Báo Cáo Image processing based control system for precise position control of pcb screeen printer

Image processing based control system for precise position control of pcb screeen printer
​
In this paper, a precise position control system of PCB screen printer incorporating the image
processing technique is introduced. The positions of two fiducial marks drilled on the PCB are used as
the sensing points for the image processing to recognize the position errors in directions of
X ư Y ưθ coordinates. The precise alignment device is composed of X ư Y ưθ tables and the
tables are controlled by stepping motors which are driven by 80c196kc microprocessor based
controller. To decrease the noise effect in the image screen of the fiducial marks, we use two CCD
cameras with ultraviolet ray type of light source. Since the effect of the illumination change is
considerably decreased by using the ultraviolet light source, we can remove the filtering preprocessing
procedure in the image processing. The centers of the fiducial marks are obtained by a least square
error method. The sum for square of the errors between the circle equation with center position
( , ) 0 0 x y of radius r and the coordinate values of the boundary pixels on the images captured from
the fiducial marks is chosen as the criterion function. The exactness of the least square method is
compared to the simple method based on the concept of the average values for the abscissa and
ordinate of the center for the fiducial marks. By applying the developed precise position control
system for a practical PCB screen printing system, we can prove the effectiveness such that it realizes
the precision about 2.5àm in the position control of X ư Y ưθ tables and the high speed processing
time about 1sec.