The invention provides, in one aspect, a head up display unit for a re-circulating gas self-contained breathing apparatus of the type having at least one sensor for determining the oxygen partial pressure of the re-circulating gas. At least one optical fiber (32) is provided for transmitting a light signal or signals from a respective light emitter, positioned outside the wearer's field of view and electrically connected to the at least one sensor, to a display (26) in the wearer's field of view to provide the wearer with a visual indication of the light emitter signal or signals.

The present invention relates to self-contained breathing apparatus such as may be used for underwater diving or in other hostile environments in which a user may need a supply of breathable gas. Such uses also include fire fighting where the atmosphere may be heavily polluted with combustion products and noxious gases, other industrial environments where the atmosphere may be polluted or otherwise unbreathable, or at high altitude where the atmosphere itself is too thin or effectively non-existent. More particularly the invention concerns a head up display for self-contained breathing apparatus

Although applicable to a wide range of other uses the present invention will be described hereinafter with particular reference to its application to underwater breathing apparatus for diving applications. It will be understood, however, that this description is provided without prejudice to the generality of the invention or its range of applications.

It is well known to provide divers with self-contained underwater breathing apparatus in order to prolong the time for which they can remain below the surface of the water. The most widely used self-contained breathing apparatus comprises a rigid container within which is housed a supply of compressed air which is allowed out of the container via a high pressure or first stage regulator and directed through a flexible hose to a mouthpiece containing a demand valve including a second stage regulator which acts automatically to open and close as the diver inhales and exhales. Such systems are known as open-circuit breathing apparatus because exhaled gas is allowed to pass directly out into the marine environment so that a stream of bubbles is emitted upon each exhalation

Proposals have in the past been made for so-called closed circuit or “re-breather” apparatus in which the carbon dioxide content of exhaled air is removed from the exhaled air outside the body, fresh oxygen is introduced to replace that consumed, and the thus-reconditioned air returns to the diver for re-breathing. In this way it is necessary for the diver only to carry two or three lungfuls of breathable gas sufficient to circulate around the closed circuit.

Such a system is described, for example, in WO99/13944. The carbon dioxide removal filter in the system described in WO99/13944 includes a chamber housing oxygen partial pressure sensors used to detect the oxygen content in the exhaled gas and to reinstate the oxygen balance by introducing oxygen through a valve controlled indirectly by the sensors. The oxygen sensor system is described as comprising three sensors with the average of the two nearest sensors, in terms of output readings, being taken to produce the control signal. The signal outputs from the sensors are fed to two hand held electronic control units through sheathed waterproof electrical cables. Each control unit comprises an on/off switch, a set of control buttons and a display for displaying breathing apparatus, environmental and operational parameters including the oxygen partial pressure of the exhaled gas as detected by the sensors.

One drawback of the arrangement described in WO99/13944 is that the handset is the primary display and therefore the diver has to constantly monitor the handset to view the data displayed. Such handsets are not ideal in poor light or poor visibility conditions or in situations where the diver's hands are occupied with other tasks. In addition, being out of the line of sight, the diver is not immediately alerted to warning signals displayed on the handsets or if the system malfunctions or shuts down. This problem is somewhat overcome in known arrangements by providing the diver with a head up display for monitoring various breathing apparatus, environmental and/or operational parameters. In one arrangement electrical signals are fed to light emitting diodes (LEDs) in a head up display unit mounted on the mouthpiece of the breathing apparatus. The signals are fed to the LEDs by means of an electrical cable which connects the LEDs to a power source contained within the breathing apparatus. One drawback of this arrangement is that it requires a waterproof, and hence relatively expensive, electrical connection between the power source and the head up display to prevent corrosion and malfunction of the connection due to water seepage along the length of the electrical cable and onto the connection terminals. This arrangement is also prone to misuse or mistreatment by the diver. The electrical connection also effectively limits the operating depth of the breathing apparatus.

There is a requirement for an improved self-contained breathing apparatus of the type having a head-up display for presenting information relating to the apparatus or other operational parameters to the diver in the diver's field view.

According to an aspect of the present invention there is provided a self contained breathing apparatus comprising at least one optical fibre for transmitting a light signal or signals from a respective light emitter positioned outside the wearer's field of view to a display in the wearer's field of view to provide the wearer with a visual indication of the said light emitter signal or signals. The optical fibre cable readily enables light signals to be transmitted directly to the user's field view independently of the position of the light emitter on the breathing apparatus. Optical fibres do not require pressure or waterproofing unlike electrical connections used in known arrangements and optical fibre cables are easily replaced at relatively low cost.

