Lens unit and manufacturing method of lens unit

Abstract

A lens unit includes a positive lens element provided with a convex surface on an incident surface and/or an exit surface; and a lens frame supporting the lens element and being provided with a projection that projects in an inner radial direction from inside the lens frame. The lens frame supports the lens element with the projection fixedly fitted into an outer peripheral portion of the lens element. The projection is provided, on an inner peripheral portion thereof, with a first surface positioned on an incident side in an optical axis direction, a second surface positioned on an exit side in the optical axis direction, and a third surface positioned between the first surface and the second surface. The first, second and third surfaces are tapered surfaces that are respectively inclined relative to the optical axis direction. A method of manufacturing the lens unit is also provided.

What is claimed is: 
     
         1 . A method for manufacturing a lens unit comprising:
 a lens element provided with a convex surface on at least one of an incident surface and an exit surface of the lens element, the lens element having a positive refractive power that condenses light rays, emitting from a light source, at a predetermined position; and   a lens frame that supports the lens element within the lens frame, the lens frame provided with a projection that projects in an inner radial direction from an inner portion of the lens frame,   wherein the lens frame supports the lens element with the projection fixedly fitted into an outer peripheral portion of the lens element,   wherein the projection is provided, on an inner peripheral portion thereof, with a first surface positioned on an incident side in an optical axis direction of the lens element, a second surface positioned on an exit side in the optical axis direction, and a third surface positioned between the first surface and the second surface, and   wherein the first, second and third surfaces are tapered surfaces that are respectively inclined relative to the optical axis direction,   wherein the method comprising:   placing the lens frame into a press-molding apparatus with the lens frame oriented so that an end of the third surface that has a smaller inner diameter than the other end, with respect to the optical axis direction, is positioned downward;   placing a glass preform onto the third surface; and   press-molding the glass preform using an upper die and a lower die of the press-molding apparatus to form the lens element.   
     
     
         2 . The method for manufacturing the lens unit according to  claim 1 , wherein a molding surface for molding one surface having a largest convex curvature out of the incident surface and the exit surface of the lens element is formed on the lower die, and a molding surface for molding the other surface of the incident surface and the exit surface of the lens element is formed on the upper die. 
     
     
         3 . The method for manufacturing the lens unit according to  claim 2 , wherein the glass preform is formed into a spherical shape,
 wherein the molding surface of the lower die comprises a concave surface, and   wherein a curvature of an outer surface of the glass preform is larger than a curvature of the molding surface of the lower die.   
     
     
         4 . The method for manufacturing the lens unit according to  claim 3 ,
 wherein the inner diameter of the end of the third surface that has a smaller inner diameter than the other end is smaller than the diameter of the glass preform; and   wherein the glass preform, before the press-molding operation, is restricted from moving downward from the position at which the glass preform comes into contact with the third surface and is supported thereby.   
     
     
         5 . The method for manufacturing the lens unit according to  claim 1 , further comprising:
 placing the lens frame, the glass preform, the upper die and the lower die into the press-molding apparatus;   heating the inside of the press-molding apparatus and softening the preform; and   pressing the glass preform by moving the upper die and the lower die to a close proximity of the glass preform.   
     
     
         6 . The method for manufacturing the lens unit according to  claim 5 , wherein the lower die is configured to be movable, in the upward and downward directions, with respect to the lens frame,
 wherein the press-molding apparatus is provided with a maximum upward restriction position of the lower die in the upward and downward directions, with respect to the lens frame,   wherein the support position, of the glass preform, defined by the third surface is determined so that the molding surface of the lower die comes into contact with the lower portion of the glass preform when the lower die moves to the maximum upward restriction position.   
     
     
         7 . The method for manufacturing the lens unit according to  claim 1 , wherein the inclination of the third surface of the lens frame is configured to generate a downward pressing force on the lens frame by a load acting downward on the glass preform that is placed on the third surface. 
     
     
         8 . The method for manufacturing the lens unit according to  claim 1 , wherein the press-molding apparatus is provided with a barrel die which guides the lower die to be movable in the upward and downward directions,
 wherein the barrel die is provided with a projection portion projecting radially inwardly from the inner peripheral surface of a receiving hole, and   wherein the lens frame is arranged inside the receiving hole of the barrel die so that the position of the lens frame with respect to the upward and downward directions is determined by a lower end of the lens frame coming into contact with the projection portion.   
     
     
         9 . The method for manufacturing the lens unit according to  claim 3 , wherein the molding surface comprises a concave surface, on which the glass preform point-contacts. 
     
     
         10 . The method for manufacturing the lens unit according to  claim 1 , wherein the inner diameter of the other end of the third surface progressively reduces, in the downward direction, to the inner diameter of the end of the third surface. 
     
     
         11 . The method for manufacturing the lens unit according to  claim 5 , wherein the upper die, the lower die and the lens frame are formed to have clearances therebetween in a radial direction to absorb dimensional changes due to differences of heat expansion rates of the upper die, the lower die and the lens frame. 
     
     
         12 . The method for manufacturing the lens unit according to  claim 7 , wherein the load acting downward on the glass preform is made by a downward pressing load of the upper die, a weight of the glass preform and that of the upper die. 
     
     
         13 . A method for manufacturing a lens unit comprising:
 a lens element provided with a convex surface on at least one of an incident surface and an exit surface of the lens element, the lens element having a positive refractive power that condenses light rays, emitting from a light source, at a predetermined position; and   a lens frame that supports the lens element within the lens frame, the lens frame provided with a projection that projects in an inner radial direction from an inner portion of the lens frame,   wherein the lens frame supports the lens element with the projection fixedly fitted into an outer peripheral portion of the lens element,   wherein the projection is provided, on an inner peripheral portion thereof, with a tapered surface that is inclined relative to the optical axis direction   wherein the method comprising:   placing the lens frame, into a press-molding apparatus, in a manner that an end of the tapered surface of the projection having a smaller inner-diameter is oriented downward;   placing a glass preform onto the tapered surface, thereby the glass preform is restricted from moving downward; and   press-molding the glass preform using an upper die and a lower die of the press-molding apparatus to form the lens element.   
     
     
         14 . The method for manufacturing the lens unit according to  claim 13 , wherein the glass preform is formed into a spherical shape,
 wherein the molding surface of the lower die comprises a concave surface, and   wherein a curvature of an outer surface of the glass preform is larger than a curvature of the molding surface of the lower die.   
     
     
         15 . The method for manufacturing the lens unit according to  claim 13 , further comprising:
 placing the lens frame, the glass preform, the upper die and the lower die into the press-molding apparatus;   heating the inside of the press-molding apparatus and softening the preform; and   pressing the glass preform by moving the upper die and the lower die to a close proximity of the glass preform.   
     
     
         16 . The method for manufacturing the lens unit according to  claim 15 , wherein the lower die is configured to be movable, in the upward and downward directions, with respect to the lens frame,
 wherein the press-molding apparatus is provided with a maximum upward restriction position of the lower die in the upward and downward directions, with respect to the lens frame,   wherein the support position, of the glass preform, defined by the tapered surface is determined so that the molding surface of the lower die comes into contact with the lower portion of the glass preform when the lower die moves to the maximum upward restriction position.