Control method for constant grinding force of ultra-lightweight aspheric mirror forming and processing

Abstract

The present application relates to the control method of constant grinding force of ultra-lightweight aspheric mirror forming processing, the present application adopts piezoelectric ceramic to convert the force signal acting on three-dimensional force measuring platform into electric signal, which becomes analog voltage signal after amplification and conditioning, and is transmitted to grinding force acquisition and processing module; the grinding force acquisition and processing module acquires three-dimensional force in real time according to the linear relationship between force and voltage signal, and finally obtains the resultant force of diamond grinding wheel acting on the surface of aspheric mirror at any time; on this basis, the maximum grinding force threshold of diamond grinding wheel acting on the surface of aspheric mirror is set on the grinding force acquisition and processing module. Through the dynamic control means of processing parameters and the sharpness of grinding wheel surface, the grinding force in the whole processing process is constant, which does not exceed the threshold of mirror breakage, and the ultra-precision forming processing of large aperture aspheric element is realized under the premise of ensuring the integrity of the mirror.

Description

Technical Field

[0001] This invention relates to the field of ultra-precision manufacturing technology for large-aperture optical components, and more specifically to a method for controlling constant grinding force in the forming and machining of ultra-lightweight aspherical mirrors. Background Technology

[0002] Compared to traditional spherical optical elements, aspherical optical elements can avoid the adverse effects of spherical aberration, coma, and other aberrations. They reduce light energy loss during beam focusing, improving focusing and calibration accuracy, and have found widespread application in modern large-scale optical systems. To reduce launch costs, space exploration optical systems impose extremely high lightweight requirements on aspherical mirrors, with mirror thicknesses reaching the millimeter level. In the ultra-precision forming and manufacturing process of large-aperture (hundreds to thousands of millimeters) aspherical mirrors made of hard and brittle materials in space exploration systems, factors such as the degradation of machining tools and inconsistent point gradients on the aspherical surface lead to fluctuating increases in machining forces. This makes the mirror surface highly susceptible to cracking and breakage under machining forces, ultimately resulting in the scrapping of the component. Maintaining stable grinding forces during the forming process, while ensuring processing efficiency and accuracy, is crucial to ensuring the integrity of the mirror surface.

[0003] Patent document CN211193241U discloses an electric constant force grinding device that measures the grinding force in real time through a force sensor and feeds it back to the control system. The grinding force is controlled by adjusting the distance between the grinding head and the workpiece through a motor, so as to maintain constant force contact between the grinding head and the workpiece surface.

[0004] Patent document CN107962480A discloses a force control method for belt grinding of a blade robot. After acquiring the voltage signals of the six channels of the sensor, the voltage signals are filtered by software and converted into force signals. Then, zero-point drift compensation and gravity compensation of the robot end load are performed on the force. Finally, constant force control is achieved through force-position hybrid control and PI / PD control.

[0005] Patent document CN106078515A discloses a constant force grinding system that integrates detection and grinding functions, including: a worktable, an online detection system, a constant force grinding system and a controller installed on the worktable. The grinding force is detected online and fed back to the controller. When the grinding force exceeds the set value, the worktable is controlled to retract horizontally to achieve the purpose of constant force grinding.

[0006] Patent document CN102059649A discloses a method for monitoring the magnitude of radial force during grinding on a grinding machine and a method for achieving constant force feed. The method detects the feed force of the workpiece or grinding wheel during the grinding process and controls the drive mechanism that drives the workpiece or grinding wheel based on the detected feed force value to apply a constant feed force to the workpiece or grinding wheel.

[0007] The aforementioned patented technologies all achieve constant force control by monitoring the grinding force in real time and then changing the depth of cut between the grinding wheel and the workpiece. However, in the ultra-precision forming process of aspherical components, the inconsistent gradient of the aspherical surface causes fluctuations in the grinding force. Changing the depth of cut between the grinding wheel and the workpiece then leads to a difference between the actual trajectory of the grinding wheel and the ideal aspherical surface morphology, ultimately affecting the forming accuracy of the component. In the ultra-precision forming manufacturing of large-diameter, hard and brittle, ultra-thin and ultra-lightweight aspherical mirrors, how to solve the problem of fluctuating increases in processing force caused by factors such as the degradation of grinding wheel processing performance and inconsistent gradients at points on the aspherical surface is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0008] Therefore, the purpose of this invention is to propose a method for controlling constant grinding force in the forming process of ultra-lightweight aspherical mirrors, thereby solving the technical problem of fluctuating growth in processing force caused by factors such as the degradation of grinding wheel processing performance and inconsistent gradient of aspherical surface points.

