Image courtesy of Cognex imaging and machine vision europe june/july 2010 www.imveurope.com


automotive production


cars.’ Fixing faults becomes more difficult and expensive the longer the production line is allowed to run incorrectly.


Inspecting for stopping power Metal components for cars are produced by forging and casting methods. High-speed vision sensors coupled with laser triangulation, high- speed vision cards and software allow every one of these components to be checked: ‘You can use this kind of machine to inspect all of the surfaces of a raw brake disc as it is produced,’ explains Grannec, referring to the forged steel blanks which are supplied to automotive manufacturers to be machined as required. ‘You can detect lack of material, a surplus of material, mould coats, or any problems with the shape of the disks. You can even perform accurate geometric measurements. Casting processes in particular are problematic, and they can be unstable,’ he says. Edixia’s system means that the manufacturers of these components are able to measure 100 per cent of production in- line, with no contact. A non-contact solution is important due to the temperatures involved: ‘When you have a warm brake disk, coming out [of the forging equipment] every four seconds, and want to inspect all the surfaces of the 90°C brake disk, you’re in trouble if you want to touch that. It used to be done by hundreds of manual operators, and now it can be automated. If you want to be able to detect a half-millimetre lack of material on a raw surface, you better have a good sensor, a good electronic vision card, and very good software.’ Similar systems are used for examining the cast components produced for engine blocks and cylinders (prior to machining).


Track and trace While the measurement-driven systems supplied by machine vision companies such as Edixia are highly capable when it comes to identifying faulty components, vision systems also provide a vital role in ensuring that no faulty components make it onto the road. So-called track and trace solutions allow manufacturers to follow an individual component as it makes its way through the production line, and gives accountability later for errors arising in manufacturing. US-based machine vision pioneer Cognex


has been involved in traceability since the early 1980s. ‘Machine vision traceability really came during the early to mid 1990s with the development of 2D symbology – the data matrix code,’ says Leigh Jordan, senior sales engineer at Cognex. ‘This was the first practical data


carrier that was useful for industry. Everything up until then worked well in the lab or on labels, but didn’t really work so well when you went into industrial applications.’ Unlike a 1D barcode, which can be read


incorrectly, a 2D data matrix code reads correctly or not at all. US-based Microscan Systems has a long history with data matrices, including the acquisition of the companies that developed the technology. John Agapakis, director of OEM business development at the company, highlights some of the other advantages of the technology for automotive applications: ‘The information is carried by the presence or absence of dot in a cell, which allows extremely low contrast marks to be read. Therefore, the mark can be placed directly on a part and still be read. This is not possible with a barcode: Barcodes require very high contrast, in the region of 80 per cent,’ he says, adding that this is the reason barcodes must be on sticky labels. ‘You can put [the 2D code] directly on a crank shaft, you can


‘DPM ensures parts are paired for best performance at the lowest cost’


put it on a piston, or an engine, and so on. This is what allows all of the applications. It’s possible to read marks in very difficult places – marks with a very low contrast, or marks with a lot of damage, substantial surface non- uniformities, or marks with a lot of occlusions from oils and cutting fluids.’ Additionally, he says, the cameras reading the marks can be encased in IP67 or IP68 rated housings, so they can be close to the mark no matter what the environment. Jordan explains the importance of track


and trace solutions: ‘If there’s been a defective batch of parts that have been brought in from a supplier, they can immediately track down the affected components. If faulty products get out into the field, you’re talking telephone digits in order to recall all of those back in, and [track and trace] allows all of these things to be absolutely quarantined,’ he says. Microscan’s Agapakis agrees: ‘The closer to the fault that you can find [the problem], the lower the cost for the manufacturer; God forbid you actually have to recall cars after they have reached consumers! The ability to know what product has gone through what process at what time gives that ability, which is called “reject spill containment” in the automotive world. Most automotive companies do this, by marking


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Data matrix codes allow automotive components to be traced as they move through production


serial numbers onto the components.’ In addition to spill containment, direct part marking (or DPM) is used to ensure parts are paired for best performance at the lowest cost: ‘Every part is produced to a certain tolerance range,’ says Agapakis. ‘For the best performance in an engine, you want to make sure that the tolerances of the components match; you want to ensure, for example, that you don’t take the widest piston and pair it with the narrowest cylinder. On the other hand, if you make the tolerances extremely tight, you have much higher production costs,’ he says. When fitting components together in this way, they are measured during production and then sorted by their tolerance range. ‘This used to be done by tying a label onto each part, and then matching those by eye, and then people started using barcodes, but the advent of data matrix has led to people using that technology.’


Contact to infinity Both Cognex and Microscan have begun incorporating liquid lenses into their readers: ‘Liquid lens technology is incredibly exciting,’ says Jordan of Cognex. ‘The lens is an oil and water meniscus, and by applying different voltages to that we can change the distortion characteristics of the lens. It’s fast to re-focus, there are no moving parts, and we can have a depth of field from contact to infinity. The readers will be able to read a code right in front of them, or a large barcode twenty feet away.’ These developments strengthen the position


of machine vision in automotive production. ‘In this industry, you have to be an expert in lighting, cameras, in software, in lasers, in cabling, in dust and temperature and other things,’ says Grannec. With imaging technology being driven forwards by the goals of efficient automotive production, our fictional robot servants have never been closer to reality.


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