阅读说明：本技术 防污染面罩和控制方法 (Anti-pollution mask and control method ) 是由 苏伟 陈伟忠 孔涛 于 2019-09-20 设计创作，主要内容包括：监测面罩的风扇旋转速度或风扇旋转速度的变化,并且由此获得与跨风扇的压力波动的幅值有关的第一值和与压力波动的速率有关的第二值。然后能够基于第一值和第二值来确定面罩是否被佩戴。这提供了对面罩是否被佩戴的可靠检测,并且只需要少量的风扇旋转信号的采样数据,因此节省了功率。(The mask is monitored for fan rotational speed or changes in fan rotational speed, and a first value related to the magnitude of pressure fluctuations across the fan and a second value related to the rate of the pressure fluctuations are obtained therefrom. It can then be determined whether the mask is worn 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 amount of sampled data of the fan rotation signal, thus saving power.)

1. A mask, comprising:

an air chamber (18);

a filter (16) for filtering air;

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

means (34, 36) for determining a rotational speed of the fan; and

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

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

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

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

3. The mask according to claim 2, wherein the first threshold depends on an average fan rotational speed.

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

5. The mask according to claim 4, wherein the controller is 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.

6. The mask according to any one of claims 1 to 5, wherein the fan rotational speed is sampled at a rate dependent on the second value when breathing is detected.

7. The mask according to any one of claims 1 to 6, wherein the controller is adapted to apply a time period during which no breathing must be detected continuously before it can be determined that the mask is not being worn.

8. The mask according to any one of claims 1 to 7, 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 to 8, wherein the fan (20) is driven by an electronically commutated brushless motor and the means for determining the speed of rotation comprises an internal sensor of the motor.

10. The mask according to any one of claims 1 to 9, wherein the module (36) for determining the rotation speed comprises a circuit for detecting a ripple on a power supply supplied to a motor driving the fan.

11. The mask according to any one of claims 1 to 10, wherein the controller (30) is adapted to determine a breathing cycle from the derived pressure or pressure variation, and to:

controlling an 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 to 11, further comprising:

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

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

13. A non-therapeutic method for controlling a contamination-preventive mask, wherein the contamination-preventive mask is not a mask for delivering therapy to a patient, the method comprising:

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

The rotational speed of the fan is determined,

characterized in that the method further comprises:

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

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

14. The method of claim 13, wherein the first value is a maximum excursion of fan rotational speed during a sampling window, and the method comprises setting a first threshold to the first value, wherein the second value is a frequency based on a time between successive maxima and minima of the fan rotational speed, and wherein the method further comprises: when the first value exceeds the threshold and the second value is within a predetermined range, it is determined that breathing is detected and thus it is determined that the mask is worn.

15. The method of claim 13 or 14, comprising turning off the fan if it is detected that the mask is not being worn.

Technical Field

The present invention relates to a contamination mask for providing filtered air to a wearer of a respiratory device using 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 face mask that provides cleaner air by filtering. To improve comfort and effectiveness, one or two fans can be added to the mask. These fans are switched on during use and are usually used at a constant voltage. For efficiency and life reasons, these fans are typically electrically commutated brushless DC fans.

The benefits of using a power mask by the wearer are: the slight strain in the lungs caused by inhalation against the resistance of the filter in a conventional non-powered mask can be relieved.

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 the contaminants are toxic substances. The power 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 is adjusted. This can be used to improve comfort by more appropriately ventilating during inhalation and exhalation sequences, or can be used to improve electrical efficiency. The increase in electrical efficiency translates into longer battery life or increased venting. Both of these aspects require improvements to existing designs.

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

For example, the pressure inside the mask can be measured with a pressure sensor, and the fan speed can be varied based on the sensor measurements. Pressure sensors are very expensive and it is therefore desirable to provide an alternative method of monitoring the pressure inside the mask. Such 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.

Fan operated masks are battery operated devices and it is therefore desirable to reduce power consumption to a minimum level and keep costs to a minimum. One problem is that: when the mask is not worn, the fan may still be in an open state, 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. Such 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 sensors dedicated to sensing mask usage.

