A minimum time laser tracking control technique for selective laser sintering

A minimum lime laser tracking control technique is desired for the Selective Laser Sintering (SLS) process in order to increase productivity. A minimum time optimal control problem is formulated with control constraints and tracking-path constraints on different spaces linked by a nonlinear geometric relation. An optimal solution of this control problem is obtained by a phase-plane technique. Since an extremely short sampling interval is desired in the computer control implementation, a simple feedback control scheme is desired in this application. Due to the variable speed of time-efficient tracking, laser power intensity must be controlled in real time for uniform laser exposure. An acousto-optic modulator is used to achieve this requirement. An experimental solidification model is used to set laser power. Models of a pair of galvanometers are identified by both frequency- and time-domain techniques. The characteristic curve of an acousto-optic modulator is measured. A complete laser tracking control system is finally designed and implemented based upon this analysis and the measured and identified subsystems.