Make the Switch to Video
"If you can't check it, you can't make it," says Marcus Young, president of AcuTwist (Ridgway, PA), a cutting tool manufacturer.
Young spoke at the International Manufacturing Technology Show 2002 in September. He referred to the fact that unless he could prove his measurements, his customers were not likely to believe that he was making products to specification.
When it comes to video measurement, one might be tempted to say, "If you don't touch it, how do you know you checked it?"
Many manufacturers are used to seeing the object they want to measure and then touching it with a contact-measuring device. Asking them to change how they do these measurement tasks may be asking a lot from them.
"Manufacturers are afraid (of video) because they don't touch the part," says Tom Groff, corporate products manager of Optical Gaging Products (OGP, Rochester, NY). Indeed, many video measurement suppliers report they must educate manufacturers that video can be a viable alternative to contact measurement tools such as coordinate measuring machines (CMMs). "If the part is flexible, or easily deflected or damaged through contact methods, then video is a serious alternative," says Groff.
He adds that video has found widespread use in applications such as medical device manufacturing, electronics, plastics and delicate metal stampings. The technology also finds use in castings and molds, where, because of inaccessibility to a part feature, a manufacturer is precluded from physical probing.
And, to put some perspective on the use of video measurement, the market for these products is expected to reach more than $44 million this year (Quality, December 2001).
Why use video?
Does the manufacturer who for 40 years has made the same round washer, which has the same inner and outer diameters, now need to switch to a video measurement system? It is a simple part with little variation and may not even be used in a critical application.
"If the part design doesn't change much, the manufacturer may be able to use already existing equipment, such as an (optical) comparator and get better parameters than with video measurement," says Dan Freifeld, president of Visicon Inspection Technologies (Napa, CA). While that may be true in some instances, others believe the switch to video may be necessary, even with a proven part.
"Are your tolerances getting tighter? Do you need increased throughput? Do you need to free up man-hours on the floor for other tasks?" asks Mike Cognac, general manager of metrology systems for The L.S. Starrett Co. (Athol, MA). "Any one of those reasons may require you to switch from a comparator to a video measurement system, even on a part you've been making the same way for 40 years." Cognac also suggests that the switch to automated video inspection can reduce the variation that naturally occurs with operator-dependent measurement machines.
Besides tighter manufacturing process requirements, there are traceability issues that video measurement can answer. For instance, manufacturers may be concerned whether they can do geometric dimension and tolerancing (GD&T). But one manufacturer, who recently implemented video measurement technology, says he was able to meet GD&T guidelines with video, despite not touching the part.
"There's almost the feeling that it [video] is illusory because you don't touch the part. You ask yourself, 'Can I believe what I am seeing?'" says Rich Domaleczny, gage and sorting supervisor for ATF Inc. (Lincolnwood, IL), a manufacturer of precision fasteners. The ability to store images of measured objects can be of value in documenting for traceability, training or for sharing with customers.
Despite advantages in using video, issues -- whether imagined or real -- in lighting, optics and software are common objections that many video measurement suppliers must overcome.
See the part
"Lighting and optics can seem mysterious to those making the switch to video measurement," says Ken Parlee, vision product manager for Mitutoyo America Corp. (Aurora, IL). But Parlee says the fear of lighting and optics should not prevent a manufacturer from considering video.
"You don't need to know the physics of lighting, just some of the issues surrounding the part you are trying to measure," says Parlee.
Parlee says the primary goal in the correct use of lighting and optics is the ability to find the intended edge of the measured part. Contact measurement methods of a part may result in a probe detecting a burr, flashing, or even dust and contaminants and reading that defect as a legitimate edge. Manufacturers of contact systems maintain that their systems have methods of ruling out such defects as real edges, but video does allow the operator to instantly see whether he is measuring the edge or a defect. Angle lighting and part rotation are two methods video measurement machines use to define difficult edges. Techniques such as backlighting, lighting through the lens and LED ringlights can be used to ensure parts can be easily seen.
But, despite all the promises of technology, Bob Larzelere, president of Deltronic (Santa Ana, CA), insists that a "hands-on attempt" is the best method to find part edges and features.
"The only way to do that [find edges and features] is by putting the part on the machine and checking if you can find what you need to see," says Larzelere.
Domaleczny agrees. He says that lighting and optics issues initially were a challenge for ATF workers, but support from his supplier helped overcome that hurdle.
Yet, even the best optics are limited in what they can show a manufacturer. "We've never hidden the fact that video has its limitations," says OGP's Groff. In a straight video system, three-dimensional, prismatic parts may be difficult to measure, as are features hidden underneath the top surface. But, suppliers have implemented technologies such as 45-degree mirrors, and laser and mechanical probes to overcome those limitations. Most suppliers agree that the primary method for determining the Z-axis of a part is to use the autofocus function of the optics. However, mechanical probes help when the manufacturer cannot obtain contrast on the part because it is parallel to the camera.
