During exhalation, the valve is opened to expel exhaled air.

The controller may be adapted to determine a breathing cycle and to control the controllable valve in dependence on a phase of the breathing cycle. Thus, pressure monitoring provides a simple way to determine the inspiratory phase, which can then be used to control the timing of the mask's vent valve, or to determine whether the mask is worn and used.

The controller may be adapted to switch off the fan during inhalation. This can be used to save power. If configured in this manner, turning off the fan during inhalation is desirable for users who have no difficulty breathing through the filter, power may be saved.

Thus, the system may enable the mask to operate in different modes and to close when the mask is not being worn.

The mask may further comprise:

a detection circuit for detecting an induced current or a voltage spike caused by rotation of the fan when the fan is not electrically driven; and

and a starting circuit for starting the electric drive of the fan in response to the output of the detection circuit.

This feature enables the fan to be activated by detecting an electrical spike caused by manual rotation of the fan while the mask is being worn. When the fan is not electrically driven, such rotation is caused, for example, by a user wearing the mask and breathing through the fan. These movements are then detected to provide automatic turning on of the fan. This approach does not require an active sensing mask to be worn, but rather, the sensing function is energized by the user's breathing. Sensing can be integrated in the fan circuit with low overhead and low power consumption.

In this way, the fan may be used as a sensor for detecting the transition of the mask from a worn state to a non-worn state and from a non-worn state to a worn state.

An example according to another aspect of the present disclosure provides a control method of a contamination prevention mask, including:

drawing gas into and/or out of an air chamber of a mask using a fan, the mask directly forming a boundary between the air chamber and an ambient environment outside the air chamber;

determining the rotating speed of the fan;

deriving a first value and a second value from the determined fan speed or change in fan speed, the first value being related to depth of breathing when the mask is worn and the second value being related to respiratory rate; and

The first value may be a maximum excursion of fan speed within a sampling window, and the method may comprise setting a first threshold to the first value, the second value may be a frequency based on a time between successive maxima and minima of fan speed, and the method may further comprise determining that breathing is detected and in turn determining that the mask is worn when the first value exceeds the threshold and the second value is within a predetermined range.

If it is detected that the mask is not being worn, the fan may be turned off.

Thus, the fan speed is used as a proxy for the pressure measurement or relative pressure measurement, and such proxy measurement is used to detect whether the mask is worn based on the depth of breathing and the breathing rate. Both of which must coincide with the user's breathing.

The method may include driving the fan with an electronically commutated brushless motor and determining the rotational speed with an internal sensor of the motor. Alternatively, the rotational speed may be obtained by detecting a ripple on the power supply supplied to the motor driving the fan. This can be applied to any type of motor, for example a conventional brushed DC motor.

The mask may include an electrically controllable valve for controllably venting the air chamber from the exterior. The breathing cycle may then be determined from the pressure monitoring system, and the method may include controlling the controllable valve according to a phase of the breathing cycle. Alternatively, the mask may simply have a pressure regulating relief valve.

Drawings

Embodiments of the present disclosure will be described in detail below with reference to the attached drawing figures, wherein:

fig. 1 shows a pressure monitoring system implemented as part of a mask;

FIG. 2 illustrates one example of components of a pressure monitoring system;

FIG. 3 shows the rotation signal during inspiration and expiration;

FIG. 4 shows a circuit for controlling current through one stator of a brushless DC motor;

FIG. 5 shows a detection circuit and a start-up circuit applied to the circuit of FIG. 4;

6A-6C illustrate different sampling options for sampling a fan rotation signal;

FIG. 7 illustrates pressure variations and fan speed variations for different breathing types including speech;

FIG. 8 shows pressure changes and fan speed changes during speech; and

FIG. 9 illustrates a first method of operating a mask and a second method of operating a mask.

Detailed Description

The present disclosure provides an anti-pollution mask. The fan speed or changes in fan speed are monitored and a first value related to the magnitude of the pressure fluctuation across the fan and a second value related to the rate of the cyclical pressure fluctuation are derived therefrom. Thereafter, whether the mask is worn may be determined based on the first value and the second value. This provides a reliable detection of whether the face mask is worn and requires only a small number of fan rotation signals to sample the data, thus saving power.

The first detection function is to provide fan speed monitoring (representative of pressure measurements) and use this to detect whether the mask is being worn, and in particular this enables detection of a transition from worn to unworn. The second detection function enables detection of a transition from not worn (and mask fan off) to worn.

