There are two methods to correct the error caused by the laser galvo mirror scanning system: pre-distortion and post-correction. In the first method, the distortion function after the error is known in advance, and the correction function is obtained on this basis. However, it is often impossible to obtain the accurate distortion function during the specific operation process. In this case, fitting needs to be carried out for each distorted line to obtain the corresponding distortion function, and then the line is corrected with this function. based on post-correction, the error produced by the scanning galvanometer is corrected. According to the actual shape of the error graph after the galvanometer scanning, approximate fitting is carried out for the distortion shape of each vertical or horizontal line in the galvanometer graph using a quadratic curve. Using the quadratic curve, the variable produced by the error of each point on the original line is fitted onto each line after the error is produced, and the corresponding variable is calculated. By applying the reverse distortion amount to the original line, the correction function is obtained. The deflection angle of the x-axis galvanometer and the y-axis galvanometer are controlled to effectively correct the scanning error.
Based on the following assumptions, a corresponding algorithm is built: first, the error of the vertical and horizontal lines of the scanning graph appears according to the quadratic curve, and the line maintains the distortion of the quadratic curve; second, the correction center is the origin of the coordinate system; third, there is no error at the four corners of the square field; fourth, there is a positive correlation between the error amount of the vertical and horizontal lines and the distance between the line and the center.
Under this algorithm, the expression of the quadratic curve is determined by the coordinates of the two endpoints and the vertex. After determining the fitting expression of the maximum error quadratic curve, the expression of the correction curve is obtained by the reverse distortion. Assuming that the error amount in the x-axis and y-axis both have linear changes, the error of other lines can be clearly understood as an infinite and reverse correction curve. In the specific operation process, there is a certain deviation between the arc vertex point of the error curve and the assumed model position, which often translates in the distortion direction. The vertex point determines the error curve, so it is necessary to ensure that the expression of the error curve is more simplified or the center point is selected as the vertex point in the specific implementation process. The error amount obtained by this laser galvo mirror algorithm is larger than the actual error amount, so a correction coefficient needs to be introduced to adjust it. After continuous debugging to determine a suitable coefficient, the corrected coordinate points are scanned and inputted to initially shape the galvanometer scanning graph and effectively correct the error.
Through the above algorithm, the problem of laser galvo mirror scanning error can be effectively solved, saves cost, shortens calculation time, and achieves the final correction goal. This algorithm has been applied in multiple universities and has achieved significant results.
In actual operation, there are multiple factors that cause laser galvo mirror scanning errors. Non-linear errors caused by random factors are difficult to control effectively. To accurately correct the error, it is necessary to accurately measure the error between the actual graph and the expected target and compensate for the difference through reverse compensation. By compensating, the measurement results can be more close to the target value, and high precision values are obtained through multiple iterations. From the perspective of principle, the main solution is to solve angle deflection and coordinate mapping accuracy, and the precision and scanning speed of the xy galva scanning are the ultimate judgment indicators.