Integrated focusing control system based on moire fringe phase difference

Abstract

The invention relates to the technical field of automatic focusing control, and discloses an integrated focusing control system based on moire fringe phase difference, which comprises a ZYNQ heterogeneous processing platform for realizing real-time acquisition and processing of moire fringe images through a USB3.0 interface and executing a double-loop control algorithm of a position loop PD + a speed loop PI for accurate focusing, according to the double-loop control algorithm, a differential advance strategy is introduced into a position loop, and an integral separation strategy is introduced into a speed loop; the integrated driving module comprises a focusing motor, a diaphragm switching driving unit and an objective lens switching driving unit, and adopts a closed-loop control framework with encoder feedback; and the IO peripheral module comprises a light source brightness adjusting interface, a state detecting interface and a motion limiting interface. According to the system, high-speed image processing is achieved through the FPGA, accurate focusing is achieved at the ARM end through the double-loop control algorithm, the system can be applied to a microscopic imaging system, optimization of the system integration degree and improvement of the production efficiency are facilitated, and meanwhile the equipment structure is more simplified.

Description

Technical Field

[0001] This invention relates to the field of automatic focusing control technology, and more specifically to an integrated focusing control system based on moiré fringe phase difference. Background Technology

[0002] With the rapid development of electronic technology, high-precision fields such as optics, advanced manufacturing, and precision cutting have placed higher demands on the automation, speed, and accuracy of lens focusing. For example, in the scanning and inspection of semiconductor wafers, the system needs to achieve rapid scanning and accurate imaging at sub-micron or even nanometer-level resolution, which poses a severe challenge to the dynamic response and positioning accuracy of focusing control. Traditional mechanical focusing methods are limited by the hysteresis and nonlinear error of the transmission mechanism, making it difficult to meet the needs of high-dynamic scenarios. Existing closed-loop control schemes based on image feedback or laser ranging rely on PC-side computation, and the system's real-time performance is limited by the computational latency of the software architecture. At the same time, the efficiency of multi-module collaborative control is low, resulting in insufficient overall integration and making it difficult to simultaneously meet the requirements of high precision and rapid response.

[0003] Chinese invention patent CN113687492A (its PCT international application publication number WO2023020324A1) discloses an autofocus system based on moiré fringes. This system generates moiré fringes on the object surface through an illumination system, a transparent grating, and a TIR prism, and determines the defocus direction and amount based on the fringe position, providing a reliable optical principle basis for high-precision focusing. However, this patent mainly focuses on the construction of the optical system and the principle of defocus signal generation, without specifically addressing how to acquire and process the moiré fringe image in real time, nor does it disclose the motor control architecture and specific implementation method used to drive the objective lens movement. In practical engineering applications, to achieve fully automatic closed-loop focusing based on this optical principle, a corresponding image processing and motion control system is still required.

[0004] To address the control implementation problem of autofocus, several solutions have been proposed in existing technologies. For example, Chinese invention patent CN118330868A discloses an integrated drive autofocus microscope control system, which receives instructions from a host computer via a control board and executes the autofocus control algorithm. However, this solution still relies on a PC-based host computer for instruction issuance, and the computational latency of the software architecture limits the system's real-time performance. Especially during multi-task parallel processing, the latency of algorithm scheduling and data communication significantly reduces the focusing response speed. Another example is Chinese invention patent CN218068433U, which discloses a rapid objective switching mechanism that achieves automatic objective switching via a servo motor drive. However, this solution focuses on the mechanical switching structure, resulting in low efficiency in the coordinated control of multiple components in the autofocus system, such as the light source, objective lens, and aperture. Asynchronous communication between the drive unit, sensor, and processing core can easily introduce timing errors, affecting the overall control accuracy.

[0005] Furthermore, image processing-based autofocus methods have become a research hotspot in recent years. For example, Chinese invention patent CN119603554A discloses a camera autofocus method based on machine learning algorithms, which analyzes image sequences using convolutional neural networks, long short-term memory networks, and deep reinforcement learning to obtain focusing parameters. However, this approach requires a large amount of training data and computational resources, and its effectiveness is highly dependent on the coverage of training samples. It is prone to focusing deviations in unknown scenes or under extreme lighting conditions. Additionally, its real-time performance is limited by the inference speed of the deep learning model, making it difficult to meet the needs of high-speed industrial inspection. Another example is Chinese invention patent CN120529175A, which discloses an image processing-based autofocus method using wavelet power spectrum and an improved hill-climbing method for focusing. However, in scenes with scarce image texture or significant noise interference, the focus detection function is prone to misjudgment, and the hill-climbing search strategy may get trapped in local extrema, leading to focusing failure or decreased accuracy.

