A compact voice coil deforming mirror based on a micro voice coil driver

Abstract

The application discloses a compact voice coil deformable mirror based on a micro voice coil driver and belongs to the field of adaptive optics. The application considers that the output force of the micro voice coil driver is two to three orders of magnitude smaller than that of a conventional voice coil driver, adopts a polyimide to replace a glass, silicon carbide and other materials with a large stiffness coefficient which are conventionally used to make a thin mirror surface, provides certain stiffness for the polyimide through a spring structure so as to meet the stiffness requirement, comprehensively considers the correlation between structure parameters, materials, working currents and other performances of the voice coil deformable mirror and the phase modulation amount, frequency and other performances of the voice coil deformable mirror, balances and optimizes the structure parameters, and obtains the compact voice coil deformable mirror with the best comprehensive performance. It is verified through experiments that the single micro driver provided in the application can reach a maximum output force of 1mN, a motor constant of 0.032N x W ‑1 / 2 ; the phase modulation amount of the compact deformable mirror reaches ±45um, and the first resonance frequency reaches 2000Hz.

Description

TECHNICAL FIELD

[0001] The present application relates to a compact voice coil deforming mirror based on a micro voice coil driver, and belongs to the field of adaptive optics. BACKGROUND

[0002] One of the important devices in adaptive optical system is deformable mirror, also known as deformable mirror (DM), which is mainly used for correcting wavefront distortion and compensating for the changes of optical system aberration caused by atmospheric turbulence, gravity and temperature, etc. In the high-resolution imaging system of eye fundus retina, it can also be used for compensating for the aberration of human eye to obtain high-resolution images of retinal cells. Common deformable mirrors include continuous mirror deforming mirror with discrete actuators, block splicing type deformable mirror, bimorph deformable mirror, thin film deformable mirror, MEMS (Micro Electromechanical System, MEMS) deformable mirror and adaptive secondary mirror. The most widely used is the piezoelectric deformable mirror, but it is limited by the material characteristics and has the disadvantages of hysteresis, low modulation, high driving voltage and large volume, etc. It does not have advantages in eye fundus imaging, biological microscopic imaging and other systems. The deformable secondary mirror based on voice coil electromagnetic driver has the characteristics of large stroke, no hysteresis, high precision and fast response, etc. It is adopted by many large telescopes and achieves good observation effect.

[0003] In 1993, Piero Salinari of the Cagliari Astronomical Observatory in Italy first proposed using a voice coil driver to control the deformable secondary mirror of an adaptive optics system [P. Salinari, C. Del Vecchio and V. Biliotti, A study of an adaptive secondary mirror [C]. in Proc. ESO Conference, ICO-16 Satellite Conference, Active and Adaptive Optics, August 1993]. They could make the diameter of the driver within 25 mm under the conditions at the time, and estimated the power range of a single driver to be 0.3 W to 0.5 W. This new type of deformable mirror based on voice coil drivers simplifies the adaptive optics system and improves the imaging resolution. In 2012, a deformable secondary mirror with 1170 drivers was installed on the VLT (Very Large Telescope, VLT) telescope [BIASI R, ANDRIGHETTONI M, ANGERER G. VLT deformable secondary mirror: integration and electromechanical tests results [C] / / Adaptive Optics Systems III. International Society for Optics and Photonics, 2012, 8447: 84472G.], with a mirror diameter of 1.12 m and a response time of 0.5 ms. The voice coil drivers of these deformable mirrors vary in diameter from 20 mm to 30 mm, which is more suitable for adaptive secondary mirrors of ground-based large aperture optical telescopes. However, the large diameter of the voice coil driver limits the application of the voice coil deformable mirror in adaptive optics systems. Therefore, it is very important to study the deformable mirror based on micro voice coil drivers, and the high density of the drivers is beneficial to high precision wavefront correction, thereby obtaining high resolution images.

[0004] In 1997, C. Divoux and O. Cugat studied the micro-coil deformable mirror [C. Divoux, O. Cugat, G. Reyne, J. Boussey-Said, and S. Basrour, "Deformable mirror using magnetic membranes: Application to adaptive optics in astrophysics," IEEE Trans. Magn. 34, 3564-3567 (1998).] The early design was limited by the level of computer and finite element analysis at that time, and the temperature rise caused by current was very obvious, and the comprehensive performance was poor. In 2006, EJ Fernandez used the MIRAO 52 deformable mirror manufactured by Imagine Eyes Company to correct the aberration of the human eye [E. J. Fernandez, L. Vabre, B. Hermann, A. Unterhuber, B. Povazay, and W. Drexler, "Adaptive optics with a magnetic deformable mirror: applications in the human eye," Opt. Express 14, 8900-8917 (2006).] But the current articles about the coil deformable mirror of the company are mainly application reports, and there is no report on theory and structure design.

