the invention comprises ( a ) a breathing bag adapted to change volume in a horizontal direction predominantly and ( b ) a means for positioning the breathing bag such that horizontal expansion continues to occur regardlessof the diver &# 39 ; s orientation or attitude in the water . more particularly , in one embodiment , the breathing bag design is a flat bladder shape , constrained on the flat sides by a housing or container andoriented horizontally such that the flat sides are parallel to the horizon . the inlet / outlet opening is on the cylindrical or curved surface of the bag , and bag expansion and volume change can occur in a horizontal direction almost completely . whatever vertical component may exist is minimized by having a large , flat horizontal surface to the bag , so that for a given tidal volume of breathing , for example , the bag moves a minimal distance vertically . in another preferred design , the housing is the same , but the bag has a tubular , spiral shape . this bag expands and contracts in a horizontal plane defined by the upper and lower plates of the housing . one end of thebreathing bag tube is closed and the other connected to a 90 degree rotatable joint which is connected to a completely ( 360 degree ) rotatable collar . a servo - mechanism senses the position of the bag and adjusts the bag to keep it in a horizontal position , regardless of the orientation of the diver . having described the invention , the following examples are given to illustrate specific applications of the invention including the best mode now known to perform the invention . there may be other ways to do the basic tasks of the present invention , once the invention is known , thus these specific examples are not intended to limit the scope of the invention described in this application . to keep the breathing bag horizontal in the water , its position in space must be sensed by a 3 - axis position indicator located within or on the breathing bag housing of the uba . position indicators are more common to the aerospace art , particularly airplanes with pitch ( up and down at the head ), yaw ( side - to - side ) and roll axes and displays common in the cockpit . a position indicator adapted for use underwater is described hereas an example : three pressure transducers are placed in a horizontal plane on the breathing bag housing , and pitch , roll and yaw are determined by the different readings on these transducers . for example , the north transducer reads pressure a , the west transducer reads pressure b , and theeast transducer reads pressure c . if a = b = c , the diver is horizontal ( pressure is relative to a common point on the uba , preferably in the center ). if b & gt ; c and both greater than a , then the diver is pitched down atthe head and rolling to the right . the degree to which this is true dependson the magnitude of the pressure signals . many other combinations could be discussed , but the principle is clear . this provides a signal for corrective action to be taken by the servo - mechanism to right the breathing bag housing to the horizontal position . the pressure transducers may be of any type current in the diving art , suchas the metal diaphragm differential pressure cells manufactured by validyneengineering corporation , northridge , calif ., or a miniaturized piezoelectric device adapted for use underwater , or pressure transducers whose working principles can be adapted for underwater use . these transducers sense differential pressure by deflection of a diaphragm or stretching of a thin film of material , which changes the resistance or other electrical properties of the material ; these in turn can be sensed as a voltage or current change . the microprocessor can be any adaptation of similar units nowadays commonly used in automobiles to monitor engine function and effect changes in the operating variables . the appropriate circuit design simply needs to be carried out and the unit programmed to obtain the desired functional performance . this is well within the skill of the present electronic art . with reference to fig1 basic elements of the uba and features of the present invention are shown . the diver breathes on mouthpiece . [ 1 ]. breathing gas circulates through hose [ 2 ]; arrows show direction of gas motion . the co 2 from the diver &# 39 ; s exhale gas is absorbed in canister [ 3 ], make - up oxygen is added by oxygen bottle [ 4 ] as needed . the breathingbag [ 5 ] provides a capacitance in the system . the uba housing [ 6 ] is generally porous to water , so all the elements are in a water environment . diluent gas bottle [ 7 ] for adjusting volume in the breathing bag is also shown . with respect to the elements of the present invention , the breathing bag housing [ 8 ] has a disc or coin shape , circular in one plane and thin in the depth dimension . a preferred diameter is in the range 12 - 15 inches andthickness about 2 - 3 inches to provide enough volume ( about 3 - 5 liters ) for tidal volume excursions in the diver &# 39 ; s breathing pattern . the breathing bag housing is moveable and rotatable through joint [ 9 ] and servo - motor [ 10 ], which also contains a microprocessor or computer function . anti - collapse structure shown as perforated tube [ 16 ] prevents total collapse of the bag . other structures , such as wire grid works modeled after devices used to prevent tennis dome collapse or other gas bag collapse can be substituted . fig1 ( a ) shows a detail of one embodiment ofa moveable and rotatable joint . joint is rotatable 360 degrees through collar [ 11 ] and the breathing bag housing