Lens spherical surface grinding method using dish-shaped grindstone

Abstract

A spherical core type lens grinding device ( 1 ) performs an operation wherein a dish-shaped grindstone ( 8 ) provided with a spherical grindstone surface ( 8 a ) which is equipped with diamond abrasive grains, is pressed against a surface-to-be-ground ( 7 a ) of a lens blank ( 7 ) to be ground, and wherein the dish-shaped grindstone ( 8 ) is rotated and is simultaneously swung, resulting in said surface-to-be-ground ( 7 a ) being ground to a spherical surface. In an initial-stage grinding process, grinding is performed at first processing pressure and first rotational speed. In an intermediate-stage grinding process, grinding is performed at second processing pressure and second rotational speed. In a last-stage grinding process, grinding is performed at third processing pressure and third rotational speed. The second processing pressure is a pressure at which the spherical grindstone surface ( 8 a ) can bite into the lens blank ( 7 ). The biting amount of the dish-shaped grindstone ( 8 ) is obtained from the hardness of the lens blank ( 7 ) and the contact area between the surface-to-be-ground ( 7 a ) and the spherical grindstone surface ( 8 a ). The second processing pressure is calculated from the biting amount thus obtained. A coarse grinding process and a precision grinding process are unified into a single process. Therefore, the surface of the lens blank can be ground to a spherical surface by using only a dish-shaped grindstone used for precision grinding.

1 . A lens spherical surface grinding method using a dish-shaped grindstone in which a dish-shaped grindstone provided with a spherical grindstone surface provided with diamond abrasive grains is pressed at a predetermined pressure against a surface-to-be-ground of a grinding target lens blank, and in such a state, the surface-to-be-ground is ground on a spherical surface while the dish-shaped grindstone is rotated and swung at a predetermined rotational speed,
 the method characterized in comprising:
 an initial-stage grinding process for performing grinding in which the processing pressure is a first processing pressure and the rotational speed is a first rotational speed; 
 an intermediate-stage grinding process for performing grinding in which the processing pressure is a second processing pressure and the rotational speed is a second rotational speed; and 
 a last-stage grinding process for performing grinding in which the processing pressure is a third processing pressure and the rotational speed is a third rotational speed, wherein
 the second processing pressure is a pressure at which the spherical grindstone surface can bite into the lens blank, a biting amount of the dish-shaped grindstone is obtained from a hardness of the lens blank and a contact area between the surface-to-be-ground of the lens blank and the spherical grindstone surface of the dish-shaped grindstone, and the second processing pressure is calculated on the basis of the biting amount; 
 the second rotational speed is set to a rotational speed at which the diamond abrasive grains of the dish-shaped grindstone can bite into the lens blank; 
 the first processing pressure is set to a value less than the second processing pressure and the first rotational speed is set to a value less than the second rotational speed; and 
 the third processing pressure is set to a value less than the first processing pressure and the third rotational speed is set to a value less than the second rotational speed and greater than the first rotational speed. 
 
   
     
     
         2 . The lens spherical surface grinding method using a dish-shaped grindstone according to  claim 1 , characterized in that
 the second processing pressure is set to a minimum value at which the diamond abrasive grains of the dish-shaped grindstone can bite into the lens blank; and   the second rotational speed is set at a maximum value at which the diamond grains of the dish-shaped grindstone can bite into the lens blank.   
     
     
         3 . The lens spherical surface grinding method using a dish-shaped grindstone according to  claim 1  or  2 , characterized in that the initial-stage grinding process is carried out until a state is formed in which the surface-to-be-ground of the lens blank is in contact with the entire spherical grindstone surface; and
 the intermediate-stage grinding process is carried out until a state is formed in which a center thickness of the lens blank is greater than a target value by a dimension set in advance. 
 
     
     
         4 . The lens spherical surface grinding method using a dish-shaped grindstone according to any of  claims 1  through  3 , characterized in that a region in which the surface-to-be-ground of the lens blank slides on the spherical grindstone surface of the dish-shaped grindstone is periodically changed in at least the intermediate-stage grinding process. 
     
     
         5 . The lens spherical surface grinding method using a dish-shaped grindstone according to any of  claims 1  through  4 , characterized in that:
 the hardness of the lens blank has a Knoop hardness of 630; 
 the second processing pressure is 10 kg/cm 2  and the second rotational speed is 1,500 rpm; 
 the first processing pressure is 2 kg/cm 2  and the first rotational speed is 400 to 600 rpm; and 
 the third processing pressure is 1.5 kg/cm 2  and the third rotational speed is 1,000 rpm. 
 
     
     
         6 . (canceled)