Printing method for modulating line width through double lasers

Abstract

The invention discloses a printing method for modulating the line width through double lasers, and belongs to the technical field of 3D printing. The method comprises the following steps that two sets of long-strip-shaped laser beams are set, and the scanning widths of the two sets of long-strip-shaped laser beams are both D; the to-be-printed pattern is divided into a plurality of printing blocks, and the width of the printing blocks is not larger than D; and when each printing block is printed, the sum of the power of the two sets of long-strip-shaped laser beams is modulated to be equal to the power needed by metal melting, the two sets of long-strip-shaped laser beams conduct synchronous scanning in the length direction of the printing blocks, and in the scanning process, according to the actual line width d of the current printing position, the laser overlapping area of the two sets of long-strip-shaped laser beams is adjusted, the width of the overlapping area is the same as the actual line width d at the current position, and the position of the overlapping area is overlapped with the position of the current to-be-printed part. According to the invention, thickness modulation can be carried out at microsecond-level time in the printing process, and when the same line is scanned, the size of the line width can be changed at will according to a printing pattern, so that the printing efficiency is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of 3D printing, and in particular relates to a printing method using dual lasers to modulate line width. Background Art

[0002] The function of an SLM metal 3D printer is to use metal powder to melt under the heat of a laser beam, cool, condense, and then stack layers to manufacture parts. SLM metal 3D printing has relatively high requirements for printing lasers. The laser beam needs to be pure single-mode output and the beam quality M2 is less than 1.1. Lasers with high beam quality usually have low laser power and cannot be used to further improve printing efficiency. In addition, the splashing of metal particles in metal 3D printing will seriously affect the printing quality. These are all common process problems in 3D printing.

[0003] Powder bed laser melting (PBL) focuses a high-energy fiber laser beam into a small spot with sufficient energy intensity to completely melt a thin layer of metal powder. A pair of scanning galvanometers moves the laser across the powder bed, where the metal powder melts and solidifies, connecting with the underlying layer and adjacent areas to form a molten pool. A protective airflow flows over the build plate, protecting the hot metal from oxidation and safely removing fumes. The molten pool is wider than the laser spot (approximately two to three times its diameter) because the heat generated by the laser conducts to the surrounding powder particles, melting them into the moving pool. Multiple melt tracks connect and overlap, forming a solid metal layer corresponding to the part's layering. The melt tracks must be deep enough to partially remelt the underlying metal layers, forming a fully dense, solid structure. Powder bed laser melting 3D printing machines build parts layer by layer in this manner.

[0004] According to the requirements of metal 3D printing process, it is usually necessary to meet the requirements of laser power P and scanning speed V to match each other appropriately, such as Figure 1 As shown, if the scanning speed is too fast and the laser power is too low, some areas of the part may not be completely melted, resulting in porosity due to "lack of melting". Conversely, if too much power is applied at the selected speed, the molten pool may overheat and the energy may penetrate too deeply, resulting in a "deep hole" effect. Between these two extremes is an "operating window" within which good part density can be obtained. Within this window, the laser energy is sufficient to completely melt the powder and the metal layer below it without penetrating too deeply. It can be seen that increasing the laser power and scanning speed simultaneously can improve processing efficiency, which is feasible to some extent. However, there is a limit to both power and speed. Once this limit is exceeded, the molten pool becomes unstable and a "spheroidization" effect occurs. As shown in Figure 2As shown in Figure 1, increasing laser power may also increase spatter, and when the scanning speed is too fast, the melt pool may become unstable. High surface tension gradients cause voids to form behind the laser beam, which expand as the laser moves, causing the melt pool to break up and eventually solidify into multiple disconnected spheres.

[0005] Therefore, in metal 3D printing, the above-mentioned process characteristics limit the ability to improve part printing efficiency by increasing the scanning speed. In order to improve printing efficiency, a larger spot and thicker scanning lines are usually used to print the filled part of the part, and a fine spot is used to print the stroke lines. Patent Nos. "CN8799127U" and "CN5867306U" respectively provide solutions for using thick lines and thin lines to scan the filled and stroked parts respectively through dual laser beams and optical zoom systems. In the above solutions, when printing any scan line, only one thickness can be selected. Since the pattern has a more complex structure, if the traditional fixed thickness scanning line is used for printing, the detailed structure of the pattern cannot be printed; in order to print the fine structure of the pattern, very fine laser beam lines are required to scan many times, which will greatly reduce the printing efficiency. Therefore, the traditional printing method cannot take into account both printing efficiency and printing accuracy at the same time. Summary of the Invention

[0006] The purpose of the present invention is to provide a dual-laser linewidth modulation printing method to solve the problem that traditional 3D printing methods cannot take into account both printing efficiency and printing accuracy at the same time.

