Free-form surface flexible polishing self-adaptive control method and device

Abstract

The invention discloses a free-form surface flexible polishing self-adaptive control method and device, and belongs to the technical field of ultra-precision four-axis polishing machine tool machining. According to the method, a high-efficiency closed-loop control system is constructed on the basis of a flexible head removal principle in combination with an automatic control technology and a pressure sensing technology, fine online capture of down pressure changes and self-adaptive adjustment of polishing parameters in the polishing process can be achieved, the limitation of the prior art is effectively overcome, and the intelligent level of the process is improved. Comprising a flexible polishing head and a downward pressure on-line detection device. The actual machining condition of the current position is analyzed by collecting downward pressure generated by deformation of the flexible polishing head in the polishing process, and technological parameters are automatically adjusted. The invention provides a more efficient and accurate free-form surface flexible polishing scheme, the machining time can be remarkably shortened, the labor intensity of technicians is relieved, and meanwhile, the machining precision is guaranteed and improved. The device has the advantages of simple structure, convenience in disassembly and assembly, high precision and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of optical surface polishing machine tool processing, and in particular relates to a flexible polishing self-adaptive control method and device. Background Art

[0002] Against the backdrop of continuous advancements in processing and detection technologies, aspheric optical components are widely used in cutting-edge fields such as deep space observation, biomedicine, and military industry due to their unique advantages over traditional components, such as high design freedom, good imaging quality, and lightweight. However, due to their complex shape characteristics, how to ensure that the processed aspheric surfaces have high processing accuracy has become an important challenge and key issue in the field of optical processing.

[0003] The surface of an optical component is generally an ultra-smooth surface, and the surface shape is mostly a complex free-form surface. Its surface error can be divided into high-frequency error, medium-frequency error and low-frequency error according to frequency. Among them, the medium-frequency error is generally introduced by the residual microstructure produced by the previous processing step, which will seriously affect the optical performance of the component.

[0004] Flexible head polishing is a common method for removing mid-frequency errors from free-form surfaces. This method offers advantages such as preventing damage to the material surface, adaptive bonding, and dynamic compensation for downforce. However, due to the low stress, low removal efficiency, and complex removal mechanism of flexible head polishing, the current common approach is to select a low downforce and perform multiple iterative polishing cycles to ensure machining accuracy. Furthermore, after each polishing step, polishing must be inspected for accuracy. The disadvantages of this process are cumbersome, costly, and time-consuming, and it is prone to over- and under-polishing, which seriously impacts the machining accuracy and efficiency of free-form optical components.

[0005] The removal function of flexible head polishing is a Gaussian-shaped process with low center and high edges. Its specific parameters are related to factors such as the radius of curvature of the surface being machined, the radius of curvature of the flexible head, the amount of pressure applied by the flexible head, and the stress-strain relationship of the flexible head. By controlling the flexible head's dwell time, rotation speed, and downward pressure, the removal effect can be precisely controlled. In actual machining, changing the polishing downward pressure requires frequent movement of the flexible head, altering its trajectory. This is a complex and computationally intensive process, so controlling the flexible head's dwell time and rotation speed is a more reasonable approach. Summary of the Invention

[0006] In response to the need for improvement in the existing technology of ultra-smooth free-form surface flexible polishing process, the present invention provides an adaptive control method and device for free-form surface flexible polishing. The method is based on the flexible head removal principle, automatic control principle and pressure sensing technology to construct a high-efficiency closed-loop control system, which can realize the fine online capture of the pressure changes during the polishing process of the flexible head polishing process and the real-time adaptive adjustment of the process parameters. The method innovatively constructs a closed-loop control system of "sensing-analysis-execution", which can greatly improve the polishing accuracy and polishing efficiency of the flexible head, improve the intelligence level of the system, and effectively overcome the limitations of the existing technology.

