Anti-shake control method and system of lens flatness detection device

Abstract

The present application relates to the field of optical precision measurement, and particularly relates to a kind of mirror flatness detection device's anti-shake control method and system, comprising: in detection chamber, establish controlled airflow field, to suppress the local airflow fluctuation induced by external airflow disturbance and objective table movement;Drive objective table to move up and down relative to measuring lens, in the process of movement and after reaching target position, the process of stationary, continuously monitor the deflection angle of objective table;When deflection angle exceeds preset safety threshold, control objective table to stop moving;After objective table reaches target position, continuously obtain the temperature variation in detection chamber, based on the preset temperature-displacement compensation relationship, calculate the displacement correction amount caused by thermal deformation, and actively compensate the target position of objective table according to displacement correction amount, so that objective table is maintained at target position until thermal equilibrium.The present application suppresses various interference factors that affect displacement accuracy, and realizes the accurate and stable displacement of objective table at nanometer level.

Description

Technical Field

[0001] This invention relates to the field of optical precision measurement technology, specifically to a method and system for stabilizing the image in a lens flatness detection device. Background Technology

[0002] In the field of optical precision measurement, the stage needs to support the sample and move up and down relative to the measuring lens. To achieve nanometer-level detection accuracy, the stability of the stage movement is required to be extremely high.

[0003] In existing technologies, common methods for suppressing stage jitter after it reaches its position include: locking the motor after the stage reaches its position; turning off the driver enable to allow the motor to be in a free state; and in stepper motor closed-loop control, stopping pulse transmission to the motor after reaching the target position and eliminating closed-loop adjustment in the program so that the motor no longer responds to external disturbances for displacement adjustment. The common drawback of these solutions is that they are all passive static maintenance strategies after reaching the target position, failing to address the root cause of the jitter. In actual working conditions, the stage's slight jitter and displacement error mainly stem from two neglected physical processes: First, there is the quasi-static displacement drift caused by thermal deformation. The continuous friction of the rotating lead screw generates heat, causing the lead screw temperature to rise and resulting in thermal expansion. Even after the stage is in place, thermal expansion will continue to develop for tens of minutes, causing the stage to drift slowly at the nanometer scale (up to 10 nm or more). The aforementioned solution of removing the closed loop has no ability to compensate for this type of thermal drift, and instead allows the error to accumulate.

[0004] Secondly, there is the micro-posture deflection and jitter during the movement. Differences in the manufacturing process of the lead screw can cause fluctuations in the transmission torque, resulting in a slight angular deflection (typically 10°) of the platform during lifting and lowering. -2 (Metric level). While this minute deflection is unlikely to trigger a safety alarm, it is sufficient to introduce nanometer-level displacement measurement errors, which cannot be eliminated by a static positioning strategy after positioning. Furthermore, airflow disturbances within the detection chamber are also an uncontrollable factor affecting stability. In summary, current technologies lack effective means to fundamentally suppress motion jitter and thermal drift. Summary of the Invention

[0005] The present invention aims to propose a shake stabilization scheme that can actively compensate for thermal deformation and monitor and suppress micro-attitude deflection.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following solution: A method for stabilizing the image in a lens flatness detection device includes: S1: Establish a controlled airflow field within the detection chamber to suppress external airflow disturbances and local airflow fluctuations induced by the movement of the stage; S2: Drive the stage to move up and down relative to the measuring lens. During the movement and when it stops after reaching the target position, continuously monitor the deflection angle of the stage. When the deflection angle exceeds the preset safety threshold, control the stage to stop moving. S3: After the stage reaches the target position, continuously acquire the temperature change in the detection chamber, calculate the displacement correction caused by thermal deformation based on the preset temperature-displacement compensation relationship, and actively compensate the target position of the stage according to the displacement correction to keep the stage at the target position until thermal equilibrium is reached.

