Many robots can be purchased with built-in and tightly integrated vision systems, a departure from times past when OEMs had to buy the robot and the vision system separately and perform the integration. Both approaches have merits and drawbacks, depending on the specific application.
"We are currently working on a new and improved vision system that will be purchased separately from the robot vendor and then integrated by CMD," says Chris White, project manager for automation at CMD. "A PPT Vision camera system will provide increased functionality at reduced cost for our applications. The new system also will be simpler to program and more interactive with the user."
Integrated vision systems often are mounted directly on a robot, which can cause a problem, according to Doug Taylor of Concept Systems. "2-D machine vision systems all calibrate from a fixed camera position. When you mount the camera on the robot, the system becomes very difficult to integrate because the fixed calibration really needs an affine transform using the robot position to remain in calibration to the robot coordinates. Currently, no vision library provides this affine transformation in a ready-to-use manner."
[Editor's note: An affine transformation or affine map is a function between affine spaces which preserves points, straight lines and planes. Also, sets of parallel lines remain parallel after an affine transformation. An affine transformation does not necessarily preserve angles between lines or distances between points, though it does preserve ratios of distances between points lying on a straight line.]
Tom Spisak of Automated Cells & Equipment points out other drawbacks to integrated vision/robot systems. "Components and package pricing are higher," he says. "They use expensive, high-flex cables, and we've seen occasional delivery problems, especially for special items."
But some use integrated vision system to great success. "Epson's vision system was developed specifically to work with its robots," explains Cale Harbour, product manager at distributor and integrator Advanced Control Solutions (ACS) "It uses a remote camera head tied to its CV1 vision controller. The Epson robot controller talks seamlessly to this unit and communicates via EtherNet/IP with the main PLC running the machine."
An integrated robot/vision system will be more expensive up-front, but it can be applied with less engineering effort. For those with extensive in-house integration expertise, separates are often a better solution.
This sidebar story is part of the February 2014 cover story "Add Vision to Robots — See the Difference."
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