BUOYANCY VEST VENT VALVE WITH RELIABLE SEATING

Abstract

A vent valve for a buoyancy control device (“BCD”) suitable for divers, where the valve may be opened by any combination of over-pressure, manual pressure relief or a powered means, where a force to a valve plug is applied by means of a spring that is constrained to prevent entirely lateral and angular movement but in which movement of the plug in the axis of the seat is unconstrained. An automatic buoyancy control device suitable for free-swimming divers, providing the functions that may include a controlled ascent rate, controlled descent rates, the imposition of a maximum depth limit, the facility to hold a set depth and to follow a dive profile or decompression profile. The device, control process and subsystems provide a high safe failure fraction.

Claims

1. A device for controlling a diver's buoyancy comprising: electro-pneumatic valves for injecting gas into an inflatable bladder and venting gas from the inflatable bladder using an automatic buoyancy controller to manage the volume of gas in the bladder that counteracts the positive feedback inherent to the expansion and compression of gas as a result of depth change, by the use of valves controlled from a calculation of the diver's depth and relative buoyancy derived directly from the diver's acceleration in the water column, without any direct measurement of gas flow or volume, where the valve control uses a series of conditions and conditional actions to add gas or remove gas, supported by a pulse width modulator to control the gas injection and venting process when moving to a desired depth under automatic control.

2. A device according to claim 1 wherein at least one gas valve pressurizes or depressurizes a pneumatic hose connecting to vent valve(s) which are opened simultaneously by that pressure and when open, vent gas from the bladder.

3. A device according to claim 1 that limits the diver's maximum ascent rate.

4. A device according to claim 1 that limits the diver's maximum descent rate.

5. A device according to claim 1 that limits the diver's maximum depth.

6. A device according to claim 1 that enables the diver to hold a selected depth.

7. A device according to claim 1 that enables the diver to follow a depth profile or a decompression profile automatically.

8. A device according to claim 1 that integrates the functions of a dive computer to generate a decompression profile that the device can follow.

9. A device according to claim 1 comprising a dive cylinder pressure sensing device enabling setting of a minimum cylinder pressure, below which the device may initiate an ascent sequence automatically.

10. A device according to claim 1 whereby a single action function is provided to stop an ascent or descent.

11. A device according to claim 1 wherein the said gas valves are arranged such that a loss of electrical or gas power causes the valves to fail in a safe state in which there is neither gas injected into the bladder nor gas vented from the bladder.

12. A device according to claim 1 wherein the said gas valves are provided with a gas supply by a module that attaches to the gas connection point for a BCD power inflator, leaving the manually controlled bladder inflator/deflator functions operable.

13. A device according to claim 1 wherein the said gas valves are provided with a gas supply by module having a single point of incoming gas connection and a plurality of gas outputs enabling the said gas valves and the BCD power inflator to be disconnected easily by the diver through a single operation.

14. A device according to claim 1 wherein the said gas valves include an electro-pneumatic 3-way solenoid valve such that the gas supply to the vent valves is opened to the ambient pressure when the 3-way solenoid valve is not energized.

15. A device according to claim 1 controlled by a process or algorithm having distinct control modes that are selected as a function of the diver's speed and acceleration.

16. A device according to claim 1 where the derivative of a diver's acceleration is used as a control parameter that is the third derivative.

17. A device according to claim 1 that combines a diver's acceleration signal with a signal proportional to the diver's speed.

18. A device according to claim 1 wherein the electro-pneumatic valves form an actuation means such that only one electro-pneumatic valve needs to be active at any one time to elucidate the desired action in the bladder, with slave valves being pneumatically operated to vent the bladder.

19. A device according to claim 1 comprising a safety means to shut down the automatic buoyancy controller without affecting the ability of the diver to perform buoyancy control manually.

20. A device according to claim 1 comprising a display and buttons to enable different functions to be configured on the surface or selected underwater by the diver.

21. A device according to claim 1 that integrates a dive computer function to generate a dive decompression profile that can be adopted by the automatic buoyancy controller.

22. A device according to claim 1 wherein menu functions are represented as icons that are selected by a Next and a Select button to enable the function represented by the icon to be configured or enabled or disabled.

23. A device according to claim 1 wherein the menu functions are managed using a touch screen when the device is on the surface, and a set of buttons when the device is pressurized or wet or in a dive mode.

24. A device according to claim 1 where an acceleration signal is obtained using a 3-axis accelerometer.

25. A device according to claim 1 where an acceleration signal is obtained using an analogue differentiator from the ambient pressure signal.

26. A device for controlling a diver's buoyancy comprising: an inflatable bladder: a plurality of electro-pneumatic valves coupled to the inflatable bladder for injecting gas into the inflatable bladder and venting gas from the inflatable bladder; and an automatic buoyancy controller to manage the volume of gas in the bladder responsive to inherent to expansion and compression of gas disposed in the inflatable bladder resulting from a depth change, by operation of at least one of the plurality of electro-pneumatic valves as controlled from a calculation of a diver's depth and relative buoyancy derived directly from the diver's acceleration in a water column, without any direct measurement of gas flow or volume, where the electro-pneumatic valve is controlled using a series of conditions and conditional actions to add gas or remove gas, supported by a pulse width modulator to control the gas injection and venting process when moving to a desired depth under automatic control.

27. A device for venting gas from a diver's buoyancy compensation bladder, the device comprising: a valve plug configured to open or to close a valve seat; a spring configured to apply force to the valve plug to close the valve seat; a piston configured to apply force to the valve plug to open the. Valve seat; and a manual pull dump configured to open the valve seat manually; wherein the spring is fully restrained for more than 50% of its length, and the movement of the valve plug is constrained by a centering mechanism that prevents the valve plug from moving laterally or angularly while the centering mechanism allowing movement with the face of the valve plug parallel to the valve seat along the axis of a line extending perpendicular to the valve seat under any combination of over-pressure or manual pulling action using the manual pull dump.

Description

DESCRIPTION OF THE DRAWINGS

[0087] The present description will be better understood from the following detailed description read in light of the accompanying drawings, wherein:

Buoyancy Vest Vent Valve with Reliable Seating

[0088] FIG. 1 shows a vent valve according to the present invention in the state where the valve is closed.

[0089] FIG. 2 shows a vent valve according to the present invention in the state where the valve is open through manual actuation or over-pressure.

[0090] FIG. 3 shows a vent valve according to the present invention in the state where the valve is open through an automatic actuation channel only.

[0091] FIG. 4 shows a vent valve according to another example of the present invention in the state where the valve is closed through an automatic actuation channel only.

[0092] FIGS. 5-7 show the inflation and deflation of a buoyancy control device (“BCD”).

[0093] FIG. 8 shows an alternative example of SUBA configuration.

[0094] FIG. 9 shows an alternative example of SUBA as constructed.

Safe Automatic Buoyancy Control Device

[0095] FIG. 10 shows an example of the overall configuration of the present invention onto a BCD.

[0096] FIG. 11 to FIG. 14 show the gas flow paths of an actuation means in a preferred example 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.

[0097] FIG. 11 shows the case where both solenoid valves are closed on initial start-up.

[0098] FIG. 12 shows the state where the first solenoid valve is energized to activate the vent valves.

[0099] FIG. 13 shows the state where a second solenoid valve is has been energized and gas flows into a fine bore pneumatic hose that activates an exhaust valve.