[0006] Therefore, while existing technologies have made progress in individual aspects such as optical principles, control systems, mechanical switching, or image processing, they still lack a complete solution that can deeply integrate real-time processing of moiré fringe images, precise driving of multi-axis motors, and collaborative control of peripheral modules. Based on this, the present invention aims to provide an integrated focusing control system based on moiré fringe phase difference. Building upon the optical principles disclosed in CN113687492A, it further provides a complete electronic control and driving scheme. This system achieves real-time acquisition and processing of moiré fringe images through a heterogeneous processing platform and employs a dual-loop control algorithm to achieve precise driving of the focusing motor. Simultaneously, it considers the collaborative control of peripheral modules such as aperture switching and objective lens switching. Thus, it provides a concrete and feasible electronic control and driving scheme for the optical principles disclosed in CN113687492A, further improving the overall technology of automatic focusing based on moiré fringes. Summary of the Invention

[0007] (a) Technical problems to be solved

[0008] To address the problems in the prior art, the purpose of this invention is to provide an integrated focusing control system based on moiré fringe phase difference. This system comprehensively considers the common needs of moiré fringe image processing, objective lens switcher, aperture switcher, and autofocus control. It integrates an image processor, autofocus controller, stepper motor drive, aperture switcher, and objective lens switcher drive into a controller with a simplified architecture.

[0009] (II) Technical Solution

[0010] To achieve the above objectives, embodiments of the present invention provide an integrated focusing control system based on moiré fringe phase difference, comprising:

[0011] The ZYNQ heterogeneous processing platform connects its FPGA to the image acquisition unit via a USB 3.0 interface for real-time acquisition and parallel processing of moiré fringe images. The ARM core reads the displacement distance difference data output by the FPGA through register mapping and executes a dual-loop control algorithm of position loop (PD) + velocity loop (PI) for precise focusing. The integrated drive module connects to the ZYNQ platform via a high-speed AXI bus and includes a focusing motor drive unit, an aperture switching drive unit, and an objective lens switching drive unit. Each drive unit adopts a closed-loop control architecture with encoder feedback.

[0012] Preferably, the image processing pipeline implemented in the FPGA logic layer of the ZYNQ heterogeneous processing platform includes a USB 3.0 protocol controller, a double buffer storage area, a Gaussian filter kernel, and an optical flow feature extraction accelerator; the ARM processor directly reads the displacement distance difference data calculated by the FPGA through the AXI bus and executes a dual-loop control algorithm of position loop and velocity loop.

[0013] Preferably, the integrated drive module has a modular structure, comprising a focusing motor drive unit, an aperture switching drive unit, and an objective lens switching drive unit. The focusing motor drive unit includes a stepper motor, an encoder, and a controller. The controller is configured to perform position-speed dual-loop control based on the encoder feedback signal. The aperture switching drive unit uses a stepper motor drive with encoder feedback. The objective lens switching drive unit integrates mechanical limit protection and electromagnetic braking functions. Each drive unit achieves precise drive through PWM signals in conjunction with the encoder.

[0014] Preferably, the closed-loop control process of the focusing motor drive unit is as follows: a database of the correspondence between objective lens position and displacement distance difference is established through a calibration system; the target position is queried based on the displacement distance difference calculated in real time by the FPGA; a speed command is generated by introducing a differential-first position loop PD controller; and the motor drive is achieved by adjusting the PWM duty cycle through an integral-separated speed loop PI controller.

[0015] Preferably, the optical flow processing flow includes: image preprocessing using a 3×3 Gaussian filter kernel implemented by FPGA, calculating the fringe displacement field using the optical flow method, calculating the full-field phase gradient based on the displacement field distribution, and finally using the least squares method to fit and obtain the sub-pixel level defocus estimation value.

[0016] Preferably, it also includes an I / O peripheral module, which is communicatively connected to the ARM core, and includes a light source brightness adjustment output port, an objective lens switching status detection port, an aperture switching status detection port, a focus success output port, a motion axis positive and negative limit input port, and an emergency stop signal input port. The light source brightness adjustment output port adopts a constant current drive circuit, the objective lens and aperture switching status detection ports adopt photoelectric isolation input circuits, and the motion axis limit input port supports differential signal reception.

