A method for five-dimensional adjustment of an end lens of a spatial filter and a device thereof

Abstract

The application discloses a kind of spatial filter end lens adjusting method and device in high-power laser system, including ghost image positioning method, pose adjustment method and five-dimensional control mechanism, so that spatial filter end lens is automatically adjusted.Ghost image positioning method determines the position of the strongest spot focal length measured to the first ghost point of end lens, according to the position relationship to determine the position of end lens in optical axis Z direction, then according to the complete diffraction ring of light beam to judge the pose of lens to meet the adjustment requirements.Five-dimensional control mechanism includes moving platform, static platform, intermediate platform, at least three branch chains and fixed support rod connecting platform.Control mechanism is connected to computer, and the purpose of adjustment is achieved by controlling multiple branch chains to cooperate and cooperate.The application has the characteristics of high sensitivity of ghost image center position error, clear low-order ghost image imaging quality, combined with laser beam diffraction imaging, can be carried out incident light single-sided limited space adjustment operation, and parallel control mechanism has high precision and can be disassembled and used.

Description

Technical Field

[0001] This invention relates to a method and apparatus for adjusting the lens at the end of a space filter in a high-power laser system, and more particularly to an automated method and apparatus for adjusting the lens at the end of a space filter that integrates ghost image positioning, pose adjustment and five-dimensional control mechanism. Background Technology

[0002] Spatial filters are a crucial component of high-power laser devices, and the adjustment of their lens elements significantly impacts the output quality of the laser beam. The two lenses and the filter aperture located on the image plane of the spatial filter must strictly adhere to coaxial and confocal requirements. If the spatial filter is misaligned, the beam passing through the two lenses will exhibit significant aberrations, severely affecting the laser beam quality. Therefore, the lenses at both ends of the spatial filter often require multi-degree-of-freedom adjustment to ensure the beam accuracy meets the coaxial and confocal requirements.

[0003] Traditional lens adjustment methods primarily employ a three-pull, three-top screw structure, but this is prone to slight misalignment due to prolonged exposure to gravity. While ball joint structures improved this, translational adjustments along the optical axis remain extremely laborious, especially when manually rotating the translational sleeve under vacuum conditions within the spatial filter. Furthermore, existing manual adjustments are non-linked movements, often resulting in changes to the adjusted angle due to translational adjustments, necessitating readjustment. Therefore, current technology still has certain shortcomings and is quite inconvenient in practical applications. Summary of the Invention

[0004] This invention achieves positioning and collimation based on the single-lens ghost imaging principle and the light spot diffraction imaging principle. By using spatial parallel multidimensional control, it solves the above problems more efficiently and conveniently on the basis of existing technologies. It provides a single-sided near-field small-range control end-lens beam collimation scheme for the automated development of spatial filter adjustment in high-power laser systems.

[0005] The device of this invention adopts the following technical solution:

[0006] A five-dimensional parallel mechanism for adjusting the end lens of a spatial filter is characterized by comprising a moving platform, a stationary platform, an intermediate platform, a branch, and a fixed support rod connecting the stationary platform and the intermediate platform.

[0007] The static platform consists of a front static platform and a rear static platform that are parallel to each other, and a connecting column connecting the front static platform and the rear static platform. The rear static platform is provided with threaded holes corresponding to the fixing flange of the space filter.

[0008] The chain has at least three links, each consisting of two pairs of ball hinges, a connecting rod, a slider, a fixed support rod, a servo motor, and a lead screw. The servo motor is mounted on the rear stationary platform, and its rotation shaft is connected to one end of the lead screw. The other end of the lead screw passes through the front stationary platform and the slider in sequence. The hinge seat has a slot for the steel ball to be inserted. The two pairs of ball hinges are fixed to the slider and the moving platform, respectively. The two ends of the connecting rod are connected to the ball hinges.

[0009] The fixed support rod is provided with a track for the slider to move.

[0010] The servo motor drives the lead screw to rotate, thereby causing the slider to move on the track of the fixed support rod, causing the ball joint to rotate, and finally realizing the five-dimensional motion control platform of the multi-chain coordinated motion control.

[0011] Each pair of ball hinges consists of a fixed hinge seat, a steel ball, and a movable hinge seat that are movably connected together.

[0012] A method for adjusting the end lens of a spatial filter, characterized in that the method includes the following steps:

[0013] Step 1. Install the above-mentioned five-dimensional parallel mechanism onto the space filter.

