U.S. patent application number 12/357060 was filed with the patent office on 2009-07-30 for self contained breathing apparatus modular control system.
Invention is credited to David E. Forsyth, Wayne K. Miller.
Application Number | 20090188501 12/357060 |
Document ID | / |
Family ID | 36969522 |
Filed Date | 2009-07-30 |
United States Patent
Application |
20090188501 |
Kind Code |
A1 |
Forsyth; David E. ; et
al. |
July 30, 2009 |
Self Contained Breathing Apparatus Modular Control System
Abstract
The claim over prior art is for an approach to an electronically
controlled or electronically monitored breathing system that
represents an improvement in electrical reliability, manufacturing
cost and efficiency, user maintenance, system reliability, user
cost and maintenance. These improvements are accomplished by
placing the major electronic, mechanical and electromechanical
control elements and sensor components in a single replaceable
module.
Inventors: |
Forsyth; David E.; (Laguna
Beach, CA) ; Miller; Wayne K.; (Fort Jones,
CA) |
Correspondence
Address: |
DORSEY & WHITNEY LLP;INTELLECTUAL PROPERTY DEPARTMENT
SUITE 1500, 50 SOUTH SIXTH STREET
MINNEAPOLIS
MN
55402-1498
US
|
Family ID: |
36969522 |
Appl. No.: |
12/357060 |
Filed: |
January 21, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11215363 |
Aug 30, 2005 |
7497216 |
|
|
12357060 |
|
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60605561 |
Aug 30, 2004 |
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Current U.S.
Class: |
128/204.22 |
Current CPC
Class: |
B63C 2011/021 20130101;
B63C 2011/188 20130101; B63C 11/24 20130101; A62B 7/08
20130101 |
Class at
Publication: |
128/204.22 |
International
Class: |
B63C 11/24 20060101
B63C011/24; A62B 7/00 20060101 A62B007/00 |
Claims
1. A modular, self-contained, removable control subsystem for a
breathing device comprising a microcontroller, measurement
electronics, input/output cabling, connectors, gas control
solenoids, gas connections, and software for the purpose of
controlling gas addition to the breathing device.
2. The modular control system of claim 1 comprising a low pressure
Oxygen measurement subsystem.
3. The modular control system of claim 1 comprising a mid
(intra-stage) pressure Oxygen measurement subsystem.
4. The modular control system of claim 1 comprising a high pressure
gas measurement subsystem.
5. The modular control system of claim 1 comprising a system power
supply.
6. The modular control system of claim 1 comprising a Barometric
sensor(s) and a pressure sensing measurement subsystem.
7. The modular control system of claim 1 comprising wireless
transceiver(s) to communicate data to and from the breathing system
measurement devices.
8. The modular control system of claim 1 comprising a wireless
transceiver(s) to communicate data between the module and
display/input devices.
9. The modular control system of claim 1 comprising a Personal
Alert Safety System (PASS) subsystem.
Description
CROSS REFERENCE TO RELATED APPLICATION(S)
[0001] The present utility patent application claims benefit of
U.S. Provisional Application Ser. No. 60/605,561, filed Aug. 30,
2004 in the names of the present applicants, subject matter of
which is incorporate herewith by reference.
FIELD OF THE INVENTION
[0002] The present invention relates: generally to respiratory
methods or devices supplying respiratory gas under positive or
ambient pressure; more specifically to electric control means for
the supply of respiratory gas under positive or ambient pressure;
most particularly to electric control means for the supply of
respiratory gas under positive or ambient pressure by a respiratory
method or device utilizing means for sensing partial pressure of a
gas constituent.
BACKGROUND OF THE INVENTION
[0003] Breathing devices like Closed and Semi Closed Circuit
Rebreathers and other closed loop breathing systems rely on
electronic control systems to monitor the oxygen level through the
use of oxygen sensors and to process the system information to
determine if a solenoid or valve needs to be opened in order to add
more oxygen into the breathing system. Up to now, this has involved
a complicated and interconnected array of components to accomplish
this task. The batteries, control electronics, sensors, and gas
control devices all must be connected with cables and varying
levels of connectors. Breathing systems to date have neither
considered these subcomponents as a complete system nor have the
control systems in general been considered as an integral part of
the system design for the rebreather itself. The resultant
breathing system designs have therefore treated the control system
as both a separate system from the rebreather and have considered
the individual components of the electronic control and sensing
system as generally separate design elements. All of the control
system subcomponents and parts have maintenance and reliability
issues that either requires regular maintenance or possible
replacement. All of the necessary electronic and mechanical
interconnects between these components represent points of failure
as well as increases assembly time, maintenance, and system
cost.
