Laser power attenuator and method based on load end full-closed loop feedback

Abstract

The invention discloses a laser power attenuator and method based on load end full-closed loop feedback, and the attenuator comprises a fixed frame, and a drive unit, a polarization rotation element, a polarization detection unit, an angle measurement unit and a controller which are integrated on the fixed frame. The angle measuring unit is used for directly measuring the actual angle of the polarization rotating element rotating around the optical axis of the polarization rotating element, and the controller is configured to carry out closed-loop control on the driving unit according to the fed-back actual angle and drive through synchronous belt transmission. The polarization rotating element and the transmission driven wheel are rigidly connected to form an integrated rotating mechanism, a measuring part of the angle measuring unit is directly mounted on a rotating shaft of the mechanism, and the polarization analyzing unit adopts a Brewster diaphragm. According to the invention, direct feedback is carried out through the load end, the influence of mechanical transmission chain errors on the control precision is eliminated, and the precision, repeatability, dynamic response speed and long-term working stability of laser power regulation and control are remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of laser technology and relates to a laser power attenuator and method based on fully closed-loop feedback at the load end. Background Technology

[0002] The application of laser technology in high-end industrial processing, precision optoelectronic detection, and cutting-edge scientific research is becoming increasingly widespread, leading to increasingly stringent demands for automated and high-precision control of laser power. Currently, laser attenuators have evolved from manual adjustment to electrification and intelligent control. The mainstream solutions fall into two categories: one is mechanical attenuation based on neutral density filters, where the attenuation is adjusted by switching or translating the filter wheel driven by a motor; the other is electrically controlled attenuation based on polarization principles, where the polarization state is changed by rotating a half-wave plate with a motor, and continuous power output is achieved through a polarization beam splitter.

[0003] To improve control precision, existing high-precision motorized laser attenuators generally adopt a closed-loop control architecture of "motor drive plus position feedback". A typical implementation involves installing a position detection element at the end of the motor shaft, and indirectly controlling the attitude of the attenuation element by monitoring the motor rotation angle, thereby regulating the laser power.

[0004] A typical existing solution is a "polarization-driven electric laser attenuator based on photoelectric encoder feedback". This solution includes an attenuation unit (half-wave plate, polarization beam splitter), a drive unit (stepper motor, gearbox), a feedback unit (angle encoder mounted on the motor shaft), and a control unit.

[0005] Its workflow is as follows: After receiving the power adjustment command, the control unit outputs a drive signal to control the stepper motor to operate according to the preset "half-wave plate rotation angle - output power" mapping relationship; the motor drives the half-wave plate to rotate through the reduction transmission mechanism, changing the laser polarization state, and achieving power attenuation after being filtered by the polarization beam splitter; at the same time, the angle encoder collects the rotation angle signal of the motor output shaft and feeds it back to the control unit; the control unit compares the target angle with the actual feedback angle, corrects the number of motor drive steps, and realizes laser power adjustment under closed-loop control.

[0006] However, the aforementioned existing technologies still have the following problems: 1. The sensor detects the rotation of the motor output shaft, not the final position of the motion platform that carries the attenuator. The gaps, backlash, elastic deformation and wear of the entire mechanical transmission chain (including couplings, reduction gears, bearings, etc.) between the motor shaft and the platform will produce position errors that cannot be detected and compensated by the encoder. This results in an uncertain deviation between the actual spatial orientation of the half-wave plate and the control command. 2. Wear accumulates in the mechanical transmission mechanism. Long-term friction between the gear meshing surfaces and coupling connection parts will cause the mechanical clearance to gradually increase. The transmission error increases synchronously with the length of use, and this wear is irreversible. This directly leads to a decrease in the long-term stability of the attenuator. Due to the lack of a full feedback mechanism at the load end, frequent calibration is required to maintain basic accuracy.

[0007] In summary, the transmission errors that are not controlled by the closed loop directly lead to difficulties in further improving the final control accuracy, repeatability, and long-term stability of the laser attenuation, thus failing to meet the requirements of ultra-high precision applications. Summary of the Invention

[0008] The purpose of this invention is to address the aforementioned problems in existing technologies by proposing a laser power attenuator and method based on fully closed-loop feedback at the load end. This solves the technical problem mentioned in the background that the transmission error in existing technologies, which is not controlled by a closed loop, directly leads to difficulties in further improving the final control accuracy, repeatability, and long-term stability of the laser attenuation, thus failing to meet the requirements of ultra-high precision applications.

