Polishing system for large-aperture optical element

Abstract

The invention discloses a polishing system for a large-aperture optical element, which relates to the technical field of optical element processing and comprises a controller, a base, a supporting structure, a driving device, a polishing head assembly and a clamping device, two groups of parallel supporting structures are mounted on the upper surface of the base; a group of driving devices in the X-axis direction are mounted on each group of supporting structures, a group of driving devices in the Y-axis direction perpendicular to the supporting structures are mounted on the two groups of driving devices in the X-axis direction, and a group of driving devices in the Z-axis direction perpendicular to the base are mounted on the driving devices in the Y-axis direction; the polishing head assembly is installed on the driving device in the Z-axis direction. The clamping device is installed on the upper surface of the base and located below the polishing head assembly. The controller is connected with the driving device and the polishing head assembly. The driving device and the polishing head assembly are accurately controlled through the controller, self-adaptive adjustment of the polishing pressure is carried out, and the element surface machining quality is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of optical element processing, and more particularly to a polishing system for large-aperture optical elements. Background Art

[0002] In the manufacturing process of large-aperture optical components, surface polishing is a critical step in ensuring high precision and quality. Widely used in aerospace, military, communications, and other fields, large-aperture optical components place extremely high demands on surface quality and form accuracy. Therefore, precise control during the polishing process is crucial. Ideally, the contact pressure between the polishing head and the optical component should be constant and uniform. However, traditional polishing techniques face numerous challenges, resulting in unstable polishing results and difficulty in ensuring surface quality.

[0003] Currently, conventional polishing systems primarily rely on constant pressure control. While simple, this approach cannot effectively adapt to surface nonuniformities due to the irregular surface shape, varying material properties, and varying contact patterns between the polishing head and the workpiece, making it difficult to maintain a constant polishing pressure. This approach cannot adjust the polishing pressure in real time, resulting in machining defects such as surface unevenness, scratches, and localized deformation, ultimately impacting the performance of the optical component. Constant pressure control also suffers from control hysteresis, making it ineffective in addressing the rapid changes in surface morphology and pressure during the polishing process, further reducing machining accuracy and efficiency. To overcome this issue, force feedback control has been gradually introduced into the polishing field in recent years. By monitoring the contact force between the polishing head and the workpiece in real time, force feedback control systems can adjust the polishing head's motion based on the feedback signal, ensuring that pressure remains as stable as possible during the polishing process. However, existing force feedback control systems still face certain limitations. Although force feedback can detect changes in contact force in real time, the system's slow response speed often lags behind actual changes in control strategy. This makes it difficult for the system to respond to pressure fluctuations during dynamic machining processes, resulting in fluctuations in surface quality and reduced polishing efficiency.

[0004] Therefore, how to improve the polishing quality of large-aperture optical elements is an urgent problem that needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention provides a polishing system for large-aperture optical elements, which is an efficient polishing control system that can accurately control polishing pressure, quickly respond to surface changes and can adaptively adjust, ensuring that large-aperture optical elements achieve uniform, stable and high-quality surface processing during the polishing process.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A polishing system for large-aperture optical elements, comprising a controller, a base, a support structure, a drive device, a polishing head assembly, and a clamping device;

[0008] Two sets of parallel support structures are mounted on the upper surface of the base; a set of X-axis drive devices is mounted on each set of support structures, and a set of Y-axis drive devices perpendicular to the support structures is mounted on the two sets of X-axis drive devices, and a set of Z-axis drive devices perpendicular to the base is mounted on the Y-axis drive devices; the polishing head assembly is mounted on the Z-axis drive devices; the clamping device is mounted on the upper surface of the base, below the polishing head assembly;

[0009] The controller is connected to the driving device and the polishing head assembly.

[0010] Preferably, the base is made of high-strength aluminum alloy, which has good deformation resistance and sufficient load-bearing capacity.

[0011] Preferably, the supporting structure is mainly composed of square aluminum profiles, and the surface is precisely processed to ensure that it has sufficient stability and accuracy.