In preferred embodiments the display is positioned at or in the region of the mouthpiece of the breathing apparatus. This readily enables light to be transmitted from light emitters located, for example, on or in the sealed carbon dioxide scrubber canister, typically worn on the back of the diver in a re-circulating type of breathing apparatus, to the mouthpiece area where it is visible to the diver.

Preferably, the display is mounted on the mouthpiece. In preferred arrangements the display is attachably/detachably mounted on the mouthpiece in fixed relation to the mouthpiece body. This readily enables the display to be removed for servicing and/or repair and/or replacement of one or more optical fibre fed to the mouthpiece display.

The display may be mounted on or in fixed relation to the mask of the breathing apparatus.

Preferably, the optical fibre terminates within a housing with the respective end of the fibre directed towards the wearer. The housing preferably comprises a guide for guiding the optical fibre in the housing and turning the fibre so that the terminal end of the fibre is directed substantially perpendicularly to the direction of the fibre entering the housing. The guide defines a path for the optical fibre ensuring that the bend radius of the optical fibre does not exceed the minimum bend radius requirements of the fibre being used.

In preferred arrangements the optical fibre is encapsulated within a protective plastics material, preferably a semi-ridged plastic rod.

The housing may have a substantially cylindrical configuration, preferably having a circular cross-section, with the terminal end of the optical fibre being located in an opening in the outer surface of the housing. This readily enables the housing containing the optical fibre terminal end to be mounted in a mounting structure provided on an outer surface of the mouthpiece.

In preferred embodiments the light emitter comprises a light emitting diode (LED). Preferably a plurality of optical fibres are provided for transmitting light signals from respective light emitters optically connected to the fibres. In this way it is possible to increase the number of signals capable of being displayed in the diver's field of view without significantly adding to the cost and complexity of the display.

The terminal ends of the optical fibres maybe arranged in an array, for example an array of two left hand and two right hand lights with the upper and lower lights in the array being arranged to emit different colours of visible light.

In preferred embodiments each light emitter is operable to emit a continuous or intermittent light signal, that is to say a continuously illuminated signal, a continuously un-illuminated signal and a variety of flashing sequence signals for different signals.

The breathing apparatus maybe a closed circuit or semi-closed circuit breathing apparatus having at least one oxygen sensor for determining the oxygen partial pressure of the re-circulating gas, and the or each light emitter may be operable to emit a light signal representing a pre-determined condition of a respective oxygen sensor. For example, a continuously illuminated green light may indicate that the oxygen partial pressure detected by a respective sensor is within a predetermined acceptable range.

The predetermined condition may comprise at least one of a maximum, minimum or predetermined oxygen partial pressure, or remaining battery life.

Preferably, the closed circuit or semi-closed circuit apparatus comprises a housing containing a carbon dioxide scrubber and/or at least one oxygen partial pressure sensor with the or each light emitter mounted on or in the housing. In preferred embodiments the or each light emitter is encapsulated within an opening in the housing. For example, the light emitter may be encapsulated within a transparent resin material sealing the opening in the housing in which the light emitters are mounted.

In one arrangement the breathing apparatus comprises an open circuit breathing apparatus and the or each light emitter is operable to emit a light signal in response to the detection of a minimum breathable gas pressure condition, that is to say the tank pressure of the compressed breathable gas.

Preferably the or each light emitter is operable to emit a warning signal in response to at least one breathing apparatus, environmental or operation parameter being detected outside a predetermined allowable range of values. For example, a warning signal could be provided to warn of decompression obligations, ascent speed violation or ceiling violation when a diver ascends above a decompression stop.

According to another aspect of the invention there is provided a head up display for a re-circulating gas self-contained breathing apparatus of the type having at least one sensor for determining the oxygen partial pressure of the re-circulating gas, characterised in that there is provided at least one optical fibre for transmitting a light signal or signals from a respective light emitter, positioned outside the wearer's field of view and electrically connected to the said at least one sensor, to a display in the wearer's field of view to provide the wearer with a visual indication of the said light emitter signal or signals.

According to another aspect of the invention there is provided a self contained breathing apparatus comprising at least one optical fibre for transmitting data from a processor positioned outside the wearer's field of view to a display in the wearer's field of view.

According to another aspect of the invention there is provided a self contained breathing apparatus comprising at least one optical fibre for transmitting data between respective transmitter and receiver means in said breathing apparatus.

