A Dozen Tips Help You Work with a Machine-Vision Integrator

Your salvation may come from working with a top-notch machine-vision system integrator that can deliver a complete vision system. Before you select an integrator, be prepared to spend time figuring out what you need. These 12 tips will help point you in the right direction:

1. Understand your manufacturing processes. Before you talk with anyone about an inspection system, you should thoroughly understand every step in your manufacturing process. Most people think they know their processes, but few can accurately describe the manufacturing steps and operations in sufficient detail to help an integrator. Integrators need information about your product, the equipment used to produce it, the quality-control steps in the production line, the speed of the line, the usual reject ratio, and other factors.

By knowing what your manufacturing processes do and how they work, you’ll better understand the types of defects that can occur during manufacturing, where the defects occur, and thus where to inspect for them. And you’ll discover how defects affect the rest of the manufacturing line. For example, manufacturing people will remove defective PCBs from a manufacturing line right away. There’s no sense in adding expensive components to a PCB that contains defects.

2. Clearly specify what you want to inspect for. Specifications for a machine-vision system can’t say, “Check for too much solder paste,” or “Look for misaligned components.” The specifications must explain how to determine when too much solder paste gets deposited on a PCB or how to measure alignment of components on a PCB. Human inspectors can make subjective decisions, but computers require quantitative information.

You must supply an integrator with complete engineering drawings of the product you want to inspect. And the information must clearly describe the types of defects to inspect for and how you measure defects. Be ready to furnish samples of good products and bad products, as well as samples of marginally good products and marginally bad products. These latter two variations help the integrator determine the limits of the good and bad products that pass through the system.

Ensure you specify realistic quality tolerances and values. Often, specifications and tolerances get “tightened” as they move from design to manufacturing and on to test. Designers may specify a tolerance of 0.25 mm, but by the time the product goes into manufacturing, engineers along the way have “tightened” the tolerance to an impossibly small 0.025 mm. Human inspectors may compensate for the smaller tolerance by accepting products closer to 0.25 mm than to 0.025 mm. But if the engineers specify a 0.025 mm tolerance to a system integrator, the resulting machine-vision system will start to reject products created within acceptable design specifications. Make sure you clearly and carefully specify what you can and cannot accept. 

In a “cost” column, account for the time needed to carefully describe your system to an integrator, the time needed to produce the system, the cost of the system, the cost of a maintenance contract, the investment in worker training, and other costs that depend on your specific manufacturing operation.

Keep in mind that machine-vision systems aren’t perfect—no inspection system works perfectly. So depending on the tolerances your manufacturing people specify, the system will either reject some marginally good products or accept some marginally bad products.

You must evaluate the cost of each operating mode. Say you plan to inspect cell-phone PCBs. A production lot contains good boards, bad boards, marginally bad boards, and marginally good boards. If you set the tolerances loosely, a vision system will pass some of the marginally bad boards. If you set the tolerances tightly, a vision system will reject some of the marginally good boards.

Which will cost more—catching all the bad boards while rejecting a few good ones, or sending a few bad boards down the line so you also pass all the good boards? The answer depends on where the boards get inspected, and how much value you lose by rejecting good boards or by further processing bad boards and catching them later, perhaps at functional test. You must perform a sound business analysis to determine how a vision system will affect your company’s finances. Enlist your cost-accounting people to help with this type of analysis. 

Even the vision components get complicated. Your system may require sophisticated cameras with adjustable-focus zoom lenses, various types of light sources, custom operator interfaces, and so on. Integrating a system of such complexity into an existing production line is best left to experts, and even experts can require considerable time and effort to set up a working vision system. 

Test & Measurement World’s July Buyer’s Guide issue and Online Buyer’s Guide list many vision-system component suppliers. You can also find information about suppliers and system integrators at the Automated Imaging Association (AIA) Web site (www.automated-imaging.org). The AIA sponsors “The Vision Show,” a forum where visitors can examine system components and talk with suppliers.

If you’re unfamiliar with machine-vision systems, what they look like, and how they work, consider visiting local companies that employ machine-vision systems. Perhaps you can use your network of personal contacts to establish communications within a company, or vision-equipment vendors may suggest a company or two to call. Later, when you identify two or three system integrators to investigate further, they can point you to companies they worked for. Seeing machine-vision equipment in operation will help you better understand what designing, building, and integrating a vision system involves.