[0100] FIG. 14 shows the state following that valve being subsequently closed and a residual gas is released into the bladder.

[0101] FIG. 15 shows a preferred arrangement of gas valves providing fail-safe features.

[0102] FIG. 16 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.

[0103] FIG. 17 shows a basic pneumatically activated vent valve according to the present invention which provides a consistent operating force and seating of the valve.

[0104] FIG. 18 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.

[0105] FIG. 19 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.

[0106] FIG. 20a-20f shows a simplified 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, and also able to perform emergency ascents, controlled ascents and follow a decompression profile through changes to the Maximum Allowed Depth.

[0107] Like reference numerals are used to designate like parts in the accompanying drawings.

DETAILED DESCRIPTION

[0108] The detailed description provided below in connection with the appended drawings is intended as a description of the present examples and is not intended to represent the only forms in which the present example may be constructed or utilized. The description sets forth the functions of the example and the sequence of steps for constructing and operating the example. However, the same or equivalent functions and sequences may be accomplished by different examples.

[0109] The invention will now be described in detail by reference to the aforementioned drawings and by use of examples. Reference is made to a BCD bladder. The form of the bladder is not important: the present invention many be applied to many different types of bladders. The sole unique feature for the bladder to be used with the present invention is that the vent valves shall be arranged such that there is an open gas path from the gas in the bladder to one of the vents: at least one vent valve is typically required to fulfil this specification depending on the range of diver attitudes for which the vent function is available.

Buoyancy Vest Vent Valve with Reliable Seating

[0110] FIG. 1 shows a vent valve according to the present invention in the state where the valve is closed. The valve in this example and the following drawings includes a provision for powered actuation, which is desirable but not a necessary feature of the valve.

[0111] The vent valves in the examples shown in FIGS. 1 to 4 have a conventional manual pull dump (233) in addition to a pneumatically or hydraulically powered piston (227). The pull dump may be on a cord (235) or a lever. A spring (205) applies a pressure to a valve plug (229) to close a seat (230), but which can be over-ridden by any combination of manual pull action, over-pressure or in these examples the powered actuation of the piston. The vent valve shown in FIGS. 1 and 2 also comprises an inner valve plug 215; however, the vent valve according to another example shown in FIG. 4 comprises only one main valve plug 229.

[0112] A compression spring (205) is constrained by walls (208) for more than half its length, which prevents entirely the spring moving laterally (side to side in the drawings). The walls (208) can be arranged from opposite sides of the spring (205) or the walls (208) can have another configuration. The compression spring (205) may be a wire spring or a wave spring, or any other type of spring that applies a force to the valve plug (229) towards the direction of the seat (230).

[0113] A compression spring (205) will apply an uneven force to the plug (229). Without further constraint, this would tend to allow the plug (229) to move at an angle with respect to the seat (230). To prevent that angular movement, the plug (229) is attached to a guide (209) that maintains the plug (229) such that the face of the plug (229) is parallel to the seat (230) at all times. In FIGS. 2 and 3 the guide (29) is constrained by a cylinder that forms part of the outer cover (201), and in FIG. 4 the guide (209) is constrained by the wall (208) that restricts the spring (205). It is highly preferable that the end of the guide remains outside the cylinder that it moves in, to prevent angular forces jamming the guide (209) in the cylinder.

[0114] A hose (207) carrying the gas from the inflator to the actuators is preferably a narrow bore hose. Kynar hoses are available with a 0.8 mm bore and an outer diameter of 3.6 mm, which have the effect of limiting the maximum flow rate when used with typical BCD gas supply pressures to around 20 liters 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 (207) would not rupture, and therefore there is no risk of the bladder in the BCD being inflated suddenly. Moreover, 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.

[0115] A one-way valve (231) is preferably fitted, and the one-way valve (231) is preferably of an umbrella flapper valve construction to provide a positive cracking pressure to prevent water ingress into the BCD when the valve is open.

[0116] Vent valves with the features shown, namely an input (7), provide pressure in which causes a piston (227) to move, opening a plug or stopper (229), allowing gas in the bladder to escape through a one-way valve (231). A manual pull-dump (233) is preserved in the preferred example, allowing manual operation of the vent by the diver at any time. The pull-dump cord (235) may be singular or may be combined.

[0117] A novel feature of the vent valves in the preferred example is the use of a wave spring to apply even pressure to the plug (229) such that seats evenly.

[0118] The use of the wave spring reduces the difference in the spring force across the plug (229) and hence reduces the angle it tries to adopt with respect to the valve seat (230). 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 having 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.

[0119] A key feature of the vent valve is that the plug (229) is not firmly attached to the piston (227), such that pulling the plug (229) via the cord (235) causes the plug (229) to lift off the seat (230) without the piston (227) having to move. The seat at the top of the piston (227) need not be attached to the plug (229).

[0120] In all FIGS. 1 to 4, the valve plug (229) is not fixed to the pneumatic piston rod (220): the rod can push the inner valve plug (215) in the example in FIGS. 1 to 2 and the main plug (229) in FIG. 4, but does not prevent over-pressure from moving the plug to open the valve, nor prevent manual actuation opening the valve.

[0121] In the case of FIG. 4, the valve plug (229) is limited in its movement by adjustment of an exterior cap to the valve to provide a limited or restricted instantaneous flow rate. In that example the instantaneous flow rate through the over-pressure action is also limited in applications where that is desirable.

[0122] In FIGS. 1 to 3 the automatic actuation of the valve does not move the main valve plug (229), but moves only the inner valve plug (215), through which gas flows. The instantaneous flow rate through that secondary valve comprising the inner valve plug (215) and seat is defined by choice of vent hole dimensions. This enables the automatic actuation of the valve to use a much lower instantaneous flow rate than that when the valve is opened manually or through over-pressure. For optimum automatic buoyancy control a ratio 8:1 or 16:1 is desired between the instantaneous flow rate in the over-pressure role and the instantaneous flow rate in the power (automated) actuation role.

[0123] The pneumatic power may be provided by an arrangement of gas valves that apply a lower gas pressure, such as 9 bar, to the hose (207) to activate the vent valve, but which in the quiescent or inactive state opens the gas line to the BCD bladder. When the gas hose (207) is a small bore hose then the volume of the gas vented to the bladder may be kept to a negligible amount.

[0124] An alternative to the pneumatic power to activate the vent valve is by use of a bellows containing a liquid such as alcohol or water or silicone oil, and pressure on the bellows by the user causes pressure to build up in the hose (7) and the valve to be opened. The spring bias to the bellows causes the liquid to pull back the piston when the pressure is removed. The pressure may be through a lever or directly on the bellows.

[0125] The bellows or the hose (207) has a means through which gas can be drained and fluid topped up, but such means may be in the form of a nipple or filling point: there is no need for a hydraulic reservoir. During the filling process, sufficient provision should be made for the thermal expansion of the hydraulic liquid: this can be accommodated by a partial fill such that expansion of the liquid extends the bellows and contraction causes them to shrink in size, but leaving sufficient movement for the manual action.

[0126] The bellows may be implemented in a variety of forms, including a thick walled balloon such as a silicone molding, or it may be a telescoping molding, or it may be a series of telescoping elements with O-ring seals.

[0127] FIGS. 5-7 show the inflation and deflation of a buoyancy control device (“BCD”).

