A B S T R A C TMaintaining depth is a diver's essential task, and that is why he/she uses a buoyancy vest for maintaining and changing depth [the so-called buoyancy control device (BCD)]. Changing depth is controlled by manually actuating pneumatic valves, which causes the BCD volume to expand or shrink and consequently change its buoyancy.Divers' desires for devices that automatically change or maintain depth have been present since the first arrival of modern diving using a buoyancy vest. This need has arisen, particularly when diving, in regard to the following: where poor visibility is present; when both hands are needed for the job in amateur diving; where decompression procedures are needed; during safety stop procedures; during automatic ascending when a diver's life functions are critical; and also when using the same technology for changing depth in small modern submarines and submarine-like vessels.The presented prototype device has been developed for automatic buoyancy control using flexible BCD. This device can limit ascending and descending velocities, allow a diving diver to request a depth at a requested velocity and hold that requested depth, ensure a diver's requested depth and velocity are controlled, minimize any depth and velocity errors in relation to disturbances from the environment, and record all captured data for dive analyses. Controlling velocity is important for proper decompression.This paper presents a mathematical model of a diver's buoyancy, the prototype development of an automatic BCD, and simulation and actual diving results. The prototype device has been fully tested by one of the leading manufacturers of diving equipment.

In this article, the design and multiobjective optimization of a non-model-based proportional-integral-derivative (PID) control system for diver's buoyancy control device (BCD) is presented. Changing and maintaining depth is an essential task in diving, for which the diver typically uses manual control of two pneumatic valves. An effective automatic control of the BCD can be beneficial in specific diving circumstances; i.e., in amateur diving, safety stop procedures, automatic ascending in case of critical life functions of the diver, poor visibility, when both of the diver's hands are required for other tasks, etc. In addition to multiple control problems caused by internal nonlinear dynamics of the BCD hardware, three main control aspects were considered: position or depth of the BCD; vertical, meaning the ascending or descending velocity of the BCD; and air supply consumption. From that, we examined and implemented a combined depth and vertical velocity control, which was configured as a cascaded controller setup with outer depth and inner vertical velocity control loops. Such controller setup could easily implement the specified limitations of the BCD's vertical velocity, which are critical for proper decompression procedure while the diver is ascending. In a simulation environment the optimization of the controller parameters was achieved with a differential evolution global optimum search algorithm. Obtained results were then compared to a manually driven BCD in a simulated environment.

No abstract