Laser ablation of accelerometer proof mass
A system for producing a proof-mass assembly includes a translation stage to receive a flapper hingedly supported by a bifilar flexure that extends radially inwardly from a support ring, wherein the bifilar flexure comprises a pair of flexure arms spaced apart by an opening or window; and a femtosecond laser optically coupled to the translation stage with focusing optics, the femtosecond laser applying a laser beam on the flexure arms over a plurality of passes to gradually thin the bifilar flexure regions, the laser periodically reducing a laser output to minimize damage from laser scanning and maximize bifilar flexure strength until the bifilar flexure reaches a predetermined thickness.
1. A method for producing a proof-mass assembly, comprising:
forming a proof mass with a curved flapper hingedly supported at a straight end by a bifilar flexure that extends radially inwardly from a support ring, wherein one side of the bifilar flexure comprises a pair of adjacent flexure arms spaced apart by a window;
scanning a femtosecond laser on the flexure arms over a plurality of passes to gradually thin bifilar flexure regions on a first side of the flexure arms;
feathering with the femtosecond laser in areas where the flexure arms connect to the curved flapper or reed and producing a gradual transition from a thick to a thin section; and
periodically reducing femtosecond laser output to minimize damage from laser scanning and maximize bifilar flexure strength until the bifilar flexure arms reach a predetermined thickness to form the proof-mass assembly.
2. The method of claim 1 , comprising ablating a second side of the flexure arms.
3. The method of claim 2 , wherein ablating the second side comprises:
scanning a femtosecond laser on the flexure arms over a plurality of passes to gradually thin the bifilar flexure regions;
periodically reducing femtosecond laser output until the bifilar flexure reaches a predetermined thickness to minimize damage from laser scanning and maximize the bifilar flexure strength.
4. The method of claim 1 , wherein the flapper comprises a circular configuration except for parts adjacent the bifilar flexure and is spaced from the support ring by an annular or arcuate gap.
5. The method of claim 1 , comprising wherein the window comprises curvaceous corners.
6. The method of claim 1 , wherein the flapper is of the same thickness as a support ring except at a top arcuate area of the support ring.
7. The method of claim 1 , wherein the proof-mass assembly is formed from a quartz wafer.
8. The method of claim 1 , comprising providing an arcuate electrode on an upper surface of the flapper opposite a first pole piece and providing another arcuate electrode on a lower surface of the flapper opposite a second pole piece.
9. The method of claim 8 , wherein each electrode forms a capacitor plate.