[0017] Preferably, the drive board integrates a configurable bridge drive circuit, whose motor output interface can be adapted to connect to a servo motor or a stepper motor, and achieve closed-loop control through the corresponding encoder feedback signal.

[0018] (III) Beneficial Effects

[0019] Through the above technical solution, this invention deeply integrates heterogeneous computing, real-time image processing, and multi-axis collaborative control, solving the problems of large response delay and insufficient accuracy in traditional microscopic focusing systems. It achieves sub-micron-level focusing accuracy and millisecond-level dynamic response, making it suitable for high-precision microscopic imaging and rapid scanning scenarios. Furthermore, based on the traditional position loop PD + velocity loop PI control structure, this invention introduces a differential-first strategy in the position loop to smooth dynamic response and suppress overshoot, and an integral separation strategy in the velocity loop to prevent integral saturation, balancing speed and steady-state accuracy, thus forming an optimized dual-loop control algorithm. This algorithm not only achieves efficient deployment on the FPGA+ARM heterogeneous platform but also supports rapid adaptation and optimization for different microscopic imaging systems through modular parameter configuration, significantly improving the dynamic response speed, anti-interference capability, and steady-state accuracy of the focusing system. Attached Figure Description

[0020] Figure 1 This is a structural diagram of the automatic focusing control system of the present invention;

[0021] Figure 2 This is a schematic diagram of the dual-loop control principle of the focusing motor in an embodiment of the present invention;

[0022] Figure 3 This is a schematic diagram of the process of the automatic focusing control system of the present invention on the product testing equipment.

[0023] In the diagram: 1. Camera, 2. Stage, 3. Objective lens, 4. Aperture, 5. Object under test, 6. Beam splitter, 7. Eyepiece, 8. Limiter, 9. Motor, 10. ZYNQ image processing controller. Detailed Implementation

[0024] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the scope of the present invention.

[0025] Example

[0026] This invention provides an integrated focusing control system based on moiré fringe phase difference. The system mainly consists of a ZYNQ heterogeneous processing platform and an integrated drive module, such as... Figure 1 As shown.

[0027] The ZYNQ heterogeneous processing platform comprises two processing units: an FPGA logic layer and an ARM processor layer. The FPGA logic layer establishes a high-speed data transmission channel with the image acquisition device via a USB 3.0 protocol controller to achieve real-time acquisition and transmission of moiré fringe images. A ping-pong caching mechanism with dual buffer storage areas ensures continuous storage and processing of image data. A Gaussian filter kernel is configured to preprocess the acquired moiré fringe images to effectively eliminate noise interference. The parallel computing architecture of the optical flow feature extraction accelerator is used to measure the displacement difference of the preprocessed moiré fringe images. The relative displacement data is then transmitted to the ARM processor layer. The ARM processor layer runs a control framework built on a real-time operating system, which includes dual-loop control threads to receive the relative displacement data transmitted from the FPGA. A differential-first strategy is introduced in the position loop to improve response speed, and an integral separation strategy is introduced in the speed loop to prevent integral saturation. This balances speed and steady-state accuracy in the coordinated control of the focusing motor.

[0028] The integrated drive module includes a focusing motor drive unit, an aperture switching drive unit, and an objective lens switching drive unit, among which... Figure 2 The focusing motor drive unit shown adopts a closed-loop control architecture with encoder feedback to achieve precise focusing through the coordinated control of position loop and speed loop and has a photoelectric limit protection device. The aperture switching drive unit adopts a high-resolution stepper motor drive scheme and integrates an encoder feedback interface to achieve closed-loop control. The objective lens switching drive unit is configured to execute a position-speed dual-loop control strategy.

[0029] Taking semiconductor testing equipment as an example, the system workflow is as follows: Figure 3 As shown, in the image acquisition and processing stage, the moiré fringe image is first acquired in real time through the USB 3.0 interface and the image preprocessing and optical flow displacement difference measurement are completed on the FPGA. Then, the relative displacement data calculated by the FPGA is transmitted to the ARM processor. Finally, in the motion control stage, the ARM processor drives the focusing motor to complete the precise focusing based on the relative displacement data calculated by the FPGA and through the dual-loop control algorithm.

