DAC February 2022

36 n SENSORS AND ENCODERS February 2022 www.drivesncontrols.com Sensors help reveal hidden secrets of art masterpieces A rt galleries and museums need to check the health of their oil paintings to ensure that they are in good condition and can remain on show for years to come. Digitising these artworks is a key tool and, during the 1990s, a European-funded project called Vasari was set up to do just that. It relied on the technologies of the time such as cameras with limited resolution and incremental encoders for positioning. Since then, these technologies have moved on considerably. The Basingstoke- based motion control specialist LG Motion took up the challenge to come up with a more effective system for scanning artworks. The company’s managing director, Gary Livingstone, had been involved in the earlier project when he was with another company. One way of improving the performance of the new scanners, compared to the earlier systems, was to use absolute encoders that would maximise the advances in camera technology since the original project. LG’s system combines the encoders with high- specification motion control equipment, and the latest imaging equipment and software. The system uses spectrometry to peek behind the surfaces of paintings to identify the artist’s original workings – or perhaps to uncover a hidden masterpiece. One gallery using the technology discovered a hidden Michelangelo. The LG system brings together the necessary technologies in a modular frame and can create high-resolution images of paintings, revealing their finest details and creating records for archivists and restorers. The scans can uncover any developing issues caused by age or transportation. The system is already being used by institutions including the National Gallery in London, which has two systems, the Rijksmuseum in Amsterdam, the National Gallery of Art in the US, which has three systems, and the Kimbell Art Museum in Texas. Each institution is using the scanners in different ways, not just to manage and catalogue their collections, but also to commercialise the high-quality digital images in the form of posters and postcards. To ensure that the scanning process produces the best images, the artwork is moved in front of the camera. Although, given the weight and value of these works, this might seem an odd way of doing things, it guarantees consistency of lighting. The combination of high-specification motion control equipment and bespoke software provides precise automated capture and assembly of the images. The system typically takes a scan every 0.1mm to create a series of 100mm 2 “tiles” across the artwork. These are then “stitched” together using an intelligent algorithm to create a high-resolution image which can capture the artwork in the visible, infrared, UV or X-ray spectra. One-to-one replication avoids digital distortion, while tiling allows the largest works to be scanned. Within minutes, huge areas of a masterpiece can be captured and preserved digitally for inspection and cataloguing. This process often reveals unseen features, and allows conservationists and historians to protect and document their artworks by reducing future handling and disturbance. The system also outputs metadata which can be stored for faster and more accessible data extraction in the future. To achieve the required precision, LG is using Heidenhain RSF MC15 scale tape encoders mounted on stainless steel backings. The scanning heads are connected via an EnDat bidirectional interface to ensure fast data transfer with high reliability. These encoders can measure down to 0.05μm (50nm), with every step beingmonitored in a closed-loop system to ensure smooth, precise movements. “With each art-scanning system capable of scanning up to 6m by 4m in size, we needed accuracy and reliability, along with the ability to re-visit specific areas of an artwork if required,” explains Gary Livingstone.“The RSF MC15 absolute encoders give us this capability.” While developed as a tool for recording and analysing works of art, the scanning technology could be deployed in horizontal versions for other applications, such as cataloguing entomology collections or scanning smaller works of art. n A UK company is helping museums and galleries around the world to scan and catalogue their works of art. The multi-spectrum scanning process – which can reveal previously hidden aspects of the art – relies on incremental encoders to deliver the necessary precision. The scanning system can reveal hidden details of artworks. The movement of the imaging system is controlled in steps as small as 50nm using scale tape encoders (shown enlarged at the bottom, right)