[0014] Step 2. Positioning of the principal optical axis (Z-axis) of the lens at the spatial filter end:

[0015] A beam deflector and a laser are fixed above the main optical axis, so that the light emitted by the laser is split into two parallel beams by the beam deflector and directed to the lens at the end of the spatial filter.

[0016] A guide rail is set along the principal optical axis for the CCD camera to move. The CCD camera is controlled by a computer to move along the principal optical axis to the end lens until the light spot in front of the end lens is scanned. The position of the strongest light spot is determined, and the position of the CCD camera relative to the end lens is recorded as the first-order ghost point position. The distance from the end lens to the first-order ghost point position is measured as f1.

[0017] The actual focal length f of the calculated lens 0， The formula is as follows:

[0018]

[0019] Where n is the refractive index of the medium, d is the center thickness of the end lens, R1 represents the radius of curvature of the incident surface of the end lens, f1 is the focal length of the first-order ghost image, and f F It is the distance from the vertex of the end lens surface to the focal point of the end lens.

[0020] Let d1 be the distance from the filter aperture plate of the spatial filter to the exit end face of the bellows. Adjust d2 between the bellows and the end lens. According to the positioning requirements of the lens principal axis Z direction, d2 = f0 - d1 is satisfied, that is, the Z direction adjustment of the principal optical axis of the end lens is completed.

[0021] Step 3. Pitch, yaw, and XY plane translational diffraction imaging positioning:

[0022] A beam splitter and a laser are placed along the principal optical axis of the spatial filter end lens. The light emitted by the laser is transmitted through the beam splitter and then incident on the spatial filter end lens. The light reflected by the end lens is then reflected by the beam splitter to form reflected light.

[0023] A standard lens, a filter, and a CCD camera are placed sequentially along the direction of the reflected light. The reflected light passes through the standard lens and the filter, and the resulting spot is captured by the CCD camera. The precise position of the standard lens is determined according to the Gaussian imaging formula, so that the CCD camera can capture a diffraction spot of appropriate size.

[0024] The computer receives and processes the light spot signal collected by the CCD camera, and controls the movement of the moving platform of the five-dimensional parallel mechanism to adjust the position and orientation of the end lens until the light spot is located at the origin of the coordinate system and a complete diffraction ring appears.

[0025] Step 4. Connect the fixed flange on the space filter using a fixed screw sleeve, and connect the lens flange using a fixed screw, ensuring that the lens flange is in a stationary position relative to the fixed flange.

[0026] It also includes step 5, which involves removing the five-dimensional parallel mechanism and dismantling the CCD camera, beam splitter, standard lens, filter, and laser.

[0027] Step 1 specifically refers to:

[0028] Step 1.1 Design a fixing sleeve and a fixing rod, which are connected by threads to form an adjustable telescopic rod. The outer surface of the fixing sleeve and the fixing rod is designed as a hexagonal prism structure, and the sleeve and the rod are disassembled and assembled with a wrench.

[0029] The space filter bellows assembly has three M8 threaded holes on the lens flange and the fixed flange, corresponding to the moving platform and the stationary platform, respectively. The fixed flange has three Φ10 through holes, forming a circle with a radius larger than the circle formed by the M8 threaded holes. The fixing sleeve can pass through the through holes and be fixed with a nut. The contact surface between the fixing sleeve and the through hole is a spherical frustum. A spherical washer is added to the nut, allowing the fixing sleeve to swing at a certain angle θ within the through hole. θ depends on the thickness b of the fixed flange, and X is the radial swing distance. The swing angle θ is calculated as follows:

[0030] (64-b 2 )X 2 +20b 2X-36b 2 =0

[0031] θ = arctan(X / b)

[0032] Step 1.2 Unscrew the fixing screw out of the screw hole on the fixing flange and loosen the fixing sleeve. The lens flange and the fixing flange are flexibly connected only by the bellows, which allows the lens flange to obtain five degrees of freedom of motion in a limited space. Then, the five-dimensional control mechanism is installed on the bellows assembly, and the static platform is connected to the fixing flange by three bolts to fix the two relative to each other. Similarly, the lens flange and the moving platform are fixed by bolts.

[0033] Step 1.3 Connect the five-dimensional parallel mechanism to the computer interface via cables, and then power it on so that all motors can be controlled by signals to achieve the adjustment purpose.

[0034] In step 3, the computer uses Hough transform to identify the diffraction ring arc and locate the center coordinates. Then, it uses spline interpolation or least squares method to iteratively adjust the center coordinates until a complete diffraction ring is acquired at the center position of the CCD camera.