[0005] The diameter of the coil driver of the conventional coil deformable mirror is about 20mm, the structure size is relatively large, and the mirror surface of the deformable mirror can be made of glass, silicon carbide and other materials, which has a certain stiffness, so the driver can be designed in multiple structures. The diameter of the micro-coil driver is in the order of millimeters, about 1-2mm, although the micro-coil driver brings advantages such as compact structure, low driving voltage, high correction accuracy, etc. to the various applications of compact coil deformable mirror, but it also brings difficulties to the design:

[0006] 1) The output force of the micro-coil driver is two to three orders of magnitude smaller than that of the conventional coil driver, so it cannot be made of materials with high stiffness coefficient such as glass and silicon carbide;

[0007] 2) How to connect the micro-coil driver and its mirror surface to make the micro-coil driver have a certain stiffness, but not as much stiffness as the conventional coil deformable mirror.

[0008] 3) General application requirements for deformable mirror with large phase modulation depth, which requires increasing the input current, and large current will cause heat loss caused by temperature rise, micro coil driver and its arrangement if the design is not reasonable, will be due to the narrow space, poor heat dissipation, resulting in temperature rise, resulting in thin mirror surface shape change, affect the correction effect and imaging quality.

[0009] 4) The previous literature reported only focused on the improvement of a certain performance of compact voice coil deformable mirror. The structure parameters, materials, working current of voice coil deformable mirror are closely related to the phase modulation amount, frequency and other performance of voice coil deformable mirror. Moreover, with the increasing demand for beam quality in adaptive optics technology in fundus retinal imaging, super-resolution microscopic imaging, laser atmospheric transmission and other applications, it is very important to reduce the volume of voice coil deformable mirror and improve its comprehensive performance.

[0010] Therefore, considering the theoretical requirements of the performance indicators of the compact voice coil deformable mirror of the micro voice coil driver, how to balance and optimize the design of the structure parameters, and obtain the compact voice coil deformable mirror with the best comprehensive performance has become a difficult problem to be solved. SUMMARY

[0011] In order to provide a compact structure, low driving voltage, high correction accuracy, and better wavefront correction ability of the deformable mirror, the application provides a micro voice coil driver, the diameter of the micro voice coil driver is in millimeter level, comprising: a thin mirror, a support, a permanent magnet, a voice coil and a spring; the permanent magnet is connected with the thin mirror through the support, and the spring is sleeved on the support; the voice coil is coaxial with the permanent magnet and located below the permanent magnet, and there is a gap between the voice coil and the permanent magnet.

[0012] Optionally, the thin mirror material is polyimide.

[0013] Optionally, the thickness of the thin mirror is 20 µm~50 µm.

[0014] Optionally, the inner radius and outer radius of the voice coil are 0.2±0.02mm and 2±0.2mm respectively, and the height is set to 1±0.05mm.

[0015] Optionally, the radius of the permanent magnet is 1±0.1mm, and the height is set to 0.2±0.02mm.

[0016] Optionally, the voice coil is a copper coil.

[0017] Optionally, the copper coil is a copper enameled wire with a wire diameter of 0.1mm.

[0018] The application also provides a compact voice coil deformable mirror based on a micro voice coil driver, the deformable mirror comprising a plurality of micro voice coil drivers and spring fixing structures according to claims 1-6; the thin mirror contained in each micro voice coil driver is the same thin mirror.

[0019] Optionally, the spring fixing structure comprises a bottom plate and a spring fixing plate; the bottom plate is provided with a plurality of regularly arranged recesses, each recess corresponding to a micro voice coil driver, and the spring fixing plate is provided with through holes corresponding to the pillars and the springs; the spring fixing structure cooperates with the springs arranged in each micro voice coil driver to provide rigidity for the voice coil driver.

[0020] Optionally, the distance between the micro voice coil drivers is 2.5; and the overall arrangement is in a hexagonal shape.

[0021] Optionally, the deformable mirror further comprises an O-ring arranged at the periphery of the thin mirror and a deformable mirror shell.

