JUNE 24--Until now, optical character recognition (OCR), a method of detecting and reading characters, has been limited to PC-based vision systems. The deployment of the In-Sight 3000 Vision Sensor from Cognex (www.cognex.com) as a stand-alone system at ZF Getriebe GmbH in Saarbrücken (www.zf.com) has made this application simpler and more economical.
ZF Friedrichshafen AG is an independent supplier of automotive driveline and chassis technology worldwide. The company manufactures automatic transmissions for some 20 car makers throughout the world. The entire production process at ZF Getriebe GmbH is controlled by rigorous quality-management system. Machine-vision processing supports production in several areas. In the past a "type plate" showing the serial and parts list numbers was manually attached to each transmission by riveting. This operation has limitations including exposing employees to a high level of noise.
The test bed-planning department accepted the task of automating the "type plate" process. This department is responsible for designing and equipping the final acceptance testing operation at ZF car driveline technology. The new concept involved replacing the "type plate" with cast lettering and placing it in a rectangular area on the transmission housing. The variable transmission data (serial and parts list numbers) were to be directly integrated in the cast housing.
This would provide a permanent and reliable means of identifying each transmission. Once marked in this way, cameras and image processing techniques could verify both the existence and the unambiguous legibility of the lettering. The planning engineer, Martin Schuler, remarks, "In this way we planned to simplify the process and enhance its efficiency while improving quality at the same time."
A feasibility study was conducted, and the contract to implement the project was awarded to Joachim Richter, a company based in Konken. This enterprise provides flexible identification systems comprising automatic engraving, lettering and marking devices and is progressively focusing on complete custom solutions in addition to its standard products.
The project was implemented and the hardware installed in August 2002, and considerable flexibility was needed from the image-processing system. Only one transmission-housing model was available for the initial laboratory phase. To achieve the desired versatility for various transmission types, the system had to be flexible and easily modifiable, which made the requirements even tougher. The project also had to remain within an economical budget framework.
Richter's Oliver Bill, the project manager, recalls, "In the form of a stand-alone system, the Vision Sensor represented a space-saving solution that was easy to use." It was good fortune that Cognex equipped its In-Sight 3000 stand-alone Vision Sensors with integrated OCV/OCR software as standard just before the project-planning phase. This played a key role in the attribution of the contract in the face of competition from two rival bids.
Thanks to the integrated Ethernet interface, the In-Sight Vision Sensors can be managed, monitored, and controlled at each stage of production from anywhere within the corporate network. These low-cost Vision Sensors house an extensive preinstalled library of Cognex's market-leading vision tools. Installation, use, and parameterization are extremely easy.
The various transmission types arrive at the inspection and marking station in a random sequence. The vision system makes sure that the engravings, including the serial number, are positioned exactly in the correct place on each casting since the type plate surfaces on the transmission housings differ due to natural variation in the casting process and the use of various outside suppliers. The benefits of Cognex's position indication software are obvious in such an environment thanks to simple programming options and reliability. Optical character recognition is one of the most demanding image-processing applications, requiring a very high performance processor to run the complex evaluation algorithms. This explains why OCR applications have previously been run exclusively by PC-based systems
The characters produced by the automatic engraver must be clearly legible within a strict, adjustable quality band. The vision system detects engravings that are too shallow or too deep and thus difficult to read with absolute dependability. The character-evaluation system also detects wear or damage to the engraving tool and issues a fault message accordingly.
Five different transmission types are currently being marked and inspected in three shifts, and a further three transmission types are to be added soon. In this application the In-Sight 3000 Vision Sensor provides a reliable solution to the tasks of position indication and optical character recognition. The favorable outcome of this project has encouraged ZF Getriebe GmbH to carry out further project studies on additional applications for vision sensors within their manufacturing facilities.
The camera with annular lamp is situated directly underneath the automatic engraver. The In-Sight 3000 stand-alone system determines the position of the text and reads the characters by OCR inspection.
The finished transmissions pass through the inspection and marking system in a three-shift operation.