[0035] Compared with the prior art, the beneficial effects of this invention are:

[0036] When the optical path transmission element of the lens adjustment device is used for Z-axis positioning of the opposite lens, it only needs to be controlled and adjusted within a 1.5-meter range on one side of the spatial filter. The ghost image has high sensitivity to center position error and can acquire a clear first-order ghost image. The positioning accuracy can reach the millimeter level (2.59mm). The parallel control mechanism has high accuracy and can be disassembled and used. Attached Figure Description

[0037] Figure 1 Schematic diagram of Z-axis positioning for ghost imaging of a lens

[0038] Figure 2 Schematic diagram of lens parallel adjustment device

[0039] Figure 3 Overall structure diagram of five-dimensional parallel mechanism

[0040] Figure 4 Single-branch structure diagram of the device

[0041] Figure 5 Exploded view of the device branch

[0042] Figure 6 collimation and diffraction spot

[0043] Figure 7 Connection diagram of fixed screw and threaded sleeve

[0044] Figure 8Fixed threaded sleeve, where a is a structural schematic diagram and b is a cross-sectional view of a.

[0045] Figure 9 Fixed screw

[0046] In the picture:

[0047] 1. CCD camera; 2. Beam deflector; 3. Laser; 4. End lens; 5. Bellows; 6. Filter pinhole plate; 7. Spatial filter; 8. Computer; 9. Standard lens; 10. Beam splitter; 11. Moving platform; 12. Lens flange; 13. Fixing sleeve; 14. Stationary platform; 15. Fixing flange; 16. Filter; 17. Fixing screw; 18. Intermediate platform; B-1. Ball joint; B-2. Steel ball; B-3. Connecting rod; B-4. Slider; B-5. Fixing support rod; B-6. Servo motor; B-7. Lead screw; B-8. Front stationary platform; B-9. Connecting column; B-10. Rear stationary platform; B-11. M8 threaded hole; B-12. Motor screw hole; B-13. Φ10 through hole connecting nut; B-14. M8 fixing thread Detailed Implementation

[0048] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0049] This invention is used when the lens at the end of the spatial filter needs adjustment. It is implemented through the following steps: (1) Install the five-dimensional control mechanism: unscrew the fixing screw 17 out of the screw hole on the fixing flange 15, loosen the fixing screw sleeve 13, and the lens flange 12 and the fixing flange 15 are flexibly connected only by the bellows 5, which allows the lens flange 12 to obtain five degrees of freedom of movement in a limited space. Then, put the five-dimensional control mechanism on the fixing flange 15, the bellows 5 and the lens flange 12, and the lens flange 12 and the fixing flange 15 are flexibly connected only by the bellows 5, which allows the lens flange 12 to obtain five degrees of freedom of movement in a limited space. Then, install the five-dimensional control mechanism on the bellows assembly, and fix the static platform 14 to the fixing flange 15 by connecting it with three bolts. Similarly, fix the lens flange 12 and the moving platform 11 by bolts. The servo motor B-6 drives the lead screw B-7 to rotate, which drives the slider B-4 to move back and forth on the track of the fixed support rod B-5. The coordinated movement of multiple branches controls the moving platform 11 to produce five-dimensional movements.

[0050] (2) Z-axis positioning of the end lens principal optical axis: A beam deflector 2 is fixed above the principal optical path. The light emitted by the laser 3 is split into two parallel beams by the beam deflector 2 and directed towards the end lens 4 of the spatial filter. Due to the transmission and reflection effect of the end lens 4, the two parallel beams will form multiple ghost images near the lens. The image farthest from the incident surface of the lens is called the first-order ghost image. The computer sends instructions to control the CCD camera 1 to move along the optical axis towards the end lens 4 until the light spot in front of the end lens 4 is scanned. The position of the CCD camera 1 is fine-tuned according to the image software to determine the position of the strongest light spot. The position of the CCD camera 1 relative to the end lens 4 is recorded as the first-order ghost point position. The distance from the end lens 4 to the first-order ghost point position is measured as f1. The actual focal length f0 of the end lens can be calculated according to the following simplified ghost image calculation formula:

[0051]

[0052] Where n is the refractive index of the medium, d is the center thickness of the end lens 4, R1 represents the radius of curvature of the incident surface of the end lens 4, f1 is the focal length of the first-order ghost image, and f F It is the distance from the vertex of the surface of end lens 4 to the focal point of end lens 4.

[0053] Let d1 be the distance from the filter aperture plate 6 of the space filter 7 to the exit end face of the bellows 5. Adjust the distance d2 between the bellows 5 and the end lens 4. According to the positioning requirements of the lens principal axis Z direction, d2 = f0 - d1 is satisfied, that is, the adjustment of the principal optical axis Z direction of the end lens 4 is completed.