[0022] In order to reduce the volume of the voice coil deformable mirror (VCDM) and improve the density of the voice coil driver, the simplest magnet and coil structure is adopted in the present application, and the soft magnetic material cannot be introduced into the coil to reduce the magnetic leakage. The motor constant of such structure is relatively small, but it provides the possibility for developing compact voice coil deformable mirrors.

[0023] The voice coil deformable mirror (VCDM) shell proposed in the present application can be designed as a square shape, which is convenient for installation on an optical clamp. Through the comprehensive design and optimization of the compact voice coil deformable mirror, the heat loss can be reduced, the influence of heat on the thin mirror surface can be reduced, the response speed and phase modulation range can be designed reasonably, so that the compact voice coil deformable mirror can have better performance. Overcome these problems, so that the deformable mirror can fit more complex waveforms, and at the same time has better performance, promotes the application field of compact voice coil deformable mirror.

[0024] The present application has the following beneficial effects:

[0025] The micro voice coil driver designed in the application considers that the output force of the micro voice coil driver is two to three orders of magnitude smaller than that of a conventional voice coil driver, adopts polyimide to replace the conventional glass, silicon carbide and other materials with large stiffness coefficients to make a thin mirror surface, in order to meet the stiffness requirement, provides certain stiffness for the thin mirror surface through a spring structure, and comprehensively considers the correlation between the structure parameters, materials, working current and the like of the voice coil deforming mirror and the phase modulation amount, frequency and other performances of the voice coil deforming mirror, balances and optimizes the structure parameters, and obtains a compact voice coil deforming mirror with the best comprehensive performance, specifically, according to the application in the field of astronomical observation and fundus retinal cell imaging, the key performance parameters such as the phase modulation amount and response speed required by the voice coil deforming mirror are calculated, and polyimide and other materials such as beryllium, aluminum, titanium, boron glass, silicon, nitrocellulose and carbon fiber reinforced plastic are adopted. The structure of the micro voice coil driver is optimized, the inner wall thickness d c-in , the outer wall thickness d c-out , the height h m and h c and other parameters of the permanent magnet and the voice coil in the voice coil driver are optimized by using the finite element method, then a 69-unit compact voice coil deforming mirror is designed, and modal analysis and optimization are performed. Finally, the maximum output force of a single micro driver can reach 1mN, the motor constant is 0.032N×W -1 / 2 ; the phase modulation amount of the compact deforming mirror reaches ±45 m, and the first resonance frequency reaches 2000Hz. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the application, the drawings needed in the embodiment description will be briefly introduced below, and obviously, the drawings in the following description are only some embodiments of the application, and other drawings can also be obtained according to these drawings without creative labor for those skilled in the art.

[0027] Figure 1 The structure of a single voice coil driver;

[0028] Figure 2A The structure explosion diagram of the voice coil deforming mirror VCDM provided in the application;

[0029] Figure 2B The overall appearance diagram of the voice coil deforming mirror VCDM provided in the application;

[0030] Among them, 1 is a front shell, 2 is a thin mirror, 3 is an O-shaped coil, 4 is a spring, 5 is a support, 6 is a spring fixing plate, 7 is a permanent magnet, 8 is a voice coil, 9 is a bottom plate, and 10 is a back shell.

[0031] Figure 3Simulation diagram of force versus current for permanent magnet in different magnetization directions along axial and radial directions.

[0032] Figure 4A Simulation diagram of the effect of magnet radius on force and motor constant in voice coil actuator structure parameters;

[0033] Figure 4B Simulation diagram of the effect of magnet height on force and motor constant in voice coil actuator structure parameters;

[0034] Figure 4C Simulation diagram of the effect of coil inner diameter on force and motor constant in voice coil actuator structure parameters;

[0035] Figure 4D Simulation diagram of the effect of coil outer diameter on force and motor constant in voice coil actuator structure parameters;

[0036] Figure 4E Simulation diagram of the effect of coil height on force and motor constant in voice coil actuator structure parameters;

[0037] Figure 4F Simulation diagram of the effect of air gap between coil and permanent magnet on force and motor constant in voice coil actuator structure parameters.

[0038] Figure 5A Simulation diagram of the change of electromagnetic force with input current in coil before and after optimization;

[0039] Figure 5B Simulation diagram of the change of motor constant with input current in coil before and after optimization.

