TBG Solutions has used National Instruments' CompactRIO control hardware, Labview software, and LabVIEW Actor Framework to control hardware and create a complex control system for a new class of subsea remotely operated vehicle (ROV).
Survey and inspection is an important part of any subsea cable's installation and operational life. Post-construction services like acoustic survey, visual inspection and depth of burial are significant for communication cables, power cables, oil pipes and gas pipes. Untethered remotely operated vehicles (ROV) and seabed crawler systems often carry out conventional survey operations. However, these vehicles tend to require a large and expensive support vessel.
Hydrobotics is a company that specialises in providing a range of commercial and engineering services to the marine industry. It saw an opportunity to create a cost-effective alternative to traditional survey and inspection ROVs. Operators can launch the new ROV from a much smaller survey vessel and use the survey vessel for forward propulsion.
Hydrobotics needed software to deliver a complete control system and operator interface for this new class of ROV. After a competitive tender assessing both technical and financial merits, the company enlisted TBG Solutions, an NI Gold Alliance Partner.
ROV system overview
The control system includes two major parts: the subsea control system at the heart of the ROV and the topside operator interface on the support vessel. While the subsea control system reads onboard sensors, controls peripherals, and controls the thrusters, the topside operator interface communicates with the subsea controller to provide an interface for controlling the vehicle and monitoring its performance.
Within the ROV are a hydraulic power unit, four hydraulic thrusters, survey equipment, peripheral devices, sensors and a control system - which all makes for a truly multidisciplinary design challenge. The ROV is connected to the support vessel with an umbilical winch to provide power and communication. The winch constantly adjusts to compensate for the rolling waves that the launch vessel sits on, thus maintaining the ROV’s vertical position. Thrusters on the ROV adjust for the horizontal position.
Topside operator interface
An operator can control and monitor the ROV with the topside operator interface, which is equipped with a touchscreen display and an array of physical joysticks, knobs and buttons.
Physical digital and analogue I/O was interfaced through a PCI-6829 multifunction data acquisition card. The touchscreen display features a selection ribbon and a number of different software screens.
The operator can monitor critical ROV elements and select which software screens to view with the ribbon across the top of the screen. The Home Screen is the main page that shows the most relevant information such as the ROV's roll, pitch, heading and depth. The System Screen can control peripherals such as lights, cameras, sensors and actuators. The Engineer Screen is an engineer's view of the system to provide additional control and is password protected. The Configuration Screen is used to setup parameters including alarm limits and performance parameters. The IO Screen is used to view all I/O of the system for debugging.
To achieve a large, maintainable and scalable system, the developers chose the LabVIEW Actor Framework for the architecture. With 22 actors (processes) running in parallel, a trusted and reliable inter-process communication was required that could quickly view any process at a given time. The LabVIEW Actor Framework proved to be excellent for managing multiple processes running in parallel that could be loaded into one main subpanel to view when needed.
Subsea control system
The subsea control system reads onboard sensors and controls peripherals and thrusters. This is achieved using analogue input channels, analogue outputs, digital inputs, digital outputs and serial communications. The cRIO-9068 chassis has a range of modules installed to read from a number of different transducers such as pressure sensors and temperature sensors.
To control the ROV position, a feedback control loop automatically calculates thruster values.
A motion reference unit (MRU) measures the actual position of the ROV and the control system then automatically calculates the amount of thrust needed to each of the four thrusters to achieve the desired position.
Labview object-orientated programming was used to encapsulate the functionality of each module on the controller. Using the dynamic dispatching properties of Labview, the team could easily use simulation code without any change to the surrounding software and run the code without any hardware present. This reduced development time because hardware could be integrated into the software before it was received.
The nature of this application made it necessary to implement fail safes to ensure that the ROV operated safely even when elements of the control hardware or software fail. The Labview reconfigurable I/O (RIO) architecture is excellent from this standpoint because most I/O is channelled through the FPGA, which is also the most reliable component of the system. The FPGA could monitor the onboard systems and in the event of a problem, revert back to a safe state.
In three months, the team designed, developed and tested a complete ROV control system. Labview was used to create a complex and flexible embedded control system that could seamlessly integrate with all types of hardware. The control system can automatically combat apposing water currents, stay on a designated heading, follow a support vessel and follow seabed contours.
Using a trusted application architecture, the LabVIEW Actor Framework, made it easy to run 22 parallel processes on the Operator Console because it provided built-in communication methods, error handling, and initialisation and shutdown procedures.
The real-time operating system on the CompactRIO made it possible to run deterministic control code whilst monitoring alarms, communicating with a range of RS232 and RS485 devices, and communicating with the Topside Operator Console.
The FPGA on the CompactRIO delivered access to a range of physical I/O but, more importantly, it could monitor the state of the ROV and always ensure it was in a safe state as soon as we powered the CompactRIO on.
The team was able to greatly reduce development time and cost because of the reuse of readily available code libraries such Labview Network Streams, and was able to quickly create professional graphical user interfaces with .net components. They successfully delivered this complex project on time, in full and to a high standard. The ROV can remain operational for 24 hours a day for weeks at a time without recovery, and operators can launch it from a much smaller support vessel than conventionally needed. This new class of ROV is set to revolutionise the survey and inspection industry by providing a faster and cheaper alternative to existing technology.
Follow the link for more information about the new class of ROV.