An infrared thermal imager active athermalization device based on grating ruler direct drive feedback

Abstract

The present application belongs to the field of infrared optical technology, and particularly relates to an active athermalization device for an infrared thermal imager based on grating ruler direct drive feedback. The present application comprises a heat insulation plane mirror window, a Zoom zoom motor, a Zoom position sensor, a Focus focusing motor, a Focus position sensor, a temperature sensor, a microcomputer controller, an optical lens assembly, and a sealed cabin. The winding of a brushless motor and a permanent magnet are used to directly drive a Zoom / Focus curve cylinder, eliminating the "rotary gap" in mechanical transmission, ensuring the lossless execution of compensation instructions, improving the dynamic response speed and positioning repeatability of the system. The grating ruler is directly attached to the surface of the Zoom / Focus curve cylinder, the actual physical position of the curve cylinder is directly detected by a grating reader, and PID position closed-loop control of the motor position is performed in the microcomputer controller, direct position measurement is achieved, intermediate link cumulative error is eliminated, the focal point can be accurately compensated to the best position, and the lens can continuously and clearly image in the range of -40 DEG C to +70 DEG C.

Description

Technical Field

[0001] This invention belongs to the field of infrared optical technology, specifically relating to an active calorimetric device for infrared thermal imagers based on direct-drive feedback from a grating ruler. Background Technology

[0002] Infrared optical systems commonly suffer from thermal defocusing. The refractive index of infrared optical materials (such as germanium) is extremely sensitive to temperature changes. When the ambient temperature changes, the focal length of the lens drifts, resulting in blurred images. Active anechoication is the mainstream technical approach to solving thermal defocusing problems, and there are many related solutions in existing technologies. Among them, Chinese patent CN118354202A proposes a rapid autofocusing method for infrared thermal imagers with temperature compensation. By simulating different temperatures and imaging distances in an experimental temperature chamber, it pre-stores the parfocal point data and dynamically fits the focus range, driving the focusing motor to move rapidly within the focus range to find the sharp point. CN121740252A discloses a compensation calibration system and method for a large-aperture closed-structure thermal imager. It uses a distributed temperature sensor group to detect the temperature of various areas of the thermal imager and constructs a mathematical model based on the temperature and focusing data for clear imaging to compensate for the impact of temperature changes on imaging. CN121578490A proposes a long focal length, large target area, mid-wave infrared continuous zoom lens. Continuous zoom is achieved through the movement of a zoom lens and a compensation lens, and thermal difference in imaging is eliminated during zooming by moving the entire rear lens group back and forth along the optical axis. The aforementioned prior art solutions use temperature sensors (single-point or distributed) to collect temperature data from the lens or thermal imager in real time. A controller calculates the required compensation amount based on a pre-stored temperature-focus position mapping relationship (or mathematical model), ultimately driving a focusing motor to move the lens group, thereby dynamically compensating for focus shift caused by temperature changes and ensuring image clarity.

[0003] Although existing technical solutions have been optimized in terms of control strategies and temperature sensing, they suffer from two defects at the mechanical execution level, resulting in the inability to execute compensation commands accurately and without errors:

[0004] (1) Mechanical transmission backlash leads to execution loss: In the existing technical solution, the motor drives the lens through mechanical structures such as gears and lead screws. There are tiny physical gaps between these transmission structures, namely "rotational backlash". This causes the compensation command issued by the controller to be lost during transmission and cannot be executed without loss, resulting in low positioning accuracy and poor repeatability of focus compensation.

[0005] (2) Indirect position measurement leads to cumulative error: Existing technical solutions rely on the encoder built into the motor to indirectly calculate the position of the lens; this method will accumulate the errors of all links in the transmission chain (such as gear backlash, belt tension, etc.), resulting in a deviation between the "command position" and the "actual position" of the lens, and ultimately failing to accurately compensate the focus to the theoretically optimal position. Summary of the Invention

[0006] To address the shortcomings of the existing technologies, the technical problem to be solved by the present invention is to provide an active calorimetric device for infrared thermal imagers based on direct-drive feedback of grating rulers, which eliminates error sources in the execution of compensation commands from both the physical transmission chain and the measurement chain, thereby improving the focus compensation accuracy.

