How do you know that all those products pouring off the assembly line are within tolerance, completely assembled and ready for shipment? Even if the line is built for remarkable consistency, there still may be a need to compile statistics for trends or to predict when a machine or tool may be wearing.
Machine vision is proving to be a valuable tool for increasing competitiveness. Not your father’s vision systems, though, but rather the new breed of personal computer-based systems and powerful sensors that are easier to use and less expensive.
Mark Sippel, vision product support manager at Omron Electronics (www.omron.com/oei), Schaumburg, Ill., considers the machine vision marketplace to include two primary segments—the application specific or original equipment manufacturer (OEM) segment and the general-purpose machine vision (GPMV) segment. “The GPMV market segment can be the most difficult to satisfy, and generally requires the greatest amount of flexibility and functionality,” he adds.
Determining whether an application specific product for a line of OEM machines or general-purpose equipment can be adapted for various uses on a manufacturing line is one thing. But what types of actual products are available?
Steve Geraghty, director at Coreco Imaging’s ipd division (www.goipd.com), a Billerica, Mass.-based machine vision vendor, defines four types of vision products: pixel sensors, vision sensors, smart cameras and vision appliances.
Geraghty says that pixel sensors, sometimes called pixel counters, offer slightly more sophisticated capabilities than traditional photoelectric sensors. Pixel sensors provide high-speed inspections in such basic, low-cost applications as presence/absence and controlled template matching.
Vision sensors, he continues, incorporate the components of a machine vision system, including the sensor (camera), digitizer, processor, software, interfaces, optics (lens) and sometimes illumination, into a compact package. Because they are programmable, these products can be used in a variety of applications, including those in which more than a simple “pass” or “fail” is needed, and when greater programming flexibility is required.
Smart cameras, he adds, are similar in construction and concept to vision sensors, the main difference being in the programming. Instead of selecting from a comprehensive, and sometime complex, set of operations, users are generally required to develop applications based on library components provided by the manufacturer.
Finally, vision appliances contain hardware similar to that of vision sensors or smart cameras but are designed for specific inspection tasks, such as optical gauging or label inspection. Each vision appliance incorporates software that is customized to the unique requirements of a particular application.
Selection tips
Geraghty points out several important features to look for in choosing a vision system:
l Ease of use to ensure correct application. Make sure that all personnel who will be using the machine vision product have a chance to walk through a demo and feel comfortable with the quantity and level of programming.
l Ethernet connectivity to other plant floor automation, and to information systems and business programs.
l Industrially hardened housing to withstand demanding plant floor environments.
l Input/Output capabilities so that the vision system can make decisions and control accordingly what happens when parts or products are accepted or rejected.
l Historical/archiving capabilities that enable users to review data accumulated from the vision system, identify the causes of any ongoing manufacturing problems and adjust them accordingly to increase quality in the most effective manner possible.
l Automatic compensation for lighting and control variations, and for lens and perspective distortion, to provide greater inspection reliability.
Omron’s Sipple points out a common problem encountered by vision integrators. “When it comes to solving a vision application, many users have learned that choosing and setting up the correct lighting is a large part of the vision application’s solution.”