[0004] All breathing device control systems require maintenance and
have attendant diagnosis and or possible replacement issues.
Successful diagnosis and replacement can be as easy as replacing a
battery or sensor to as complicated as sending the entire breathing
unit in for a factory trained technician to diagnose and service.
The latter option comes at an additional cost of significant down
time. On current, non-modular systems, parts can be very difficult
to remove and replace; especially in the field or on short notice.
A significant array of available spare parts is therefore necessary
to be able to repair any control related failure in most breathing
systems.
[0005] Manufacturer upgrades to the control system typically
consists of sending the entire unit or a significant portion
thereof back for retrofitting. This is both costly and
inefficient.
[0006] In rebreathing systems, a popular implementation has been
that the separate pieces have been combined into a single large
"head" which comprises the entire top assembly of a rebreather.
This "head" typically including breathing hose mounts, scrubber and
breathing bag supply paths, some of the electronics, sensors and or
the gas injection solenoid. The "head" therefore, is a
substantially sized and priced piece of the breathing system with a
great deal more functionality and cost than just the control
subsystem and includes a great deal of mechanically oriented parts
and mountings which are not as likely to fail or need replacement
as the control and sensing subsystem. Within the "head", the
components of the control and sensing subsystem are still treated
as individual components with all the attendant difficulties
remaining concerning cost and reliability.
SUMMARY OF THE INVENTION
[0007] The invention is summarized by considering that
manufacturers and users of breathing systems are concerned with
costs, reliability maintenance, and serviceability of these
breathing systems. Claims are made for Closed and Semi Closed
configurations of rebreathing systems that minimize electronic and
mechanical failures by incorporating the microcontroller and
associated electronics, measurement subsystem electronics, input
and output cabling, connectors, gas control solenoids and software
into a single removable module. Claims are made for the integration
of the low pressure Oxygen, intra-stage Oxygen pressure, high
pressure gas supply and ambient barometric pressure measurement
subsystems and for the integration of the controller power supply.
Claims are also made for wireless transmission of the data to and
from the sensors and or measurement subsystems and to and from the
user interface via the display subsystems. A claim is also made for
the integration of a Personal Alert Safety Subsystem into the
modular controller. This single module approach offers significant
benefits in manufacturability, reliability, serviceability and
maintenance. The additional benefit of reducing the technical
knowledge required to perform maintenance and replacement tasks is
also realized.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The accompanying drawings which are incorporated in and form
a part of the specification illustrate preferred embodiments of the
present invention and, together with a description, serve to
explain the principles of the invention. In the drawings:
[0009] FIG. 1 is a picture of a complete electronically controlled
mixed gas closed circuit rebreather.
[0010] FIG. 2 is a drawing of one example of a modular controller
assembly.
[0011] FIG. 3 is a front view drawing of one example of the
interface between the modular controller and scrubber assembly.
[0012] FIG. 4 is a 3/4 view drawing of one example of the interface
between the modular controller and scrubber assembly.
[0013] FIG. 5 is a schematic representation of a mixed gas closed
circuit rebreather.
[0014] FIG. 6 is a schematic block diagram of the example modular
controller.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
[0015] For purposes of example, this preferred embodiment is
demonstrated on a closed circuit breathing system known as an MK15
style electronically controlled mixed gas closed circuit underwater
rebreather (FIG. 1) which has had its scrubber housing (FIGS. 3 and
4) and external case modified to accept the modular controller
assembly (FIG. 2).
[0016] This example describes a mechanical module which serves as a
containment for the electronic, mechanical and sensor components of
the control system as referenced in claim 1. Other configurations
as outlined in the claims are possible and practical such as
remote, non-module contained sensors or use in other types of
breathing systems.
[0017] The modularized control system for this example is a
microcontroller based system with the hardware and software
necessary to provide the ability to sense the partial pressure of
Oxygen within a breathing loop using standard Oxygen partial
pressure sensors such as Teledyne R22Ds [available from
Oxycheq.com]. (2, 4 and 6). The controller (22) and associated
firmware also has the ability to control the injection of low
pressure (standard SCUBA interstage pressures of between 165 psi
and 95 psi) Oxygen with a solenoid (62) such as the Wattmiser model
by SnapTite [2W12w-1NB-V0A4 distributed by FasanAll] into a
breathing loop.