[0007] In order to achieve the above object, the technical solution of the present invention is as follows: The present invention relates to a printing method for dual-laser linewidth modulation, which comprises the following steps: S1. Set two sets of long laser beams, and the scanning width of the two sets of long laser beams is D; S2. Divide the pattern to be printed into several printing blocks, the width of the printing block is not greater than D; S3. When printing the scanning lines in each printing block, the power of the two sets of long laser beams is modulated to be less than the power P required to melt the metal, and the sum of the powers of the two sets of long laser beams is equal to the power required to melt the metal. The two sets of long laser beams are scanned synchronously along the length direction of the printing block. During the scanning process, the overlapping area of ​​the lasers of the two sets of long laser beams is adjusted according to the actual line width d at the current printing position, so that the width of the overlapping area is the same as the actual line width d at the current position and the position overlaps with the position of the current part to be printed.

[0008] Preferably, the powers of the two groups of long strip laser beams in S3 are modulated to half of the power P required to melt the metal.

[0009] Preferably, during the S3 scanning process, the overlapping area of ​​the lasers of the two groups of long strip laser beams is adjusted according to the actual line width d of the current printing position, so that the width of the overlapping area is the same as the actual line width d at the current position and the position overlaps with the position of the current part to be printed. The specific method is: the left edge of the scanning line is used as the printing path of the left long strip laser beam, and the width of the part of the left long strip laser beam located on the right side of the corresponding printing path is the same as the actual line width d; the right edge of the scanning line is used as the printing path of the right long strip laser beam, and the width of the part of the right long strip laser beam located on the left side of the corresponding printing path is the same as the actual line width d; and the parts of the two groups of long strip laser beams located between the left and right printing paths are overlapped, so that the sum of the powers of the overlapping parts is P.

[0010] Preferably, when the pattern to be printed is divided into a plurality of printing blocks in S2, the widths of the printing blocks are all the same as the scanning width D of the long strip laser beam.

[0011] Preferably, the step S3 further determines the scan lines in the printing block. If the line widths of the scan lines at all positions in the length direction are the same as the scan width D of the long laser beam, the process proceeds to step S4. Otherwise, the process proceeds to step S3. S4. Adjust the power of one of the groups of long laser beams to the power P required to melt the metal, and use a single long laser beam to print the scan line.

[0012] Preferably, in S4, when the scanning lines in one of the printing blocks are determined to have a line width at each position that is the same as the scanning width D of the long laser beam, it is determined whether there are any scanning lines in the unprinted block that satisfy the requirement that the line width at each position is the same as the scanning width D of the long laser beam. If so, the powers of the two groups of long laser beams are adjusted to the power P required to melt the metal, and the two printing blocks are printed simultaneously using the two groups of long laser beams.

[0013] Preferably, the two groups of long strip laser beams in S1 are modulated by an acousto-optic modulator, specifically: the laser beam is injected into the acousto-optic modulator, two ultrasonic frequency signals are input to the acousto-optic modulator at the same time to form first-order diffracted light and second-order diffracted light, and the frequencies of the two ultrasonic waves are modulated so that the first-order diffracted light and the second-order diffracted light are deflected, and the deflection speed satisfies v 2 / v 1≥D / d', where v 2 represents the deflection speed of the first-order diffracted light and the second-order diffracted light, v 1 represents the scanning speed of the galvanometer unit, d' is the spot diameter, and the offset direction is perpendicular to the scanning direction of the galvanometer, thereby forming two sets of long strip laser beams; The S3 controls the overlapping area of ​​the two groups of long strip laser beams by controlling the range of ultrasonic frequency input to the acousto-optic modulator.

