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June 17, 2003

5 Min Read
E-shots Web Exclusive: Giving your plant vision

At the very least vision sensors can serve as another set of eyes on the shop floor, but when integrated to their fullest, they can become a hub for process automation, quality control and inspection, and a myriad of other responsibilities. For this product to achieve its full potential, however, it’s necessary to ask the right questions from the supplier and examine your own operation, in order to choose a vision system that fully meets the needs of your plant.

Addressing the need to adequately plan for choosing a vision system, Cognex Corp. (Natick, MA), a manufacturer of vision equipment for industry, has released an informational packet on the topic entitled, "Buying a Vision Sensor: 10 Questions You Must Ask." Along with 10 queries essential for making an informed purchase, the guide also includes a variety of vision tips and different tests that can be performed to make sure vision systems have the capabilities to fulfill any vision needs. Following are synopses of the 10 questions.

What is the importance of part-location tools, and how can I assess their performance?

Part-location tools are based off software that’s tasked with locating the desired component within the camera’s field of view. Variables that affect this include part rotation (components shifting in transit), optical-scale changes (discrepancies in the component-to-camera distance), inconsistent lighting (light fluctuations due to external sunlight etc.), and variations in part appearance (manufacturing inconsistencies that create disparate parts).

What role do built-in network communications play, and what capabilities should I look for?

Allowing vision systems to communicate pass/fail inspection results to quality control PC workstations, network-enabled vision sensors also permit vision equipment to link with PLCs, robots, and other automation. Cognex says it’s wise to make sure the system supports a wide range of standard network protocols including SMTP, FTP, DHCP, DNS, TCP/IP client/server, and Telnet. For connection to automation devices that support industrial protocols, check for Ethernet/IP and ModBus/TCP.

Does this vision sensor make it easy to set up applications and create custom graphical user interfaces?

Requiring operator interface for part-changeover modifications, tolerance adjustments, or failure definition, a custom graphical user interface that’s configurable depending on system setup simplifies operation. Rudimentary options should include display of pass/fail results data and turning inspection on or off as desired.

Does the sensor have sufficient image preprocessing tools?

Since the sensors are used to pinpoint very specific part defects that may have subtle characteristics, a quality vision sensor will use a variety of preprocessing tools to assess the raw part image. Some standard functions that augment this feature include the ability to improve contrast between part edges and background, extraneous image-data filtering, part-surface reflection elimination, and rough-texture smoothing.

What should I look for in character reading and verification capabilities?

Creation date, material, and location are among the myriad of printed data that now appear on many parts, and ensuring that the information is present and legible is important. Some options that help vision systems with this task include statistical font training (where a reference image is created from a series of images to account for variations), image preprocessing tools (can sharpen contrast around characters), and instant image recall (immediately brings up failed images so line operators can determine the defect cause).

How can I determine the repeatability of a vision sensor’s gauging tools?

Accuracy is of obvious importance in vision sensors, but consistent accuracy is even more vital. Vision sensors tasked with checking critical dimensions, need a full suite of gauging tools. One simple way to check repeatability is to measure a part under identical circumstances—lighting, position, camera distance—and determine if there are unaccepted deviations.

How do I evaluate industrial code-reading tools, and what are some specific features to look for?

No matter if they’re are made by dot peen, etching, hot stamping, or with an ink jet, vision sensors should be able to read 2-D codes. Even if the markings are poorly formed or degraded, a quality vision sensor can still determine the code. There are some common capabilities that should be checked for before procurement, including code quality verification capability (verifies codes according to established standards), read/second rate (according to production line speed), and instant image recall (ability to instantly view a failed code and determine the defect’s root).

What should I know about vision sensor accessories?

Vision sensors come with an array of accessories, which ultimately can determine the efficacy of the new system. In terms of lighting accessories, the vision system vendor should offer a variety of options, including ring lights, back lights, and dark-field lights to cover the spectrum of part shapes and the plant’s ambient illumination.

For communications, ensure that peripherals like I/O and network gateway modules are present for quick connections to robots, PLCs, and other automation devices. LCD displays with antiglare impact shielding are a good idea for monitors, and the camera enclosures should protect against dust and water.

Does the vision sensor require a PC?

Standalone vision sensors that don’t require a PC should be available for configuration and production modes. Out of the box, users should be able to set it up quickly, and it shouldn’t require that a PC is dragged out onto the shop floor every time a parameter’s changed.

What types of product support services are offered?

From initial install to down-the-road troubleshooting, vendors shouldn’t abandon their customers. Some questions to ask include whether the rep is a vision specialist, how the application will be evaluated once installed, is product support available post-purchase, and is there online "self-help" or onsite training available to acquaint staff with the tool.

For more information contact Cognex Corp. (Natick, MA) at (508) 650-3000 or visit its website at www.cognex.com.

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