The AIA provides an online—and print—directory of system integrators. In addition, most machine-vision original equipment manufacturers (OEMs) work with system integrators, so they should offer a list of integrators. The manufacturers may also list the specialties of the integrators—packaging inspection, PCB inspection, color inspection, LCD inspection, and so on. No matter how you locate integrators, budget time to gather information about their capabilities. 

• Did the integrator do what was specified?

• What types of unexpected problems arose during the development?

• Did the integrator meet the schedule and budget?

• How well does the integrator respond to service calls?

• What pitfalls did you encounter during startup?

• Would the client go back to the integrator for another system?

• If the client had to do the project again, what would he or she do differently?

Because your vision system may require modifications to your production line, also look for integrators that have engineering experience and who can design production-line equipment. Integrators need a breadth of experience with industrial controls, motion control, actuators, and sensors. You need more than a garage-shop operation with a hardware guru and a C++ programmer.

You’ll benefit from a tour of the integrator’s facilities. You can see work in progress and examples of other machine-vision systems the company built. You may also see samples of the end products the company built vision systems to inspect. A visit also gives you the opportunity to meet the engineers and technicians you’ll work with, and a plant visit should give you a sense about the stability of the company.

Does the company look well established and prosperous? Does it have work in progress that you can examine? Or does the facility look like it houses a small operation with one person responsible for everything?  

But integrators need the flexibility to pick and choose equipment from other suppliers, too. Ask each integrator on your short list what suppliers they work with regularly, and find out what other suppliers they use and why they use them. Perhaps they needed a camera with specific characteristics or a lens with unusual features. Find integrators that exhibit flexibility in solving machine-vision problems in more than one way.

On the other hand, too much flexibility in specifying equipment from many suppliers may suggest little detailed understanding of specific hardware and software. Thus, an integrator unfocused on a few suppliers may spend time learning how to use new equipment at your expense.

As the integrator works on a quotation, you’ll participate in many discussions and meetings with the integrator’s engineers as they learn more about your needs, the equipment on your production line, the production environment, and other technical details. Your request for a quotation must include your detailed performance criteria, drawings of the components or products undergoing inspection, and other related information.

Don’t underestimate the amount of time it takes to nail down specifications. Integrators should ask a lot of questions, and they may ask for a plant tour that will let them see the production equipment in use, where the vision system will go, who will operate it, and so on. 

During the tests, look for repeatability and accuracy. The system should not only find the good and bad sample products, but it should do so over and over again. The system should not fail good products, nor should it pass bad parts—unless those parts exist within the marginally good or marginally bad categories and are rejected or passed according to preset tolerances.

Be sure you test the user interface and any controls accessible to an operator, whether the controls exist as hardware or as menu selections on a monitor. If you required certain options, be sure they exist and they operate as specified. Testing at the integrator’s site makes it easier to make minor last-minute changes in hardware or software. In most cases, some tweaking of the system should be written into the contract. Of course, you’ll have to pay for it.

A final acceptance test at your plant—using the same qualified samples—gives you a last opportunity to check the vision system for proper operation before you sign off on the purchase. In this type of test, the system operates as an integral part of your production line and gets tested under real production conditions.

The equipment the integrator provides comes with manufacturer warranties. Determine whether you or the integrator assumes responsibility for warranty claims and service. The integrator may simply pass the warranties on to you—the customer—with the understanding that it’s your responsibility to work directly with the equipment manufacturers. Or the integrator may take responsibility for warranty support.

Obviously, you’ll ask other questions and request other information from a system integrator. You’ll check its business standing and have attorneys check contracts and agreements. But the 12 basic points above should help you with the technical aspects of finding an integrator with whom you’ll work well. T&MW

FOR FURTHER READING

The Test & Measurement World Web site provides an "Inspection Corner" in its Articles section. This part of our site includes many helpful articles about machine vision and inspection topics.

ACKNOWLEDGMENT

Special thanks to system integrators Lance Fisher and Ronald Stroope of Daystar (Plainfield, CT), and Ed Matunas of WEI (Old Saybrook, CT) for sharing their experiences and insights.