WZL, RWTH’s Laboratory for Machine Tools and Production Engineering, develops new and optimizes existing solutions through a practice-oriented research and development process for production industries’ clients, and helps manufacturers improve their competitiveness.
Robots are
flexible production entities for handling, mounting, welding or other production processes that can be effectively deployed in production systems that manufacture small series first-time-right and easily switch from one product type to another. Still, their potential is left largely unexploited because too much time is needed to set up robot processes, program robots movement, rig it or align process fixtures. Optical metrology in combination with industrial robots is a key enabler to achieve this level of flexibility at an economic cost.
Scientists at WZL confirm that the affordable combination of off-the-shelf robot and metrology technology yields better economics than expensive specialty equipment or manual work. Invisible iGPS laser beams continuously track the locations of the robot’s tool center point, and feed back the filtered data in closed loop to improve absolute robot precision. WZL masters this unique concept to improve the manufacturing quality of numerous dynamic industrial applications, including handling, assembly, burnishing, deburring, welding and pleating. Björn Damm, team leader of the imaging processes and coordinate metrology groups, remarks that: “metrology is not a necessary evil. In particular, optical metrology technologies will be the ears and eyes of versatile and self-optimizing production systems of the future!”
“The combination of industrial robot workhorses with innovative large-scale metrology offers distinct advantages compared to equipment specifically designed for a particular manufacturing task,” says J. Jans, Nikon Metrology Executive V.P. Marketing. “Today too many manufacturing tasks are performed by hand, or when automated the task is performed by expensive dedicatedly designed precision equipment.”
Nikon Metrology already has an impressive track record in metrology-assisted production. In a project aimed at stretching the accuracy limits of industrial robots, Airbus applied Nikon Metrology metrology to improve the precision of robotic drilling and riveting at CAD specified wing locations. As a result, the aerospace giant’s wing drilling and riveting cell ha become capable of reaching an accuracy level that is 10 times better than previously.
Nikon Metrology iGPS stirs up manufacturing communities by turning an entire manufacturing cell into a single metrology enabled environment. iGPS robot sensors capture their individual elevation and azimuth angles with respect to multiple iGPS transmitters that a
re within line of sight, based on the timing of the arriving invisible coded laser pulses. This is iGPS’ unique approach: to continuously track robot tool center point positions, and, possibly, also the part that is clamped by the robot(s). By returning the acquired metrology data to the robots using a closed feedback loop, robot positioning improves drastically. iGPS plays an important role in this innovative metrology-adjusted process, which nearly eliminates the influence of robot warm-up, drift and backlash. Employing this approach, Nikon Metrology therby transforms industrial robots into highly accurate and efficient in-line manufacturing stations.
Dynamic manufacturing
“Dynamic applications are much more challenging because robots need continuous adjustment when manufacturing tasks are actually taking place,” says A. Schönberg, responsible research assistant for the robot cell and member of the imaging processes group. When two robot-clamped parts are being welded, for example, the positioning of the parts ideally requires real-time adjustment, not just at the start and end point of a seam weld. WZL is heavily involved in optimizing this critical real-time adjustment process that determines the precision of dynamic manufacturing procedures. An approach being investingated employs Kalman filtering.
Originally used to allow the spaceship of the Apollo program to land on the moon, Kalman filtering will guide dynamic robot movement with higher precision. From a mathematical point of view, Kalman is the optimum filter type for vector-based Gauss-Markov-Processes, as no other linear method exists that reaches smaller errors between the actual and predicted state of a system.
R. Schmitt, Professor of the Chair of Production Metrology and Quality Management, concludes: “Top-notch iGPS metrology, combined with WZL specialist know-how, will lead to flexible and affordable robot technology that may fit numerous manufacturing applications. This very interesting and promising topic will be targeted on a highly scientific level in an upcoming EU-project.”l
Candidate partners are welcome to contact WZL,