[0012] Preferably, the drive device includes a ball screw and a screw-nut transmission mechanism. The screw-nut transmission mechanism is fixed to the support structure and connected to one end of the ball screw, driving the ball screw to rotate. The polishing head assembly is mounted on the ball screw of the drive device in the Z-axis direction. The screw-nut transmission mechanism is connected to the controller. The output shaft of the screw-nut transmission mechanism is connected to one end of the ball screw, enabling fine height adjustment, so that the Z-axis height of the polishing head assembly can be precisely adjusted to suit optical components of different specifications.

[0013] Preferably, the screw-nut transmission mechanism of the driving device in the Y-axis direction is fixed to the I-shaped plate with bolts, and the I-shaped plate is sleeved on the ball screw of the driving device in the X-axis direction; the screw-nut transmission mechanism of the driving device in the Z-axis direction is fixed to the I-shaped plate with bolts, and the I-shaped plate is sleeved on the ball screw of the driving device in the Y-axis direction.

[0014] Preferably, the polishing head assembly includes a low-friction cylinder, a flange, a pressure sensor, an air motor, and a polishing plate; the guide rod of the low-friction cylinder is connected to the flange, and the floating joint of the low-friction cylinder head is fixedly connected to the upper surface of the flange; the pressure sensor is fixed to the lower surface of the flange via a connector using bolts; the air motor is fixedly connected to the lower surface of the pressure sensor using bolts, and the drive shaft of the air motor is connected to the polishing plate; the pressure sensor and the air motor are respectively connected to a controller. The pressure sensor can sense pressure changes between the polishing head and the surface of the optical element, monitor the contact pressure in real time during the polishing process, and then transmit the pressure data to the controller. The controller can adjust the polishing pressure in real time during the polishing process through dynamic feedback control to ensure that the pressure is always maintained within the optimal range, thereby improving the polishing quality and efficiency; the controller controls the low-friction cylinder to move the floating joint and the flange, thereby determining the working position and adjusting the contact pressure of the polishing plate.

[0015] Preferably, the low-friction cylinder and the ball screw of the driving device are connected by bolts through an L-shaped mounting plate.

[0016] Preferably, the clamping device adopts an adjustable clamping jaw structure, and the inner side of the clamping jaw is made of soft and elastic material.

[0017] Preferably, a displacement sensor is provided on the ball screw of the driving device on which the polishing head assembly is mounted, and is connected to the controller for collecting the displacement of the polishing disc when the polishing disc moves.

[0018] Preferably, the process of the controller performing dynamic feedback control according to the pressure data includes:

[0019] Step 1: Construct the contact dynamics model between the polishing pad and the large-aperture optical element based on the dynamic force balance equation, which can be expressed as:

[0020]

[0021] Where m is the equivalent mass of the polishing disc, c is the damping coefficient, k is the contact stiffness, z is the displacement of the polishing disc, and F act is the output thrust of the low-friction cylinder; F contactis the pressure data; the equivalent mass is determined according to the mass of the polishing disc and the inertia of its moving parts; the damping coefficient reflects the energy dissipation characteristics of the system during movement; the contact stiffness k is related to the contact characteristics between the polishing disc and the large-aperture optical element, and is the equivalent stiffness when the two are in contact. It is affected by factors such as material properties and contact area. The contact stiffness is determined according to the material and contact area of ​​the polishing disc and the large-aperture optical element; the displacement of the polishing disc is measured by the displacement sensor installed on the drive device, and the displacement of the polishing disc is monitored in real time to ensure precise adjustment and control; the low-friction cylinder and pneumatic motor that drive the movement of the polishing disc serve as actuators. The low-friction cylinder is responsible for controlling the up and down movement of the polishing head to ensure that the contact pressure between the polishing disc and the surface of the optical element remains constant, and the pneumatic motor is responsible for driving the polishing disc to rotate and provide the power required for polishing; the output thrust of the low-friction cylinder is determined by the input air pressure and piston size;

[0022] Step 2: Based on the real-time pressure data F contact , calculate the real-time polishing pressure P real =F Contact / A, where A is the contact area between the polishing disk and the large-aperture optical element;

[0023] Step 3: Calculate the error based on the real-time polishing pressure and the target polishing pressure, expressed as e(t) = P target -P real (t); P target Indicates the target polishing pressure;

[0024] Step 4: Use the improved PI control algorithm to adjust the polishing pressure. The improved PI control algorithm expression is:

[0025]

[0026] Among them, P control (t) represents the desired polishing pressure after adjustment at time t; K p and K i are proportional gain and integral gain respectively;

[0027] Step 5: The contact dynamics model and the improved PI control algorithm are used to derive the controller transfer function G(s) through Laplace transform, which is expressed as:

[0028]

[0029] Where s represents the Laplace variable, which represents the complex frequency in the frequency domain. This transfer function describes the dynamic response of the controller, drive device, and polishing head assembly, providing a basis for system stability analysis.

