Research On The Size Measurement System For Hot Forgings Based On The Image Edge Recognition

As a part of equipment manufacturing industry,large forgings have a wide range of application in the field of electric power,petrochemical industry,metallurgy,shipbuilding,aerospace,etc.They are often used in the occasion for high performance requirements just like nuclear power unit and chemical reaction vessel.Therefore,the quality of large forgings relating the property and lives safety of people.However,current measurement methods have some problems like low measurement accuracy and low measurement efficiency.In some place,manual measurement method is even still used,workers have to hold measurement tools to measure forgings in high temperature environment.Low accuracy of size measurement for forgings leads to not only bad inner structure but also great waste of resources.Therefore,it has important significance to improve the techonolgy of measuring for forgings.Based on lots of research before,aiming at the problems of current measurement method,a measurement method for large forgings based on image edge recognition has been proposed in this paper.The details are as follows:Fistly,measurement system is built.Green laser and CCD camera are fixed on the platform which can slide on the guide rail.The position information of the platform can be got by the pulse coder.The pulse coder can deliver the information to PLC.The pulse coder,the servo motor and the PLC constitute a closed loop system.Images captured by CCD can be delivered to the computer by TCP/IP.The PLC is connected to the computer by RS-232 C interface.The program in the computer can display images and position information in real time.Secondly,a method for identifying edges of forgings is proposed.The optic axis of CCD camera and the laser line are not in the same plane,which leads to that the laser line in images will break when the laser illuminate on the forging.Recognizing the laser line in images by HSI model.Then monitor the change of laser's gray level in images.Thirdly,factors affecting the measuring accuracy are analyzed.Improving the working efficency of the system by determining the ROI(region of interest).Reducing the high temperature radiation effects on CCD camera by adding a band-pass filter.Determining the optimal position of CCD camera and forgings by the establishment of rough surface scattering model.Determining the width of laser stripe for minimum measurement error by analyzing the influence of the width of the laser stripe on CCD camera's imaging.Finally,the experimental system is built to measure an actual forging.The experimental data are recorded.According to the analysis and processing of the measurement data,the feasibility and effectiveness of the system are verified.