Scanning processing device for laser beam with long depth of field

Abstract

The invention relates to a scanning processing device for a laser beam with a long depth of field, which belongs to the field of laser processing and comprises a reflecting galvanometer for enabling laser to scan on a printing working surface, a Fresnel lens is further arranged in front of the reflecting galvanometer, the incident surface of the Fresnel lens is a plurality of annular curved surfaces which are tightly connected in sequence from inside to outside, and the reflecting galvanometer is arranged in front of the Fresnel lens. The emergent surface of the Fresnel lens is a plane, so that the Fresnel lens is divided into a plurality of annular light-transmitting areas, and the focal lengths of the light-transmitting areas are different. According to the device, for lasers refracted by different light-transmitting areas, due to different focal lengths and different field depths, laser beams with long field depths are formed after mutual superposition, the field depths of laser spots are greatly prolonged, for irregular-height printing faces, focusing is not needed, and the machining quality or the machining speed cannot be affected by height jump.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of laser processing, and particularly relates to a scanning processing device of a long-depth-of-field laser beam. BACKGROUND

[0002] The current laser processing, such as laser cutting, laser welding, laser marking and laser 3D printing, is usually performed by scanning a single laser beam reflected by a galvanometer mirror on a two-dimensional work plane or a curved surface. Laser processing is an advanced rapid processing and manufacturing technology. According to the scanning mode of the galvanometer mirror, there are two modes of laser scanning and focusing, i.e., a pre-scan mode and a post-scan mode. In the post-scan mode, an F-Theta flat-field lens is needed, which is expensive and has a large volume. In the 3D printing industry, the cost of the F-Theta flat-field lens limits the application of multi-laser heads, and the large volume of the F-Theta flat-field lens also makes it impossible to reduce the volume of the 3D galvanometer printing head, thereby limiting the application of the 3D galvanometer printing head in more small and medium-sized occasions. In the pre-scan mode, a real-time dynamic voice coil motor is used to drive a focusing lens to focus the light path system. In this mode, the voice coil motor and the linear guide rail need to be compensated for position at all times, and the stability of the voice coil motor and the linear guide rail is required to be very high.

[0003] The patent with the authorized publication number CN115416299B discloses a laser galvanometer printing scheme without focusing. In this scheme, the laser beam can be printed without focusing within the allowable depth of field. However, the depth of field of the laser beam is usually not large, and therefore the range that can be printed by each laser head is also limited.

[0004] In addition, in the laser processing industry, there are many cases of laser processing and etching of three-dimensional surfaces, i.e., the work surface to be processed is not a plane but various irregular curved surfaces. In this case, a dynamic focusing system in the pre-scan mode is used to adjust the focal length of the laser beam in real time to ensure that the focal point can be accurately focused on the printing work surface on different curved surfaces. For an arbitrary irregular work surface, the focal length of the scanning laser is as shown in FIG. 1. When the laser moves along the scanning direction, the focusing motor must dynamically adjust the focal length in real time to ensure that the focal point always coincides with the printing work surface. In actual applications, the driving motor of the focal length adjusting lens is also limited by the frequency response. In some places where the height of the printing surface changes greatly, the focal length cannot be changed to the correct position instantaneously, which affects the laser printing or processing effect, as shown in FIG. 2. Figure 1 To reduce the error of the laser spot caused by the height jump of the printing work surface, the scanning speed of the laser must be reduced, which greatly affects the efficiency of the laser printing or processing. Figure 2 ​SUMMARY

[0005] The application aims to provide a long-depth-of-field laser beam scanning processing device to solve the problem of height jump affecting processing quality or processing speed when processing irregular height printing surface.

[0006] In order to achieve the above-mentioned purpose, the technical scheme of the application is as follows: The application relates to a long-depth-of-field laser beam scanning processing device which comprises a reflecting galvanometer for scanning laser on a printing work surface, and a Fresnel lens arranged in front of the reflecting galvanometer, the incident surface of the Fresnel lens is a plurality of annular curved surfaces which are connected closely from inside to outside, the exit surface of the Fresnel lens is a plane, the Fresnel lens is divided into a plurality of annular light transmission zones, and the focal lengths of the light transmission zones are different.

[0007] Preferably, the focal lengths of the light transmission zones increase from inside to outside.

[0008] Preferably, the ratios of the distances from the centers of the light transmission zones to the center of the Fresnel lens to the focal lengths of the corresponding light transmission zones are the same.

[0009] Preferably, the widths of the annular curved surfaces of the incident surface of the Fresnel lens are the same.