[0018] The mechanical module (22) is made of Delrin and machined in
such a way as to create an o-ring gland (20) on one end to
facilitate a bore-seal (28) into the breathing loop area of the
rebreather scrubber canister housing (24). The inside of this
module is machined such that a printed circuit board may be placed
inside in a manner which allows encapsulation by a potting
material, such as Epic S7285. Towards the end of the module (22),
which is placed into the rebreather scrubber canister housing (24),
are gas path and access holes sufficient to provide for the removal
and replacement of the gas sensors (2, 4, and 6) as well as
providing a vent port (12) connected to the output port of the gas
solenoid (62).
[0019] There is a low pressure (less than 200 psi), O.sub.2
cleaned, gas fitting mounted on the inside of the module (22). The
inside of the module (22) at the point of the gas entry (14) is
machined such that a gas-tube barb may be fitted on the inside of
the module (22) and provide a low pressure gas tube fitting to the
input port of the gas solenoid (62).
[0020] An isolation barrier is formed by the isolation gasket (8)
machined into the controller module (22) to provide separation
between the inhalation and exhalation sections of the scrubber
housing (24).
[0021] A printed circuit board (PCB) is manufactured (using
industry standard printed circuit board techniques such as created
with ORCAD Capture/Layout and ordered through PCBPRO.com) which is
shaped to conform to the area defined inside the module (22). The
PCB provides a means for mechanical placement and circuit
communications and control paths between the elements of the
control subsystem including the gas control solenoid (62) and said
Oxygen sensors (2, 4 and 6). The PCB also provides for the means of
electrical interconnection to waterproof bulkhead protected cables
(10 and 16) which are mounted on the side of the module (22). These
cables, (10 and 16), provide a signal interconnect for the user
worn primary (38) and secondary (42) display devices.
[0022] The top of the module (22) provides a separate waterproof
compartment (18) for the installation of a standard alkaline 9 volt
battery (18) which provides power to the plurality of control
system components.
[0023] The control subsystem is defined by several main components;
a microprocessor (90) such as the Motorola MC68HC908JL8CDW (FIG.
3-13) [MC68HC908JL8CDW-ND as ordered through Digikey distribution,
an acquisition and measurement subsystem consisting of a
multiplexer a Maxim 8:1 analog multiplexer such as a MAX4783EUE [as
ordered direct from Maxim-IC.com] (88, 96) and a high resolution
(34 bit) Analog-to-Digital converter such as a Maxim MAX32555ETL
[as ordered direct from Maxim-IC.com] (92 and 98), a power supply
consisting of a standard 9 v battery (18) and standard voltage
regulating circuitry (100) such as a Toko 3.3 volt regulator
TK73733SCL [TK73733SCL-ND as ordered through Digikey Distribution],
a solenoid control subsystem consisting of a solenoid firing
circuit (94) and a solenoid Wattmiser model by SnapTite
[2W12w-1NB-V0A4 distributed by FasanAll] (62), and sensors and
feedback devices consisting of sensors and associated conditioning
electronics for sensors (2, 4, 6, 112). Input channels and
associated software is provided as necessary for other
implementations of additional functional configurations of the
modular control system such as external temperature (116), body
temperature (114), O.sub.2 supply pressure (110), solenoid current
sense (108), diluent supply pressure (106), biometric sensors
(104), O.sub.2 intra-stage pressure sensors (102), and ambient
pressure (120).
[0024] The circuit components are connected together using a
Printed Circuit Board (PCB) using industry standard printed circuit
board techniques such as created with ORCAD Capture/Layout such
that the shape conforms as necessary to fit the space provided in
the module.
[0025] In this example the measurement system for the secondary
monitor (96, 98) is powered independently by the secondary display
so as to decrease the likelihood of linked failures between the
primary and secondary system. The acquisition and measurement of
the Oxygen sensors (2, 4 and 6) are performed by the secondary
display unit (42) via direct control of the multiplexer (96) and
ADC (98) by the microcontroller contained within the secondary
display unit (42).
[0026] The sensors of the system are connected to the multiplexer
(88). The output of the multiplexer (88) is in turn connected to
the ADC (92). The digital controls of both the analog multiplexer
(88) and the ADC (92) are connected to the microprocessor as is the
solenoid firing circuit (94) (solid state relay such as IR PVN012)
which fires the gas addition solenoid (62).
