Hexapod kinematic mountings for optical elements, and optical systems comprising same

Abstract

“Hexapod” mountings are disclosed for use with optical elements. An exemplary mounting includes a base, a platform that is movable relative to the base, and six legs having nominally identical length. Three pairs of legs, having substantially equal stiffness, extend between the base and platform and support the platform relative to the base. In each pair of legs, respective first ends are coupled together in a Λ-shaped manner forming a respective apex. Respective second ends are splayed relative to the apex, desirably forming an angle of substantially 109.5° at the apex. The apices are mounted equidistantly from each other on a circle on the platform. The respective second ends of the pairs of legs are mounted at respective locations on a circle on the base. The axes of each pair of legs define a respective leg plane substantially perpendicular to the base plane. Each leg has an actuator that, when energized, changes a length of the respective leg. Coordinated energization of the actuators in selected legs produces a desired movement of the platform relative to the base in all six degrees of freedom of motion.

1 . A hexapod kinematic mounting, comprising:
 a base defining a base plane;   a platform situated relative to the base and movable relative to the base; and   six legs each having nominally identical length and a respective leg axis, the legs having substantially equal stiffness and being arranged in three pairs of legs extending between the base and platform and supporting the platform relative to the base, each pair of legs having first and second ends, the first ends of each pair being coupled together in a Λ-shaped manner forming a respective apex and the respective second ends being splayed relative to the apex, the apices being situated substantially equidistantly from each other at respective locations on a circle on the platform, and the respective second ends of the pairs of legs being mounted at respective locations on a circle on the base such that the respective axes of each pair of legs define a respective leg plane that is substantially perpendicular to the base plane, each leg comprising an actuator serving, when energized, to change a length of the respective leg such that a coordinated energization of the respective actuators in selected legs produces a desired movement of the platform relative to the base in all six degrees of freedom of motion.   
   
   
       2 . The mounting of  claim 1 , wherein the respective legs of each pair form an angle of substantially 109.5° at the respective apex. 
   
   
       3 . The mounting of  claim 1 , wherein the leg actuators are respective piezoelectric actuators. 
   
   
       4 . The mounting of  claim 3 , wherein each piezoelectric actuator comprises a respective coarse actuator and a respective fine actuator. 
   
   
       5 . The mounting of  claim 4 , wherein the coarse actuator and the fine actuator are arranged in tandem along the respective leg axis. 
   
   
       6 . The mounting of  claim 1 , wherein each leg further comprises a respective leg-extension flexure situated relative to the leg actuator to provide at least one, but not all six, degrees of freedom of motion accompanying leg extension and retraction caused by the respective leg actuator. 
   
   
       7 . The mounting of  claim 1 , wherein each leg further comprises a respective leg-length monitor. 
   
   
       8 . The mounting of  claim 1 , wherein:
 the first ends of each pair of legs comprise respective flexures providing the respective end with at least two, but not all six, degrees of freedom of motion; and   the second ends of each pair of legs comprise respective flexures providing the respective end with at least two, but not all six, degrees of freedom of motion.   
   
   
       9 . The mounting of  claim 1 , further comprising at least one height monitor situated and configured to measure and monitor position of the platform relative to a fixed reference. 
   
   
       10 . The mounting of  claim 9 , wherein the fixed reference is the base. 
   
   
       11 . A kinematically mounted optical element, comprising:
 an optical element;   a base defining a base plane;   a platform movable relative to the base;   at least one hold affixing the optical element to the platform; and   a hexapod situated between the base and the platform so as to support the platform relative to the base, the hexapod comprising six legs each having a respective leg axis, the legs having nominally identical length and substantially equal stiffness and being arranged in three pairs each having first and second ends, the first ends of each pair being coupled together in a Λ-shaped manner forming a respective apex and the respective second ends being splayed relative to the apex, the apices being situated substantially equidistantly from each other at respective locations on a circle on the platform, and the respective second ends of the pairs of legs being mounted at respective locations on a circle on the base such that the respective axes of each pair of legs define a respective leg plane that is substantially perpendicular to the base plane, each leg comprising an actuator serving, when energized, to change a length of the respective leg such that a coordinated energization of the respective actuators in selected legs produces a desired movement of the platform relative to the base in all six degrees of freedom of motion.   
   
   
       12 . The optical element of  claim 11 , wherein the optical element is a mirror. 
   
   
       13 . The optical element of  claim 11 , wherein the respective legs of each pair form an angle of substantially 109.5° at the apex. 
   