[0009] The following solutions achieve ultra-precision forming of large-diameter aspherical components by dynamically controlling the processing parameters and the sharpness of the grinding wheel surface, ensuring that the grinding force remains constant throughout the entire processing process and does not exceed the threshold for mirror breakage, thus ensuring the integrity of the mirror surface.

[0010] This invention provides a method for controlling constant grinding force in the forming process of ultra-lightweight aspherical mirrors, comprising the following steps:

[0011] S1. A three-dimensional force measuring stage is installed on the worktable of the ultra-precision grinding machine. Piezoelectric ceramics are used to convert the force signal acting on the three-dimensional force measuring stage into an electrical signal. After amplification and conditioning, this signal becomes an analog voltage signal and is transmitted to the grinding force acquisition and processing module. Based on the linear relationship between the force and voltage signals, the grinding force acquisition and processing module acquires the three-dimensional force F in real time. x F y and F z ;

[0012] S2. During the reversal of the three-dimensional force measurement platform, a certain inertial force F will be generated during acceleration and deceleration. i The force F collected x Inertial force F i The grinding force G acting on the surface of the aspherical mirror along the X direction by the grinding wheel. x The relationship between them is G x =F x -F i ;

[0013] Therefore, during the grinding process, the grinding force acquisition and processing module obtains the speed v of the left and right feed motion of the three-dimensional force measuring table from the CNC system in real time. x The grinding force of the diamond grinding wheel acting on the surface of the aspherical mirror along the X direction is calculated by formula (1):

[0014]

[0015] Where: m t Let m be the rest mass of the three-dimensional force measuring table. o The mass of the aspherical mirror and its fixture;

[0016] S3. Then, collect the Z-direction force F measured by the three-dimensional force measuring table when it is stationary and without the aspherical mirror and fixture installed. z0 And the Z-force F when the aspherical mirror and fixture are installed. z1 , calculated by formula (2): where g is the acceleration due to gravity;

[0017]

[0018] S4. According to formula (3), the resultant force of the diamond grinding wheel acting on the surface of the aspherical mirror at any time is calculated:

[0019] G = G x +G y +G z (3);

[0020] S5. Set the maximum grinding force threshold G of the diamond grinding wheel acting on the surface of the aspherical mirror on the grinding force acquisition and processing module. T .

[0021] Furthermore, during the grinding process, the aspherical mirror only performs left and right feed movements with the three-dimensional force measuring stage, i.e., G y =F y G z =F z .

[0022] Furthermore, the maximum grinding force threshold G in S5 T It is related to the lightweight aperture structure of the aspherical mirror, the mirror thickness, the mechanical parameters of the mirror material, and the size factors of the diamond grinding wheel.

[0023] Furthermore, when G≤ηG T During processing, the mirror surface will not break; the safety factor is η, where η < 1.

[0024] Furthermore, when G > ηG TAt that time, the grinding force acquisition and processing module calculates the feed rate attenuation coefficient ζ according to the following formula (4), and reduces the actual feed rate of the reflector moving left and right along the X-axis to reduce the actual grinding force G and ensure that G≤ηGT.

[0025]

[0026] After the feed rate attenuation coefficient ζ is calculated, it is sent to the feed rate module of the CNC system. By reducing the feed rate, the feed rate during the grinding process is reduced, thereby reducing the grinding force.

[0027] Furthermore, an electrolytic electrode is used to perform online electrolytic machining on the diamond grinding wheel to uniformly remove the thin layer of binder on the surface of the grinding wheel, expose the diamond abrasive grains, and restore the grinding performance of the grinding wheel.

[0028] Furthermore, the diamond grinding wheel uses a conductive bronze binder and is connected to the anode of the electrolytic power supply via a brush. The electrolytic electrode is connected to the cathode of the electrolytic power supply and is mounted on the grinding wheel cover in an insulated manner. The working surface of the electrolytic electrode is a toroidal surface, and the meridional radius of curvature R of the electrolytic electrode is... m Radius of curvature R s With the total radius R of the diamond grinding wheel w Circular radius R a The relationship between them is shown in formula (5), where d is the gap between the working surface of the electrolytic electrode and the surface of the diamond grinding wheel;

[0029]

[0030] Furthermore, the relative positions of the electrolytic electrode and the diamond grinding wheel along the axial direction and radial direction can be adjusted.