[0009] The objective of this invention can be achieved through the following technical solutions: A laser power attenuator based on load-side closed-loop feedback includes a mounting frame, on which the following are integrated: Drive unit; A polarization rotating element receives incident laser light, and the driving unit drives the polarization rotating element to rotate around its own optical axis to change the polarization direction of the incident laser light. The polarization analyzer unit has its optical path arranged coaxially with the output optical path of the polarization rotation element. It is used to selectively transmit or reflect the polarized light modulated by the polarization rotation element, thereby outputting attenuated laser light. An angle measuring unit is used to directly measure the actual angle of rotation of the polarization rotation element around its optical axis; The controller is electrically connected to both the drive unit and the angle measuring unit. The controller is configured to receive a target angle command and, based on the actual angle fed back by the angle measurement unit, perform closed-loop control on the drive unit so that the actual angle of the polarization rotation element approaches the target angle.

[0010] Furthermore, the drive unit includes a stepper motor and a transmission mechanism; The transmission mechanism includes a driving wheel, a driven wheel, and a transmission belt. The driving wheel is mounted on the output shaft of the stepper motor, the driven wheel is rigidly connected coaxially to the polarization rotation element, and the transmission belt meshes between the driving wheel and the driven wheel.

[0011] Furthermore, the polarization rotation element is coaxially arranged with the driven wheel, and the high-precision angle sensor of the angle measuring unit is directly mounted on the rotation shaft of the driven wheel.

[0012] Furthermore, the polarization rotation element is a half-wave plate, and the polarization analyzer is a Brewster window.

[0013] Furthermore, the driven wheel has a synchronous pulley with a rotating shaft at its center, and the half-wave plate is rigidly fixed to the end of the synchronous pulley by a pressure ring, forming an integrated rotating mechanism.

[0014] The rigid connection between the half-wave plate and the driven wheel forms an integrated rotating mechanism. Its beneficial effects are that it directly reduces the rotational inertia of the motion load, improves the rigidity and coaxiality of the structure, and indirectly helps to maintain accuracy over a long period of time.

[0015] Furthermore, the high-precision angle sensor includes a circular grating and a reading head. The circular grating is directly sleeved and fixed to the end of the rotating shaft, and the reading head is fixedly mounted on the mounting bracket.

[0016] Furthermore, the Brewster window pane is mounted on a fixed base by a pressure plate. The fixed base is connected to the fixed frame by at least one set screw. The working angle of the Brewster window pane can be adjusted and locked by turning the set screw.

[0017] The above structural design allows for fine-tuning of the Brewster window angle during assembly or use to ensure it operates at the optimal Brewster angle, thereby achieving the best polarization selectivity and the highest attenuation contrast, further optimizing the limits and consistency of attenuation performance.

[0018] Furthermore, the driven wheel is supported on the fixed frame by a bearing, and a stop ring is provided on the bearing to axially limit the driven wheel.

[0019] A laser power attenuation method based on the above-mentioned laser power attenuator and using load-side fully closed-loop feedback includes the following steps: S1: Obtain the target rotation angle of the polarization rotation element corresponding to the target laser power; S2: The driving unit drives the polarization rotation element to rotate according to the control signal; S3: The actual rotation angle of the polarization rotation element is obtained in real time by an angle measuring unit directly set on the rotation axis of the polarization rotation element; S4: Compare the actual rotation angle with the target rotation angle to generate an error signal; S5: Adjust the control of the drive unit according to the error signal so that the actual rotation angle approaches the target rotation angle, thereby realizing closed-loop control of the output laser power.

[0020] Furthermore, the polarization rotation element is a half-wave plate, and the attenuation is achieved through a Brewster window. In step S2, by controlling the rotation angle of the half-wave plate, the polarization direction of the laser incident on the Brewster window is continuously changed, and the laser power is continuously adjusted according to Malus's law. The main technical effects of this invention are reflected in the following aspects: 1. Achieve full closed-loop angle feedback, directly improving control accuracy.

[0021] This invention constructs a fully closed-loop feedback for the half-wave plate by directly and rigidly connecting a high-precision angle measurement unit to the half-wave plate shaft. This scheme effectively reduces the indirect measurement errors that may be introduced by the gaps, elastic deformation, and reverse backlash of all transmission links (such as synchronous belts and pulleys) between the motor and the wave plate. This allows the feedback signal obtained by the control system to truly and directly reflect the actual angle of the wave plate, thereby improving the control accuracy and repeatability of laser power.

[0022] 2. Compensates for long-term accuracy drift, enhancing operational stability.

