Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
  • B63C—LAUNCHING, HAULING-OUT, OR DRY-DOCKING OF VESSELS; LIFE-SAVING IN WATER; EQUIPMENT FOR DWELLING OR WORKING UNDER WATER; MEANS FOR SALVAGING OR SEARCHING FOR UNDERWATER OBJECTS
  • B63C11/00—Equipment for dwelling or working underwater; Means for searching for underwater objects
  • B63C11/02—Divers' equipment
  • B63C11/18—Air supply
  • B63C11/22—Air supply carried by diver
  • B63C11/2245—With provisions for connection to a buoyancy compensator
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
  • B63C—LAUNCHING, HAULING-OUT, OR DRY-DOCKING OF VESSELS; LIFE-SAVING IN WATER; EQUIPMENT FOR DWELLING OR WORKING UNDER WATER; MEANS FOR SALVAGING OR SEARCHING FOR UNDERWATER OBJECTS
  • B63C11/00—Equipment for dwelling or working underwater; Means for searching for underwater objects
  • B63C11/02—Divers' equipment
  • B63C11/04—Resilient suits
  • B63C11/08—Control of air pressure within suit, e.g. for controlling buoyancy ; Buoyancy compensator vests, or the like
  • B63C2011/085—Buoyancy compensator vests

Definitions

• the present invention relates to the automatic control of diver buoyancy and buoyancy compensation.
• the present invention relates to a device for use on buoyancy compensation devices worn by divers, to provide functions such as the imposition of a depth limit, a controlled ascent rate, or to follow a decompression profile automatically, in a safe manner.
• buoyancy of divers may change underwater, such as from increases in ambient pressure compressing the gas inside neoprene often used by divers to provide thermal protection, or from the consumption of the gas carried in pressurised cylinders. Additionally, novice divers are typically over-weighted such that they require a matching positive buoyancy to be able to swim freely
• BCD buoyancy compensation device
• Some automatic buoyancy devices have been developed and two devices are in the market.
• One device is for lifting objects, such as mines, in a controlled manner: this releases the contents of a very small gas cylinder into a bladder and then controls the rate of ascent by opening a vent valve: the gas is always at the
• a device is commercially available for the rescue of divers on oxygen rebreathers, whereby if a preset depth or time is exceeded, it releases the contents of a cylinder into a life-safer device that guarantees a head up position: the diver is assumed to be unconscious or dead at the point the device is activated.
• the ascent rate is able to be limited because the position of the gas in the bladder is known as it designed to provide a head up position for the diver, and does not have to hold any set depth: the device takes the diver directly to the surface without any stops on the way.
• GB patent GB798366A describes a device that closes off a gas injection means when a BCD has a reached a maximum volume of gas, and can also vent gas by a volume sensitive means, i.e. when the maximum volume in a BCD is exceeded.
• a volume sensitive means i.e. when the maximum volume in a BCD is exceeded.
• the vent valves on BCDs are spring loaded such that when the internal pressure exceeds the lift pressure (i.e. when the BCD bladder is full), the BCD vents all additional gas. This feature forms part of the requirements incorporated into EN 1809:1997 as a basic safety requirement for divers' BCDs.
• GB24499495A describes a device that is a subset of the pre-existing and commercially available mine and incapacitated diver recovery systems, but GB24499495A, and others such as US20021277062A and US201083373A, fail to include any workable means to regulate the diver's ascent rate of a normal diver's bladder, so once gas is injected into the bladder and an ascent initiated, the device would likely injure or kill the diver by an uncontrolled ascent as the gas in the bladder expands with reducing ambient pressure and further accelerates the diver toward the surface.
• US20021277062A and US201083373A fail to include any workable means to regulate the diver's ascent rate of a normal diver's bladder, so once gas is injected into the bladder and an ascent initiated, the device would likely injure or kill the diver by an uncontrolled ascent as the gas in the bladder expands with reducing ambient pressure and further accelerates the diver toward the surface.
