As amazing as the human eye is, just about everyone knows that it’s unreliable in repetitive work, especially when the work involves judging slight differences in size. To avoid the mistakes that workers are bound to make from time to time, most manufacturers rely on automation for their quality checks these days.

Polaris Industries Inc. is no different. At its welding shop in Spirit Lake, Iowa, this manufacturer of motorcycles and side-by-side utility vehicles has had a long history of using touch and proximity sensors for checking parts in its welding fixtures. It uses these sensing techniques to verify that the operators have populated the fixtures with the right combination of components before welding them in the shop’s 15 robotic arc-welding cells. Recently, however, the company installed a vision system and discovered what other manufacturers have found—that today’s vision technology can be reliable “eyes” for integrated manufacturing.

The longstanding obstacle to machine vision at Polaris’ welding shop has been the environment. Historically, vision has not done well in dark and dirty operations that generate smoke. The perception at the shop was that the investment in lighting, programming, and keeping the environment and equipment clean was simply too great.

That changed, however, when welding engineer Jeff Steiner heard from Omaha, Neb.-based distributor Hartfiel Co. about vision technology from Dalsa Corp.’s Intelligent Product Division, in Billerica, Mass. Upon learning that the technology could check set-ups within 200 milliseconds (msec), Steiner wanted to see how this might streamline the inspection of loaded fixtures, which had been a bottleneck in a cell welding chassis components for Ranger utility vehicles.

The cell uses a work-changing device that resembles a two-seat Ferris wheel. The seats are opposite each other, such that one seat is in front of the welding robots while the other is facing the operator for loading. Each station has a pool-table-size fixture that is flexible enough to accommodate a family of frames that go into the different models in the Ranger line. Some of the parts in this family look similar, but vary slightly in size. Although the engineering staff has guarded against many loading errors by designing the parts to be as unique as possible, and the fixtures to hold them in only one orientation, this precaution had its limits. It was still possible for the operator either to forget a part, or, in certain locations, to insert the incorrect size into the fixture.

To ensure that the right parts were inser-ted, the cell’s two SK6 six-axis robots from Motoman Inc., of West Carrollton, Ohio, provided another line of defense. They checked the parts with touch sensors before welding began. Although touch sensing did the job fairly well, it required as much as 30 seconds of cycle time to check each part, which adds up to significant time after thousands of parts.

Productivity would suffer even more whenever the robots would find a problem. In these instances, the operator would have to take the time to retract the fixture, correct the problem, return the fixture to the welding position in front of the robots, and run the inspection routine again. Only then could production resume.

Justifying electronic eyes

The vision system improved production by relieving the robots of their touch probe inspection burden. Two Dalsa cameras are mounted on a frame built over the parts bins that are behind the operator as he faces the fixture that he is loading. While the robots are welding on one side of the two-station work changer, two stationary cameras inspect the set-up after the operator finishes populating the fixture. Not only does this arrangement conserve cycle time, but it also keeps the cameras away from the heat, spatter and fume produced by the welding process.

Another way that Dalsa’s iNspect software boosts efficiency is to display a color-coded picture of the parts on a monitor, green for good parts and red for bad ones. “The operators can identify any problems on their own, make the correction and try cycling it in again,” says Steiner. Consequently, the combination of relieving the robots of inspection duty and giving the operators the ability to check themselves reduced cycle time by 12.5 percent, which alone justified the project.

Besides increasing production, the software reduces scrap production in two ways. The first is by preventing the operator from running the wrong welding program. “Our controls engineer tied the vision system to the ladder logic of the Motoman MRC controller,” explains Steiner. Consequently, the vision software can compare the selected welding ...