[0031] Furthermore, the working surface of the electrolytic electrode is provided with holes for the outflow of grinding fluid, and there is a grinding fluid chamber between the electrolytic electrode and its connecting base.

[0032] Furthermore, based on the grinding force G acting on the aspherical mirror by the diamond grinding wheel detected in real time, the grinding force acquisition and processing module calculates the growth rate of the grinding force and calculates the current value of the grinding wheel in online electrolysis according to formula (6). The control signal is sent to the electrolysis power supply so that the electrolysis power supply outputs the corresponding current value to the electrolysis electrode, thereby realizing the online electrolysis of the diamond grinding wheel, exposing the diamond abrasive grains, restoring the grinding performance of the grinding wheel, suppressing the growth of the grinding force, and finally achieving the purpose of stabilizing the grinding force.

[0033]

[0034] In the formula: K is a linear coefficient, which is related to the conductivity of the grinding fluid, the electrolytic electrode, and the grinding wheel speed.

[0035] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects:

[0036] Based on real-time monitoring of three-dimensional grinding force, this invention achieves ultra-precision forming of large-diameter aspherical components by dynamically controlling the processing parameters and the sharpness of the grinding wheel surface, ensuring that the grinding force remains constant throughout the entire processing process and does not exceed the threshold for mirror breakage, thus ensuring the integrity of the mirror surface. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0038] Figure 1 The attached figure is a schematic diagram of the system corresponding to the method for controlling constant grinding force in the forming and processing of ultra-lightweight aspherical mirrors provided by the present invention.

[0039] Figure 2 The attached diagram illustrates the diamond grinding wheel, electrolytic electrodes, and electrolytic power supply.

[0040] Figure 3 The attached diagram shows a schematic view of the electrolytic electrode and the connecting base from one perspective;

[0041] Figure 4 The attached diagram illustrates the electrolytic electrode and the connecting base from another perspective;

[0042] Figure 5 The attached figure is a cross-sectional view of the electrolytic electrode plate;

[0043] In the diagram: 1—Three-dimensional force measuring platform; 2—Aspherical reflector; 3—Diamond grinding wheel; 4—Electrolytic electrode; 5—Grinding wheel cover; 6—Grinding (electrolytic) fluid pipeline A; 7—Grinding (electrolytic) fluid flow regulating valve A; 8—Grinding (electrolytic) fluid flow regulating valve B; 9—Grinding (electrolytic) fluid pipeline B; 10—Electrolytic power supply; 11—CNC system; 12—Grinding force acquisition and processing module;

[0044] 4-1—Attitude Adjustment Bolt A; 4-2—Attitude Adjustment Bolt B; 4-3—Radial Adjustment Screw; 4-4—Attitude Adjustment Bolt C; 4-5—Attitude Adjustment Bolt D; 4-6—Mounting Base; 4-7—Axial Position Adjustment Hole; 4-8—Connecting Base; 4-9—Electrolytic Electrode Plate; 4-10—Spherical Surface; 4-11—Grinding Fluid Chamber; X—Radial; Y—Axial. Detailed Implementation

[0045] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0046] See appendix Figure 1-5 The present invention has a three-dimensional force measuring stage 1 installed on the worktable of an ultra-precision grinding machine. The force signal acting on the three-dimensional force measuring stage is converted into an electrical signal by piezoelectric ceramics. After amplification and conditioning, it becomes an analog voltage signal and is transmitted to the grinding force acquisition and processing module 12.

[0047] The piezoelectric ceramic is a component of the three-dimensional force measurement stage. The three-dimensional force measurement stage mainly includes a lower plate, a piezoelectric ceramic, an upper plate, and an external protective cover. The piezoelectric ceramic is fixed between the upper and lower plates. After a force is applied to the upper plate, the piezoelectric ceramic emits an electrical signal to characterize the magnitude of the force.

[0048] During the grinding process of aspherical mirrors, the grinding force acquisition and processing module acquires the three-dimensional force F in real time based on the linear relationship between force and voltage signals. x F y and F z Because the aspherical mirror only moves left and right along with the three-dimensional force measuring stage 1 during the grinding process, F y and F z This refers to the Y-axis grinding force G exerted by the diamond grinding wheel on the surface of the aspherical mirror. y and Z-axis grinding force G z G y =F y G z =F z .

