Robotic Ultrasonic Inspection: ABB Robots in NDT Cells

Carbon fibre parts can hide flaws that nobody sees from the outside, such as delaminations between layers, so aircraft makers send sound into them and listen for the echoes. For decades that meant a technician sliding a probe across the part by hand. Robotic ultrasonic inspection puts the probe on a robot arm instead, often behind a jet of water, and records every point it scans. This post traces the method from Floyd Firestone's 1940 patent to robot cells for composites. It also covers a French project, reported this month, that wants to automate checks on thick naval composites, and where ABB robots could fit in.

Aviation Structural Mechanic 1st Class Charles Martens performs an ultrasonic inspection on the horizontal stabilizer of an F/A-18C Hornet aboard USS Carl Vinson, 2011. Photo: U.S. Navy / Rosa A. Arzola via Wikimedia Commons (public domain)

How ultrasonic testing went from hand probes to robot arms

The first attempts to find flaws inside solid material with ultrasound came in the 1930s. Floyd Firestone of the University of Michigan applied for a patent on a practical ultrasonic testing method on 27 May 1940, and US Patent 2,280,226 was granted on 21 April 1942. His principle was to send high frequency vibrations into the part and time the echoes, which would reveal something like a hole or crack inside a casting. Sperry Products brought the first practical commercial flaw detector, the Supersonic Reflectoscope, to market in 1945. Those early instruments ran on vacuum tubes, were large and heavy, and needed mains power.

A CRT based ultrasonic flaw detector showing echo readings on its screen. Photo: Abhijit Nandi / Wikimedia Commons (CC BY-SA 3.0)

Solid-state electronics in the 1960s shrank flaw detectors into battery-powered boxes a technician could carry into the field. In 1984 Panametrics, whose business is now part of Evident, introduced the EPOCH 2002, the first field portable all-digital flaw detector. The probe still has to be coupled to the part, usually through a liquid couplant. A patent filed in 1962 by James F. McNulty of Automation Industries in El Segundo, California describes the two classic ways: immerse the crystal and the specimen in liquid, or press the crystal on through a thin film of liquid such as oil. Both survive today as immersion tanks and hand-held contact probes.

An Olympus EPOCH 600 portable ultrasonic flaw detector at Fassberg in 2019. Photo: Boevaya mashina / Wikimedia Commons (CC BY-SA 4.0)

For flat plates, cylinders and cones, factories built bridge and gantry scanners. A 2014 paper from the University of Strathclyde and TWI says these have long given the most stable positioning, but each is usually built for parts of one shape and size. Curved composite parts are harder: parts designed to be identical can deviate from CAD and spring back differently out of the mould, and scanning them by hand is slow. TWI's IntACom project in Wales, presented at an aerospace NDT symposium in 2013, aimed to cut inspection time for complex composite parts by a factor of four with a cell of two six-axis robot arms. Their probes sat in water jet nozzles, so a column of water carried the sound to the part.

PaR Systems' robotic inspection cell in Hangar N at Cape Canaveral during a 2014 open house; this gantry carries an automated X-ray system. Photo: NASA / Cory Huston (public domain)

Robot cells and a French naval project in 2026

On 14 October, JEC Composites reported on ICOME 2 in France. IRT Jules Verne, Naval Group, Chantiers de l'Atlantique and SolidSail Mast Factory have €1.152 million over two years to automate the testing of large, thick naval composite structures, from data acquisition to analysis, so that inspection stops slowing production. An earlier 18-month study compared X-ray radiography, conventional ultrasonics and air-coupled ultrasonics on flat specimens with built-in defects, for structures 10 to 60 mm thick. On one monolithic panel, conventional ultrasonics found nearly all the defects, while air-coupled ultrasonics overestimated their area about twofold. Conventional ultrasonics missed defects at foam-to-foam interfaces in a sandwich specimen, and X-ray struggled with planar defects.

