Remote Control Explorations

Conducting scientific experiments on the ocean floor 13,200 feet beneath the surface requires a remotely operated vehicle that's flexible, compact, and reliable. The technical staff at Monterey Bay Aquarium Research Institute (www.mbari.org) designed and built the ROV Tiburon during the early 1990s. The vehicle is not only rated for 4,000 meters, it is all-electric as well, propelled by electric motors rather than hydraulic motors to produce fine, precise positioning.

Some of the electronics used in the ROV are now outdated, so MBARI is incrementally updating systems on the vehicle and the I/O system in particular. MBARI originally built custom hardware for the vehicle and it has become increasingly hard for technicians to maintain the system and find replacements for failed components.

"The first project we're doing is a Benthic biology toolsled upgrade," says Dale Graves, an engineer at MBARI. "We're building a controller using Wago I/O (www.wago.com) that will control switching power to cameras, sensors, and instruments, switching valves for the hydraulic system, and miscellaneous digital and analog I/O used on the vehicle."

As an example, the Benthic biology toolsled is equipped to help scientists delve into the biology of deep-sea CO₂ disposal and lava-flow. The goals of the CO₂ disposal project is to evaluate the sensitivities of deep-sea organisms to elevated CO₂ levels, either through large-scale deep-sea CO₂ release or by the longer-term elevation of oceanic pH by air-sea exchange. Non-vent lava-flow ecosystem studies are targeting subsea eruptions on the Juan de Fuca and Gorda Ridges.

The toolsled is a separate package that mounts to the bottom of the vehicle for specific scientific explorations. Graves says that the Benthic toolsled is the workhorse of their scientific operations and is used for setting instruments on the sea floor and collecting sediments, organisms, or rocks.

Remote Communications

The Tiburon utilizes an umbilical or tether which attaches the ROV to a support vessel, the R/V Western Flyer. The 5,000-meter umbilical consists of three single mode fibers and three power conductors. All the data and telemetry for the vehicle's thrusters, sensors, instruments, and cameras are communicated using the fiber optic interface. The system implements a custom multiplexer that converts the data and video into light wavelengths for transmission through the fibers up to the surface.

Graves says that this approach provides a series of serial ports down on the bottom to support a variety of devices, and is plugged topside into a laptop computer running a LabView graphical user interface (www.ni.com). The Wago Modbus Controller on the toolsled plugs into an RS-232 port on the vehicle, and interfaces a distributed network of analog and digital I/O throughout the vehicle.

The I/O is used to switch power and turn cameras and instruments on/off, isolate serial ports, read analog inputs, and control sensors with analog outputs. Graves says that they are in the process of integrating a new HDTV camera on the vehicle, and the Wago I/O system has also been added to the topside network to control the pan, tilt, and other camera functions.

The major challenge of the retrofit program has been simplifying the control system using off-the-shelf components and software, plus reducing the weight and increasing the compactness of the controls.

"The biggest challenge in the upgrades has been packaging, since keeping the weight down is one of the biggest issues on the vehicles," says Graves. "The ROV only supports a specific amount of payload. So if the control system adds 10 lbs to the vehicle, that's 10 lbs less that the scientist can collect."

The compact I/O modules fit into the existing 6-inch I.D. cans the Tiburon uses to house control electronics. These machined titanium cans have walls thick enough to keep the housing from collapsing or imploding from the approximately 6,000 psi pressure on the ocean floor.

"Originally, we anticipated using the Wago I/O system in a pressure-tolerant environment," says Graves. "The I/O would be placed in an oil-filled, acrylic cylinder where it would see full pressure, or the pressure depending on the depth of the vehicle." Graves says they pressure-tested the I/O and qualified most of the modules, and only had to replace a crystal in one of the modules that imploded at approximately 5,000 ft.

The MBARI technical team decided not to use the system in a pressure-tolerant environment and instead enclosed the I/O system in a one atmosphere can strong enough to withstand the pressure. "We're basically using the I/O system like a plant floor would for distributed I/O on the vehicle."

Using an acrylic can rather than the titanium cans offers the possibility of significantly reducing the weight of the systems in the future. One plan is to incorporate the oil-filled tubes with I/O systems with built-in, add-on points. By configuring the I/O system with additional, non-working points in the node, those modules could be programmed in sequence to provide expansion if more I/O was required.

An additional challenge for this project is interfacing the I/O system and LabView software to the existing software architecture in the Tiburon. There are several layers of software on the vehicle, but the core operating system is VxWorks. A custom-built, Unix-based program has been developed as the primary graphical user interface for the vehicle.

To interface the new I/O system on the Benthic toolsled to the existing software architecture, MBARI plans to utilize LabView to use serial communications to manage the I/O system and a separate Ethernet port to communicate to the vehicle network.

One example of why this is important is the need to manage power effectively on the ROV. Since the vehicle's total power is limited to 15 kW, the system must take power away from certain areas like the thrusters and maintain power to sensors, lights, and cameras.

"There are items on the toolsled that require power such as a large 1 kW motor, so we need to communicate to the core software architecture that we need power to run that motor," says Graves. The LabView interface provides both a method for communicating with this software and also supports a primary goal of the upgrade program. Using LabView enables MBARI to implement a GUI that technicians and pilots can utilize to make software modifications without needing the services of the core engineering team.