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by Michael W. Metzger

Today’s recovering economy demands manufacturers become as productive, efficient and competitive as possible--while usually providing fewer resources to help them do so. In addition, quality must not be compromised as costs are mandated to be lowered.

It’s a challenge, but advances in optical inspection and microscopes for industry are helping to meet these demands and fuel productivity growth over a wide range of industries.

Optical inspection and microscopy span a huge range of manufacturing industries. Manufacturers of electronics, medical devices, automobiles and more all share a need for optical microscopes for inspection.

Stereomicroscopes, compound microscopes and video measuring instruments make up the bulk of what is being used in today’s manufacturing environments. Each of these inspection tools is like a building block configurable to the exact needs of the end user. Designers of optical instruments account for maximum versatility in specifications to keep costs low and capabilities high. Because of this building-block design, automation is one of the key component specifications to consider when evaluating optical microscopes and inspection requirements.

The stereomicroscope

One of today’s most popular optical inspection devices--especially in environments requiring low-power zoom magnification--is the stereomicroscope, which is ideal for operations that call for hand-held manipulation of a part to see all sides of the item under inspection. Stereomicroscopes also provide the advantage of having a long working distance, which is the free space between the lens and the part being inspected. The large working distance also supports the operational need for hand-held manipulation of the part.

The compound microscope

The compound microscope for industrial applications has a variety of fixed-magnification objective lenses located on a turret under the reflected-light illuminator. This tool is for higher magnification requirements than the stereomicroscope can provide. It is also well-equipped to provide specialized optical techniques to help enhance the contrast of the image so the detector can see it. Compound microscopes are used in industry for materials image analysis, image acquisition, part inspection for defects and measuring. They can be configured with advanced optical techniques (e.g., polarized light, differential-interference contrast, brightfield/darkfield illumination and fluorescence) all on the same system.

The importance of these advanced contrasting techniques for the compound microscope can be illustrated through the real-life experience of a paper manufacturer. When evaluating the behavior of colored ink dots on the paper, the optical technique of darkfield illumination was clearly required to see how the ink dots behaved on the test paper. Did the ink bleed, run or mix improperly? The darkfield technique enhanced the color contrast by reflecting the light from an oblique angle back through the optical system, as illustrated on page 29. This reflection technique returned each color separated from the rest and provided a more realistic image to the detector--the same as our eyes tell us the color should be. The company previously used a conventional microscope with only brightfield illumination to view the ink. The darkfield-produced image was a dramatic improvement because brightfield illumination transmitted the colors axially, and the resulting color mix produced a lower-contrast image.

Video measuring microscopes

“Video measuring microscopes” is a term used for several application-specific microscope configurations that gather discrete geometric data and analyze images. Some users refer to these by different names, including automated optical microscopes, vision systems, toolmakers’ microscopes or video measuring systems. This tool is popular because it combines the best assets of stereomicroscopes, compound microscopes, digital technology, computers and precision positioning components such as stages.

What was once only a manual inspection operation is now becoming a reproducible task suitable for automation. In industrial microscopy and inspection, advances in computers, precision stages, filters, lens magnifications, illumination and digital image acquisition make connectivity and motorization a rapidly emerging trend. The medical device, automotive and semiconductor industries require immense amounts of noncontact inspection and strict controls of processes to ensure compliance to high-quality standards and productivity. To meet such high demands, these industries are striving to eliminate potential sources of error wherever possible. Metallurgical evaluation of grain sizes and boundaries, as well as materials sciences, are experiencing improvements in productivity and quality assurance. This can be attributed to the automation of acquiring images and performing complex image analysis.

Industrial inspection operations have historically been operator-dependent. Parts for inspection were typically loaded manually under an optical instrument, and a highly trained technician reviewed the generated images. For microscopy, most task-specific applications have experienced little change over time. These operations still require inspection for defects; identifying the absence, presence or position of components and small features; classifying defects and determining their location; or as an aide in an assembly operation for alignment. Parts will still need to be measured under magnification to determine feature geometry and measure quantity or relationships to blueprint specifications. Incidentally, once the inspection process is complete, the report still needs to be generated.

For industrial engineers, good work- design principles have always indicated that whenever possible you should combine, eliminate or automate manufacturing operations and procedures. Current and future technologies in optical instrumentation are helping the engineer meet this goal and therefore save time and money while increasing productivity.

It’s now realistic to expect that routine inspection for defects, measurement of feature relationships inside and outside the field-of-view, and automatic report generation can be achieved on one instrument. Vision systems are routinely blurring the lines among stereomicroscopes, compound microscopes and coordinate measuring machines. Eyepiece-free digital microscopes with motorized optics and components now allow operators to simply place a slide into the jaws of an automated system, where the internal optics scan the sample and allow for remote Internet access for image control and acquisition. Some microscopes have a range of magnification from as low as 36! to as high as 4,320!. This is achieved by combining two optical systems into one instrument. This type of tool is designed for inspection at low magnification as well as measurement at extremely accurate, high magnification.

New technologies in software, lighting, precision motion controls and optics are being integrated to enhance component-level functional limitations by combining capabilities. Physics often limit the nature of what we can do by providing inverse relationships like the correlation between high magnification and shallow depth-of-focus. This makes optical inspection, measuring and image analysis difficult because only a wafer-thin section of the sample will be in focus at any one time under high-power magnification. An inspector wants to see the entire part in focus from top to bottom.

Fortunately, through software, computer image controls and a precision Z-axis motor drive, high-magnification images are now easily stacked together to provide a more useful extended depth-of-focus. The same can be done by stitching together high-resolution, small fields-of-view to provide a larger field-of-view at a more accurate and functional resolution. Optical instrument manufacturers have also found ways to integrate laser-safe products and accessories on the microscope. This can incorporate through-the-lens laser light to assist focusing and to scan surfaces to return Z height data for surface form measurements and analysis.

The driving forces for automation in optical instruments are the optical, computer and digital-imaging technologies. These three legs form a strong foundation for advancements in the utilization and functionality of today’s optical inspection tools. Digital sensor technology is rapidly closing the gap to the levels of sensitivity and resolution of the human eye.

Broadband informational flow is allowing remote connectivity of microscopes and imaging devices to operators over the Internet. New technologies in illumination, such as white-light LEDs are allowing more precision in computer control of illumination, reduced heat to the sample and a more evenly distributed illumination over the field-of-view. The combination of optical microscope, digital camera technology and computer is joining the growing digital-to-data revolution. Optical instrumentation is at that strategic inflection point where capabilities are taking off to meet the level of one’s imagination.

Clearly, communication is the name of the future in manufacturing. It allows companies to be competitive, reduce costs, improve quality and build better product. Information viewed through a microscope is now routinely converted to a digital packet of information at the factory floor. That important information can be channeled nearly instantly as functional data back to production control, up to management and over to the vendor. Software and computers are driving forces to coordinate activities and connect the human to the digital camera.

This overall mix of technology provides the capabilities necessary to take attribute data or the go/no-go decisions operators make based on the image they see and transform that information into variable data that can be fed back into manufacturing for better statistical process control.

About the author

Michael W. Metzger is the department manager of measuring instruments for Nikon Instruments Inc., headquartered in Melville, New York. Metzger manages all sales and marketing efforts for Nikon’s premier optical and digital measuring products throughout North and South America. Metzger joined Nikon in 1991 and has more than 29 years of experience in optical and dimensional metrology. He has been an ASQ Certified Quality Engineer and was also certified by the U.S. Navy as an optical and measuring specialist.