The purpose of both detection functions is to avoid the need for significant power consumption from any sensor and without significant additional hardware complexity.

Fig. 1 shows a monitoring system implemented as part of a mask.

The figure shows a subject 10 wearing a mask 12, the mask 12 covering the nose and mouth of the subject. The purpose of the mask is to filter the air before the subject inhales it. To this end, the mask body itself serves as the air filter 16. Air is drawn into the air chamber 18 formed by the mask by inhalation. During inspiration, the outlet valve 22 (e.g., a check valve) closes due to the low pressure within the air chamber 18.

The filter 16 may be formed solely from the mask body, or may have multiple layers. For example, the mask body may include an outer cover formed from a porous fabric material that serves as a pre-filter. Inside the outer cover, the finer filtration layer is reversibly attached to the outer cover. The finer filter layer may then be removed for cleaning and replacement, and the outer cover may be cleaned, for example, by wiping. The housing also serves a filtering function, for example, to prevent large debris (e.g., dirt) from entering the finer filter, which is used to filter fine particulate matter. There may be more than two layers. The multiple layers together serve as the overall filter for the mask.

When the subject exhales, air is expelled through the outlet valve 22. The valve opens to enable easy exhalation, but closes during inhalation. The fan 20 assists in removing air through the outlet valve 22. Preferably, more air is expelled than is exhaled, thereby supplying additional air to the face. This increases comfort due to reduced relative humidity and cooling. During inspiration, unfiltered air is prevented from being inhaled by closing the valve. The timing of the outlet valve 22 is therefore dependent on the breathing cycle of the subject. The outlet valve may be a simple passive check valve operated by a pressure differential across the filter 16. However, it may alternatively be an electrically controllable valve.

If the mask is worn, only elevated pressure will be present in the chamber. In particular, the chamber is closed by the face of the user. When the mask is worn, the pressure within the closed chamber will also vary according to the subject's breathing cycle. A slight pressure increase will occur when the subject exhales, and a slight pressure drop will occur when the subject inhales.

If the fan is driven at a constant drive level (i.e., voltage), the different prevailing pressures will appear as different loads to the fan because there are different pressure drops across the fan. Such varying loads will result in different fan speeds.

The first detection function is based in part on the following recognition: the speed of the fan may be used to represent a pressure measurement across the fan. It is also based in part on the following recognition: the pressure level and the cycle frequency rate may be used to determine whether the mask is worn. The present disclosure combines these considerations to create a mask that can save power by closing when not worn and does not require complex or expensive additional sensors.

For a known pressure (e.g. atmospheric pressure) on one side of the fan, pressure monitoring enables the pressure, or at least the pressure change, on the other side of the fan to be determined. For example, the other side is a closed chamber and thus has a pressure different from atmospheric pressure. However, by detecting equal pressure on each side of the fan, it can be determined that the chamber is not closed, but is connected to atmospheric pressure on both sides.

Thus, this lack of variation in fan speed can be used to determine that the mask is not being worn and therefore not being used. This information can be used to turn off the fan to save power.

The applicant has proposed (but not yet published) a pressure monitoring system having means for determining the fan speed, and a controller for deriving pressure from the fan speed or detecting pressure changes. It is then also proposed to use this pressure information to determine whether the mask is worn.

The means for determining the rotational speed may comprise an already existing output signal from the fan motor, or a separate simple sensing circuit may be provided as an additional part of the fan. However, in either case the fan itself is used, so that no additional sensors are required.

Fig. 2 shows an example of components of the proposed pressure monitoring system. The same components as in fig. 1 are denoted by the same reference numerals.

In addition to the components shown in fig. 1, fig. 2 also shows a controller 30, a local battery 32, and a means for determining the fan speed 36.

The fan 20 includes fan blades 20a and a fan motor 20 b. In one example, the fan motor 20b is an electronically commutated brushless motor and the means for determining the rotational speed includes an internal sensor of the motor. Electronically commutated brushless DC fans have an internal sensor that measures the position of the rotor and switches the current through the coils in a manner that the rotor rotates. Therefore, internal sensors have been provided in such motors to enable feedback control of the motor speed.

The motor may have an output port on which the internal sensor output 34 is provided. Thus, there is a port carrying a signal suitable for determining the rotational speed.

