Method of manufacturing a molded article, manufacturing device and objective lens for optical pickup

Abstract

The present invention relates to a method of manufacturing a molded article in the form of an optical element such as a glass lens by heat-softening a glass material such as optical glass and press molding it with high precision in a pressing mold as well as an objective lens for optical picking up. The method of manufacturing comprises press-molding a molding material to make a molded article, measuring an optical property of the molded article, correcting pressing rate of at least one of the pressing molds based on the optical property thus measured, and further press-molding to make a molded article with the corrected pressing rate. A pressing device comprising a pair of pressing molds having molding surfaces processed to prescribed shape, and a means of driving one of the pair of pressing molds at a prescribed rate to press mold a molding material supplied between the pressing molds is disclosed. The device further comprises a means for detecting an optical property, a shape or a number of the molded articles and a means for controlling driving of said means of driving by correcting pressing rate of the molds based on the detected property, shape or number.

What is claimed is:  
     
         1  A method of manufacturing a molded article by pressing a heat-softened molding material with a pair of pressing molds having molding surfaces processed to prescribed shapes, comprising 
 press-molding a molding material to make a molded article,  
 measuring an optical property of the molded article,  
 correcting pressing rate of at least one of the pressing molds based on the optical property thus measured, and  
 further press-molding to make a molded article with the corrected pressing rate.  
 
     
     
         2  The method of manufacturing according to  claim 1 , wherein the correction of the pressing rate is conducted based on a predetermined correlation between the pressing rate and the optical property.  
     
     
         3  A method of manufacturing a molded article by pressing a heat-softened molding material with a pair of pressing molds having molding surfaces processed to prescribed shapes, wherein 
 each time a prescribed number of molded articles is press-molded, pressing rate of at least one of the pressing molds is corrected and  
 a molded article is further molded at the corrected pressing rate to maintain an optical property of the molded article within a prescribed range.  
 
     
     
         4  The method of manufacturing according to  claim 3 , wherein the correction of the pressing rate is conducted based on a predetermined correlation between the number of molded articles being continuously molded and optical properties of the articles having been molded.  
     
     
         5  The method of manufacturing according to  claim 1  or  3 , wherein said optical property is spherical aberration.  
     
     
         6  A method of manufacturing a molded article by pressing a heat-softened molding material with a pair of pressing molds having molding surfaces processed to prescribed shapes, comprising 
 press-molding a molding material to make a molded article,  
 measuring a shape of the molded article,  
 correcting pressing rate of at least one of the pressing molds based on the shape thus measured, and  
 further press-molding to make a molded article with the corrected pressing rate.  
 
     
     
         7  The method of manufacturing according to  claim 6 , wherein the correction of the pressing rate is conducted based on a predetermined correlation between the pressing rate and the shape, said shape being the paraxial radius of curvature of either a first surface or a second surface of the molded article.  
     
     
         8  A pressing device comprising a pair of pressing molds having molding surfaces processed to prescribed shape, and a means of driving one of the pair of pressing molds at a prescribed rate to press mold a molding material supplied between the pressing molds, wherein the device further comprises a means for detecting an optical property, a shape or a number of the molded articles and a means for controlling driving of said means of driving by correcting pressing rate of the molds based on the detected property, shape or number.  
     
     
         9  An objective lens for optical picking up, having a numerical aperture of greater than or equal to 0.6, a paraxial radius of curvature of less than or equal to 3 mm, an effective lens diameter of greater than or equal to 5 mm, and a maximum surface inclination of greater than or equal to 45 degrees with a third-order spherical aberration of within ±0.02 λrms at a prescribed wavelength (λ) of less than or equal to 430 nm.  
     
     
         10  An objective lens for optical picking up, having a numerical aperture of greater than or equal to 0.6, a paraxial radius of curvature of less than or equal to 3 mm, an effective lens diameter of greater than or equal to 5 mm, and a maximum surface inclination of greater than or equal to 45 degrees with a wave front aberration of within ±0.04 λrms at a prescribed wavelength (λ) of less than or equal to 430 nm.