[0007] In this method, a controlled airflow field is pre-established within the detection chamber before the stage begins motion. This controlled airflow actively counteracts external airflow disturbances and suppresses self-induced local airflow fluctuations during stage motion. This eliminates airflow disturbances, an environmental interference factor affecting the stable motion of the stage, providing a stable flow field environment for subsequent motion control. Attitude monitoring is extended from the motion process to the stationary phase after reaching the target position, achieving continuous monitoring of the stage's deflection angle throughout the entire cycle. Motion is immediately stopped when the deflection angle exceeds a preset safety threshold, preventing abnormal tilting and collision risks during motion and eliminating potential attitude deviations caused by external interference during the stationary phase. This ensures attitude safety protection without time blind spots. Unlike existing technologies that passively stop the stage after it reaches its position by removing the closed loop or locking the motor, this method maintains effective closed-loop control during the stationary phase, continuously acquiring temperature changes and actively calculating and executing micro-displacement compensation based on a preset temperature-displacement compensation relationship. This active compensation, by maintaining the target position, specifically eliminates the slow, nanoscale thermal drift error caused by the thermal expansion and contraction of the metal structure due to the frictional heat of the lead screw and subsequent cooling, so that the stage can always be accurately maintained in the target position during long periods of static waiting, until thermal equilibrium is reached.

[0008] Furthermore, in S1, a controlled airflow field is established within the detection chamber, including: The operation of multiple fans located in the detection chamber is controlled by a multi-channel closed-loop control method to adjust the speed of multiple fans, so that the controlled airflow field forms a stable laminar flow or controlled cyclone in the moving area of ​​the stage.

[0009] Furthermore, the continuous monitoring of the stage deflection angle in S2 also includes: Obtaining the deflection angle in 10 -2 The micro-amplitude deflection data at the metric level is used to determine the stage jitter status.

[0010] Furthermore, S2 also includes: adjusting the speed of multiple fans in the controlled airflow field according to the shaking state, so as to adjust the airflow distribution and suppress micro-shaking.

[0011] Furthermore, in S3, the temperature change is obtained through multiple temperature probes installed in the lead screw and detection chamber; the preset safety threshold is T=0.01°.

[0012] Furthermore, in S3, the temperature-displacement compensation relationship is as follows: ΔS = k × ΔT × L; Where ΔS is the displacement correction, ΔT is the temperature change, k is the thermal expansion coefficient of the lead screw material, and L is the corresponding structural feature length; Alternatively, the temperature-displacement compensation relationship can be obtained through a temperature-displacement compensation data table calibrated in advance through experiments.

[0013] Furthermore, the displacement of the stage is detected by a grating ruler with nanometer-level resolution; in S3, the displacement correction is based on the reading of the grating ruler as the compensation reference.

[0014] Furthermore, multiple fans employ a multi-channel closed-loop control method to adjust their speed, specifically including: Based on the vibration status obtained from the angle sensor, the fan speed is dynamically adjusted to adjust the airflow distribution of the controlled airflow field in real time.

[0015] A shake-stabilization control system for a lens flatness detection device includes: The platform is lifted by a motor; The displacement detection unit includes a grating ruler for detecting the displacement of the stage; An attitude monitoring unit, including an angle sensor, is mounted on the stage and is used to detect the deflection angle of the stage. The temperature monitoring unit includes multiple temperature probes, which are installed in the lead screw and detection chamber to acquire the amount of temperature change; An airflow stabilization unit, comprising multiple fans, is disposed within the detection chamber to create a controlled airflow field within the detection chamber; The controller is configured to perform the anti-shake control method of a lens flatness detection device as described in any of the preceding claims.

[0016] Furthermore, the controller is further configured to: continuously receive temperature changes during the stationary phase after the stage reaches the target position, periodically calculate displacement corrections, and control the motor to perform micro-displacement compensation so that the stage remains at the target position until thermal equilibrium is reached.

[0017] The beneficial effects of this invention are: This invention establishes a controlled airflow field in advance within the detection chamber, thereby actively counteracting external environmental disturbances and local airflow fluctuations induced by the movement of the stage. This eliminates environmental interference factors affecting the stable movement of the stage from the perspective of the flow field, and avoids additional interference caused by the asymmetric thrust of a single fan.

