Powered air-purifying respirator (PAPR) with eccentric venturi air flow rate determination

A powered air-purifying respirator (PAPR). The PAPR comprises an air pump comprising an electric motor, an eccentric venturi communicatively coupled to an air channel of the air pump, wherein the eccentric venturi comprises a first sensor port and a second sensor port, a differential air pressure sensor mechanically coupled to the first sensor port and the second sensor port, and a controller that is communicatively coupled to an electrical output of the differential air pressure sensor and to the electric motor, wherein the controller is configured to control the speed of the electric motor to maintain a predefined rate of flow of purified air based on the electrical output of the differential air pressure sensor.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

BACKGROUND

Powered air-purifying respirators (PAPRs) are self-contained apparatus for providing breathable air to workers and first responders in an environment that has dust-laden or aerosol-laden air. The PAPR typically comprises a blower driven by an electric motor that draws air from the environment through a filter and provides filtered air to a human being.

SUMMARY

In an embodiment, a powered air-purifying respirator (PAPR) is disclosed. The PAPR comprises an air pump comprising an electric motor, an eccentric venturi communicatively coupled to an air channel of the air pump, wherein the eccentric venturi comprises a first sensor port and a second sensor port, a differential air pressure sensor mechanically coupled to the first sensor port and the second sensor port, and a controller that is communicatively coupled to an electrical output of the differential air pressure sensor and to the electric motor, wherein the controller is configured to control the speed of the electric motor to maintain a predefined rate of flow of purified air based on the electrical output of the differential air pressure sensor.

In another embodiment, a powered air-purifying respirator is disclosed. The PAPR comprises an air pump comprising an electric motor, an eccentric venturi communicatively coupled to an air channel of the air pump, wherein the eccentric venturi comprises a first sensor port and a second sensor port that tap into an interior of the eccentric venturi each at a point opposite a center point of the air pump, a differential air pressure sensor mechanically coupled to the first sensor port and the second sensor port, and a controller that is communicatively coupled to an electrical output of the differential air pressure sensor and to the electric motor, wherein the controller is configured to control the speed of the electric motor to maintain a predefined rate of flow of purified air based on the electrical output of the differential air pressure sensor.

In yet another embodiment, a powered air-purifying respirator is disclosed. The PAPR comprises an air pump comprising an electric motor, an eccentric venturi communicatively coupled to an air channel of the air pump, wherein the eccentric venturi comprises a first sensor port and a second sensor port and wherein the eccentric venturi comprises a throat portion, a conductor portion upstream of the throat portion, and a diffuser portion downstream of the throat portion, wherein a central axis of the diffuser portion makes an angle of greater than 5 degrees with a central axis of the throat portion, a differential air pressure sensor mechanically coupled to the first sensor port and the second sensor port, and a controller that is communicatively coupled to an electrical output of the differential air pressure sensor and to the electric motor, wherein the controller is configured to control the speed of the electric motor to maintain a predefined rate of flow of purified air based on the electrical output of the differential air pressure sensor.

DETAILED DESCRIPTION

The present disclosure teaches a powered air-purifying respirator (PAPR) with an eccentric venturi. The eccentric venturi is used to provide an indication of a flow rate of air delivered to a breathing apparatus. More specifically, two ports into the eccentric venturi provide an indication of differential pressure which can be processed to estimate the air flow rate, as described in more detail here below. The use of a venturi to derive the estimate of the air flow rate may provide a more accurate estimation of the true air flow rate than alternative flow sensing techniques. The use of the eccentric venturi taught herein is thought to provide both accuracy and a modest physical size compatible with the desire for a conveniently portable PAPR. The accurate estimation of the true air flow enables a more precise control of the PAPR which best supports the antagonistic design objectives of providing adequate flow of purified air and extending the battery life of the PAPR by constraining electric power delivered to an electric motor driving the air pump. Said in other words, accurate estimation of the true air flow enables delivering just enough purified air but not delivering too much air (where too much air would deplete a battery of the PAPR prematurely).

The present disclosure further teaches locating the two differential air pressure ports or taps on an outer radius of the air pump package, which is thought to provide a more accurate sensing of the air flow rate. Not wishing to be bound by theory, it is thought that the mass of air flow through the venturi is not distributed uniformly during use but is greatest along the outer radius of the air pump as it enters the venturi, and hence sensing the differential air pressure at that point of concentrated mass of air flow results in more resolution and an associated greater accuracy.