• patents of this type where the concept has neither been reduced to
• An automatic BCD needs input valves and vent valves to add gas or vent gas from the bladder.
• the vent valves need to operate with a practical power consumption and in a way that allows the gas to actually vent: if there is just one vent then the gas will not vent in many diver attitudes because water pressure closes the gas pathway between the vent and where the gas is located within the bladder (the uppermost part of the bladder usually - what is "uppermost" depends
• At least three vent valves are required to vent gas from a bladder that may be in any orientation, and for some bladder shapes, even more are needed to ensure an open gas path between where the gas is located and a vent valve that is at a lower relative ambient pressure - otherwise the gas will not vent from the bladder when required.
• vent or exhaust valves can be installed if one-way valves are fitted to each of them: without the one-way valves the bladder would flood as multiple ports would be open simultaneously.
• Such vent valves with one-way valves were fitted to some rebreathers from 1999. Similar valves have been available for dry suits (a diver's buoyancy compensation device where the bladder is integrated with the diver's thermal protection), for at least 25 years.
• the US patent application US2001036781 A describes vent valves connected to ropes that allow multiple valves to be opened by means of a single action. It is well known therefore that multiple vent valves can be opened or closed on a BCD by a single action, and using one-way valves within the vent valve to avoid the bladder flooding.
• the US patent application US2002182013A is another example of a device for opening the inflation and deflation valves and describes a means to operate a plurality of valves manually.
• Pneumatically controlled vent valves are known but are not used hitherto for automatic buoyancy control. Pneumatically controlled vent valves have been in use previously in some submarines, for controlling buoyancy. US 6,217,257 describes a BCD where there are multiple vent valves controlled pneumatically, with one-way valves to prevent water ingress. Such a valve is suitable as a vent for the present application.
• WO 9,937,534 is an example of a concept patent which makes very broad claims for a device that has the obvious features desirable in an automatic buoyancy control device, including preventing a diver from exceeding a predetermined depth, and for controlling the ascent rate, based on depth detection and CPU calculations.
• depth detection and CPU calculations There are no depth detection and CPU calculations in that patent application and there is no known means to provide the features described with even current technology using the structures described in that patent.
• the accuracy and resolution required from a depth sensor to provide a set depth where the data is ambient pressure is 28 bits.
• ADC Analogue to Digital Converter
• US 5,496,136 and US 5,746,543 are examples where inventors try to control the buoyancy by a means involving determining the volume of the bladder by measuring the flow into and out of the BCD. How these flows translate into actual control of the inlet and outlet valves is not disclosed.
• the concept of measuring volume by measuring the flows does not work in practice, because any error between an input and output flow sensor accumulates in the integration process that is essential to estimate volume, and then subtracting the two integrals results in such substantial errors as to make the implementation impossible.
• a 1% error in the integration differentials would amount to an error of 200ml even the first time the gas is injected, and then this error would increase linearly every time gas is injected or vented.
• volume of gas in a bladder also depends on the temperature. Due to the large surface area of a bladder the temperature of the gas in a bladder will generally differ considerably from the temperature it is injected at. Moreover, the act of reducing pressure of a gas in an injector also changes its temperature. There is no solution in DE 4,125,407 to the fundamental problem of the errors that accumulate when deriving a parameter that is the difference of two large integrals. There is also no solution to the problem that changes in ambient pressure will also cause the volume in the bladder to change, dramatically.
• a typical ambient pressure sensor generates a 0 to 1 Volt signal over a pressure range of 0 to 10 bar (equating to 0 to 100m of water depth if the salinity is zero and the water density is 1 kg / litre), then the speed of the diver ascending at a rate of 10m/minute would generate a signal of 1 .67 mV per second, and the acceleration of the diver would be a full scale signal which is an order of magnitude or more less than this.