[0128] FIG. 8 shows an alternative example of SUBA configuration.

[0129] FIG. 9 shows an alternative example of SUBA as constructed.

Safe Automatic Buoyancy Control Device

[0130] FIG. 10 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:

[0131] 1. A means to connect to a pressurized gas supply (3).

[0132] 2. A hose (7) carrying the pressurized gas supply to a plurality of electrically operated gas valves.

[0133] 3. An electrically operated gas valve that is able to pressurize 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.

[0134] 4. At least one or more vent valves per bladder, each being pneumatically activated.

[0135] 5. 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.

[0136] 6. Housings and interconnect required to connect and protect the above subsystems.

Examples may optionally include a diver display, dive computer and user controls.

[0137] An example of a novel means to take a gas supply is show in detail in cross-section diagrams forming FIG. 10 and FIG. 14, and shown externally in FIGS. 11 to 13, comprising a means to connect to a pressurized gas supply (3) in this case by use of a novel gas supply fitting detailed in FIG. 16, 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 (11).

[0138] The gas supply device in the example of the invention comprises just three main parts, shown in section in FIG. 16: 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.

[0139] The important feature of the preferred and novel gas supply fitting (3) taking a gas feed from the manual inflator shown in FIG. 16 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 example have a conventional manual pull dump (33) in addition to the gas powered piston (27). Moreover the manual inflator has a pull-cord (8) in the examples 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 examples 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.

[0140] 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 0.8 mm bore and an outer diameter of 3.6 mm, which have the effect of limiting the maximum flow rate when used with typical BCD gas supply pressures to around 20 liters 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. Moreover, 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.

[0141] An example of an actuator means according to the present invention is shown in cross-section in FIGS. 11 to 14, 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. In the preferred example 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 energized by sufficient electrical power. A 3-way valve has two states and three ports, A, B and C: when not energized then Port A is connected to Port B, but not to Port C. When energized, the Port A is connected to Port C but not to Port B. In the example these ports are arranged as shown in FIG. 15. 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, and a second valve is a 3-way valve (21) which pressurizes 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 FIG. 17 or combined with the actuator block (42) as shown in FIGS. 11 to 14. When the 3-way valve is not activated it drains the gas hose (25) to the vent valves (2) into the bladder: a very small gas volume is vented as the preferred example uses fine bore hoses (7) and (25). Gas paths within a manifold (22) are used to implement the main gas paths in this example, along with internal gas hose (26) and gas connectors (19).

[0142] 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. 14 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).

[0143] An alternative using two 2-way electrically operated gas valves in series instead of the arrangement in FIG. 15, such that opening the first 2-way, gas valve pressurizes the hose (25) to the vent valves and the second 2-way gas valve vents that hose to the bladder, has less desirable safety characteristics than the preferred combination described herein. In the case where to 2-way valves are used in series, to add gas to the bladder both gas valves would be opened simultaneously, and to vent the bladder the first solenoid valve would be opened and the second closed. The reason this is not the preferred example is that if electrical power were to fail while the vent valves were active, then pressure would be trapped in the second hose (25) that would keep the valves open. In this case, the diver would lose all buoyancy, which is not a fail-safe condition. 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 FIG. 15, and described in FIGS. 11 to 14. Use of two 2-way valves in parallel is not an option because energizing the valve to pressurize 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.

[0144] In some examples it may be desirable to have a pull-cord or lever (4) on the manual inflator (5) such as that illustrated in FIG. 10, 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 (11) on the manual inflator.

[0145] Vent valves (2) with the features shown in FIG. 17 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 example, 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 example 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.

[0146] 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.

[0147] 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). In order to obtain a figure for acceleration that is sufficiently accurate for control purposes, a resolution would be required from a depth sensor that is not available using current technology: mathematical, modelling reveals that at least 28 bits of accuracy is required if the pressure sensor signal were to be digitized and the acceleration calculated using a digital means. To overcome this, the present invention uses an analogue circuit shown in block form in

[0148] FIG. 19 to obtain these differentials, directly from the sensor data.

[0149] The values for signal levels shown in FIG. 19 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.

[0150] It is not feasible to obtain dive acceleration data from a digital process that has the digitized ambient pressure sensor signal as input due to the magnitude of the signals involved. A 0 to 1V pressure sensor measuring 0 to 10 bar (0 to 100 m of fresh water), would give a signal of diver speed at a 10 m/min ascent rate of just 1.67 mV, and the diver's acceleration is more than an order of magnitude lower still. The critical control acceleration data would be two orders of magnitude lower, and typically at least 8 bits of acceleration data are needed using the control process described herein. These requirements combine to create the need for a 28 to 30 bit ADC: such a device does not exist in a form suitable for integration with dive electronics.

[0151] To provide the acceleration data, the present invention uses either a 3-axis accelerometer or a novel arrangement shown in block form in FIG. 19 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.

[0152] The present invention provides the means to offer the diver facilities such as: [0153] 1. Control the descent rate or impose a maximum descent rate. [0154] 2. Control the ascent rate or impose a maximum ascent rate. A plurality of ascent rates may be supported, for emergency, controlled and normal ascents. [0155] 3 Follow a depth profile or profiles automatically. [0156] 4. By integration with a processing unit, for example, with a dive computer (40), it may provide the ability to follow a decompression profile automatically. [0157] 5. 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.

[0158] 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 110 m/min: this is generally not survivable if the diver has any significant gas loading in his tissues.

[0159] 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 center frequency of 0.3 Hz, and a low pass filter of 0.1 Hz is sufficient, bounded by a vertical depth change (e.g. a 0.5 m window the diver should be in). There is no predictive element required to the filter that removes respiratory effects: it may be a conventional FIR (Finite Impulse Response Filter), such as a fifth order Chebyshev Low Pass filter. It is advantageous to combine parts of the filter with the differentiator, such as shown for the first differentiator in the example in FIG. 19.

[0160] For a better understanding of the control process, the example given by the Ada code in FIG. 17 some of the calculations used in the code will be described.

[0161] 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.

[0162] 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 vice 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.

[0163] In a buoyancy control system, 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).

[0164] 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). To simplify the presentation of this, the controlled buoyancy is considered as the integral of injected/drain gas flow rate and average depth.

[0165] 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.

[0166] In addition to values derived from sensors, the control algorithm makes use of external parameters. Typical values for these in an example are: [0167] ABC_Sample_Time_s=0.01; [0168] Ambient_Pressure_Sea_Level_bar=1.0; [0169] Salinity=1020;—gms per liter if accurate depth in meters is required Diver_Weight_kg=120.0; [0170] Exhaust_Atm_Rate_lps=−1.5; [0171] Injector_Atm_Rate_lps=1.1; [0172] Speed_Descent_max_mps=0.5; [ [0173] Speed_Ascent_max_mps=−0.33333; [0174] Accel_Descent_max_mpss=0.035; [0175] Accel_Ascent_max_mpss=−0.035; [0176] BC_Inj_Rate_Atmlps=1.1; [0177] BC_Drain_Rate_Atmlps=−1.5; [0178] Ambient_Pressure_Sea_Level_bar=1.013;—One atm is 1.013 bar.

[0179] 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.

