Look where you're going
- September 6, 2003
by Kip Hanson
Automated vision machines measure parts quickly and accurately
If you have a handful of parts to check, you'll probably pick up a micrometer. If you're going to measure a truckload of them, only an automated solution will do. But measurement systems come in a variety of shapes and sizes, and offer more options than a new car. Deciding
which one is best for your shop can be a real challenge.
Coordinate measuring machines, the workhorses of the metrology world, have been around longer than paper tape. The clunky machines our grandfathers once used have evolved into sleek, feature- rich systems found in even the smallest machine shop. But for all their versatility, CMM's are like a blind man - they can't measure what they can't touch.
Marty Morgan, business manager for Carl Zeiss Industrial Metrology, LCC, Maple Grove, MN, says vision systems are ideal for these hands-off situations. "If you're measuring features too small for a stylus, or for very delicate workpieces, vision is the only way to go."
These optical wonders are good for more than o-rings and circuit boards, though. Vision machines measure parts to accuracies every bit as tight as comparable contact methods, and just like their mechanical cousins, are becoming increasingly automated. As a result, many shops are augmenting or even replacing their CMMs with vision measuring systems.
Zeiss product manager Long Phan explains that automated vision systems go much further than a simple camera and motorized stage, and carry sophisticated lighting, hi-res optics, and laser or white-light scanning capability. Ironically, some systems even include hard probes, blurring the line between CMM and vision measurement. Most important of these capabilities, says Phan, is the software. "We've designed tools that make these systems easy to use, and effective at picking up difficult features and edges."
A big toolbox
That's a key factor when it comes to automation. Peter Detmers, vice president of sales for Mitutoyo Canada Inc., Mississauga, ON, says set up of a vision system is relatively simple. "In teach mode, you basically walk the system through an initial measurement. Otherwise, you can program offline, based on a CAD file. In those cases where you have edge issues that can't be seen from the model, or problems where the color or opacity of the part doesn't present itself very well, we have tools that allow the system to determine the best lighting based on surface and edge conditions."
These tools, together with high quality optics, are a big part of a vision machine's ability to check parts quickly and accurately. As a result, says Detmers, high throughput processing is a real sweet spot for a CNC-style machine. "Because these machines use a camera to â€˜see the edges', it doesn't need to remain long in any one location to extract data points. It simply takes images, collecting data from various sections of the part, and uses the coordinate position of these data points to determine the feature size, location, form etc. While the machine is moving to the next position, the computer processes the data it just collected, and prepares for the next measurement. This makes it very fast."
Jeff Bourque, manager of communications for Nikon Metrology, Inc., Brighton, MI, agrees. "We recently worked with a medical parts manufacturer in Chicago that makes a lot of injection-molded parts, but very miniature stuff, used primarily for diabetic applications. Volumes are high enough that they need to measure automatically, and very quickly, checking for things like blockages in the inside diameter of the product. An automated vision inspection system was a perfect fit."
For all their capability, vision systems don't come cheap. Bourque says a basic CNC machine starts in the neighborhood of $50K, and goes up from there. But equipped with the right tooling, this same system can inspect thousands of parts with virtually no human intervention. Picture an array of small circuit boards, or machined parts laid out in a checkerboard pattern. With a quick X-Y motion, each part can be presented to the camera, inspected, and moved on. Dimensional data is then sent to an SPC program for analysis, or even to the machine tool that just made that part. "This integration with other manufacturing processes is an exciting aspect of automated vision systems. It allows companies to reduce manpower and increase quality, and they find themselves more competitive with low-cost countries," adds Bourque.
One company who knows integration is Hexagon Metrology, Inc., North Kingstown, RI. Scott Everling, manager of the metrology and systems group, says he's seen a big call recently for robotic part handling. "An increasing number of shops are looking to automate the inspection process."
Don't forget the temperature
Everling warns it's not as simple as just sticking another CNC out on the shop floor. "Shops don't consider the environment needed for accurate measurement. Everybody's all caught up in how we're going to communicate with the robot, or pass the information collected from the vision system back to the server. But now you're trying to measure a 50 micron radial run-out on a shop floor that fluctuates 10 degrees in a day, on a system that sits next to a 1000-ton stamping press."
That's a little like asking a brain surgeon to operate on your plow horse out in the back forty. Optical measurement - especially an automated system, which eliminates any human interaction - is incredibly accurate. "We worked with a company that made components for the next-generation Hubble, the James Webb Space Telescope. These were hexagon-shaped, beryllium copper lenses measuring one meter across, with an optical surface profile tolerance of 150 nanometers. You weren't allowed to run a probe across them. The only way to do something like this is with a vision scanning system," says Everling.
While this example is overkill for the shop down the street machining next-generation skateboard widgets, it illustrates the technology's capability. Automated vision systems are a valuable partner in today's fast-paced manufacturing dance, offering speed, accuracy and, if needed, integration with manufacturing cells and robotic handling systems. If you're looking to gain a competitive edge, take a look at automated vision inspection systems. SMT