Fine Alignment of Thermographic Images for Robotic Inspection of Parts with Complex Geometries

Abstract

Increasing the efficiency of the quality control phase in industrial production lines through automation is a rapidly growing trend. In non-destructive testing, active thermography techniques are known for their suitability to allow rapid non-contact and full-field inspections. The robotic manipulation of the thermographic instrumentation enables the possibility of performing inspections of large components with complex geometries by collecting multiple thermographic images from optimal positions. The robotisation of the thermographic inspection is highly desirable to improve assessment speed and repeatability without compromising inspection accuracy. Although integrating a robotic setup for thermographic data capture is not challenging, the application of robotic thermography has not grown significantly to date due to the absence of a suitable approach for merging multiple thermographic images into a single presentation. Indeed, such an approach must guarantee accurate alignment and consistent pixel blending, which is crucial to facilitate defect detection and sizing. In this work, an innovative inspection platform was conceptualised and implemented, consisting of a pulsed thermography setup, a six-axis robotic manipulator and an algorithm for image alignment, correction and blending. The performance of the inspection platform is tested on a convex-shaped specimen with artificial defects, which highlights the potential of the new combined approach. This work bridges a technology gap, making thermographic inspections more deployable in industrial environments. The proposed fine image alignment approach can find applicability beyond thermographic non-destructive testing.

Robotization of the IR-Thermographic technique – impact on the visualisation quality and considerations on the data workflow

“…Typically, an expert adjusts the IR camera acquisition parameters and the experimental setup geometry to define these critical settings. After defining the input parameters, they are inserted into the offline programming user interface (2) created in MATLAB (refer to [17] for more information). The graphical user interface enables the creation of a raster inspection tool path for the sample, based on the user-specified maximum spacing between consecutive image acquisition poses and offset from the sample edges.…”

“…The acquired data, which consists of thermographic temperature map evolutions, is processed individually using a PPT algorithm or any alternative method. Subsequently, the data is aligned and corrected in step 5A using the Fine Pixel-based Alignment Method (FiPAM), the details of which can be found in [17]. Alternatively, the acquired temperature map evolutions for each pose can be merged with the FiPAM and then post-processed with a thermographic algorithm such as the PPT.…”

“…This issue leads to a clear misalignment of thermographic images in robotic thermographic inspections. In a practical solution presented in [17], each picture's plotting position and potential aberrations are corrected to provide a misalignment-free full-field view of the sample being examined. This method is suitable when the rough position of the camera (the shooting pose of each image) is known.…”

“…Due to incorrect alignment and blending, the composite thermography image may contain erroneous artifacts, which could result in a false-positive defect diagnosis. The authors of [17] tackled the problems of thermographic picture fusion by creating a process for automatically transforming, aligning, and blending thermographic acquisition data. This work demonstrates the improvements that can be achieved with the new robotized IR-thermographic inspection platform.…”

Robotic Non-Destructive Testing

“…That is the case with the two remaining papers of this Special Issue. Mineo et al [ 10 ] introduce an image alignment method to facilitate the visualisation and analysis of robotic thermographic inspections of parts with complex geometries. This work bridges a technology gap, making thermographic inspections more deployable in industrial environments.…”