Defect Detection and Full Surface Characterization of High Curvature Cathode Filaments

Abstract

Surface defects of cathode filaments of microwave magnetron would cause magnetron failure and scrapped microwave systems. Therefore, surface defects on cathode filaments must be carefully inspected. Conventionally, filaments are manually and visually inspected using their amplified images under an optical microscope. This is because automatic defect detection of cathode filaments is a challenging problem. The difficulty comings from its complex surface shape with multiple turns of high curvature spiral circles, which occlude each other. Such complex shape prevents capturing of sharp focusing images, which are essential for a computerized automatic detection algorithm. Further, the variable nature of production defects complicated the process of automatic defect detection task. To solve these problems, this paper proposes an automatic defect detection method to deal with issues related to complex shapes containing occlusions as well as high curvatures, particularly for the quality inspection of spiral shaped cathode filaments. The method includes a novel digital scanner, which sequentially brings all sections of the filament sides into sharp focusing of the optical imaging system. The method also employs multiple optical systems to imaging multi-sides of the spiral filament. The computational algorithm primarily uses line-detectors. In an evaluation experiment, the proposed method was used to automatically inspect over 14 million cathode filaments. Experimental results indicate that its false negative rate was 0.0065%, and its false positive rate was 6.83%. This indicates that the proposed method could successfully detect all kinds of surface defects at over 99.99% accuracy. It reduces the workload for manual inspection from 100% down to 93.17%, over an order of magnitude reduction. Further, the efficiency of the proposed method is 70 spiral filaments per minute, satisfying the requirements of online quality detection of existing manufacturing lines of filament cathodes. Introduction Cathode magnetron are widely used in both military applications1,2 as well as household microwaves3,4. The core of a cathode magnetron is the cathode filament, which is typically made of thorium tungsten or barium-tungsten alloy. When excited at a high voltage, the cathode filament of a magnetron cathode within a microwave oven would generate Tera Hertz frequency microwaves causing water molecules to move, vibrate, and bump into other food molecules at high frequencies. In this way, the filament inside a cathode converts electromagnetic energy into heat, which is quickly absorbed by the food. Therefore, the filament within a cathode magnetron is the core component of a microwave oven. Though the chemical composition of the cathode filament determines the escape power, emission stability, and lifespan of a microwave oven. However, when the chemical composition is optimized and fixed, the manufacturing quality of the cathode filament determines the International Conference on Modeling, Analysis, Simulation Technologies and Applications (MASTA 2019) Copyright © 2019, the Authors. Published by Atlantis Press. This is an open access article under the CC BY-NC license (http://creativecommons.org/licenses/by-nc/4.0/). Advances in Intelligent Systems Research, volume 168