CN121696775B - Multi-mode self-adaptive aspheric lens polishing surface type control method - Google Patents

Abstract

The application relates to a multi-mode self-adaptive aspheric lens polishing surface type control method, and aims to solve the problems that rigidity and vibration parameters cannot be adapted in a partitioning mode according to lens curvature in the prior art, and over-polishing and under-polishing are easy to occur. The method comprises the steps of firstly obtaining surface curvature distribution data of a lens to be polished, defining the positions of high and low curvature areas, providing a polishing disc rotating around an axis, embedding Ni-Ti-based shape memory alloy wires in an array manner in an elastic matrix of the polishing disc, embedding a plurality of piezoelectric ceramic ultrasonic vibrators, introducing differential currents into alloy wires in different areas according to the curvature data, adjusting the rigidity of the corresponding areas of the polishing disc through martensite-austenite phase transformation, adapting the high rigidity of the high curvature areas to the low rigidity and adapting the high rigidity of the low curvature areas, and synchronously controlling the ultrasonic vibrators to output vibration parameters matched with the curvature areas during polishing so as to realize multi-mode coupling polishing. The method effectively avoids the over-polishing and under-polishing defects, gives consideration to machining precision and efficiency, and meets the requirements of the high-end field on the nano-level surface type precision of the aspherical lens.

Description

Multi-mode self-adaptive aspheric lens polishing surface type control method

Technical Field

The application relates to the technical field of polishing processes, in particular to a multi-mode self-adaptive aspheric lens polishing surface type control method.

Background

Aspherical lenses have been widely used in high-end fields such as precision optical imaging, laser processing, aerospace detection, and the like, by virtue of their excellent optical properties, such as reduction of aberrations, improvement of condensing efficiency, simplification of optical system structures, and the like. The surface type precision is a core index for determining the optical performance of the aspherical lens, the polishing process is used as the final key process of the aspherical lens processing, the core aim is to avoid introducing new surface type defects while removing residual errors of the previous process, and finally the nano-scale surface type precision control is realized.

The currently mainstream aspheric lens polishing technology mainly comprises three types of fixed-rigidity polishing disc polishing, single-mode self-adaptive polishing and preliminary multi-mode polishing. The fixed-rigidity polishing disk polishing technology adopts resin, metal or single-rigidity elastomer as a polishing disk substrate, the contact rigidity is kept fixed in the polishing process, and the processing conditions are adjusted depending on preset parameters or experience of operators, so that the fixed-rigidity polishing disk polishing technology is suitable for processing low-precision aspheric lenses. The single-mode self-adaptive polishing technology can be divided into two types, namely, only stiffness-changing adaptation and only ultrasonic vibration assistance, wherein the stiffness of a polishing disk is adjusted through an elastic modulus-adjustable material or a mechanical driving mechanism, but the precise zonal adjustment and control based on lens curvature distribution cannot be realized, the response speed is slower, and the abrasive particle cutting track is refined and the removal efficiency is improved through an integrated ultrasonic vibration unit, but the differential requirements of contact pressure in different curvature areas are not considered. Although the preliminary multi-mode polishing technology tries to combine rigidity adjustment and ultrasonic vibration, linkage logic of two modes and lens curvature distribution is not established, and only unified parameters are adopted to carry out full-area polishing, so that the adaptation of curvature, rigidity and vibration cannot be realized.

However, there are still many core technology short plates in the prior art for complex curvature distribution characteristics of aspherical lenses. Firstly, the existing fixed rigidity or single rigidity-variable technology cannot adaptively adjust the contact rigidity of a polishing disk according to the curvature distribution of a lens, the contact area of the polishing disk and the lens is small in a high curvature area due to large surface curvature and concentrated in pressure, local over-polishing is easily caused, the contact area is large in a low curvature area due to scattered cutting force, under-polishing is easily caused, and finally the overall surface type precision of the lens is difficult to meet the severe requirements of the high-end field.

In summary, the existing aspheric lens polishing technology lacks key designs such as zoned self-adaptive stiffness adjustment based on curvature distribution, a cooperative coupling mechanism of stiffness and ultrasonic vibration, and the like, so that the machining precision and efficiency are difficult to be considered, the requirements of the high-end field on the nanoscale surface type precision of the aspheric lens cannot be met, and a multi-mode self-adaptive polished surface type control method capable of realizing curvature, stiffness and vibration adaptation is needed.

Disclosure of Invention

Aiming at the defects of the prior art, the application aims to provide a multi-mode self-adaptive aspheric lens polishing surface type control method which can realize the precise partition adaptation and cooperative regulation and control of the contact stiffness of a polishing disk and ultrasonic vibration parameters based on the surface curvature distribution of the aspheric lens, effectively avoid the defects of over-polishing in a high-curvature area and under-polishing in a low-curvature area, and meet the use requirements of the high-end field on the nanoscale surface type precision of the aspheric lens.

The above object of the present application is achieved by the following technical solutions:

a multi-mode self-adaptive aspheric lens polishing surface type control method is characterized by comprising the following steps of 1, obtaining surface curvature distribution data of a lens to be polished, determining positions of a high curvature area and a low curvature area of the lens, 2, providing a polishing disc rotating around an axis, embedding Ni-Ti-based shape memory alloy wires with the diameter of 0.3 mm-0.7 mm in an elastic matrix of the polishing disc in an array mode, electrically connecting the shape memory alloy wires with a micro current controller, embedding a plurality of piezoelectric ceramic ultrasonic vibrators in the elastic matrix of the polishing disc, 3, introducing differential current to the shape memory alloy wires in different areas through the micro current controller, and triggering martensitic-austenitic phase transformation of the shape memory alloy wires by utilizing current to realize adjustment of the contact rigidity of the corresponding areas of the polishing disc, wherein the shape memory alloy wires in the corresponding areas of the polishing disc are controlled to be in martensite phase for reducing the contact rigidity, the shape memory alloy wires are controlled to be in the low curvature area, and the piezoelectric ceramic ultrasonic vibrators are controlled to be in the polishing area, and the vibration precision is matched with the polishing lens in the vibration area, and 4, and the polishing precision is controlled to be synchronous.

