Research On Measuring Algorithm For Safety Clearance Of Printed Circuit Board

Printed circuit board(PCB)is a core part of modern electronics and electrical products.Printed circuit board's safety distance is one of the most important contents on the safety standards.Printed circuit board's safety distance is related to safety performance of electronics and electrical products,including short circuit,electric shock protection,and it determine the product's performance to withstand voltage.Safety distance mainly including creepage distances and clearances.Now the common method carried out by inspection and quarantine bureau for printed circuit board creepage distances and clearances are as follows:first,selection measurement path by quality control staff,then measuring gage length of each segment path using calipers,micrometer,points,plug or other measuring implement,finally,each measuring gage length of each segment path is added for the result.This measurement method is time consuming effort,especially for some measurement path that need to avoid the holes and various shapes groove,Artificial choose the shortest path is easy to choose the wrong.Existing methods have been unable to meet the testing needs quality inspection departments.To solve these problems,machine vision technology is used for automatic measurement of printed circuit board safe distance.Both sides of the printed circuit board image are captured respectively by industrial cameras.Image noise is reduced and the image contrast is enhanced by image preprocessing.Automatic threshold segmentation algorithm is used to identify the wire in the region of interesting automatically to segment the wire from the background.And the clearances between the wires was automatically calculated according to the wire edges information.By identifying pad region and selecting the measuring pathaccordance with the principle set forth in safety standards automatically to calculate the clearance between pins and creepage distance between pins.Finally,some experiments are carried out to test the accuracy of measurement methods.And the measurement results are compared with calibration results.The experiments results are as follows: the deviations between measuring results and the calibration results in wires' clearances measuring is less of 0.04 mm,the deviations between measuring results and the calibration results in pins' clearances measuring is less of 0.1mm,the deviations between measuring results and the calibration results in pins' creepage distances measuring is less of0.2mm.In short,the measurement method meets the measurement requirements of printed circuit board safe distance.In this thesis,automatic measurement of clearances and creepage distances in printed circuit board is achieved by using machine vision technology.The measuring method has many advantages such as simple operation and high accuracy.It provides a new method for the measurement of printed circuit board safe distance.