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MPC Chooses Cognex to Error-Proof Oil Cap Assembly

Miniature Precision Components

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Machine vision is a key component of automation strategy

With molding machines ranging in size from 25 to 550 tons, Miniature Precision Components, Inc. (MPC) supplies the automotive and commercial industries with high-quality injection-molded parts and assemblies. Supplying parts to the world’s leading automotive companies leaves no room for error. That’s why MPC uses three vision sensors to error-proof the automated assembly of oil caps at its Prairie du Chien, WI facility.

Quality through automation

“Machine vision has been a key component of our automation strategy,” explains Shane Harsha, MPC Manufacturing Engineering Manager. An automated oil cap assembly system is a case in point. MPC recently augmented traditional tooling and sensor technology with vision sensors from Cognex.

Control Part Orientation

The MPC oil cap assembly system installs o-ring seals into molded thermoplastic caps and then prints on top of the caps. The system uses two vibratory bowl feeders about four feet in diameter. One feeds o-rings and the other feeds oil caps into the process.

Tight control of o-ring and cap orientation is critical to ensure the seal is properly installed so that the finished oil cap will function as intended. The cap must be in the correct orientation prior to pad printing in order to meet stringent quality requirements. O-rings that were very slightly warped or not perfectly flat occasionally made it past the tooling and were loaded upside down, causing the machine to shut down. Having operators flip these seals and restart the machine damaged the plant's efficiency.

Eliminate Flipped O-Rings

MPC selected three Cognex vision sensors to ensure proper o-ring and cap orientation.The first vision sensor detects inverted o-rings between the vibratory feeder bowl and inline conveyor. A second vision sensor checks that the o-ring is positioned properly on the dial fixture before the cap is pressed on. A third ensures proper cap orientation prior to assembly and printing.

To detect the inverted o-rings in this application, MPC used a Cognex vision sensor to identify the o-ring in the image by pattern, then verify the presence or absence of the sealing bead. The pattern sensor looks for the pattern of the sealing bead on the o-ring and then signals when it is detected. The pattern sensor remains in a fixed position relative to the part-finding sensor so that it is always in the correct location to look for the shape of the sealing bead. If the sealing bead is missing, a Cognex vision sensor sends an output through an optic coupler to a pneumatic solenoid that blows the inverted o-ring off of the line and back into the feeder bowl to be recirculated.

Simple Setup, Powerful Performance

Following this initial success, MPC chose to completely error-proof the oil cap assembly process. Two more vision sensors are at the next station where the cap is pressed onto the loaded o-ring. One is mounted on the moving pick-and-place arm. This allows the vision sensor to ensure the o-ring is properly loaded before the cap is pressed on. The other is fixed above the inline conveyor that feeds caps to the process. By training on two patterns, the vision sensor can determine cap orientation. If it is not in the correct orientation for installation, the vision sensor signals the pick-and-place arm controller to rotate the cap 180 degrees before placing it on the assembly dial.

The upgrade was very cost-effective and delivered greatly improved repeatability, helping MPC achieve more efficient production of defect-free oil caps.“[Cognex] vision sensors have helped us achieve zero-defect rates in the manufacturing process,” notes Harsha, “while lowering scrap. They are the perfect solution for many of our inspection and error-proofing applications.”

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