[0030] Step 6: Use the Routh-Hurwitz criterion to analyze the closed-loop characteristic equation established based on the transfer function to obtain the stability condition to ensure the stability of the system;

[0031] The closed-loop feature direction is expressed as:

[0032] ms 2 +cs+k+K p s+K i =0

[0033] The stability condition is expressed as:

[0034]

[0035] Step 7: Use the pole placement method to set the desired poles s1 = -α, s2, s3 = -β ± jγ; substitute the desired extreme values ​​into the closed-loop characteristic equation to derive the gain optimization formula, which is expressed as:

[0036] K pold =m(α+2β)-c,K iold =mαβ 2 +mαγ 2

[0037] Among them, K pold Indicates the optimized proportional gain; K iold Represents the optimized integral gain; α represents the damping ratio of the system, reflecting the damping characteristics of the system; β and γ represent parameters related to the dynamic characteristics of the system, which are used for pole configuration and gain optimization respectively;

[0038] Step 8: Adaptively adjust the gain based on the real-time feedback error, and dynamically adjust the proportional gain K by observing the sensitivity of the error to the gain. p Integral gain K i , the gain adjustment formula is expressed as:

[0039]

[0040] Among them, η p and η i They represent the adjustment coefficients of the proportional gain and the integral gain, respectively, and are used to dynamically adjust the gain; sgn represents the sign function, which is used to indicate the direction of the error change trend; Represents the error e versus proportional gain K p The partial derivative of , which shows the effect of the change in proportional gain on the error; It represents the error e versus the integral gain K i The partial derivative of , which shows the effect of the change of integral gain on the error;

[0041] Step 9: Calculate the optimal gain based on the gain optimization formula and the gain adjustment formula, and substitute the optimal gain into the improved PI control algorithm to adjust the polishing pressure to obtain the desired polishing pressure; the expression of the optimal gain is:

[0042] K pnew =K pold +ΔK p , K inew =K iold +ΔK i

[0043] Among them, K pnew represents the optimal proportional gain; K inew represents the optimal integral gain;

[0044] Step 10: Calculate the expected pressure data according to the expected polishing pressure, generate the expected output thrust of the low-friction cylinder and the expected polishing disk displacement based on the contact dynamics model, adjust the polishing head assembly according to the expected output thrust of the low-friction cylinder, and adjust the drive device according to the expected polishing disk displacement.

[0045] Through the above technical solutions, it can be seen that compared with the prior art, the present invention discloses a polishing system for large-aperture optical elements, which is composed of a base, a support structure, a drive device, a polishing head assembly, a clamping device and a controller. Taking into account the unique needs of large-aperture optical elements, it combines advanced mechanical control, dynamic feedback adjustment and intelligent polishing technology, aiming to solve the technical bottleneck that the traditional constant pressure control method of the traditional polishing system cannot effectively cope with the changes caused by the irregularities of the workpiece surface in the processing of large-aperture optical elements, which often leads to uneven processing quality. By designing the polishing system, introducing dynamic control based on force feedback and adaptive gain adjustment, and adjusting the control gain in real time, the system can cope with various polishing conditions, accurately control the contact pressure during the polishing process, effectively reduce the standard deviation of pressure fluctuations during the polishing process, overcome the adverse effects of workpiece surface irregularities on processing quality, thereby improving the processing accuracy and consistency of large-aperture optical elements, and ensuring the accuracy, stability and efficiency of the processing process. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0047] Figure 1 A schematic structural diagram of a polishing system for large-aperture optical elements provided by the present invention;

[0048] Figure 2 A schematic structural diagram of the clamping device provided by the present invention;

[0049] Figure 3 This is a schematic structural diagram of the polishing head assembly provided by the present invention.

