Retaining ring measurement
Vision sensor improves ring measurement process
Rotor Clip is the world’s leading manufacturer of retaining rings, producing billions of rings annually at its 238,000 square foot production facility in Somerset, New Jersey. From steering wheel assemblies to household appliances, Rotor Clip retaining rings help secure components onto shafts and inside bores. Rings are produced in a wide range of sizes, from 1/25” (1mm) to 35” (889mm).
While the company has long relied on micrometers for measuring ring dimensions, operators were having trouble measuring rings that were less than half an inch in size. “When you have a ring that is about 1/8” in diameter, it’s very difficult for an operator to handle and place them in a micrometer,” explains Ed Engracia, a Design Engineer for Rotor Clip. “Also, when the operator is using a vernier caliper, there’s a lot of room for error. The operator could be pressing too hard in one instance, too lightly in another.”
Measurement speed, according to Engracia, was another problem. Manually measuring six small-sized rings, he says, can take an operator up to 20 minutes.
To speed up the measurement process and improve accuracy, the company recently added an In-Sight® 1000 machine vision system from Cognex to its manufacturing line. The In-Sight 1000 is a high-performance, general purpose vision system which incorporates a full library of vision software tools, built-in discrete I/O, a vision spreadsheet interface for application set up, and built-in Ethernet communications in a compact, self-contained unit.
According to Engracia, one of the primary reasons the In-Sight system was selected was due to its ability to store individual measurement programs or “jobs” that corresponded to each ring type via the vision spreadsheet interface. “We had to make things as easy as possible for our operators since they had no previous experience with machine vision,“ he says. “In-Sight was attractive because it had built in functions, which made it easy to customize a job for each part we wanted to measure with the vision system. So all the operator needs to do is call up the job to start.”
To set up the programs, Engracia selected vision tools and parameters from the spreadsheet’s drop-down menus. The vision spreadsheet then automatically generated tool results into worksheet cells, which were linked together to set up the measurement routine for each part.
Engracia designed the inspection station so the micrometer equipment and vision system are housed in the same hooded enclosure. Operators retrieve retaining rings from collection bins, and after a few thickness measurements are taken by micrometers, a single ring is placed on a four-inch backlight component under the vision sensor. Backlighting, according to Engracia, provides the optimal image contrast to get good dimensional data.
Once the operator brings up the measurement program that corresponds to the ring’s size, In-Sight captures an image of the ring from seven inches above and transfers it to its built-in vision processor. There, a number of vision software tools are used to analyze the image.
“We measure a lot of different features,” says Engracia. “On some rings, we only look at outside diameter and lug size, whereas for another ring type we might need to measure the inside diameter, min sections, max sections, and lug hole diameters. Needless to say, it was important to have a range of vision tools to choose from so we could handle the different rings.”
More specifically, Engracia uses the In-Sight PatFind® pattern location tool, which verifies the presence/absence of the part and applies a virtual fixture to “fixture” the part for the different measuring functions, the Find Circle Tool, which measures diameters, and the Find Segment Tool, which measures segment sizes.
As the measurements occur, operators can get a real-time view on a color LCD screen that is built into the inspection station enclosure. “We were able to create a custom user interface with In-Sight that displays the various dimensions of the ring taken with the camera, and pass/fail lights in green and red which indicate if the part is good or bad,” explains Engracia. “If any of the dimensions fall outside of tolerance, it’s usually an indication of the die being out of adjustment, in which case they have to stop the production equipment and make adjustments to the dies.”
One interesting feature of the new inspection station is that the micrometer equipment and vision sensor are linked via Ethernet, thus allowing thickness measurement data from the micrometers to be uploaded into the In-Sight program. The combined micrometer and vision data is then sent over into a Quality Assurance database, giving QA engineers instant access to statistical data on each part in the event there is a customer complaint. “If we need to backtrack on any problems that arise, it’s a lot easier for us to get the data we need from a database versus looking through paperwork,” Engracia explains. “In-Sight puts everything into computer form, so the QA guys can just cut and paste the data into their statistical software.”
In-Sight’s built-in Ethernet communications also makes life easier for Engracia when he needs to monitor or control vision activity remotely. “If someone’s having a problem on the floor, I can check it right from my desk and sometimes troubleshoot right from there. I can also load new In-Sight programs remotely as they are needed.”
Since the In-Sight system was implemented since January 2003, it has improved Rotor Clip’s measurement accuracy, and the company has been able to reduce its overall measurement time by 75%. “Since our guys no longer have to handle such small parts, they can get the measurements done in far less time. What used to take 20 minutes for six rings is now down to five,” says Engracia.
The company is currently in the process of adding another In-Sight system, the In-Sight 4001 -- which provides high-resolution optics (1024 x 768 pixels) for capturing high-accuracy images of larger parts. This sensor will be designated for inspecting retaining rings up to four inches in diameter.