In the step 3, the electric current which is fed to the high curvature area corresponding to the shape memory alloy wire is 0.4A-0.6A, so that the temperature of the shape memory alloy wire is kept below 60 ℃ and is in a martensitic phase, the contact stiffness of a polishing disc in the corresponding area is 1500N/m-2000N/m, the electric current which is fed to the low curvature area corresponding to the shape memory alloy wire is 1.0A-1.3A, the temperature of the alloy wire is raised to 70 ℃ to 80 ℃ and is converted into an austenitic phase, and the contact stiffness of the polishing disc in the corresponding area is 4000N/m-4500N/m.

In the step 4, the piezoelectric ceramic ultrasonic vibrator is preferably embedded in a region along the radial direction of the polishing disk, and the piezoelectric ceramic ultrasonic vibrator is controlled to output high-frequency low-amplitude vibration of 70khz to 80khz and 0.5 μm to 1 μm for the region of high curvature of the lens, and is controlled to output low-frequency high-amplitude vibration of 20khz to 30khz and 3 μm to 5 μm for the region of low curvature of the lens.

As the preferable mode of the invention, the shape memory alloy wires and the miniature current controller are electrically connected through a plurality of independent conductive slip rings, the static rings of the conductive slip rings are connected with the miniature current controller, the movable rings are connected with the shape memory alloy wires in all areas through radial partition current collecting plates in the polishing disc, and the number of the annular channels of the conductive slip rings is consistent with the number of the partitions of the shape memory alloy wires.

Preferably, the method further comprises a laser pretreatment step between the step 1 and the step 2, wherein a pulse laser generating device is adopted to carry out photo-thermal softening treatment on the polished area according to the curvature distribution of the lens.

As a preferable mode of the invention, when the photo-thermal softening treatment is carried out, the laser energy density of the pulse laser generating device is 5J/cm < 2 > -8J/cm < 2 > and the scanning frequency is 500Hz for a high curvature area, and the laser energy density is 10J/cm < 2 > -12J/cm < 2 > and the scanning frequency is 200Hz for a low curvature area.

Preferably, the hardness sensor feeds back and corrects the laser parameters in real time to ensure the softness when the photothermal softening treatment is performed.

As a preferred aspect of the present invention, in step 1, the lens surface curvature distribution data is acquired by a three-dimensional laser scanner.

As the optimization of the invention, after the step 4 is finished, the method further comprises a laser induced phase change strengthening step, the pulse laser generating device is switched to a low energy density mode, the whole area scanning is carried out on the polished surface of the lens at the energy density of 3J/cm <2> -5J/cm <2>, and the scanning frequency of 100Hz, and the phase change of the microstructure on the surface is realized through photo-thermal induction, so that the wear resistance of the surface of the lens is improved.

In the polishing operation process of the step 4, the surface type interferometer is also synchronously adopted to collect the surface type error data of the lens in real time, if the local surface type error is detected to exceed a set value, the current amplitude of the shape memory alloy wire in the corresponding area is adjusted to correct the contact stiffness, and meanwhile, the frequency of the piezoelectric ceramic ultrasonic vibrator is adjusted until the surface type error is reduced to be within the set range, so that the correction of the surface type precision is realized.

In summary, the beneficial technical effects of the application are as follows:

According to the application, the three-dimensional laser scanner is arranged to acquire surface curvature distribution data of the lens to be polished, and the differential current is introduced into alloy wires in different areas by combining the Ni-Ti-based shape memory alloy wires embedded in the elastic matrix of the polishing disk and the miniature current controller to trigger martensite-austenite phase transformation, so that the partition self-adaptive adjustment of the contact stiffness of the corresponding areas of the polishing disk is realized, the core problems that the stiffness cannot be accurately adapted according to the curvature distribution of the lens, the over-polishing of the high-curvature area and the under-polishing of the low-curvature area are caused in the prior art are solved, the contact pressure of the different-curvature areas is effectively balanced, the overall surface type precision of the lens is remarkably improved, and the requirements of the high-end field on the nanoscale surface type precision are met.

The elastic substrate of the polishing disk is internally embedded with a plurality of piezoelectric ceramic ultrasonic vibrators arranged in radial subareas, vibration parameters of which the output is matched with a lens curvature area are synchronously controlled during polishing, and a multi-mode coupling regulation and control mechanism is formed by regulating the rigidity of the subareas, so that the defects that the rigidity regulation and the ultrasonic vibration are independently controlled and the machining precision and the efficiency cannot be considered in the prior art are overcome, the high-frequency low-amplitude vibration of a high-curvature area can refine abrasive particle cutting tracks and protect microscopic surface types, the low-frequency high-amplitude vibration of the low-curvature area can improve the material removal efficiency, and the cooperative optimization of the precision and the efficiency is realized.

According to the application, the array embedded design of the Ni-Ti-based shape memory alloy wires is adopted, the stiffness adjustment is realized by triggering the phase change through the current heating, compared with the existing mechanical driving or elastic material adjustment mode, the response speed is faster, the independent radial multi-area adjustment and control can be realized, the problems of insufficient zoning accuracy and slow response of the existing stiffness changing technology are solved, the contact requirements of the polishing disk in the rotation process and the different curvature areas of the lens can be dynamically adapted, and the suitability and stability of the polishing process are improved.

Drawings

FIG. 1 is a simplified flow chart of a method for controlling polishing surface type of a multi-modal adaptive aspherical lens.

