A new, fully automated, fine art infrared scanning system shows how a scientific tool with micron positioning accuracy can be created from standard industrial automation components. The system is the brainchild of motion control specialist, SmartDrive®. Working with BishopWisecarver’s exclusive European partner, HepcoMotion® has optimised the process of infrared scanning, greatly extending the scope of the technology.
The system control and specifically developed image stitching software enables distortion-free digital photographs of large works to be taken for further study and record. For the art conservation world this system represents a significant imaging breakthrough.
The SmartDrive system is called SatScan and the technology mimics that used in mapping systems with the optics ‘flying’ over or across the subject. Small images are taken from a perpendicular position and then stitched. SatScan works in a similar way by moving digital and infrared camera heads incrementally around artwork using encoder technology to achieve precision positioning.
“We know the position of the carriage to within ±1 micron,” explains the system’s designer, Dennis Murphy, Managing Director of SmartDrive. “We’re achieving this from automation components with industrial tolerances of 100 — 200 microns. In scientific terms we are also using relatively low resolution, off-the-shelf cameras. But by acquiring a small field of view — maybe just an inch or two square — and holding it perpendicular to the painting we can take images that are completely distortion free.”
SmartDrive scanner application.
Each image has uniform scale throughout so valid measurements can be taken anywhere on the complete constructed image. The scale makes individual tiles easier to match and automatically join in software. The user can select the digital quality by adjusting the camera lens. In the fully zoomed mode the resolution of the system can create images at over one thousand DPI over a large area. Single exposure digital cameras in contrast suffer from parallax issues creating distortion on the resultant image.
The first large scale SatScan was installed at the Hamilton Kerr Institute near Cambridge, a center of excellence for conservation services that is world renowned for its work on tempura easel paintings. It provided the expert knowledge needed for the art version of the SatScan development and is now using the system on a daily basis. Infrared imaging is just one of a range of tools used by the Institute’s conservators and is primarily used to see any under-drawings on the canvas or to examine previous re-touching. For example it will show if an egg tempura painting has been retouched with oils. The information it provides guides the restoration process and also enriches the history of the work. It can also help with authentication by revealing details that may show consistency with a certain artist.
The painting in the photograph is a portrait of Sir William Fitzwilliam, Earl of Southampton, courtesy of the Fitzwilliam Museum in Cambridge, UK. The visible-light picture (colour image) shows Sir William stood overlooking what appears to be a river scene, but when imaged in infrared (black & white image) it becomes clear the painting is not in its original state. In fact it would appear that most of the background has been repainted over the top of what appears to be a traditional archway. Also brought into sharper focus is the somewhat faded tile pattern on the floor.
Historically infrared scanning at the Institute has been a time consuming and costly exercise. Even the latest generation equipment had significant pitfalls. It involved manually moving a Vidicon analogue TV camera into position, capturing a small infrared image and then uploading it using manual stitching software. “Imaging even a small painting was a day’s work using this method,” explains Chris Titmus imaging consultant at Hamilton Kerr. “And even then the complete image wasn’t clean, as stitching was by eye and the edges of most images were blurred.”
A further problem with the old system was the danger of image burning onto the camera tube, necessitating regular replacement and adding to the process cost. “Just having the camera switched on would cost in the region of £30 ($50USD) per hour,” Chris adds.
The new SatScan system is completely automatic. “Once the work is in position we press a button, the image capture process begins and the software stitches it all together,” Chris continues. “In an hour or so we can achieve what used to require a whole day. Indeed the system is also allowing us to take on work we wouldn’t have considered before. In the past it would only have been viable to look at selected areas of some paintings whereas now we can examine the whole thing.”
Another major benefit is the size of the painting or alter piece that can be scanned by the system. The Hamilton Kerr Institute recently used SatScan to image a painted oak panel that was two inches thick and seven feet tall.
The source of all the mechanical elements for the system was HepcoMotion, who designed the system mechanics on 3D CAD. It then built and thoroughly tested the system at its factory in Tiverton, Devon.
Dennis Murphy explains, “Whilst the system load is small, about 20kg for lights and the camera, we needed a large frame to accommodate large works of art. The HKI SatScan is designed to scan areas of 4.5m x 3.5m. This makes for a large installation and its metalwork — mostly aluminum extrusion — weighs over 400 kg. The HepcoMotion technical team designed a strong lightweight frame that was capable of handling the inertia of such a moving load yet maintains rigidity so that “wobble” is minimized and the micron positioning of the cameras that is so crucial is not compromised. Furthermore we had to ensure everything was sufficiently robust, especially given the value of many of the subjects involved.”
The SBD system was selected for carrying the camera heads in both the horizontal and vertical axes. This sealed belt drive is designed for high loads and demanding duty cycles and provides an exceptionally clean linear solution. Each of the guideways is fitted with a scale and optical read head to provide positioning feedback. The high strength, aluminum SBD units are mounted onto the SatScan gantry that is made from the MCS aluminum machine construction system. A small GV3 guideway was chosen to provide fine adjustment of camera carriage in the Z axis. Screwjacks are responsible for adjusting the incline angle of the 4.5m x 3.5m frame to accord with the painting.
SmartDrive took careful consideration of load/motor inertia matching and the use of precision SmartDrive Taranis® technology digital drives, the combination of which produces smooth quiet and accurate motion.
In addition, the Windows compatible user interface and stitching technology took SmartDrive nearly three and half years to develop. The patent applied for advanced algorithms ensure the stitching is accurate even when there is little or no data in the image to automatically work on.
SmartDrive is working on three versions of their automated system. In addition to the Art system developed for Hamilton Kerr for larger works it has developed another for examining museum artifacts in standard 500mm square trays, typically archaeological collections, entomology or botanic specimens, also developed is a microscope slide scanner version for imaging objects whose size is measured in microns rather than metres.
The Hamilton Kerr rig is also undergoing further development. The inclusion of a laser to provide dimensioning and profile data is currently in progress. Chris Titmus adds, “We have already tested it out on an alter piece from Westminster Abbey. During the course of restoration we needed to assess if the screen had grown or shrunk through changes in humidity. If the screen contracts too much, paint will flake off and conversely over-expansion will put pressure on the joints. The laser simply adds even more value by providing a micron accurate “Z” element to the high resolution X-Y data SatScan already acquires. We can easily view this three dimensional data in many CAD packages, the possibilities are endless”
Rupert Featherstone, Director of the Institute adds “The SatScan system has proven itself to be a remarkable breakthrough for art restoration and preservation, the development has provided the Hamilton Kerr Institute with leading edge technology that will ensure we continue to lead the field in conserving the nation’s heritage.”
Bishop-Wisecarver Corporation: Manufacturer of the original DualVee® guide wheel and industry leader in guided motion technology, is the exclusive North and Central American partner and distributor for HepcoMotion products since 1984.
Hamilton Kerr Institute
.: Design World :.
Filed Under: Material handling • converting, Drives (servo) + amplifiers, Electronics • electrical, Encoders • optical, Linear motion • slides, Motion control • motor controls, Stages • gantries, Vision • machine vision • cameras + lenses • frame grabbers • optical filters