A monolithic adjusting mechanism for optical element based on modified 6-PSS parallel mechanism

Adjusting mechanisms with micrometer stroke, nanometer accuracy, high load capacity and compact structure are needed in the deep ultraviolet lithography objective lens. We propose a monolithic adjusting mechanism based on 6-PSS (prismatic-spherical-spherical) parallel mechanism to advisably meet these requirements. Six prismatic joints of the 6-PSS parallel mechanism are optimized into three, which improves the reliability and reduces the cost of the adjusting mechanism. To realize monolithic configuration, a thinned fillet flexure hinge is proposed to work as the spherical joint of the 6-PSS parallel mechanism. This simplifies the alignment process and improves the mechanical accuracy. Structure analysis including positional relationship and transmission ratio is carried out to provide a basis for determining the primary structural dimension of the adjusting mechanism. Verification test results show that the numerical result of the transmission ratio agrees with the experimental one. The axial stroke of the adjusting mechanism is 74.4 μm, the accuracy is within 40 nm, and the surface figure variation of the optical element during the adjusting process is less than 1.5%, which satisfies the operation requirement of the lithography objective lens and shows a bright prospect to actuate other objects in the applications of micro-nano.