[0018] This invention extends attitude monitoring to the entire cycle of motion and stillness, which can prevent abnormal large-angle tilts and capture micro-deflections of a few tenths of a degree. It eliminates dynamic measurement errors caused by factors such as lead screw torque fluctuations from the attitude dimension, making safety protection without time blind spots.

[0019] Unlike existing technologies that passively remove the closed loop after the stage is in place, this invention maintains effective closed-loop control during the static stage. It actively calculates and periodically performs micro-displacement compensation based on temperature changes, completely eliminating the slow nanoscale thermal drift caused by lead screw friction heating and subsequent cooling from the perspective of thermal deformation. This ensures that the stage remains precisely in the target position during long-term static periods.

[0020] This invention covers the entire cycle of stage movement and stillness, and synergistically suppresses various interference factors that affect displacement accuracy, achieving precise and stable displacement of the stage at the nanometer level. Attached Figure Description

[0021] Figure 1 This is a flowchart of the anti-shake control method for a lens flatness detection device according to the present invention.

[0022] Figure 2 This is a schematic diagram showing the positions of the lead screw, grating ruler, temperature sensor, and stage within the device in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram showing the position of the angle sensor on the stage in Embodiment 1 of the present invention; Figure 4 This is a schematic diagram showing the position of the fan inside the device in Embodiment 1 of the present invention.

[0023] In the diagram, 1 is a lead screw; 2 is a linear encoder; 3 is a temperature sensor; 4 is a fan; 5 is an angle sensor; and 6 is a stage. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of the invention.

[0026] At the same time, it should be understood that, for ease of description, the dimensions of the various parts shown in the accompanying drawings are not drawn according to actual scale.

[0027] Furthermore, for clarity and brevity, descriptions of well-known structures, functions, and configurations may have been omitted. Those skilled in the art will recognize that various changes and modifications can be made to the examples described herein without departing from the spirit and scope of this disclosure.

[0028] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and equipment should be considered part of the specification.

[0029] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.

[0030] The present invention will now be described in detail with reference to the accompanying drawings and embodiments: Example 1 A method for stabilizing the image in a lens flatness detection device, applied to a system, such as... Figures 2-4 As shown, the system includes: Stage and drive unit: The stage is used to support the sample and its vertical movement along three lead screws is achieved by servo motors. The servo motors are controlled by servo drivers, which receive motion commands from the controller.

[0031] One of the root causes of vibration lies in the lead screw: due to manufacturing limitations, the threads of the lead screw are not perfectly uniform. When the lead screw rotates, the contact stress between the threads and the nut changes periodically, causing slight fluctuations in the transmission torque. This torque fluctuation is directly transmitted to the platform, manifesting as a slight angular deflection of the platform during lifting and lowering (i.e., yaw vibration).

[0032] The root cause of thermal drift also lies in the lead screw: as the lead screw rotates, the continuous friction between it and the nut generates heat. This heat enters the lead screw body and the bearing seats at both ends through heat conduction, causing the temperature of the metal structure to rise. Due to the physical property of metals expanding and contracting with temperature changes, the lead screw undergoes thermal expansion along its axial direction, and its actual length changes. For measurements with nanometer-level precision, even a tiny amount of thermal expansion is enough to cause a non-negligible displacement error.

[0033] Displacement detection unit: A grating ruler with a resolution of nm is installed on the side of the stage, with one grating ruler next to each lead screw. The reading head of the grating ruler moves synchronously with the stage, reading the current displacement of the stage in the lifting direction in real time, and feeding this displacement signal back to the controller as a real-time position reference for the full closed-loop motion control.

[0034] It is important to note that the grating ruler measures the relative displacement of the stage relative to its mounting surface. When the lead screw expands due to heat, its actual length changes, but the grating ruler itself does not detect this thermal deformation; it only reads the actual spatial position of the stage. Therefore, when the lead screw lengthens due to thermal expansion, the actual position of the stage will drift upwards. Although the grating ruler can read this drift, if the control system does not provide targeted compensation, the stage will deviate from its original target position. One of the core aspects of this invention is utilizing the grating ruler's real position sensing capability to actively correct the target position through temperature compensation, thereby offsetting thermal drift.

