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Heavy loads lifted with synchronized control

Heavy loads lifted with synchronized control

The transfer and jacking of oil platforms, drilling mud tanks, and other large, heavy loads demand compact and robust engineering solutions that can fit into tight spaces and tolerate extreme ambient conditions. Add to this the precise positioning and motion control of loads with variable centers of gravity, and the task seems daunting.

Three of four servothrusters are visible at each corner of the drilling mud tank.

Scoda srl, the systems division of Atos group in Angera, Italy, deals with demands like these on a regular basis. One of its recent projects is a compact and easy-to-install jacking system consisting of four digital servothrusters that are controlled and synchronized through a PLC control unit integrated into a rugged AISI 316 stainless steel control console with IP-65 protection.

Each electrohydraulic servo-thruster consists of an electrohydraulic servocylinder conforming to ISO 6022 specifications with a built-in load cell. It is manufactured with high strength materials suitable for low temperature, low friction PTFE seals, and specific guide rings to withstand high radial forces. An integral magnetostrictive transducer provides position feedback and a load cell monitors force.

Each servothruster contains its own HPU and control valve manifold. The main control housed within a 316L stainless steel enclosure synchronizes position of each thruster to within ±0.1% of stroke.

Each thruster also contains its own hydraulic power unit meeting Europe’s Machine Directive 2006/42/CE. Each HPU is designed for operation in low temperatures. The HPU’s 316L stainless steel reservoir is sealed from the environment and has a cooling loop to accommodate high ambient temperatures.

A hydraulic integrated circuit manifold for each thruster contains Atos servoproportional valves with onboard digital electronics for alternative closed-loop control of position, speed, and force. TÜV-certified safety valves have built-in inductive proximity sensors and pressure relief valves to meet 2006/42/CE for load compensation, and secure the system for emergency shutdown.

Servoproportional valves with onboard digital electronics provide alternated closed-loop control of position, speed and force.

Control firmware developed by Scoda processes the feedback signals from the position transducers and load cells to synchronize the position of the four servocylinders to within ±0.1% of their working stroke. A center-of-mass damping function compensates for oscillations during the load motion.

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