[0023] This invention employs a full feedback angle measurement scheme, whose adjustment accuracy does not change with the slight wear of the front transmission components, and whose stability depends only on the angle sensor body with high angle resolution, ensuring the output stability and reliability of the attenuator under long-term continuous operation, thereby significantly extending the calibration and maintenance cycle.

[0024] 3. Optimize dynamic response performance to adapt to high-speed modulation scenarios.

[0025] This invention uses lightweight, low-inertia belt drive to replace traditional gear and rigid coupling transmission, reducing the inherent inertia and damping effects of mechanical transmission, reducing the mechanical lag in half-wave plate angle adjustment, and designing the half-wave plate and synchronous pulley as an integrated rotating mechanism with rigid connection, which greatly reduces the rotational inertia of moving parts. Attached Figure Description

[0026] Figure 1 This is a structural schematic diagram of an embodiment of the present invention; Figure 2 This is a schematic diagram of the exploded structure according to an embodiment of the present invention; Figure 3 This is a partial structural schematic diagram of an embodiment of the present invention; Figure 4 This is a schematic diagram illustrating the working principle of laser attenuation in an embodiment of the present invention.

[0027] Explanation of reference numerals in the attached drawings: 1. Fixing bracket; 11. Controller; 12. Fixing base; 121. Set screw; 2. Stepper motor; 21. Drive wheel; 3. Driven pulley; 31. Drive belt; 32. Rotating shaft; 33. Bearing; 34. Retaining ring; 4. Half-wave plate; 41. Pressure ring; 5. Brewster window film; 51. Tableting; 6. High-precision angle sensor; 61. Circular grating; 62. Reading head. Detailed Implementation

[0028] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.

[0029] like Figure 1-3 As shown, a laser power attenuator based on load-side closed-loop feedback includes a mounting frame 1, on which the following are integrated: The drive unit includes a stepper motor 2 and a transmission mechanism; The transmission mechanism includes a driving wheel 21, a driven wheel 3, and a transmission belt 31. The driving wheel 21 is mounted on the output shaft of the stepper motor 2. The driven wheel 3 is rigidly connected to the polarization rotation element on the same axis. The transmission belt 31 is engaged between the driving wheel 21 and the driven wheel 3. A polarization rotating element, which is a half-wave plate 4, receives incident laser light. The driving unit drives the polarization rotating element to rotate around its own optical axis to change the polarization direction of the incident laser light. The polarization rotating element is coaxially arranged with the driven wheel 3. The polarization analyzer is a Brewster window 5. The optical path of the Brewster window 5 is arranged coaxially with the output optical path of the polarization rotation element. It is used to selectively transmit or reflect the polarized light modulated by the polarization rotation element, thereby outputting attenuated laser light. An angle measuring unit is used to directly measure the actual angle of rotation of the polarization rotation element around its optical axis. The high-precision angle sensor 6 of the angle measuring unit is directly mounted on the rotation shaft 32 of the driven wheel 3. The controller 11 is electrically connected to both the drive unit and the angle measuring unit. The controller 11 is configured to receive a target angle command and perform closed-loop control on the drive unit based on the actual angle fed back by the angle measurement unit, so that the actual angle of the polarization rotation element approaches the target angle.

[0030] like Figure 1-3As shown, the driven wheel 3 is a synchronous pulley with a rotating shaft 32 at its center. The half-wave plate 4 is rigidly fixed to the end of the synchronous pulley by a pressure ring 41 to form an integrated rotating mechanism. The diameter of the synchronous pulley is larger than that of the driving wheel 21. The driven wheel 3 is supported on the fixed frame 1 by a bearing 33. A stop ring 34 is provided on the bearing 33 to axially limit the driven wheel 3.

[0031] The high-precision angle sensor 6 includes a circular grating 61 and a reading head 62. The circular grating 61 is directly sleeved and fixed to the end of the rotating shaft 32, and the reading head 62 is fixedly mounted on the mounting bracket 1.

[0032] The Brewster window pane 5 is mounted on a fixed base 12 via a pressure plate 51. The fixed base 12 is connected to the fixed frame 1 via at least one set screw 121. The working angle of the Brewster window pane 5 can be adjusted and locked by turning the set screw 121.

[0033] In the polarization rotation element, the half-wave plate 4 can be replaced by a Faraday rotator, a liquid crystal tunable waveplate, or other elements with polarization direction control function; in the angle measurement unit, the high-precision circular grating 61 can be replaced by a high-precision magnetic grating encoder, a laser interferometric angle sensor, or other angle detection elements that maintain direct feedback function at the load end.

