Correction of FPC solder position error based on mutual information entropy

Purpose - The purpose of this paper is to study the application of advanced computer image processing techniques for solving the problem of solder position error correction for flexible printed circuit (FPC) solder. Design/methodology/approach - To correct position error, image information is defined according to information theory, and the mutual information entropy (MIE) is applied in evaluating the correlation between the images. A reference image is acquired which is used to evaluate the correlation with the inspecting image. The MIE increases as the FPC solder positioning accuracy increases. When the referent and inspecting FPC solders are aligned with the same place, the MIE is at a maximum. According to the principle, a genetic algorithm integrated with MIE as a fitness function is applied to search for the best optimal correction parameters to improve positioning accuracy. Findings - The method is verified by a simulation and applied to the inspection system. As a result of experiment using four FPC solder samples, it has been demonstrated that the method can correct position errors. Research limitations/implications - The method of defective detection is not involved, although that of searching for and locating FPC solder is presented. Originality/value - The method of correcting position error based on MIE has high flexibility and can help improve positioning accuracy. In particular, it provides a new way to correct position error and can be implemented on any sort of target which is regular or irregular based on image technology.