Ten questions you must ask when buying a machine vision system

 Whether you are a new machine vision user or an experienced user, you can effectively complete the machine vision system selection process with answers to ten key questions and helpful suggestions for evaluating product specific features. 

1. Is the vision system easy to set up applications, create custom operating interfaces and manage the vision system network? 

Setting up a vision application shouldn't require you to be a machine vision expert. Does the setup interface help you complete all steps of a vision application, including setting up acquisition settings, positioning and inspecting components, and transmitting results to other equipment on the factory floor? Does it require programming knowledge, or is it a configurable system? Is it easy to set up the software to calibrate the system to perform work in real application units rather than pixels? When you add a tool to your app, does it show you a quick look at passing and failing tools to help you understand how your app's settings are performing? Does it allow you to build a complete operator interface to be able to change tolerances or support production line changeovers? Does the system provide maintenance tools to back up, restore or clone the system and perform firmware upgrades? 

2. What is the importance of component positioning tools? How can I evaluate their performance? 

Component positioning software tools locate components within the camera's field of view. This is often the first step in any vision application, from simple robotic pick-and-place operations to complex assembly verification tasks. It is also a critical step because it often determines the success or failure of the application. If you cannot locate the component, then you cannot inspect, measure or identify the component. 

While it sounds simple enough, positioning components can be extremely challenging in a real production environment. The vision system is trained to recognize components based on patterns, but even a tightly controlled manufacturing process allows for some variation in the way components appear to the vision system. Therefore, the vision system's component positioning tools must be smart enough to quickly and accurately compare training patterns to actual items moving on the production line and allow for some variation in component appearance. It is important for a component matching tool to be able to tolerate relatively large changes in comparison and ignore lighting changes, while always positioning the correct component with sufficient reliability. 

3. Does the vision system have a comprehensive image preprocessing tool library? 

Image preprocessing tools alter the original image to emphasize desired features while minimizing undesirable features. This sets the stage for performance gains with more powerful tools that can significantly increase the accuracy and power of the entire system. Preprocessing tools can: 

●Improve the contrast between the component and its background; 

●Hide unimportant and potentially confusing image features; 

●Eliminate “bright spots” caused by component surface reflections, and 

●Smoothen rough surface texture. 

Make sure the vision system you choose includes comprehensive image preprocessing tools. 

4. What character reading and verification features should I look for? 

Whether you're reading alphanumeric codes embossed on automotive components or verifying date and batch code information on pill bottles or packaging, you'll want to look for a variety of capabilities when evaluating character reading and verification tools, including: 

Powerful OCR technology for handling process changes 

TOCR tools should be able to handle typical printing variations such as stroke width changes, character skew, background changes, character sticking and a wide range of printing process changes. Having a high read rate is extremely important. 

Easy font training 

This feature builds fonts by learning character models that appear as a series of images. Images should contain multiple examples of each character and cover the entire range of qualities likely to occur in production. 

Built-in image preprocessing tools 

These tools should have the ability to sharpen the contrast of character edges and filter out unimportant background in images. 

Flexible domain functionality 

Flexible field functionality refers to the ability to field both fixed and variable string lengths. 

5. How can I determine the repeatability of a vision system measurement tool? 

If one of your applications involves critical dimensional measurements, the vision system’s measurement tools must be precise and have very high repeatability. 

The vision system should have a full set of measurement tools, allowing you to select the appropriate tools to meet the needs of your measurement application without having to write custom scripts or functions. 

For high-precision measurements, the vision system should be able to correct lens distortions that may affect measurements, especially in the outer areas of the image. 

6. Evaluate industrial code reading tools? What specific features should I look for? 

Industrial environments require vision systems that can read 2D data matrix codes with degraded quality, poor mark quality, or location variations from component to component. The vision system should achieve good reading results regardless of the component material (such as metal, glass, ceramic, plastic, etc.) and the component marking method used (such as dotting, etching, hot stamping, inkjet, etc.). 

In addition to these criteria, other specific code reading capabilities you need to look for include: 

Code quality verification 

Look for visual products that can verify code quality against established standards. 

This can provide valuable information about how well the marking process is performing. 

Reading speed 

Depending on your production line speed and throughput needs, you may need a very high-speed barcode reader. The fast vision systems currently available can read more than 7,200 codes per minute. 

7. What networking and communications features should I look for? 

Networking is an essential feature for many vision applications as a means of sharing information, supporting decision-making and enabling efficient integrated processes. For example, networking enables vision systems to transmit pass/fail results to a PC for analysis, or to communicate directly with PLCs, robots, and other factory automation equipment in integrated process control systems. 

If you need to connect your vision system to PCs at an enterprise level, choose a system that supports a comprehensive library of standard networking protocols: 

●TCP/IP client/server enables vision systems to easily share structural data with other vision systems and control devices over Ethernet without developing any code. 

●FTP (File Transfer Protocol) allows inspection images to be stored on the network for later analysis. 

●Telnet is an Internet standard protocol that allows remote login and connection from a host device. 

●DHCP (Dynamic Host Configuration Protocol) allows the vision system to automatically obtain its network IP address from the server, allowing for true plug-and-play performance. 

●DNS (Domain Name Service) allows you to assign a meaningful name to each vision system, such as "Bottling Line System 1", instead of having to use a numeric IP address. 

For a vision system to integrate with PLCs, robots, and other automation equipment on your factory floor, the system you choose must also support the following protocols: 

●Industrial Ethernet protocols, such as EtherNet/IP, PROFINET, MC protocol, POWERLINK and Modbus TCP. These enable vision systems to connect to most common PLCs and other devices via a single Ethernet cable, eliminating the need for complex wiring schemes and expensive network gateways. 