Turning now toFIG. 1, a system100is described. In an embodiment, the system100comprises a breathing apparatus112and a powered air-purifying respirator (PAPR)120. In use, the PAPR120supplies purified air to the breathing apparatus112for inhalation by a human user, for example through a hose and into a hood of the breathing apparatus112. In some embodiments, the breathing apparatus112may be considered to be part of the PAPR120. In an embodiment, the breathing apparatus112may be a hood that is placed over a head of a user and a hose which connects to the PAPR120. In another embodiment, the breathing apparatus112may be a full body suit that the user dons and seals where a hose delivers purified air from the PAPR120to the interior of the full body suit, for example to an area proximate to a head of the user.

In an embodiment, the PAPR120comprises a controller102, an electric battery104, an electric motor106, a filter107, an air pump108, an eccentric venturi110, and a differential pressure sensor114. The PAPR120may further comprise an absolute pressure sensor116and a temperature sensor118. The illustration of the PAPR120inFIG. 1is not intended to represent physical relationships of components but rather to depict functional flows and interrelationships among components. In an embodiment, a motor drive may be located between the controller102, the electric battery104, and the electric motor106. While in operation, the controller102provides control signals to the electric motor106that cause the electric motor106to increase speed, decrease speed, or maintain current speed. The electric motor106receives electric power from the electric battery104.

The electric motor106is mechanically coupled to the air pump108such that when the electric motor106turns, the air pump108turns, and as the electric motor106turns faster or slower, the air pump108likewise turns faster or slower, respectively. The air pump108comprises a centrifugal fan that draws air through the filter107from the outside environment. The filter107desirably blocks passage of particulate matter and aerosol droplets in the environmental air, thereby purifying the air for safe breathing by a human user of the system100. Over time the filter107may become progressively saturated with particulate matter and/or aerosol droplets, and that progressive saturation would tend to reduce the flow rate of filtered breathable air to the breathing apparatus112if the speed of the air pump108remains unchanged. The controller102adapts the control signal to the electric motor106to cause the electric motor106to turn fast enough to maintain a desired rate of flow of breathable air to the breathing apparatus112, up to a maximum operating limit of the electric motor106.

The controller102is able to determine the flow rate of breathable air based on the differential pressure indicated by the differential pressure sensor114. In an embodiment, the controller102determines the flow rate of breathable air further based on the absolute pressure indicated by the absolute pressure sensor116and the temperature indicated by the temperature sensor118. By further basing the determination of air flow rate based on the absolute pressure and the temperature, the controller102is able to accurately estimate the air flow rate at different location elevations (e.g., at a first work site at 100 feet above sea level as well as at a second work site at 4,000 feet above sea level) without recalibration of the system100.

Turning now toFIG. 2, details of the eccentric venturi110are described. The view illustrated inFIG. 2is a sectional view C-C′ of the section cut C-C′ illustrated inFIG. 3. A venturi generally comprises a flow path with a narrowing in its middle portion which may be called a throat of the venturi. An entrance portion of the flow path of the venturi may be called a conductor and an exit portion of the flow path of the venturi may be called a diffuser. The eccentric venturi110comprises a conductor150, a throat152, and a diffuser154. In an embodiment, the eccentric venturi110comprises a first port156and a second port158that both open into an interior of the eccentric venturi110, the first port156opening into an interior of the conductor150and the second port158opening into an interior of the throat152. The ports156,158provide differential pressure sensing taps to the differential pressure sensor114. The flow of air through the eccentric venturi110is from right to left inFIG. 2, entering at the conductor150, flowing next to the throat152, flowing next into the diffuser154, and then flowing out of the eccentric venturi110.

The view of the eccentric venturi110illustrated inFIG. 2is a section view of the eccentric venturi110, where the section perspective is indicated inFIG. 3. The conductor150has a first central axis160, and the diffuser154has a second central axis162that makes an angle α with the first central axis160. In an embodiment, the angle α is about 10 degrees, but in another embodiment the angle α may be about 8 degrees, about 9 degrees, about 12 degrees, about 15 degrees, or about 18 degrees. The angle α is less than 35 degrees. While not illustrated inFIG. 2, in an embodiment, the throat152may have a third central axis that is offset at an angle to both the first central axis160and the second central axis162, where the third central axis makes an angle with the first central axis160that is less than the angle α. The angle offset between the first central axis160and the second central axis162is at least one feature in which the eccentric venturi110may be said to be eccentric. While not wishing to be limited by theory, it is thought that the angular offset between the central axes160,162makes the profile of the interior of the eccentric venturi110more gradual and less sharply stepped where the maximum air flow occurs which reduces the tendency of turbulence developing, where turbulence inside the eccentric venturi110could reduce the accuracy of estimation of the air flow rate.

