Acceleration Clamp Assist

Abstract

Forces are minimized in an object supported relative to a surface by providing a first, preferably static force sufficient to retain the object is position when at rest, preferably through a clamping arrangement having a first actuator, measuring or predicting an acceleration and applying a second, preferably dynamic force corresponding to the acceleration. The first and second forces are preferably arranged to be additive or reinforcing but the arrangement can be made fail-safe at the expense of increased power consumption by arranging the first force in accordance with the maximum anticipated acceleration and counteracting the first force with the second force for lesser or zero accelerations. The second force is preferably provided by a clamp of arbitrary configuration which can be moved into and out of engagement with the object. By minimizing forces applied to the object in such a manner, damage such as creep and propagation of crystal lattice dislocations over time can largely be prevented.

1 .- 15 . (canceled)  
   
   
       16 . A method of reducing forces applied to an object relative to a surface including steps of 
 applying a first force to said object sufficient to prevent motion of said object on said surface when at rest,    applying a second force to said object corresponding to an acceleration of said surface.    
   
   
       17 . A method as recited in  claim 16 , including the further step of measuring said acceleration of said surface.  
   
   
       18 . A method as recited in  claim 16 , including the further step of predicting said acceleration of said surface.  
   
   
       19 . A method as recited in  claim 16 , including the further step of 
 moving a clamp into or out of engagement with said object.    
   
   
       20 . A method as recited in  claim 16 , wherein said second force reinforces said second force.  
   
   
       21 . An apparatus comprising 
 a mount configured to receive an optical element,    a holding element configured to hold the optical element onto said mount,    a variable assist clamp configured to apply a variable force to hold the optical element to the mount, and    a control system, coupled to the mount and configured to control the variable assist clamp such that force applied by the variable assist clamp is substantially commensurate with acceleration of the mount.    
   
   
       22 . The apparatus as recited in  claim 21 , wherein the optical element comprises a reticle, mask, lens or mirror.  
   
   
       23 . The apparatus as recited in  claim 21 , wherein the holding element comprises a chuck, reticle stage, hard mount, flexured mount, clamp, flexured clamp, spring preloaded clamp or a moving carriage.  
   
   
       24 . The apparatus as recited in  claim 21 , wherein the mount comprises a chuck, reticle stage, hard mount, flexured mount, clamp, flexured clamp, spring preloaded clamp or a moving carriage.  
   
   
       25 . The apparatus as recited in  claim 21 , wherein the variable assist clamp comprises a piezo electric actuator, bellows actuator, preload clamp spring, spring washer clamp, universal joint or 1 DOF flexure in series with a preload spring or spring washer and a piexo-electric actuator or bellows actuator.  
   
   
       26 . The apparatus as recited in  claim 21 , wherein the holding element applies a substantially static force to hold the optical element to the mount.  
   
   
       27 . The apparatus of  claim 21 , wherein the variable clamp applies a dynamically variable force.  
   
   
       28 . The apparatus as recited in  claim 21 , wherein the variable clamp applies a stepped clamping force to hold the optical element to the mount.  
   
   
       29 . The apparatus as recited in  claim 21 , wherein the variable clamp applies a linearly variable clamping force to hold the optical element to the mount.  
   
   
       30 . The apparatus as recited in  claim 21 , wherein the control system comprises an acceleration reporting device.