[0040] Figure 6A Simulation diagram of thermal analysis results of mirror temperature under different currents;

[0041] Figure 6B Simulation diagram of thermal analysis results of mirror thermal deformation under different currents.

[0042] Figure 7 Simulation diagram of time response of voice coil actuator, i.e. simulation diagram of change of deformation variable with time.

[0043] Figure 8 is a simulation diagram of the relationship between the first resonant frequency of the deformable mirror and the thin mirror thickness.

[0044] Figure 9 is a simulation diagram of the relationship between the coupling coefficient of the deformable mirror and the thin mirror thickness.

[0045] Figure 10 is a simulation diagram of the response functions of four examples.

[0046] Figure 11A is a simulation diagram of the fitting error comparison of the first 14 Zernike terms of four examples;

[0047] Figure 11B is a simulation diagram of fitting error of P3 and two ALPAO deformable mirrors. DETAILED DESCRIPTION

[0048] To make the objects, technical solutions and advantages of the present application clearer, the embodiments of the present application will be further described in detail below with reference to the drawings.

[0049] Embodiment one:

[0050] The present embodiment provides a micro voice coil driver, which is in millimeter scale, as shown in the figure, the micro voice coil driver comprises a thin mirror 2, a support 5, a permanent magnet 7, a voice coil 8 and a spring 4; the permanent magnet 7 is connected with the thin mirror 2 through the support 5, and the spring 4 is sleeved on the support 5; the voice coil 8 is coaxial with the permanent magnet 7 and is located below the permanent magnet 7, and there is a gap between the voice coil 8 and the permanent magnet 7; the thin mirror 2 is made of a material that is easy to deform. Figure 1 The inner radius and the outer radius of the voice coil of the micro voice coil driver are 0.2±0.02mm and 2±0.2mm respectively, and the height is set to 0.4±0.04mm; a copper coil can be used, and specifically it can be a 0.1mm copper enameled wire. The radius of the permanent magnet is 1±0.1mm, and the height is set to 0.2±0.02mm.

[0051] The material that is easy to deform used to prepare the thin mirror 2 can be selected from polyimide, such as beryllium, aluminum, titanium, boron glass, silicon, nitrocellulose, carbon fiber reinforced plastic, etc.; the thickness of the thin mirror 2 is preferably between 20 µm and 25 µm.

[0052] Embodiment two:

[0053] The present embodiment provides a 69-unit compact voice coil deformable mirror based on the micro voice coil driver provided in embodiment one, as shown in the figures, the compact voice coil deformable mirror comprises a front shell 1, a thin mirror 2, an O-ring 3, a spring 4, a support 5, a spring fixing plate 6, a permanent magnet 7, a voice coil 8, a bottom plate 9 and a back shell 10.

[0054] Figure 2A Figure 2B The spring fixing structure comprises a bottom plate and a spring fixing plate; a plurality of regularly arranged recesses are formed on the bottom plate, and each recess corresponds to placing a micro voice coil driver; a through hole for the support and the spring to pass through is formed on the spring fixing plate; the spring fixing structure cooperates with the spring provided in each micro voice coil driver to provide rigidity for the voice coil driver.

[0055] The spring fixing structure comprises a bottom plate and a spring fixing plate; a plurality of regularly arranged recesses are formed on the bottom plate, and each recess corresponds to placing a micro voice coil driver; a through hole for the support and the spring to pass through is formed on the spring fixing plate; the spring fixing structure cooperates with the spring provided in each micro voice coil driver to provide rigidity for the voice coil driver.

[0056] ​​In the single voice coil driver, the permanent magnet 7 is connected with the thin mirror 2 through the support column 5, the spring 4 is sleeved on the support column 5, the force of the voice coil driver is transmitted to the thin mirror 2 through the support column 5 and the local mirror surface is deformed; the voice coil 8 is coaxial with the permanent magnet 7 and located below the permanent magnet 7, and there is a gap between the voice coil 8 and the permanent magnet 7. The pupil diameter in the front shell 1 is 17 mm.

[0057] The early reported micro voice coil driver has large heat, low first resonance frequency and poor comprehensive performance. The micro voice coil driver provided in the embodiment is optimized in structure and material, and the phase modulation amount and response speed of the deformed mirror are combined with the application requirements, and a compact voice coil deformed mirror with better comprehensive performance is provided.

