Precision calibration method for high-precise rotary encoder

A precision calibration method for being applied in a high-precise rotary encoder system, comprising:

• (1) providing the high-precise rotary encoder system comprising a rotary encoding body having an optical position surface, a laser speckle image capturing module having a 2D image sensor, an angle calibrating module, a controlling and processing module, and a deposing angle adjust module;
• wherein the deposing angle adjust module is connected to the 2D image sensor for making a precision calibration angle be included between the horizontal axis of the 2D image sensor and the horizontal axis of the rotary encoding body;
• (2) making the rotary encoding body continuously rotate by a constant small angle until the rotary encoding body rotates a full circle, and using the laser speckle image capturing module to treat a laser speckle image capturing process to the optical position surface during the rotation of the rotary encoding body, so as to obtain N+1frames of laser speckle image from the optical position surface and then store the N+1frames of laser speckle image in a data base of the controlling and processing module;
• moreover, a plurality of primary variation angles being defined by the angle calibrating module as the N+1frames of laser speckle image is captured;
• (3) using at least one image comparison library comprised by the controlling and processing module to treat a first frame of laser speckle image and a (N+1)-th laser speckle image frame in the N+1frames of laser speckle image with a key features matching process, so as to calculate a particular image displacement;
• (4) determining whether the particular image displacement is smaller than or equal to a small circumferential displacement produced as the rotary encoding body is rotated by the constant small angle, if yes, proceeding to step (5);
• otherwise, proceeding to the step (2);
• (5) using the at least one image comparison library to treat each of two adjacent frames of laser speckle image in the N frames of laser speckle image with the key features matching process for obtaining N number of image displacements, and then N number of secondary variation angles corresponding to the N laser speckle image frames and the N number of image displacements being respectively calculated;
• (6) immediately turning the rotary encoding body by an arbitrary angle and simultaneously using the laser speckle image capturing module to capture an immediate laser speckle image frame form the optical position surface;
• therefore, the controlling and processing module is able to calculate an immediate angle coordinate corresponding to the immediate laser speckle image by using the at least one image comparison library as well as based on the primary variation angles, the secondary variation angles and the N number of image displacements;
• wherein when the step (5) is executed, a α rotation matrix being used for treating the image displacements with a displacement vector transforming process.