Video measurement is one of metrology's most versatile instruments with applications ranging from the microscope to the comparator.

This is an example of scanning with video. Here, a key and the corresponding edge trace image is captured. The green plus signs are the individual data points identified by the software. The image shows how little of the key is visible in the field of view (FOV) at one time, although edge trace is able to automatically bring the entire edge into the FOV sequentially during the measurement process. Photo: Optical Gaging Products

As video technology has improved, its uses seem limited only by the supplier's and the end user's vision.

Advances in optics, lighting, software and hardware are pushing the boundaries of traditional video measurement systems. These new features are turning old technologies into new ones and even pushing some tools to the sub-micron, nano realm.

But, using video to measure the smallest of the small parts is not video's only strength. Improved construction allows many shop-

hardened tools to be placed near production and some portable units to be moved as needed. New software allows for scanning capabilities never before seen and advanced focusing and optics allow more measurement certainty than ever. Tools from coordinate measuring machines to optical comparators are integrating video.

Proper illumination is key to capturing accurate images of a part. Here, a SmartRing light helps measure an engine block. Photo: Optical Gaging Products

Exploring the nano world

One area that some manufacturers have focused on is nanomeasurement. Companies such as Nikon Instruments Inc. (Melville, NY) are diving into this market. And, at least according to one survey, the water is nice in that technology pool.

Lux Capital (New York), a venture capital firm that focuses on nanotechnology, released The Nanotech Report 2003. According to the report, nanotechnology will draw more than $3 billion in worldwide research and development (R&D) dollars in 2003, including hundreds of millions of dollars in corporate R&D. More than $2 billion in U.S. government funding has been earmarked for nanotechnology since 2000, putting it on track to be the largest U.S. government-funded science initiative since the space race and eclipsing the Human Genome Project. In all, more than 700 companies are involved in nanotechnology.

"I do see some strong trends in the business, and industry needs to concentrate on the world of tomorrow," says Mike Metzgar, department manager of measuring systems at Nikon. "I think there is a big push to go from the micro world to the nano world."

According to Metzgar, driving this trend are makers of medical devices, wireless technology, semiconductors, automobiles and defense contractors.

"The metrology world used to be millimeters and then it went to micrometers," Metzgar says. "Now I see R&D going for new products and new technology that keeps getting smaller- smaller cell phones, smaller wireless technology and the architecture on semiconductor devices. They all want to get it smaller because they want to move more information with less energy."

To meet these challenges companies such as Nikon have begun to supply equipment including one product that features a dual-optical system that delivers a range of magnifications from 36X to 4,320X. It has stage scale resolutions that have been enhanced to 0.01 micrometer and wide illumination options to ensure precise detection of edges in complex parts.

"What becomes important is the magnification that is selected, the optical contrasting techniques that are selected and the quality of the optics, because you can't have distortion in your optics," Metzgar says. "Also, the staging platform for your hardware becomes critical so that you can move things precisely enough to be able to effectively make measurements at that level."

New capabilities

To reach these levels, many suppliers of video measurement systems have made improvements to their systems. A range of new features has recently been introduced that showcases these advances in terms of zoom optics, imaging and illumination that allows different parts with varied surfaces to be measured. These are all key because with noncontact video measurement systems it is the image of the part that is measured, not the part itself. The quality of the image must be as precise as possible because distortion leads to measurement error.

For instance, sophisticated measuring techniques, advanced focusing technology, and custom lens designs that provide a high-contrast image with virtually zero distortion are part of some new products offered by Optical Gaging Products Inc. (OGP, Rochester, NY), according to Tom Groff, corporate product manager.

Historically, a fixed-lens system provided better clarity compared to a system equipped with a zoom lens because each lens element of the fixed lens can be optimized for a particular magnification of the lens system. Customers prefer the versatility of a zoom lens to the complexity and high cost of numerous fixed lenses. According to Groff, OGP developed the TeleStar Telecentric Zoom from the ground up with two objectives in mind: better optical quality and improved accuracy. The zoom lens offers a flatter optical field, minimal distortion and clarity. This design translates into crisp images on prismatic parts and a substantial increase in accuracy when measuring with video. OGP has also developed the AccuCentric self-calibration technique for all of the company's zoom lenses that counteract any adverse effects of moving elements in a zoom lens. With AccuCentric, at every magnification change the system automatically recalibrates the magnification, allowing zooms lenses to maintain accuracy levels that rival fixed lens systems.