[0058] Principle analysis:

[0059] In the field of astronomical observation applications, the worst case of atmospheric turbulence with a coherence length r0 of 5 cm is considered. Taking an 8.4 m aperture telescope as an example, the wavefront phase difference to be corrected by the driver is related to the mean square residual of the wavefront, and the mechanical stroke of the voice coil driver required for atmospheric turbulence correction is [R. Hamelinck, "Adaptive deformable mirror: based on electromagnetic actuators," Technische Universiteitndhoven (2019)]

[0060] (1)

[0061] wherein, r0 is the coherence length of atmospheric turbulence, D is the aperture of the telescope, l and the observation wavelength is 550 nm. In the field of fundus retinal imaging, when the reference wavelength is 600 nm, the pupil diameter of the human eye is generally 2 mm to 7.5 mm, and the maximum wavefront aberration can reach 53 mm without refractive correction. Therefore, considering the above application requirements, the deformation of the voice coil deformed mirror VCDM needs to reach ±27 m.

[0062] The magnetic induction intensity of any point in the static magnetic field of the voice coil driver can be written as:

[0063] (2)

[0064] Therefore, the magnetic induction intensity of the current-carrying coil at a certain point in space can be obtained as:

[0065] (3)

[0066] wherein m0 is the vacuum permeability, is the current element, is the unit vector along the direction vector , r is the distance from the current element to a point in space. According to the relationship between magnetic induction intensity and magnetic field intensity, the magnetic field intensity of the current-carrying coil at any point in space is:

[0067] (4)

[0068] The permanent magnet in the voice coil driver is in the magnetic field generated by the current-carrying coil, so the electromagnetic force can be represented as:

[0069] (5)

[0070] where V is the volume of the permanent magnet, B r is the residual magnetism of the permanent magnet, and H is the Z-direction component of the magnetic field intensity of the current-carrying coil, i.e., the component in the direction of the motion of the permanent magnet.

[0071] In order to simplify the model when simulating the current, a circular cylinder is used instead of the coil winding, and the current is set to flow uniformly through the conductor cross section. The number of turns of the coil is represented by N, and the cross-sectional current of the entire winding (unit A) is:

[0072] (6)

[0073] where the number of turns of the coil N is mainly determined by the cross-sectional area of the winding, and in addition, it is related to the winding method of the wire. Since there is a gap between the wires, the cross-sectional area of the entire winding is larger than the sum of the cross-sectional areas of the actual wires; the filling factor is generally taken as 1.1~1.2.

[0074] Introducing "motor constant" as a measurement factor:

[0075] (7)

[0076] where F is the electromagnetic force output by the micro voice coil driver, and P is the power of the micro voice coil driver. According to equations (5) and (7), the motor constant can be written as:

[0077] (8)

[0078] It can be seen that the motor constant is a physical quantity independent of the coil current, and can objectively evaluate the structural parameters of the driver.

[0079] The response speed of the voice coil deformable mirror to atmospheric turbulence disturbance is the highest. For atmospheric turbulence with wind speed v, the Greenwood frequency can be approximated as:

[0080] (9)

[0081] For the worst case, the wind speed v is 10 m / s and r0 is 5 cm, the Greenwood frequency is about 86 Hz. The working bandwidth of the compact deformable mirror is limited by the structure, material and working current of the deformable mirror, and needs to be much smaller than the first mechanical resonance frequency. With a working bandwidth of 100 Hz as the target, the time response of the driver should be less than 1 ms.

[0082] In actual cases, the magnetic field distribution of the magnet and the coil edge is complex, and the force generated is related to the current size and direction, the coil geometry, the size of the permanent magnet and the air gap, etc. The accurate solution of the force needs to be obtained by simulation calculation with the finite element method. The optimization of specific parameters needs to be accurately solved by the finite element method. The simulation method of finite element is introduced in the literature [Riccardi A, Brusa G, Vecchio C D, et al. The adaptive secondary mirror for the 6.5 conversion of the Multiple Mirror Telescope [C] / / Beyond Conventional Adaptive Optics. 2001].

[0083] The optimization process of the geometric and physical parameters of the magnet and coil by the finite element method to improve the efficiency of the voice coil driver is as follows:

[0084] I. Basic model and parameters of the magnet and coil

[0085] The compact voice coil deformable mirror requires a small size of the driver, especially the diameter of the driver. The overall diameter of the driver in this example is constrained to be about 2 mm. When simulating the driver model, the model is simplified as much as possible to highlight its main features.