• the signal is of very low frequency, so is in the part of the frequency spectrum with the most noise. Even disregarding noise, the acceleration signal full scale would be less than the least significant bit from a 20 bit ADC that digitises the ambient pressure sensor signal.
• US2010003083 also describe BCDs with multiple bladders, but in the current context of an automatic buoyancy control dive, the change in attitude by use of multiple bladders has such a low rate of acceleration as not to be useful.
• a well designed BCD should keep the gas in the right position such that the diver has a neutral attitude underwater.
• US 6,666,623B1 includes some claims for a device for controlling the buoyancy of a diver jacket so as to control his rate of ascent. Two different rates can be selected; a second diver can override the setting in order to safely send a disable diver to the surface. This suffers from the same limitations as WO
• the present invention relates to devices, techniques and methods to manage the buoyancy compensation device worn by a diver, whereby gas is added to the bladder via an electrically controlled gas valve, and vented by the simultaneous operation of three or more pneumatically activated valves, in a safe manner.
• the control unit determines the period that the valves should be opened using an algorithm using inputs from sensors measuring depth and derivatives of the depth (the first derivate obtaining speed, and the second derivative the acceleration of the diver).
• the device uses a novel combination of sensors to obtain the ambient pressure, speed and acceleration of the diver within the accuracy and resolution limits of practical sensors and ADC converters.
• the gas valves are arranged in a novel manner such that removal of the gas supply to the device, or removal of electrical power, leaves the manual control functions operational as a manual buoyancy control device, and whereby failure of any hose or actuator does not create an unreasonably dangerous situation for the diver.
• a novel gas connection fitting is described that is able to tap the gas supply to the manual inflator to provide a gas supply for the actuators.
• a novel control means is described for an automatic buoyancy compensator which sufficiently damps the natural positive feedback loop within a bladder, such that the ascent speed, or descent speed is limited, and the diver can hold a desired depth.
• a novel gas vent device is described which enables the device to operate consistently, whether the powered gas piston is used to open the valve or if the valve is opened manually.
• Figure 1 Shows an example of the overall configuration of the present invention onto a BCD.
• Figure 2 to Figure 5 show the gas flow paths of an actuation means in a preferred example embodiment of the present invention in each of the four states where two solenoid valves are used to control the injection of gas into a bladder and into a fine bore hose to pneumatic vent valves.
• Figure 2 shows the case where both solenoid valves are closed on initial start-up
• Figure 3 shows the state where the first solenoid valve is energised to activate the vent valves
• Figure 4 shows the state where a second solenoid valve is has been energised and gas flows into a fine bore pneumatic hose that activates an exhaust valve
• Figure 5 shows the state following that valve being subsequently closed and a residual gas is released into the bladder.
• Figure 6 shows a preferred arrangement of gas valves providing fail-safe features.
• Figure 7 shows the cross section of a device providing enabling a gas supply to be tapped off from a manual injector to supply an automatic buoyancy control device, leaving the manual injector functions operating as well as the ability of the diver to disable the device by unplugging the gas supply.
• Figure 8 shows a basic pneumatically activated vent valve according to the present invention which provides a consistent operating force and seating of the valve.
• Figure 9 shows the main four modes of acceleration drop for negative initial speed. Vectors of the positive waypoint, speed and acceleration direct to depth. Vectors of the negative waypoint, speed and acceleration direct to surface. IV mode includes the motion with/without speed limit.
• Figure 10 shows a block schematic generating speed and acceleration signal from a pressure sensor using analogue means, and combining part of a filter to reduce the effect of respiration on the data with the differentiator producing a speed signal.
• Figure 1 1 shows a control process example in the Ada language for controlling the gas injection and venting of a bladder to achieve accurate control of diver depth, enabling the diver to move from a current depth to a set depth without exceeding predefined ascent or descent rates.