Detailed Description

The present application will be described in further detail with reference to the accompanying drawings.

As shown in fig. 1, before the aspheric lens is polished, first, surface curvature distribution data of the lens to be polished needs to be acquired, and subsequent accurate adaptation and adjustment are realized based on the surface curvature distribution data. Specifically, a mature three-dimensional laser scanner in the prior art can be adopted to complete data acquisition, the device scans the surface of the lens by emitting laser beams, calculates the space coordinates of each point by utilizing the phase difference or the flight time of laser reflection signals, and then fits to obtain complete surface curvature distribution data, after the acquisition is completed, the data are subjected to noise reduction and smoothing treatment by a conventional image processing algorithm, and then a high curvature area and a low curvature area of the lens are divided according to the size of the curvature radius, wherein the area with smaller curvature radius and steeper surface radian is a high curvature area, the area with larger curvature radius and relatively gentle surface is a low curvature area, and the specific positions and the range of the two areas are defined, so that data support is provided for the regulation and control of subsequent polishing parameters.

Subsequently, a polishing disk rotating around an axis for polishing work is prepared. The main body of the polishing disk comprises an elastic matrix, the elastic matrix can be made of materials such as silicone rubber and polyurethane elastomer which are commonly used in the prior art, and the materials have moderate elastic modulus, so that a foundation can be provided for subsequent rigidity adjustment, and good fit with the surface of the lens in the polishing process can be ensured. In the elastic matrix, ni-Ti-based shape memory alloy wires are arranged in an array embedding mode, the diameter of each alloy wire is 0.3-0.7 mm, the size range can ensure the structural strength and the phase change response sensitivity of the alloy wires, and the influence on the overall elasticity of the elastic matrix due to overlarge diameter can be avoided. The Ni-Ti based shape memory alloy wires are functional materials with martensite-austenite phase transformation characteristics, and are characterized in that the crystal structure transformation can be generated when the temperature is changed, so that the elastic modulus is obviously different, the array embedding is particularly realized in a mode of concentric arrays along the radial direction of the polishing disc, in particular, in the elastic matrix, the Ni-Ti based shape memory alloy wires are embedded in a mode of concentric arrays along the radial direction of the polishing disc, each shape memory alloy wire is processed into an annular structure, the sizes of all annular shape memory alloy wires are different, namely, the inner diameter and the outer diameter of each annular shape memory alloy wire are sequentially increased, and a group of annular parts with gradient distribution of diameters are formed. The annular shape memory alloy wires with different sizes are sleeved in sequence along the radial direction of the polishing disc, and the adjacent annular alloy wires keep uniform intervals, so that the central axes of all the annular alloy wires are overlapped with the rotation axis of the polishing disc, and finally, a plurality of annular rigidity adjusting layers which are concentrically distributed are formed in the elastic matrix.

The concentric annular array design has the core advantages that the polishing disc can be divided into a plurality of independent rigidity regulating areas along the radial direction, each annular shape memory alloy wire corresponds to one radial partition, when differential current is introduced into annular alloy wires in different radial partitions through a miniature current controller, the annular alloy wires in different positions can respectively generate martensite-austenite phase transformation, the integral rigidity of an elastic matrix corresponding to the radial partition is further changed, the small-diameter annular alloy wires positioned at the inner side of the polishing disc correspond to the high-curvature area of a lens, the small-amplitude current is introduced to enable the annular alloy wires to keep the martensite phase, the contact rigidity of the radial partition is reduced, the large-diameter annular alloy wires positioned at the outer side of the polishing disc correspond to the low-curvature area of the lens, and the contact rigidity of the radial partition is improved through the large-amplitude current is introduced to enable the annular alloy wires to be converted into the austenite phase. Through the structural design, the polishing disc can form rigidity distribution gradually increasing from inside to outside along the radial direction, the inner side of the polishing disc corresponds to a high curvature area of the matched lens, and the outer side of the polishing disc corresponds to a low curvature area of the matched lens, so that the differentiation requirement is realized, the precise adaptation of the contact pressure of each area in the polishing process is ensured, and the feasibility and the accuracy of partition rigidity adjustment are structurally ensured.

In the specific implementation, the number of the annular shape memory alloy wires can be reasonably set according to the lens curvature distribution complexity of the diameter of the polishing disk, for example, 3-5 annular alloy wires can be set for the polishing disk with the diameter of 80mm to respectively cover radial partitions such as an inner ring, a middle ring and an outer ring, the annular alloy wires are made of conventional Ni-Ti binary alloy or Ni-Ti-Cu ternary alloy, the annular structure can be prepared through the existing processing technologies such as die forging and laser cutting, the roundness and the dimensional accuracy of the annular structure are ensured, and the uniformity of rigidity adjustment due to structural deviation is avoided.

Meanwhile, the Ni-Ti-based shape memory alloy wire is electrically connected with a micro current controller, the micro current controller can be a constant current source module based on an MCU (micro control unit) in the prior art, has a multi-channel independent output function, can accurately adjust the amplitude of each output current, has high response speed, and can meet the requirement of dynamic regulation in the polishing process. In addition, a plurality of piezoelectric ceramic ultrasonic vibrators are embedded in the elastic matrix of the polishing disk, the vibrators are mature components in the existing ultrasonic processing field, the working principle is that alternating voltage is applied through an ultrasonic driving power supply, so that the piezoelectric ceramic plates generate high-frequency mechanical vibration, the vibration frequency is usually adjustable within the range of 20 kHz-100 kHz, the embedding mode of the piezoelectric ceramic ultrasonic vibrators can be bonded or embedded and fixed, firm connection between the piezoelectric ceramic ultrasonic vibrators and the elastic matrix is ensured, vibration energy can be effectively transmitted to the surface of the polishing disk, the distribution of the vibrators is required to be matched with the follow-up partition regulation and control logic, and the matched vibration effect of each curvature corresponding area is ensured.

