Safe Automatic Buoyancy Control Device

Abstract

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.

Description

TECHNICAL FIELD[0001]The present invention relates to the automatic control of diver buoyancy and buoyancy compensation. In particular, 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.BACKGROUND OF THE INVENTION[0002]The 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 underwater. These buoyancy compensation requirements are commonly satisfied by the use of buoyancy compensation device (hereafter, BCD) in the form of an inflatable bladder into which gas is a...

AI Technical Summary

Benefits of technology

[0041]A novel control means is described for an automatic buoyancy compensator which sufficiently damps the natural positive f

Problems solved by technology

Additionally, novice divers are typically over-weighted such that they require a matching positive buoyancy to be able to swim freely underwater.

However, it generally requires many hundreds or thousands of hours of diving experience to do this level of buoyancy control comfortably, so the majority of divers choose to use a BCD to manage their buoyancy.

It takes tens or hundreds or hours of experience for the diver to use the BCD optimally: without that experience the diver may add too much gas at one time, or fail to add enough.

If the diver loses partial or full control of their buoyancy, the diver may exceed their desired depth profile or accelerate towards the surface in a dangerous manner.

The control of the BCD is complicated by Boyle's Law, which compresses the gas in the BCD during descent and causes the same gas to expand when the ambient pressure reduces during ascent, resulting in an inherently unstable positive feedback loop.

Failure to follow a correct depth or decompression profile can result in serious or mortal injuries from barotrauma, decompression sickness, narcosis, blackout, oxygen toxicity or drowning.

Many divers find free-swimming buoyancy control so difficult, that they prefer to ascend or descend on a fixed line: an anchor chain, shot line or buoy rope.

Serious problems often arise in the event the diver fails to find the line or the line becomes adrift.

Moreover none of the prior art address the fundamental safety problems of what happens when a valve or controller fails.

The result is, that even if the devices proposed could actually work, they would reduce diver safety rather than enhance it, by introducing many new failure modes which are not fail-safe.

The Safe Failure Fraction of the proposals to date is close to zero (inherently dangerous), whereas for a commercial product to be viable it should be close to one (inherently fail safe).

These devices are impractical for a free-swimming diver.

No automatic buoyancy device for free-swimming divers is available currently despite very many attempts to create such a device, spanning decades.

However, the inventions needed to implement these desirable features have hitherto failed to overcome the basic physical problems and as a consequence have been unable to be realised successfully.

The problems in this application are much more difficult problems than simply returning a diver or mine to the surface at a controlled rate.

A prototype of the proposed system did not work due to a combination of problems: the resolution available from the pressure sensors is insufficient for such a simple control system to work in practice and experiments were curtailed due to water ingress problems.

The device as proposed created a series of fundamental safety problems for the diver including uncontrolled ascents.

The relief of gas once a maximum volume is reached is quite different to the problem of determining the volume of a bladder in its normal range: the prior art fails to propose a viable solution to this critical problem which is the basis of most attempts to provide a free-swimming automatic buoyancy control device.

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.

There are many patents of this type, where the concept has neither been reduced to practice nor modelled mathematically, and as a consequence the inherent flaws or impossibility of the proposal have escaped the attention of the proposer.

One problem with the use of multiple vent valves is the power required by some of the proposals.

When several electrical solenoids are activated simultaneously, the combined power consumption would be 45 W: such power is not available without large batteries such as those used for underwater lighting.

It is certainly not available in a small dive computer as some of the proposals suggest.

The problem that needs to be overcome by a practical automatic BCD is that of determining how much gas to add or vent from the bladder, which equates to the problem of how long to open an injector valve or vent valve.

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.

No depth sensor, or even Analogue to Digital Converter (ADC) suitable for use on a portable piece of div

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