The Research And Design Of Video Extensometer

Material tester is an experiment for testing mechanics capability of materials.It is widely used in metallurgy architecture petrochemical processing education scientific research and so on. At present, we use strain gauge to do this work.But this kind of tester's precision is not so good, especially low when measuring minute displacement ,so that large observation magement error occurs.Then it is hard to get a precise description of testing material mechanics capability at the rupture moment.and it is impossible to observe the transverse dimensional change and its mechanics capability. Attention is paid to researching a new kind of photoelectric extensometer and a self-contained data processing system,develop the material tester's capability.Campare to traditional extensometer , the photoelectric extensometer can achieve real-time measuring,and has a better precision(field range 110cm precision 3um),and even at the rupture moment it is still able to get the exact value.Because of un-contact measure,it is less conditioned by outer circumstances,so it will be widely applied.Its flow of work is as follow:first,CCD scan the material that glared by illumination source,then it transmits the data of reticles'location every time to Video Capture Card and then to PC.there our programmed software process these data,we can work out the material shape change of any time. In structure,it has two parts :hardware and software.hardware part is consisted of light source CCD and Video Capture Card and so on.the software is programmed by VC++,it is able to real our measure algorithm-- least squares fitting process and cubic spline interpolation fitting process.Light source is very important in the measure system,it has great influence on video and measure precision.we make red diode as light source.It is bright and its light efficency is good,and little volume,easy to control.so it is the best choice in our system.Our CCD is Toshiba TCD2557D,it is a high sensitive RGB CCD,has great resolution(5340 pixels),it is enough for our experiment.In algorithm processing,in order to get a better precision ,we adopt fitting process. least squares fitting process gets a better result than cubic spline interpolation fitting process,In the experiment,the length of CCD and material is 1.1m.CCD is over against the material bottom mark line.When the system works,there are six wave crests on the display,the crest is the location of mark line.Red diode is applied,so we choose the red crest as measure data.after data processing,we get the satisfactory result,so our design is feasible.