Alternatively, the means for determining the rotational speed may comprise a circuit 36 for detecting a ripple on the power supply connected to the motor 20 b. This ripple originates from the closing current through the motor coil, resulting in an induced change of the supply voltage due to the limited impedance of the battery 32. For example, the circuit 36 includes a high pass filter so as to process only signals in the frequency band in which the fan is rotating. This provides a very simple additional circuit and is much less costly than conventional pressure sensors.

This means that the motor can be of any design, including a two-wire fan without built-in sensor output terminals. It will also work with DC motors with brushes.

The controller may use the rotational speed information to determine the breathing cycle based on the corresponding pressure information.

If the outlet valve 22 is an electronically switched valve, the breathing cycle timing information can be used to control the outlet valve 22 according to the phase of the breathing cycle. Thus, pressure monitoring provides a simple way to determine the inspiratory phase, which information can then be used to control the timing of the outlet valve 22 of the mask.

In addition to controlling the outlet valve, the controller may also turn off the fan during inspiration or expiration. The controller may also turn off the fan when it is detected that the mask is not being worn. This gives the mask different modes of operation and can thus be used to save power.

For a given drive level (i.e., voltage), the fan speed across the fan increases at a lower pressure due to the reduced load on the fan blades. This results in enhanced flow. Thus, there is an inverse relationship between fan speed and pressure differential.

This inverse relationship may be obtained during calibration or may be provided by the fan manufacturer. For example, the calibration process involves analyzing fan speed information over a period that indicates that the subject is regularly inhaling and exhaling with normal breathing. The acquired fan speed information may then be matched to the breathing cycle, and the threshold for distinguishing between inhalation and exhalation is then set accordingly.

Fig. 3 schematically shows rotor position (as measured sensor voltage) versus time.

The rotational speed may be measured from the frequency of the AC component of the DC voltage to the fan (caused by switching events in the motor). This AC component results from the change in current drawn by the fan, which is imposed on the impedance of the power supply.

Fig. 3 shows the signal during inspiration as curve 40 and the signal during expiration as curve 42. During exhalation, there is a decrease in frequency due to the increased pressure gradient resulting in an increased load on the fan. Thus, the observed frequency variation is caused by different fan performance during the breathing cycle.

During exhalation, the fan operates to force air out of the area between the face and the mask. This improves comfort as exhalation becomes easier. This also draws additional air to the face, reducing temperature and relative humidity. Between inspiration and expiration, the fan operation increases comfort as fresh air is drawn into the space between the face and the mask, thereby cooling the space.

During inspiration, the outlet valve closes (actively or passively), and the fan may be turned off to conserve power. This provides a mode of operation based on detection of the breathing cycle.

If the fan is turned off during part of the breathing cycle and thus does not provide pressure information, the precise timing of the inspiration phase and expiration phase can be inferred from the previous breathing cycle.

For fan assisted exhalation, power needs to be restored before the outlet valve opens again. This also ensures that the next inhalation-exhalation cycle remains in place and that sufficient pressure and flow are obtained.

Using this approach, power savings of approximately 30% can be easily achieved, thereby extending battery life. Alternatively, the power of the fan may be increased by 30% to improve efficiency.

Measurement of fan speed allows control for increased comfort with different fan and valve configurations.

In a fan configuration where the filter is in series with the fan, pressure monitoring may be used to measure the flow resistance of the filter, particularly based on the pressure drop across the fan and filter. This may be done during a period of time when the rear face mask is switched on and not yet worn to the face. This resistance can be used to represent the age of the filter.

A first detection function, as described above, utilizes a fan to provide a representative pressure measurement that is then used to detect that the mask is not being worn. The pressure information may also be used for many other functions as described above. This first detection function requires that the fan is active and thus able to detect a transition from being worn (fan on) to not being worn. When the mask is donned (or donned for the first time), the user may operate the manual switch to again activate the fan.

However, it is desirable to be able to turn the fan on automatically when the mask is worn for the first time or after any previous automatic shut-off. This may be achieved using a dedicated sensor, but this requires long periods of sensor activity, or at least periodic sensing operations. This would again complicate the mask and lead to undesirable power consumption.

The second detection function described above avoids the need for a main switch or any sensor. In effect, the fan itself again acts as a sensor. With special electronics, the sensing task can be performed even when the fan is off.