[0030] Those skilled in the art should understand that the above embodiments are merely preferred embodiments of the present invention. Without departing from the principles of the present invention, appropriate adjustments can be made to the system configuration, control parameters, etc., and all such adjustments should be considered to fall within the protection scope of the present invention.

Claims

1. An integrated focusing control system based on moiré fringe phase difference, characterized in that, include: The ZYNQ heterogeneous processing platform connects its FPGA to the image acquisition unit via a USB 3.0 interface for real-time acquisition and parallel processing of moiré fringe images. The ARM core reads the displacement difference data output from the FPGA via register mapping and executes a dual-loop control algorithm (position loop and velocity loop) for precise focusing. An integrated drive module, connected to the ZYNQ platform via a high-speed AXI bus, includes a focusing motor drive unit, an aperture switching drive unit, and an objective lens switching drive unit. Each drive unit employs a closed-loop control architecture with encoder feedback. The dual-loop control algorithm executed by the ARM core includes a position loop optimization strategy and a velocity loop optimization strategy. The position loop optimization strategy employs differential-first approach, while the velocity loop optimization strategy employs integral-separation approach.

2. The system according to claim 1, characterized in that, The differential-first approach refers to moving the differential term from the error input channel to the feedback channel, and only differentiating the actual position feedback to avoid output jumps caused by sudden changes in the set value.

3. The system according to claim 1, characterized in that, The integral separation refers to cutting off the integral action to prevent integral saturation when the velocity error is greater than a threshold, and reintroducing the integral to eliminate steady-state error when the error is less than the threshold.

4. The system according to claim 1, characterized in that, The ZYNQ heterogeneous processing platform's image processing pipeline implemented in the FPGA logic layer includes: a USB 3.0 protocol controller and a double buffer storage area for real-time image data reception; a 3×3 Gaussian filter kernel for image preprocessing; and an optical flow feature extraction accelerator for calculating the fringe displacement field and outputting displacement distance difference data. The ARM core directly reads the displacement distance difference data calculated by the FPGA through register mapping.

5. The system according to claim 1, characterized in that, The integrated drive module adopts a modular design. The focusing motor drive unit includes a stepper motor, an encoder, a photoelectric limit protection device, and a controller. The controller is configured to execute a position-speed dual-loop control strategy, wherein the speed loop receives the actual speed signal fed back by the encoder, and the position loop receives the actual position signal fed back by the encoder. The photoelectric limit protection device is used to trigger a protection signal when the stepper motor runs to the limit position. The aperture switching drive unit adopts a stepper motor drive scheme with encoder feedback; The objective lens switching drive unit adopts a position-speed dual-loop control strategy; each drive unit uses PWM encoder hardware control to achieve precise drive.

6. The system according to claim 5, characterized in that, The closed-loop control process of the focusing motor drive unit is as follows: a database of objective lens position-phase difference correspondence is established through a calibration system; the target position is queried based on the displacement distance difference calculated in real time by the FPGA; a speed command is generated by introducing a differential-first position loop controller; and the motor drive is achieved by adjusting the PWM duty cycle through an integral-separated speed loop PI controller.

7. The system according to claim 4, characterized in that, The implementation process of the optical flow feature extraction accelerator includes: calculating the stripe displacement field of the preprocessed image using FPGA, calculating the full-field phase gradient based on the displacement field distribution, and using the least squares method to fit and obtain the sub-pixel level defocus estimation value.

8. The system according to claim 1, characterized in that... It also includes an I / O peripheral module that communicates with the ARM core, including a light source brightness adjustment output port, an objective lens switching status detection port, an aperture switching status detection port, a focus success output port, a motion axis positive and negative limit input port, and an emergency stop signal input port. The light source brightness adjustment output port adopts a constant current drive circuit, the objective lens and aperture switching status detection ports adopt photoelectric isolation input circuits, and the motion axis limit input port supports differential signal reception.

9. An integrated focusing control method based on moiré fringe phase difference, applied to the system described in any one of claims 1-8, characterized in that... Includes the following steps: Moiré fringe images are acquired in real time via a USB 3.0 interface and transmitted to an FPGA for preprocessing. Image filtering and optical flow feature extraction are performed in the FPGA. The processing results are transmitted to an ARM processor via an AXI bus. The ARM processor reads the displacement distance difference data, queries the objective position-displacement distance difference database to determine the target position, and drives the objective to move to the target position through a dual-loop control algorithm of position loop and velocity loop.

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