[0014] The two groups of long strip laser beams in S1 are obtained by splitting an incident laser beam into two beams through a laser beam splitting mechanism; The laser beam splitting mechanism includes a concave lens group, a beam splitting prism and a convex lens group arranged in sequence along the laser light path, and the concave lens group, the beam splitting prism and the convex lens group are coaxially arranged; The method for S1 to form two groups of long laser beams with a scanning width of D is as follows: S1.1. Direct incident laser light of diameter d0 into the concave lens array, which diffuses the incident laser light. S1.2. Adjust the distance between the concave lens group and the beam splitter prism so that the incident laser beam has a diameter of 2D when it enters the beam splitter prism. The beam splitter prism splits the incident laser beam into two long laser strips with a width of D. S1.3. The two long laser beams are refracted through concave lenses, forming two long laser beams with a scan width of D. The S3 modulates the overlapping area of ​​the two groups of long strip laser beams by adjusting the distance between the beam splitter prism and the convex lens group.

[0015] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects: 1. The dual-laser linewidth modulation printing method of the present invention provides two sets of long strip laser beams to divide the pattern to be printed into several printing blocks. When printing the scan lines in each printing block, the power of the two sets of long strip laser beams is modulated to a value less than the power P required to melt the metal, and the sum of the powers of the two sets of long strip laser beams is equal to the power required to melt the metal. The two sets of long strip laser beams scan synchronously along the length of the printing block. During the scanning process, the overlapping area of ​​the lasers of the two sets of long strip laser beams is adjusted according to the actual line width d at the current printing position, so that the width of the overlapping area is the same as the actual line width d at the current position and the position overlaps with the position of the current portion to be printed. The line width of the scanned print is not constant, but can be modulated in microseconds during the printing process. When scanning the same line, the line width can be arbitrarily changed according to the printing pattern.

[0016] 2. The dual-laser linewidth modulation printing method of the present invention first determines the scan lines within a print block before printing. If the line widths of the scan lines at all locations along their length are the same as the scan width D of a single long laser beam, the power of one of the long laser beams can be adjusted to the power P required to melt the metal, and the scan lines can be printed using a single long laser beam. For multiple such print blocks, the two long laser beams can be used to print simultaneously, ensuring efficient printing. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is the relationship between laser power and scanning speed during SLM metal 3D printing; Figure 2 is a schematic diagram of the phenomenon that the molten pool is unstable due to excessive scanning speed; FIG3 shows a diagram of dividing a pattern to be printed into several printing blocks; FIG4 is a schematic diagram showing the principle of two sets of long laser beams jointly printing the scan lines in the printing block; Figure 5 Schematic diagram of determining the laser overlap area for two sets of long laser beams; Figure 6 A schematic diagram of an optimized printing method for the entire printed pattern; Figure 7 This is a schematic diagram of the principle of using an acousto-optic modulator to modulate a long light spot in Example 3; Figure 8 This is a structural diagram of the laser beam splitting mechanism used in Example 4; Figure 9 This is a schematic diagram of the principle of the laser beam splitting mechanism used in Example 4 to modulate two groups of long strip-shaped light spots. DETAILED DESCRIPTION

[0018] In order to further understand the content of the present invention, the present invention is described in detail with reference to the examples. The following examples are used to illustrate the present invention but are not used to limit the scope of the present invention.

[0019] Example 1: The present invention relates to a printing method for dual-laser linewidth modulation, which comprises the following steps: S1. Set up two groups of long strip laser beams, which are generated by two galvanometer modules respectively. The scanning width of the two groups of long strip laser beams is D, that is, the light spots of the scanning lasers generated by the two galvanometer modules are both long strip spots, and the length of the long strip spots is D. The long strip spots can be formed by a combination of several circular spots arranged along a straight line and tangent to each other in sequence.