[0054] (3) Pitch, yaw and XY plane translation diffraction imaging positioning: Place the beam splitter 10 and the laser 3 along the principal optical axis of the lens at the end of the space filter, so that the light emitted by the laser 3 is transmitted through the beam splitter 10 and then incident on the lens at the end of the space filter. The light reflected by the lens at the end of the lens 4 is reflected by the beam splitter 10 to form reflected light.

[0055] A standard lens 9, a filter 16, and a CCD camera 1 are placed sequentially along the direction of the reflected light. The reflected light passes through the standard lens 9 and the filter 16 and converges into a spot that is then captured by the CCD camera 1. The precise position of the standard lens 9 is determined according to the Gaussian imaging formula, so that the CCD camera can capture a diffraction spot of a suitable size.

[0056] Computer 8 receives and processes the light spot signal collected by CCD camera 1, and controls the movement of the moving platform 11 of the five-dimensional parallel mechanism to adjust the position and orientation of the end lens 4 until the light spot is located at the origin of the coordinate system and a complete diffraction ring appears.

[0057] Finally, the fixed flange 15 on the space filter 7 is connected via the fixed threaded sleeve 13, and the lens flange 12 is connected via the fixed screw 17. Since the fixed threaded sleeve 13 and the fixed screw 17 are retractable threaded connections, the lens flange 12 is kept in a stationary position relative to the fixed flange 15. The bolts and nuts on the dynamic and static platform 14, fixed flange 15, and lens flange 12 are then removed, and the five-dimensional control mechanism is carefully moved out. The installed CCD camera 1, beam splitter 10, and laser 3 are then dismantled.

[0058] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any transformations or substitutions that can be conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of the present invention.

Claims

1. A five-dimensional parallel mechanism for spatial filter end lens adjustment, characterized in that, The five-dimensional parallel mechanism comprises a moving platform (11), a static platform (14), an intermediate platform (18), a plurality of branches and a fixed support rod (B-5) connecting the static platform (14) and the intermediate platform (18). The static platform (14) is composed of a front static platform (B-8) and a rear static platform (B-10) which are parallel to each other, and a connecting column (B-9) connecting the front static platform (B-8) and the rear static platform (B-10), wherein a threaded hole (B-14) corresponding to the fixing flange (15) of the spatial filter is arranged on the rear static platform (B-10). Each of the branches is composed of two pairs of ball hinges (B-1), connecting rods (B-3), sliding blocks (B-4), fixed support rods (B-5), servo motors (B-6) and lead screws (B-7), wherein the servo motor (B-6) is installed on the rear static platform (B-10), the rotating shaft of the servo motor (B-6) is connected with one end of the lead screw (B-7), the other end of the lead screw (B-7) passes through the front static platform (B-8) and the sliding block (B-4) in sequence, the ball hinges (B-1) are provided with clamping grooves for embedding steel balls (B-2), and the two pairs of ball hinges (B-1) are fixed on the sliding block (B-4) and the moving platform (11) respectively, and the connecting rods (B-3) are connected with the ball hinges (B-1) at two ends. The fixed support rod (B-5) is provided with a track for the movement of the sliding block (B-4). The ball hinges (B-1) are connected with the sliding block (B-4) and the moving platform (11) through the connecting rods (B-3), the servo motor (B-6) drives the rotation of the lead screw (B-7), thereby driving the movement of the sliding block (B-4) on the track of the fixed support rod (B-5), rotating the ball hinges (B-1), and then pushing or pulling the moving platform (11) through the connecting rods (B-3), so as to realize the coordinated movement control of the moving platform (11) through the plurality of branches to generate five-dimensional actions. Each pair of ball hinges (B-1) is composed of a fixed hinge seat, a steel ball (B-2) and a movable hinge seat.