[0086] Based on the above discussion, the finite element analysis software ANSYS Maxwell is used to simulate the electromagnetic simulation of the driver model. As shown in Figure 1 The initial structure size is as follows: the air gap h g between the mover and the stator is 0.05 mm. The height h m of the permanent magnet is 0.1 mm, and the outer radius r m is 1 mm. The inner diameter and outer diameter of the voice coil are d c-in = 0.2 mm and d c-out = 2.2 mm, respectively, and the height h c is 1 mm. The material of the permanent magnet is NdFe35.

[0087] The thin mirror material used in this example is polyimide. The O-ring, spring, and post are made of 316 stainless steel. The adhesive between the post and the mirror is FR-4 epoxy; for the coil winding, 0.1 mm diameter copper enameled wire is used, and the safe current carrying capacity of the copper wire is 5~8A / mm 2 , the maximum passing current of the enameled wire is selected as 0.441A. From the perspective of accelerating heat dissipation, the shell of the deformable mirror, the spring fixing plate and the bottom plate are all made of aluminum alloy material, and the parameters of the materials used are shown in Table 1.

[0088] Table 1 Parameters of materials

[0089]

[0090] II. Optimization of the parameters of the magnet and the coil

[0091] Figure 3 It can be seen that, whether parallel magnetization or radial magnetization, the electromagnetic force has a good linear relationship with the current, which is consistent with the theoretical expectation of formula (5). For the same current, the output force under radial magnetization is greater than that under axial magnetization, and the former is 1.5 times greater, and the radial magnetization direction of the permanent magnet is obviously better.

[0092] Figure 4A and 4B respectively show the electromagnetic force and the motor constant K as functions of the radius and height of the magnet. The increase of the radius and height of the magnet will lead to the increase of the electromagnetic force and the motor constant. The difference lies in the growth rate of the electromagnetic force and the motor constant. When the height of the magnet increases, their growth rate will decrease. It should be noted that the magnet is the mover of the driver, and increasing its volume will reduce the response speed of the driver, thus bringing adverse effects. Therefore, the optimized radius of the magnet is 1 mm, and the optimized height is 0.2 mm. From Figure 4C It can be seen that, as the inner diameter of the coil increases, both the electromagnetic force and the motor constant decrease. Therefore, the inner diameter of the coil is determined to be 0.2 mm. Similarly, according to Figure 4D , the outer diameter of the coil is determined to be 2 mm. Figure 4E Although the electromagnetic force increases with the increase of the height of the coil, the motor constant first increases and then decreases. This is because the wires far from the magnet contribute less to the electromagnetic force. Considering the efficiency of the driver, the optimized height of the coil is selected to be 0.4 mm. Figure 4F It shows that the larger the air gap, the smaller the electromagnetic force and the motor constant. Therefore, the optimized air gap of the voice coil driver is 50μm.

[0093] Figure 5A It shows that the output force of the optimized voice coil driver is proportional to the current. Figure 5A The output force of the voice coil driver with the optimized structure parameters marked by the black square in the figure is obviously greater than Figure 5AThe initial output force is marked by the middle red circle, and the maximum output force is ±1 mN. The maximum electromagnetic force of the optimized driver is about twice that of the initial driver. Figure 5B It is proved that the motor constant is only related to the structure of the driver and almost does not change with the current. The motor constant of the optimized driver is 0.032 N×W -1 / 2 , about three times that of the initial driver.

[0094] Figure 6A The temperature change of the deformable mirror when different currents are used in the coil is shown. The maximum temperature of the mirror surface increases continuously with the increase of the current. This is because a larger current generates more heat in the deformable mirror. For the overall heat dissipation capacity of the deformable mirror, when the coil current is 0.1A corresponding to the current density of 10A / mm 2 , the temperature rise of the VCDM does not exceed 1 degree Celsius. Although part of the mirror surface is covered by the front shell of the VCDM, the circular pupil area is open. Different heat dissipation conditions lead to uneven temperature distribution on the thin mirror. In addition, the average temperature of the thin mirror surface increases nonlinearly with the current. Figure 6B The thermal deformation of the thin mirror due to temperature is shown. It can be seen that the PV value of the mirror deformation increases with the increase of the current. When the current density is 6A / mm 2 corresponding to 0.06A in Figure 6B , the PV value of the thermal deformation of the mirror is 12.36 nm, which is about 0.022λ when λ=550nm. The rms value of the mirror deformation is around 0, which gradually deviates from 0 with the increase of the current. Therefore, the maximum control current of the single voice coil driver should not exceed 0.06A.