[0020] S2. Refer to the attached Figure 3 As shown, the pattern to be printed is divided into several printing blocks. The width of the printing block is not greater than D. To facilitate the division and subsequent steps, the width of the printing area is generally uniform. It can be seen that the width of the laser scanning line in each printing area is often uneven. S3. When printing the scan lines in each print block, the power of the two long laser beams is modulated to a value less than the power P required to melt the metal, and the sum of the powers of the two long laser beams is equal to the power required to melt the metal. Generally, the power of the two long laser beams is modulated to half the power P required to melt the metal, that is, P / 2. The two long laser beams are scanned synchronously along the length of the print block. During the scanning process, the overlapping area of ​​the laser beams of the two long laser beams is adjusted according to the actual line width d at the current printing position, so that the width of the overlapping area is the same as the actual line width d at the current position and the position overlaps with the position of the current portion to be printed, as shown in FIG. Figure 5 As shown, the specific method is: the left edge of the scanning line is used as the printing path of the long strip laser beam on the left, and the width of the part of the long strip laser beam on the left (laser beam 1) located on the right side of the corresponding printing path is the same as the actual line width d; the right edge of the scanning line is used as the printing path of the long strip laser beam on the right, and the width of the part of the long strip laser beam on the right (laser beam 2) located on the left side of the corresponding printing path is the same as the actual line width d; and the two groups of long strip laser beams are overlapped between the left and right printing paths, so that the power sum of the overlapping part is P. When the two groups of long strip laser beams scan at the same scanning speed and continuously adjust the overlapping area, the area of ​​the scanning line is printed. Its working principle is as follows Figure 4 As shown, the power of each set of long laser beams (laser beam 1 and laser beam 2) is 50% of the power required for the printing process. The two galvanometer beams are combined, and the superimposed energy is the laser energy required for the printing process. The scanning lines of the two galvanometers overlap at a certain ratio. Because the power of each laser beam is only 50% of the power required for printing, only the overlapping portion of the two laser beams has enough laser energy to print the sintered metal powder. Before being heated to the melting point and melted, the metal powder exists in a solid powder state. The non-overlapping portion of the two beams lacks energy to form the metal powder. After the laser scan, the state is the same as before printing. At this time, the equivalent line width of the scanned print is the overlapping portion of the two laser beams.

[0021] Example 2: This embodiment is a further improvement of embodiment 1, and the specific steps are as follows: S1. Set up two groups of long strip laser beams, which are generated by two galvanometer modules respectively. The scanning width of the two groups of long strip laser beams is D, that is, the light spots of the scanning lasers generated by the two galvanometer modules are both long strip spots, and the length of the long strip spots is D. The long strip spots can be formed by a combination of several circular spots arranged along a straight line and tangent to each other in sequence.

[0022] S2. Refer to the attached Figure 3 As shown, the pattern to be printed is divided into several printing blocks. In this embodiment, the width of the printing blocks is the same as the scanning width D of the long strip laser beam; S3. Before printing the scan lines in each printing block, the scan lines in the printing block are first determined. If the line widths of the scan lines at all positions along the length direction are the same as the scan width D of the long laser beam, then the subsequent steps of S3 are skipped and the process proceeds directly to S4. Otherwise, the powers of the two sets of long laser beams are modulated to be less than the power P required to melt the metal, and the sum of the powers of the two sets of long laser beams is equal to the power required to melt the metal. Generally speaking, the powers of the two sets of long laser beams are modulated to half of the power P required to melt the metal, that is, P / 2. The two sets of long laser beams are scanned synchronously along the length direction of the printing block. During the scanning process, the overlapping area of ​​the laser beams of the two sets of long laser beams is adjusted according to the actual line width d at the current printing position, so that the width of the overlapping area is the same as the actual line width d at the current position and the position overlaps with the position of the current portion to be printed. The specific implementation method and working principle are the same as those in Example 1 and will not be elaborated in this embodiment.

[0023] S4. Further determine whether there are any scanning lines in the unprinted block whose line width at each position is the same as the scanning width D of the long laser beam. If so, adjust the power of both sets of long laser beams to the power P required for melting the metal, and use the two sets of long laser beams to print the two printing blocks simultaneously. If not, adjust the power of one set of long laser beams to the power P required for melting the metal, and use a single long laser beam to print the scanning line. Figure 6 This embodiment is more suitable for scenarios where the print pattern is relatively regular. This is because, when the print pattern is relatively regular, there are a large number of scan line widths in the middle of the print pattern that are the same as the scan width D of a single long laser beam. Therefore, step S3 is used to print the scan lines in the print block at the edge of the print pattern, and step S4 is used to print the area where the scan line width is the same as the scan width D of a single long laser beam. This can improve printing efficiency.