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

WO 2018/215225 discloses a solution in which the rotational speed of the fan is used as a substitute for the pressure measurement. The pressure or pressure variation is determined based on the rotational speed of the fan. By using this pressure information, it can be determined whether the mask is worn.

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

This method works well if the fan speed signal is sampled at a high sampling rate, since the signal can then be analyzed in detail. However, a lower sampling rate is preferred 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 may be low. For example, if the sampling rate is too low, short spikes in the respiratory signal may be missed during speech. This may generate an erroneous shut down signal.

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

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

EP 0661071 discloses a device and a method for automated stop-start control in the administration of Continuous Positive Airway Pressure (CPAP) treatment. When it is determined that the patient is wearing the mask, administration of CPAP treatment is initiated. Conversely, when it is determined that the patient is no longer wearing the mask, administration of CPAP treatment is stopped. In one example, whether the mask is worn may be determined based on an analysis of the supply current of 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.

Disclosure of Invention

The invention is defined by the claims.

According to an example of one aspect of the present invention, there is provided a contamination prevention mask, including:

an air chamber;

a filter, for example, a filter that directly forms a boundary between the air chamber and an ambient environment outside the air chamber;

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

means for determining a rotational speed of the fan; and

a controller adapted to:

deriving a first value and a second value from the determined fan rotational speed or change in fan rotational speed, the first value relating to depth of breathing when the mask is worn and the second value relating to breathing rate when the mask is worn; 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 when a breath is detected, which means that there is a positive correlation between the first value and the depth of breath. The second value relates to the breathing rate at the time the breath is detected, which means that there is a positive correlation between the second value and the breathing rate.

More generally, the first value may, for example, relate to (i.e., be related to) the magnitude of the pressure fluctuation across the fan (whether or not the pressure fluctuation is caused by breathing), and the second value may, for example, relate to (i.e., be related to) the rate of the pressure fluctuation (whether or not the rate of the pressure fluctuation is caused by breathing). By "rate of pressure fluctuation" is meant the rate of cyclic pressure fluctuation caused by respiration, not the instantaneous rate of pressure change. 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 invention relates to an anti-pollution mask. This means a device whose main purpose is to filter the ambient air to be breathed by the user. The mask does not perform any form of patient handling. In particular, the pressure levels and flows caused by fan operation are merely intended to assist in providing comfort (by affecting the temperature or relative humidity in the air chamber) and/or 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 substitute 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 in the chamber have an effect on the load conditions of the fan, thus altering the fan electrical characteristics. Similarly, the fan electrical characteristics may determine the properties of the chamber, such as the volume of the chamber, and whether the chamber is an open volume or a closed volume.

To detect whether the mask is worn, the fan rotation signal is analyzed so that false positives (i.e., the mask is falsely detected as not worn) and false negatives (the mask is falsely detected as worn) are avoided. This is achieved by taking into account both 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 rate of breathing when breathing is detected. In this way, not only normal breathing (as in the solutions that the applicant has proposed but not disclosed) can be detected, but also pressure fluctuations related to the speaking period. This enables a reliable detection of breathing at a reduced sampling rate.

By determining whether the mask is worn, this mask design enables power to be saved when the mask is not worn without any additional sensors. In particular, if no pressure differential across the mask is detected, this indicates that both sides of the mask 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 such detection but erroneous detection results are avoided by additionally taking into account the rate of cyclic pressure fluctuations.

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

The sampling window is selected to be sufficient to capture at least one complete respiratory cycle, e.g., the sampling window is selected to be 6 seconds to capture a complete respiratory cycle at the lowest respiratory rate of 10 breaths/minute. The data sampling rate within the window can be selected to be 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/minute, the sampling rate may be 2Hz (4 times the maximum breath rate).

However, an alternative option is to sample the fan rotational speed at a rate dependent on the second value when breathing is detected. In this way, a minimum sampling rate can be maintained to save power,

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

The average fan rotational speed may be obtained by measurement of a previous sample or may be known from a drive signal applied to the fan by the controller. Both of these options are intended to be encompassed by the present invention.

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

The controller may then be 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. 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, which corresponds to a typical range of breathing rates.

The controller may be adapted to apply a time period during which no breathing has to be detected continuously before it can be determined that the mask is not being worn. In this way, the risk of switching off the fan by mistake is reduced.