[0007] The technical solution adopted in this invention is as follows:

[0008] An active athermalization device for an infrared thermal imager based on direct-drive feedback of a grating ruler includes a heat-insulating plane mirror window, a zoom motor, a zoom position sensor, a focus motor, a focus position sensor, a temperature sensor, a microcomputer controller, an optical lens assembly, and a sealed chamber.

[0009] The sealed chamber is a ball table structure sealed outer shell, which houses the optical lens assembly, Zoom motor, Zoom position sensor, Focus motor, Focus position sensor, temperature sensor, and microcomputer controller. The internal circuit board of the microcomputer controller generates heat, resulting in a high and uniform internal temperature.

[0010] The optical lens assembly includes a lens barrel, a zoom curve barrel, a focus curve barrel, and a lens group;

[0011] The heat-insulating plane mirror window is located at the front opening of the sealed chamber, serving to isolate the external environment from the interior of the sealed chamber.

[0012] The temperature sensor is mounted on the lens barrel and is used to detect the temperature of the optical lens assembly;

[0013] The microcomputer controller has a built-in PID position closed-loop control algorithm and stores the Focus sharp point position data at each focal length and temperature. The microcomputer controller is connected to the temperature sensor, the zoom motor, the focus motor, the zoom position sensor, and the focus position sensor.

[0014] Preferably, both the Zoom motor and the Focus motor adopt a brushless motor structure, including motor windings and a permanent magnet; the motor windings are the stator, and the permanent magnet is the rotor; the permanent magnet is directly fixed to the surface of the Zoom and Focus cylinders, realizing direct drive of the motor to the cylinders.

[0015] Preferably, both the Zoom position sensor and the Focus position sensor adopt a grating ruler structure, including a grating ruler and a reading head; the grating ruler is directly attached to the surface of the Zoom curved cylinder and the Focus curved cylinder, and the grating reading head is used to directly detect the position of the curved cylinder.

[0016] The aforementioned active calorimetry device for infrared thermal imagers based on direct-drive feedback from a grating ruler achieves active calorimetry through a process of "temperature sensing - data lookup - direct-drive execution - feedback closed loop." Its specific working principle is as follows:

[0017] Temperature sensing and command generation: The temperature sensor detects the lens barrel temperature in real time (due to the design of the heat-insulating window and sealed chamber, this temperature is very close to the temperature of the components inside the lens barrel). Based on the received temperature data, the microcomputer controller calls the "Focus sharp point position data under different temperatures × different focal lengths" pre-stored in memory to generate the target position command for the Focus motor.

[0018] Brushless direct drive motor: Both the Zoom and Focus motors use brushless motor windings and permanent magnets to directly drive the Zoom / Focus curved cylinder. This structure eliminates the traditional gear transmission mechanism, completely eliminating the backlash problem in mechanical transmission. This allows the motor's rotation to be converted into the axial displacement of the curved cylinder without delay or loss, thus ensuring extremely high positioning accuracy and fast dynamic response.

[0019] Optical encoder feedback and PID closed-loop control: During the movement of the curved cylinder driven by the motor, an optical encoder attached to the surface of the cylinder, in conjunction with a reading head, directly measures the actual physical position of the cylinder (rather than indirectly calculating it through the motor shaft rotation angle). The optical encoder feeds back the high-precision position signal to the microcomputer controller in real time. The controller internally employs a PID (proportional-integral-derivative) position closed-loop control algorithm, comparing the actual position with the target position and continuously correcting the motor output, thereby achieving rapid action response and extremely high position accuracy through active compensation, ensuring that the image remains clear within the range of -40℃ to +70℃.

[0020] The beneficial effects obtained by adopting the above technical solution are as follows:

[0021] (1) The present invention uses the winding of a brushless motor and a permanent magnet to directly drive the Zoom / Focus curve cylinder. The permanent magnet is directly fixed on the surface of the curve cylinder, eliminating intermediate transmission links such as gears and lead screws, eliminating the "backlash" in mechanical transmission, so that every tiny rotation of the motor can be converted into the precise displacement of the lens in a 1:1 ratio, ensuring the lossless execution of compensation commands, and improving the dynamic response speed and positioning repeatability of the system.

