Detection And Calibration Procedure For The Center Of Pressure Of The Force Plate

The center of pressure(COP) is an important reference data of the human body biomechanical study. The human body curve of COP directly reflects the ankle muscular nerve control and applying pattern, which is significant for illness diagnosis and rehabilitation.In order to measure the curve, a strain force plate was made. It composes of measuring force platform, A/D datum collection, PC/104 and software. Due to the properties of components of the sensor or the ambient environment, errors could occur, which make the force plate inaccuracy. Thus, this paper designed the detection system of the force plate and calibrated the output characteristics. This research is as follow:Firstly, the detection system of the force plate was designed by Microsoft Visual Studio2010, and the software programs used the latest generation of programming language--C#.By making use of the systematic interface operation, the error of the force plate can be gauged conveniently. The detection interface for the force plate combined with SQL Server 2008 database software, which made the test data can be saved. This system could detect the accuracy of the force plate and record the test data. The test data was use for calibration when the force plate was inaccuracy.Secondly, the sources of error were analyzed, the Least-Squares method was proposed.Based on the reference location data and the force plate signals output data, a nonlinear model to calibrate the output characteristic of the COP is developed. Then, in view of least square error, the optimum solution of the model could be got. The model was applied to the force plate, and the results show that the calibration procedure reduced COP error of the force plate to 2 mm.Thirdly, after the calibration of the force plate, we found that the errors were different in different places. The errors in the middle of the load platform were small and the errors on the edge of the load platform were large. In order to get a higher accuracy, a correction method based on two-dimensional interpolation is applied. The thesis carried through study on triangle grid mesh in two-dimensional region to obtain the distribution of the errors in different places. Then errors a compensation method was developed to solve the problem of the errors distribution. The results show that the calibration procedure reduced COP errors of the force plate to 1 mm.Through a series of characteristic calibration experiments, the center of the pressureerrors were reduced over 90% and less than 1 mm, which provided reference for later research and application of the force plate.