[0180] When the initial acceleration and speed is zero the control process calculates the control time for when the acceleration/deceleration must be switched on/off as follows:

[0181] 1. If

[00001]$w\le \frac{V_{\max }^2}{\alpha }$

(V.sub.max is maximum speed, α is acceleration),
the time when the acceleration changes its sign is

[00002]$r_1=\sqrt{\frac{w}{\alpha }}.$

The time 2t.sub.1 is the time when the deceleration force must be switched off. This ideal system reaches the set position with zero speed and acceleration for the minimum time. Gas consumption depends on the speed limit.

[0182] If

[00003]$w>\frac{V_{\max }^2}{\alpha },$

then the time when the body moving with acceleration is

[00004]$t_1=\frac{V_{\max }}{\alpha }$

and the time when the motion has the maximum speed is

[00005]$t.Math..Math.2=\frac{w}{V_{\max }}-\frac{V_{\max }}{\alpha }.$

[0183] The deceleration time equals t.sub.1.

[0184] 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. Using 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.

[0185] The limiting effect of water on the body is calculated using the following relationships:

[0186] Force applied to the body F.sub.b=F.sub.a−F.sub.g−F.sub.r,

[0187] Where: F.sub.a is buoyancy force; F.sub.g is gravity force; F.sub.r is resistance force Resistance force F.sub.r=C×S×ρ=V.sup.2/2

[0188] Where C is shape factor; S is cross-sectional area of the body; p is fluid density; V is velocity of the body. This formula is valid in a limited range of sizes and velocities of bodies in water: from about 10 cm to 10 m and 1 cm/s to 10 m/s. The most difficult part of this formula is to determine the shape factor C. For two bodies of different size, weight, material, but the same shape, this coefficient C is the same. For example, for a sphere C=0.4, for a body drop-shaped and oblong ellipsoid C=0.05 to 0.1. The smaller the bubbles, then the smaller their rate of ascent. Typically, this rate is 0.3 to 0.5 m/sec depending on the bubble size. This is 18 m to 30 m per minute. The average density of the human body 1070 kg/m3 but the weighting and environmental protection of a diver as well as the equipment carried can cause this to vary significantly when the diver is considered as a whole is. As a consequence, calculation cannot provide a reliable shape factor, therefore it was determined experimentally. The known maximum ascent rates are achieved by divers who take a head-up profile, and achieved a 110 m/min rate would suggest a shape factor that is 3 to 4 times more efficient than a bubble. The control code given is stable over this 4 to 1 range of Reynolds coefficients (shape factors, C).

[0189] There are two modes for the buoyancy control: [0190] maximum speed control mode when the magnitude of the waypoints to the set depth are above the magnitude of the waypoints for deceleration from the maximum speed, [0191] set position mode when the waypoints to the set depth are less than the waypoints for deceleration from the maximum speed.

[0192] Control may start with nonzero initial speed or/and acceleration.

[0193] In Maximum speed control mode, the time to deceleration from the maximum speed is:

[00006]$\mathrm{t\_d}=\frac{\mathrm{\alpha \_c}}{\mathrm{F\_d}},$

where a_c is current acceleration; F_d is the buoyancy size increment rate. Differences between the maximum speed where the acceleration is zero and the current speed are:

[00007]$\mathrm{V\_d}=\frac{\mathrm{\alpha \_c}}{2}\times \mathrm{t\_d},\mathrm{or}.Math..Math.\mathrm{V\_d}=\frac{{\mathrm{\alpha \_c}}^2}{2.Math.\mathrm{F\_d}}$

[0194] In this mode, the waypoint displacement to the set depth is more than the waypoint displacement for deceleration from the maximum speed, 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.

[0195] 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.

[0196] In the second main control mode, Set Position Mode, to minimize sensitivity to external and feedback factors the control in the ‘set position goal mode’ routine includes three phases:

[0197] 1. reduction of the speed to the minimum value,

[0198] 2. motion under constant speed until the deceleration area is reached,

[0199] 3. reduction of the speed to zero in the deceleration area.

[0200] The following equations may be used in the control process. Note that the t1 interval includes drain (t1_d) and injection (t1_i).

[00008]$t.Math..Math.1.Math.\mathrm{\_d}=\sqrt{\frac{2\times \mathrm{dV}}{\left(\mathrm{F\_d}+\frac{{\mathrm{F\_d}}^2}{\mathrm{F\_i}}\right)/\mathrm{weight}},}$$t.Math..Math.1.Math.\mathrm{\_i}=\sqrt{\frac{2\times \mathrm{dV}}{\left(\mathrm{F\_i}+\frac{{\mathrm{F\_i}}^2}{\mathrm{F\_d}}\right)/\mathrm{weight}}}$

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.

[0201] The same equations are used to calculate the time of the gas switching events in the t3 interval.

[0202] The following further equations are derived:

[00009]$t.Math..Math.1.Math.\mathrm{\_i}=\sqrt{\frac{2\times \mathrm{dV}}{\left(\mathrm{F\_i}+\frac{{\mathrm{F\_i}}^2}{\mathrm{F\_d}}\right)/\mathrm{weight}},}$$t.Math..Math.1.Math.\mathrm{\_d}=\sqrt{\frac{2\times \mathrm{dV}}{\left(\mathrm{F\_d}+\frac{{\mathrm{F\_d}}^2}{\mathrm{F\_i}}\right)/\mathrm{weight}}}$

where dV is 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.

[0203] And:

[00010]$t.Math..Math.3.Math.\mathrm{\_d},t.Math..Math.5.Math.\mathrm{\_d}=\sqrt{\frac{2\times \mathrm{dV}}{\left(\mathrm{F\_d}+\frac{{\mathrm{F\_d}}^2}{\mathrm{F\_i}}\right)/\mathrm{weight}},}$$t.Math..Math.3.Math.\mathrm{\_i},t.Math..Math.5.Math.\mathrm{\_i}=\sqrt{\frac{2\times \mathrm{dV}}{\left(\mathrm{F\_i}+\frac{{\mathrm{F\_i}}^2}{\mathrm{F\_d}}\right)/\mathrm{weight}}}$

[0204] From these, the characteristics of the position control can be determined when the initial speed and acceleration are positive.

[0205] If the start acceleration and velocity is not zero, the t1 interval including drain (t0, t1_d) and injection (t1_i) is calculated as following:

[00011]$t.Math..Math.0=\frac{\mathrm{\alpha \_ini}}{\mathrm{F\_d}},$

where a_ini is initial acceleration.

[00012]$t.Math..Math.1.Math.\mathrm{\_d}=\sqrt{\frac{2\times \left(d.Math..Math.V+\mathrm{a\_ini}*t.Math..Math.0/2\right)}{\left(\mathrm{F\_d}+\frac{{\mathrm{F\_d}}^2}{\mathrm{F\_i}}\right)/\mathrm{weight}}}+t.Math..Math.0,.Math.t.Math..Math.1.Math.\mathrm{\_i}=\sqrt{\frac{2\times \left(d.Math..Math.V+\mathrm{a\_ini}*t.Math..Math.0/2\right)}{\left(\mathrm{F\_i}+\frac{{\mathrm{F\_i}}^2}{\mathrm{F\_d}}\right)/\mathrm{weight}}}$

where dV is required speed reduction; F_d is drain flow rate; F_i is injected flow rate; weight is total diver and SCUBA equipment weight.

