External Electromagnet FPCB Micromirror for Large Angle Laser Scanning

Abstract

An external electromagnet plus moving PM (permanent magnet) FPCB (flexible printed circuit board) micromirror is proposed in this paper that can overcome two limitations associated with the previous FPCB micromirror with a configuration of an external PM plus moving coil, i.e., (1) it reduces the overall width beyond the mirror plate, and (2) increases the maximum rotation angle. The micromirror has two external electromagnets underneath an FPCB structure (two torsion beams and a middle seat) with two moving PM discs attached to the back and a metal-coated mirror plate bonded to the front of the FPCB middle seat. Modeling and simulation were introduced, and the prototype was fabricated and tested to verify the design. The achieved performance was better than that of the previous design: a maximum resonant rotation angle of 62° (optical) at a driving voltage of ±3 V with a frequency of 191 Hz, the required extra width beyond the mirror plate was 6 mm, and an aperture of 8 mm × 5.5 mm with a roughness of <10 nm and a flatness of >10 m (ROC, radius of curvature). The previous FPCB micromirror’s performance was: strain limited maximum rotation angle was 40° (optical), the extra width beyond the mirror plate was 14.7 mm, and had an aperture of 4 mm × 4 mm with a similar roughness and flatness.

Electromagnetic FPCB micromirror based scanning laser rangefinder

“…The second configuration of the EEM-FPCB micromirror shown in Figure 2-4. As mentioned earlier, further results of the second configuration design can be found in a published journal [54]. The design of the second configuration is similar to the first configuration, with the main difference of the second configuration having shorter and wider torsion beams with no copper.…”

“…The flexible properties of the FPCB material results in a higher yield bonding compared to MEMS micromirrors. FPCB micromirrors can achieve a larger aperture, high mirror flatness, and high bonding yield, all at a low cost (especially at low volume production) [20,39,[53][54][55]. FPCB micromirrors are proposed as a more suitable alternative laser scanner for the application of scanning laser rangefinding.…”

“…Deeper study and results have been further reported in a submitted paper (under review) to the "Journal of Micromechanics and Microengineering". Additionally, the second configuration design (described in the following section 2.4) has been reported in a published journal paper [54] in "Journal of Micromachines". The first configuration is similar to the second configuration, except with the main difference of a copper film added in the torsion, which can be seen in Compared to the FPCB magnetic micromirror, this FPCB micromirror does not have the problem of relatively large permanent magnets blocking the scanning FOV.…”

Origami Inspired Laser Scanner

“…Regarding the inner structure, comprehensively discussed in literatures [ 15 , 16 , 17 , 18 ], a laser galvanometer consists of a mirror, an angular actuator, and control electronics. The mirror needs high reflectance and low inertia.…”

“…Regarding the advantages of the proposed method, rotary joints are classified into 3 types: Ball bearings, torsional beams [ 15 , 16 , 17 , 18 , 32 ], and origami hinges of this work. Ball bearings can rotate endlessly and have the widest scanning range, but the friction degrades their accuracy or makes them hard to be controlled.…”