When a mask with a fan is worn on the face and the user starts breathing, the fan rotates even without turning on the fan as air is forced through the fan. The speed detection function is based on determining this rotation without using an additional sensor in case the fan is switched off. This signal is then used to turn on the fan for proper operation of the mask.

As described above, a fan using an electronically commutated brushless DC motor has an internal sensor that measures the position of the rotor and switches the current through the coils in such a way that the rotor rotates.

However, when the fan is off, there is no longer a signal related to the fan speed even if the fan is mechanically rotating.

Fig. 4 shows an H-bridge circuit which functions as an inverter to generate an alternating voltage flowing to the stator coil 50 from the DC power supplies VDD, GND. The inverter has a set of switches S1 to S4 to generate an alternating voltage across the coil 50.

When the fan is off, no electrical signal is available from the power supply lines VDD, GND. However, since the stator coil 50 moves relative to the magnet in the rotor when the fan is forced to rotate, an electrical signal is generated due to electromagnetic induction.

These inductive signals cannot be measured on the power supply line because the coil is connected to the electronic circuit, but the electronic circuit is normally deactivated when the fan is not driven in rotation. These signals can only be measured at the supply line if the electronic switch is connected in the correct way.

This problem can be solved by using a pulse generated directly on one pole of the stator coil.

This method will be described in conjunction with fig. 5.

The H-bridge circuit is disposed between the high voltage rail VDD + and virtual ground. Virtual ground GND is connected to the low voltage rail VDD-through transistor arrangement Q1.

The virtual ground may vary between VDD + and VDD-depending on the operating state of the circuit.

The fan has a switch control circuit 52, and the fan circuit including the switch, the coil, and the control circuit is connected to VDD + and GND as supply voltage lines. The control circuit provides switching signals to the switches, but these control signal lines are not shown to avoid confusion in fig. 5. For example, the control circuit includes a hall sensor for rotor position sensing.

One coil terminal Co1 provides an output to the detection circuit 54. A high-pass filter of a capacitor C1 and a resistor R1 is used between the detection circuit 54 and the coil terminal Co1 because of the presence of the superimposed DC voltage. The pulse from the high pass filter is rectified by diode D2 and causes charge to be stored in storage capacitor C2.

The storage capacitor establishes the base voltage of a transistor arrangement Q1 (shown as a Darlington bipolar transistor pair). The storage capacitor prevents the transistor arrangement from turning on and off quickly in phase with the pulses.

Once sufficient charge is stored on capacitor C2, transistor arrangement Q1 will turn on (creating a closed circuit) and the fan will begin to run as the supply voltage subsequently increases to full VDD + top VDD-voltage swing. This operation produces enough pulses to keep the fan running.

This provides a very simple implementation.

To turn off the fan using the circuit of fig. 5, for example, based on the detection that the mask is not being worn as described above, the base of the transistor arrangement Q1 may be driven to ground long enough to stop the fan from rotating. This may be accomplished using a turn-off circuit 51, such as a transistor that discharges capacitor C2.

For ultra low power, the switch Q1 may be replaced with a MOSFET and an optional gating amplifier. Digital logic circuitry may be used to route the coil rotation signal and the mask worn or unworn signal to the gate driver.

When the fan in FIG. 5 is off, all switches S1-S4 are open (no actuation). At this point there is no power supply.

The pulse charging capacitor C2 will raise the voltage of the base of Q1 and eventually turn it on. The level of virtual ground GND is then pulled down to VDD-. At this time, current may flow from VDD + to VDD-. This powers the coil and fan control circuitry 52 and the fan then begins to operate as long as there is sufficient voltage.

When C2 is charged and Q1 is turned on, the turn-off circuit 51 is used to discharge the capacitor C2 to stop the fan. For example, an npn transistor or a FET transistor may be used to short the capacitor C2. The short-circuit signal may be derived from the breathing pattern. If no frequency fluctuations are measured, the capacitor C2 is short-circuited to switch off the transistor arrangement and, because GND-rises, returns to the voltage VDD +, thereby lowering the supply voltage.

The present disclosure provides enhancements to the automatic shut down function described above, i.e., detection that the mask is not being worn. The detection of the mask not being worn is used in the same manner as described above, but the detection is more accurate while also achieving a low sampling rate of the fan rotation signal.

The present disclosure may be implemented using a system as shown in fig. 2, but using a different approach and thus using analysis performed by the controller.