"I'd estimate that 60% to 70% of the systems going out the door have some sort of touch probe or laser probe technology," says Groff.
A laser, says Parlee, can be difficult to program and costly. And, more than a few suppliers suggested that a video measurement machine equipped with a probe is not a substitute for a CMM.
As if manufacturers did not have enough to contend with in deciding whether video is the technology for their application, two suppliers offer alternatives to traditional technology.
Most suppliers of video measurement equipment use a similar strategy in their technology: a camera, light source, glass stage and an X-Y table that moves the part under the camera. Visicon uses linescan technology, similar to that used in a photocopier or computer scanner, to capture the image. The part is held stationary and the camera moves across the part.
"By moving in one axis, we reduce losing accuracy caused by moving on an X-Y axis," says Freifeld. Such an approach, he adds, allows the company to invest in bettering its optics and lighting, rather than investing in more sophisticated encoders to move an X-Y table.
By rotating the part, Visicon systems can detect intricate features wherever they appear on the part, and the accompanying software allows the manufacturer to perform pattern matching on similar features, allowing for faster measurement.
"We leave some of the 3-D applications to our competitors. Large, prismatic parts are not for us," says Freifeld. Most of his applications are in the electronics and medical industries.
Cognac says his company offers an adapter that transforms a traditional optical comparator to a manual video measuring system. Introduced at IMTS 2002, the Nova combines a 1¿inch CCD color camera with zoom optics on a Starrett comparator. "It lets a manufacturer leverage (video) measurement technology while preserving existing equipment," says Cognac.
A common challenge
Regardless of the approach to optics and lighting, one factor common to all video measurement is software. "The software is key to the usability and capability of the video system," says Groff. Video measurement software must often meet differing needs.
"The operators tend to be the ones using the equipment on a daily basis, so the software has to be easy for them to use. But, usually the engineers are the ones who actually do the programming, so the software has to have the power they need," says Larzelere. And, it must have the sophistication to be used by supervisors who are making manufacturing process-level decisions.
Despite these needs, the most frequent programming task is to recognize parts and features, and collect the data. In such instances, most video measurement systems have a learn mode that allow operators to create simple programs.
"It's more intuitive than programming a comparator," says Cognac.
There is still a learning curve. "There weren't enough of our operators who were accustomed to working with this level of software when we first installed the system," says Domaleczny.
Where is the video measurement machine to be used? Many contact measurement systems are found on the production floor, and so are video measurement systems-in some instances. Freifeld says that most of his equipment is used on the shop floor, but those shop floors often are in the electronics and medical industries, which are inherently clean.
Like contact systems, video measurement systems are subject to the effects of temperature vibration, dust and other contaminants.
"If a manufacturer is currently using a CMM and getting by with environmental issues, he should be able to do the same using video," says Larzelere. Like CMMs, many video systems are used in environmentally controlled areas.
Other issues that manufacturers must consider are accuracy, repeatability and resolution. Often, these terms are used interchangeably, but each relates to a different attribute of the system. Many suppliers adhere to VDI/VDE, which are German standards, for defining accuracy, and so a manufacturer can compare accuracy among different contact and non-contact systems. However, recent reports from CMM manufacturers seem to indicate a move away from VDI/VDE toward ISO 10360, Geometrical Product Specifications -- Acceptance and reverification tests for coordinate measuring machines.
Regardless of the standard used, suppliers agree that for a manufacturer to determine whether or not video will work, the equipment should be tested in the plant environment and with the parts that it will inspect every day.
"Never buy a piece of equipment without doing a gage reproducibility and repeatability study," says Cognac.
Cost is another issue. Entry-level manual systems can cost $10,000 or less. Automation, better optics and lighting, flexible software and parts-handling options can put the price tag for an average measurement system at $30,000 to $50,000. Freifeld says he has seen sensors alone that cost $100,000 to $200,000 each, but the need for such devices is rare.
Finally, like any other change in equipment or quality practice, the switch to video must be embraced by the entire company. "There are a lot of vision systems sitting in factories with covers on them because there was no buy into the technology," says Parlee.
This was not the case at ATF. Despite some initial misgivings, and the learning curve, the company has successfully implemented video to its operations and is using it for more and more applications.
"We definitely made the right choice in selecting what we did," says Domaleczny, "I foresee us using the technology as the final judge for all our safety-critical parts. That's about 50% of our business."
Throughput, documentation and traceability issues may cause manufacturers to adopt noncontact video measurement technology.
GD&T can still be done using video.
Lighting, optics and software have advanced in capability and ease of use.
Prices for video measurement systems can start at less than $10,000, and be as much as $100,000. Typical systems cost $30,000 to $50,000.