[0035] Attitude monitoring unit: An angle sensor is installed on the platform. In this embodiment, a MEMS tilt sensor is used, with a resolution of up to 0.01°. The angle sensor is mounted on the surface of the platform, and the detection axis is parallel to the plane of the platform.

[0036] The working principle of the angle sensor is as follows: when the stage tilts slightly due to factors such as fluctuations in the lead screw torque, the micromechanical structure inside the sensor will produce changes in capacitance or resistance due to changes in the gravitational component. This change is converted into an angle value output by the signal conditioning circuit.

[0037] The angle sensor operates continuously during the movement and stationary states of the stage, providing real-time feedback of the stage's deflection angle to the controller. Its function is divided into two levels: Safety protection level: When the deflection angle exceeds the preset safety threshold (set to 0.01° in this embodiment), it is determined to be an abnormal tilt, and the controller immediately executes stop protection; Jitter monitoring level: When the deflection angle is within the safe threshold but there is a 10 -3 When there are minute fluctuations at the metric level, the data is recorded as jitter status information, which is used to assess the current motion stability and can provide a basis for airflow adjustment.

[0038] Temperature monitoring unit: Temperature probes are installed at the following key locations (this embodiment uses a PT100 platinum resistance temperature sensor with an accuracy of ±0.01℃): Near the bearing housing at the upper end of the lead screw: Monitor the temperature at the upper end of the lead screw; Near the bearing housing at the lower end of the lead screw: Monitor the temperature at the lower end of the lead screw; Middle of the lead screw: Monitor the lead screw temperature; Inspect the inner wall of the chamber: monitor the ambient temperature of the chamber.

[0039] The temperature probe works by measuring the linear change in resistance of a platinum resistance thermometer with temperature, allowing for precise determination of the current temperature. The multiple measuring points are designed to obtain spatial distribution information of the temperature field, enabling the controller to more accurately assess the overall thermal state of the lead screw, rather than relying solely on a single point temperature.

[0040] Airflow stabilization unit: Multiple miniature high-speed fans are installed below the detection chamber; in this embodiment, four are arranged circumferentially along the moving area of ​​the stage. The speed of each fan can be independently adjusted by a controller.

[0041] The physical principle behind fan-induced vibration suppression lies in the fact that when the airflow generated by multiple fans forms a uniform and stable flow field within the chamber, this flow field establishes a relatively stable air pressure distribution around the stage. When the stage experiences slight vibrations due to fluctuations in the screw torque, its surface undergoes instantaneous relative motion with respect to the surrounding air. According to fluid mechanics principles, this relative motion is hindered by air viscosity; that is, the uniform flow field exerts a physical damping effect on the stage's slight motion. This damping effect is analogous to placing the stage within an air bearing or air guide shaft, thus suppressing the slight vibrations.

[0042] like Figure 1 As shown, the method of the present invention includes the following steps: The steps for establishing a controlled airflow field are as follows: The controller first starts all four miniature fans, using a multi-channel closed-loop control method to independently adjust the speed of each fan according to the preset initial speed curve. The airflow generated by each fan superimposes and couples with each other in the detection chamber, ultimately forming a stable controlled airflow field within the motion area of ​​the stage.

[0043] This step is performed before the stage begins to move. Its purpose is to establish a stable flow field environment before the movement begins, so that the stage is under the protection of a controlled airflow field from the beginning, rather than passively dealing with airflow disturbances after the movement begins.

[0044] Motion control and attitude monitoring steps: The controller controls the servo motor to operate through the driver, driving the stage to move up and down along the lead screw from the initial position to the target position.

[0045] During the movement, the angle sensor continuously detects the deflection angle of the stage at a preset sampling frequency (100Hz in this embodiment), and the controller receives the angle data from the angle sensor in real time and makes a judgment: First-level judgment (safety protection): If the deflection angle exceeds the preset safety threshold of 0.01°, the controller determines that an abnormal tilt has occurred, immediately sends an emergency stop command to the drive, the motor stops running, and simultaneously triggers an audible and visual alarm signal to prompt the operator to check. This protection mechanism covers both moving and stationary processes, with no blind spots.