An Olympus OmniScan MX2 phased array ultrasonic flaw detector at Fassberg air base, 2019. Photo: Boevaya mashina / Wikimedia Commons (CC BY-SA 4.0)

The partners now want a robotised phased-array ultrasonic system, which steers the beam electronically with many small elements, and they plan to swap their single-element probe for a multi-element one. Such robot cells are already on the market. Spain's Tecnatom says its Taurus family of robot-based systems has been used for automated NDT for more than 15 years, with more than 50 references in 16 countries. Taurus can work with water jet, local immersion, total immersion and air-coupled ultrasonics, as well as eddy current, thermography and digital X-ray. Tecnatom says it supplies Airbus, Boeing, Embraer, Lockheed Martin and COMAC, and for very large parts it sells PEGASUS, a rigid Cartesian gantry.

PaR Systems operations engineer Lu Bell conducts a phased array ultrasonic inspection in Hangar N at Cape Canaveral, 2013. Photo: NASA / Dimitri Gerondidakis (public domain)

We could not find a published ultrasonic inspection cell built on ABB robots, so this section only sets ABB's own specifications against what the job needs. The 2014 TWI paper lists what an NDT robot needs: precise mechanics, joints that can be calibrated accurately, and position data streamed at up to 500 Hz. ABB's GoFa cobot with the Ultra Accuracy option has a path accuracy of 0.03 mm, and ABB names composite layers in aerospace manufacturing and precision quality checks in metrology among its uses. For wet cells, ABB offers the IRB 1300 in IP67 and Foundry Plus 2 versions, which seal all electrical components against liquids and dust.

An ABB GoFa cobot with a pointed probe tool over a test table, from ABB's 2024 Ultra Accuracy launch photos. Photo: ABB

What robotic ultrasonic inspection still has to solve

ICOME 2 has a second objective besides automating data acquisition on parts whose geometry and surface condition vary: software that analyses the data and maps defects, so inspectors can focus on the areas needing a closer look and every result stays traceable. SolidSail Mast Factory builds composite masts for wind-assisted ship propulsion, so some of the parts are big. For an arm scanning parts that size, ABB's IRB 7710 and IRB 7720 would be candidates. They carry up to 620 kg and, with the OmniCore controller, hold path accuracy down to 0.6 mm at up to 1600 mm/s, and ABB pitches them for high accuracy contact work such as machining.

Two engineers program an ABB IRB 7710 or IRB 7720 large robot with a FlexPendant. Photo: ABB

The TWI and Strathclyde authors also found problems with path planning software. Off-line programming tools written for machining produce paths that often need fixing before they suit NDT. Many could not keep two robots fully synchronised for through-transmission testing, where one robot holds the transmitter and another holds the receiver on the far side of the part. Changing a path to re-inspect a suspect area meant downloading a whole new path to the robot controller, so the authors wrote their own MATLAB toolbox to drive the robot from an outside computer. ABB says GoFa programs written offline in RobotStudio with Ultra Accuracy match reality 99 percent, which would save touch-ups if someone built a cell like this.

Engineers review a 3D robot cell layout on screen, with a FlexPendant on the desk and an ABB IRB 7710 or IRB 7720 behind them. Photo: ABB

Ultrasonic inspection is qualified work. Testia, which sells ultrasonic testing services and NDT training, cites the EN 4179 and ISO 9712 qualification standards for its UT inspection work. Before scanning, technicians calibrate their instruments on reference standards, as US Air Force inspectors do before checking an F-16C for delamination. In a robot cell, that skill moves into path planning, probe setup and reading the scans. Cost is the other brake: the IntACom authors noted that composite parts are still expensive to make, partly because of raw materials and partly because of labour-intensive methods. Our post on carbon fibre composites covers the manufacturing side.

US Air Force Senior Airman Charles Cross applies water based couplant to a reference standard to calibrate an ultrasonic unit for delamination checks, 2025. Photo: U.S. Air Force / Erin Dunkleberger via Wikimedia Commons (public domain)

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