Laser profile sensors used on innovative robotic weld inspection system
A non-contact laser profile displacement sensor from Micro-Epsilon is playing a pivotal role in a new groundbreaking automatic inspection system specifically designed to inspect thin section steels and thin gauge welds on ships and other marine vessels.
The inspection system, X-Scan, is a novel automatic inspection system that inspects the weld and classifies it by means of laser, ultrasound and electromagnetic methods. The system uses a crawling robot that deploys remote volumetric surface and visual inspection to verify the integrity of welds on the hull plates of ships during manufacture and in the servicing of shipping vessels. Micro-Epsilon's scanCONTROL LLT 2700-100 laser profile sensor is an integral part of the X-Scan system, providing the laser profile data required to verify and analyse the quality of thin steel and welds.
In the marine industry, structural failure is a major cause of the loss of ships, tankers and other marine vessels, resulting in pollution of oceans, seas and coastal waters, loss of life or long delays while repairs are carried out. Each year, dozens of ships sink - many as a result of leaking structures due to corrosion and poor weld quality.
Most of the inspection techniques used today have proven to be disruptive to the manufacturing process and are far from cost effective. New generations of ships are being built from thinner section steels in order to lower the cost of build and ship operations and so 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.
By combining ultrasonic phased array, electromagnetic ACFM (Alternating Current Field Measurement) and laser optical methods, X-Scan enables the detection and sizing of surface breaking and sub-surface flaws or defects. By developing laser-based tracking and a self-controlled robot, X-Scan enables automatic inspection following the weld run.
Alvin Chong, X-Scan Project Leader and Research Fellow at the Brunel Innovation Centre comments: "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 successfully 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 accurately follow the centre of the weld line 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," he adds.
X-Scan is a collaborative project between EU companies and research organisations. Their objective is 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 (FP7/2007-2013) under grant agreement no. 283284. The X-Scan Consortium comprises seven collaborators from four member states, including three SMEs, each representing a different EU country. The seven members are TWI Ltd (UK), Brunel University (UK), Innora Robotics and Automation Ltd (Greece), Vermon S A (France), Spectrumlabs (Greece), Technitest Ingenieros SL (Spain) and Lloyd's Register EMEA (UK). For the X-Scan project, Innora was the RTD provider (designer and manufacturer of the robot). For more information, go to http://www.x-scan.eu/
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, for example, and by adding extra inspection techniques.
X-Scan is suitable for new and old builds. The device enables the volumetric inspection of thin gauge welds and consequently the detection of surface breaking and sub-surface flaws such as porosity, lack of weld penetration, lack of fusion, cracking, etc.
By combining three inspection techniques into 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. Even in its current form, the system provides defect imaging and analysis at much greater speed and convenience than currently exists.
Laser profile inspection
Micro-Epsilon's scanCONTROL 2700 non-contact laser profile displacement sensor provides an integrated controller in the sensing head. Despite this, the sensor is still incredibly compact. The user requires no other components to evaluate the measurement data and the unit is also easy 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 and clearance; weld seam inspection; detection of beads (bulges or bumps) of adhesive; door edge detection; robot guidance and positioning; groove width and depth measurement.
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 up to 64,000 measuring points per second.
The scanCONTROL 2700 series uses the laser line triangulation measurement principle. The sensor has an integrated, highly sensitive CMOS array, which enables measurements of almost any difficult surface such as shiny or reflective surface, 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 coordinate 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 sensor uses an innovative CMOS array with a real time, high-speed electronic shutter, which captures the entire profile and processes the information instantaneously.
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