The filter for example directly forms the boundary between the air chamber and the ambient environment outside the air chamber. This provides a compact arrangement, avoiding the need for convective transfer 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 the two layers together may be considered to 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 comprises one or more further filter layers. This provides a particularly compact arrangement and enables a large filter area because the mask body performs the filtering function. Thus, when the user inhales, ambient air is provided directly to the user through the filter.

Maximum pressure in the air chamber during use, e.g. below 4cm H₂O, e.g. less than 2cm H₂O, e.g. less than 1cm H₂O, which is higher than the pressure outside the air chamber. If a fan is used to provide increased pressure in the air chamber (e.g., flow into the air chamber during inhalation), only a small increase in pressure need be provided, for example, 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, it is also possible to facilitate the supply of fresh filtered air to the air chamber, even during exhalation, and thus to improve the comfort of the user. In this case, the pressure in 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 enable the motor to rotate. 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 circuitry for detecting ripple on a power supply to a motor driving the fan. This ripple results from the switched current through the motor coils, which cause induced variations in the supply voltage due to the finite 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 circuitry required for a motor that does not already have a suitable 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 controlled valve. This can be used to make the mask more comfortable. By closing the valve (actively or passively) during inhalation, unfiltered air is prevented from being inhaled. During exhalation, the valve is opened so that the exhaled air is expelled.

The controller may be adapted to: a breathing cycle is determined and the controlled valve is controlled in dependence on the phase of the breathing cycle. Such pressure monitoring thus provides a simple way to determine the inspiratory phase, which can then be used to control the timing of the exhaust valve to the mask, or to determine whether the mask is being 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, it is desirable for a user who has no difficulty breathing through the filter to turn off the fan during inspiration to conserve power.

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

The mask may further include:

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

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

This feature enables the fan to be activated when the mask is worn by detecting electrical spikes caused by manual rotation of the fan. This rotation is caused, for example, by a user wearing a mask and breathing through the fan when the fan is not electrically driven. These movements are then detected in order to provide an automatic turning on of the fan. This approach does not require an active sensing mask to be worn, but instead the sensing function is energized by the user's breathing. Such sensing may be integrated into the fan circuit, thereby having low overhead and low power consumption.

In this way, the fan may act 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 invention provides a method of controlling a contamination mask, comprising:

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

determining a rotational speed of the fan;

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

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

The first value may be a maximum swing of fan rotational speed during a sampling window, and the method comprises 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 the fan rotational speed, and the method may further comprise: when the first value exceeds the threshold and the second value is within a predetermined range, it is determined that breathing is detected and thus it is determined that the mask is worn.

Turning off the fan if it is detected that the mask is not worn.

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

The method can comprise the following steps: electronically commutated brushless motors are used to drive the fan, and the rotational speed is determined by internal sensors of the motor. Alternatively, the rotational speed may be obtained by detecting a ripple on the power supply supplied to the motor that drives the fan. This can be applied to any type of motor, for example, a conventional brushed DC motor.

The mask may include an electrically controlled 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 comprise controlling the controlled valve in dependence on the phase of the breathing cycle. Alternatively, the mask may have only a pressure regulating relief valve.

Drawings

Examples of the invention will now be described in detail with reference to the accompanying drawings, in which:

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;

figure 3 shows the rotation signal during inspiration and during expiration;

FIG. 4 shows a circuit for controlling current through one of the stators 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 the fan rotation signal;

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

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

FIG. 9 illustrates a first mask method of operation; and is

FIG. 10 illustrates a second method of operation of the mask.

Detailed Description

The present invention provides an anti-contamination mask. The fan rotational speed or a change in the fan rotational speed is monitored and a first value related to the magnitude of the pressure fluctuations across the fan and a second value related to the rate of the cyclical pressure fluctuations are obtained therefrom. It can then be determined whether the mask is worn 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 amount of sampled data of the fan rotation signal, thus saving power.

The first detection function is to provide fan rotational speed monitoring (as a substitute for pressure measurement) and use this to detect whether the mask is being worn, and in particular, this enables the transition from worn to unworn to be detected. The second detection function enables detection of a transition from not worn (and mask fan off) to worn.

The purpose of both of these 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.

