Six critical considerations for successful machine vision applications

July 11, 2013
As anyone who has been involved in a machine vision project knows, approximately 80 percent of the success of a vision system is related to illumination. Other considerations important to the success of a vision project include camera selection, ease of programming, availability of technical support and project definition. Some tips to get the most out of your machine vision system:
1. Choose the right light. Choosing the right light (LED, halogen, etc.) plus the right color (blue, white, red, IR) and the illumination technique (dark field, ring light, spot light, bright field, coaxial) are key for project success. Sometimes you have to think outside the box when selecting lighting, like using a different color light to bring out different features based not only on color, but the wavelength of illumination. For instance, finer detail can be seen better with blue illumination than with red. You can play this to your advantage when you want to enhance or reduce contrast. Consider all lighting conditions including reflections and direct sunlight potential. No matter the camera attributes or software tools, if the illumination is not right, the project will fail. Before establishing a proposal for a project, make sure you understand the illumination needs. Otherwise, you might end up incurring additional hardware costs that were not considered in the proposal.

2. Modifications required. Software quality control and quality assurance are essential to project success. Software control is more important than hardware control. Off-the-shelf vision software programs will need to be modified to fit each unique application.

3. Plan for the future. Before the design and build of a vision inspection system, consider how to make it easy to re-program and use for future applications. Find out whether support is readily available for the camera and lighting. Get hands-on programming experience first, then get the programming training. Otherwise you may have trouble keeping up with the training. The camera resolution and software are absolutely critical. Don't purchase a lower cost, lower resolution camera just because it works on this part. Think of the future. One camera and software manufacturer has an online users discussion group. That's very helpful, with answers often available within minutes of posting.

4. Versatility required. Don't purchase a system designed for specific parts (like O-rings) that must be "programmed" to do your different parts (such as grommets or seals). There are systems just for O-rings, for example, that fail miserably on non-O-ring parts. Consider a 4 to 6 axis robot to handle parts instead of custom, lower-cost pick & place systems. The cost may be higher, but the versatility and ability to program different parts is well worth the added cost.

5. Match environment. Vision hardware must be chosen precisely for the environment. Optics must match the desired field of view. Illumination must be robust. Tested software libraries help keep the complexities to a minimum.

6. Prepare for upgrades. When considering a vision system, always bear in mind the effects of Windows upgrades on the future of the system. A complete backup image system will give the vision system an additional five years of life.

Test read rate performance

To evaluate industrial code reading tools, start by measuring the vision system's reading speed. To do this, present a well-marked code to the vision system and have it read the code hundreds of times under pristine conditions to determine the number of reads per minute.

Make sure you have a 100% read rate under these optimized conditions, or you may face problems later when conditions might be less than ideal. For example, at a production line speed of 2000 parts per hour, a read rate of 99.7% would fail to read the ID codes on 48 parts in just one eight-hour shift.

After establishing the system's reading speed, you should run a more challenging read rate test to determine the impact of factors such as line vibration, variable lighting condition and extremely high line speeds on the vision system's reading performance in your application.

To test this, present a large sample of codes of good, bad, and marginal quality to the vision system. At the same time, simulate vibration and motion blur by shaking the part and sliding it back and forth beneath the camera as it acquires an image.

This test will provide a good initial assessment of how well the vision system's read rate will hold up under real-world production conditions.

10 questions to ask

Whether you are new to machine vision or an experienced user, consider the following 10 questions when selecting a stand-alone vision system:

1. Does the vision system make it easy to set up applications, create custom operator interfaces and administer vision system networks?
2. What is the importance of part location tools, and how can you assess their performance?
3. Does the vision system have a complete set of image pre-processing tools?
4. What should you look for in character reading and verification capabilities?
5. How can you determine the repeatability of a vision system's gauging tools?
6. How do you evaluate industrial code reading tools and what are some specific features to look for?
7. What networking and communications features are available?
8. What should you know about vision system accessories?
9. Does the vendor offer a wide range of hardware options? Are they rugged enough for your environment?
10. Does the supplier provide the support and learning services you need?

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