[0024] Example 3 While Examples 1 and 2 require two galvanometer systems to generate two long laser beams, this embodiment is a further improvement of Examples 1 and 2. Specifically, this embodiment no longer uses two galvanometer systems. Instead, the two long laser beams are modulated by a single acousto-optic modulator. Specifically, S1. Shoot the laser beam into the acousto-optic modulator, input two ultrasonic frequency signals into the acousto-optic modulator at the same time, form first-order diffraction light and second-order diffraction light, modulate the frequencies of the two ultrasonic waves, and deflect the first-order diffraction light and the second-order diffraction light at a speed that satisfies v 2 / v 1≥D / d', where v1 represents the scanning speed of the galvanometer unit, d' is the spot diameter, and the offset direction is perpendicular to the scanning direction of the galvanometer, thereby forming two sets of long strip laser beams; S2. The pattern to be printed is divided into several printing blocks. In this embodiment, the width of the printing blocks is the same as the scanning width D of the long strip laser beam; S3. By controlling the range of ultrasonic frequency input to the acousto-optic modulator, the overlapping area of ​​the two sets of long laser beams can be controlled.

[0025] Example 4 Embodiments 1 and 2 require two sets of galvanometer systems to generate two sets of long strip laser beams. This embodiment is a further improvement of Embodiments 1 and 2. Specifically, this embodiment no longer uses two sets of galvanometer systems, but uses a laser beam splitting mechanism to split an incident laser beam into two beams to obtain two sets of long strip laser beams; refer to the attached Figure 8 As shown, the laser beam splitting mechanism is set in front of the XY axis galvanometer of the original scanning system. The laser beam splitting mechanism includes a concave lens group, a beam splitting prism and a convex lens group arranged in sequence along the laser light path. The concave lens group, the beam splitting prism and the convex lens group are coaxially arranged. It should be noted that Figure 8 The XY axis galvanometer and FTheta field mirror are commonly used components in laser scanning systems and are existing technologies. This embodiment adds a laser beam splitting mechanism to the existing scanning system, and no further explanation is given on the original scanning system.

[0026] Refer to the attached Figure 9 As shown, the S1 forms two groups of long laser beams with a scanning width of D in the following manner: S1.1. Direct incident laser light of diameter d0 into the concave lens array, which diffuses the incident laser light. S1.2. Adjust the distance between the concave lens group and the beam splitter prism so that the incident laser beam has a diameter of 2D when it enters the beam splitter prism. The beam splitter prism splits the incident laser beam into two long laser strips with a width of D. S1.3. Two groups of long laser strips are refracted through concave lenses to form two groups of long laser beams with a scanning width of D. Assume that the refractive index of the material of the beam splitter prism is n , No. i The inclination angle of the exit surface is θ i , the deflection angle of the light beam after exiting is α i ,but α i The calculation formula is as follows: ; It can be seen from this that the deflection angle α iIt is related to the refractive index of the material of the beam splitter and the inclination angle of the output surface. When a beam splitter is given, the deflection angle α i is constant and unchanging; And since the width of the incident laser beam when entering the beam splitter is 2D, and the beam splitter is coaxial with the concave lens, after the beam is split, the width of the two laser beams is D, and after the beam is split, the power of the two laser beams is P / 2; S2. Divide the pattern to be printed into several printing blocks; S3. The overlapping area of ​​the two groups of long laser beams is modulated by adjusting the distance between the beam splitter prism and the convex lens group, such as Figure 9 As shown, according to the imaging law of the convex lens group, the angle between the two laser beams after splitting is β It can be expressed by the following formula: , Among them, the initial diameter of the incident laser d 0 It is determined based on the incident laser and is a constant value in the system. In step S1, in order to ensure that the width of the long laser strip after beam splitting is D, the spacing between the concave lens group and the beam splitter prism has been adjusted. L 1 , the deflection angle of the laser emitted from the exit surface of the beam splitter prism α It is also constant, so we only need to adjust the distance between the beam splitter prism and the convex lens group. L 2 , you can adjust the angle between the two laser beams after splitting β , and then adjust the overlapping area of ​​the two long laser beams.

[0027] The present invention has been described in detail above with reference to the embodiments. However, the contents described are only preferred embodiments of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A dual-laser linewidth modulation printing method, characterized in that: It includes the following steps: S1. Set two sets of long laser beams, and the scanning width of the two sets of long laser beams is D; S2. Divide the pattern to be printed into several printing blocks, the width of the printing block is not greater than D; S3. When printing the scanning lines in each printing block, the power of the two sets of long laser beams is modulated to be less than the power P required to melt the metal, and the sum of the powers of the two sets of long laser beams is equal to the power required to melt the metal. The two sets of long laser beams are scanned synchronously along the length direction of the printing block. During the scanning process, the overlapping area of ​​the lasers of the two sets of long laser beams is adjusted according to the actual line width d at the current printing position, so that the width of the overlapping area is the same as the actual line width d at the current position and the position overlaps with the position of the current part to be printed.