[0050] In the accompanying drawings: 1-base, 2-support structure, 3-drive device, 31-ball screw, 32-screw nut transmission mechanism, 4-polishing head assembly, 41-low friction cylinder, 411-floating joint, 42-flange, 43-pressure sensor, 44-pneumatic motor, 45-polishing disk, 46-mounting plate, 47-connector, 5-clamping device, 51-clamping claw. DETAILED DESCRIPTION

[0051] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0052] The embodiment of the present invention discloses a polishing system for large-aperture optical elements, such as Figure 1 As shown, it includes a controller, a base 1, a support structure 2, a drive device 3, a polishing head assembly 4 and a clamping device 5; two sets of parallel support structures 2 are installed on the upper surface of the base 1; a set of X-axis drive devices 3 is installed on each set of support structures 2, and a set of Y-axis drive devices 3 perpendicular to the support structure is installed on the two sets of X-axis drive devices 3, and a set of Z-axis drive devices 3 perpendicular to the base 1 is installed on the Y-axis drive devices 3; the polishing head assembly 4 is installed on the Z-axis drive device 3; the clamping device 5 is installed on the upper surface of the base 1, below the polishing head assembly 4; the controller connects the drive device 3 and the polishing head assembly 4.

[0053] Furthermore, the base 1 is made of high-strength aluminum alloy, which has good anti-deformation ability and sufficient load-bearing capacity. The base is the basic part, responsible for supporting the heavy load of the entire device and ensuring the stability of the moving parts.

[0054] Furthermore, the support structure 2 is primarily composed of square aluminum profiles, with a precision-machined surface to ensure sufficient stability and accuracy. A drive device 3 is mounted on the support structure 2 to ensure that each moving component follows a precise trajectory, minimizing mechanical errors.

[0055] Furthermore, the drive unit 3 includes a ball screw 31 and a screw-nut transmission mechanism 32. The screw-nut transmission mechanism 32 is fixed to the support structure 2 and connected to one end of the ball screw 31, driving the ball screw 31 to rotate. The polishing head assembly 4 is mounted on the ball screw 31 of the drive unit in the Z-axis direction. The screw-nut transmission mechanism 32 is connected to the controller. The drive unit 3 uses a high-precision ball screw 31 as its core drive source, which has extremely high transmission accuracy and stability. The output shaft of the screw-nut transmission mechanism 32 is connected to one end of the ball screw 31, allowing for fine height adjustment, allowing the Z-axis height of the polishing head assembly 4 to be precisely adjusted to suit optical components of different specifications.

[0056] Furthermore, the screw and nut transmission mechanism of the driving device in the Y-axis direction is fixed to the I-shaped plate with bolts, and the I-shaped plate is sleeved on the ball screw of the driving device in the X-axis direction; the screw and nut transmission mechanism of the driving device in the Z-axis direction is fixed to the I-shaped plate with bolts, and the I-shaped plate is sleeved on the ball screw of the driving device in the Y-axis direction.

[0057] Further, such as Figure 3 As shown, the polishing head assembly 4 includes a low-friction cylinder 41, a flange 42, a pressure sensor 43, an air motor 44 and a polishing disc 45; the guide rod of the low-friction cylinder 41 is connected to the flange 42 and passes through the flange, and the floating joint 422 at the head of the low-friction cylinder 41 is fixedly connected to the upper surface of the flange 42; the pressure sensor 43 is fixed to the lower surface of the flange 42 through the connecting piece 47 by bolts; the air motor 44 is fixedly connected to the bottom of the pressure sensor 43 by bolts, and the transmission shaft of the air motor 44 is connected to the polishing disc 45; the pressure sensor 43 and the air motor 44 are respectively connected to the controller. The polishing disc 45 is the part that is in direct contact with the surface of the optical element and is responsible for physically removing the optical element; the pneumatic motor 44 is the power source of the polishing disc 45, and precisely drives the polishing disc 45 to rotate at a stable speed. The rotary drive mechanism has high speed stability and can maintain a constant speed during operation to avoid surface defects caused by speed fluctuations; the pressure sensor 43 can sense the pressure changes between the polishing disc 45 and the surface of the optical element, monitor the contact pressure during the polishing process in real time, and then transmit the pressure data to the controller. The controller can adjust the polishing pressure in real time during the polishing process through dynamic feedback control to ensure that the pressure always remains within the optimal range, thereby improving the polishing quality and efficiency; the low-friction cylinder is controlled by the controller to move the floating joint and flange to determine the working position and adjust the contact pressure of the polishing disc.

