Grinding apparatus for manufacturing optical device, method for manufacturing optical device, and precise measuring apparatus for measuring shape and size of mold used to manufacture optical device or shape and size of optical device

Abstract

When a large optical device is incorporated into a large telescope or the like, a support state and a load distribution are different from those when an object to be ground is placed on a workpiece supporting fixture of a processing machine, and a surface shape measured in a state of being mounted on the processing machine is different from a surface shape in an incorporated state. Thus, there has been no apparatus for manufacturing an optical device that is deformed by its own weight. The present invention provides a grinding apparatus for manufacturing an optical device that is deformed by its own weight, including a workpiece supporting fixture having a workpiece support surface shaped so as to closely contact a rear surface opposite to a ground surface of an object to be ground that is to be an optical device in a grinding state, wherein a plurality of piezoelectric actuator holes each having an open portion in the workpiece support surface and a central axis oriented vertically are provided at predetermined hole locations of the workpiece supporting fixture, and a piezoelectric actuator and a load cell are incorporated in each of the piezoelectric actuator holes in a liftable manner.

1 . A grinding apparatus for manufacturing an optical device that is deformed by its own weight, comprising a workpiece supporting fixture having a workpiece support surface shaped so as to closely contact a rear surface opposite to a ground surface of an object to be ground that is to be an optical device in a grinding state, wherein a plurality of piezoelectric actuator holes each having an open portion in the workpiece support surface and a central axis oriented vertically are provided at predetermined hole locations of the workpiece supporting fixture, and a piezoelectric actuator and a load cell are incorporated in each of the piezoelectric actuator holes in a liftable manner. 
     
     
         2 . The grinding apparatus according to  claim 1 , wherein a plurality of thermal expansion actuator holes each having an open portion in the workpiece support surface and a central axis oriented vertically are provided at predetermined sub hole locations, and a thermal expansion columnar component and a heater for heating the columnar component are incorporated in each of the thermal expansion actuator holes. 
     
     
         3 . The grinding apparatus according to  claim 1 , further comprising a control device for creating a simulated floating support state by comparing a measured load value measured by each of the load cells and a calculated load value to be obtained when the aspherical optical device is incorporated into a product at each of the hole locations, and controlling a projecting length of the piezoelectric actuator at each of the hole locations such that a difference between the measured load value and the calculated load value is equal to or less than a predetermined value. 
     
     
         4 . A method for manufacturing an optical device that is deformed by its own weight, by using a grinding apparatus according to  claim 1 , the method comprising alternately performing: a measuring step of obtaining a dimensional difference by comparing an intermediate shape and size of a ground surface of an object to be ground that is to be an optical device and a target shape and size of the ground surface at a predetermined point on the ground surface in a simulated floating support state; and a grinding step of performing grinding based on the dimensional difference at the predetermined point on the ground surface in a grinding state in which the object to be ground is in close contact with a workpiece support surface, without moving the object to be ground from the grinding apparatus. 
     
     
         5 . A precise measuring apparatus for precisely measuring a shape and size of a mold used to manufacture a non-axisymmetric convex aspherical optical device or a shape and size of a non-axisymmetric concave aspherical optical device, wherein a collimated light generating device, a half mirror, a CGH mask corresponding to a shape and size of a ground surface to be obtained, and a material to be ground are sequentially disposed, a reference flat surface is disposed adjacent to the material to be ground, zero-th order diffracted light obtained by allowing collimated light from the collimated light generating device to travel straight through the CGH mask without being diffracted when transmitted through the CGH mask is projected onto the reference flat surface and light reflected from the reference flat surface is diffracted when transmitted through the CGH mask again to be first-order diffracted light, which is reflected by the half mirror and changes an optical path in a lateral direction to enter an interferometer as a first light beam, and first-order diffracted light obtained by diffracting collimated light from the collimated light generating device when transmitted through the CGH mask is projected onto the ground surface of the material to be ground that is to be a mold or an optical device and light reflected from the ground surface travels straight through the CGH mask without being diffracted when transmitted through the CGH mask again to be zero-th order diffracted light, which is reflected by the half mirror and changes an optical path in the lateral direction to enter the interferometer as a second light beam, the collimated light generation source, the half mirror, the CGH mask, the material to be ground, the reference flat surface, and the interferometer being arranged such that the interferometer can observe an interference fringe between the first light beam and the second light beam. 
     
     
         6 . A precise measuring apparatus for precisely measuring a shape and size of a mold used to manufacture an axisymmetric convex aspherical optical device or a shape and size of an axisymmetric concave aspherical optical device, wherein a collimated light generating interferometer, a reference flat surface half mirror, and a null lens are sequentially disposed with optical axes of the collimated light generating interferometer, the reference flat surface half mirror, and the null lens being aligned with an axis of symmetry of a material to be ground that is to be a mold or an optical device. 
     