As with the system described above, analysis of the fan rotation signal (by looking at the fan speed or changes in the fan speed) produces a first value that is related to the magnitude of the pressure fluctuations across the fan. The first value is related to the depth of breath when the first value is consistent with the respiration signal. The first value may comprise a difference between a maximum fan speed and a minimum fan speed within the sampling window. Furthermore, a second value is derived, which is related to the rate of the cyclic pressure fluctuation, i.e. which is related to the respiration rate when the second value coincides with the respiration signal.

In this application, the term "depth of breath" is generally used to refer to a quantity or flow rate characteristic associated with a particular type of breath, rather than a breath rate. For example, light breathing, speaking breathing, and normal breathing are discussed below as different breath types. For example, in the case where the subject is stationary, the light breathing type may be considered to have a low depth of breath. The normal breathing pattern has a greater depth of breath. One known measurement that may be used as a measure of such depth of breath is tidal volume, i.e. the volume per breath. However, as is clear from the above discussion, in one example, the first value may correspond to a pressure fluctuation across the fan. Thus, this is not an actual measurement of tidal volume, but provides similar correlation to different types of breathing as tidal volume measurements. Thus, the measurement "relates" to the depth of breath, as a tidal volume measurement is a measure of the depth of breath (and thus also relates to the depth of breath).

For example, if a large tidal volume is delivered in a given unit of time, the large tidal volume will correspond to a high flow rate, and thus a large pressure differential, and a large fan speed differential. If a small tidal volume is delivered within the same given time unit, the small tidal volume will correspond to a low flow rate, and thus a small pressure differential, and a small fan speed differential.

The rate of cyclic pressure fluctuations, and thus the rate of cyclic fluctuations in the fan rotation signal, corresponds to the respiration rate, since one breath corresponds to one complete cycle of pressure fluctuations across the fan, and thus one complete cycle of fan rotation signal fluctuations. Thus, the frequency based on the time between successive maxima and minima in fan speed is actually related to the breathing rate.

Accordingly, the specification and claims should be read accordingly.

The respiratory rate of normal adults ranges from 12-18 breaths/minute (BrPM). When the subject begins to exercise, the breathing rate also increases. In extremely high intensity activities, the respiration rate can reach 30 BrPM.

The sampling of the fan rotation signal needs to be performed at a rate sufficient to collect the changes produced by the breathing signal. In order to sample the fan rotation signal without distortion of the component due to breathing, the sampling rate should be at least 2 times the maximum signal frequency (fs ≧ 2fmax) according to Shannon sampling theory. Here, the maximum breathing frequency is 30BrPM, i.e., 0.5 Hz.

Therefore, one method is to set fs ≧ 2fmax ═ 1 Hz. Thus, in theory, a sampling rate of 1Hz may be used. However, in practice, a sampling rate of 1Hz is not sufficient.

FIG. 6A shows the fan speed signal (y-axis) over time (x-axis) for a sample period of 2s at 30 BrPM. The sampling rate is 1Hz and the sampling points may all be at zero fan speed.

Therefore, as shown in fig. 6B and 6C, a sampling rate of at least 2Hz is required. Thus, a 2Hz sampling rate is the minimum sampling rate of a 30BrPM respiratory signal.

Thus fs-4 f is obtained.

Here, fs is the minimum sampling rate and f is the real-time breathing rate.

There are two possible ways to set the sampling rate.

In practice, the breathing frequency is not maintained at a stable value, but instead it depends on the user's breathing characteristics (normal breathing, speaking, laughing, etc.). This means that there is no fixed minimum sampling rate.

One approach is to set the sampling rate based on the fastest breathing rate as the worst case. Based on the fastest breathing rate, a fixed sampling rate may be set. This is not a power efficient method, since in some cases of low breathing frequency the sampling rate will be higher than what is actually needed. The fastest breathing rate of 30BrPM means that the fixed sampling rate can be 2 Hz.

An alternative approach is to set the sampling rate in a dynamic manner based on the number of previous breathing cycles (e.g., one or two). As a result, the frequency fs is dynamically adjusted in real time according to the breathing characteristic.

The breathing frequency can be determined in real time using the following equation: 1/2 (t)_max-t_min)，

t_maxIs the time of the largest data point in the respiratory cycle.

t_minIs the time of the smallest data point in the respiratory cycle.

