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.

We claim: 
     
         1 . A device for controlling a diver's buoyancy comprising a bladder, electro-pneumatic valves, and a processing unit, the electro-pneumatic valves comprising at least one gas valve configured to inject gas into the bladder and at least one vent valve configured to vent gas from the bladder, where the diver's relative buoyancy is computed by the processing unit from parameters that include as a primary control parameter signals proportional to the ambient pressure a signal that is a first derivative of the ambient pressure and a signal proportional to the second derivative of ambient pressure, wherein the second derivative is used to select control modes with a computation used to activate and deactivate the electro-pneumatic valves. 
     
     
         2 . A device according to  claim 1  wherein the at least one gas valve pressurise or depressurise a pneumatic hose connecting to at least three vent valves 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 vent valves are configured to be opened by a pneumatic pressure and configured to be closed by a counterforce created by or assisted by a wave spring in addition to a pull-cord enabling the valve to be opened manually, and in which water ingress into the bladder is restricted by use of a one-way valve in series with the vented gas flow. 
     
     
         12 . 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. 
     
     
         13 . 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. 
     
     
         14 . 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. 
     
     
         15 . 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 energised. 
     
     
         16 . 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. 
     
     
         17 . 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. 
     
     
         18 . A device according to  claim 1  that combines a diver's acceleration signal with a signal proportional to the diver's speed. 
     
     
         19 . 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. 
     
     
         20 . A device according to  claim 1  comprising a safety means to shut down the automatic buoyancy control system without affecting the ability of the diver to perform buoyancy control manually. 
     
     
         21 . 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. 
     
     
         22 . A device according to  claim 20  that integrates a dive computer function to generate a dive decompression profile that can be adopted by the automatic buoyancy controller. 
     
     
         23 . A device according to  claim 20  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. 
     
     
         24 . A device according to  claim 20  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 pressurised or wet or in a dive mode. 
     
     
         25 . A device according to  claim 1  where an acceleration signal is obtained using a 3-axis accelerometer. 
     
     
         26 . A device according to  claim 1  where an acceleration signal is obtained using an analogue differentiator from the ambient pressure signal.