After the preparation in the earlier stage is completed, the core parameter regulation and polishing operation stage is entered. According to the lens curvature distribution data obtained before, differential currents are introduced to Ni-Ti-based shape memory alloy wires in different areas through a miniature current controller, wherein the different areas are radial partitions of a polishing disc corresponding to a high curvature area and a low curvature area of the lens one by one, the shape memory alloy wires in the same partition can be connected in parallel through a preset radial partition current collecting plate in the polishing disc, and the current collecting plate is an existing metal conductive plate and is used for collecting alloy wire lines in the same area and is convenient to connect with an external control unit. The method comprises the steps of triggering martensite-austenite phase transformation of the shape memory alloy wire by utilizing heat when current passes through the alloy wire, introducing smaller-amplitude current to the alloy wire in a corresponding polishing disc partition aiming at a high curvature area of a lens, keeping the temperature of the alloy wire below the phase transformation temperature of the alloy wire, wherein the alloy wire is in a martensite phase, the elastic modulus of the alloy wire is smaller, further reducing the contact stiffness of the area of the polishing disc, avoiding the over-polishing problem caused by small contact area and concentrated pressure of the high-curvature area, introducing larger-amplitude current to the alloy wire in the corresponding polishing disc partition aiming at the low-curvature area of the lens, increasing the temperature of the alloy wire to be above the phase transformation temperature, promoting the alloy wire to be transformed from the martensite phase to the austenite phase, obviously increasing the elastic modulus of the alloy wire at the moment, and improving the contact stiffness of the area of the polishing disc so as to meet the requirement of the low-curvature area on cutting force and avoid under-polishing. The phase transition temperature of the Ni-Ti based shape memory alloy wire is an inherent characteristic, and the Ni-Ti alloy with different component proportions can be selected to obtain a required phase transition temperature range, and the phase transition of the alloy wire can be accurately controlled by matching with the adjustment of the current amplitude, so that the quantitative adjustment of the contact stiffness is realized.

And according to the high curvature area and the low curvature area of the lens, the hardness change of each area of the polishing disc is referred to, and the contact pressure between the polishing disc and the lens is dynamically adjusted, so that grinding with different intensities is realized for different areas of the lens.

In the polishing operation process, the polishing disk rotates around the axis of the polishing disk under the drive of the driving motor, and maintains a certain polishing pressure with the surface of the lens, and in the polishing operation process, a plurality of piezoelectric ceramic ultrasonic vibrators are synchronously controlled to work, and vibration parameters matched with the curvature area of the lens are output. Specifically, the piezoelectric ceramic ultrasonic vibrators corresponding to the subareas are controlled to output high-frequency low-amplitude vibration aiming at the high-curvature area of the lens, the frequency of the vibration is higher, the amplitude is smaller, the cutting track of abrasive particles can be thinned, the material removal amount in unit time is reduced, over-polishing is avoided while the machining precision is ensured, the piezoelectric ceramic ultrasonic vibrators corresponding to the subareas are controlled to output low-frequency high-amplitude vibration aiming at the low-curvature area of the lens, the frequency of the vibration is lower, the amplitude is larger, the impact cutting effect of the abrasive particles on materials can be enhanced, the material removal efficiency is improved, and the machining progress of the low-curvature area is ensured. The cooperation of the rigidity adjustment and the ultrasonic vibration forms multi-mode coupling polishing, namely, the problem of mismatching of contact pressure in different curvature areas is solved through linkage of two regulation and control modes, the cutting effect is optimized, and finally, the face type precision correction of the lens is finished, and the nanoscale face type control target is realized.

It should be noted that, the electrical connection under the polishing disk rotation state can be realized through the independent conductive slip ring of multichannel among the prior art, the quiet ring and the miniature current controller fixed connection of conductive slip ring, the rotating shaft synchronous rotation of rotating ring and polishing disk, and the rotating ring passes through flexible wire and is connected with the inside radial subregion collecting plate of polishing disk, the ring track quantity of conductive slip ring is unanimous with the subregion quantity of shape memory alloy silk, ensure that each way differentiation electric current can both be stably transmitted, avoid wire winding, contact failure scheduling problem to appear in the rotatory in-process, guarantee the reliability of regulation and control.

When the rigidity adjusting process is implemented in detail, the selected Ni-Ti-based shape memory alloy wire has a definite phase transition temperature range, the martensite-austenite phase transition temperature is set to be 60-80 ℃, and the phase transition temperature range is subjected to targeted screening, so that the interference of the polishing operation environment temperature on the metallographic phase can be avoided, the phase switching can be realized rapidly through current heating, and the regulation and control reliability and response efficiency are both considered.

Aiming at radial subareas of the polishing disc corresponding to the high-curvature area of the lens, current with the amplitude of 0.4A-0.6A is introduced into the annular shape memory alloy wire of the area through the miniature current controller. According to Joule's law, heat generated by current passing through the alloy wire is positively correlated with square current, resistance and energizing time, and by combining the inherent resistance characteristics of the selected Ni-Ti based shape memory alloy wire, the current amplitude can accurately maintain the temperature of the alloy wire below 60 ℃, i.e. below the lower limit of the phase transition temperature thereof, while the alloy wire maintains the martensitic phase state. Because the elastic modulus of the Ni-Ti-based shape memory alloy of the martensite phase is lower, the contact stiffness of the corresponding polishing disk partition can be reduced to 1500-2000N/m, and the stiffness level can be adapted to the characteristics of small contact area between a high curvature area and the polishing disk and easy concentration of pressure, so that excessive removal of local materials is effectively avoided.