[0034] The working principle of this invention is as follows: Optical attenuation process: The incident laser first passes through a rotatable half-wave plate 4. The function of the half-wave plate 4 is to rotate the polarization direction of the linearly polarized light passing through it. Subsequently, the polarization-modulated laser light is incident on the fixed Brewster window 5 at a specific angle. According to optical principles, when light is incident at a Brewster angle, light whose vibration direction is parallel to the incident surface is almost completely transmitted, while light whose vibration direction is perpendicular to the incident surface is mostly reflected. Therefore, the Brewster window 5 acts as a highly efficient polarization selector (analyzer).

[0035] Ultimately, the laser power transmitted from the Brewster window 5 depends on the angle between the polarization direction of the incident light and the transmission axis of the Brewster window 5, and the output laser power is continuously adjusted according to Malus's law.

[0036] Full closed-loop control process: The control unit receives the target rotation angle command. Internally, the controller 11 converts the target power into the target rotation angle required by the half-wave plate 4, based on the mathematical model of Malus's law.

[0037] The controller 11 sends a pulse signal to the driver of the stepper motor 2, causing the stepper motor 2 to rotate. The torque of the stepper motor 2 is transmitted through the synchronous belt, driving the half-wave plate 4, which is rigidly connected to the synchronous belt pulley, to rotate.

[0038] The crucial feedback mechanism comes into play here: the circular grating 61, which rotates synchronously with the half-wave plate 4, detects the actual rotation angle of the half-wave plate 4 in real time and in situ through its reading head 62. The angle measuring unit is rigidly connected coaxially to the polarization rotation element and is used to directly measure the actual angle of rotation of the moving part carrying the polarization rotation element (i.e., the rotating shaft 32 on the driven wheel) around its optical axis. This angle signal comes directly from the moving part of the load itself, completely avoiding errors such as elastic deformation, slight slippage, or backlash that may exist in the entire synchronous belt drive chain from the motor shaft to the half-wave plate 4.

[0039] The circular grating 61 and the reading head 62 feed back the detected actual angle value to the control unit in real time. The closed-loop control algorithm (such as PID algorithm) inside the control unit immediately calculates the deviation between the target angle and the actual feedback angle, i.e., the error signal.

[0040] Based on the magnitude and direction of the error signal, the control unit dynamically adjusts the drive signal sent to the stepper motor 2 (such as adjusting the pulse frequency or direction), directing the motor to perform compensatory rotation until the error between the actual angle and the target angle fed back approaches zero.

[0041] Thus, a complete closed-loop control cycle, from setting to driving to direct detection and comparison at the load end, and then to correction, is completed. The system runs continuously, ensuring that the half-wave plate 4 can always be driven and stabilized at the precise angle required by theoretical calculations, regardless of minor errors in the transmission mechanism or wear over time. This achieves extremely high precision, high repeatability, and long-term stable controllability of the laser power.

[0042] In summary, this invention, through its innovative "direct angle feedback at the load end" mechanical architecture, combined with efficient optical attenuation principles and closed-loop control strategies, fundamentally solves the technical defects of traditional semi-closed-loop attenuators.

[0043] like Figure 1-4 As shown, a laser power attenuation method based on fully closed-loop feedback at the load end includes the following steps: S1: Obtain the target rotation angle of the polarization rotation element corresponding to the target laser power; S2: The driving unit drives the polarization rotation element to rotate according to the control signal; S3: The actual rotation angle of the polarization rotation element is obtained in real time by an angle measuring unit directly set on the rotation axis 32 of the polarization rotation element; S4: Compare the actual rotation angle with the target rotation angle to generate an error signal; S5: Adjust the control of the drive unit according to the error signal so that the actual rotation angle approaches the target rotation angle, thereby realizing closed-loop control of the output laser power.

[0044] The polarization rotation element is a half-wave plate 4, and the attenuation is achieved through a Brewster window plate 5; In step S2, by controlling the rotation angle of the half-wave plate 4, the polarization direction of the laser incident on the Brewster window plate 5 is continuously changed, and the laser power is continuously adjusted according to Malus's law.

[0045] Figure 4 The optical path of the laser is symbolically illustrated as it sequentially passes through a half-wave plate 4 driven by a motor and a Brewster window 5. The half-wave plate 4 rotates the polarization direction of the incident laser; the Brewster window 5 acts as an analyzer, modulating the output light power based on the selective transmission characteristics of light with different polarization directions using the Brewster angle. The illustration visually demonstrates the principle of continuously adjusting the output laser power according to Malus's law by precisely controlling the rotation angle (θ) of the half-wave plate 4.