Subject 10 is shown wearing a mask 12, 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., check valve) closes due to the low pressure in the air chamber 18.

The filter 16 may be formed solely from the body of the mask or may have multiple layers. For example, the mask body may include an outer cover formed of a porous fabric material that serves as a pre-filter. Inside the outer cover, the finer filter layer is reversibly attached to the outer cover. The finer filter layer can then be removed for cleaning and replacement, and the housing can be cleaned, for example by wiping. The housing also performs a filtering function, for example, to protect the finer filter from large debris (e.g., dirt), while the finer filter performs filtering of 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 removed than is exhaled so that additional air is supplied to the face. This improves comfort due to reduced relative humidity and cooling. During inhalation, the inhalation of unfiltered air is prevented by closing the valve. Thus, the timing of the outlet valve 22 depends on the subject's breathing cycle. The outlet valve may be a simple passive check valve operated by a pressure differential across the filter 16. Alternatively, however, the outlet valve may also be an electrically controlled valve.

If the mask is worn, only elevated pressure will exist inside the chamber. In particular, the chamber is closed by the face of the user. When the mask is worn, the pressure inside 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 manifest themselves as different loads on the fan, since there are different voltage drops across the fan. Such varying loads will cause different fan speeds.

The first detection function is based in part on the following recognition: the rotational speed of the fan may be used as a substitute for the pressure measurement across the fan. The first detection function 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 invention combines these considerations to create a mask that can save power by being turned off when not being worn and that does not require complex or expensive additional sensors.

Pressure monitoring enables the pressure, or at least the change in pressure, on one side of the fan to be determined given the pressure (e.g. atmospheric pressure) on the other side of the fan. The other side is for example a closed chamber, which thus has a pressure different from atmospheric pressure. However, by detecting that the pressure on each side of the fan is equal, 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 that the mask is not being used. This information can be used to turn off the fan to save power.

Applicants have proposed (but not yet published) a pressure monitoring system having a module for determining the rotational speed of the fan and a controller for deriving a pressure or detecting a change in pressure from the rotational speed of the fan. Applicants have then also proposed using this pressure information to determine whether the mask is being worn.

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

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

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

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 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 supplied to the motor 20 b. This ripple results from the switched current through the motor coils, which can cause induced variations in the supply voltage due to the finite impedance of the battery 32. The circuit 36 for example comprises a high-pass filter so that only signals in the frequency band in which the fan is rotating are processed. This provides a very simple additional circuit and is of much lower cost 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. The motor will also work with a brushed DC motor.

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 depending on the 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 outlet valve 22 of the mask.

In addition to controlling the outlet valve, the controller may also turn off the fan during inspiration times or during expiration times. 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 increases due to the lower cross-fan pressure as the load on the fan blades decreases. This results in an enhanced flow. Thus, there is an inverse relationship between fan speed and pressure differential.

This inverse relationship may be obtained during the calibration process or may be provided by the fan manufacturer. For example, the calibration process involves analyzing fan speed information over a period in which the subject is instructed with commands to regularly inhale and exhale in a normal breathing manner. The captured fan speed information can then be matched to the breathing cycle, from which thresholds can then be set for distinguishing inspiration from expiration.

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 (caused by switching events in the motor) of the DC voltage to the fan. 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 plot 40 and the signal during expiration as plot 42. During exhalation, there is a decrease in frequency due to an increase in load on the fan caused by an increase in pressure gradient. 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 region between the face and the mask. This improves comfort as it makes it easier to exhale. This also allows additional air to be drawn onto the face, reducing temperature and relative humidity. Between inspiration and expiration, the fan operation improves comfort as fresh air is drawn into the space between the face and the mask, cooling the space.

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

If the fan is turned off for part of the breathing cycle and therefore no pressure information is provided, the precise timing of the inspiration phase and expiration phase can be inferred from the previous breathing cycle.

For fan assisted exhalation, the power supply needs to be restored just before the outlet valve opens again. This also ensures that the next inhalation-exhalation cycle remains properly timed and that adequate pressure and flow can be achieved.

By using this method, power savings of about 30% can be easily achieved, thereby extending battery life. Alternatively, the power to the fan can be increased by 30% to improve efficiency.

