Subsea Cable Survey and Inspection ROV Control System

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"The LabVIEW Actor Framework proved perfect for managing multiple processes running in parallel that could be loaded into one main subpanel to view when needed."

- Lewis Gear, TBG Solutions

The Challenge:
Creating a reliable and flexible control system for a new class of subsea cable survey and inspection remotely operated vehicle (ROV).

The Solution:
Using CompactRIO, LabVIEW, and LabVIEW Actor Framework to seamlessly control a wide variety of hardware and create a complex control system for a new class of subsea ROV.

Author(s):
Lewis Gear - TBG Solutions

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. 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 newly designed ROV from a much smaller survey vessel and use the survey vessel for forward propulsion.

Hydrobotics needed a software solution 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 ROV consists of a hydraulic power unit, four hydraulic thrusters, survey equipment, peripheral devices, sensors, and a control system, which make a truly multidisciplinary design challenge. We connected the ROV 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. 

Figure 1. Subsea ROV With Survey Equipment Deployed

ROV Control 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.

 

Figure 2. Control System Overview

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.

Figure 3. The ROV

Topside Operator Interface

The operator can control and monitor the ROV with the topside operator interface. The operator can control the ROV from a touchscreen display and an array of physical joysticks, knobs, and buttons as seen in Figure 5.

 

Figure 4.  Operator Console

We interfaced any physical digital and analogue I/O through a PCI-6829 multifunction data acquisition card. The touchscreen display features a selection ribbon and a number of different software screens as shown in Figure 6.

Figure 5. Operator Interface Home Screen

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 all 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, we chose the LabVIEW Actor Framework for the architecture. With 22 actors (processes) running in parallel, we needed a trusted and reliable inter-process communication that could quickly view any process at a given time. The LabVIEW Actor Framework proved perfect for managing multiple processes running in parallel that could be loaded into one main subpanel to view when needed. Figure 7 shows the LabVIEW actors in the system.

Figure 6. LabVIEW Actor Framework Class Hierarchy

Subsea Control System

The subsea control system reads onboard sensors and controls peripherals and thrusters. We achieve this 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 as shown in Figure 8.

Figure 7. ROV Feedback Control

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.

We used LabVIEW object-orientated programming to encapsulate the functionality of each module on the controller. Using the dynamic dispatching properties of LabVIEW, we 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 we could integrate hardware into the software before it was received.

Figure 8. I/O Class Hierarchy

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 ideal 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.

Conclusion

In three months, we designed, developed, and tested a complete ROV control system. We used LabVIEW 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.

Figure 9. The ROV in Operation

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.

We could greatly reduce development time and cost because of the reuse of readily available code libraries such LabVIEW Network Streams and being able to quickly create professional graphical user interfaces with .net components. We 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.

Figure 10. The ROV on Deck

Author Information:
Lewis Gear
TBG Solutions
TBG Solutions, 3A Midland Court
Balborough S43 4UL
United Kingdom
lewis.gear@tbg-solutions.com

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