2. The dual-laser linewidth modulation printing method according to claim 1, characterized in that: The powers of the two groups of long strip laser beams in S3 are both modulated to half of the power P required to melt the metal.

3. The dual-laser linewidth modulation printing method according to claim 1, characterized in that: During the S3 scanning process, the overlapping area of ​​the lasers of the two groups of long strip laser beams is adjusted according to the actual line width d of the current printing position, so that the width of the overlapping area is the same as the actual line width d at the current position and the position overlaps with the position of the current part to be printed. The specific method is: the left edge of the scanning line is used as the printing path of the left long strip laser beam, and the width of the part of the left long strip laser beam located on the right side of the corresponding printing path is the same as the actual line width d; the right edge of the scanning line is used as the printing path of the right long strip laser beam, and the width of the part of the right long strip laser beam located on the left side of the corresponding printing path is the same as the actual line width d; and the parts of the two groups of long strip laser beams located between the left and right printing paths are overlapped, so that the sum of the powers of the overlapping parts is P.

4. The dual-laser linewidth modulation printing method according to claim 1, characterized in that: When the pattern to be printed is divided into a plurality of printing blocks in S2, the widths of the printing blocks are all the same as the scanning width D of the long strip laser beam.

5. The dual-laser linewidth modulation printing method according to claim 4, characterized in that: The S3 also determines the scan lines in the printing block. If the line widths of the scan lines at all positions in the length direction are the same as the scan width D of the long laser beam, the process proceeds to S4. Otherwise, the process proceeds to S3. S4. Adjust the power of one of the groups of long laser beams to the power P required to melt the metal, and use a single long laser beam to print the scan line.

6. The dual-laser linewidth modulation printing method according to claim 5, characterized in that: In S4, when the scanning lines in one of the printing blocks are determined to have a line width at each position that is the same as the scanning width D of the long laser beam, it is determined whether there are any scanning lines in the unprinted block that meet the requirement that the line width at each position is the same as the scanning width D of the long laser beam. If so, the powers of the two groups of long laser beams are adjusted to the power P required to melt the metal, and the two printing blocks are printed simultaneously using the two groups of long laser beams.

7. The dual-laser linewidth modulation printing method according to claim 1, characterized in that: The two groups of long strip laser beams in S1 are modulated by an acousto-optic modulator. Specifically, the laser beam is injected into the acousto-optic modulator, and two ultrasonic frequency signals are input to the acousto-optic modulator at the same time to form first-order diffracted light and second-order diffracted light. The frequencies of the two ultrasonic waves are modulated so that the first-order diffracted light and the second-order diffracted light are deflected, and the deflection speed satisfies v 2 / v 1≥D / d', where v 2 represents the deflection speed of the first-order diffracted light and the second-order diffracted light, v 1 represents the scanning speed of the galvanometer unit, d' is the spot diameter, and the offset direction is perpendicular to the scanning direction of the galvanometer, thereby forming two sets of long strip laser beams; The S3 controls the overlapping area of ​​the two groups of long strip laser beams by controlling the range of ultrasonic frequency input to the acousto-optic modulator.

8. The dual-laser linewidth modulation printing method according to claim 1, characterized in that: The two groups of long strip laser beams in S1 are obtained by splitting an incident laser beam into two beams through a laser beam splitting mechanism; The laser beam splitting mechanism includes a concave lens group, a beam splitting prism and a convex lens group arranged in sequence along the laser light path, and the concave lens group, the beam splitting prism and the convex lens group are coaxially arranged; The method of forming two groups of long laser beams with a scanning width of D in S1 is as follows: S1.

1. injecting incident laser light with a diameter of d0 into a concave lens group, which is used to diffuse the incident laser light; S1.

2. Adjust the distance between the concave lens group and the beam splitter prism so that the incident laser beam has a diameter of 2D when it enters the beam splitter prism. The beam splitter prism splits the incident laser beam into two long laser strips with a width of D. S1.

3. The two long laser beams are refracted through concave lenses, forming two long laser beams with a scan width of D. The S3 modulates the overlapping area of ​​the two groups of long strip laser beams by adjusting the distance between the beam splitter prism and the convex lens group.

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