Very Low-Cost In-Process Gauging System J. W. V. Miller, V. Shridhar, E. Wicke, and C. Griffth University of Michigan-Dearborn ABSTRACT A vision system to gauge two types of automotive parts has been developed. One of the part types is a power steering connector in which the depth and width of the groove, and the distance between the start of the groove and the end of the power steering line are gauged. For the second type of part, a crimped connector attached to a brake hose, measurements of interest are the two diameters of the crimp and the bell length where the hose is inserted into the connector. A standard video camera is used to acquire the image of a back-illuminated image of the part which is digitized and captured with a frame grabber. The basic hardware to accomplish the gauging tasks consists of a standard video camera, light source, frame grabber and industrial personal computer. In order to minimize hardware costs, a standard 50mm C-mount camera lens and extension tube was used with the video camera. Consideration had been made to use more expensive telecentric optics so that parts placement would not cause a change in magnification with a resulting loss of accuracy. With the 50 mm lens, however, magnification effects were lessened due to the greater standoff distance between camera and part. For image acquisition, a low-cost PCI-bus frame grabber-card was chosen. With this type of card, high-speed video capture is possible due to the very wide bandwidth of the PCI bus. Combined with a Pentium-based PC, rapid image acquisition and analysis can be performed so that every part can be gauged at full production rates. Since the gauging rate exceeds the production rate by a significant factor, a single computer and frame grabber with camera multiplexer can process data in real time from up to four measurement stations simultaneously. Keywords: vision ,video, measurement, inspection, real-time, manufacturing, automotive 1. INTRODUCTION Currently, it is possible to purchase the components for a vision system at a cost well under $4000 for some applications. New personal computers have processing capabilities that were only available in much more expensive work stations several years ago. Advances in multimedia hardware have provided very inexpensive image acquisition capabilities, and improved image analysis techniques have reduced the need for highly regulated (and expensive) illumination sources. Many applications, of course, cannot be addressed with this type of hardware, especially if extensive image analysis and processing must be accomplished in a short time or if special hardware is required for image acquisition. However, for suitable applications, economical solutions are possible. The following paper describes a low-cost gauging system for two families of automotive parts, a power steering connector and a brake hose connector. In order to gauge these parts, a video camera is used to acquire a back-illuminated image or silhouette of the part. The video image is then digitized with a frame grabber and stored in computer memory. The digitized image is processed so that key features in the image can be identified and the distance in pixels between these features calculated and converted to inches with a calibration factor. Both part types to be gauged by the system need to be fabricated correctly. If a given part is out of tolerance, it can significantly degrade the safety and reliability of a vehicle where it has been installed. A back-illuminated image of a power steering connector is shown in Fig. 1. Here, the feature of interest is the groove which appears as the “notch” in the narrower part of the profile. Fig. 2 is an image of a brake hose crimp. The features of interest here are the minimum diameters of the two crimped regions and the location of the leftmost minimum diameter to the end of the fitting. The basic hardware to accomplish the gauging tasks consists of a standard video camera, light source, frame grabber and industrial personal computer. Figure 1. Power Steering Connector Figure 2. Brake Hose ConnectorA standard 50mm C-mount camera lens and extension tube was used with the video camera. For image acquisition, a low-cost PCI-bus frame grabber-card was selected. With a Pentium CPU, rapid image analysis can be performed so that every part can be gauged at production rates. In fact, gauging speed exceeds production rates by a significant factor so that a single computer and frame grabber is able to gauge parts at up to 4 gauging stations. Each station consists of a video camera and illumination source plus any necessary fixturing hardware. A camera multiplexer is used with the image capture hardware to access image data from each camera. In order to provide a user-friendly system, a graphical user interface has been developed which displays inspection results, keeps a log file of results, and provides setup and calibration modes. A tolerance file can be created and modified for each station through the interface. Various aspects of the system are described in the following narrative starting with optics and illumination considerations. This is followed by descriptions of the computer hardware and the gauging algorithms developed for this system. Aspects of the graphical user interface are then presented. In the last section, results and general observations are presented. 2. OPTICS AND ILLUMINATION Since the parts would be back illuminated, it was assumed that few lighting problems would be encountered. While this was basically true, light reflecting off of the camera lens would sometimes cause bright areas within the silhouetted part and caused measurement problems as illustrated in Fig. 3. To minimize this problem both software modifications, described later, and optical modifications were made. The classic optical solution, circular polarization, was employed by inserting a polarizer between the object and camera lens at a 45° angle to the direction of illumination. This insured that light could not be reflected off of the polarizer onto the part and the polarizer removed any light reflected off of the camera lens. Rather than use a highly