[0027] The primary control system microprocessor (90) has
sufficient inputs and outputs such that the embodied firmware may
calculate all appropriate considerations into a sufficiently
accurate level of partial pressure of Oxygen within the breathing
loop for and during human inhalation and exhalation.
[0028] The firmware will then make a determination as to the need
for addition of Oxygen by the module (22) into the breathing loop
(24). If necessary, the firmware in the microprocessor (90) will
utilize the solenoid control subsystem (94) to cause the solenoid
(62) to open for a sufficiently long duration such that sufficient
Oxygen is added to the breathing system to maintain the desired
level of Oxygen within the breathing system.
[0029] Additional firmware is embodied such that the user primary
display device (38) may inform the user of low battery and other
error conditions as well as of the level of Oxygen in the system.
The control subsystem is enabled to turn on via action of a
pressure switch (110) acting on the systems intermediate Oxygen
pressure as detected in the gas flow path (14).
[0030] The firmware for accomplishing the above tasks is written in
assembly language and downloaded using standard industry
programming devices specific for the processor of choice. The
firmware is structured in a number of extensible code spaces
divided between interrupt driven timed structures and loop driven
structures. The time driven structures provide timed standard code
spaces with the time intervals occurring at 200 us, 10 ms, 50 ms,
100 ms, 1 sec, 10 sec, 1 minute, and 1 hour. The loop driven
structures are divided between a Primary Loop and two Round-Robin
Loop spaces. All code spaces in the Primary Loop space are executed
through the entire loop space as frequently as possible but without
regard to exact time. One of the Round-Robin code spaces is
executed once per pass of the Primary Loop code space and is used
for less time critical applications.
[0031] The overall code structure is divided between 3 levels of
functions dealing with Core, Standardized Support, and Application
Specific code functions--all code in those spaces executing in one
of the above mentioned timed or loop driven code spaces. Each of
the measurement functions is carried out on a timed and table
driven process which accumulates one set of measurements every 50
ms. As each measurement is selected, the multiplexer is set to pass
that measurement parameter through to the ADC (Analog to Digital
Converter), the ADC is then instructed to make the measurement
which is then stored in RAM in the microprocessor. This is a
Round-Robin process initiated by a timer in the 50 ms code space.
Execution Flags are set as each measurement is taken to cause an
additional Round-Robin process to execute which averages the value
of each measurement and determines if the measurement is valid in
terms of ADC functionality.
[0032] The PO.sub.2 evaluation consists of a number of steps. These
steps are to first acquire the raw ADC readings. These are then
averaged and turned into voltage readings for each sensor. These
are stored and also translated via the calibration variables to
PO.sub.2 values. The PO.sub.2 and millivolt values are examined for
each sensor for validity and low level error bits are set
accordingly for each sensor as required. For the sensors that are
determined to have valid readings, they are averaged together and
then evaluated individually relative to the averaged value to
determine if it is in fact valid to include each sensor in the
average. Sensors that are too far apart must have different
algorithms applied to determine the most likely true PO.sub.2
level. Appropriate High and Low Level errors are set depending both
on the relationship of the sensors to each other as well as the
resultant PO.sub.2 determination.
[0033] History Transmission: A generic core based queue management
system is used to handle multiple RS232 transmission requests. This
system manages the task of transmitting a block of data byte by
byte and does not require any other involvement from the
applications code except to provide a request flag set and to
provide the necessary data pointers to the block of data. Once the
transfer is complete, the system sets a data transfer complete flag
that is specific to each data request to enable any action that is
waiting on that specific transfer.
[0034] Watchdog Timer: This is a firmware driven timer that exists
to validate the selection and execution of either the Diagnostic
Mode or the Active Mode. This is meant to monitor the system for
major errors in internal program flow has not engaged one of the
two major wakeup modes. If triggered and the unit is the Master, it
will declare a high level error and attempt to failover to the
lower processor. If the lower processor does not exist, the Active
Mode will attempt to be forced.
[0035] Low Battery Detection: Both battery inputs have an ADC
request generated once per 100 ms. This is averaged in a Round
Robin routine and then translated from the resistor divider output
level into true battery voltage levels. These levels are then
compared against thresholds for error conditions and appropriate
flags are set. This is a Low Level error since even if the battery
is too low to fire the solenoid, there will be no High Level error
generated except as the PO.sub.2 reaches a dangerously low level of
0.18PO.sub.2.
