By substituting robots for human operators, Doerfer Co. created an ABS assembly system that was precise and flexible.

Doerfer Co.’s advanced automation division (Greenville, SC) builds automated assembly machines for a number of industries. Recently, the company designed and constructed a system to assemble antilock braking system (ABS) components for a manufacturer with plants in China, Germany and the United States. Historically, the manufacturer had relied on a series of manual production lines to build its products, but this approach was no longer accurate enough to meet its customers’ needs. It was also inflexible, an increasing problem in light of its customers’ rapidly evolving product lines.

To solve these twin problems, engineers at Doerfer Co. created a flexible system employing a battery of robots from Stäubli Robotics (Duncan, SC). “The accuracy of the Stäubli robots was a major factor in choosing them,” says Doerfer controls group manager Robert Belk. “Their precision solved the problem of positioning parts more accurately and repeatedly…. In addition, the robots’ cycle time studies were very impressive.”

“Because the robots are pressing parts together, they need to maintain tolerances within a few microns,” says Doerfer program manager Bill Hein. “We were very concerned with the precision and repeatability required…. [The robots’] performance and accuracy contributed greatly to the value of our designs.”

In its final configuration, the new system includes a number of different robots performing a variety of tasks, including gauging, screw driving and pressing parts into the assemblies. Doerfer engineers chose a mix of six-axis pedestal-mounted RX160 and TX90L models, because of the machines’ longer reach and the fact that they could easily flip the parts for processing on all sides.

Currently, the company’s German plant has more robots, so that it can be fully automated, while the Chinese and U.S. lines are only semiautomated, with employees performing a handful of loading operations. Eventually, all three lines will be fully automated to accommodate the company’s production needs. However, at present, this semiautomated approach is the most cost effective.

During the design phase of the project, engineers carefully considered how the robots were going to grasp the components. According to Hein, “Once the robot gripped the part, we didn’t want it to let go while the part was being brought to a station, flipped, moved and rotated. This would help to maintain both flexibility and speed.” The solution, he says, included a combination of pneumatic grippers and vacuum cups, depending on the task being performed at each station.

The robots also employ a vision system, which allows them to locate and inspects parts during production. “Vision is needed for locating the product due to random arrangement on the pallets,” says Doerfer project manager Justin Nardone. “It also scans the product to be sure it’s the correct part for the process. Our team mounted the camera on the end of the robot arm. It’s not stationary over the conveyor. A photograph is taken to locate identifying features of the part, and the gripper position is tweaked based on feedback from the vision system.”

Finally, Nardone says the robots have been fully integrated into the plant’s digital process management system, so that they can be assured of performing their tasks correctly and consistently. “The production lines are software-intensive, because they are very database heavy,” Nardone says. “Each part has its own identity within the database. When the part arrives at a workstation, software gauges that part, sets the database interface and takes full control of the robot.”

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