New approach for MEMS scanning mirror for laser projection systems
Fraunhofer IPMS already demonstrated a technol. for resonant 2D MEMS scanning mirrors, where the resonant driving principle has been established for mirror and frame. Using frequencies of 2500 Hz for the frame and 28 kHz for the mirror full color laser projection systems have been developed. Multiple Lissajous patterns are needed for the generation of one picture. Thus efficiency and frame rate are limited. Recently, a new approach has been invented: still a resonantly moving mirror is used for the fast movement but the frame is driven by a quasi-static drive. Among the several driving mechanisms possible the piezoelec. drive is the most promising. By choosing appropriate piezoelec. materials MEMS process integration is feasible. Besides a quasi-static deviation to generate pictures further options arise. The picture generation algorithm can be simplified if the movement along the rows is stepwise and the movement back is one fast step. This saw tooth like motion could be achieved through the high frequency response of piezoelec. materials. The setup of the chip is similar to the existing 2d scanning mirrors: Inside the mirror with an area of 0.25 to 9 mm2 is mounted on two spring bearings to the frame and resonantly driven through comb structures. The frame bearing to the chip is realized through flat bending actuators. Either the position change has to be considered at the picture generation or a layout has to be designed in a way that ensures a Pivot point in the middle of the mirror.