2. A method of adjusting a spatial filter end lens, characterized by, The method comprises the following steps: Step 1: installing the five-dimensional parallel mechanism of claim 1 on the spatial filter; Step 2: positioning the main optical axis Z of the end lens of the spatial filter: Fixing a beam bender (2) and a laser (3) above the main optical axis, so that the light emitted by the laser (3) is divided into two parallel beams by the beam bender (2) and is respectively emitted to the end lens (4) of the spatial filter; Providing a guide rail for the movement of the CCD camera along the main optical axis, and moving the CCD camera along the main optical axis to the end lens (4) through computer control until the front light spot of the end lens (4) is scanned, determining the position of the strongest light spot, recording the position of the CCD camera (1) relative to the end lens (4) as the first-order ghost point position, and measuring the distance from the end lens (4) to the first-order ghost point position as f1; The actual focal length f of the end lens is calculated 0， The formula is as follows: where n is the refractive index of the medium, d is the central thickness of the end lens (4), R1 represents the radius of curvature of the entrance face of the end lens (4), f1 is the focal length of the first order ghost image, f F is the distance from the surface vertex of the end lens (4) to the focal point of the end lens (4); The distance d1 between the filtering pinhole plate (6) of the spatial filter (7) and the exit end surface of the bellows (5) is set, the distance d2 between the bellows (5) and the end lens (4) is adjusted, and the positioning requirement in the direction of the main axis Z of the lens is met, i.e., d2=f0-d1, so that the main optical axis Z of the end lens (4) is adjusted; Step 3. Pitch yaw and X-Y plane translation diffraction imaging positioning: The light splitter (10) and the laser (3) are placed along the direction of the main optical axis of the spatial filter end lens, so that the light emitted by the laser (3) is transmitted through the light splitter (10) and then incident on the spatial filter end lens (4), and the reflected light of the spatial filter end lens (4) is reflected through the light splitter (10) to form reflected light; The standard lens (9), the optical filter (16) and the CCD camera (1) are placed in sequence along the direction of the reflected light, so that the light spot after the reflected light passes through the standard lens (9) and the optical filter (16) is collected by the CCD camera (1), the accurate position of the standard lens (9) is determined according to the Gaussian imaging formula, and the CCD camera can collect the diffraction light spot with an appropriate size; The computer (8) receives the light spot signal collected by the CCD camera (1) and processes it, controls the motion of the moving platform (11) of the five-dimensional parallel mechanism, adjusts the position and posture of the end lens (4), and finally the light spot is located at the origin of the coordinate system and a complete diffraction ring appears. Step 4. The fixed flange (15) on the spatial filter (7) is connected through the fixed screw sleeve (13), and the lens flange (12) is connected through the fixed screw rod (17), so that the lens flange (12) is kept in a static position relative to the fixed flange (15).

3. The method of claim 2, wherein the spatial filter end lens is adjusted by, Step 5. The five-dimensional parallel mechanism of claim 1 is removed, and the CCD camera (1), the light splitter (10), the standard lens (9), the optical filter (16) and the laser (3) are removed.

4. The method of claim 2, wherein the spatial filter end lens is adjusted by, The step 1 is specifically: Step 1.

1. The fixed screw sleeve (13) and the fixed screw rod (17) are designed, and a telescopic rod is formed through threaded connection. The outer surfaces of the fixed screw sleeve (13) and the fixed screw rod (17) are designed as hexagonal prism structures, which can be disassembled by a wrench. The lens flange (12) and the fixed flange (15) in the spatial filter bellows assembly are provided with three M8 threaded holes corresponding to the moving platform (11) and the static platform (14), and three Φ10 through holes are formed in the fixed flange (15), the radius of the circle formed by the through holes is greater than the radius of the circle formed by the M8 threaded holes, the fixed screw sleeve (13) can pass through the through hole and be fixed by a nut, the contact surface between the fixed screw sleeve (13) and the through hole is a spherical table surface, a spherical gasket is added to cooperate with the nut, so that the fixed screw sleeve can swing by a certain angle θ in the through hole, and θ depends on the thickness b of the fixed flange. The calculation method of the swing angle θ is as follows: (64-b 2 )X 2 +20b 2 X-36b 2 =0 θ=arctan(X / b) Step 1.2 Unscrew the fixed screw (17) from the screw hole of the fixed flange (15), unscrew the fixed screw sleeve (13), and only the bellows (5) is used to form a flexible connection between the lens flange (12) and the fixed flange (15), which makes the lens flange (12) have five degrees of freedom movement in a limited space; then install the five-dimensional control mechanism on the bellows assembly, and tightly connect the static platform (14) to the fixed flange (15) through three bolts, so that the two are relatively fixed; similarly, the lens flange (12) and the moving platform (11) are fixed by bolts; Step 1.3 Connect the five-dimensional parallel mechanism to the interface of the computer (8) through a cable, then power on so that all motors can be controlled by signals to achieve the adjustment purpose.

5. The method of claim 2, wherein the spatial filter end lens is adjusted by, In step 3, the computer (8) uses Hough transform to identify the diffraction ring arc and locate the center coordinates, and then uses spline interpolation method or least squares method to iteratively adjust the center coordinates until a complete diffraction ring is collected at the center position of the CCD camera (1).

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