In preferred embodiments the said optical fibre is connected to respective breathing apparatus hand held display means and/or head up display means. Alternatively or additionally the optical fibre may be connected to data input means. For example, the optical fibre may transmit data between a first processor located in the wearer's field of view to a second processor located outside the wearer's field of view.

Referring toFIG. 1, a mouthpiece assembly10for a self-contained breathing apparatus, for example a closed circuit or semi-closed circuit breathing apparatus, comprises a main cylindrical body portion12, a pair of hose connector tubes14and16coaxially disposed at opposite axial ends of the cylindrical12and a mouth engagement part18extending radially from the cylindrical body12for insertion in the mouth of the diver or other user of the breathing apparatus. The first connector tube14connects the mouthpiece10to an inhalation hose (not shown) for delivering breathable gas to the user while the second tube16connects the mouthpiece to an exhalation hose (not shown) for re-circulating exhaled gas. A pair of hose connector rings20and22are provided at the respective axial ends of the cylindrical body for securing the inhalation and exhalation hoses to the mouthpiece in sealing engagement as is well know in the art.

The hose connector ring20on the inhalation side of the mouthpiece10is provided with a display24, which may be considered to define a head-up display, for presenting visual light signals to the user. The display may, for example, display signals indicating the attainment or non-attainment of various apparatus, environmental or operational pre-conditions. The display24comprises a 2×2 array of lights26ato26din the outer surface of a cylindrical housing28located in an open part-cylindrical mounting member30positioned on the outer surface of the connector ring20with which the mounting part30is integrally formed (moulded). The cylindrical housing28is received within the interior of the cylindrical mounting member30with the lights26ato26dangularly positioned in the circumferential gap between the respective circumferential ends of the mounting member30so that the lights26ato26dare visible to the user and positioned directly in the user's field of view.

The drawing ofFIG. 2shows the display24and hose connector ring20only, with the cylindrical housing28of the display located in the cylindrical mounting part30of the connector ring20. As can be seen in the drawing ofFIG. 2, four optical fibre cables32ato32d, of a multi-core cable comprising polyethylene (fibre optic) rods, enter the interior of the housing28in a direction parallel to the axis of the housing on the side of the housing adjacent to the hose connector tube14when in the assembled configuration ofFIG. 1. The optical fibre cables32ato32dturn through substantially 90 degrees within the cylindrical housing28so that their respective terminal ends are positioned in the respective light apertures26ato26dat the other axial end of the housing such that the respective terminal end faces of the optical fibres are directed radially outwards of the housing28. This arrangement is more readily understood from the exploded view of the display shown inFIG. 3.

Referring to the drawing ofFIG. 3, the head-up display24comprises optical fibre cables32ato32d, a toroidal end cap34having a central aperture36through which the cables32ato32dpass, a guide and clamp element38for guiding the cables through the aperture36and a guide element40for guiding the cables through the remaining part of the interior of the housing. The guide element40includes four respective guide ways42ato42dwhich guide the ends of the cables32ato32dthrough a 90 degree bend so that the terminal ends of the cables are aligned with the respective apertures26ato26din the housing28. The guide ways42ato42dhave a bend radius no less that the minimum bend radius of the optical fibre cable.

The assembled head-up display24is received in the part cylindrical mounting part30with the apertures26ato26dpositioned in the circumferential gap region between the respective circumferential ends44and46of the cylindrical mounting part30. A keyway and slot arrangement (not shown) is provided between the cylindrical housing28and the mounting part30to prevent rotation of the display24in the mounting30. The mounting part30preferably has a an internal diameter slightly less than the outer diameter of the housing28so that the display24is held by the resilient action of the mounting30against the housing28thereby providing an interference fit to resist displacement of the display in the mounting30. As will be explained in greater detail below the optical fibres32ato32dtransmit light signals to the display24from light emitters located elsewhere on the breathing apparatus and outside the divers normal field of view when wearing the breathing apparatus. In the illustrated embodiment optical fibres32aand32bare optically connected to respective red light emitting LEDs and optical fibres32cand32dare optically connected to respective green light emitting LEDs. Optical fibres32aand32cdisplay light signals relating to a first oxygen sensor control unit (not shown) and similarly optical fibres32band32dtransmit light signals relating to a second oxygen sensor control unit (also not shown). Such oxygen sensor control units are well known in the art and are used, inter alia, for controlling the amount of oxygen that is introduced into the re-circulating gas flow in a closed circuit or semi-closed circuit re-breather type apparatus.

