## 1 Introduction  
Offshore structures such as pipelines, risers, and umbilicals require regular inspection and monitoring to assess their integrity, which will lead to improvements in safety and environmental protection and potentially increase their operational lifetime. With health and safety requirements becoming more stringent, the regular inspection of structures is becoming an essential element as part of preventive maintenance (PM). Offshore structures have to withstand harsh operating environments: cyclic wave loading, wind loading, corrosion, accidental damage, and marine growth [1]. Damage occurring during installation, in service, and due to aging can pose significant hazards to people, assets, and the environment. To prevent catastrophic failures, these structures must be inspected, repaired, and, if necessary, removed on a periodic basis. Inspection or repair in the said environment is not easy and is associated with high safety requirements. These processes are usually carried out by trained divers, or the equipment for inspection or repair is deployed using remotely operated vehicles (ROVs). The procedures to be carried out by human divers are associated with human safety and limited to certain depths under water. The use of ROVs is very expensive and suffers from stability problems in the operating environment. Hence, robotic and automated systems are being investigated for deployment and for carrying out the required tasks under these extreme conditions for diagnostics of structural faults. Depending on the type of structure and needs of the inspection method adopted, various robotic systems have been developed that vary in terms of complexity and method of deployment. A brief review on robotic systems for inspection was provided in [2] and in frameworks for in-process robotic inspection systems [3; 4]. The design and development of a robotic automated system for such an extreme environment requires the consideration of various factors such as materials, minimum human intervention, weight, ruggedized structure and enclosures, reliability, umbilical size, and safety. There is vast literature on the development of distributed control systems and on utilizing communication technologies to provide control methods--[5; 6; 7; 8], to mention a few. However, due to the very nature of the operational environment, the use of hydraulic systems that are controlled remotely has been a norm in the subsea industry, and the use of electric drive and control systems using fieldbus technology in subsea applications is relatively recent. As outlined by [PERSON] [9], the transition from hydraulic to electric actuators and control systems in subsea applications is important in cases where high precision and tight dynamic control over the actuators are required. The importance of fieldbus technology is also emphasized for \"control in the field\" to have superior control for benefits of higher throughput and Health and Safety Executive (HSE) benefits in offshore, high-risk environments [10]. This is also an essential step forward in developing autonomous systems in harsh environments. With the identification of digitalization and improved controllability, detailed studies were carried out on various fieldbus systems in order to develop standard communication and protocol systems for subsea equipment by Subsea Instrumentation Interface Standardisation (SIIS), and Controlled Area Network (CAN) was identified as one of the most robust in terms of fault tolerance with multidrop systems [11]. A further case study was carried out [12] for oil and gas applications to apply CAN Open protocols with sensing systems in subsea equipment, which showed similar results to [11] with regard to the limitations of the network when applied to a subsea environment as compared to land-based systems. The work presented here is application focused towards actuator control with fieldbus technology for the inspection of subsea structures in harsh environments.