High Precision Small Contact Angle Measurement System

The contact angle is considered as one of the most important parameters to measure the surface energy of a solid material,and it is also an important parameter of the wettability of the material surface.So,the contact angle measurement system is widely used in many fields such as modern industry,for example,medicine,semiconductor,material protection,life sciences and other fields.The current development of image processing technology and machine measurement technology provides possibilities for continuous improvement of contact angle measurement accuracy and automation level.The subject first completed the build of hardware and software for a high-accuracy contact angle measurement system.The system realizes manual sample injection of contact angles and precise automatic measurement of angle values.The theoretical calculation value of contact angle measurement is accurate to four decimal places.Secondly,the software part of this measurement system is characterized by modularization,customization,virtual instrumentation,automation and high precision.The software are mixed programming with Labview and Matlab,and GUI interface is used to directly control CMOS camera through USB.In a contact angle photogrammetry experiment in which a group of original imaging quality is relatively low,it is shown that the standard deviation of contact angle by this system is approximately 0.5°,while the manual measurement contact angle error is approximately 2.0°,which is obtained by the system.So,it is drawn that this automatic measurement of the contact angle is more accurate than the manual measurement result and can improve the accuracy of the measurement of the small contact angle.Thirdly,regarding the applicability of the measurement principle of this system,this study found that in the case of a contact angle range of 0°-10°,different contact angles are obtained with volume angle method,volume height method,circle fitting method,and ellipse fitting method separately.Measurement methods have different theoretical errors.Through experimental and theoretical analysis,the angle measured by JC2000 DM contact angle meter is the standard.Although the contact angle error rate measured by the four methods is between 0 and 10%,the overall contact angle error rate measured by the circle fitting method is smaller than the other three average errors.5%-10%.So,the available circle fitting method is the best contact angle measurement method in this case.Finally,in the search of one of the key links in this system,a Canny operator based on particle swarm optimization is proposed for image edge detection in the image algorithm analysis.Through experiments,it is proved that the edge detection image obtained by the operator can get a clear and continuous droplet contour.The precision of angle value obtained by using other edge detection operators to measure the angle of contact angle is improved.Therefore,it is concluded that the application of particle swarm optimization(PSO)Canny operator can improve the angle value accuracy of small contact angle.In this paper,starting from the search for the contact angle measurement method and the image algorithm analysis technology,the high accuracy of the small contact angle measurement is achieved,and the measurement speed is fast and the precision is high.