[0058] Furthermore, the low-friction cylinder 41 and the ball screw 31 of the driving device 3 are connected by bolts through the L-shaped mounting plate 46 .

[0059] Furthermore, the clamping device 5 adopts an adjustable clamping claw structure, and the inner side of the clamping claw 51 is made of soft and elastic material, such as Figure 2 As shown. The clamping device is used to fix the large-aperture optical element to be polished to ensure that it does not move during the polishing process. The clamping jaws can be precisely adjusted according to the different sizes and shapes of the optical element. The inner side of the clamping jaws is made of soft and elastic material to avoid indentations or scratches on the surface of the optical element during the clamping process. The clamping device 5 is fixed to the base 2 by bolts to ensure that the contact position between the optical element and the polishing disk 45 is accurate. In one embodiment, the clamping device includes a fixed disc and a clamping jaw structure. The clamping jaw structure includes three groups of arc-shaped clamping jaws and a spring, one end of which is rotatably connected to the fixed disc and the other end abuts against each other, and the three groups of arc-shaped clamping jaws are evenly distributed on the arc-shaped disc; one end of the spring is connected to the fixed end of the arc-shaped clamping jaw, and the other end is fixed to the fixed disc. The spring is used to adjust the rotation angle of the clamping jaw so that the clamping jaw can clamp elements of different sizes.

[0060] Furthermore, a displacement sensor is provided on the ball screw 31 of the driving device 3 on which the polishing head assembly 4 is mounted, and is connected to the controller for collecting the displacement of the polishing disc 45 when the polishing disc 45 moves.

[0061] On the other hand, in a specific embodiment, the process of the controller performing dynamic feedback control according to the pressure data includes:

[0062] S1: The contact dynamics model between the polishing plate and the large-aperture optical element is constructed based on the dynamic force balance equation, which is expressed as:

[0063]

[0064] Where m is the equivalent mass of the polishing disc, c is the damping coefficient, k is the contact stiffness, z is the displacement of the polishing disc, and F act is the output thrust of the low-friction cylinder; F contact is pressure data; the equivalent mass is determined based on the mass of the polishing disc and the inertia of its moving parts; the damping coefficient reflects the energy dissipation characteristics of the system during movement; the contact stiffness is related to the contact characteristics between the polishing disc and the large-aperture optical element, and is the equivalent stiffness when the two are in contact. It is affected by factors such as material properties and contact area, and is determined based on the material and contact area of ​​the polishing disc and the large-aperture optical element; the displacement of the polishing disc is measured by a displacement sensor installed on the drive device, and the displacement of the polishing disc is monitored in real time to ensure precise adjustment and control; the low-friction cylinder and pneumatic motor that drive the movement of the polishing disc serve as actuators. The low-friction cylinder is responsible for controlling the up and down movement of the polishing head to ensure that the contact pressure between the polishing disc and the surface of the optical element remains constant, and the pneumatic motor is responsible for driving the polishing disc to rotate and provide the power required for polishing; the output thrust of the low-friction cylinder is determined by the input air pressure and piston size;

[0065] S2: According to the real-time measured pressure data F contact , calculate the real-time polishing pressure P real =F Contact / A, where A is the contact area between the polishing disk and the large-aperture optical element;

[0066] S3: Calculate the error based on the real-time polishing pressure and the target polishing pressure, expressed as e(t) = P target -P real (t); P target Indicates the target polishing pressure;

[0067] S4: The polishing pressure is adjusted using an improved PI control algorithm. The expression of the improved PI control algorithm is:

[0068]

[0069] Among them, P control (t) represents the desired polishing pressure after adjustment at time t; K p and K i are proportional gain and integral gain respectively;

[0070] S5: Contact dynamics model and improved PI control algorithm Through Laplace transform, the controller transfer function G(s) is derived and expressed as:

[0071]

[0072] Where s represents the Laplace variable, which represents the complex frequency in the frequency domain. This transfer function describes the dynamic response of the controller, drive device, and polishing head assembly, providing a basis for system stability analysis.