• Figure 1 shows an example of the overall configuration of the present invention onto a BCD bladder (1 ), having each of the following essential parts of the overall system for automatic buoyancy control:
• An electrically operated gas valve that is able to pressurise a gas hose that powers a means to produce a mechanical motion within a vent valve, and also a second electrically operated gas valve able to apply gas to inflate the bladder.
• vent valves per bladder each being pneumatically activated.
• a controller which contains sensors to measure pressure and either circuitry or sensors to measure the first and second derivatives of pressure, run a control code using those parameters and produce signals to open or close at least two electrically operated gas valves.
• Embodiments may optionally include a diver display, dive computer and user controls.
• FIG. 1 An example embodiment of a novel means to take a gas supply is show in detail in cross-section diagrams forming Fig. 1 and Fig. 5, and shown externally in Fig. 2 to 4, comprising a means to connect to a pressurised gas supply (3) in this case by use of a novel gas supply fitting detailed in Figure 7, that attaches to a conventional manual inflator (5) to provide a gas supply to a fine bore hose (7) but which allows the inflator to be disabled by disconnecting the incoming gas supply using a conventional SCUBA inflator nipple (9) and connector (1 1 ).
• the gas supply device in the example embodiment comprises just three main parts, shown in section in Figure 7: a barrel (13) that extends the hose from the manual inflator to the bladder, a second barrel (15) that extends the standard BCD gas nipple (9), and a shell (17) that holds these two elements in place and provides a connector fitting (19) into which plugs a gas hose (7) that provides a gas feed to the actuators.
• the important feature of the preferred and novel gas supply fitting (3) taking a gas feed from the manual inflator shown in Figure 7 is that in the event of an unwanted increase in buoyancy the diver need only disconnect the connection from the gas cylinder to the BCD, just has the diver would with a manual BCD, and vent manually.
• the vent valves (2) in the preferred embodiment have a conventional manual pull dump (33) in addition to the gas powered piston (27).
• the manual inflator has a pull-cord (8) in the example embodiments connecting to a vent valve in the actuator block (42). There is no need for the diver to perform any diagnostics to determine whether the manual inflator has failed open, or the automatic system: the diver simply needs to disconnect the gas supply.
• the present invention also allows the diver to vent gas using manual pull- dumps: in the preferred embodiments these are integral to the vent valves of the present invention.
• the gas feed to the actuator valves is flow limited such as by use of a small bore hose (7) or orifices such that the vents can always dump gas at a greater rate than it can be injected.
• a hose (7) carries the gas from the inflator to the actuators is preferably is a narrow bore hose.
• Kynar hoses are available with a 0.8mm bore and an outer diameter of 3.6mm, which have the effect of limiting the maximum flow rate when used with typical BCD gas supply pressures to around 20 litres of gas flow per minute, and have a burst pressure exceeding the gas supply cylinder high pressure, such that if the first stage cylinder pressure regulator were to fail, then the hose (7) would not rupture, and therefore there is no risk of the bladder in the BCD being inflated suddenly.
• use of a very small bore hose means that should the hose break, the flow rate into the bladder is much lower than the minimum vent rate if the diver uses the manual vent controls on the vent valves.
• FIG. 2 to 5 An example embodiment of an actuator means according to the present invention is shown in cross-section in Fig. 2 to 5, whereby a plurality of gas valves (20) and (21 ) are arranged such that when activated route the gas from the hose (7) is routed to either the bladder volume (23) or to a second hose (25) that actuates all the vent valves simultaneously.
• a novel arrangement of valves are used, whereby the first valve is a normally closed 2 way valve and the second valve is a three way valve.
• a 2-way normally closed valve simply opens the gas supply route between two ports, A and B, when energised by sufficient electrical power.
• a 3-way valve has two states and three ports, A, B and C: when not energised then Port A is connected to Port B, but not to Port C. When energised, the Port A is connected to Port C but not to Port B. In the example embodiment these ports are arranged as shown in Figure 6.