Z-axis measurements, meaning measurements along the optical axis and perpendicular to the image plane, require precise autofocus technology. Autofocus enables the machine to find the best image contrast by monitoring the camera output signal while scanning through the Z-axis. Within the past year, a new advanced focus technology was developed that allows video systems to note the best focus contrast of multiple points within the field of view. By scanning through optimal focus for every area on a part, a video system can dynamically generate geometries that are at any 3-D orientation. This is much faster than acquiring each individual surface point.

Another advance is edge-tracing software that can trace an unknown part perimeter with video. In general, there are different ways to scan parts including laser scanning, continuous contact probe scanning and video scanning. Edge trace software allows users to scan with video. Simply select a start and end point. "It's like driving by the rear-view mirror," says Groff. "By knowing what happened behind you (already acquired points), the system uses this information to predict the edge contour going forward, and based on that it continues on the unknown edge. This technique works well with edges that extend beyond the field of view, driving XY stages as required, automatically. This tool can reduce hours of programming time to minutes."

Proper illumination is critical to good imaging for video measurement. OGP's SmartRing light, which features a Fresnel lens, has six concentric rings of LEDs that can be selected individually or in any combination. They also can be selected in any of eight segments. This wide range of control makes it possible to illuminate surface features to highlight edges at any orientation for better edge detection performance. The Fresnel lens allows the angle of light from each ring of LEDs to strike the surface while the ring light is at a constant working distance.

Another interesting lighting technique that Groff likes to share is one that dates back to early days of optical comparators called light sectioning. "Unlike true sectioning where you literally slice a part in half to measure it, we can section parts without destructive testing by shining a slit of light onto a surface and measuring that light with edge detection software." This is especially useful for manufacturers of such products as turbine engine components, blades, and cutting tools, with compound curves and angles, among others.

Shop-floor uses

Portability is another strength of many new systems. Starrett, among other companies including Mitutoyo, OGP and View Engineering offer systems that can be placed right on the shopfloor near production. Their primary strengths are mechanical stability, powerful software, ease of use, versatility, and illumination capabilities, all of which contribute to consistent, reliable operation.

For Starrett, the key factor is material consistency. The machine's base, stages and Z columns are all constructed of the same material, ensuring uniform measuring results. Overall, matching materials mean less fluctuation of individual components in changing temperature environments.

View Engineering (Simi Valley, CA) offers a benchtop system that brings together hardware and software capabilities with the portability of a compact benchtop configuration.

Because the Benchmark system can be moved and quickly set up to perform a variety of tasks at different locations on the production floor, it can address critical process control points, such as incoming inspection, in-process QA sampling and final inspection.

Other uses

Video is finding homes in a variety of other places including those not traditionally considered a video measurement system. The L.S. Starrett Co. (Athol, MA), for instance, now can replace an optical comparator lens with a special video camera. The comparator can be attached to a 13-inch color video monitor. The lens incorporates a 6.5:1 zoom lens with 32 millimeters of working distance, allowing for maximum use of the stage travel of the comparator. The crossline generator allows for multiple crossline images including solid, dashed and matted.

This optical-to-video adapter uses the same quick-change bayonet mount that an operator would use to change from a 10X lens to a 50X lens, without any tools. In essence, it provides a quick, simple, cost-effective alternative to newer video measuring technology. This will allow users to obtain excellent surface illumination at higher magnifications than would normally be possible with comparators.

"The adapter allows traditional optical comparators to be converted into manual video measuring systems by simply replacing the comparator lens with the new camera-based, video zoom package," says Craig Smith, Starrett Metrology Systems Division general manager.

These are just a few of the changes to video systems. As the systems improve, it may just come down to whoever has the most imagination.

Sidebar: Tech Tips

1. There is a big push to go from the micro world to the nano world in video measurement.

2. Within the last year, an advanced focus technology was developed that allows video systems to search smaller areas and grab multiple points within the field of view.

3. Portability is another strength of many new systems.