LEONI Machine Vision System delivers detailed automotive engine inspections on the fly

The detailed nature of automotive manufacturing imposes a high cost for errors — even minor, easily missed defects. Such was the issue for one major automaker who found that improperly clamped hoses on its oil and coolant lines were behind some of the most common sources of warranty claims. The automaker invited LEONI vision engineers to develop a solution, beginning at one of several assembly plants for the car model in question.

The facility LEONI visited produces two engine models: a 4-cylinder engine that required inspection of hose clamps in six spots and a 6-cylinder model that needed inspection of four clamped connections. Human operators attach the hoses with spring clamps that are initially held open by a clip inserted through a notch. Manual release of the clip clamps it shut, allowing it to apply pressure around the hose.

Toward the end of the line, human operators checked that all clips were fully released and the clamps correctly positioned and orientated. But the task demanded sustained attention to multiple details that, over time, could make even experienced inspectors prone to fatigue-induced errors. Automating the inspection was an obvious solution, but the application posed several challenges for the team.

A Moving Target

LEONI vision engineers singled out two considerations that would affect the design of their application. First, human operators often attached clamps so that their clips were not entirely visible from a particular angle, which put a priority on ensuring they were correctly oriented on the hose. This would not only ensure cameras had an unbroken line of sight and minimize perspective error when verifying a clip was released, it would also facilitate easier removal of the clamp for maintenance purposes in a fully assembled and integrated vehicle.

Another consideration for LEONI’s vision engineers was that both engine models swung from chains as they traveled down the assembly line, which meant they were in constant, erratic motion as they traveled through the inspection station.

LEONI developed a solution that measured each clamp’s position (i.e., its proximity to the end of the hose) and orientation (i.e., on which side of the hose the latch was located). Encoders embedded upstream-fed engine position data to LEONI’s vision systems, and precision laser switches triggered their imaging sequence when the engines reached the correct position.

LEONI Vision

LEONI’s inspection station positioned four 2-MP cameras aimed at areas of interest and chose optics with a long depth of field to accommodate image capture on the fly. The system also flooded the engines with evenly distributed, diffused light from multiple high-intensity bar lights to minimize the effect of shadow in image details while also allowing a faster shutter speed to eliminate any motion blur.

Image data from LEONI’s system linked back to the line’s programmable logic controller to shuttle engines with a suspected defect aside. It also fed image data to human operators to alert them where clamp position or orientation might need correction.

Final Adjustments for Success

During initial testing of the system, the LEONI team found that some final minor adjustments were needed. “Machine vision likes consistency, and while the manually applied clamps were often correctly applied to hoses and engine, their orientation was occasionally outside the vision system’s threshold,” said James Reed, Vision Product Manager at LEONI. “As a result, the system produced a few false negatives.”

The automaker retrained its assembly operators to adhere to a more repeatable orientation for clamps. Likewise, Reed adds, LEONI adjusted the tolerance of its system to define the correct clamp position to be within 5 millimeters of its nominal position on a hose.

Because LEONI’s solution was a retrofit, it adapted to the existing line speed. However, with the final adjustments, its system read rate accuracy approached 100%, supporting a significant reduction in costly warranty claims for improperly attached hoses. As a result, the automaker now plans to implement LEONI’s automated inspection system at several of its other assembly plants.