Technology for treading carefully

The latest automated solutions can solve barcode reading and inspection challenges in tyre manufacturing

Tracking and traceability are primary requirements for all tyre manufacturers. For quality control and compliance purposes, tyres are tracked at every step of the production process. However, black rubber is hardly a material that lends itself to automated reading technologies, setting a challenge for those looking to supply solutions to this fast-paced area of automotive manufacturing.
 
According to Gianbattista Gualeni, senior application engineer for machine vision at Datalogic, two different automated mark-reading technologies are used in tyre plants, one for barcode reading and the other for colour-mark inspection. Both technologies must operate at high performance rates for a large range of tyre sizes and shapes on the same production line.
 
“For colour-mark inspection, the dynamic range in reflectiveness is particularly challenging, since black rubber can vary from extreme absorption to high reflectivity after finishing,” says Gualeni. “The design of the lighting system is critical in eliminating the range in contrasts.

"Additionally, because the surface of the tyre is not flat, colour marks can be placed on top of characters or other features on the tyre, causing them to become distorted or incongruent. Inspecting these colour codes while still assessing the quality of the mark requires powerful software algorithms.”

Colour-mark inspection
Datalogic’s colour-mark inspection solution is a standalone system which inspects tyres for coloured marks added after the finishing process. The marks indicate to vehicle manufacturers the rotational placement of the tyre to match with the wheel hub. The system includes a top-and-bottom machine vision inspection system. The top reader uses two colour M-Series cameras in an IP67 enclosure connected to an MX-80 vision processor. The bottom inspection system uses another pair of colour cameras in combination with a large format mirror.

The system also includes LED illuminators, a frame and enclosure, as well as a power control cabinet. As a standalone system, integration into existing conveyor lines is straightforward, as is connection to existing communications protocols. Typically, this might be an Ethernet TCP/IP connection from the system to a host PC, although digital I/O outputs to a PLC can also be facilitated.
 
“The colour-mark inspection system typically reads at a 99.9% confirmation rate for false-positive results in a controlled environment,” states Gualeni. “In this case a false-positive indicates that the colour mark is either not present or below the customer’s determined quality threshold.”

Barcode reading
So what of reading barcodes on tyres? The biggest challenge here is the small height of the barcode compared with the size of the tyre. The application becomes more difficult since barcode quality is often poor or damaged due to the typically aggressive production environment. Datalogic’s solution is the STS400. Shipped pre-configured and ready for use without any calibration, the system is based on Matrix 410 2D imagers in array form. The imagers overlap within the reading area and provide redundant coverage of the tyres. Moreover, the system can detect the absence of a barcode.

“The STS400 also interfaces with a supervisory software program, WebSentinel, which saves images in real time from the barcode reader,” says Gualeni. “WebSentinel allows the manufacturer to view images of any tyre that passed under the array. Managers can use these images to understand the operation and improve efficiencies in the plant.”
 
Gualeni says that the STS400’s reading and redundant capability are immune to the effects of tyre spray treatments. Since multiple images are acquired for the same tyre, if one image presents reflections over the barcode the following image will be at a different angle and will not show the reflection. Additional compensation for reflections is provided by the side-to-side overlap in the reading area of the adjacent Matrix 410 imagers, since these devices also record images of the tyre at different angles. 
 
“Ultimately, the primary advantage of any imager versus lasers is reading performance,” says Gualeni. “Historically, lasers have been used in tyre manufacturing. The next step chronologically was linear cameras, which offered improved performance but at a higher cost. The most current solution is an array of 2D imagers, which delivers the best performance of any solution, and at the lowest price point. Two-dimensional imagers can capture the entire barcode, which has a very low code height. Capturing the entire code in one image ensures very aggressive decoding performance.”

Tyre traceability
Among the tyre manufacturers able to testify to this fact is Continental, which has recently enhanced its tyre traceability thanks to an automated Datalogic STS400 solution. Continental production ranges from 40,000 to 80,000 tyres per day. The previously implemented laser technology was not able to guarantee an effective read rate because of the low aspect ratio codes of the barcodes, shrinkage of the practical height and resolution (due to vulcanisation) and spray treatments. Each no-read item required additional manual handling with a significant impact on production costs.

Continental wanted to overcome these issues with a solution that could be replicated in any of its production plants worldwide, and so selected Datalogic’s STS400. Siegfried Rainer, head of manufacturing and quality systems of Continental HQ, says: “We selected Datalogic because their omni-directional reading solution for tyre identification provides the highest read rates and has the potential to adapt to our future needs.”

Minimising read failures
When the lifecycle of a tyre spans multiple locations and buildings, accurate tyre identification is essential not just for managing quality control and compliance but for keeping tabs on WIP, sorting and routing. Cognex is another technology supplier that says it can integrate proprietary machine vision knowledge, identification expertise and high-performance barcode reading technology into pre-configured systems that meet tyre industry requirements.[sam_ad id=17 codes='true']

The company has recently introduced Cognex Tire Solutions, a suite of products designed to solve barcode and low-contrast, embossed character-reading challenges for tyre manufacturers. “These solutions are designed to support code-reading applications to minimise read failures and increase throughput and production efficiency, all while decreasing costly rework,” says Carl Gerst, vice-president and business unit manager, ID products. 
 
With patented algorithms for high-speed barcode reading and optical character recognition (OCR), Cognex Tire Solutions aim to reduce costs and underpin process improvement. The suite of products offers features such as ‘1DMax+ with Hotbars’ algorithms that Cognex says provide the highest read rates in the industry, even with damaged or low-contrast barcodes. Furthermore, DataMan fixed-mount readers means no moving parts, which in turn decreases maintenance costs, while image-based readers allow operators to see what the reader 'sees' for troubleshooting support and ongoing improvement efforts.
 
Also part of the suite is Cognex’s Xpand technology, which enables barcode readers to cover a larger field of view with less equipment, while the DS1000 series 3D sensor reads embossed characters on curved, dark surfaces at speeds of up to one tyre revolution per second. OCRMax vision technology is said to yield high-contrast reading results from low-contrast reading environments, and DS1000 software delivers 3D and 2D vision toolsets for additional inspection capabilities. Finally, the Cognex Connect communications suite makes it easy to integrate Cognex Tire Solutions with factory networks.

Specific applications
The uptake in the latest reading technology is evident worldwide. However, some tyre manufacturers prefer to approach independent system integrators who can make whole-market hardware and software choices based on specific applications. UK-based Machine Vision Technology is among those that offer this route. The company says it has seen growing demand from customers who need to record and store the DOT codes of every tyre fitted to a vehicle. In fact, MVT says that a major automotive supplier recently approached the company to devise a reliable and economic vision system for this very application.
 
DOT codes comprise information such as the manufacturer’s ID and date of manufacture, which has to be recorded against the vehicle when built. In this particular application, for which MVT developed a 3D solution, the challenges to overcome included: over 300 tyre and wheel combinations across a range of vehicles, wheel and tyre sizes; a target process cycle time of 16 seconds, including tyre handling and rotation; and a need for the code to appear on only one side of the tyre. In light of its success in solving these issues, MVT believes it is earning a reputation as a company that is capable of solving difficult OCR projects with which others often struggle.