In particular, a pair of consecutive minimum and maximum values is used to determine half of the cycle period.

The resulting frequency is then used to determine whether the frequency corresponds to a reasonable range of respiratory signals (12-30 BrPM). The frequency f is a second value related to the rate of pressure fluctuation. If the rate (i.e., frequency) is within the allowable range, the pressure fluctuations are caused by breathing, otherwise, the pressure fluctuations may be caused by other air disturbances.

In addition to setting the appropriate fan rotation signal sampling rate, the amount of sample data to be stored in memory needs to be determined. The sampling time window (T) determines the required data buffer size and updates (overwrites) the data in real time during breath tracking. Based on the respiration rate of 10-30BrPM, the sampling time window requires recording of at least one respiration cycle. Based on 10BrPM, the sampling period is 6 seconds.

The threshold values for the first and second values are used to determine whether the detected pressure signal is a true respiration signal. If the threshold is not set correctly, it is likely that the fan will be shut down incorrectly, or it may be necessary to shut down the mask while it is still in operation.

Fig. 7 shows pressure (Pa, curve 70, using the left y-axis) and fan speed (RPM, curve 72, using the right y-axis). The diagram shows a normal breathing phase 74, a light breathing phase 76 and a speaking phase 78.

A first value, such as the difference between the maximum fan speed and the minimum fan speed within the sampling window, may be measured from fig. 7 as:

normal breathing: signal peak valley 7792-7310 at 482 RPM;

light breathing: peak valley value 7630-;

speaking: peak valley 7791-.

If a normal breathing threshold is used in analyzing light breaths, light breaths will be detected as no breath. Therefore, the breathing threshold should take into account the worst case (lightest breath). However, if the threshold is too low, there is a risk of false detection.

The lightest breath occurs during the lowest active state (e.g., sitting) with a breath volume of 0.5L. The fan rotation signal difference (Δ RPM) can be tested at different fan speed settings based on a breathing rate of 12BrPM and a volume of 0.5L.

Table 1 below shows test data based on 12BrPM, 0.5L at different fan speed settings with some leakage.

TABLE 1

Fan speed setting	ΔRPM	Threshold value
			5000RPM	165RPM	82RPM
6500RPM	347RPM	173RPM
			7400RPM	365RPM	132RPM
8500RPM	464RPM	232RPM

The indication may set the threshold value in dependence of the prevailing fan speed setting, i.e. preferably, the first threshold value of the first value is made dependent on an average fan speed within the sampling window, which average fan speed generally corresponds to the fan speed setting. The fan speed setting may be known to the controller and provided as an input, or the actual average fan speed may be measured (e.g., based on a low pass filtered version of the fan rotation signal).

The threshold is set to approximately half the value of Δ RPM. This is because the use of a reduced sampling rate means that the peaks and troughs of the true respiration signal may not be sampled, as shown in figure 6B.

Fig. 8 shows a plot of speaking time periods similar to fig. 7 (pressure curve 70 and RPM curve 72). The graph shows that the pressure signal amplitude changes more significantly during speech than during normal breathing. However, the fan rotation signal shows a smaller signal amplitude than during normal breathing. This is because the response time of the pressure sensor is much faster than the fan signal. Sudden inspiration after speaking is detected by pressure sensing, but the fan signal does not reflect this peak signal as quickly.

This is also an advantage of using the fan rotation signal. The fan rotation signal will react for a longer time so that the reduced sampling rate can capture the effect of the sudden inspiration signal after speaking. For a sampling rate of 2Hz, a time period of at least 0.5s is required for the peak respiratory signal.

Analysis of the speaking respiration signal shows that the fan rotation signal always reacts longer than 0.5s, so even at a minimum sampling rate of 2Hz, the fan rotation feedback signal can pick up the speaking signal, while the pressure signal may not.

Table 2 below shows when a pressure peak occurs and when a rotation signal peak occurs in 12 consecutive drops in the pressure signal 70 of fig. 8.

TABLE 2

The detection of a breath is based on applying a first threshold to a first value, e.g., Δ RPM > threshold, and a range to a second value, e.g., 12 ≦ f ≦ 30. If both of these conditions are met, then breathing is detected and the system will keep the fan on.

If f <12 or f >30, or Δ RPM ≦ threshold, then breathing has disappeared.

When breathing has disappeared, a delay period may be applied during which breathing must not be detected continuously before it can be determined that the mask is not being worn. For example, a 10 second period of time may be provided later before the shutdown is implemented.