[00013]${\mathrm{way}}_{t.Math..Math.0}=V_{\mathrm{ini}}.Math.t.Math..Math.0+{\alpha }_{\mathrm{ini}}.Math.\frac{t.Math..Math.0^2}{6},{\mathrm{way}}_{t.Math..Math.1}=V_{\mathrm{ini}}.Math.t.Math..Math.0+{\alpha }_{\mathrm{ini}}.Math.\frac{t.Math..Math.0^3}{6}$

[0206] The same equations apply when the initial acceleration is negative.

[0207] The next set of equations add in the effect of changes in the water pressure (i.e. depth) and resistance in moving through the water column

[0208] The control process manages the distinct phases of diver's movement.

First Phase, Phase A: Force Equalization

[0209] 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.

Second Phase, Part B: Achieve the Desired Speed with Non Zero Start Acceleration

[0210] 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):

[0211] hold the initial acceleration until the speed drops to the corresponding value then decrease the acceleration to zero;

[0212] increase the acceleration until its maximum value then wait until the speed drops to the corresponding value then decrease the acceleration to zero.

Third Phase: Constant Speed Motion

[0213] During this phase the acceleration is zero: the system calculates phase duration time to pass through the waypoints with constant speed.

Fourth Phase: Motion with Limited Acceleration

[0214] The bladder capacity limits the maximum buoyant acceleration.

[0215] The deceleration profile from the initial speed to zero depends on the initial deceleration and speed. There are four main types of profile (mode of motion). Each profile has its own characteristic waypoints.

[0216] In addition to the two obvious modes of approaching the waypoint linearly, there is a third mode where if the profile waypoint is less than the waypoint to the set position the control process increases acceleration and speed towards their maximum values and at each time clock step calculates the deceleration waypoint with new initial parameters. In the case when the deceleration profile is more than the waypoint to the set position or profile, the control generates motion in the reverse direction the device decelerates until the diver stops (acceleration and speed are zero) and only then provides motion to the set position.

[0217] For this section the following notations are adopted: [0218] ds—increment of waypoint; [0219] v_ini—initial speed; [0220] v_max—maximum speed; [0221] aini—initial acceleration; [0222] a_max—initial maximum acceleration; [0223] t—time; [0224] fb—rate of buoyancy force increment (depends on gas injection/drain, water pressure and total weight).

[0225] Each of the four modes I to IV will now be considered in turn, taken from the graph in FIG. 18, and also three other cases V to VII to provide exhaustive coverage. The following equations apply in Mode I:

[00014]$t_3=\frac{\mathrm{\alpha \_max}}{\mathrm{fb\_inj}},.Math.{\mathrm{ds}}_3=-\frac{{\mathrm{\alpha \_max}}^3}{6*{\mathrm{fb\_inj}}^2}$$d.Math..Math.{\alpha }_1=\mathrm{\alpha \_max}-\mathrm{\alpha \_ini},.Math.t_1=-\frac{{\mathrm{da}}_1}{\mathrm{fb\_drain}},.Math.{\mathrm{dv}}_1=\frac{\mathrm{\alpha \_max}+\mathrm{\alpha \_ini}}{2}.Math.t_1,.Math.{\mathrm{dv}}_2=-\left(\mathrm{v\_ini}+{\mathrm{dv}}_1+\frac{\mathrm{\alpha \_max}}{2}.Math.t_3\right)$$t_2=\frac{{\mathrm{dv}}_2}{\mathrm{\alpha \_max}},.Math.{\mathrm{ds}}_2=\left(\mathrm{v\_ini}+{\mathrm{dv}}_1+\frac{{\mathrm{dv}}_2}{2}\right).Math.t_2,.Math.\mathrm{s\_mode}.Math.\left(1\right)={\mathrm{ds}}_1+{\mathrm{ds}}_2+{\mathrm{ds}}_3$

[0226] The following equations apply in Mode II:

[00015]$\mathrm{\alpha \_p}=\sqrt{\frac{2*\mathrm{v\_ini}*\mathrm{fb\_drain}*\mathrm{fb\_inj}+{\mathrm{\alpha \_ini}}^2*\mathrm{fb\_inj}}{\mathrm{fb\_inj}-\mathrm{fb\_drain}}}$$d.Math..Math.{\alpha }_1=\mathrm{\alpha \_p}-\mathrm{\alpha \_ini}$$t_1=-\frac{{\mathrm{da}}_1}{\mathrm{fb\_drain}}$${\mathrm{dv}}_1=\frac{\mathrm{\alpha \_p}+\mathrm{\alpha \_ini}}{2}.Math.t_1,.Math.{\mathrm{ds}}_1=\mathrm{v\_ini}*t_1+\left(\frac{\mathrm{a\_ini}}{2}+\frac{{\mathrm{da}}_1}{6}\right).Math.t_1^2,.Math.t_2=\frac{\mathrm{\alpha \_p}}{\mathrm{fb\_inj}}$${\mathrm{dv}}_2=\frac{\mathrm{\alpha \_p}}{2}.Math.t_2,.Math.\mathrm{ds}.Math..Math.2=\left(\mathrm{v\_ini}+{\mathrm{dv}}_1\right).Math.t.Math..Math.2+\frac{\mathrm{\alpha \_p}}{3}.Math.t.Math..Math.2^2,.Math.\mathrm{s\_mode}.Math.\left(2\right)={\mathrm{ds}}_1+{\mathrm{ds}}_2$

[0227] The following equations apply in Mode III:

[00016]$t_1=\frac{\mathrm{a\_ini}}{\mathrm{fb\_inj}}$${\mathrm{dv}}_1=\frac{\mathrm{\alpha \_ini}}{2}.Math.t_1,.Math.{\mathrm{a\_v}}_0=\sqrt{{\mathrm{a\_ini}}^2+2*\mathrm{v\_ini}*\mathrm{fb\_inj}}$$t_{01}=\frac{\mathrm{a\_ini}-\mathrm{a\_v}.Math..Math.0}{\mathrm{fb\_inj}}$${\mathrm{ds}}_{01}=\mathrm{v\_ini}*t_{01}+\frac{\mathrm{a\_ini}}{2}.Math.t_{01}^2-\frac{\mathrm{a\_ini}-\mathrm{a\_v}.Math..Math.0}{6}.Math.t_{01}^2,.Math.t_{02}=t_1-t_{01}$${\mathrm{ds}}_{02}=\frac{\mathrm{a\_v}.Math..Math.0}{3}.Math.t_{02}^2$${\mathrm{ds}}_1={\mathrm{ds}}_{01}+{\mathrm{ds}}_{02}$$t_2=\sqrt{\frac{2*\left(\mathrm{v\_ini}+{\mathrm{dv}}_1\right)}{\mathrm{fb\_inj}-\frac{{\mathrm{fb\_inj}}^2}{\mathrm{fb\_drain}}}}$${\mathrm{da}}_2=-\mathrm{fb\_inj}*t_2$${\mathrm{dv}}_2=\frac{{\mathrm{da}}_2}{2}.Math.t_2$${\mathrm{ds}}_2=\left(\mathrm{v\_ini}+{\mathrm{dv}}_1\right).Math.t_2+\frac{d.Math..Math.{\alpha }_2}{6}.Math.t_2^2$$t_3=\sqrt{\frac{2*\mathrm{v\_ini}+{\mathrm{dv}}_1}{-\mathrm{fb\_drain}+\frac{{\mathrm{fb\_drain}}^2}{\mathrm{fb\_inj}}}}$${\mathrm{da}}_3=-{\mathrm{da}}_2$${\mathrm{dv}}_3=-\frac{d.Math..Math.{\alpha }_3}{2}.Math.t_3$${\mathrm{ds}}_3=\frac{d.Math..Math.{\alpha }_3}{3}.Math.t_3^2$$\mathrm{s\_mode}.Math.\left(3\right)={\mathrm{ds}}_1+{\mathrm{ds}}_2+{\mathrm{ds}}_3$

[0228] Mode IV covers the case where there is the motion with and without any acceleration limit.