can be raised through 90 degreesthrough hinge pin [ 12 ]. alternatively , it may be preferred to design this joint with a full 180 degree capability for easier positioning of the breathing bag housing whenthe diver is almost prone , facing up . in these cases , it would be desirableto have an extension capability in the tube that contains the rotatable collar , so that the uba housing can be safely cleared . the alternative is to design the length of the tube such that the breathing bag housing clears the uba for all 360 degrees . the joint may be a complex assembly ofseveral single moveable joints rotating in one plane only , or may be a ball - type joint completely rotatable in all directions . the specifics of the joint design are within the skill of the art . only typical examples are presented here . the position of the bag is sensed by a 3 - axis orientation indicator [ 13 ], whose signal is sent to the servo - motor and control computer / microprocessor [ 10 ]. fig2 shows how the breathing bag housing would look under different conditions of diver orientation . in fig2 ( a ) the diver and uba are upright , and the breathing bag housing [ 8 ] is horizontal as shown . in fig . 2 ( b ) the diver and uba are in the prone position , and the breathing bag housing [ 8 ] is close to the back of the diver . in fig2 ( c ) the diver and uba are prone on the side , and the breathing bag will extend outward from the back as shown . in fig2 ( d ) the diver and uba are semi - prone , facing up . the bag assumes the horizontal position shown , clearing the uba housing . alternatively , a protective , porous , rigid , second housing [ 15 ], illustrated in fig2 ( a ) and 2 ( c ), can surround the bag movement area . thehousing [ 15 ] can be any rigid , porus , protective structure such as wire grid etc . well known from similar structures in the art . fig3 shows a schematic of the spiral breathing bag [ 5 ] and housing [ 8 ]. the spiral bag needs a mechanism to keep one end collapsed , yet extensible . collapsed part of the breathing bag [ 14 ] is shown in fig3 also , for a volume of air that does not fill the complete volume of the tubular , spiral breathing bag . keeping one end collapsed is accomplished by an axial flat - wire spring imbedded in the bag material , for example , but other ways known to the art may also be used . the spring must be of a stiffness to substantially retract the bag under zero pressure differential , yet allow expansion without much pressure differential . the pressure differential for expansion vs . the amount expansion is the elastic characteristic of the bag . this should be kept below about 2 - 3 inches of water for the purposes of this invention , preferably below 1 inch of water equivalent pressure . when the bag of fig3 inflates or deflates , it moves in a spiral path and expands horizontally . thus the housing must be porous to allow movement ofwater therethrough and rigid to contain the ultimate expansion of the bag . as long as the housing or restrictive structure of the discs is kept horizontal , the elastance of this system is minimal . horizontal placement is accomplished by the servomechanism and microprocessor adjusting the rotatable joints . in an especially preferred embodiment , the bag is bladder - shaped , as shown in fig1 and thin and circular like a short cylinder . preferably , the bag has a mesh tube or other porous structure inserted inside to prevent collapse of the walls when evacuated . this function is provide in uba &# 39 ; s ofthe art in many similar ways . thus , minimal elastance is produced from a large , flat surface kept in a horizontal orientation . changes in volume ofthe bag due to a tidal breath , for example , result in a relatively small change in vertical dimension . we estimate this to be about 2 - 3 inches , typically , and preferably about 1 inch . the breathing bag housing is rigid and porous and should not need any further protection . however , because it is moveable and protruding , a second housing may be desired . this housing should also be rigid and porous , but must be large enough to contain all possible configurations ofthe breathing bag housing . this adds a large bubble on the divers back which may limit access to narrow passageways , but will provide protection from snagging or bumping of the bag housing on foreign objects . one way the size of this second housing can be reduced is to give the rotatable joint [ 11 ] moveable as well as extensible capability . this is done by the joint being mounted on tracks and moved by another motor controlled by themicroprocessor or computer . these and other variations are well within the current skill of the electronic and mechanical arts . obviously , many modifications and variations of the present invention are possible in light of the above teachings . it is therefore to be understoodthat , within the scope of the appended claims , the invention may be practiced otherwise than as specifically described .
this invention comprises a minimal elastance underwater breathing apparatusuba ) in which the elastance component of uba impedance is substantially eliminated by forcing the breathing bag to expand and contract in a horizontal plane with small vertical displacements and hence minimal elastance . the invention further includes a servo - mechanism operating with a microprocessor , 3 - axis position sensor and rotatable joints which act to keep the breathing bag oriented horizontally no matter what the diver &# 39 ; s position . the principles of the present invention may be adapted to existing uba with redesign and additions .