Automated vision system delivers the right parts to production
Steve Scheiber, Contributing Technical Editor -- Test & Measurement World, 5/22/2007 8:13:00 AM
Delivering small items such as hearing-aid speakers, cell-phone connectors, and automobile pressure sensors to automated assembly equipment requires inspecting the parts upstream to ensure that the right parts are presented in the correct position, not backward or upside down. Inspection of such parts, once a manual activity, has succumbed to automation because of both the parts' increased miniaturization and greater complexity. But finding automated equipment that can handle tiny parts, especially at very high volumes, has been difficult.
One company that has addressed this need is Integrated Mechanization Solutions, based in Almelo, the Netherlands. Nol Brouwers, managing director for the company, explained, "There was no adequate solution for feeding micro parts. We can't use conventional bowl feeders, for example, because of adhesive forces, and the irregular component shapes do not lend themselves to reliable sorting. So, in partnership with the University of Twente and Bosch Rexroth, we developed the Vision Inspection Feeding System (VIFS), an optical system that can inspect parts in-line and minimize the likelihood that bad, wrong, or incorrectly positioned parts arrive at the assembly step."
Browers added, "The process supplies parts randomly to the system on an input tray lighted from the top using a dome. The color of the light depends on the part types in each specific application.
"The vision characteristics of the system are extremely important. We paid particular attention to the lighting and camera capabilities. Based on inspection results, the system picks each part up, rotates it, orients it, and replaces it. Then, the system captures another image, this time using backlighting and geometric shape recognition. Zooming in on a very small field of view permits very high precision for further adjustment, as well as inspection for surface defects or physical damage. Combining supply and inspection functionality can achieve a position accuracy of 0.01 mm."
Brouwers contends that automation systems must offer flexibility to provide the best value to users. "We built the inspection feeding system from standard components, so the system is open, generic, and flexible. Handling a wide variety of part types requires changing only the software. We incorporated PC controls, real-time software, and the Matrox advanced vision software library, all managed by a Windows operating system. To optimize cycle time and improve performance, the system incorporates a vibration function. Vibrating the tray separates parts that are too close together or wrong-face up.
"Requirements for particular visual checks are customer-specific, but they can easily be added to the software toolbox. As we gain experience with different applications, we will be able to extend the vision library so that many of these unusual requirements will become standard."
Asked how he would change the development project if he had it to do over again, Brouwers replied, "I'd spend more time with the university, especially working with the students on feeding systems. Cameras and lighting and the accompanying software can be regarded as academic topics. Feeding small parts is much less obviously an academic issue."
