Mobility creates safety
For maintenance of a ship, the hull must be lifted out of the water up to the height of the dock. It is secured on a movable platform using wedges and winches and is then lifted to the level of the wharf.
The control over the process of bringing the platform closer to the keel is a delicate operation during which the transport operator should be able to move as freely as possible. To achieve this, Barillec chose a system based on the Siemens Simatic S7-1200 controller, KTP400 Basic Panel and 277 IWLAN mobile panel. The lifting system is operated using a mobile handheld device which gives the operator the required freedom of movement for controlling the system from right next to the ship while fulfilling the requirements for maximum mobility and safety.
The mobile panel communicates with a higher level Siemens Simatic S7-300F controller via IWLAN. Because of the radio connection, the control system runs in one of the control system CPUs and in the safety mode reserved for the mobile panel. The data is carried using Industrial Ethernet/Profinet/Profisafe.
2000 tons controlled using a mobile panel
The hydraulic ship lifting system can be used for ships of up to 90 m in length, 17 m in width, and 2000 tons in weight. It consists of a 76X17 meter carrier platform supported by six parallel iron girders. Each girder is driven on the ends by two hydraulic units. Each has its own control cabinet with a micro PLC Simatic S7-1200 and a Simatic HMI KTP400 Basic Panel. This allows each unit to be operated manually and independently. The local interface also allows latch mechanisms to be released or winches to be synchronised in order to prepare for an operating sequence.
Keeping big machines under control
Each controller of the hydraulic units receives signals from several sensors via cable connections. These include analog laser position encoders on the two winches; latch position encoders on the lifting system, which involves the alternating use of two winches; and pressure sensors for measurement of the hydraulic pressure of each winch. The height of each iron girder for the support of the platform is constantly measured on the level of the two hydraulic units using a cable extension transducer that is directly connected with the Profinet network. The distance between the two iron girders may differ by at most 2,5 cm if the transport operator has not decided in favour of inclined transportation of the platform. With the exception of the cable extension transducer, which is directly connected via Profinet, the S7-1200 controller assigns the local sensors using a cable connection.
The radio network covers the entire work area using a Scalance W antenna mounted on a 15 m mast. To expand the IWLAN radio zone, this interface was intentionally slowed from 54 Mbit/s to 24 Mbit/s due to the limited throughput rate of the application.
All 12 of the hydraulic units installed around the lifting system have an independent transponder that is not connected to the control system network. This sends an RFID signal in a conical area with a range of 8 m. When starting the control system session with a mobile controller, transport operators must identify themselves with an RFID signal in one of the 13 radio ranges in order to ensure secure execution using IWLAN.
For more information contact Keshin Govender, Siemens, +27 (0)11 652 2412, [email protected], www.siemens.co.za
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