●Fieldbus network, including CC-Link, DeviceNet and Profibus. A protocol gateway accessory is often required to add a vision system to a Fieldbus network. 

●RS-232 and RS-485 serial protocols, which are required to communicate with most robot controllers. 

Finally, as vision systems are increasingly used throughout the manufacturing process, the need to manage these systems in a centralized manner becomes increasingly important. Make sure the vision system you choose integrates the appropriate software that allows you to easily monitor the operation of all your vision systems remotely from any location over the network—whether inside or outside the factory floor. 

8. What should I know about vision system accessories? 

Many times, people pay too much attention to the evaluation of vision systems and ignore the importance of accessories. The choice of accessories can go a long way toward ensuring trouble-free integration of the system and, where lighting needs to be provided, may even determine the success or failure of the application. 

To ensure that you can integrate your system quickly and easily, it is important to purchase your vision system from a supplier that offers a comprehensive range of compatible accessories. This will allow you to see if each accessory has been tested and proven to be compatible with the vision system. More importantly, during the application evaluation process, sales personnel should be able to help identify light sources and optical component solutions that provide the opportunity to ensure successful vision applications. 

Accessories you should look for include: 

● Light sources - Any two production areas have different ambient lighting conditions, and components may exhibit a wide range of surface characteristics. Almost every machine vision solution requires a unique lighting approach to meet its application goals and optimize performance. Your vision system supplier should offer a variety of different light source options, including: ring lights, which provide soft, even illumination from all directions; backlights, which create maximum contrast between the element and its background; darkfield lighting , which provides low-angle illumination for image acquisition of surface-irregular components. 

● Communication modules - Make sure your supplier offers a variety of communication peripherals, such as I/O modules and networked gateway modules, that support easy and fast connections between vision systems and PLCs, robots and other factory automation equipment and networks. 

●Operator Panel - Networked operator panel allows for easy plug-and-play setup and deployment as well as continuous vision system monitoring without a PC. When choosing an operator panel, look for a type that has an intuitive, touch-screen interface and supports multiple camera views. Other features to look for include high-speed visualization, which allows you to view images and overlay graphics on the production line so operators can easily modify inspection parameters and view inspection results on the equipment. It should also be rugged enough to withstand the challenges of harsh production environments, with an LCD display that protects against the effects of glare and a NEMA-rated mounting bezel to provide a dust- and water-tight seal when mounted within a panel or enclosure. 

Integrated light source 

Integrated light sources provide great convenience and ease of use in vision systems. Integrated light sources simplify the system by eliminating the need to purchase, install and power additional light sources. Having an integrated light source makes the vision system smaller and more compact than other systems that require a larger external light source and power source, making it easier to install and use in hard-to-reach spaces on the production line. The vision system you are looking for should be able to control brightness and strobe of integrated and external light sources without the need for additional equipment. This eliminates the need to purchase additional light sources or power supplies. 

9. Does the vision system supplier offer a wide range of hardware options? Are they rugged enough for my environment? 

The vendor you choose should be able to offer you a wide selection of systems that vary in performance, resolution, and durability. You can't buy "completely universal" machine vision. Your application may require a line scan camera rather than an area scan system or a color system. You may also require higher resolution to meet your tighter tolerance standards, or a system that can withstand washdown environments. Your supplier should be able to offer options that meet both your inspection needs and your actual application environment. 

Other questions include: Do you have space on your production line to install a vision system? If space is limited, options should be provided that fit the actual size of the space as well as image acquisition options. For example, if your product has limited viewing space, a line scan camera may be an option you could consider. Unlike area scan cameras, which need to see the entire component to take a complete snapshot, line scan cameras only need to see a small portion of the product to build the entire image into memory. Think of this comparison as between a photo copier (area scan) and a desktop scanner (line scan). 

If the vision system installation space is limited, a smaller package will occupy less space and require less installation space. If you have considered practical space constraints, now the question to ask is what resolution is required for your particular application. The resolution of a vision system is the size of the imager used, expressed in pixels. Generally speaking, the more pixels you have, the more data you collect per feature. The more data you have per feature, the more accurate and repeatable your measurements will be. To understand resolution, ask yourself, what field of view do I need? Do I need to capture the width of the assembly line, a portion of a larger component, or the entire component itself? What do I need to see in the image to inspect this component? Use these answers to determine the target resolution. For example: Your inspection requires counting the number of components on a pallet. If your field of view is the width of your assembly line (say 12 inches), and your vision system has a resolution of 40x480, then you will have 640 pixels equal to 12 inches. This works out to 53 pixels per inch (or 0.018 inches per pixel). If you only need to count the number of components on each pallet, this resolution may be sufficient for your needs. However, if you need to measure the width of each component and the tolerance range is +/-0.001 inches, then higher pixels will give you more data about each feature to ensure tolerance accuracy. 

Sometimes, even with a specific light source and filtering capabilities, the features you are inspecting do not provide sufficient contrast in a monochromatic vision system. Color systems help you complete your inspection by showing you the subtle features and color differences you need. 

Some vision systems are assembled into rugged IP- and NEMA-rated metal packages that provide protection against dust and moisture, eliminating the need for separate housing accessories. However, if your facility's environment is particularly harsh, or equipment needs to be flushed frequently, you should ask your potential supplier if they can provide prequalified external packaging for the system. 

10. Does the vision system supplier provide the support and learning services I need? 

Even a high-performance vision system is only as good as the supplier behind it. Whether you purchase a vision system from a reseller, a system integrator, or directly from the manufacturer, it is important to understand upfront the full range of support services that can be provided to you. Make sure the vision vendor you choose understands your unique support needs and provides you with all the resources you'll need at every stage of your project, from application development and system integration to deployment and beyond.