[0007] The technical solution adopted by the present invention is:

[0008] The core of this invention is to propose an adaptive control method and supporting device based on real-time downforce feedback. The polishing system mainly consists of a flexible polishing head, a downforce detection module, a multi-axis linkage machine tool, and a central control unit. The downforce detection module innovatively adopts a transfer-type integrated design and has the following key features:

[0009] The core carrier of this module adopts a stepped shaft hollow tool holder structure, with a replaceable elastic chuck at the front end and a multi-petal elastic collet in the clamping cavity, which is compatible with various flexible polishing heads with a clamping diameter range of Φ6-Φ25mm; a standard tool holder shape is set at the tail end of the tool holder to achieve rapid clamping with the machine tool spindle; in the axial mechanism design, a multi-stage buffer structure is adopted. The first stage is a micro-motion structure set between the tool holder and the elastic chuck. The micro-motion structure allows the elastic chuck and the associated flexible polishing head to perform small axial movements, and a buffer pad is set on the contact surface between the two to play a role in buffering and vibration isolation; the second stage is a precision coil spring set on the periphery of the elastic chuck. The pressure is accurately set by adjusting the spring end cover, thereby realizing the detection of small pressure fluctuations by the piezoelectric ceramic sensor.

[0010] The piezoelectric sensing unit adopts a ring-shaped distribution design. A group of annular piezoelectric ceramics is set at the bottom of the detection cavity. At the same time, four groups of small piezoelectric ceramics are arranged symmetrically at 90 degrees on the inner wall of the detection cavity. This layout can not only detect axial pressure changes in real time, but also synchronously monitor lateral off-load torque. The signal fusion algorithm eliminates non-axial interference. In conjunction with a high-speed data acquisition card, it can achieve millisecond-level response, ensuring the real-time downforce feedback.

[0011] At the control level, the present invention establishes a multi-parameter coupling control model, in which the computer control unit achieves adaptive adjustment through the following steps: During the polishing process, the downforce detection module can collect the downforce generated by the deformation of the polishing head online in real time and transmit it to the computer. After the computer collects the downforce signal, it first performs wavelet noise reduction on the original pressure signal to extract the characteristic waveform of the effective frequency band. Then, combined with the stress-strain relationship of the flexible polishing head, it calculates the downforce of the flexible head at the current position and the thickness of the excess to be removed. After obtaining this information, it substitutes it into the current flexible head removal function to solve for the dwell time required to completely remove the excess. Then, a fuzzy PID algorithm is used to dynamically correct process parameters such as the spindle speed and feed rate. Finally, the machine tool CNC system realizes real-time compensation of the polishing trajectory and dwell time. In particular, for different material properties, the system has a built-in expert database that can automatically match the optimal polishing parameter combination based on the pressure fluctuation spectrum characteristics.

[0012] In practice, the operator can set the target pressure threshold and tolerance range through the human-machine interface. During the polishing process, if the actual pressure value exceeds the set range, the control unit will immediately start the parameter adjustment program.

[0013] In particular, since the removal function of the flexible head is a Gaussian type with a low center and high edges, polishing at the current position will inevitably affect the area that has been processed. Therefore, in order to ensure the accuracy of the overall processing effect, a global detection of the area to be polished should be performed before the first polishing. The global margin algorithm and removal amount prediction algorithm should be embedded in the processing path planning stage, and the convolutional neural network is used to estimate the removal function, so as to plan the optimal polishing trajectory in advance and avoid the local over-polishing and under-polishing problems caused by the overlapping effect of flexible polishing.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] 1. This invention provides a more efficient and accurate online detection solution. Through the coordinated design of a composite buffer mechanism and a piezoelectric array, the system can stably detect tiny downward pressure fluctuations, significantly improving over traditional strain gauge sensors. In a reflector polishing experiment, the downward pressure control accuracy reached ±0.8N (3σ), stabilizing the surface roughness Ra value at 0.8nm±0.15nm.