[0046] Of course, the above are just typical examples of this application. In addition, this application may have many other specific implementation methods. All technical solutions formed by equivalent substitution or equivalent transformation fall within the scope of protection claimed in this application.

Claims

1. A laser power attenuator based on load-side closed-loop feedback, comprising a mounting bracket (1), characterized in that, The fixing frame (1) integrates: Drive unit; A polarization rotating element receives incident laser light, and the driving unit drives the polarization rotating element to rotate around its own optical axis to change the polarization direction of the incident laser light. The polarization analyzer unit has its optical path arranged coaxially with the output optical path of the polarization rotation element. It is used to selectively transmit or reflect the polarized light modulated by the polarization rotation element, thereby outputting attenuated laser light. An angle measuring unit is used to directly measure the actual angle of rotation of the polarization rotation element around its optical axis; The controller (11) is electrically connected to the drive unit and the angle measuring unit, respectively; The controller (11) is configured to receive a target angle command and perform closed-loop control on the drive unit based on the actual angle fed back by the angle measurement unit, so that the actual angle of the polarization rotation element approaches the target angle.

2. A laser power attenuator based on fully closed-loop feedback at the load end according to claim 1, characterized in that, The drive unit includes a stepper motor (2) and a transmission mechanism; The transmission mechanism includes a drive wheel (21), a driven wheel (3) and a transmission belt (31). The drive wheel (21) is mounted on the output shaft of the stepper motor (2). The driven wheel (3) is rigidly connected to the polarization rotation element on the same axis. The transmission belt (31) meshes between the drive wheel (21) and the driven wheel (3).

3. A laser power attenuator based on fully closed-loop feedback at the load end according to claim 2, characterized in that, The polarization rotation element is coaxially arranged with the driven wheel (3), and the high-precision angle sensor (6) of the angle measuring unit is directly arranged on the rotation shaft (32) of the driven wheel (3).

4. A laser power attenuator based on fully closed-loop feedback at the load end according to claim 3, characterized in that, The polarization rotation element is a half-wave plate (4), and the polarization analyzer is a Brewster window (5).

5. A laser power attenuator based on fully closed-loop feedback at the load end according to claim 4, characterized in that, The driven wheel (3) is a synchronous pulley with a rotating shaft (32) at its center. The half-wave plate (4) is rigidly fixed to the end of the synchronous pulley by a pressure ring (41) to form an integrated rotating mechanism.

6. A laser power attenuator based on fully closed-loop feedback at the load end according to claim 5, characterized in that, The high-precision angle sensor (6) includes a circular grating (61) and a reading head (62). The circular grating (61) is directly sleeved and fixed to the end of the rotating shaft (32), and the reading head (62) is fixedly mounted on the mounting bracket (1).

7. A laser power attenuator based on fully closed-loop feedback at the load end according to claim 6, characterized in that, The Brewster window plate (5) is mounted on a fixed base (12) by a pressure plate (51). The fixed base (12) is connected to the fixed frame (1) by at least one set screw (121). The working angle of the Brewster window plate (5) can be adjusted and locked by turning the set screw (121).

8. A laser power attenuator based on fully closed-loop feedback at the load end according to claim 7, characterized in that, The driven wheel (3) is supported on the fixed frame (1) by a bearing (33), and a stop ring (34) is provided on the bearing (33) to axially limit the driven wheel (3).

9. A laser power attenuation method based on load-side fully closed-loop feedback, applied to the laser power attenuator as described in any one of claims 1-8, characterized in that, Includes the following steps: S1: Obtain the target rotation angle of the polarization rotation element corresponding to the target laser power; S2: The driving unit drives the polarization rotation element to rotate according to the control signal; S3: The actual rotation angle of the polarization rotation element is obtained in real time by means of an angle measuring unit directly set on the rotation axis (32) of the polarization rotation element; S4: Compare the actual rotation angle with the target rotation angle to generate an error signal; S5: Adjust the control of the drive unit according to the error signal so that the actual rotation angle approaches the target rotation angle, thereby realizing closed-loop control of the output laser power.

10. A laser power attenuation method based on fully closed-loop feedback at the load end according to claim 9, characterized in that, The polarization rotation element is a half-wave plate (4), and the attenuation is achieved through a Brewster window plate (5); In step S2, by controlling the rotation angle of the half-wave plate (4), the polarization direction of the laser incident on the Brewster window plate (5) is continuously changed, and the laser power is continuously adjusted according to Malus's law.

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