With different fan and valve configurations, the measurement of the fan rotational speed allows control to improve comfort.

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 can be done during a period of time when the rear face mask is switched on and not yet worn on the face. This resistance can be used as a substitute for the age of the filter.

The first detection function described above utilizes a fan to provide a substitute for pressure measurement, which 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, thus enabling the detection of 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 that the fan be able to turn on automatically when the mask is worn for the first time or after any previous automatic shut-down. This can be achieved by using a dedicated sensor, but this requires a long-term activation of the dedicated sensor, or at least a periodic sensing operation. This would again complicate the mask and would 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, this 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 will rotate even if not switched on, as air is forced through the fan. The speed detection function determines this rotation without using an additional sensor in case the fan is switched off. This signal is then used to turn on the air fan to operate the mask properly.

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 rotational 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 into the stator coil 50 from the DC power supplies VDD, GND. The inverter has a set of switches S1-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 electric signal is generated due to electromagnetic induction.

These inductive signals cannot be measured on the power supply line because the coil is connected to an electronic circuit that 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 explained with reference to fig. 5.

An H-bridge circuit is provided between the high voltage rail VDD and the 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 cluttering 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 a base voltage for 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 then increases to full VDD + top VDD-voltage swing. This operation generates 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 of the mask 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 by using a turn-off circuit 51 (e.g., a transistor that discharges capacitor C2).

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

When the fan is off in FIG. 5, 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 at the base of Q1 and eventually turn it on. Then, the level of the virtual ground GND is pulled down to VDD-. At this time, current can flow from VDD + to VDD-. This provides power to 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 on, the shutdown circuit 51 is used to discharge 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, thereby reducing the supply voltage, since GND + rises back to the voltage VDD +.

The present invention provides an enhancement 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 invention may be implemented using a system as shown in fig. 2, but with a different method and therefore analysis implemented by the controller.

As in the system described above, analysis of the fan rotation signal (by looking at the fan rotational speed or changes in the fan rotational 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 coincides with the breathing signal. The first value may comprise a difference between a maximum fan rotational speed and a minimum fan rotational speed during the sampling window. In addition, a second value is derived, which is related to the pressure fluctuation cycle rate, i.e. when the second value coincides with the respiration signal, the second value is related to the respiration rate.

In this application, the term "depth of breath" is generally used to refer to the volume or flow rate characteristics associated with a particular type of breath, rather than the 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 at rest, 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 metric that may be used as a measure of such depth of breath is tidal volume (i.e., 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 measure of tidal volume, but provides similar correlation to different types of breaths as tidal volume measurements. Thus, the first value "relates" to the depth of breath, just as the tidal volume measurement is a measure of depth of breath (and thus is related to depth of breath).

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

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 component distortion 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 sampling rate of 2Hz is the minimum sampling rate for a 30BrPM respiratory signal.

It follows therefore that:

fs＝4f

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 rather, the breathing frequency 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 frequency (as the worst case). Based on this 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 depending on the breathing characteristics.

The breathing frequency can be determined in real time using the following formula:

f＝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 breathing cycle.

In particular, a pair of successive 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 respiration, 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 the data is updated (overwritten) in real time during the breath tracking. Based on a 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 properly, 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 operating.

Fig. 7 shows pressure (in Pa, plot 70, using the left y-axis) and fan rotational speed (in RPM, plot 72, using the right y-axis). The normal breathing phase 74, light breathing phase 76 and speaking phase 78 are shown.

From fig. 7, a first value (e.g., the difference between the maximum fan rotational speed and the minimum fan rotational speed during the sampling window) can be measured 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. Based on a breathing rate of 12BrPM and a breath volume of 0.5L, the fan rotation signal difference (Δ RPM) can be tested at different fan speed settings.

Table 1 below shows this 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 for the first value is made dependent on the average fan rotational speed during the sampling window, which 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 for periods of speaking similar to fig. 7 (pressure plot 70 and RPM plot 72). The graph shows that the pressure signal amplitude changes during speech are more pronounced 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 over 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 a sharp breathing signal.

Analysis of the spoken respiratory signal showed: the fan rotation signal always reacts longer than 0.5s, so that even with a minimum sampling rate of 2Hz, the fan rotation feedback signal is able to capture the speech signal, while the pressure signal may not be able to capture the breathing signal.