[0016] 2. The present invention provides an adaptive control method for flexible polishing of free-form surfaces. By combining the real-time downward pressure signal with the stress-strain model of the flexible head, a dynamic mapping relationship between material removal amount and residence time is established. Combined with the time-varying control model constructed based on the fuzzy PID algorithm, the coordinated optimization of process parameters such as the spindle speed, feed speed, and workpiece speed can be achieved, which greatly improves the surface processing accuracy and avoids the multiple iterations of the traditional polishing process, thereby improving the efficiency of the entire processing process and product quality.

[0017] 3. The present invention provides a unique annular piezoelectric ceramic layout (1 main ring + 4 auxiliary measuring points) combined with a space vector decomposition algorithm, which can separate the axial polishing force and the lateral offset load torque in real time, effectively eliminating the lateral interference caused by sudden changes in surface curvature, and improving the signal-to-noise ratio of the detection system.

[0018] 4. By combining high-frequency sampling sensing technology with real-time signal processing technology, the present invention shortens system response delay to less than 5ms. In the area of ​​sudden change in curvature radius, the downforce adjustment overshoot is less than 3%, which is significantly reduced compared to traditional PID control.

[0019] 5. The present invention has the advantages of simple structure, easy assembly and disassembly, low cost and high precision, which is conducive to commercialization. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is the front view of the present invention;

[0021] Figure 2 is an axonometric drawing of the present invention;

[0022] Figure 3 This is a cross-sectional view of the downforce online detection module of the present invention;

[0023] Figure 4 This is a schematic diagram of the present invention working on a polishing machine;

[0024] Figure 5 is a schematic diagram of the piezoelectric ceramic array of the present invention;

[0025] Figure 6 It is a workflow diagram of the present invention;

[0026] Among them: 1. Flexible polishing head; 2. Down force online detection module; 2-1. Collet end cover nut; 2-2. Elastic collet; 2-3. Elastic collet seat; 2-4. Spring end cover; 2-5. Precision coil spring; 2-6. Piezoelectric ceramic array; 2-7. Spring sleeve; 2-8. Fixed signal cable; 2-9, 2-14. High-speed sealing ring; 2-10. Communication cable; 2-11. High-speed electric slip ring; 2-12, 2-16. Sensor housing; 2-13. Bearing; 2-15. Hollow tool holder; 2-17. Annular piezoelectric ceramic; 2-18. Small piezoelectric ceramic; 3. Spindle; 4. Workpiece to be polished; 5. Computer; 6. Four-axis polishing machine. DETAILED DESCRIPTION

[0027] In order to better understand the purpose, structure and function of the present invention, the present invention is further described in detail below with reference to the accompanying drawings.

[0028] like Figures 1 to 4As shown, the present invention provides an online detection device for flexible polishing of free-form surfaces, comprising a flexible polishing head 1, an online downforce detection module 2, a computer 5, and a four-axis polishing machine 6; the flexible polishing head 1 and the online downforce detection module 2 are both installed on the machine spindle 3 of the four-axis polishing machine 6, and during the polishing process, the online downforce detection module 2 collects the downforce in real time and transmits the signal to the computer 5, which analyzes the signal and controls the four-axis polishing machine 6 to adjust relevant process parameters.

[0029] The down-force online detection module 2 includes elastic chucks 2-1 to 2-3, pressure regulating devices 2-4 to 2-6, 2-7, a piezoelectric ceramic array 2-6, a high-speed electric slip ring 2-11, a split housing 2-12, 2-16, a bearing 2-13, a hollow tool handle 2-15 and two sets of high-speed sealing rings 2-9, 2-14; the elastic chucks 2-1 to 2-3 are installed on the top of the hollow tool handle 2-15 to clamp the flexible polishing head 1, wherein a micro-motion structure is provided between the elastic chuck seat 2-3 and the hollow tool handle 2-15 to ensure that the elastic chuck performs a small axial movement, and a buffer pad is provided on the contact surface between the two to play a role in filtering and vibration isolation.