• a first valve (20) is a 2-way normally closed valve which when actuated injects gas into the bladder via an outlet (28) with a gas pathway to the bladder
• a second valve is a 3-way valve (21 ) which pressurises a second hose (25) when the valve (21 ) is activated, and pressure in that hose (25) powers gas pistons (27) that open the vent valves (2), such as those shown in Figure 8 or combined with the actuator block (42) as shown in Fig.
• the supply hose (7) to the gas valves (20) and (21 ) is preferably flow limited by its bore, and the vent valves (2) such as shown in Fig. 5 incorporate springs (37) and optionally (38) that close the valve when it is not powered. It is possible but not preferable to add a further flow restriction by use of an orifice or choice of small bores within the connectors (24) to the gas hose (7) or gas routing manifold (22).
• This non- preferred arrangement of 2-way gas valves also uses twice as much electrical power to inject gas into the bladder as the novel and preferred arrangement shown in Figure 6, and described in Figure 2 to Figure 5.
• Use of two 2-way valves in parallel is not an option because energising the valve to pressurise the hose (25) to the vents (2) would not have means to relieve the pressure so the vents would operate continuously, and hence not function correctly.
• a pull-cord or lever (4) on the manual inflator (5) such as that illustrated in Fig. 1 , to shut off the gas supply to the gas valves only, but leave the gas supply to the manual injector connected.
• the diver would still be able to disable both means to add gas to the bladder by disconnecting the incoming gas hose at the connector (9) and (1 1 ) on the manual inflator.
• Vent valves (2) with the features shown in Figure 8 namely an input gas hose (25), pressure in which causes a piston (27) to move and open a plug or stopper (29), allowing gas in the bladder to escape through a one-way valve (31 ).
• a manual pull-dump (33) is preserved in the preferred embodiment, allowing manual operation of the vent by the diver at any time.
• the pull-dump cords (35) may be singular or may be combined: a minimum of three of the vent valves (2) must be fitted to the bladder in positions such that there is an open gas path between the retained gas in the bladder and at least one vent valve when the bladder is immersed in water.
• a novel feature of the vent valves in the preferred embodiment is the use of a wave spring (37) to apply even pressure to the plug (29) such that seats evenly. Retainers (39) prevent the spring (37) from being displaced laterally.
• the use of the wave spring avoids the valve leaking if it is operated manually with a motion that in a conventional vent valve would tend to cause the plug (29) to take up an angle instead of remaining level with respect to the valve seat (30).
• a key feature of the vent valve is that the plug (29) is not firmly attached to the piston (27), such that pulling the plug (29) via the cord (35) causes the plug (29) to lift off the seat (31 ) without the piston (27) having to move.
• a wave spring is a type of compression spring built from a series of thin washers that have a wave-like profile. Compressing the washers, which are normally welded together, results in a reactive force that is even around the circumference of the spring.
• a wave spring can also provide a greater extension for a particular spring force and spring bound size than a conventional wire compression spring, which can be advantageous in this application.
• the controller for the electrically powered gas valves (20), (21 ) in the present invention uses sensor signals from the pressure, first differential of the pressure (i.e. speed), and the second differential of the pressure (acceleration).
• Figure 10 are indicative only, to describe why a discrete circuit is used or separate sensors to obtain the speed and acceleration data instead of digital means using the ambient pressure data.
• the present invention uses either a 3-axis accelerometer or a novel arrangement shown in block form in Figure 10 whereby through the use of two analogue differentiators, which have a gain greater than unity, the acceleration signal can be extracted from the ambient pressure signal and presented to an ADC of an accuracy that is readily available.
• This latter approach has sufficient magnitude and accuracy to enable the overall control system to operate in a stable manner when each of the two analogue differentiator stages have a gain of 300.
• the combined gain of 90,000 raises the acceleration differential into the range that a 16 to 18 bit ADC, such as a low cost Sigma-Delta ADC.