     
         7 . A precise measuring apparatus for precisely measuring a shape and size of a mold used to manufacture an axisymmetric concave aspherical optical device, or a shape and size of an axisymmetric convex aspherical optical device, wherein an F-light generating device, a half mirror, a Hindle shell whose upper surface has a convex shape with a larger aspherical degree than that of a ground surface to be obtained and whose lower surface has a same concave shape as that of the ground surface to be obtained, and which is designed such that F-light generated by the F-light generating device is transmitted through the half mirror and travels straight to enter the Hindle shell from the upper surface, be refracted, and be emitted in a normal direction from the lower surface, and a material to be ground that is to be a mold or an optical device are sequentially disposed with optical axes of the F-light generating device, the half mirror, the Hindle shell, and the material to be ground being aligned with an axis of symmetry of the material to be ground, and an interferometer is disposed lateral to the half mirror such that light reflected by the ground surface of the material to be ground is reflected by the half mirror after passing through the Hindle shell, changes an optical path in a lateral direction, and enters the interferometer. 
     
     
         8 . The precise measuring apparatus for precisely measuring a shape and size of an optical device according to  claim 5 ,
 wherein the material to be ground is placed on a workpiece supporting fixture, the workpiece supporting fixture having a workpiece support surface shaped so as to closely contact a rear surface opposite to a ground surface of an object to be ground that is to be an optical device in a grinding state, wherein a plurality of piezoelectric actuator holes each having an open portion in the workpiece support surface and a central axis oriented vertically are provided at predetermined hole locations of the workpiece supporting fixture, and a piezoelectric actuator and a load cell are incorporated in each of the piezoelectric actuator holes in a liftable manner.   
     
     
         9 . A grinding apparatus for manufacturing an optical device that is deformed by its own weight, wherein a precise measuring apparatus according to  claim 5 , and a workpiece supporting fixture are incorporated into a frame having a vibration-free integral structure, the workpiece supporting fixture having a workpiece support surface shaped so as to closely contact a rear surface opposite to a ground surface of an object to be ground that is to be an optical device in a grinding state, wherein a plurality of piezoelectric actuator holes each having an open portion in the workpiece support surface and a central axis oriented vertically are provided at predetermined hole locations of the workpiece supporting fixture, and a piezoelectric actuator and a load cell are incorporated in each of the piezoelectric actuator holes in a liftable manner. 
     
     
         10 . The precise measuring apparatus for precisely measuring a shape and size of an optical device according to  claim 6 ,
 wherein the material to be ground is placed on a workpiece supporting fixture, the workpiece supporting fixture having a workpiece support surface shaped so as to closely contact a rear surface opposite to a ground surface of an object to be ground that is to be an optical device in a grinding state, wherein a plurality of piezoelectric actuator holes each having an open portion in the workpiece support surface and a central axis oriented vertically are provided at predetermined hole locations of the workpiece supporting fixture, and a piezoelectric actuator and a load cell are incorporated in each of the piezoelectric actuator holes in a liftable manner.   
     
     
         11 . The precise measuring apparatus for precisely measuring a shape and size of an optical device according to  claim 7 ,
 wherein the material to be ground is placed on a workpiece supporting fixture, the workpiece supporting fixture having a workpiece support surface shaped so as to closely contact a rear surface opposite to a ground surface of an object to be ground that is to be an optical device in a grinding state, wherein a plurality of piezoelectric actuator holes each having an open portion in the workpiece support surface and a central axis oriented vertically are provided at predetermined hole locations of the workpiece supporting fixture, and a piezoelectric actuator and a load cell are incorporated in each of the piezoelectric actuator holes in a liftable manner.   
     
     
         12 . A grinding apparatus for manufacturing an optical device that is deformed by its own weight, wherein a precise measuring apparatus according to  claim 6 , and a workpiece supporting fixture are incorporated into a frame having a vibration-free integral structure, the workpiece supporting fixture having a workpiece support surface shaped so as to closely contact a rear surface opposite to a ground surface of an object to be ground that is to be an optical device in a grinding state, wherein a plurality of piezoelectric actuator holes each having an open portion in the workpiece support surface and a central axis oriented vertically are provided at predetermined hole locations of the workpiece supporting fixture, and a piezoelectric actuator and a load cell are incorporated in each of the piezoelectric actuator holes in a liftable manner. 
     
     
         13 . A grinding apparatus for manufacturing an optical device that is deformed by its own weight, wherein a precise measuring apparatus according to  claim 7 , and a workpiece supporting fixture are incorporated into a frame having a vibration-free integral structure, the workpiece supporting fixture having a workpiece support surface shaped so as to closely contact a rear surface opposite to a ground surface of an object to be ground that is to be an optical device in a grinding state, wherein a plurality of piezoelectric actuator holes each having an open portion in the workpiece support surface and a central axis oriented vertically are provided at predetermined hole locations of the workpiece supporting fixture, and a piezoelectric actuator and a load cell are incorporated in each of the piezoelectric actuator holes in a liftable manner.