Control Developments has developed a design for a highly efficient fixed volume 'positive displacement' buoyancy control device. Called the ABCD1, it is intrinsically stable, is scalable in terms of net positive/negative buoyancy, and can be networked to provide a stable and precise underwater buoyancy and attitude control. It realises high efficiency and stability by exploiting the creation of small differential displacements whilst maintaining an approximate neutral buoyancy when the internal forces are in equilibrium; this means that only small amounts of energy are required to generate significant changes in buoyancy, and energy recovered during the reduction of buoyancy is used regeneratively to maintain battery charge. The unit is stand-alone, containing its own energy source, displacement controller, depth sensor and control system, and needs only a single (sealed) external control signal.

KEY FEATURES:

• A fixed volume, variable mass unit not suffering from the intrinsic instability of air bags or air displacement systems.
• The conversion of lost potential energy into electrical energy by regenerative methods.
• Stand alone and autonomous depth control, requiring only a command signal.
• Networking capabilities to provide a stable plane underwater using three of more ABCD units.
• Internal tilt sensor to allow buoyancy to be a function of attitude.
• Can be configured for fixed buoyancy (at variable depths) or fixed depth (at variable payloads).
• Net buoyancy not dependent on orientation - no associated unstable 'flips' associated with air displacement systems.
• Tuneable compromises between precision, speed of response and energy efficiency.
• Failsafe operation - reverts to zero net buoyancy if there is an internal system failure.
• Self learning stability criteria, using pressure and rate-of-change of pressure as inputs.
• Scalable from a net buoyancy adjustment of +/- 100 Newtons to +/- 10000 Newtons, or beyond.