• Other gain values can be used and should be matched in any case to the voltage range of the pressure sensor, and ADC input voltage range.
• the amplification uses preferably either chopper type operational amplifiers or amplifiers of equivalent performance as the signals are close to DC in frequency.
• the present invention provides the means to offer the diver facilities such as:
• a dive cylinder pressure sensing device By integration with a dive cylinder pressure sensing device, it may set a minimum cylinder pressure, below which the device may initiate an ascent sequence automatically.
• the recommended safety ascent rate in decompression diving is almost universally 10 m/min, and the maximum of 18 m/min to 20 m/min depending on the training agency involved.
• the maximum ascent rate achievable for a diver identified from accident studies is 1 10m/min: this is generally not survivable if the diver has any significant gas loading in his tissues.
• the diver's respiration causes a natural oscillation in the diver's buoyancy that is preferably removed from the input pressure, speed and acceleration data.
• This can be achieved using a Kalman (digital) filter.
• Respiration has a centre frequency of 0.3Hz, and a low pass filter of 0.1 Hz is sufficient, bounded by a vertical depth change (e.g. a 0.5m window the diver should be in).
• a vertical depth change e.g. a 0.5m window the diver should be in.
• the smallest imbalance of the forces applied to the body in the water provides motion, either towards the surface or towards the sea bottom.
• the direction depends on the imbalance sign.
• the relation between the depth and the imbalance forces has positive feedback within a buoyancy compensator: as the depth increases, the volume of gas in the bladder reduces with Boyles Law so the acceleration increases, and visa versa for ascent.
• the positive feedback is greatest near the surface: the volume changes as a fraction of the change in depth relative to surface pressure.
• the acceleration itself is the integral of the injected and drained gas flows, adjusted for temperature and ambient pressure, which change the displacement of the diver's buoyancy bladder along with the SCUBA equipment. It is not possible to measure these parameters directly, so the acceleration that the other parameters combine to produce is measured and the buoyancy is determined from that acceleration data. The acceleration is limited by the maximum buoyancy (positive and negative).
• the diver's acceleration is proportional to the imbalance of the force applied to the body.
• the increment in the buoyancy force is proportional to the increment of the bladder volume.
• Changes in the bladder volume are proportional to temperature of the gas it encloses, and the change to the gas volume from injecting or venting gas and the change in volume of the enclosed gas (which is inversely proportional to the depth).
• the controlled buoyancy is considered as the integral of injected/drain gas flow rate and average depth.
• the path of the dive is considered as a series of waypoints, or "way” in the example code.
• the magnitude of a waypoint is a displacement from the start position.
• Reference to "position” refers to an ambient pressure value or a depth: the lateral position of the diver is unknown and not relevant.
• control algorithm makes use of external parameters. Typical values for these in an example embodiment are:
• Salinity 1020; - gms per litre if accurate depth in metres is required
• BC_lnj_Rate_Atmlps 1.1 ;
• BC_Drain_Rate_Atmlps -1 .5;
• Ambient_Pressure_Sea_Level_bar 1.013; ⁇ One atm is 1.013 bar.
• Variations of these variables are not critical, but errors can make the control loop take longer achieve the desired depth. Significant errors in declaring these parameters can cause a low magnitude damped overshoot using the process algorithm given. Some parameters such as the diver's weight can tolerate large errors, as the drag on the diver depends not just on weight by also on the diver's attitude in the water and body position.
• the deceleration time equals t, .
• the buoyancy bladder volume which decreased during descent and increased during ascent must be restored by the end of the control period in order for the diver to regain their steady state.
• the difference between the injected and the drain gas is proportional to the change in water pressure, which is a ratio of the start depth to the end depth, i.e. the depths at the beginning and end of the set of waypoints, as well as temperature.
• the buoyancy control uses the set depth function in the example code, the injection and drain rates, the current acceleration, speed and start depth, the buoyancy control calculates the time intervals in which the injection/drain is on or off to compensate for the depth and temperature change.