[0030] Furthermore, if Figure 3 As shown, the spring sleeve 2-7 is fixed on the hollow shank 2-15, and a precision coil spring 2-5 is arranged between the spring end cover 2-4 and the spring sleeve 2-7, and the gap between the two can be adjusted.

[0031] Furthermore, if Figure 5 As shown, the piezoelectric ceramic array 2-6 is mounted on the hollow tool handle 2-15, wherein the body of the annular piezoelectric ceramic 2-17 is placed tightly against the elastic chuck seat, the annular piezoelectric ceramic bottom plate is fixed on the spring sleeve 2-7, and at the same time, four groups of small piezoelectric ceramics 2-18 are symmetrically arranged at 90° on the inner wall of the detection cavity.

[0032] The high-speed electric slip ring 2-11 is fixed on the hollow tool handle 2-15, and its inner ring is rigidly connected to the hollow tool handle 2-15 and rotates with the hollow tool handle 2-15 during the polishing process; its outer ring and the sensor housing 2-12, 2-16 are fixed together on the motor housing of the machine tool spindle 3, and can translate with the spindle, but does not rotate with the spindle.

[0033] In the downforce online detection module 2, a fixed signal cable 2-8 is provided between the annular piezoelectric ceramic plate in the piezoelectric ceramic array 2-6 and the high-speed electric slip ring 2-11 for transmitting signals when the main shaft rotates at high speed, and a communication cable 2-10 is provided between the outer ring of the high-speed electric slip ring 2-11 that does not rotate with the main shaft 3 and the computer 5; during the polishing operation, the downforce signal collected by the piezoelectric ceramic array 2-6 can be finally transmitted to the computer 5 through the fixed signal cable 2-8, the brushes inside the high-speed electric slip ring 2-11 and the communication cable 2-10.

[0034] A tool holder is provided at the tail of the down-force online detection module 2 for easy clamping onto the machine tool spindle 3. If the flexible polishing head is an airbag polishing head requiring continuous air supply, the air pipe can be arranged through a reserved channel in the hollow tool holder 2-15.

[0035] like Figure 6 As shown, the present invention provides a method for adaptive control of flexible polishing of free-form surfaces, comprising the following steps:

[0036] S1. To ensure accurate machining results, install the flexible polishing head 1 and the downforce online detection module 2 onto the machine tool spindle 3, install the component to be polished 4 onto the four-jaw chuck of the four-axis polishing machine 6, and adjust the chuck to ensure that the installation error is within the allowable range.

[0037] S2. Manually operate the machine tool control software on computer 5 to move the X-axis position to move the flexible polishing head 1 to the polishing starting position, and then perform tool setting, adjust the Y-axis and Z-axis positions of the flexible polishing head 1 and the spindle deflection angle until the surface of the flexible polishing head 1 is just tangent to the surface of the workpiece 4 to be polished, that is, the two are in point contact and the flexible polishing head 1 does not generate downward pressure; after the tool setting is completed, set the coordinates at this time to zero, and then withdraw the polishing head for a distance.

[0038] S3. Before the formal polishing, a global inspection of the surface of the workpiece 4 to be polished is required. The above-mentioned online downforce detection device can be selected, or other high-precision sensors can be selected. After the inspection is completed, the inspection results are input into the computer 5. The computer processes the inspection results and plans the optimal polishing trajectory based on the global margin and removal prediction model.

[0039] S4. Computer 5 automatically generates a machine tool motion program as a preset trajectory program based on the above-mentioned optimal polishing trajectory. During the formal polishing process, the computer uses the real-time feedback of the flexible head downward pressure information, combined with the time-varying control model constructed based on the fuzzy PID algorithm, to achieve coordinated optimization of process parameters such as spindle speed, feed speed, and workpiece speed, thereby ensuring accurate processing results.

