质量控制和检查头显示器

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Cognex ensures long-term customer satisfaction and cost-efficient quality control for BMW in Munich

BMW clients expect the best and demand the most accurate equipment when buying a car from the Munich based manufacturer. Increased demand for a “head-up display” (HUD), meant that BMW needed to find a quality control system for their HUDs. This system would need to cope with the speed of their production line while maintaining high safety standards.

Quality control for HUDs at the facilities of the automobile manufacturer BMW, is presently installed on the production-lines of the 5- and 6-series, and is an example of the most performing industrial image processing.

A new perspective for BMW drivers

The advantages of a HUD as an option in a car have created a rapid increase in demand. The HUD is a driver information device, developed and produced by Siemens VDO Automotive. The image-producing unit of the head-up display projects a virtual image onto the windscreen by means of an array of optical mirror systems. The displayed image is projected in the viewing field of the driver at a distance of about 2m. The driver can therefore perceive all important information regarding the vehicle and navigation within his normal field of viewing. In this way, the driver has optimal access to information with minimum disruption of concentration.

如果HUD甚至略微错位，这将干扰驾驶员对周围环境的感知，例如街道标记，房屋的垂直线或车库进入。

Image Quality: The decisive criterion

That is why the imaging quality of the projected display in the vehicle is the decisive criterion for acceptance of the HUD by the user. Automobile manufacturer BMW in Munich was concerned with the introduction of a head-up display as an optional equipment feature for the new car types of the 5- and 6-series. For this purpose, the department for Technical Integration at the Research- and Innovation Center of BMW in Munich needed a precise quality control suitable for industrial use. The fact that up to this point there was no appropriate quality control system based on image processing available meant the objective was to develop an absolutely new product within a very tight time frame.

一个全新的解决方案

测量方法的控制成像定性ty of HUDs had previously been developed in the laboratory, but there was still a long way to go to reach a solution for the production process. These studies provided important target specifications for the preparation of the system design for this quality assurance project. To add to the technical constraints, this quality control system would have to cope with the interaction of the windscreen and the projection of the HUD installed in the vehicle. Even minor defects in a completely assembled vehicle would not be tolerated at the end of the assembly line.

On the basis of the system design specifications, BMW’s “Technical Integration”-division (hereafter referred to as “TI”) contacted several suppliers of machine vision systems seeking a solution based on image processing which would work with the required quality assurance system of the head-up display. In mid 2002, they decided to work with Gefasoft GmbH, a Partner System Integrator (PSI) of Cognex. Their system solution demonstrated an advanced approach which convinced those responsible at BMW.

时机和可追溯性

必须确定测量参数，然后在不中断生产的情况下快速有效地检查。生产线的定时频率确定了可用于测试的时间，当然，用于头顶显示器的完整测试系统必须通过在预定义的时间范围内运行并应对相应数量的车辆来证明经济上的可行性。测试系统必须适合左侧和右侧转向。另一个要求意味着，HUD的测试系统也需要完全可追溯，并嵌入整个公司网络的信息基础架构中。

精确而公正

Ultimately, the testing system of the HUD has to provide an objective result regarding quality, evaluating and assessing with much greater precision and reliability than the user. It was already clear in the feasibility study and during project planning, that this could only be handled with a PC-based high performance image processing system. Efficient hardware was required, and the algorithms of the vision software would be demanded to function with utmost reliability and precision.

No jams or standstills are tolerated on BMW’s two-shift assembly lines. The complete image acquisition- and- evaluation process of 50 acquired test images must be completed within a time-frame of less than two minutes.

完整的testing-equipment has to be swung into the vehicle as production is in progress, positioned exactly, secured in place, and then needs to be removed from the vehicle again. This means a time-slot of approximately 30 seconds for image acquisition and image processing calculations in the test-cycle.

Cognex PC-based vision systems: the highest degree of reliability

投影虚拟图像的各种视觉质量使图像的评估变得更加困难。但是，在不断变化的环境生产条件下，图像处理不能成为质量控制错误的原因。除其他问题外，这包括在不同的照明条件下的问题主题“显示的对比”。

Vision tools from the CVL (Cognex Vision Library) proved to be of great advantage. They provide interactive access to different programming levels, in-depth vision-software, including an option for a more precise detail-optimization. That is enabled the final solution –the selection of the tools, parameterization, linking and detail optimization –to be completed with a higher degree of safety and within a shorter development time.

Reliable detection in difficult conditions

Cognex vision tools perform to the highest of standards without compromising accuracy or safety. The most important individual features in the object image, such as edges, measurements, shapes, angles, bends and shades, are specifically and separately identified. The spatial conditions and relations between these central features of the acquired image are compared with the real-time image. The position of the object is then precisely determined according to this information.

Certain features can therefore be recognized at a considerably higher level of reliability, precision and speed. The influences of changing conditions of illumination and contrast are eliminated by a simultaneous investigation of the contour and the structure of the object image. These qualities proved to be of advantage in the detection of deformations and distortions of the HUDs. The functional safety of the vision tools also satisfied standards specified by BMW, which required it to be above 99%.

Meeting high standards

The image processing system must fulfill certain standards at BMW, and Cognex has for many years been among the suppliers who meet these requirements. The only real issue of interest is the reliable operation of the complete system. A stand-alone system could not be permitted on a globally parameterized production system. The most important issue for those working at the plant was that the image processing be fully and reliably integrated into the plant diagnosis system.

长期可追溯性以达到客户满意度

The cooperation with Gefasoft proved to be of great benefit; the enterprise contributed greatly to the solution thanks to their flexibility and their capacity to react quickly within a limited schedule. By 2004, the first head-up display testing systems were installed. The positive results of the operation resulted in the head-up display testing systems also being installed in the normal series production in the factory at Dingolfing. Today, approximately a dozen HUD testing systems are in operation for BMW around-the-clock, ensuring the faultless quality of the HUDs. The test results are stored in a database in the central server, thus providing for total traceability. The test-images are archived, and in case of customer requests, the flawless condition of the product at the time of delivery can be proven, even years later.