• F a buoyancy force
• F g gravity force
• F r resistance force
• C shape factor
• S cross-sectional area of the body
• p fluid density
• V velocity of the body.
• Control may start with nonzero initial speed or/and acceleration.
• F _d where a _ c is current acceleration; F _ d is the buoyancy size increment rate.
• the control calculates the current acceleration, speed and V_d. If the differences between the maximum and current speed is more than V_d the control injects gas into the buoyancy bladder. At the moment when the system reaches the V_d point the control closes the injection valve and starts to drain gas from the bladder until the acceleration drops to zero.
• the error of the maximum speed control depends on the F_d accuracy and the water resistance. Feedback in the buoyancy control can increase the accuracy of the motion.
• t1 interval includes drain (t1_d) and injection (t1_i).
• F i F d where dV is required speed reduction; F _ d is drain flow rate; F _ i is injected flow rate; weight is the sum of the total diver and SCUBA equipment weight.
• dV required speed reduction (between constant speeds when acceleration is zero);
• F _ d is drain flow rate;
• F _ i is injected flow rate;
• weight is total diver and SCUBA equipment weight.
• the characteristics of the position control can be determined when the initial speed and acceleration are positive.
• Phase A force equalisation
• the control is complicated by the situation when the minimum buoyancy bladder size increment is less than it needs to be for the buoyancy control. It occurs when the initial acceleration is more than the maximum acceleration which the buoyancy bladder could generate.
• the first and second "a" phases could be replaced by the following control (which is a function that depends on the distance to the set position):
• the system calculates phase duration time to pass through the waypoints with constant speed.
• the bladder capacity limits the maximum buoyant acceleration.
• s_mode(l) ds, +ds 2 + ds.
• da i a _ p - a _ini
• a_p ds2 (v ini + dv, )t2 + ⁇ t2 >2
• s_mode(2) ds ⁇ + ds 2
• Mode IV covers the case where there is the motion with and without any acceleration limit.
• Mode V is where motion has a negative initial speed and negative acceleration.
• the following equations apply in this mode under the twin negative conditions:
• da 2 —fb _ drain * t 2
• dv 3 -(v _ ini + ⁇ / j + dv 2 + dv 4 ) dv.
• s_mode(6) ds x + ds 2 + ds ⁇
• fb _ drain ds2 (v ini + dv,)t2 + ⁇ F t2 2 ,
• da 2 —fb _ drain * t 2
• s_mode(6) ds x + ds 2 + ds
• Mode VII is the case where the diver has positive initial speed and acceleration.
• the relevant equations are:
• s_mode(7) ds, + ds 2 + ds.
• the control process described herein can be expressed as an exponential control algorithm but the additional complexity appears to provide no tangible benefits.
• Calculation of the buoyancy control is based on knowledge of the injection and drain gas flow rates. These parameters can be updated in an adaptive control loop.
• the gas injection rate when the gas control valves (20), (21 ) are open depends on the nozzle or orifice size, gas factor, orifice pressure drop and ambient pressure. All these parameters are sufficiently stable and predictable for stable control.
• the flow via the vents valves (2) is very sensitive to the valve opening and the difference between the buoyancy bladder pressure and the ambient pressure.
• the error of the drain flow rate estimation is the most critical parameter in these calculations.
• To minimise the effect of drain flow rate variations in the buoyancy control it is possible to design the valve with an adaptive buoyancy control with additional feedback that adjusts the drain rate using the system acceleration and deceleration.
• the same principle can be used in estimation of the injected gas rate. However, the cost of this would be significant, and it is likely to cause audio noise which would be unacceptable to the diver.
• the control process detailed herein is sufficient for stable control without this extra layer of complexity.