[0049] During the acceleration and deceleration process of the three-dimensional force measurement stage 1 during reversal, a certain inertial force F will be generated. i The force F collected x Inertial force F i The grinding force G acting on the surface of the aspherical mirror along the X direction by the grinding wheel. x The relationship between them is G x =F x -F i Therefore, during the grinding process, the grinding force acquisition and processing module obtains the speed v of the left and right feed motion of the three-dimensional force measuring table in real time from the CNC system 11. x The grinding force of the diamond grinding wheel acting on the surface of the aspherical mirror along the X direction is calculated by formula (1):

[0050]

[0051] Where: m t The static mass of the three-dimensional force measuring stage can be accurately measured before the three-dimensional force measuring stage 1 is installed. o To measure the mass of the aspherical mirror and fixture, the Z-axis force F was collected when the three-dimensional force measuring table was stationary and the aspherical mirror and fixture were not installed. z0 And the Z-force F when the aspherical mirror and fixture are installed. z1 , calculated by formula (2): where g is the acceleration due to gravity.

[0052]

[0053] According to Formula 3, the resultant force exerted by the diamond grinding wheel on the surface of the aspherical mirror at any given moment can be calculated:

[0054] G = G x +G y +G z (3);

[0055] In the grinding force acquisition and processing module 12, the maximum grinding force threshold G of the diamond grinding wheel acting on the surface of the aspherical mirror is manually set. T If the grinding force exerted by the diamond wheel on the surface of the aspherical mirror exceeds this threshold during the processing of the component, the mirror surface of the aspherical mirror will break.

[0056] The maximum allowable grinding force threshold is related to factors such as the lightweight aperture structure of the aspherical mirror, the mirror thickness, the mechanical parameters of the mirror material, and the size of the diamond grinding wheel.

[0057] Maximum grinding force threshold G T This can be determined experimentally. Specifically, by analyzing the lightweight aperture structure of the aspherical reflector, the area with the largest span of the lightweight aperture is the weakest and most fragile part. An experimental specimen with the same lightweight aperture structure as the weakest point is designed. The material of the experimental specimen is the same as that of the aspherical reflector, and the mirror thickness is the same as the thickness of the aspherical reflector after forming and machining. Then, the experimental specimen is ground using the same diamond grinding wheel used for form grinding. Pressure is applied at the center of the lightweight aperture in the experimental specimen, and the pressure is measured simultaneously in real time until the experimental specimen breaks. The pressure at this point is the maximum grinding force threshold G of the aspherical reflector. T .

[0058] During a single grinding process of aspherical mirrors, the grinding force G exerted by the diamond wheel on the aspherical mirror fluctuates due to the inconsistent gradient at different points on the surface of the component.

[0059] To ensure absolute safety during processing, a safety factor η (η < 1) is set, where G ≤ ηG. T This avoids the possibility of the mirror breaking during the processing.

[0060] When G > ηG T At that time, the grinding force acquisition and processing module 12 calculates the feed rate attenuation coefficient ζ according to the following formula (4), and reduces the actual feed rate of the reflector moving left and right along the X-axis to reduce the actual grinding force G, ensuring that G≤ηG T .

[0061]

[0062] After the feed rate attenuation coefficient ζ is calculated, it is sent to the feed rate module of the CNC system 11. By reducing the feed rate, the feed rate during the grinding process is reduced, thereby reducing the grinding force.

[0063] As the grinding process progresses, the mirror material is removed layer by layer, and the diamond abrasive grains on the diamond wheel surface become passivated, increasing the grinding force. When simply reducing the feed rate and sacrificing a small amount of machining efficiency is no longer sufficient to significantly reduce the grinding force, see Appendix. Figure 2 This invention uses an electrolytic electrode 4 to perform online electrolytic processing on a diamond grinding wheel, uniformly removing the thin layer of binder on the surface of the grinding wheel, exposing the diamond abrasive grains, restoring the grinding performance of the grinding wheel, and achieving the purpose of reducing and stabilizing the grinding force.