And for radial partition of the polishing disc corresponding to the low curvature area of the lens, current with the amplitude of 1.0A-1.3A is introduced into the annular shape memory alloy wire of the area through the micro current controller. The larger current amplitude can generate more joule heat, so that the temperature of the alloy wire is quickly increased to 70-80 ℃, and the temperature range is in the phase transition temperature range of the alloy, thereby promoting the alloy wire to be completely transformed from the martensite phase to the austenite phase. The elastic modulus of the Ni-Ti-based shape memory alloy of the austenite phase is obviously higher than that of the martensite phase, so that the contact stiffness of the corresponding polishing disk partition is improved to 4000N/m-4500N/m, the stiffness level can meet the requirements of large contact area between a low curvature area and the polishing disk and enough cutting force, the material is ensured to be removed sufficiently, and the problem of underpolishing is avoided.

The method has the advantages that the temperature of the alloy wire can be accurately controlled by adjusting the current amplitude, so that the phase state is stably regulated and controlled, the quantitative adjustment of the contact stiffness is finally realized, the dynamic balance of the polishing pressure and the material removal efficiency of different curvature areas is ensured, and the parameter guarantee is provided for the nanoscale surface type precision control. Meanwhile, the parameter range has good compatibility, and current fine adjustment of +/-0.1A can be carried out according to specific components of the Ni-Ti-based shape memory alloy wire actually selected, such as Ni-Ti binary alloy or Ni-Ti-Cu ternary alloy, and the material and thickness of the elastic matrix of the polishing disk, so as to adapt to different processing scenes.

The piezoelectric ceramic ultrasonic vibrators and the radial rigidity subareas of the polishing disc form accurate adaptation, the accurate adaptation is arranged in a manner of being embedded along the radial subareas of the polishing disc, namely the subareas of the vibrators are completely consistent with the rigidity regulation subareas of the annular shape memory alloy wire, at least one piezoelectric ceramic ultrasonic vibrator is embedded in each radial subarea, the vibrators in the same subarea are connected in parallel through a circuit, and the independent ultrasonic driving modules are used for controlling the vibration parameters of each subarea to be independently regulated.

In the multi-mode coupling stage of polishing operation, according to the differential processing requirements of the high and low curvature areas of the lens, the output parameters of the piezoelectric ceramic ultrasonic vibrators in corresponding subareas are precisely matched and regulated. Aiming at a lens high-curvature area, the surface radian is steeper, the contact area with a polishing disc is small, the corresponding polishing disc area is kept low in rigidity through the regulation and control of a shape memory alloy wire, at the moment, a piezoelectric ceramic ultrasonic vibrator of the area is controlled to output 70 kHz-80 kHz high-frequency and 0.5-1 mu m low-amplitude vibration, the cutting track of abrasive particles on a polishing interface can be greatly thinned through the high-frequency vibration, the impact force of a single abrasive particle on the lens surface is reduced, microscopic surface damage caused by the concentration of the cutting force under the low-rigidity adaptation is avoided, the material removal rate can be controlled to be in a mild interval through the low-rigidity pressure buffering effect, the overerase risk of the high-curvature area is doubly avoided from the aspects of cutting strength and contact pressure, and meanwhile, the surface processing quality is improved.

Aiming at a low curvature area of a lens, the surface of the lens is relatively gentle, the contact area with a polishing disc is large, the high rigidity is maintained by regulating and controlling a shape memory alloy wire to ensure cutting force corresponding to the polishing disc partition, at the moment, a piezoelectric ceramic ultrasonic vibrator controlling the partition outputs low-frequency vibration of 20 kHz-30 kHz and high-amplitude vibration of 3 mu m-5 mu m, the low-frequency vibration can enhance the impact cutting effect of abrasive particles on the surface of a material, the stable contact pressure caused by high rigidity is matched, the material removal efficiency in unit time is obviously improved, the hidden danger of scattering and undershooting of cutting force caused by large contact area in the low curvature area is solved, the contact state of abrasive particles and the surface of the material can be optimized by high-amplitude vibration, the failure of the abrasive particles due to overlarge contact area is avoided, and synchronous advancing of processing efficiency and the surface type correction progress is ensured.

The vibration parameter range accords with the conventional working characteristic of the piezoelectric ceramic ultrasonic vibrator, 20 kHz-100 kHz is a common frequency range for ultrasonic processing, micron-sized amplitude can be accurately regulated and controlled through driving power supply power, the vibration parameter range can be optimally cooperated with rigidity parameters of corresponding subareas, a high-curvature area forms a combination of low rigidity and high-frequency low-amplitude vibration, the precision of a focusing surface and the surface quality, a low-curvature area forms a combination of high rigidity and low-frequency high-amplitude vibration, the processing efficiency and the removal uniformity are considered, finally, the vibration regulation and control accurately adapted to the subareas and the rigidity regulation form a multi-mode coupling effect, and the whole surface type precision correction effect of the aspherical lens is comprehensively ensured.

In order to realize the accurate supply of differential current to different radial subarea shape memory alloy wires under the rotation state of the polishing disk, simultaneously avoid the problems of wire winding, poor contact and the like, stable electric connection is established between the shape memory alloy wires and the miniature current controller through a plurality of independent conductive slip rings, and the connection structure is a key for guaranteeing the rigidity adjustment reliability of the subareas.

The conductive slip ring adopts a mature multipath independent loop structure in the prior art, the core of the conductive slip ring comprises a static ring and a movable ring, the static ring is a fixed part and is directly connected with the multichannel output end of the miniature current controller in one-to-one correspondence through a wire to ensure stable input of control signals and currents, the movable ring is a rotating part and is coaxially fixed with the rotating shaft of the polishing disk, can synchronously rotate around the axis along with the polishing disk, and is electrically connected with a radial partition current collecting plate preset in the polishing disk through a plurality of flexible conductive wires. The annular shape memory alloy wires of each radial partition are all connected to the radial partition collector plates of the corresponding area in a summarizing way through the inner leads, namely all the annular shape memory alloy wires in the same radial partition are connected into the collector plates of the partition in parallel, and then are connected with the corresponding wiring ends of the movable ring in a unified way through the collector plates.