• Adaptive filter and control parameters to smooth the control feedback signal to enable lower ADC resolutions and slower sample rates are used. These remove or reduce or compensate for variations in input date from:
• the user interface to the automatic buoyancy system may incorporate all the features of a dive computer
• the dive computer can generate a dive profile, which can provide a series of targets such that when the diver selects a controlled ascent, the buoyancy system will follow the decompression profile.
• the profile may be adjusted for factors such as the preferred ascent rates, the depth of the first or final stops, the conservatism applied to the chosen algorithm, and give prompts for gas changes at appropriate depths.
• the automatic buoyancy controller will generally require extra data or menus to be added to the dive computer display.
• Dive computer displays tend to be cluttered already, and this is a special problem underwater because small fonts are not readable.
• Another problem is the number of selection points into a menu is very small underwater: a device may have a Next and Select button but does not generally have a touch screen to select any of a set of icons directly or to enter data.
• New differential pressure or differential capacitive touch displays may overcome this obstacle, but at the present time these touch panel technologies do not work reliably underwater: water is both conductive and applies a uniform pressure.
• the touch controls may be effective on the surface but disabled when the display is wet, but it is also possible to manage the larger amount of data that is generated by an automatic buoyancy compensator using a conventional two button display.
• the automatic buoyancy controller and associated dive computer may simplify the presentation of data and options by using a menu represented by icons controlled by a Next and Select button.
• a surface menu may have large numbers of icon menus, and dive mode have very few. It is preferable that the diver should be able to select the functions of the buoyancy controller with the minimum number of actions.
• the Next button highlights and icon, and Select button enables or toggles its function.
• a menu tree using submenus below particular icons is particularly advantageous in avoiding presentation of too much data.
• the process described can be executed in a 100ms loop on modern microcontrollers such as the ARM 7 and ARM 9, or on FPGAs. In this case all the computation can be performed in a fast loop using a time triggered architecture, with the dive computer functions calculated on a much slower loop. Typically the fast loop has a 100ms interval and the slow loop for a dive computer has a 4 second interval.
• the dive computer decompression profile can be suspended until the stop is reached.
• the dive computer (40) can update the decompression profile using the actual depth profile that was used, including the gases (and any gas switches), and the actual PP0 2 in a rebreather.
• Data logging can be carried out by the buoyancy controller or dive computer (40), such that the dive log can be downloaded after the dive, or series of dives.
• the dive computer (40) normally has a surface mode and a dive mode.
• the device will normally enter the dive mode when it is pressurised or when contacts are wet, preventing reconfiguration of critical parameters underwater.
• the automatic buoyancy control system is used with a rebreather, a fast and simple means is desirable to stop an ascent, for example if the PP0 2 is falling at a faster rate than is acceptable the ascent may require to be aborted in order for the PP0 2 to be restored or for the diver to bail out.
• Buoyancy control could provide the following descent/ascent motion modes:
• buoyancy control system cannot control diver attitude efficiently.
• Alternative means are much better at this function (i.e. use far less energy).
• Calculation of acceleration/deceleration can be used to increase system safety, estimating the spent buoyancy gas.
• the control code providing an example embodiment of the control process in Figure 1 1 provides a well damped response, such that moving from one depth to another gradually accelerates the diver to a desired ascent or descent rate, maintains that rate or speed, then slows the diver as the diver approaches the desired depth, without oscillating or over-shoot (depth excursions).
• control process in Figure 1 1 is suitable for re-entrant use, and would require a loop time of 100ms or less to perform adequate control.
• This loop time can be achieved on ARM 7 and ARM 9 microcontrollers, or using FPGAs with floating point processors.
• the floating point requirements can be converted to fixed point arithmetic.
• a dual redundant bladder is required.
• the second bladder can be operated using a separate power inflator and vent valves, and may be entirely manually controlled.
• the redundant bladder may exist alongside the bladder that is controlled automatically or even may be included in the same

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• 2013
  • 2013-03-28 WO PCT/IB2013/000581 patent/WO2013144711A1/en active Application Filing

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