[0036] Fault System: The fault system consists of a High and Low
level tracking system. Each specific error is generated by
individual independently operating routines. These errors are
usually in bytes or flags specific to each area of operation. Once
per second, these errors are translated into High and Low Level
error bytes that are then checked by the Active and Diagnostic Mode
routines.
[0037] In addition to the core structure, the Generic Core provides
a number of processes to support the applications code. These
consist of the SPI and RS232 request queue management and drivers
for external communications, multiple pushbutton debounce and state
management, internal ADC support, and Math routines.
[0038] Sensor Data Management: Sensor data management is the core
critical process of the controller. This is the process that
determines the best truth to be obtained from 3 channels and the
connected 3 sensors regarding the level of Oxygen in the monitored
breathing loop. At first glance, this is not a complicated process.
Most implementations of breathing loop controllers will address
determining the "correct" Oxygen level from three good sensors with
one of several philosophies--The differences that those
philosophies produce in reported PO.sub.2 levels are negligible.
Due to the malleability of the output of fuel cell based Oxygen
sensor cells, it is a standard practice to detect and allow for a
sensor to be out of range of the other sensors by averaging the
remaining two sensors. The definition of "out of range" is
arbitrary and differences in out of range definitions do not
produce significantly different PO.sub.2 results. These standard
approaches produce acceptable results under these limited
circumstances of predominately functional sensors and measurement
systems.
[0039] In addition, it is common to apply the same rules for Oxygen
level determination for all purposes such as Solenoid Control,
Operator Display, Alarm Control, and Calibration Condition. While
applying the same rules for determining Oxygen levels for these
purposes makes sense when everything is predominately functional,
as conditions degrade for whatever reason, the requirements of each
purpose may diverge and one Oxygen Level determination process will
no longer produce optimum results. As an example, the situation of
all three sensors producing greatly divergent readings results in
different demands from the above listed processes: Operator O.sub.2
Display has a mandate to display the known PO.sub.2 level but in
this case, there is no means of determining an actual PO.sub.2
level and the most appropriate display is to indicate an error
condition. The Solenoid Control process has the primary goal of
maintaining a defined setpoint. A secondary goal is to behave in a
manner most likely to keep the operator alive regardless of the
inexactness of the precise Oxygen level. In this case, since it is
more likely that sensors are falsely low due to the chemistry of
their construction; the averaging of the two highest sensors is
most likely to produce an Oxygen level that may not be accurate but
will remain within a livable Oxygen level. The Alarm Control's job
is to indicate when it is likely that the Oxygen level has reached
a dangerous level. In this case, since it is not known which if any
of the sensors are accurate, it is necessary and desirable to err
on the conservative side more so than the Solenoid Control system.
A meaningful system would be to allow the alarm for O.sub.2
dangerously high to be run by the highest sensor alone since that
is the most likely to be accurate due to the most common causes of
O.sub.2 failure. On the other hand, the alarm for O.sub.2
dangerously low conditions would run off the average of the two
lowest sensors. This is due to the most likely failure mode being
to produce a output lower than the actual Oxygen level. The average
of the two lowest sensors will produce an Alarm Level that will
functionally catch an actual dangerously low O.sub.2 level if there
is any nominal relationship between the sensor outputs and actual
O.sub.2 levels, there is a much better chance that these rules
under this circumstance will produce far more meaningful results
than simply using the same approach for all purposes. These rules
change a number of times depending on both what the sensors are
outputting relative to one another then also change again when
additional error sources are taken into account such as wire
breaks, failures in connectors or measurement electronics, etc.
[0040] The result of all this is a dual level matrix of rules. The
first level associates the 4 main processes (Display, Solenoid,
Alarm, and Calibration Condition) to the number of sensors that are
producing information that is assessed as meaningful (3 channels, 2
channels, 1 channel, no channels). In each of these 16 rule areas,
the output of the existing sensors are also assessed in a matrix
determining the explicit rules for all of the circumstances of how
close or not the sensors are tracking each other (3 close, 2 close,
none close) for each of the 4 main processes listed above.
[0041] The exact nature of an expanded rule generation for
different purposes may change depending on the philosophies of the
designers and/or upon the explicit operational or design goals of
the system but the elements of accessing different processes with
different rules makes significant contributions to the ability to
maintain mission capable system in the event of system failures or
functional degradations. As in the example above, it is possible to
function with one simple rule for all purposes (such as use the
middle sensor), it may not always produce as meaningful a result
under all possible circumstances.
* * * * *