It is particularly important that the number of independent loops of the conductive slip ring is completely consistent with the number of radial partitions of the shape memory alloy wire. For example, if the polishing disk is divided into 3 rigidity regulation and control subareas along the radial direction, the corresponding conductive slip ring is provided with 3 independent annular channels, each annular channel corresponds to current transmission of one radial subarea respectively, different amplitude differential currents output by the miniature current controller are ensured, and the differential currents can be accurately transmitted to the corresponding shape memory alloy wire subareas through the independent annular channels, so that the current crosstalk and interference of different subareas cannot occur. The independence and the accuracy of the rigidity adjustment of each radial partition are guaranteed from the circuit connection level, so that the polishing disk can realize stable partition rigidity adaptation according to the curvature distribution of the lens, and reliable circuit support is provided for multi-mode coupling polishing.

In addition, the radial partition current collecting plate can be made of copper foil, aluminum substrate and other existing high-conductivity metal plates, is fixed inside the polishing disc elastic matrix in an adhesion or embedding mode, is matched with the radial partition outline of the polishing disc, is subjected to insulation treatment on the surface to avoid short circuits among different partition current collecting plates, and is made of abrasion-resistant and bending-resistant silver-plated copper wires or alloy wires, so that the wires are not easy to break in the long-term rotation process of the polishing disc, and the service life and stability of electric connection are further improved.

After the surface curvature distribution data of the lens to be polished and the positions of the high curvature area and the low curvature area are obtained through a three-dimensional laser scanner, in order to further optimize the cutting effect of subsequent polishing operation and reduce the processing difficulty difference of different curvature areas caused by uneven material hardness, a laser pretreatment step is additionally arranged before a polishing disc is prepared, and the step carries out targeted photo-thermal softening treatment on the lens polishing area through a pulse laser generating device so as to lay a uniform and free-cutting material foundation for subsequent multi-mode coupling polishing.

The adopted pulse laser generating device is a mature nanosecond pulse laser in the prior art, and the core working principle is that the laser energy is concentrated to act on the thin layer area on the surface of the lens by utilizing the photo-thermal effect of the pulse laser, so that the temperature of the surface layer of the material is quickly increased to the softening point, but the melting temperature is not reached, thereby reducing the hardness and cutting resistance of the material and avoiding damaging the internal tissues of the lens. In a specific photo-thermal softening treatment process, a pulse laser generating device respectively adopts differentiated laser parameters for a high curvature area and a low curvature area according to the determined lens curvature distribution data, and for the lens high curvature area, the surface radian is steeper, the contact pressure is easy to concentrate in the subsequent polishing, if excessive softening possibly causes surface collapse, the softening effect is enhanced by adopting the combination of the low energy density of 5J/cm < 2 > -8J/cm < 2 > and the high scanning frequency of 500Hz, the softening depth is controlled by the low energy density, generally 1 mu m-3 mu m, the performance change of deep materials is avoided, the high scanning frequency can ensure the uniform distribution of laser energy on the surface of the high curvature area, the mild and uniform softening is realized, and for the lens low curvature area, the surface is relatively gentle, the contact area is large in the subsequent polishing, the cutting force is dispersed, the cutting efficiency is required to be more fully softened, and therefore, the softening effect is enhanced by adopting the combination of the high energy density of 10J/cm < 2 > -12J/cm < 2 > and the low scanning frequency of 200Hz, the high energy density can prolong the cutting strength of the material, the cutting resistance strength is reduced, the low scanning frequency can ensure the high-amplitude and the high-amplitude vibration condition is suitable for the high-amplitude and the vibration condition.

In order to accurately control the softening degree of each area and avoid the situation of insufficient softening or excessive softening, a real-time feedback regulation mechanism is introduced in the photo-thermal softening treatment process, the hardness of the softened lens surface is detected in real time through a hardness sensor, the hardness sensor is a microhardness sensor with the precision reaching HV0.01 in the prior art, a detection probe can synchronously move along with a laser scanning track, surface hardness data of high-curvature and low-curvature areas are acquired in real time, and the data are transmitted to a total control system. The control system presets a target softening hardness range which is matched with a subsequent polishing process, when the hardness of a certain area is detected to be higher than the target range, namely insufficient softening, the laser energy density of the area can be automatically adjusted upwards, the scanning frequency is adjusted upwards by 0.5J/cm & lt 2 & gt or reduced by 50Hz each time, when the hardness of the certain area is detected to be lower than the target range, namely excessive softening, the laser energy density is automatically adjusted downwards or the scanning frequency is increased, and by the dynamic correction mechanism, the softening degree of the high-curvature area and the low-curvature area of the lens can be ensured to be accurately matched with the cutting requirement of the subsequent polishing, so that a front guarantee is provided for realizing the control of the nano-level surface type precision.

In the step 1, collection of curvature distribution data of the lens surface is completed by adopting a mature three-dimensional laser scanner in the prior art, and the equipment can avoid scratch or pollution to the surface to be processed of the lens by virtue of non-contact measurement characteristics, can realize micrometer measurement accuracy, and completely meets the requirements of follow-up partition adaptation regulation and control on data accuracy.