[0010] Compared with the prior art, the technical scheme provided by the application has the following beneficial effects: The long-depth-of-field laser beam scanning processing device provided by the application is provided with a Fresnel lens in front of the reflecting galvanometer, the incident surface of the Fresnel lens is a plurality of annular curved surfaces which are connected closely from inside to outside, the exit surface of the Fresnel lens is a plane, the Fresnel lens is divided into a plurality of annular light transmission zones, and the focal lengths of the light transmission zones are different. The laser beams refracted by different light transmission zones have different depths of field, and the long-depth-of-field laser beam is formed after mutual superposition, the depth of field of the laser spot is greatly prolonged, and for the irregular height printing surface, the focusing is not needed, and the processing quality or processing speed is not affected by the height jump. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 The figure is a schematic diagram of laser processing of an irregular height work surface; Figure 2 The figure is a schematic diagram of error caused by laser processing of an irregular height work surface; Figure 3 The figure is a structural schematic diagram of the long-depth-of-field laser beam scanning processing device; Figure 4 The figure is an equivalent optical path diagram of the Fresnel lens for generating the long-depth-of-field laser beam; Figure 5 The figure is a schematic diagram of the incident surface of the Fresnel lens; Figure 6 This is a schematic diagram of the depth of field during single-laser processing. Figure 7 This is a schematic diagram of the depth of field of the laser beam formed by the scanning processing apparatus of the present invention.

[0012] Illustration: 1-Fresnel lens, 2-Reflecting galvanometer, 3-Printing surface, 11-Transmitting area. Detailed Implementation

[0013] To further understand the content of this invention, the invention will be described in detail with reference to the embodiments. The following embodiments are used to illustrate the invention, but are not intended to limit the scope of the invention.

[0014] See attached document Figure 3 As shown, this invention relates to a scanning processing apparatus for a long depth-of-field laser beam, comprising a reflecting mirror 2 for scanning the laser on a printing surface, and a Fresnel lens 1 disposed in front of the reflecting mirror 2. (See attached diagram) Figure 4 As shown, the incident surface of Fresnel lens 1 consists of multiple annular curved surfaces that are tightly connected sequentially from the inside out, while the exit surface of Fresnel lens 1 is a plane; as... Figure 5 As shown, the widths of the annular surfaces are all the same. Each annular surface and the regions extending along the thickness direction of the Fresnel lens 1 from its inner and outer rings form a light-transmitting area 11, thus dividing the Fresnel lens 1 into multiple annular light-transmitting areas 11. By setting the curvature of the annular surfaces, the focal lengths of each light-transmitting area 11 are different, and the focal lengths of the light-transmitting areas 11 are... f i Increase sequentially from the inside out. f i Indicates the number from the inside out. i The focal length of the light-transmitting area 11 corresponding to the annular curved surface. (The rest of the text appears to be incomplete and requires further context.) i Taking the light-transmitting area 11 corresponding to the annular curved surface as an example, the diameter of its focused light spot is... ω Its laser beam depth of field is Δ f The laser wavelength is λ For collimated laser beam focusing, the following formula applies: , ; in, δ The allowable diffuse spot radius, Ri For the first i The distance from the center of the light-transmitting area corresponding to the annular curved surface to the center of Fresnel lens 1; From the two formulas above, it can be seen that when the ratio of the distance from the center of the light-transmitting area to the center of the Fresnel lens to the focal length of the corresponding light-transmitting area is the same, the diameter of the focused light spot in each light-transmitting area is... ω and depth of field Δf They are the same value.

[0015] For a single laser, the diameter of the focused spot ω and depth of field Δ f like Figure 6 As shown, when the laser passes through, as Figure 3 The scanning and processing device for a long depth-of-field laser beam shown in the diagram has a focal length difference between any two adjacent transparent areas, which is the depth of field of the laser focusing spot. That is, for the first... i Each of the light-transmitting areas has: The focal point distribution of the laser beam after being focused by the multi-focusing region 11 is as follows: Figure 7 As shown, the total depth of field of its equivalent focal point is also n times that of a single spot, where n is the number of annular surfaces. In this way, the depth of field of the laser spot can be greatly extended. For irregular height printing surfaces, there is no need to adjust the focus, and the processing quality or processing speed will not be affected by height jumps.

[0016] The present invention has been described in detail above with reference to the embodiments, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made in accordance with the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A long depth of focus laser beam scanning machining apparatus comprising a reflecting galvanometer for scanning a laser beam over a printing work surface, characterized in that: The front of the reflecting mirror is also provided with a Fresnel lens, the entrance surface of the Fresnel lens is a plurality of annular curved surfaces which are connected closely from inside to outside, the exit surface of the Fresnel lens is a plane, and the Fresnel lens is divided into a plurality of annular light transmission zones, and the focal lengths of the light transmission zones are all different.

2. The long-depth-of-focus laser beam scanning machining apparatus according to claim 1, characterized in that: The focal lengths of the light transmission zones increase from inside to outside.

3. The long-depth-of-focus laser beam scanning machining apparatus according to claim 2, characterized in that: The ratio of the distance from the center of the light transmission zone to the center of the Fresnel lens to the focal length of the corresponding light transmission zone is the same.

4. The long-depth-of-focus laser beam scanning machining apparatus according to claim 1, characterized in that: The widths of the annular curved surfaces of the entrance surface of the Fresnel lens are the same.

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