In the above example, the first value related to the depth of breath is the maximum excursion of the fan speed within the sampling window. However, this is the simplest implementation. Other analyses of the fan speed may be used to determine a signal indicative of the depth of breath. For example, a rate of change of fan speed may additionally or alternatively be used. Furthermore, if extreme sample values are determined to be abnormal, these values may be ignored in the analysis. Thus, additional constraints, or additional parameters, may be considered in the analysis of the fan speed to generate a value indicative of the depth of breath.

In the above example, the second value related to the breathing rate is a frequency based on the time between successive maxima and minima in the fan speed. However, this is also the simplest implementation. The frequency may alternatively be derived from the intersection of the threshold fan speeds.

In another example, a machine learning algorithm may be applied to the fan speed signal, and then a value indicative of the breathing rate and a value indicative of the depth of breathing may be extracted. Then, it would not be necessary to explicitly extract the maximum and minimum values of the fan rotation signal, or any particular time period, from the fan rotation signal.

Fig. 9 illustrates a mask operation method for detecting a transition from worn to unworn. The method may optionally begin with automatically turning on the fan in step 80.

Subsequently, the method comprises:

in step 90, initialization is performed. This involves setting the data buffer sample time (e.g., 6s), the sample rate (e.g., 2Hz), the first value threshold, the second value range, and the delay period (e.g., 10 seconds). The first threshold value is set according to table 1. The table may be different for different systems or fans.

In step 91, air is drawn into and/or out of the mask air chamber using a fan;

in step 92, determining the speed of the fan; and

in step 94, a first value and a second value are derived from the determined fan speed or change in fan speed, the first value being related to the magnitude of the pressure fluctuation across the fan, and the second value being related to the rate of the pressure fluctuation.

In step 96, the method includes determining whether the mask is worn based on the first value and the second value, as described above. If the mask is not worn and this is detected for the duration of the delay time, the fan can be turned off to save power.

This implements the first detection function described above.

The method may include driving the fan with an electronically commutated brushless motor and determining the rotational speed with an internal sensor of the motor. Alternatively, the rotation speed may be obtained by detecting a fluctuation in power supply to a motor that drives the fan.

The method may include determining a respiratory cycle from a pressure monitoring system. When an electrically controlled outlet valve is used, the outlet valve may be controlled in dependence on the phase of the breathing cycle.

Fig. 9 further illustrates a mask operation method for detecting a transition from unworn to worn. The method comprises the following steps:

in step 100, an induced current or voltage spike caused by rotation of a fan when the fan is not electrically driven is detected; and

in step 102, electric drive of the fan is initiated in response to the detected induced current or voltage spike.

The method may also include (subsequently) turning off the fan in step 104 if it is detected that the mask is not being worn. The detection may be based on steps 91-96 of fig. 9.

Similarly, the initial step 80 of turning on the fan in FIG. 9 may be performed based on

steps

100 and 102 of the method shown in FIG. 9.

The mask may cover only the nose and mouth (as shown in fig. 1), or may be a full mask.

The example shown is a mask for filtering ambient air.

The mask design described above has a main air chamber formed by the filter material through which the user inhales air.

Also as described above, an alternative mask design has a filter in series with the fan. In this case, the fan helps the user to draw air through the filter, thereby reducing the user's breathing effort. An outlet valve enables exhaled air to be expelled, and an inlet valve may be provided at the inlet.

The present disclosure may be applied again to detect pressure changes caused by breathing to control the inlet and/or outlet valves. In this example, the fan needs to be turned on during inhalation to help the user inhale air through the inline filter, but during exhalation, the fan can be turned off when the outlet valve is open. Thus, when fan operation is not required, the derived pressure information can again be used to control the fan to save power. Detection of whether the mask is worn may also be achieved.

It can be seen that the present disclosure can be applied to many different mask designs, with fan assisted inhalation or exhalation, and with air chambers formed by filter membranes or with sealed air tight air chambers.

Thus, one option, as described above, is to use only a fan to draw air from inside the air chamber to the outside, for example when the air outlet valve is open. In this case, the pressure within the mask volume may be maintained below the external atmospheric pressure by a fan, so that during exhalation, there is a net flow of clean filtered air into the mask volume. Thus, the low pressure may be caused by the fan during exhalation or by the user during inhalation (when the fan may be turned off).