[0046] Second-level judgment (shake monitoring and airflow adjustment): If the deflection angle is within the safe threshold, but there is a 10 -3 For minute fluctuations in the metric range (e.g., 0.001°-0.005°), the controller records this data as jitter status information. This minute fluctuation indicates that the torque fluctuation of the lead screw is affecting the stability of the stage. To actively suppress this minute jitter, the controller can dynamically fine-tune the speed of each fan according to the jitter amplitude and frequency, change the airflow field distribution, and apply stronger viscous damping to the minute vibration of the stage, forming a closed loop.

[0047] Once the stage reaches the target position, the motor stops driving, and the stage enters a resting phase. The purpose of this resting phase is usually to allow the system to reach thermal equilibrium or for the measurement conditions to stabilize.

[0048] During the static waiting phase, attitude monitoring continues. This is because although there is no active movement during the static phase, external vibration transmission or internal stress release may still cause slight deflection of the stage. This solution extends attitude monitoring to the static phase, achieving full-cycle, blind-spot-free attitude safety protection.

[0049] Active thermal drift compensation steps after positioning: After the stage reaches the target position and enters the stationary phase, thermal drift becomes the main factor affecting positional accuracy. Details are as follows: During the movement of the stage, the friction between the lead screw and the nut generates heat, causing the lead screw temperature to rise. Due to the physical property of thermal expansion and contraction of metals, the lead screw undergoes thermal expansion along its axial direction. Let the initial temperature of the lead screw be T0, the current temperature be T1, the effective working length of the lead screw be L, and the coefficient of thermal expansion of the material be k. Then, the theoretical elongation of the lead screw due to thermal expansion is: ΔL = k × (T1- T0) × L = k × ΔT × L; The elongation ΔL will directly cause the stage to deviate from its original target position, resulting in upward drift.

[0050] After the motion stops, the lead screw no longer generates new frictional heat, but the heat already accumulated inside it will not dissipate immediately. During the resting phase, the temperature of the lead screw will gradually decrease, tending to match the ambient temperature, which is the cooling process.

[0051] During the cooling process, the lead screw gradually contracts, causing the stage to drift downwards. This complete process of thermal expansion and contraction can last for tens of minutes, with a total drift exceeding 10 nm, which is not negligible in nanometer-scale measurements.

[0052] This invention predefines a temperature-displacement compensation relationship to convert the temperature change ΔT into the required displacement correction ΔS. This embodiment uses the following formula: ΔS = k × ΔT × L; Where: ΔS: displacement correction (positive value indicates upward compensation, negative value indicates downward compensation); k: coefficient of thermal expansion of the lead screw material (in this embodiment, the lead screw material is bearing steel, k≈1.2×10⁻⁶). -5 / ℃); ΔT: Current temperature T current The difference between the reference temperature T0 and the reference temperature, ΔT = T current - T0; L: Effective working length of the lead screw.

[0053] In actual calculations, ΔT is taken as the weighted average of the temperature changes measured by each temperature probe. The weighting coefficients are determined through experimental calibration based on the distance of each measuring point from the lead screw and the heat conduction path, so as to more accurately reflect the overall thermal state of the lead screw.

[0054] After the static waiting phase begins, the controller performs the following operations at a preset cycle: Read the current temperature value of each temperature probe and calculate the weighted average of ΔT; Substitute ΔT into the temperature-displacement compensation relationship ΔS = k × ΔT × L to calculate the current required displacement correction ΔS; Using the current reading of the grating ruler as the position reference, the target position is updated to the original target position + ΔS; A displacement command is sent to the driver to control the motor to perform nanometer-level position adjustments, so that the stage returns to the target position. Record the ΔS value and execution time of this compensation.