In the specific acquisition process, a lens to be polished is fixed on a measurement platform through vacuum adsorption or a flexible clamp, so that the coincidence of the center of the lens and a measurement reference axis of a three-dimensional laser scanner is ensured, and the data distortion caused by clamping deviation is avoided. The three-dimensional laser scanner can be a device of the type of a triangulation method or a time-of-flight method, and the working principle of the three-dimensional laser scanner is that the whole surface of the lens is scanned by emitting continuous laser beams, the laser beams are reflected after being irradiated on the surface of the lens, a photoelectric detector arranged in the scanner captures reflected signals, and the three-dimensional space coordinates of each scanning point are calculated by combining the time difference or the phase difference between the laser emission and the laser reception. In order to ensure the integrity of data coverage, the scanning path can be set to be in a spiral or grid format, and the scanning resolution is set according to the size and the precision requirement of the lens, so that no measurement blind area is ensured.

After scanning is completed, data analysis software of the scanner can process the acquired massive three-dimensional coordinate points, firstly, abnormal points caused by environmental interference or equipment noise are removed through a filtering algorithm, then, discrete coordinate points are fitted into a complete lens surface three-dimensional model through a least square method and other curved surface fitting algorithms, and then, curvature values of each point on the model are solved through a curvature calculation module, and finally, a global surface curvature distribution map is generated. According to the magnitude of curvature value, can definitely divide high curvature area and low curvature area of lens, regard preset curvature radius threshold value as the boundary generally, the curvature radius is less than this threshold value, the area that surface radian is steeper judges as high curvature area, the curvature radius is greater than this threshold value, the area that the surface is mild relatively judges as low curvature area, record specific position coordinates and coverage of two types of areas simultaneously, provide accurate data support for follow-up laser preprocessing, polishing dish rigidity adjustment and ultrasonic vibration parameter matching.

After the multi-mode coupling polishing and the surface type precision correction in the step 4 are completed, in order to further optimize the mechanical properties of the polished surface of the lens and prolong the service life of the lens under complex working conditions, the method is additionally provided with a laser-induced phase change strengthening step. The step and the laser preprocessing step share the same pulse laser generating device, and the function conversion can be realized only by switching the working modes of the main control system, so that special equipment is not required to be additionally configured, the overall process layout is simplified, and the equipment investment cost is reduced.

In the specific strengthening process, the pulse laser generating device is switched to a low-energy density working mode, and the whole polished surface of the lens is uniformly scanned in the whole domain by adopting the combination of the energy density of 3J/cm <2 > -5J/cm <2 > and the scanning frequency of 100 Hz. Through targeted optimization, the design of low energy density can avoid damage to the corrected nanoscale surface shape caused by excessive energy, accurately raise the temperature of a thin layer on the surface of the lens to the vicinity of the phase transition critical temperature and trigger microstructure transformation, and the scanning frequency of 100Hz can ensure that laser energy is uniformly distributed on the surface, avoid uneven performance caused by local energy concentration, and simultaneously consider the strengthening efficiency and the treatment effect.

The core working principle is that the precise photo-thermal effect of the pulse laser is utilized to induce the microscopic structure phase change of the lens surface material, when the laser energy acts on the surface thin layer, the material atoms obtain energy and rearrange, the disordered grain structure possibly existing after polishing can be changed into a compact and uniform fine grain or amorphous structure, and the optimization of the microscopic structure can obviously improve the surface hardness and the abrasion resistance of the material. It should be noted that, the strengthening process only acts on the extremely thin area of the lens surface, so that the optical performance and the overall structural stability of the lens are not affected, and the whole process is non-contact processing, so as to avoid damaging the molded surface type precision.

Through the laser-induced phase change strengthening step, the wear resistance of the polished surface of the lens can be greatly improved, slight friction or particle impact possibly occurring in the subsequent assembly and use processes can be effectively resisted, the long-term stability of the optical performance of the lens is ensured, and the application scene of the lens in high-end fields with severe requirements on the wear resistance of the lens in aerospace, laser processing and the like is further expanded.

In the multi-mode coupling polishing operation process of the step 4, in order to monitor the surface type precision change in real time and correct the machining error in time, the method synchronously introduces the surface type interferometer to carry out real-time detection and closed-loop regulation and control, and ensures that the final surface type precision of the lens stably reaches the preset standard through the dynamic circulation of detection, judgment and adjustment.

The adopted surface type interferometer is mature high-precision optical detection equipment in the prior art, and can be a Fizeau type interferometer or a Michelson type interferometer, the detection precision of the surface type interferometer can reach the nanometer level, and the surface type precision requirement of the high-end aspheric lens can be completely matched. The interferometer irradiates the polished surface of the lens by emitting monochromatic parallel light, generates surface-type interference fringes by utilizing the interference principle of light, acquires interference fringe images by an image sensor, and analyzes and calculates the deviation value of each point phase on the surface of the lens relative to an ideal surface type, namely surface-type error data by a built-in algorithm. In the detection process, the detection view field of the surface type interferometer corresponds to the polishing area of the polishing disk in real time, and can synchronously move along with the rotation and the feeding of the polishing disk, so that dead angle-free real-time monitoring of the whole lens polishing process is realized, and the collected surface type error data can be transmitted to a total control system in real time through a data interface, thereby providing a basis for regulation and control decisions.

The total control system is preset with the face type error allowance range which is adapted to the lens use requirement, and the set value is generally set to be within lambda/20 according to the high-end field application requirement. The control system compares the acquired local surface type error data with a preset set value in real time, when detecting that the surface type error of a certain area exceeds the set value, if the surface type error of a high curvature area exceeds the set value, the error exceeds the standard due to over-polishing or the error is larger due to under-polishing, a cooperative adjustment mechanism is started immediately, on one hand, a command is sent to a miniature current controller aiming at the radial subarea of a polishing disc corresponding to the area, the current amplitude of the shape memory alloy wire is finely adjusted, the contact stiffness is corrected by changing the phase duty ratio of the alloy wire, the current is downwards adjusted to reduce the stiffness in the over-polishing area, the current is upwards adjusted to improve the stiffness in the under-polishing area, on the other hand, the command is synchronously sent to an ultrasonic driving module, the frequency of a piezoelectric ceramic ultrasonic vibrator corresponding to the subarea is adjusted, the abrasive grain cutting strength is optimized, the frequency is adjusted to refine cutting in the over-polishing area, and the frequency is downwards adjusted to enhance the cutting in the under-polishing area.