[0229] The following equations apply in Mode IV when acceleration is less than the maximum:

[00017]$t_1=\sqrt{\frac{2*\mathrm{v\_ini}}{\mathrm{fb\_drain}-\frac{{\mathrm{fb\_drain}}^2}{\mathrm{fb\_inj}}}}$${\mathrm{da}}_1=-\mathrm{fb\_drain}*t_1$${\mathrm{dv}}_1=\frac{d.Math..Math.{\alpha }_1}{2}.Math.t_1$${\mathrm{ds}}_1=\mathrm{v\_ini}*t_{01}+\frac{{\mathrm{da}}_1}{6}.Math.t_1^2$${\mathrm{da}}_2=-{\mathrm{da}}_1$$t_2=-\frac{{\mathrm{da}}_2}{\mathrm{fb\_inj}}$${\mathrm{dv}}_2=-\frac{d.Math..Math.{\alpha }_2}{2}.Math.t_2$${\mathrm{ds}}_2=\frac{{\mathrm{da}}_2}{6}.Math.t_2^2$$\mathrm{s\_mode}.Math.\left(4\right)={\mathrm{ds}}_1+{\mathrm{ds}}_2$

[0230] The following further equations apply in Mode IV for the limited acceleration condition:

[00018]$t_3=\frac{\mathrm{a\_max}}{\mathrm{fb\_inj}}$${\mathrm{dv}}_3=\frac{\mathrm{\alpha \_max}}{2}.Math.t_3$${\mathrm{ds}}_3=-\frac{\mathrm{a\_max}}{6}.Math.t_3^2$$t_1=-\frac{\mathrm{a\_max}}{\mathrm{fb\_drain}}$${\mathrm{dv}}_1=\frac{\mathrm{\alpha \_max}}{2}.Math.t_1$${\mathrm{ds}}_1=\mathrm{v\_ini}*t_1+\frac{\mathrm{a\_max}}{6}.Math.t_1^2$${\mathrm{dv}}_2=-\left(\mathrm{v\_ini}+{\mathrm{dv}}_1+{\mathrm{dv}}_3\right)$$t_2=\frac{{\mathrm{dv}}_2}{\mathrm{a\_max}}$${\mathrm{ds}}_2=\left(\mathrm{v\_ini}+{\mathrm{dv}}_1+\frac{{\mathrm{dv}}_2}{2}\right).Math.t_2$$\mathrm{s\_mode}.Math.\left(4\right)={\mathrm{ds}}_1+{\mathrm{ds}}_2+{\mathrm{ds}}_3$

[0231] The following equations apply in Mode IV when the initial acceleration is zero but speed is positive:

[00019]$t_1=\sqrt{\frac{2*\mathrm{v\_ini}}{\mathrm{fb\_inj}-\frac{{\mathrm{fb\_inj}}^2}{\mathrm{fb\_drain}}}}$${\mathrm{da}}_1=-\mathrm{fb\_inj}*t_1$${\mathrm{dv}}_1=\frac{d.Math..Math.{\alpha }_1}{2}.Math.t_1$${\mathrm{ds}}_1=\mathrm{v\_ini}*t_{01}+\frac{{\mathrm{da}}_1}{6}.Math.t_1^2$${\mathrm{da}}_2=-{\mathrm{da}}_1$$t_2=-\frac{{\mathrm{da}}_2}{\mathrm{fb\_drain}}$${\mathrm{dv}}_2=-\frac{{\mathrm{da}}_2}{2}.Math.t_2$${\mathrm{ds}}_2=\frac{{\mathrm{da}}_2}{6}.Math.t_2^2$$\mathrm{s\_mode}.Math.\left(4\right)={\mathrm{ds}}_1+{\mathrm{ds}}_2$

[0232] The following equations apply in Mode IV when the initial acceleration is zero but speed is positive, and acceleration is limited (e.g. the bladder is empty or full):

[00020]$t_3=\frac{\mathrm{a\_max}.Math.\mathrm{\_bck}}{\mathrm{fb\_drain}}$${\mathrm{dv}}_3=\frac{\mathrm{\alpha \_max}.Math.\mathrm{\_bck}}{2}.Math.t_3$${\mathrm{ds}}_3=\frac{\mathrm{a\_max}.Math.\mathrm{\_bck}}{6}.Math.t_3^2$$t_1=-\frac{\mathrm{a\_max}.Math.\mathrm{\_bck}}{\mathrm{fb\_inj}}$${\mathrm{dv}}_1=\frac{\mathrm{\alpha \_max}.Math.\mathrm{\_bck}}{2}.Math.t_1$${\mathrm{ds}}_1=\mathrm{v\_ini}*t_1+\frac{\mathrm{a\_max}}{6}.Math.t_1^2$${\mathrm{dv}}_2=-\left(\mathrm{v\_ini}+{\mathrm{dv}}_1+{\mathrm{dv}}_3\right)$$t_2=\frac{{\mathrm{dv}}_2}{\mathrm{a\_max}.Math.\mathrm{\_bck}}$${\mathrm{ds}}_2=\left(\mathrm{v\_ini}+{\mathrm{dv}}_1+\frac{{\mathrm{dv}}_2}{2}\right).Math.t_2$$\mathrm{s\_mode}.Math.\left(4\right)={\mathrm{ds}}_1+{\mathrm{ds}}_2+{\mathrm{ds}}_3$

[0233] A fifth mode, 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:

[00021]$t_1=\frac{\mathrm{a\_ini}}{\mathrm{fb\_drain}}$${\mathrm{dv}}_1=\frac{\mathrm{\alpha \_ini}}{2}.Math.t_1$${\mathrm{ds}}_1=\mathrm{v\_ini}*t_1+\frac{\mathrm{a\_ini}}{3}.Math.t_1^2$$t_2=\sqrt{\frac{2*\left(\mathrm{v\_ini}+{\mathrm{dv}}_1\right)}{\mathrm{fb\_drain}-\frac{{\mathrm{fb\_drain}}^2}{\mathrm{fb\_inj}}}}$${\mathrm{da}}_2=-\mathrm{fb\_drain}*t_2$${\mathrm{dv}}_2=\frac{d.Math..Math.{\alpha }_2}{2}.Math.t_2$${\mathrm{ds}}_2=\left(\mathrm{v\_ini}+{\mathrm{dv}}_1\right)*t_2+\frac{{\mathrm{da}}_2}{6}.Math.t_2^2$$\mathrm{s\_mode}.Math.\left(5\right)={\mathrm{ds}}_1+{\mathrm{ds}}_2$

[0234] The following equations apply in this mode under the twin negative conditions when there is a limit to the deceleration:

[00022]$t_1=\frac{\mathrm{a\_ini}}{\mathrm{fb\_drain}}$${\mathrm{dv}}_1=\frac{\mathrm{\alpha \_ini}}{2}.Math.t_1$${\mathrm{ds}}_1=\mathrm{v\_ini}*t_1+\frac{\mathrm{a\_ini}}{3}.Math.t_1^2$$t_2=\sqrt{\frac{2*\left(\mathrm{v\_ini}+{\mathrm{dv}}_1\right)}{\mathrm{fb\_drain}-\frac{{\mathrm{fb\_drain}}^2}{\mathrm{fb\_inj}}}}$${\mathrm{da}}_2=\mathrm{fb\_drain}*t_2$$t_4=\frac{\mathrm{a\_max}.Math.\mathrm{\_frw}}{\mathrm{fb\_inj}}$${\mathrm{dv}}_4=\frac{\mathrm{\alpha \_max}.Math.\mathrm{\_frw}}{2}.Math.t_4$${\mathrm{ds}}_4=\frac{\mathrm{a\_max}.Math.\mathrm{\_frw}}{6}.Math.t_4^2$$t_2=-\frac{\mathrm{a\_max}.Math.\mathrm{\_frw}}{\mathrm{fb\_drain}}$${\mathrm{dv}}_2=\frac{\mathrm{\alpha \_max}.Math.\mathrm{\_frw}}{2}.Math.t_2$${\mathrm{ds}}_2=\left(\mathrm{v\_ini}+{\mathrm{dv}}_1\right)*t_2+\frac{\mathrm{a\_max}.Math.\mathrm{\_frw}}{6}.Math.t_2^2$${\mathrm{dv}}_3=-\left(\mathrm{v\_ini}+{\mathrm{dv}}_1+{\mathrm{dv}}_2+{\mathrm{dv}}_4\right)$$t_3=\frac{{\mathrm{dv}}_3}{\mathrm{a\_max}.Math.\mathrm{\_frw}}$${\mathrm{ds}}_3=\left(\mathrm{v\_ini}+{\mathrm{dv}}_1+{\mathrm{dv}}_2+\frac{{\mathrm{dv}}_3}{2}\right).Math.t_3^2$$\mathrm{s\_mode}.Math.\left(5\right)={\mathrm{ds}}_1+{\mathrm{ds}}_2+{\mathrm{ds}}_3+{\mathrm{ds}}_4$

[0235] Mode VI is where there is positive initial speed, but negative initial acceleration. The following equations apply in this mode:

[00023]$t_3=\frac{\mathrm{\alpha \_max}.Math.\mathrm{\_bck}}{\mathrm{fb\_drain}},.Math.{\mathrm{dv}}_3=\frac{\mathrm{\alpha \_max}.Math.\mathrm{\_bck}}{2}.Math.t_2$${\mathrm{ds}}_3=-{\mathrm{dv}}_3*t_3+\frac{\mathrm{\alpha \_max}.Math.\mathrm{\_bck}}{2}.Math.t_3^2$$d.Math..Math.{\alpha }_1=\mathrm{\alpha \_max}-\mathrm{\alpha \_ini},.Math.t_1=-\frac{{\mathrm{da}}_1}{\mathrm{fb\_inj}}$${\mathrm{dv}}_1=\frac{\mathrm{\alpha \_max}.Math.\mathrm{\_bck}+\mathrm{\alpha \_ini}}{2}.Math.t_1$${\mathrm{dv}}_2=-\left(\mathrm{v\_ini}+{\mathrm{dv}}_1+{\mathrm{dv}}_3\right)$$t_2=\frac{{\mathrm{dv}}_2}{\mathrm{\alpha \_max}.Math.\mathrm{\_bck}},.Math.{\mathrm{ds}}_2=\left(\mathrm{v\_ini}+{\mathrm{dv}}_1+\frac{{\mathrm{dv}}_2}{2}\right).Math.t_2,.Math.\mathrm{s\_mode}.Math.\left(6\right)={\mathrm{ds}}_1+{\mathrm{ds}}_2+{\mathrm{ds}}_3$

[0236] Under the boundary condition where the time between the change in acceleration is zero, the following equations apply:

[00024]$\mathrm{\alpha \_p}=-\sqrt{\frac{2*\mathrm{v\_ini}*\mathrm{fb\_drain}*\mathrm{fb\_inj}+{\mathrm{\alpha \_ini}}^2*\mathrm{fb\_drain}}{\mathrm{fb\_drain}-\mathrm{fb\_inj}}}$$d.Math..Math.{\alpha }_1=\mathrm{\alpha \_p}-\mathrm{\alpha \_ini}$$t.Math..Math.1=-\frac{\mathrm{da}.Math..Math.1}{\mathrm{fb\_inj}}$${\mathrm{dv}}_1=\frac{\mathrm{\alpha \_p}+\mathrm{\alpha \_ini}}{2}.Math.t_1,.Math.{\mathrm{ds}}_1=\mathrm{v\_ini}*t_1+\left(\frac{\mathrm{a\_ini}}{2}+\frac{{\mathrm{da}}_1}{6}\right).Math.t_1^2,.Math.t_2=\frac{\mathrm{\alpha \_p}}{\mathrm{fb\_drain}}$${\mathrm{dv}}_2=\frac{\mathrm{\alpha \_p}}{2}.Math.t_2,.Math.\mathrm{ds}.Math..Math.2=\left(\mathrm{v\_ini}+{\mathrm{dv}}_1\right).Math.t_2+\frac{\mathrm{\alpha \_p}}{3}.Math.t.Math..Math.2^2,.Math.\mathrm{s\_mode}.Math.\left(6\right)={\mathrm{ds}}_1+{\mathrm{ds}}_2$

[0237] The converse condition of positive speed and negative acceleration is described by:

[00025]$t_1=-\frac{\mathrm{a\_ini}}{\mathrm{fb\_drain}}$${\mathrm{dv}}_1=\frac{\mathrm{\alpha \_ini}}{2}.Math.t_1,.Math.{\mathrm{a\_v}}_0=\sqrt{{\mathrm{a\_ini}}^2+2*\mathrm{v\_ini}*\mathrm{fb\_inj}}$$t_{01}=\frac{\mathrm{a\_ini}+\mathrm{a\_v}.Math..Math.0}{\mathrm{fb\_drain}}$${\mathrm{ds}}_{01}=\mathrm{v\_ini}*t_{01}+\frac{\mathrm{a\_ini}}{2}.Math.t_{01}^2-\frac{\mathrm{a\_ini}*\mathrm{a\_v}.Math..Math.0}{6}.Math.t_{01}^2,.Math.t_{02}=t_1-t_{01}$$\mathrm{ds}.Math..Math.02=-\frac{\mathrm{a\_v}.Math..Math.0}{3}.Math.t.Math..Math.{02}^2$${\mathrm{ds}}_1={\mathrm{ds}}_{01}+{\mathrm{ds}}_{02}$$t_2=\sqrt{\frac{2*\mathrm{abs}\left(\mathrm{v\_ini}+{\mathrm{dv}}_1\right)}{-\mathrm{fb\_drain}+\frac{{\mathrm{fb\_drain}}^2}{\mathrm{fb\_inj}}}}$${\mathrm{da}}_2=-\mathrm{fb\_drain}*t_2$${\mathrm{dv}}_2=\frac{{\mathrm{da}}_2}{2}.Math.t_2$${\mathrm{ds}}_2=\left(\mathrm{v\_ini}+v_1\right).Math.t_2+\frac{d.Math..Math.{\alpha }_2}{6}.Math.t_2^2$$t_3=\sqrt{\frac{2*\mathrm{abs}\left(\mathrm{v\_ini}+{\mathrm{dv}}_1\right)}{\mathrm{fb\_inj}-\frac{{\mathrm{fb\_inj}}^2}{\mathrm{fb\_drain}}}}$${\mathrm{da}}_3=-{\mathrm{da}}_2$${\mathrm{dv}}_3=-\frac{{\mathrm{da}}_3}{2}.Math.t_3$${\mathrm{ds}}_3=\frac{d.Math..Math.{\alpha }_3}{6}.Math.t_3^2$$\mathrm{s\_mode}.Math.\left(6\right)={\mathrm{ds}}_1+{\mathrm{ds}}_2+{\mathrm{ds}}_3$