Turning now toFIG. 3, further details of the air pump108are described. The illustration of the air pump108is intended to be quasi-representational but not specifically to scale. The air pump108encloses a centrifugal fan (not shown) that is turned by the electric motor106. Air is drawing through the filter107into an inlet (not shown) that is located in the center of the air pump108. The centrifugal fan accelerates and pushes inlet air in a counterclockwise direction (from the perspective illustrated inFIG. 3) and out the diffuser154of the eccentric venturi110. The outside radius of the air pump108is the outside portion of the circumference of the air pump108. In an embodiment, the ports156,158are located on this outside edge of the air pump108, as illustrated inFIG. 3. While not wishing to be bound by theory, it is thought that the mass flow rate of air in the air pump108and through the eccentric venturi110is not uniformly distributed but is greater close to the outside radius of the air pump108and on the side of the eccentric venturi110where the ports156,158are placed. It is thought that locating the ports156,158at this point of greater air mass concentration may increase the resolution and/or the accuracy of the determination of differential pressure sensor.

Turning now toFIG. 4, a method230is described. The method230may be performed by the controller102to develop control signals to command the electric motor106. At block232, air density ρ is calculated based on absolute air pressure and temperature in the local environment. Determination of air density ρ enables determination of air flow independently of elevation of the location the system100is used at (i.e., the system100need not be separately calibrated for use at a first elevation and at a second elevation different from the first elevation). The absolute pressure may be provided by the absolute pressure sensor116, and the temperature may be provided by the temperature sensor118.

At block234, the air flow rate through the eccentric venturi110(i.e., the output flow rate of breathable air to the breathing apparatus112) is determined based on differential pressure in the eccentric venturi110and based on the air density ρ. In an embodiment, the air flow rate may be determined based on:
Q=K√{square root over (2δP/ρ)}  EQ 1
where Q is the estimated flow rate of air, K is a constant, δP is the differential pressure output by the differential pressure sensor114, and ρ is the air density. In another embodiment, the estimated air flow rate may be determined from the differential pressure and the density ρ in a different way.

At block236, if the electric motor106is already being operated at its maximum, the method proceeds to block238. At block238, the air flow rate Q is compared to a pre-defined low air flow alarm threshold. If Q is greater than the low air flow alarm threshold, processing returns to block232. If Q is less than the low air flow alarm threshold, the processing flows to block240where a low air flow alarm is presented. The low air flow alarm may be an aural tone that is sounded, a visual alert, or both. At bock236, if the electric motor106is not being operated at its maximum, processing proceeds to block242.

At block242, the estimated air flow rate Q is compared to a pre-defined flow rate upper and lower limit. If the air flow rate Q is within the flow limits, processing returns to block232. If the air flow rate Q is outside of flow limits, processing passes to block244. If air flow rate Q is less than the lower air flow limit, processing proceeds to block246where a command to increase the speed of the electric motor106is generated and transmitted by the controller102to the electric motor106. If air flow rate Q is greater than the maximum air flow limit, processing proceeds to block248where a command to decrease the speed of the electric motor106is generated and transmitted by the controller102to the electric motor106. After the processing of block246and block248processing returns to block232. In an embodiment, the return to block232from block238,242,246, and248is preceded by a time delay. Said in other words, the processing of method230may constitute a processing loop that is repeated periodically at some desirable rate, for example 10 times per second, once per second, once every ten seconds, or some other periodic rate.

FIG. 5illustrates a computer system380suitable for implementing one or more embodiments disclosed herein. For example, the controller102may be implemented at least partially as a computer system. The controller102may not have all of the features described below that are present in a fully-featured computer system such as that described below (e.g., the controller102may not have a network interface and may not have secondary storage). The computer system380includes a processor382(which may be referred to as a central processor unit or CPU) that is in communication with memory devices including secondary storage384, read only memory (ROM)386, random access memory (RAM)388, input/output (I/O) devices390, and network connectivity devices392. The processor382may be implemented as one or more CPU chips.