An alternative is to use only a fan to draw air from the surroundings into the air chamber. In this case, the fan operates to increase the pressure within the air chamber, but in use the maximum pressure within the air chamber is maintained outside the air chamberPressure 4cm H higher₂Below O, especially because high pressure assisted breathing is not intended. Thus, a low power fan may be used.

In all cases, the pressure within the air chamber is preferably maintained at 2cm H above the external atmospheric pressure₂O or less, or even 1cm H₂O or less or even 0.5cm H₂O or less. Thus, anti-contamination masks are not masks for providing continuous positive airway pressure and for delivering therapy to a patient.

The mask is preferably battery powered, so low power operation is of particular interest.

Detection of the breathing cycle is a preferred feature for additional use as a monitoring capability, but this is optional.

As described above, embodiments utilize a controller to perform various desired functions, which may be implemented in software and/or hardware in a variety of ways. A processor is one example of a controller that employs one or more microprocessors that are programmed with software (e.g., microcode) to perform the required functions. However, the controller may be implemented with or without a processor, and may also be implemented as a combination of dedicated hardware for performing certain functions and a processor (e.g., one or more programmed microprocessors and associated circuits) to perform other functions.

Examples of controller components that may be employed in various embodiments of the present disclosure include, but are not limited to, conventional microprocessors, Application Specific Integrated Circuits (ASICs), and Field Programmable Gate Arrays (FPGAs).

In various embodiments, a processor or controller may be associated with one or more storage media, such as volatile and non-volatile computer memory, such as RAM, PROM, EPROM and EEPROM. The storage medium may be encoded with one or more programs that, when executed on one or more processors and/or controllers, perform the desired functions. Various storage media may be fixed in the processor or controller or may be transportable, such that the program or programs stored therein can be loaded into the processor or controller.

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed disclosure, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims shall not be construed as limiting the scope.

Claims

1. A mask, comprising:

an air chamber (18);

a filter (16) for filtering air;

a fan (20) for drawing air from outside the air chamber (18) into the air chamber interior and/or from the air chamber interior to the exterior;

means for determining a rotational speed of the fan; and

a controller (30), characterized in that the controller is adapted to:

deriving from the determined fan speed or change in fan speed a first value and a second value, the first value relating to depth of breathing when the mask is worn and the second value relating to rate of breathing when the mask is worn; and

2. A mask according to claim 1, wherein the first value is a maximum excursion of fan speed within a sampling window and the controller is adapted to set a first threshold to the first value.

3. A mask as defined in claim 2, wherein the first threshold is dependent on an average fan speed.

4. A mask as claimed in claim 2 or 3, wherein the second value is a frequency based on the time between successive maxima and minima of the fan speed.

5. A mask according to claim 4, wherein the controller is adapted to determine that breathing is detected and hence that the mask is worn when the first value exceeds the threshold and the second value is within a predetermined range.

6. A mask as claimed in any one of claims 1, 2, 3 and 5, wherein the fan speed is sampled at a rate dependent on the second value while breathing is detected.

7. A mask as claimed in any one of claims 1, 2, 3 and 5, wherein the controller is adapted to impose a time period within which no breathing must be continuously detected before it is determined that the mask is not being worn.

8. A mask as claimed in any one of claims 1, 2, 3 and 5, wherein the controller is adapted to turn off the fan if it is determined that the mask is not being worn.

9. The mask according to any one of claims 1, 2, 3 and 5, wherein the fan (20) is driven by an electronically commutated brushless motor and the means for determining the rotational speed comprises an internal sensor (34) of the motor.

10. The mask according to any one of claims 1, 2, 3 and 5, wherein the means for determining the rotational speed comprises a circuit (36) for detecting a ripple on a power supply to a motor driving the fan.

11. The mask according to any one of claims 1, 2, 3 and 5, wherein the controller (30) is adapted to determine a breathing cycle from the derived pressure or pressure variation, and to:

controlling the outlet valve (22) in dependence on the phase of the breathing cycle; and/or

The fan is turned off during the suction time.

12. The mask according to any one of claims 1, 2, 3 and 5, further comprising:

a detection circuit for detecting a peak value of an induced current or a peak value of an induced voltage caused by rotation of the fan when the fan is not electrically driven; and

a start circuit for starting electric drive of the fan in response to an output of the detection circuit.