   
       14 . An optical system, comprising:
 a frame;   a base mounted to the frame and defining a base plane;   a platform movable relative to the base;   an optical element mounted to the platform; and   a hexapod situated between the base and the platform so as to support the platform relative to the base, the hexapod comprising six legs each having a respective leg axis, the legs having nominally identical length and substantially equal stiffness and being arranged in three pairs each having first and second ends, the first ends of each pair being coupled together in a Λ-shaped manner forming a respective apex and the respective second ends being splayed relative to the apex, the apices being mounted equidistantly from each other at respective locations on a circle on the platform, and the respective second ends of the pairs of legs being mounted at respective locations on a circle on the base such that the respective axes of each pair of legs define a respective leg plane that is substantially perpendicular to the base plane, each leg comprising an actuator serving, when energized, to change a length of the respective leg such that a coordinated energization of the respective actuators in selected legs produces a desired movement of the platform relative to the base in all six degrees of freedom of motion.   
   
   
       15 . The optical system of  claim 14 , wherein the respective legs of each pair form an angle of substantially 109.5° at the apex. 
   
   
       16 . The optical system of  claim 14 , wherein the leg actuators are respective piezoelectric actuators. 
   
   
       17 . The optical system of  claim 16 , wherein each piezoelectric actuator comprises a respective coarse actuator and a respective fine actuator. 
   
   
       18 . The optical system of  claim 14 , wherein each leg further comprises a respective leg-extension flexure situated relative to the leg actuator to provide at least one, but not all six, DOF of motion accompanying leg extension and retraction caused by the respective leg actuator. 
   
   
       19 . The optical system of  claim 14 , wherein each leg further comprises a respective leg-length monitor. 
   
   
       20 . The optical system of  claim 14 , wherein:
 the first ends of each pair of legs comprise respective flexures providing the respective end with at least two, but not all six, DOF of motion; and   the second ends of each pair of legs comprise respective flexures providing the respective end with at least two, but not all six, DOF of motion.   
   
   
       21 . The optical system of  claim 14 , further comprising at least one monitor situated and configured to measure and monitor position of the optical element relative to a fixed reference. 
   
   
       22 . The optical system of  claim 14 , wherein the optical element is a reflective optical element. 
   
   
       23 . The optical system of  claim 14 , wherein the optical system is an EUVL optical system. 
   
   
       24 . The optical system of  claim 23 , wherein the optical system is an EUVL projection-optical system. 
   
   
       25 . The optical system of  claim 14 , wherein:
 the optical system comprises multiple optical elements; and   at least one optical element is mounted to the frame by a respective base, platform, and hexapod.   
   
   
       26 . A kinematically mounted optical element, comprising:
 an optical element;   a base defining a base plane;   a platform movable relative to the base;   at least one hold affixing the optical element to the platform; and   a hexapod situated between the base and the platform so as to support the platform relative to the base, the hexapod comprising six legs each having a respective leg axis, the legs having nominally identical length and being arranged in three pairs each having first and second ends, the first ends of each pair being coupled together in a Λ-shaped manner forming a respective apex and the respective second ends being splayed relative to the apex, the apices being mounted equidistantly from each other at respective locations on a circle on the platform, and the respective second ends of the pairs of legs being mounted at respective locations on a circle on the base such that the respective axes of each pair of legs define a respective leg plane that is substantially perpendicular to the base plane, each leg comprising an actuator serving, when energized, to change a length of the respective leg such that a coordinated energization of the respective actuators in selected legs produces a desired movement of the platform, with substantially no cross-coupling, relative to the base in all six degrees of freedom of motion.   
   
   
       27 . The optical system of  claim 26 , wherein the legs have substantially equal stiffness. 
   
   
       28 . The optical system of  claim 26 , wherein the respective legs of each pair form an angle of substantially 109.5° at the apex. 
   
   
       29 . An optical system, comprising an optical element as recited in  claim 26 . 
   
   
       30 . A hexapod kinematic mounting, comprising:
 a base defining a base plane;   a platform situated relative to the base and movable relative to the base; and   six legs each having nominally identical length and a respective leg axis, the legs being arranged in three pairs of legs extending between the base and platform and supporting the platform relative to the base, each pair of legs having first and second ends, the first ends of each pair being coupled together in a Λ-shaped manner forming a respective apex and the respective second ends being splayed relative to the apex such that the respective legs of the pair form an angle of substantially 109.5° at the apex, the apices being mounted equidistantly from each other at respective locations on a circle on the platform, and the respective second ends of the pairs of legs being mounted at respective locations on a circle on the base such that the respective axes of each pair of legs define a respective leg plane that is substantially perpendicular to the base plane, each leg comprising an actuator serving, when energized, to change a length of the respective leg such that a coordinated energization of the respective actuators in selected legs produces a desired movement of the platform relative to the base in all six degrees of freedom of motion.