[0073] S6: Use the Routh-Hurwitz criterion to analyze the closed-loop characteristic equation established based on the transfer function to obtain the stability condition and ensure the stability of the system;

[0074] The closed-loop feature direction is expressed as:

[0075] ms 2 +cs+k+K p s+K i =0

[0076] The stability condition is expressed as:

[0077]

[0078] S7: Set the desired poles s1 = -α, s2, s3 = -β ± jγ by pole placement. Substitute the desired poles into the closed-loop characteristic equation to derive the gain optimization formula, which is expressed as:

[0079] K pold =m(α+2β)-c,K iold =mαβ 2 +mαγ 2

[0080] Among them, K pold Indicates the optimized proportional gain; K iold Represents the optimized integral gain; α represents the damping ratio of the system, reflecting the damping characteristics of the system; β and γ represent parameters related to the dynamic characteristics of the system, which are used for pole configuration and gain optimization respectively;

[0081] S8: Adaptively adjust the gain based on the real-time feedback error, and dynamically adjust the proportional gain K by observing the sensitivity of the error to the gain p Integral gain K i , the gain adjustment formula is expressed as:

[0082]

[0083] Among them, η p and η i They represent the adjustment coefficients of the proportional gain and the integral gain, respectively, and are used to dynamically adjust the gain; sgn represents the sign function, which is used to indicate the direction of the error change trend; Represents the error e versus proportional gain K p The partial derivative of , which shows the effect of the change in proportional gain on the error; It represents the error e versus the integral gain K i The partial derivative of , which shows the effect of the change of integral gain on the error;

[0084] S9: Calculate the optimal gain according to the gain optimization formula and the gain adjustment formula, substitute the optimal gain into the improved PI control algorithm to adjust the polishing pressure and obtain the desired polishing pressure; the expression of the optimal gain is:

[0085] K pnew =K pold +ΔK p , K inew =K iold +ΔK i

[0086] Among them, K pnew represents the optimal proportional gain; K inew represents the optimal integral gain;

[0087] S10: Based on the desired polishing pressure, the system calculates the desired pressure data. Based on the contact dynamics model, it generates the desired low-friction cylinder output thrust and the desired polishing plate displacement. The polishing head assembly is adjusted based on the desired low-friction cylinder output thrust, and the drive mechanism is adjusted based on the desired polishing plate displacement. This dynamic adjustment allows the system to adapt to surface variations of large-diameter optical components, ensuring that the polishing pressure remains within the optimal range, thereby ensuring consistent machining quality.

[0088] The polishing system of this invention enables real-time adjustment of polishing pressure, effectively avoiding the processing defects caused by traditional constant pressure control. Employing dynamic control based on force feedback and an improved PI control algorithm, the system dynamically adjusts gain based on real-time feedback, ensuring the stability and efficiency of the polishing process. Furthermore, the system optimizes gain adjustment through online parameter identification technology, making the polishing process more precise and significantly improving the processing quality and consistency of large-aperture optical components, meeting the requirements of high-precision machining.

[0089] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Reference can be made to the common and similar parts between the various embodiments. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method description.

[0090] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A polishing system for large-aperture optical elements, characterized in that: It includes a controller, a base, a support structure, a drive device, a polishing head assembly and a clamping device; Two sets of parallel support structures are installed on the upper surface of the base; a set of X-axis drive devices is installed on each set of support structures, and a set of Y-axis drive devices perpendicular to the support structures is installed on the two sets of X-axis drive devices, and a set of Z-axis drive devices perpendicular to the base is installed on the Y-axis drive devices; The polishing head assembly is mounted on the driving device in the Z-axis direction; The clamping device is mounted on an upper surface of the base and is located below the polishing head assembly; The controller is connected to the drive device and the polishing head assembly.

2. A polishing system for large-aperture optical elements according to claim 1, characterized in that: The base is made of aluminum alloy.

3. The polishing system for large-aperture optical elements according to claim 1, characterized in that: The supporting structure consists of square aluminum profiles.

4. The polishing system for large-aperture optical elements according to claim 1, characterized in that: The driving device includes a ball screw and a screw nut transmission mechanism. The screw nut transmission mechanism is fixed on the supporting structure and connected to one end of the ball screw to drive the ball screw to rotate; the polishing head assembly is sleeved on the ball screw of the driving device in the Z-axis direction; the screw nut transmission mechanism is connected to the controller.

