Machine Vision is Critical to Success in Photonics Automation Assembly

Until now, the application of machine vision in highly detailed inspection and assembly of micro -components has been mostly limited by the integration skills and to some extent the cost of fully responsive systems meeting the comprehensive needs of the photonics assembly market. With the application of proven machine vision techniques and the development of application-specific software for the photonics industry, these barriers are dismantled to the point where extremely exacting inspection and assembly of micro-components are coming into their own.

Machine vision is key to automating the assembly and inspection process. 'The location of components is so critical that the machine builder can no longer rely on accurate placement with fixtures,' explains Tim Looney, senior applications engineer at Intelligent Automation, Cambridge, MA. 'In addition to accurate placements, contact with the inspected parts can be considered detrimental to the integrity of the product. The use of machine vision allows for feedback of the fiber/components position without contact, all at incredibly fast speeds.'

There are a number of terms that seem to be used interchangeably when it comes to this relatively new market for machine vision. These include photonic assembly automation or optoelectronic assembly automation or fiber optic assembly automation and micro-optoelectronics mechanical assembly (MOEMs) automation. 

Regardless of which name you prefer, machine vision is well suited for this market.  Here are five reasons why, according to many observers:  

1. currently most assembly work is done by hand; 
2. once the economy recovers, demand for fiber optic products should grow; 
3. according to the National Institute of Standards and Technology, packaging (including methods for aligning optical elements and integrating electronic components) currently accounts for 60 - 80 percent of manufacturing expenses; 
4. manual methods of assembly generally result in yields under 50% and 
5. as photonics technology advances tolerances will become increasingly tighter.

In reality, there are two assembly markets: active and passive fiber optic components. Active components consist of the semiconductor laser technology that is necessary to provide the light in a fiber optic network. These devices are generally easier to assemble. They require the integration of electronics and wiring into the package using traditional assembly technologies, such as soldering, laser welding, adhesives and die and wire bonding techniques. Receivers, transmitters, modulators, amplifiers and switches are examples of active components.

Passive components operate on the light passing through the fiber and do not require power or electronics. Their function is to filter, divide or combine the light signals traveling though an optical fiber. These components are much more labor intensive and costly to manufacture. Passive devices include couplers, isolators, and wavelength division multiplexers and demultiplexers.

Several companies appear to be targeting this market. Adept Technology, San Jose, CA has purchased several motion control companies to shore up its fiber optics expertise (NanoMotion and Pensar Tucson) as well Hexavision to enhance their machine vision alignment capabilities. Newport Corporation, Irvine, CA has acquired several companies including Unique Equipment. It is also noted that CyberOptics, Minneapolis, MN has spun out a company called Avanti Optics Corporation, promoting their LegoT photonic assembly principle.

Cognex Corporation, Natick, MA has a department that is focused on the fiber optic market and recently announced an application-specific machine vision system for inspecting polished fiber ends. Intelligent Automation, Cambridge, MA has created a subsidiary called Next Fiber Systems to go after the fiber optic assembly and test market.

It may be useful to review exactly what is involved in photonics and how the technology stands to benefit from machine vision. Photonics is the technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification, and detection by optical components and instruments, lasers, and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and other sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and information processing.

For the purpose of automation, the market is best defined as the handling and assembly of components and fiber that supports the high-speed network communication enabled by light passing through glass fiber and components. The total market for photonics communication includes long-haul links, regional and metropolitan networks, cable TV, and short-distance data links.

 'Some applications for machine vision in photonics production would be location of minute components for material handling, precision inspection of components prior to assembly, alignment of components prior to assembly, and post assembly inspection,' explains Charlie Duncheon, vice president at Adept Technology Inc., San Jose, CA. The components used in photonics product solutions are extremely small. Fiber optic assembly requires accuracies measured in nanometers, according to Duncheon. Small gradients of work cell temperature variation can create relatively large shifts in component positions.

'Machine vision can provide real time adaptive control for variations in the work cell,' Duncheon continues. 'The human eye is not capable of insuring yields in such precision demanding environments.' In some cases, 'manual operations have provided cycle times as long as hours and yields as low as 20% on very expensive assemblies.' The micropositioners used in precision alignment have limited ranges of motion due to resolution requirements, Duncheon continues. 'Machine vision can get the components located within the range of these positioners prior to final nanometer level alignment.'

AccuSentry, Marietta, GA is another machine vision company addressing machine vision-based assembly automation for the photonics market.  In one assembly application they use zoom lenses to locate fiber and features within the fiber to macroscopically align to 8 microns. Additional finer alignment is performed before the assembly is epoxied. Following epoxy the AccuSentry system also inspects the assembly for epoxy and cosmetic concerns.

'Machine vision has a bright future in the photonics industry as a support technology enabling higher yields in manufacturing of various optical components and modules,' says Alain Beauregard, president and chief technology officer, StockerYale Inc, Salem, NH. 'The challenges are great and a range of new techniques will have to be developed to allow the application of machine vision to the photonics industry.' Some potential uses of machine vision photonics include the automated assembly of components, sub-components, and modules, continues Beauregard. Some actual uses involve five-axis alignment with optical-type materials.

Some applications may require the application of specific coatings to enable high-resolution optical recognition. The machine vision optics created by design teams at Edmund Industrial Optics, Barrington, NJ, enables some electronic imaging applications by modifying its off-the-shelf optics with special coatings to adapt them to specific photonics machine vision applications.

The emergence of machine vision in the photonics automation market is still a nascent technology. Look for innovations in this area in the next few years, particularly in DWDM fiber optic device inspection and assembly.

James F. Manji is a free-lance writer in Brunswick, OH. He specializes in manufacturing automation and technology topics.

Nello Zuech is President of Vision Systems International, an independent consultancy in the field of machine vision.