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

TABLE 2

Circulation of	Pressure peak time(s)	RPM Peak time(s)
			1	0.5	0.8
2	1	1.1
			3	0.3	0.6
4	0.2	0.6
			5	0.5	0.6
6	0.5	0.9
			7	0.5	0.9
8	0.3	0.6
			9	1.3	1.7
10	0.6	0.8
			11	0.7	0.4
12	0.6	0.4

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 no breathing must be detected continuously before it can be determined that the mask is not being worn. For example, the shutdown may be implemented after a period of 10 seconds is provided.

In the above example, the first value related to the depth of breath is the maximum excursion of the fan rotational speed during the sampling window. However, this is the simplest implementation. Other analyses of the fan rotational speed may also be used to determine a signal indicative of the depth of breath. For example, a rate of change of fan rotational speed may additionally or alternatively be used. Furthermore, if extreme sample values are determined to be anomalous, these values may be ignored in the analysis. Thus, additional constraints or additional parameters may be taken into account in the analysis of the fan rotation speed in order to generate a value representing the depth of breathing.

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

In further examples, a machine learning algorithm may be applied to the fan rotational speed signal, and then a value representing the breathing rate and a value representing the breathing depth may be extracted. This would then eliminate the need to explicitly extract the maximum and minimum values of the fan rotation signal or the maximum and minimum values for 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), sample rate (e.g., 2Hz), first value threshold, second value range, and delay period (e.g., 10 seconds). The first value threshold 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 a rotational speed of the fan; and is

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

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 condition is detected for the duration of the delay time, the fan may be turned off to save power.

This implements the first detection function described above.

The method can comprise the following steps: electronically commutated brushless motors are used to drive the fan and the speed of rotation is determined by internal sensors of the motor. Alternatively, the rotational speed may be obtained by detecting a ripple on the power supply supplied to the 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, it may be controlled depending on the phase of the breathing cycle.

Fig. 10 illustrates a mask operation method for detecting a transition from unworn to worn. The method comprises the following steps:

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

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

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

Similarly, the initial step 80 of turning on the fan in FIG. 6 may be performed based on steps 100 and 102 of the method of FIG. 10.

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

The illustrated example 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 assists the user in drawing air through the filter, thereby reducing the user's respiratory effort. An outlet valve enables exhaled air to be expelled, and an inlet valve may be provided at the inlet.

The invention may again be applied to detecting pressure changes caused by breathing to control the inlet and/or outlet valves. In this example, the fan needs to be on during inhalation to assist the user in inhaling air through the inline filter, but the fan can be off during exhalation 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 face mask is worn may also be implemented.

It will be seen that the invention can be applied to many different mask designs having fan assisted inhalation or exhalation and having an air chamber formed by a filter membrane or having a sealed air tight air chamber.

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 inside the mask volume may be maintained below the external atmospheric pressure by the fan, so that there is a net flow of clean filtered air into the mask volume during exhalation. Thus, the low pressure may be caused by the fan during exhalation and by the user during inhalation (when the fan may be turned off).

An alternative option is to use only a fan to draw air from the surroundings into the air chamber interior. In this case, the fan is operated to increase the pressure in the air chamber, but in use the maximum pressure in the air chamber remains below 4cm H₂O, which is higher than the pressure outside the air chamber, in particular because high pressure assisted breathing is not intended. Thus, a low power fan may be used.

In all cases, the pressure inside the air chamber is preferably kept below 2cm H₂O, or even less than 1cm H₂O, or even less than 0.5cm H₂O, which is higher than the external atmospheric pressure. 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 as an additional use of monitoring capability, but this is optional.

As discussed above, embodiments utilize a controller to perform the various functions required, which can be implemented in a variety of ways using software and/or hardware. A processor is one example of a controller that employs one or more microprocessors that are programmed using 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 to perform certain functions and a processor (e.g., one or more programmed microprocessors and associated circuitry) to perform other functions.

Examples of controller components that may be employed in various examples 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, e.g., 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 within the processor or controller or transportable, such that the one or more 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 invention, 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 word "a" or "an" does not exclude a plurality. Although some measures are recited in mutually different dependent claims, this 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.