Optical processing head, optical machining apparatus, and control method and control program of optical processing head

1. An optical processing head for a laser processing apparatus comprising: a first optical element that is a planoconvex lens having a convex surface on a downstream side and converts light emitted by a light source into first parallel light; a second optical element that is a planoconcave lens having a concave surface on a downstream side and is arranged downstream of said first optical element and converts the first parallel light into first divergent light; a third optical element that is a planoconvex lens having a convex surface on a downstream side and is arranged downstream of said second optical element and converts the first divergent light into second parallel light; and a fourth optical element that is a planoconvex lens having a convex surface on an upstream side, is arranged downstream of said third optical element and converts the second parallel light into convergent light which is condensed toward a processing surface, wherein letting f1 be a focal length of said first optical element, B be a focal length of said third optical element, f4 be a focal length of said fourth optical element, and m be an enlargement magnification of the optical processing head,

f

3

≤

3

⁢

⁢

f

4

2

m

2

⁢

f

1

+

f

4

is satisfied, and wherein a distance between the first and the second optical elements is smaller than a distance between the third and the fourth optical elements and wherein letting f2 be a focal length of said second optical element,

f

2

≅

0.25

×

(

m

2

⁢

f

1

+

f

4

f

4

2

⁢

f

3

2

+

f

3

)

.

2. The optical processing head according to claim 1 , wherein at least one of said second optical element and said third optical element is arranged to be movable along an optical axis.

3. The optical processing head according to claim 1 , wherein

said first optical element, said third optical element, and said fourth optical element are planoconvex lenses, and

said second optical element is a planoconcave lens.

4. The optical processing head according to claim 3 , wherein a focal length of said second optical element is not larger than a focal length of said third optical element.

5. The optical processing head according to claim 3 , wherein the second optical element is accommodated in a lens holder.

6. The optical processing head according to claim 5 , wherein the lens holder comprises a female holder and a male holder.

7. The optical processing head according to claim 1 , wherein said second optical element and said third optical element are arranged to make a virtual image focus of said second optical element that receives the first parallel light, coincide with a focus of said third optical element that receives the first divergent light.

8. An optical machining apparatus comprising:

an optical processing head defined in claim 1 ;

a light source; and

a light transmitting portion that transmits light emitted by said light source to said optical processing head.

9. A control method of controlling an optical processing head defined in claim 1 , comprising:

inputting a defocus value of the light on the processing surface; and

moving at least one of the second optical element and the third optical element along an optical axis in accordance with the defocus value.

10. The optical processing head control method according to claim 9 , wherein in the moving, when the input defocus value is larger than a current condensed spot diameter, the second optical element is moved to an upstream side.

11. A control program of controlling an optical processing head defined in claim 1 , causing a computer to execute:

inputting a defocus value of the light on the processing surface; and

moving at least one of the second optical element and the third optical element along an optical axis in accordance with the defocus value.

12. The optical processing head according to claim 1 , wherein a half mirror is interposed between two adjacent lenses among the first, the second, the third, and the fourth optical elements, and reflects a visible light component without interrupting the light emitted by the light source such that the processing surface can be observed.

13. An optical processing head comprising: a first optical element that is a planoconvex lens having a convex surface ort a downstream side and that converts light emitted by a light source into first parallel light; a second optical element that is a planoconcave lens having a concave surface on a downstream side, arranged downstream of said first optical element and converts the first parallel light into first divergent light, and movable along an optical axis; a third optical element that is a planoconvex lens having a convex surface on a downstream side and is arranged downstream of said second optical element and converts the first divergent light into second parallel light; and a fourth optical element that is a planoconvex lens having a convex surface on an upstream side and is arranged downstream of said third optical element and converts the second parallel light into convergent light which is condensed toward a processing surface characterized in that letting f1 be a focal length of said first optical element, f3 be a focal length of said third optical element, f4 be a focal length of said fourth optical element, and m be an enlargement magnification of the optical processing head,

f

3

≤

3

⁢

⁢

f

4

2

m

2

⁢

f

1

+

f

4

is satisfied, and

wherein a distance between the first and the second optical elements is smaller than a distance between the third and the fourth optical elements and

wherein letting f2 be a focal length of said second optical element,

f

2

≅

0.25

×

(

m

2

⁢

f

1

+

f

4

f

4

2

⁢

f

3

2

+

f

3

)

.