[0055] This compensation process is repeated periodically, with each compensation typically in the nanometer range. As the settling time progresses, the screw temperature gradually stabilizes, the rate of change of ΔT gradually decreases, and the value of ΔS for each compensation also decreases. When the detected ΔT change is less than the preset convergence threshold for several consecutive times (e.g., |ΔT| < 0.005℃ is detected three times consecutively), the controller determines that the screw has reached thermal equilibrium, stops the periodic compensation, and the settling phase ends.

[0056] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Based on the technical essence of the present invention, any simple modifications, equivalent substitutions, and improvements made to the above embodiments within the spirit and principles of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for stabilizing the image in a lens flatness detection device, characterized in that, include: S1: Establish a controlled airflow field within the detection chamber to suppress external airflow disturbances and local airflow fluctuations induced by the movement of the stage; S2: Drive the stage to move up and down relative to the measuring lens. During the movement and when it stops after reaching the target position, continuously monitor the deflection angle of the stage. When the deflection angle exceeds the preset safety threshold, control the stage to stop moving. S3: After the stage reaches the target position, continuously acquire the temperature change in the detection chamber, calculate the displacement correction caused by thermal deformation based on the preset temperature-displacement compensation relationship, and actively compensate the target position of the stage according to the displacement correction to keep the stage at the target position until thermal equilibrium is reached.

2. The anti-shake control method for a lens flatness detection device according to claim 1, characterized in that, In S1, a controlled airflow field is established within the detection chamber, including: The operation of multiple fans located in the detection chamber is controlled by a multi-channel closed-loop control method to adjust the speed of multiple fans, so that the controlled airflow field forms a stable laminar flow or controlled cyclone in the moving area of ​​the stage.

3. The anti-shake control method for a lens flatness detection device according to claim 1, characterized in that, In S2, continuous monitoring of the stage deflection angle also includes: Obtaining the deflection angle in 10 -3 Deflection data at the metric level is used to determine the stage's jitter status.

4. The anti-shake control method for a lens flatness detection device according to claim 3, characterized in that, S2 also includes: adjusting the speed of multiple fans in the controlled airflow field according to the shaking state, so as to adjust the airflow distribution to suppress shaking.

5. The anti-shake control method for a lens flatness detection device according to claim 1, characterized in that, In S3, the temperature change is obtained through multiple temperature probes installed in the lead screw and detection chamber; the preset safety threshold is T=0.01°.

6. The anti-shake control method for a lens flatness detection device according to claim 1, characterized in that, In S3, the temperature-displacement compensation relationship is as follows: ΔS = k × ΔT × L; Where ΔS is the displacement correction, ΔT is the temperature change, k is the thermal expansion coefficient of the lead screw material, and L is the corresponding structural feature length; Alternatively, the temperature-displacement compensation relationship can be obtained through a temperature-displacement compensation data table calibrated in advance.

7. The anti-shake control method for a lens flatness detection device according to claim 1, characterized in that, The displacement of the stage is detected by a grating ruler with nanometer-level resolution; in S3, the displacement correction is based on the reading of the grating ruler as the compensation reference.

8. The anti-shake control method for a lens flatness detection device according to claim 2, characterized in that, Multiple fans employ a multi-channel closed-loop control method to regulate their speed, specifically including: Based on the vibration status obtained from the angle sensor, the fan speed is dynamically adjusted to adjust the airflow distribution of the controlled airflow field in real time.

9. A shake-proof control system for a lens flatness detection device, characterized in that, include: The platform is lifted and lowered by a motor. An optical grating ruler is used to detect the displacement of the stage. An angle sensor, mounted on the stage, is used to detect the deflection angle of the stage; Multiple temperature probes are installed in the lead screw and detection chamber to acquire the temperature change. Multiple fans are disposed within the detection chamber to create a controlled airflow field within the detection chamber; The controller is configured to perform the anti-shake control method of the lens flatness detection device according to any one of claims 1 to 8.

10. The anti-shake control system of the lens flatness detection device according to claim 9, characterized in that: The controller is further configured to: continuously receive temperature changes, periodically calculate displacement corrections, and control the motor to perform micro-displacement compensation during the static phase after the stage reaches the target position, so that the stage remains at the target position until thermal equilibrium is reached.

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