[0095] The mass of the magnetic actuator is 4.6786 mg, and the initial speed is 0 m / s. The time response of the voice coil driver obtained using Maxwell is shown in Figure 7, the acceleration of the permanent magnet is proportional to the current, and all the permanent magnets can reach the specified position within 0.65 milliseconds. The first resonance frequency is mainly related to the stiffness of the thin mirror and the stiffness of the driver. When the mirror material is determined, the mirror stiffness is affected by the thickness of the mirror. The stiffness of the voice coil driver is determined by the spring. As Figure 8 shown, for the same mirror thickness, the first resonance frequency is positively correlated with the spring stiffness. However, excessive spring stiffness will consume too much electromagnetic force, so the thickness of the thin mirror 2 is preferably between 20 µm and 50 µm.

[0096] The coupling coefficient is a key indicator of compact voice coil deformable mirrors, mainly affected by the thickness of the thin mirror and the stiffness of the driver. As Figure 9It is shown that the coupling coefficient increases with the increase of the thin mirror thickness. In addition, the greater the stiffness, the smaller the coupling coefficient. The compact voice coil deformable mirror parameters of four different mirror thicknesses, 69 actuators are listed in Table 2, and their response functions are shown in Figure 10

[0097] Table 2

[0098]

[0099] III. Comparison verification

[0100] In order to evaluate the wavefront correction ability of the four deformable mirrors shown in Table 2, the first 14 modes of Zernike aberration are fitted. In the fitting experiment, four deformable mirrors are driven to generate Zernike shapes with a PV value of 8 μm. The results are shown in Figure 11A All four deformable mirrors have good fitting for the first 14 Zernike aberrations, with the maximum RMS value of only 53 nm. From the fitting error, it can be seen that the best coupling coefficient ranges from 23% to 28%. Therefore, P3 is taken as the best deformable mirror and compared with two 69-unit voice coil deformable mirrors of ALPAO Company. The inter-actuator spacing of the voice coil deformable mirror DM69-25 of the company is 2.5 mm, and the inter-actuator spacing of the voice coil deformable mirror DM69-15 is 1.5 mm. It can be seen from Figure 11B P3 has better correction performance than the other two deformable mirrors, especially for Zernike aberrations containing defocus components.

[0101] Some steps in the embodiments of the present application can be implemented by software, and the corresponding software program can be stored in a readable storage medium, such as an optical disc or a hard disk, etc.

[0102] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.​

Claims

1. A miniature voice coil driver, characterized in that, The miniature voice coil driver has a diameter on the order of millimeters and includes: a thin mirror, a support, a permanent magnet, a voice coil, and a spring; the permanent magnet is connected to the thin mirror via the support, and the spring is sleeved on the support; the voice coil is coaxial with the permanent magnet and is located below it, with a gap between them. The thin mirror material is polyimide; The inner and outer radii of the voice coil are 0.2±0.02mm and 2±0.2mm, respectively, and the height is set to 0.4±0.04mm. The radius of each permanent magnet is 1±0.1mm, and the height is set to 0.2±0.02mm; The spacing between the miniature voice coil drivers is 2.5 mm; the overall arrangement is hexagonal.

2. The miniature voice coil driver according to claim 1, characterized in that, The voice coil is a copper coil.

3. The miniature voice coil driver according to claim 2, characterized in that, The copper coil is a 0.1mm diameter copper enameled wire.

4. A compact voice coil deformable mirror based on a miniature voice coil driver, characterized in that, The deformable mirror includes several miniature voice coil actuators and spring fixing structures as described in claims 1-3; the thin mirrors included in each miniature voice coil actuator are the same thin mirror.

5. The deformable mirror according to claim 4, characterized in that, The spring fixing structure includes a base plate and a spring fixing plate; the base plate has a number of regularly arranged recesses, each recess corresponding to a miniature voice coil driver; the spring fixing plate has corresponding through holes for the support and spring to pass through; the spring fixing structure cooperates with the springs in each miniature voice coil driver to provide stiffness for the voice coil driver.

6. The deformable mirror according to claim 4, characterized in that, The deformable mirror also includes an O-ring disposed around the thin mirror and a deformable mirror housing.

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