[0064] The diamond grinding wheel uses a bronze binder, which has good electrical conductivity, and is connected to the anode of the electrolytic power supply 10 via a brush. The electrolytic electrode 4 is connected to the cathode of the electrolytic power supply 10 and is mounted on the grinding wheel cover 5 in an insulated manner. The working surface of the electrolytic electrode 4 is a toroidal surface, and the meridional radius of curvature R of the electrolytic electrode 4 is... m Radius of curvature R s With the total radius R of the diamond grinding wheel w Circular radius R a The relationship between them is shown in formula (5), where d is the gap between the working surface of the electrolytic electrode and the surface of the diamond grinding wheel.

[0065]

[0066] To ensure both high electrolytic efficiency and preservation of the original shape and precision of the diamond grinding wheel during electrolytic machining, a uniform gap layer is required between the electrolytic electrode 4 and the surface of the diamond grinding wheel 3.

[0067] The structure of electrolytic electrode 4 is as follows Figure 3 and 4As shown. The mounting base 4-6 is made of insulating material and is installed on the grinding wheel cover 5 by passing four bolts through the axial position adjustment hole. This allows the entire electrolytic electrode plate 4-9 to move axially along the main shaft, that is, to adjust the relative position of the electrolytic electrode plate 4-9 and the diamond grinding wheel 3 along the axial direction.

[0068] The radial adjusting screw 4-3 is used to adjust the radial position of the electrolytic electrode plate 4-9 and the diamond grinding wheel 3. The radial adjusting screw 4-3 is threadedly connected to the mounting base 4-6. By screwing the radial adjusting screw 4-3 in or out, the radial position of the electrolytic electrode plate 4-9 can be adjusted. Furthermore, the radial adjusting screw 4-3 is hollow, allowing the passage of grinding (electrolyte) fluid.

[0069] Attitude adjustment bolts A4-1, B4-2, C4-4, and D4-5 are used to adjust the pitch (rotation about the Y-axis) and yaw (rotation about the Z-axis) of the electrolytic electrode plate 4-9 relative to the diamond grinding wheel 3, and to fix the position of the electrolytic electrode plate 4-9. The connecting base 4-8 is used to mount the electrolytic electrode plate 4-9. Holes are provided on the working surface of the electrolytic electrode plate 4-9 for the outflow of grinding (electrolyte) fluid. Under the action of an electric field, the metal bond on the surface of the diamond grinding wheel 3 undergoes an electrochemical reaction.

[0070] like Figure 5 The figure shows a cross-sectional view of the electrolytic electrode plate 4-9. Advantageously, the radial adjustment screw 4-3 and the connecting base 4-8 are in spherical contact (4-10 spherical surface), which ensures the sealing of the grinding (electrolyte) fluid flowing through the pipe A6 when the connecting base 4-8 and the electrolytic electrode plate 4-9 can make small range of pitch and yaw movements.

[0071] More advantageously, there is a grinding fluid chamber 4-11 between the connecting base 4-8 and the electrolytic electrode plate 4-9, which can ensure that the grinding (electrolytic) fluid can flow out from all the holes on the working surface of the electrolytic electrode plate 4-9, so that the entire electrode surface generates a uniform electric field on the grinding wheel surface, thereby generating a uniform electrochemical reaction on the grinding wheel surface, and ultimately ensuring the uniform removal of the metal binder on the grinding wheel surface.

[0072] However, during the grinding process of aspherical mirrors, as the volume of material removed increases, the wear of the grinding wheel gradually intensifies, and the corresponding grinding force gradually increases.

[0073] In the embodiments of the present invention, the grinding force acquisition and processing module 12 calculates the growth rate of the grinding force based on the grinding force G acting on the aspherical mirror 2 by the diamond grinding wheel 3 in real time, and calculates the current value of the online electrolysis of the diamond grinding wheel using formula (6), and sends a control signal to the electrolysis power supply 10 so that the electrolysis power supply 10 outputs the corresponding current value to the electrolysis electrode 4, thereby realizing the online electrolysis of the diamond grinding wheel, exposing the diamond abrasive grains, restoring the grinding performance of the grinding wheel, suppressing the growth of the grinding force, and finally achieving the purpose of stabilizing the grinding force.

[0074]

[0075] In the formula: K is a linear coefficient, which is related to factors such as the conductivity of the grinding (electrolyte), the electrolytic electrode, and the rotational speed of the diamond grinding wheel.

[0076] The results were confirmed through process experiments and manually input into the grinding force acquisition and processing module.

