A Research Into The Measurement Of Laser Beam Parameters And Correction Of Scanning System Drift In Stereolithography Apparatus

The photosensitive resin used in HRPL family of Stereolithography(SL) system is cured by laser beam which is directed by scanning system of the drawing laser. The laser mirror scanning system is composed of the laser, optics assembly, mirror positioning system and power supplies for the laser and mirrors. It is the principle part of the SL system. To be effective, a SL system must have information about the focus, laser beam oscillation mode, beam power, intensity distribution or profile, and scanning system drift of the drawing laser in order to carry out the accurate and efficient production of parts. Thus an on-line real-time detecting system for laser beam parameters is very important, which not only helps to realize the detection and compensation of laser parameters which make decisive influence on the curing model of photosensitive resin used in SL system, but also assists in detection and correction of scanning system drift of the drawing laser,which plays a very important role in avoidance of layer offset.Based on the present research status on laser parameters measurement at home and aboard and combined with features of HRPL family of SL system, a novel kind of beam profiling method, small-area pin-hole matrix scanning method, is put forward to acquire intensity distribution of laser spot. By profiling the laser spot projecting on the working platform, the intensity distribution data and its position is acquired, which is used to calculate the diameter of laser spot, laser power with the employment of middle value filtering of a window, Gaussian mathematical model and linear model and the two dimensional and three dimensional profile display is realized. These parameters mentioned above are key ones which make a decisive influence on the stability of the technological process of SLA. The timely adjustment of laser parameters or processing parameters which are used to compensate for the change of laser parameters can be realized through real-time feedback, thus the workpiece process is kept to be stable, which plays a very important role in the improvement of the part accuracy.Furthermore, the position of laser beam is calculated based on the data acquired through matrix scanning over a pinhole. Since the drift of scanning system is embodied by position of laser beam, two sensors, which are used to profile the laser beam over them, are arranged along the diagonal of the work platform, thus the position of laser beam scanning over the sensor is calculated. The offset drift of the scanning system is worked out according to the change of the position of laser beam, and the gain drift is figured out through the variation ratio of the positions of laser beam above two sensors. The two drift values are used to correct the command map of the scanning system, and the detection and correction of drift of scanning system is realized and the phenomenon of layer offset and change of scale ratio are avoided.