[0238] Mode VII is the case where the diver has positive initial speed and acceleration. The relevant equations are:

[00026]${\mathrm{da}}_1=-\mathrm{a\_ini}$$t_1=-\frac{{\mathrm{da}}_1}{\mathrm{fb\_inj}}$${\mathrm{dv}}_1=\frac{\mathrm{\alpha \_ini}}{2}.Math.t_1$${\mathrm{ds}}_1=\mathrm{v\_ini}*t_1-\frac{{\mathrm{da}}_1}{3}.Math.t_1^2$$t_2=\sqrt{\frac{2*\left(\mathrm{v\_ini}+{\mathrm{dv}}_1\right)}{\mathrm{fb\_inj}-\frac{{\mathrm{fb\_inj}}^2}{\mathrm{fb\_drain}}}}$${\mathrm{da}}_2=-\mathrm{fb\_inj}*t_2$${\mathrm{dv}}_2=\frac{{\mathrm{da}}_2}{2}.Math.t_2$${\mathrm{ds}}_2=\left(\mathrm{v\_ini}+{\mathrm{dv}}_1\right).Math.t_2+\frac{d.Math..Math.{\alpha }_2}{6}.Math.t_2^2$$t_2=\sqrt{\frac{2*\left(\mathrm{v\_ini}+{\mathrm{dv}}_1\right)}{-\mathrm{fb\_drain}-\frac{{\mathrm{fb\_drain}}^2}{\mathrm{fb\_inj}}}}$${\mathrm{da}}_3=-{\mathrm{da}}_2$${\mathrm{dv}}_3=-\frac{{\mathrm{da}}_3}{2}.Math.t_3$${\mathrm{ds}}_3=\frac{d.Math..Math.{\alpha }_3}{6}.Math.t_3^2$$\mathrm{s\_mode}.Math.\left(7\right)={\mathrm{ds}}_1+{\mathrm{ds}}_2+{\mathrm{ds}}_3$

[0239] The control process described herein can be expressed as an exponential control algorithm but the additional complexity appears to provide no tangible benefits.

[0240] 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.

[0241] 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 minimize 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.

[0242] 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: [0243] Respiration [0244] In closed loop diving systems, changes to the breathing loop volume [0245] i. via ADV/OPV valves used manually [0246] ii. a gradual increase in buoyancy due to O.sub.2 consumption [0247] iii. O.sub.2 injection in the system with active PPO.sub.2 control [0248] iv. Gas mixture injection in SCR. [0249] Diver rotation [0250] Diver motion which generate forces up or down the water column.

[0251] The coding of the system can be simplified greatly, as shown in FIGS. 20a-20f, by using a pulse width modulator with an expert system, i.e., A system that combines a set of conditions based on the likely actions of an expert diver, with actions when those conditions are met. Such an expert system can reduce the dependence of the buoyancy controller on environmental parameters.

[0252] The user interface to the automatic buoyancy system may incorporate all the features of a dive computer

[0253] 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.

[0254] 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.

[0255] It is possible to execute all or part of the control process on a dive computer. The process described can be executed in a 100 ms 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 100 ms interval and the slow loop for a dive computer has a 4 second interval. During an actual ascent under control of the buoyancy controller, the dive computer decompression profile can be suspended until the stop is reached. During the decompression stop, 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 factual PPO.sub.2 in a rebreather.

[0256] 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.

[0257] The dive computer (40) normally has a surface mode and a dive mode. The device will normally enter the dive mode when it is pressurized or when contacts are wet preventing reconfiguration of critical parameters underwater.

[0258] Where 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 PPO.sub.2 is falling at a faster rate than is acceptable the ascent may require to be aborted in order for the PPO.sub.2 to be restored or for the diver to bail out.

[0259] Minimization of the position error, gas consumption and valve energy depends on the BCD structure (gas movement paths, restrictions, characteristics of the control elements and their stability, and can be optimized in the control algorithm.

[0260] The greater the required maximum ascent/descent buoyancy speed then the more gas must be spent. A well optimized automatic buoyancy control system will generally use much less gas than a novice or intermediate level diver uses performing these functions manually.

[0261] Usually decompression is performed by in a step-by-step mode involving relatively fast motion and then long waits at the set depth. Buoyancy control with exponential depth changes (without fast motion and stops) provides the minimum gas consumption for buoyancy control. In the ideal case the gas consumption equals zero.

[0262] To provide buoyancy control with the maximum response rate it is necessary (before diving) to equalize the forces applied to the body so the buoyancy bladder and the breathing loop size are preferably close to a middle position when the diver's speed and acceleration is zero. In this case the maximum result force in ascent/descent direction is half of the buoyancy bladder size. In other words, the diver should be correctly weighted, and will use more gas if the diver is not: this weight may be greater than for a diver without any active buoyancy control by several kilograms.

[0263] Buoyancy control could provide the following descent/ascent motion modes: [0264] Step-by step mode [0265] Constant speed motion [0266] Motion along required depth profile [0267] Restrictions to the maximum speed at which the diver may ascend or descend

[0268] A buoyancy control system cannot control diver attitude efficiently. Alternative means are much better at this function (i.e. use far less energy).

[0269] Calculation of acceleration/deceleration can be used to increase system safety, estimating the spent buoyancy gas.

[0270] FIGS. 20a-20f shows a simplified 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, and also able to perform emergency ascents, controlled ascents and follow a decompression profile through changes to the Maximum Allowed Depth. The example combines elements of an expert system with that of a proportional controller, on this case a pulse width modulator

[0271] The control code, providing an example of the control process in FIGS. 20A-20f 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).

[0272] FIGS. 20a-20f shows a simplified 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, and also able to perform emergency ascents, controlled ascents and follow a decompression profile through changes to the Maximum Allowed Depth. The example combines elements of an expert system with that of a proportional controller, on this case a pulse width modulator

[0273] The control process in FIGS. 20A-20f is suitable for re-entrant use, and would require a loop time of 100 ms or less to perform adequate control. This loop time can be achieved on microcontrollers, or using FPGAs with floating point processors. The floating point requirements can be converted to fixed point arithmetic.

[0274] In some environments a dual redundant bladder may be 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. The redundant bladder may exist alongside the bladder that is controlled automatically or even may be included in the same overall BCD cover where the BCD comprises a bladder and outer cover.

[0275] This invention is not limited to the specific examples disclosed herein which is intended to be illustrative and it covers all modifications and alternatives coming within the scope and spirit of the invention as defined in the attached claims.