Shadow Mask Inspection System for Color TV Picture Tubes

This is an On-line flexible video based system for automated inspection / measurement of the shadow mask used in television and computer monitors. The system consists of a vision system, integrated with a positioning system and user friendly software developed on a windows platform.

Image Processing System

The Shadow Mask Inspection System is used for measuring the slot width, bridge width and pitches (Horizontal and Vertical) of the apertures of the Shadow Mask. The system has a video camera positioned on the top of the Shadow Mask. The Shadow Mask is firmly held in position with the help of suitable fixtures and the arrangement has X and Y movement.

The video camera captures the image of the shadow mask at the desired location specified by the user. The image captured by the camera is digitized using a PC add-on Frame Grabber Card. The captured data is accessible by the Software. The image is then processed using advanced image processing algorithms and the result is displayed on the PC. A diffused lighting arrangement is provided to enhance the quality of the acquired images.

Vision Software

The flexible Vision Software allows the user to select the type and shape of the mask apertures to be measured/inspected.

In addition, an option to select the gun or screen side of the mask is provided. User defined inputs such as tolerance limits for each parameter being measured, region of interest (ROI) for measurement etc., can be entered for each analysis. The shadow mask is inspected for the following parameters at different locations on the mask namely slot width, bridge width, horizontal and vertical pitch of the apertures. The front screen displays a mimic diagram which represents the mask under inspection. The expected and measured values of the apertured dimensions are also displayed. The pass/fail status is indicated on the mimic screen by red/green dots at the corresponding x-y locations. A provision for displaying the on-line picture of the mask under inspection, when needed, is provided to manually calculate the aperture size, pitch and other parameters of the Shadow Mask.

The results of each inspection, accepted tolerances and user defined values are stored in the database for further processing and report generation. Detailed and summary reports based on batch ID, type of masks selected and parameters measured are provided. Bar graphs and Histograms are used to provide detailed SPC reports and analysis. An option to make a hard copy of the same is also provided.

Applications

The primary application of the Vision System is for inspection of shadow masks used in television and computer monitors. The system can be used as a quality control tool during the manufacturing of masks. The modular design of the software system allows a great degree of customization in relatively short time for other inspection applications involving gauging and measurement.