Referring now toFIG. 4, in one embodiment the ends of the optical fibre cables32ato32dare optically connected to respective LED light emitters (not shown) located in the lid50of a carbon dioxide scrubber container52containing the afore-mentioned first and second oxygen sensor control units. The LEDs connected to the control units are encapsulated in resin in a port54into opening the interior of the canister52. The port54is located in the lid50so that the optical fibre cables32ato32dmay be readily connected and disconnected from the canister lid50. The optical fibre cables32ato32dare connected to the canister lid50in a similar way that they are connected to the display24in the sense that the port54provides a cylindrical housing for receiving the terminal ends of the optical fibres which pass through a toroidal end cap56and a cable guide and clamp element58which hold the cable ends in alignment with their respective LED light emitters in the port54.

Referring now toFIGS. 5ato5h, inFIG. 5anone of the four lights in the display24are illuminated indicating that the breathing apparatus is not ready for use, that is to say it is not in the dive mode and therefore the apparatus is not ready for use.

InFIG. 5bboth the lower left hand and right hand lights are continuously illuminated. As previously mentioned the lower light positions26cand26dare connected to respective green light emitting LEDs. When these lights are continuously illuminated as inFIG. 5bthe lights indicate that both oxygen sensor control units associated with the respective LEDs are configured in the dive mode and that the detected oxygen partial pressure is within acceptable limits. When these lights are continuously illuminated it is safe to use or continue to use the breathing apparatus. InFIG. 5cboth the left hand and right hand lights in apertures26cand26d, that is say the two green lights, are flashing which indicates that the oxygen partial pressure has fallen below an acceptable minimum, for example by 0.2 bar, as determined by both first and second oxygen sensor control units. InFIG. 5dthe red light in aperture26aand the green light in aperture26cof the display are indicated as flashing alternatively, which indicates that the battery powering the first oxygen sensor control unit is low and that further use will result in the battery being drained. Also inFIG. 5dthe green light in aperture26dis continuously illuminated indicating that there are no problems associated with the second oxygen sensor control unit. InFIG. 5eall four lights are flashing simultaneously which indicates that the deviation of one sensor differs from the average of the two nearest, in terms of output, by more than a set amount, for example 1.2 bar. InFIG. 5fthe red and green lights in apertures26aand26care flashing simultaneously while on the right hand side of the display only the green light in aperture26dis illuminated. This indicates that there is a problem with the first oxygen control unit but not the second which is functioning correctly. InFIG. 5gboth red lights in apertures26aand26b, on the left and right hand side of the display, are flashing. A high frequency flash indicates that a high oxygen partial pressure has been detected by both oxygen sensor control units, for example over 1.6 bar. A slow flash rate indicates a low oxygen partial pressure, for example below 0.4 bar. InFIG. 5hboth red lights in apertures26aand26bare illuminated continuously, alerting the diver to a condition that requires immediate attention thus warning the diver that he must look immediately at the breathing apparatus handset display where various equipment and environmental and operational parameters are displayed.

From the above description ofFIG. 5ato5hit will be appreciated that various types of warning signals can be communicated to the diver using different combinations of light signals on the head-up display24. These signals may be warning signals or simply signals to reassure the diver that the breathing apparatus is functioning correctly as in the display ofFIG. 5b. The display therefore provides the diver with a constant appraisal of safety related parameters for immediately alerting the diver to problems or potential problems as they occur so that the diver may check the data on the more detailed hand held displays of the breathing apparatus.

Although aspects of the invention have been described with reference to the embodiments shown in the accompanying drawings, it has to be understood that the invention is not limited to the precise embodiments shown and that various changes and modifications may be effected without further inventive skill and effort. For example, the display arrangement of the present invention may be used in open circuit breathing apparatus as well as closed circuit or semi-closed circuit apparatus. For instance, the display may be adapted to indicate a low detected pressure of the available compressed gas in the tank of an open circuit breathing apparatus. In addition the display may be adapted to provide warning signals or decompression obligations, ascent speed violation or ceiling violation when the diver ascends above a decompression stop in a dive sequence.

In other arrangements the breathing apparatus is provided with at least one optical fibre for transmitting data between data processing nodes at various positions on the breathing apparatus. For instance, data may be transmitted from a central processor or control unit mounted in the canister to a hand held display and/or head up display of the breathing apparatus. Similarly data may be transmitted from a hand held controller having a data input function to a central control unit.