Hot crimping structure and method for fixing a lens to a lens frame, and hot crimping tool therefor

1. A hot crimping structure for fixing at least one lens element to a lens frame made of synthetic resin, said lens element being accommodated in a lens holder opening of said lens frame, a portion of said lens frame being crimped by heat to serve as a crimped edge which lies on a surface of said lens element adjacent to a rim of said lens element,

wherein said lens frame comprises an outward expansion surface which extends outwards from a close vicinity of said rim of said lens element, and

wherein a hot crimping tool is brought into contact with said outward expansion surface to form a recess on said outward expansion surface by heat, to thereby produce said crimped edge by movement of melting synthetic resin which is melted due to the formation of said recess.

2. The hot crimping structure according to claim 1 , wherein said outward expansion surface lies in a plane orthogonal to an axis of said lens element.

3. The hot crimping structure according to claim 1 , wherein said outward expansion surface is formed as a substantially truncated conical surface which is rotation-symmetrical about an axis of said lens element.

4. The hot crimping structure according to claim 1 , wherein said lens frame comprises a stop portion formed on an inner peripheral surface of said lens frame in said lens holder opening, and

wherein said rim of said lens element is held tight between said crimped edge and said stop portion.

5. The hot crimping structure according to claim 1 , wherein said recess is formed as an annular recess on said outward expansion surface so that said crimped edge is produced as an annular crimped edge.

6. The hot crimping structure according to claim 1 , wherein said lens frame comprises another lens holder opening provided adjacent to said lens holder opening, said another lens holder opening having a diameter greater than a diameter of said lens holder opening, and

wherein another lens element having a diameter greater than a diameter of said lens element is accommodated in said another lens holder opening.

7. A hot crimping method of fixing at least one lens element to a lens frame made of synthetic resin, a lens holder opening for accommodating said lens element being formed on said lens frame, an inward stepped portion which is engaged with that portion of one side surface of said lens element adjacent to a rim of said lens element being formed on said lens frame in said lens holder opening, a portion of said lens frame being crimped by heat to serve as a crimped edge which lies on the portion of the other side surface of said lens element adjacent to said rim of said lens element,

wherein said hot crimping method comprises: forming an outward expansion surface on an inner peripheral surface of said lens frame so that said outward expansion surface extends outwards from a close vicinity of said rim of said lens element;

preparing a hot crimping tool including an annular crimping edge having an acute angle in cross section, an outer diameter of said annular crimping edge being greater than a diameter of said lens holder opening; and

bringing said hot crimping tool into contact with said outward expansion surface to form a recess on said outward expansion surface by heat of said hot crimping tool to thereby produce said crimped edge by movement of melting synthetic resin which is melted due to the formation of said recess.

8. The hot crimping method according to claim 7 , wherein said outward expansion surface lies in a plane orthogonal to an axis of said lens element.

9. The hot crimping method according to claim 7 , wherein said outward expansion surface is formed as a substantially truncated conical surface which is rotation-symmetrical about an axis of said lens element.

10. A hot crimping tool for fixing at least one lens element to a lens frame made of synthetic resin, said lens element being accommodated in a lens holder opening of said lens frame, said hot crimping tool being brought into contact with a portion of said lens frame to crimp said portion by heat of said hot crimping tool so as to produce a crimped edge which lies on a surface of said lens element adjacent to a rim of said lens element,

wherein said hot crimping tool comprises an annular crimping edge which is formed at an end of said hot crimping tool to have an acute angle in cross section, and

wherein said annular crimping edge is inserted into said lens frame in a direction substantially orthogonal to a radial direction of said lens frame, and is brought into contact with said portion of said lens frame to form a recess to thereby produce said crimped edge by a movement of a melting synthetic resin which is melted due to said formation of said recess.

11. The hot crimping tool according to claim 10 , wherein said hot crimping tool is rotationally symmetrical about an axis of said lens element.