After the adjustment is completed, the area is continuously detected by the surface type interferometer in real time, and if the surface type error is not reduced to be within the set range, the control system can repeat the adjustment process until the error meets the requirement. The closed-loop mechanism of real-time detection and dynamic cooperative adjustment can timely compensate the surface type deviation caused by factors such as material characteristic fluctuation, parameter tiny drift and the like in the polishing process, avoid error accumulation, ensure that the surface type precision of each area of the lens can reach the standard stably, and finally realize the surface type precision correction target with high precision and high stability.

The embodiments of the present application are all preferred embodiments of the present application, and are not limited in scope by the present application, so that all equivalent changes according to the structure, shape and principle of the present application are covered by the scope of the present application.

Claims (8)

1. The multi-mode self-adaptive aspheric lens polishing surface type control method is characterized by comprising the following steps of:

Step 1, acquiring surface curvature distribution data of a lens to be polished, and determining positions of a high curvature area and a low curvature area of the lens;

step 2, providing a polishing disc rotating around an axis, wherein Ni-Ti-based shape memory alloy wires with the diameter of 0.3 mm-0.7 mm are embedded in an elastic matrix in the polishing disc in an array manner, the shape memory alloy wires are electrically connected with a miniature current controller, and a plurality of piezoelectric ceramic ultrasonic vibrators are embedded in the elastic matrix of the polishing disc;

Step 3, according to the curvature distribution data obtained in the step 1, a differential current is introduced into the shape memory alloy wires in different areas through the micro current controller, and the martensite-austenite phase transformation of the shape memory alloy wires is triggered by current heating, so that the contact stiffness of the corresponding area of the polishing disc is adjusted;

controlling the shape memory alloy wire in the area corresponding to the polishing disc to be in a martensite phase for the area of high curvature of the lens so as to reduce the contact stiffness;

Step 4, synchronously controlling a plurality of piezoelectric ceramic ultrasonic vibrators to output vibration parameters matched with the curvature area of the lens in the polishing operation process, and performing multi-mode coupling polishing on the lens to finish surface type precision correction;

In the step 3, the current which is led into the high curvature area and corresponds to the shape memory alloy wire is 0.4A-0.6A, so that the temperature of the shape memory alloy wire is kept below 60 ℃ and is in a martensitic phase, the contact stiffness of a polishing disc in a corresponding area is 1500N/m-2000N/m, the current which is led into the low curvature area and corresponds to the shape memory alloy wire is 1.0A-1.3A, so that the temperature of the alloy wire is increased to 70 ℃ to 80 ℃ and is converted into an austenitic phase, and the contact stiffness of the polishing disc in the corresponding area is 4000N/m-4500N/m;

In the step 4, the piezoelectric ceramic ultrasonic vibrator is arranged in a zoned manner along the radial direction of the polishing disc, the piezoelectric ceramic ultrasonic vibrator controls the corresponding zoned vibrator to output 70 kHz-80 kHz and high-frequency low-amplitude vibration with the amplitude of 0.5-1 μm for the high curvature area of the lens, and controls the corresponding zoned vibrator to output 20 kHz-30 kHz and low-frequency high-amplitude vibration with the amplitude of 3-5 μm for the low curvature area of the lens.

2. The method for controlling the polishing surface type of the multi-mode self-adaptive aspheric lens according to claim 1, wherein the shape memory alloy wires and the miniature current controller are electrically connected through a plurality of independent conductive slip rings, static rings of the conductive slip rings are connected with the miniature current controller, movable rings are connected with the shape memory alloy wires of all areas through radial partition current collecting plates in the polishing disc, and the number of ring channels of the conductive slip rings is consistent with the partition number of the shape memory alloy wires.

3. The method according to claim 1, further comprising a laser pretreatment step between step 1 and step 2, wherein a pulse laser generator is used to perform a photo-thermal softening treatment on the polished area according to the curvature distribution of the lens.

4. The method for controlling the polishing surface profile of a multi-mode adaptive aspherical lens according to claim 3, wherein the pulse laser generator has a laser energy density of 5J/cm2 to 8J/cm2 and a scanning frequency of 500Hz for a high curvature region, and a laser energy density of 10J/cm2 to 12J/cm2 and a scanning frequency of 200Hz for a low curvature region when the photo-thermal softening treatment is performed.

5. The method according to claim 4, wherein the laser parameters are fed back and corrected in real time by the hardness sensor to ensure the softness while the photo-thermal softening process is performed.

6. The method according to claim 1, wherein in step 1, the lens surface curvature distribution data is obtained by a three-dimensional laser scanner.

7. The method according to claim 1, further comprising a laser induced phase transition strengthening step after the step 4 is completed, switching the pulse laser generating device to a low energy density mode, performing global scanning on the lens polishing surface at an energy density of 3J/cm2 to 5J/cm2 and a scanning frequency of 100Hz, and realizing surface microstructure phase transition by photo-thermal induction so as to improve the wear resistance of the lens surface.

8. The method for controlling the polishing surface type of the multi-mode self-adaptive aspheric lens according to claim 1 is characterized in that in the polishing operation process of the step 4, surface type error data of the lens are synchronously collected in real time by adopting a surface type interferometer, if the local surface type error is detected to exceed a set value, the current amplitude of the shape memory alloy wire in a corresponding area is adjusted to correct the contact stiffness, and meanwhile, the frequency of the piezoelectric ceramic ultrasonic vibrator is adjusted until the surface type error is reduced to be within a set range, so that the correction of the surface type precision is realized.