Springs are all around us, keeping mechanical parts moving smoothly in all sorts of applications, from tension springs in drawers to compression springs in push-button light switches, the types found in stairwells. The average car contains around 8000 springs. So uncompromising quality and reliability are crucial in spring production. In partnership with the Steinbeis Transfer Center for Quality Assurance and Image Processing in Ilmenau, engineers from Wafios AG in Reutlingen have developed an innovative, user-friendly image processing system to ensure one hundred per cent quality control in spring production. Both project partners were rewarded with the 2008 Löhn Award.
Wafios specializes in wire processing machines. Innovative image processing systems which intervene in a machine’s control loop during production help keep error rates low. The Steinbeis Transfer Center builds small batches of cameras for custom applications as diverse as mains power supplies and sensor boards, sometimes complete with special casings for use on heavy machinery. The cameras are used to monitor processes.
So how does this work? A special camera is mounted on a spring winding machine. Images from the camera are used by the image processing system to inspect the geometry – such as the length or diameter – of up to 600 springs per minute. Each spring is photographed just before it is cut. As the spring falls, the special software has around 50 milliseconds to measure its visual properties and compare them with control limits and tolerances.
For instance: if a spring is too long, the software interrupts the process and automatically corrects the spring length, ensuring the next spring has the correct length. The faulty spring is ejected through a gate.
Although highly specialized, the system is easy to use. The operator simply presses the analysis button to start a new inspection plan for each new spring geometry – without having to understand the image processing system.
Integrating hardware and software into Wafios machinery was another challenge. Production moves at a fast rate, placing high demands on image processing. Disruptions such as vibrations, spring reverberation, wear, dirt, and even breakage also need to be taken into account.