[0077] To ensure the smooth progress of the electrolytic reaction and the long-term use of metal protective covers for machine tools, as well as to be user-friendly for operators, the electrolyte in the grinding (electrolyte) is generally a neutral or weakly alkaline electrolyte, such as potassium sulfate or sodium carbonate.

[0078] In the description of this invention, it should be understood that the terms "Y-axis", "Z-axis", "X-axis", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0079] The control method for constant grinding force in the forming process of ultra-lightweight aspherical mirrors provided by this invention corresponds to the system shown in the appendix. Figure 1-5 It includes:

[0080] Three-dimensional force measuring stage 1 is installed on the worktable of an ultra-precision grinding machine; an aspherical reflector 2 is placed on its top.

[0081] Diamond grinding wheel 3 is located on aspherical mirror 2 and is supported and driven by an external structure, with an outer grinding wheel cover 5.

[0082] Electrolytic electrode 4 is installed on the outer cover 5 of the grinding wheel and located between the outer cover 5 of the grinding wheel and the diamond grinding wheel 3, and is used for online electrolytic machining of the diamond grinding wheel;

[0083] The diamond grinding wheel 3 is connected to the anode of the electrolytic power supply 10 via a brush, and the electrolytic electrode 4 is connected to the cathode of the electrolytic power supply 10 and is installed on the outer cover 5 of the grinding wheel in an insulated manner.

[0084] The grinding force acquisition and processing module 12 is electrically connected to the piezoelectric ceramic three-dimensional force measurement stage 1 and to the electrolytic power supply 10.

[0085] The CNC system 11 and the grinding force acquisition and processing module 12 are electrically connected to the CNC system 11.

[0086] The grinding (electrolyte) pipeline includes a grinding (electrolyte) pipeline A6 that directly supplies the electrolytic electrode and a grinding (electrolyte) pipeline B9 that is connected to the outside. The two are connected and a grinding (electrolyte) flow regulating valve A7 is installed between them. A grinding (electrolyte) flow regulating valve B8 is installed on the externally connected grinding (electrolyte) pipeline B9.

[0087] 4-3—Radial adjusting solenoid; 4-6—; 4-8—Connecting base; 4-9—Electrolytic electrode plate; 4-10—Spherical surface; 4-11—Grinding fluid chamber; X—Radial; Y—Axial.

[0088] Electrolytic electrode 4, see appendix Figure 2-5 The electrolytic electrode 4 includes a mounting base 4-6. The mounting base 4-6 uses four bolts (4-1 attitude adjustment bolt A; 4-2 attitude adjustment bolt B; 4-4 attitude adjustment bolt C; 4-5 attitude adjustment bolt D) to adjust the pitch (rotation about the Y-axis) and yaw (rotation about the Z-axis) of the electrolytic electrode plate 4-9 relative to the diamond grinding wheel 3, and to fix the position of the electrolytic electrode plate 4-9. A connecting base 4-8 is used to mount the electrolytic electrode plate 4-9. The working surface of the electrolytic electrode plate 4-9 has holes for the outflow of grinding (electrolyte) fluid, which, under the action of an electric field, causes an electrochemical reaction in the metal bond on the surface of the diamond grinding wheel 3. The mounting base 4-6 has four axial position adjustment holes 4-7.

[0089] The radial adjusting screw 4-3 and the connecting base 4-8 have a spherical contact (4-10 spherical surface). This ensures the sealing of the grinding (electrolyte) fluid flowing through pipe A6 when the connecting base 4-8 and the electrolytic electrode plate 4-9 can make a small range of pitch and yaw movements. Between the connecting base 4-8 and the electrolytic electrode plate 4-9, there is a grinding fluid chamber 4-11, which ensures that the grinding (electrolyte) fluid can flow out from all the holes on the working surface of the electrolytic electrode plate 4-9.