5. The polishing system for large-aperture optical elements according to claim 1, characterized in that: The polishing head assembly includes a low-friction cylinder, a flange, a pressure sensor, an air motor and a polishing plate; the guide rod of the low-friction cylinder is connected to the flange, and the floating joint of the low-friction cylinder head is fixedly connected to the upper surface of the flange; the pressure sensor is fixed to the lower surface of the flange through a connecting piece with bolts; the air motor is fixedly connected to the bottom of the pressure sensor with bolts, and the drive shaft of the air motor is connected to the polishing plate; the pressure sensor and the air motor are respectively connected to the controller.

6. The polishing system for large-aperture optical elements according to claim 5, characterized in that: The low-friction cylinder and drive unit are connected via an L-shaped mounting plate.

7. The polishing system for large-aperture optical elements according to claim 1, characterized in that: The clamping device adopts an adjustable clamping jaw structure, and the inner side of the clamping jaw is made of elastic material.

8. The polishing system for large-diameter optical elements according to claim 4, characterized in that: A displacement sensor is provided on the ball screw of the driving device for mounting the polishing head assembly and is connected to the controller.

9. The polishing system for large-aperture optical elements according to claim 5, characterized in that: The process of dynamic feedback control by the controller based on the pressure data collected by the pressure sensor includes: S1: The contact dynamics model between the polishing plate and the large-aperture optical element is constructed based on the dynamic force balance equation, which is expressed as: Where m is the equivalent mass of the polishing disc, c is the damping coefficient, k is the contact stiffness, z is the displacement of the polishing disc, and F act is the output thrust of the low-friction cylinder; F contact is the pressure data; S2: According to the real-time measured pressure data F contact , calculate the real-time polishing pressure P real =F Contact / A, where A is the contact area between the polishing disk and the large-aperture optical element; S3: Calculate the error based on the real-time polishing pressure and the target polishing pressure, expressed as e(t) = P target -P real (t); P target Indicates the target polishing pressure; S4: The polishing pressure is adjusted using an improved PI control algorithm. The expression of the improved PI control algorithm is: Among them, P control (t) represents the desired polishing pressure after adjustment at time t; K p and K i are proportional gain and integral gain respectively; S5: Contact dynamics model and improved PI control algorithm Through Laplace transform, the controller transfer function G(s) is derived and expressed as: Where s represents the Laplace variable; S6: The Routh-Hurwitz criterion is used to analyze the closed-loop characteristic equation established based on the transfer function to obtain the stability condition; The closed-loop feature direction is expressed as: ms 2 +cs+k+K p s+K i =0 The stability condition is expressed as: K i >0,c(k+K p )-mK i >0; S7: Set the desired poles s1 = -α, s2, s3 = -β ± jγ by the pole placement method. Substitute the desired extreme values ​​into the closed-loop characteristic equation to derive the gain optimization formula, which is expressed as: K pold =m(α+2β)-c,K iold =mab 2 +magic 2 Among them, K pold Indicates the optimized proportional gain; K iold represents the optimized integral gain; α represents the damping ratio of the system; β and γ represent parameters related to the dynamic characteristics of the system respectively; S8: Adaptively adjust the gain based on the real-time feedback error. The gain adjustment formula is expressed as: Among them, η p and η i They represent the adjustment coefficients of proportional gain and integral gain respectively; sgn represents the sign function; Represents the error e versus proportional gain K p The partial derivative of It represents the error e versus the integral gain K i The partial derivative of S9: Calculate the optimal gain according to the gain optimization formula and the gain adjustment formula, substitute the optimal gain into the improved PI control algorithm to adjust the polishing pressure and obtain the desired polishing pressure; the expression of the optimal gain is: K pnew =K pold +ΔK p ,K inew =K iold +ΔK i Among them, K pnew represents the optimal proportional gain; K inew represents the optimal integral gain; S10: Calculate expected pressure data according to the expected polishing pressure, generate expected low-friction cylinder output thrust and expected polishing disk displacement based on the contact dynamics model, adjust the polishing head assembly according to the expected low-friction cylinder output thrust, and adjust the drive device according to the expected polishing disk displacement.

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