QMT Features: March 2007
100% quality check
A vision systems solution automatically measures engine manifolds as part of an in-line production process at Mahle Filter Systems to guarantee 100% quality of parts produced. By Earl Yardley, Industrial Vision Systems.

The use of vision in the automotive industry is continuing to grow as new and diverse applications are found. For plastic mould manufacturers in this industry there is an expectation to deliver zero PPM defects to their automotive customers; this equates to no flashing, no shorts, and part tolerances to ever decreasing finite levels. Industrial Vision Systems has developed a solution to automatically measure engine manifolds as part of the in-line production process at Mahle Filter Systems.

Intake or inlet manifolds form part of automotive engines that supply the fuel/air mixture to the cylinders. An exhaust manifold then collects these exhaust gases from multiple cylinders and channels them into one pipe. Designed using a polyamide reinforced with glass fibers, these flow-moulded manifolds must be perfectly formed to fit to the cylinder head of the engine. If the mix of polyamide and glass fiber is not correct, shrinkage of the manifold will occur resulting in an improper fit. As well, the injection moulded manufacturing process may introduce unwanted artifacts that may need to be repaired before final assembly.

To ensure the integrity of these manifolds, Mahle called upon Industrial Vision Systems to develop an automated system that checks the bolt holes used to mount the manifold to the engine. Industrial Vision Systems integrated the system onto the line at Mahle with a Sepro robot presenting the moulded part to the vision system as part of the process.

Imaging process

To image the through-hole bolts on such a large part, the manifold is illuminated with a high-intensity 46-in white linear LED lighting unit. By placing the manifold on a white reflective plastic background, white light is reflected through all seven of the manifold’s bolt holes (Figure 1). This reduces the cost of the illumination required and ensures that light is evenly reflected through the bolt holes.

Before any inspection of these holes can be accomplished, a single high resolution digital FireWire camera from Neurocheck is used to image a blow-by pipe that forms part of the manifold. These pipes vent blow-by gasses, a mixture of unburned fuel, air and combustion products that leak past the engine’s piston rings while the engine is running. Such vents avoid pressurising the crankcase, which would otherwise force oil from the engine. Measuring the width of this pipe ensures the accuracy of the flow-moulding process and, once verified, that further bolt-hole inspections can take place.

This blow-by pipe required special illumination to ensure that it could be imaged correctly. Using a white LED spotlight, light was directed to one side of the pipe and reflected back from the rear of the manifold. This light then created a silhouette of the pipe that presented the imaging system with white-on-black and black-on-white edges of the part that could be easily measured (Figure 2).

After images of the blowhole are transferred in real time, the IVS Neurocheck software measures the diameter of the part. As images are captured, a calibration routine determines the real-world values that that make up each pixel. Two regions of interest (ROIs) are then defined at the right hand and left hand side of the image. A threshold level within these ROIs is then set and the edges of the pipe are then determined. After this, a software gauge measures the distance between them. This measurement is then correlated with known part variances and the blow-by pipe either accepted as a known good feature or, in the case of a failure, used to indicate automatically to the controller that the flow-moulding process is inaccurate.

Once the blow-by pipe is verified, the bolt holes used to attach the manifold to the engine block are inspected. To determine the distance between the holes, the centre of gravity of each hole must be calculated. To accomplish this, three digital Firewire cameras are positioned on an overhead gantry in such a way that each camera images three bolt holes. To determine the distances between each of the bolt holes, the centroid of each hole must be determined and the distance between each hole then computed. Because three bolt holes are imaged with each camera, the distances between individual holes can be determined.

Multiple cameras

For each of the three cameras used in the system, the same image processing functions are performed. To calculate the proper linear measurements between all seven bolt holes, each camera is used to image three centroid measurements. To accomplish this, the system must generate a global measurement list that accurately describes the distance between individual bolt holes and the distances between the two that are farthest apart. Because each camera images three such holes, the distance between the first three, second three and final three can be measured by computing the distance using images from each of the cameras.

By overlapping captured images, data from camera one and two can then be combined to provide a measurement list across seven holes. Then, by using data from the third camera, a measurement list is created that shows the distance between all seven bolt holes. In Neurocheck, the Combine Measurement list is used in two stages to determine this data.

After each blow-by pipe and bolt holes are inspected, integrated industrial control functions within the Neurocheck software are used to send I/O data to the programmable logic controller integrated within the Sepro robot x-y-z positioning system. Should a part fail the test, then the manifold is rejected. Parts that have passed inspection (Figure 3) are then moved to a separate conveyor system where they are shipped for packaging to automotive suppliers.

As each manifold is presented to the inspection system as it emerges from the flow moulding system, it is inspected while hot. As can be imagined, dimensions of such parts will be slightly larger that those of the finished shipped parts. To account for this, single parts are removed from the flow-moulding system by the robot at hourly intervals and allowed to cool. These are then re-positioned within the machine vision system and the parameters of the blow-by pipe and the bolt holes measured.

Because there is a known shrinkage that occurs during this process, the values generated are then compared with those of known hot parts. By comparing these differences with known calibration coefficients can then alert the operator as to whether the flow moulding system is performing as expected.

Mahle is now using the system to guarantee 100 percent quality of parts produced. The use of vision systems as part of the production process offers Mahle the confidence that every product shipped to their customers is within specification.


Tel: +44 (0) 1865 823322

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