[0090] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0091] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for controlling constant grinding force in the forming process of ultra-lightweight aspherical mirrors, characterized in that, Includes the following steps: S1. A three-dimensional force measuring stage is installed on the worktable of the ultra-precision grinding machine. Piezoelectric ceramics are used to convert the force signal acting on the three-dimensional force measuring stage into an electrical signal. After amplification and conditioning, it becomes an analog voltage signal and is transmitted to the grinding force acquisition and processing module. The grinding force acquisition and processing module acquires three-dimensional force F in real time based on the linear relationship between force and voltage signals. x F y and F z ; S2. During the reversal of the three-dimensional force measurement platform, a certain inertial force F will be generated during acceleration and deceleration. i The force F collected x Inertial force F i The grinding force G acting on the surface of the aspherical mirror along the X direction by the grinding wheel. x The relationship between them is G x =F x -F i ; Therefore, during the grinding process, the grinding force acquisition and processing module obtains the speed v of the left and right feed motion of the three-dimensional force measuring table from the CNC system in real time. x The grinding force of the diamond grinding wheel acting on the surface of the aspherical mirror along the X direction is calculated by formula (1): （1）； Where: m t Let m be the rest mass of the three-dimensional force measuring table. o The mass of the aspherical mirror and its fixture; S3. Then, collect the Z-direction force F measured by the three-dimensional force measuring table when it is stationary and without the aspherical mirror and fixture installed. z0 And the Z-force F when the aspherical mirror and fixture are installed. z1 , calculated by formula (2): where g is the acceleration due to gravity; （2）； S4. According to formula (3), the resultant force of the diamond grinding wheel acting on the surface of the aspherical mirror at any time is calculated: （3）； S5. Set the maximum grinding force threshold G of the diamond grinding wheel acting on the surface of the aspherical mirror on the grinding force acquisition and processing module. T ; During the grinding process, the aspherical mirror only performs left and right feed movements with the three-dimensional force measuring stage, i.e., G y =F y G z =F z ; Maximum grinding force threshold G in S5 T It is related to the lightweight aperture structure of the aspherical mirror, the mirror thickness, the mechanical parameters of the mirror material, and the size factors of the diamond grinding wheel; When G≤ηG T At that time, the mirror surface will not break during the processing; The safety factor is η, where η < 1; When G > ηG T At that time, the grinding force acquisition and processing module calculates the feed rate attenuation coefficient ζ according to the following formula (4), and reduces the actual feed rate of the reflector moving left and right along the X-axis to reduce the actual grinding force G and ensure that G≤ηGT; （4）； After the feed rate attenuation coefficient ζ is calculated, it is sent to the feed rate module of the CNC system. By reducing the feed rate, the feed rate during the grinding process is reduced, thereby reducing the grinding force. Online electrolytic machining of diamond grinding wheels is performed using electrolytic electrodes to uniformly remove the thin layer of bonding agent on the surface of the grinding wheel, expose the diamond abrasive grains, and restore the grinding performance of the grinding wheel. Based on the grinding force G of the diamond grinding wheel acting on the aspherical mirror detected in real time, the grinding force acquisition and processing module calculates the growth rate of the grinding force and calculates the current value of the grinding wheel in online electrolysis according to formula (6). The control signal is sent to the electrolysis power supply so that the electrolysis power supply outputs the corresponding current value to the electrolysis electrode, thereby realizing the online electrolysis of the diamond grinding wheel, exposing the diamond abrasive grains, restoring the grinding performance of the grinding wheel, inhibiting the growth of the grinding force, and finally achieving the purpose of stabilizing the grinding force. （6）； In the formula: K is a linear coefficient, which is related to the conductivity of the grinding fluid, the electrolytic electrode, and the grinding wheel speed.

2. The method for controlling constant grinding force in the forming process of ultra-lightweight aspherical mirrors according to claim 1, characterized in that, The diamond grinding wheel uses a conductive bronze binder and is connected to the anode of the electrolytic power supply via a brush. The electrolytic electrode is connected to the cathode of the electrolytic power supply and is mounted on the grinding wheel casing in an insulated manner. The working surface of the electrolytic electrode is a toroidal surface with a meridional radius of curvature R. m Radius of curvature R s With the total radius R of the diamond grinding wheel w Circular radius R a The relationship between them is shown in formula (5), where d is the gap between the working surface of the electrolytic electrode and the surface of the diamond grinding wheel; （5）。 3. The method for controlling constant grinding force in the forming process of ultra-lightweight aspherical mirrors according to claim 2, characterized in that, The relative positions of the electrolytic electrode and the diamond grinding wheel along the axial direction and radial direction can be adjusted.

4. The method for controlling constant grinding force in the forming process of ultra-lightweight aspherical mirrors according to claim 2, characterized in that, The working surface of the electrolytic electrode has holes for the outflow of grinding fluid, and there is a grinding fluid chamber between the electrolytic electrode and its connecting base.

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