Research On Detection Of Motor Rotor Position Based On Image Measurement Technology

At the present stage, detecting rotor position of rotate motor have defect:the fix of the sensor is inconvenient, and it is also limited in special measurement environment. Due largely to image measurement technology, the new detecting method was researched. The basic task of image measurement technology was that extracting useful information from image frame sequence to realize measurement, which was important research area of machine vision. The parameter of the feature or movement of measuring target was set up by the way of digital image, then those needed parameter was found by processing and calculating digital image using related software or hardware, the procedure of whole image measurement was very convenient and this method could application widely. This technology was gradually became one of research hotspot in the present field of digital image. So taking advantage of this hotspot technology to detect the position of motor rotor was discussed by this subject.The detection of the motor rotor position was realized by measuring the rotation angle of rotor. So the project of this image measurement was designed:firstly, the surface image of rotor was collected by high speed CCD continuously when the motor was rotating, then convert collected image from Descartes coordinate to polar coordinate, lastly the every two converted images was calculated by phase correlation and the final rotation angle could be found easily. Because of this detection need accuracy and real-time, the improvement about this project was implemented as follows:firstly, in order to assure measurement accuracy, decreasing the measurement effect arisen from interference was taken; because of the measurement time must be as few as possible, preprocessing collected images to reduce interference was unsuited. It was a good way to reconstruct calculated image and the final calculated image had the advantage of resisting interference, this reconstructed image would attached to rotor surface. Secondly, how to decrease the calculating amount was studied, which can reduce measurement time. At the step of polar transformation, sampling part of pixels that related to calculated result closely according to measuring accuracy and the gray value of those pixels were calculating target, this method not only reduced the size of calculated image, but also avoided oversampled and undersampled area. The detection demand high precision, for realize higher precision, sub-pixel measurement technology was proposed.Some experiments were implemented to verify above measurement method, the results show that the reconstructed image could measure accurately, meanwhile it had good stability to most interference, this result was superior to the image that it can’t reconstruct. Since the adaptive sample method was used in polar transformation, the calculated time was reduced obviously and the measurement was also right. The experiment which selected one stepping motor as measurement object was made. The result shows that the accuracy rate of pixel precision can reach100%, and it can adapt a range of environment changes; at the same time, the measurement result of sub-pixel precision is not good enough and this sub-pixel measurement method need further study in the next days. The hardware implement of this image measurement technology is feasible according to analyze hardware support of FPGA. To sum up, the image measurement method which is found by this research subject can provide reliable method to detect motor rotor position.