Ship builders sight automated inspection

Written by: Paul Fanning | Published:

A non-contact laser profile displacement sensor is playing a pivotal role in the development of an automatic inspection system to assess the surface and weld quality of ships structures.

The inspection system, X-Scan, is a novel automatic inspection system that inspects the surface and welds of ship hulls by combining three sensing techniques; laser, ultrasound and electromagnetic methods. The system has also been integrated into a crawling robot that is able provide automated inspection during the manufacture and servicing of ships and vessels.

Micro-Epsilon's scanCONTROL LLT 2700-100 laser profile sensor has become a crucial part of the X-Scan system, providing the control and performance required to verify and analyse the quality of steel used in ship hulls and the corresponding weld integrity at critical joins.

Structural failures
In the marine industry, structural failure is a major cause of ship, tanker and other marine vessel loss. Each year, dozens of ships sink, many as a result of leaking structures due to corrosion and poor weld quality. The results can be devastating and can result in long delays while repairs are carried out, pollution of waterways and, worst of all, loss of life.

Most of the inspection techniques used today are disruptive to the manufacturing process and are far from cost effective. And with the next generation of ships being built from thinner sections of steel in order to lower the cost of build and ship operations, typical assessment methods are not as effective as they were for thicker sections. Therefore, there is a genuine need for a more reliable, faster, cost effective and safer inspection technique.

This led to X-Scan being applied. The system uses a combination of an ultrasonic phased array, electromagnetic Alternating Current Field Measurement (ACFM) technique and an optical laser, to enable the detection and sizing of surface and sub-surface flaws and defects.

By developing the system alongside a laser-based tracking and self-controlled robot, X-Scan now enables automatic inspection of welds following a weld run.

Alvin Chong, X-Scan project leader and a research fellow at the Brunel Innovation Centre, says: "The scanCONTROL 2700-100 has been very reliable and is a critical part of the X-Scan system. First, it provides very high-resolution measurements that we require in order to detect small weld defects, which may measure just a few millimetres in diameter, or even down to a few microns if the defect is a weld crack or notch.

"Second, the scanCONTROL sensor outputs the profile measurement data to the X-Scan's robot control system for guidance purposes. This is very important too, as we need the robot to follow the centre of the weld line accurately at all times. The robot cannot be allowed to deviate from this centre line, otherwise the ultrasonic and ACFM inspection systems will not be effective."

X-Scan is a collaborative project between EU companies and research organisations. The objective has been to develop and produce novel inspection techniques and devices specifically for the inspection of thin steel section welds for the shipping industry.

The research leading to these results has received funding from the European Union's Seventh Framework Programme managed by REA-Research Executive Agency.

The X-Scan Consortium comprises seven collaborators from four member states, including three SMEs, each representing a different EU country. The members include TWI (UK), Brunel University (UK), Innora Robotics and Automation (Greece), Vermon (France), Spectrumlabs (Greece), Technitest Ingenieros (Spain) and Lloyd's Register EMEA (UK). For the X-Scan project, Innora was the research technology development provider and led the design and manufacture of the robot.

At present, X-Scan can be used for automatic inspection of ships in dry dock. However, the system could be expanded and further developed to include a 'marinised' robot, and by adding extra inspection techniques.

X-Scan is suitable for both new and old ships and vessels and the device enables the detection of flaws in material porosity, lack of weld penetration, lack of fusion and also cracking.
Combining three inspection techniques in a single automatic inspection system saves considerable time and money. In addition, the system eliminates both the need for working at height, and the need for high-risk radiography equipment.

Although the system is a prototype, the developers are working on making it more compact and user-friendly. However, even in its current form the system provides defect imaging and analysis at much greater speed and convenience than currently exists.

The scanCONTROL LLT 2700-100 used on the X-Scan system has a measuring range of 100mm and is supplied with a protective cover plate attached to the base of the sensor (with a protective window) through which the laser beam passes. The sensor provides a profile frequency of 100Hz and can measure up to 64,000 points per second.

The scanCONTROL 2700 series uses the laser line triangulation measurement principle. The sensor has an integrated, highly-sensitive Complementary Metal-oxide Semiconductor (CMOS) array, which enables measurements of almost any difficult surface, including those that are shiny or reflective, independent of the reflection from the target. This means excellent accuracy, resolution and reliability are achieved, even at high measurement speeds.

A line optical system projects a laser line onto the surface of the object being measured. The back-scattered light from the laser line is registered on a CMOS matrix by a high-quality optical system.

Along with distance information (z-axis), the controller calculates the true position along the laser line (x-axis) from the camera image and outputs both values in the sensor's 2D co-ordinate system. A moving target or traversing sensor generates a 3D representation of the object being measured.

The system itself comprises a sensor and integrated controller, which calculates the dimensions of the weld profile.

For the X-Scan system, the laser profile scanner operates in a scanning mode, where the sensor works in combination with the robot/motion control device. The CMOS array uses a real time, high-speed electronic shutter, which captures the entire profile and processes the information instantaneously.

Inspection for wider application
Micro-Epsilon's scanCONTROL 2700 non-contact laser profile displacement sensor provides an integrated controller in the sensing head, that although compact, has proven to be incredibly effective.

Users require no other components to evaluate measurement data and the unit is also straight forward to set up, configure and adapt for different applications.

The compact design and integrated controller makes the unit ideal for industrial automation tasks and machine building applications, where space is often restricted.

Typical uses include the measurement of angles, channels, gaps, edges, clearances, weld seams, adhesive quality inspection, door edge detection, robot guidance and positioning, groove width and depth measurements.

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