No Need for Rulers
No need for rulers: new vision system inspects the tiny and the weightless
Anyone in the micro-assembly and testing industry knows the difficulties in handling the components: they're tiny, almost weightless, and highly sensitive to electrostatic charge. Inspecting and sorting these parts for assembly can be a painstaking task.
When sorting parts, an operator traditionally places the parts into a vibratory bowl feeder, a bowl with ridged sides. When the bowl is switched on, the parts jiggle and separate themselves on the ridges, but micro-assembly components tend to stick together or have too little mass to be transported by vibration. Other alternatives, like robotics systems or manual supply, often lack either speed or accuracy. In micro-assembly there is a need for a system that combines the functions of feeding, orientation and inspection of parts.
IMS (Almelo, The Netherlands) develops and builds high-tech production equipment for the high precision, electronics and medical industry. Since the company's specialty is in micro-assembly and testing, they frequently face the challenges of feeding and inspecting micro-parts. IMS sought a solution, and together with the University of Twente (Enschede, The Netherlands) and Bosch Rexroth (Lorh am Main, Germany), they developed the Vision Inspection Feeding System (ProVIS).
According to Martin Langkamp, IMS Marketing Manager, the ProVIS is a multi-purpose, modular system for the supply and recognition, inspection, handling, and placing of parts. ProVIS is based on a standard frame and equipment control system called ProMicro, also by IMS. Bosch Rexroth supplies most of the other hardware components such as the linear motors, motion controllers, and vacuum components. Since cameras are required for recognition and inspection, ProVIS uses two: a Basler for recognition, and a Thales Optem for inspection. The Matrox Imaging Library (MIL) software development kit performs all the product recognition and inspection tasks.
To use the system, a technician calibrates the ProVIS with a part that is within tolerance to create what's known as the Golden Template. Then the camera takes pictures of the parts on the inspection stage. Finally, specific processing modules in MIL analyze the parts. First the Geometric Model Finder (GMF) module locates the parts in the image, so the Metrology module can measure the features of each part. The results, both good and bad parts, are displayed on the monitor. Parts that pass inspection can be used for assembly; parts that cannot be recognized are most likely lying on their sides or too close to another part, so they are re-fed into the system by the vibratory tray. If the inspection shows a part to be out of tolerance, the system tags it; if the system is feeding parts for assembly, the non-conforming parts will be kept out of the assembly step. The system can also be programmed to find surface defects.
The ProVIS needs a high-level software tool for complex vision recognition and inspection functions. "The Matrox Imaging Library (MIL) is ideal for us," says Langkamp, "because it has all the functionality we require. MIL offers many possibilities for these types of measurements." The Metrology module figures prominently in the solution, and is used for finding dimensions and checking tolerances, complex operations that are processing-intensive. With the appropriate optical system the measurement results are accurate to +/- 0.01 mm.
"A great challenge we had," explains Langkamp, "was the lighting." Without appropriate lighting, the cameras is unable to produce usable images. The ProVIS features a dome with blue light above the tray where the products are fed to the system. The inspection of the parts' dimensions, the fundamental task of the system, is backlit. "The right combination of illumination and zoom lenses gives us the accuracy we need for such tiny parts," adds Langkamp. Like most assembly applications time is important, and all the visual inspections and data processing has to be completed within the allowed cycle time, typically 1 to 5 seconds, depending on the complexity of the inspection operation. L notes that the support they received from both Matrox Imaging and DVC, their local Matrox Imaging distributor, were instrumental in reaching their targets.
Making the connections
IMS built two prototypes in 2004 and 2005. The first industrialized version of the system was delivered in January 2007; a second is delivered in 2007 and a third is delivered in 2008. IMS has frozen development of the ProVIS and considers this as a standard product for the micro-assembly industry. In order for IMS to achieve their future goals, they must work with "well-established, reliable suppliers like Matrox Imaging," says Langkamp, and he believes IMS has an edge on the competition. "Most feeder systems can't offer the combination of accuracy, speed and flexibility that the ProVIS has," he explains. "Substitutes like bowl feeders are not flexible and reliable enough to meet the challenges of micro assembly." What's more, the modular build-up in functionality of the ProVIS means the system can be customized for their customers with little effort.