[0040] S5. After polishing is completed, the surface of the workpiece to be polished 4 is cleaned and a global inspection is performed again. If the inspection is qualified, the polishing is successful at this time, and the workpiece is removed and transported to the next process; if it is unqualified, it needs to be polished again, and then this step is repeated.

[0041] It will be understood that the present invention is described by way of some embodiments, and it will be appreciated by those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are intended to be protected by the present invention.

Claims

1. An online downforce detection device for a flexible polishing machine tool, characterized in that: It includes a flexible polishing head, a downforce detection module, and a machine tool spindle; the flexible polishing head and the downforce detection module are both installed on the machine tool spindle, and the downforce online detection module adopts a transfer-type integrated design, one end of which can be clamped on the machine tool spindle, and the other end has an elastic chuck that can clamp various types of flexible polishing heads. The downforce detection module has a built-in piezoelectric ceramic sensor that can detect downforce changes in real time during the polishing process.

2. The downforce online detection device according to claim 1, characterized in that: The device includes: an elastic collet, a pre-tightening end cover, a spring, an annular piezoelectric ceramic array, a high-speed electric slip ring, a hollow tool handle, a split housing, a bearing, and a high-speed sealing ring. The elastic collet, the pre-tightening end cover, the annular piezoelectric ceramic, the inner ring of the high-speed electric slip ring, and the hollow tool handle are rigidly connected and rotate with the main shaft; the outer ring of the high-speed electric slip ring is fixed and the split housing remains stationary and does not rotate with the main shaft.

3. According to the downforce online detection device described in claim 2, the tool handle has a hollow structure and a reserved air path, so that it is compatible with an airbag polishing head that requires inflation.

4. The downforce online detection device according to claim 3, characterized in that When the spindle rotates at high speed, the annular piezoelectric ceramic and the inner ring of the high-speed electric slip ring are fixed on the hollow tool holder and remain relatively stationary. A fixed cable is set between the two to transmit the downward pressure signal. During the polishing process, the downward pressure signal collected by the piezoelectric ceramic sensor is finally transmitted to the computer through the fixed cable and the high-speed electric slip ring.

5. According to the downforce online detection device described in claim 4, after the signal is transmitted to the computer, the deformation of the flexible head is calculated and the computer is used to determine whether the polishing at that position is in place. If not, the process parameters are automatically adjusted, the dwell time that needs to be extended is estimated, and the spindle speed is determined to be adjusted according to the situation.

6. An online downforce detection device and adaptive control method for a flexible head polishing machine tool using the method of any one of claims 1 to 4, characterized in that: The following steps are involved: S1. Install the flexible polishing head and the downforce online detection device onto the machine tool spindle; S2. Install the workpiece to be polished and adjust the fixture to ensure that the installation error is within the allowable range; S3. Start the spindle and ensure the flexible polishing head is rotating stably before setting the tool. Move the flexible polishing head to the starting point of the process and adjust its position and angle until the polishing head is tangent to the surface being processed, achieving point contact with the surface without generating downward pressure. S4. Perform a global inspection on the surface of the workpiece to be polished, input the inspection results into the computer and calculate the optimal polishing trajectory. S5. After the polishing head is withdrawn a certain distance, the processing program is run to start polishing. The computer determines whether the polishing is in place at that position based on the downward pressure information fed back by the sensor and automatically adjusts process parameters such as the dwell time and spindle speed until the entire polishing process is completed. S6. Remove the polishing head, clean the processed surface, and inspect the workpiece surface polishing condition. If qualified, remove the workpiece and transfer it to the next process; if unqualified, polish again and repeat this step.

7. The adaptive flexible polishing control method according to claim 5, characterized in that: During the polishing process, the computer's adaptive parameter adjustment does not change the preset flexible head motion trajectory. It only automatically adjusts other process parameters such as the dwell time based on the downward pressure information fed back by the sensor to ensure stable and accurate processing results.

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