[0022] (2) The present invention directly attaches the grating ruler to the surface of the Zoom / Focus curved cylinder, directly detects the actual physical position of the curved cylinder through the grating reading head, and performs PID position closed-loop control on the motor position in the microcomputer controller; it realizes direct position measurement, bypasses the transmission chain, eliminates the cumulative error of all intermediate links, provides the controller with the most realistic and accurate position feedback, ensures fast action response and high position accuracy, can accurately compensate the focus to the theoretically optimal position, and ensures that the lens can continuously and clearly image within the range of -40℃ to +70℃. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the overall structure of an active calorimetric device for an infrared thermal imager based on direct-drive feedback of a grating ruler, according to the present invention.

[0024] Figure label:

[0025] A. Heat-insulated plane mirror window; B. Zoom motor; C. Zoom position sensor; D. Focus motor; E. Focus position sensor; F. Motor winding; G. Motor permanent magnet; H. Microcomputer controller; I. ​​Temperature sensor. Detailed Implementation

[0026] The technical solution of the present invention will now be described more clearly and completely with reference to the accompanying drawings.

[0027] This invention provides an active calorimetry device for infrared thermal imagers based on direct-drive feedback from a grating ruler, such as... Figure 1 As shown, it includes a heat-insulating plane mirror window A, a zoom motor B, a zoom position sensor C, a focus motor D, a focus position sensor E, a temperature sensor I, a microcomputer controller H, an optical lens assembly, and a sealed chamber; it is divided into the following functional modules:

[0028] (1) Optical lens assembly: including lens barrel, zoom curve barrel, focus curve barrel and lens group.

[0029] (2) Drive mechanism: A brushless motor is used as the actuator. The rotor (permanent magnet) and stator (winding) of the brushless motor are directly coupled to the curved cylinder of the optical lens assembly, eliminating intermediate transmission links such as gears and lead screws, and realizing direct drive.

[0030] (3) Position feedback mechanism: A grating ruler is directly attached to the surface of the Zoom and Focus curve cylinders. The grating read head is fixed at the stationary position of the lens cylinder to directly read the displacement data of the curve cylinder.

[0031] (4) Temperature sensing mechanism: Temperature sensors are arranged in key parts of the lens barrel to collect ambient temperature data.

[0032] The workflow of this embodiment includes a "calibration phase" and a "working phase":

[0033] Step S1: Full-temperature-range data calibration (offline)

[0034] The device was placed in a high and low temperature test chamber, and the optimal focal plane was found at different temperature points (e.g., -40℃ to +70℃, every 5℃) using an image sharpness evaluation function. The physical position data of the grating ruler corresponding to each temperature point was recorded, and a lookup table or fitting curve of "temperature-grating ruler absolute position" was established and stored in the microcomputer controller.

[0035] Step S2: Temperature Monitoring and Command Generation (Online)

[0036] During operation, the temperature sensor collects the lens barrel temperature T_real in real time. The microcomputer controller uses T_real to query a pre-stored lookup table to obtain the theoretical target position P_target at the current temperature.

[0037] Step S3: Direct drive closed-loop control

[0038] The microcomputer controller calculates the difference between the current position P_current (feedback in real time from the grating ruler) and the target position P_target.

[0039] The controller outputs control signals to the brushless motor drive module to drive the brushless motor to rotate.

[0040] Because of the direct drive structure, the motor rotation directly drives the curved cylinder to move, with no transmission backlash or delay.

[0041] Step S4: Real-time calibration of the grating ruler

[0042] The grating ruler detects the actual displacement of the curved cylinder in real time with a high sampling rate and feeds the signal back to the microcomputer controller. The controller uses a PID algorithm to continuously adjust the motor output based on the actual position fed back by the grating ruler until P_current = P_target, thus completing high-precision, heatless compensation.

Claims

1. An active calorimetric device for infrared thermal imagers based on direct-drive feedback from a grating ruler, characterized in that, Includes a heat-insulating plane mirror window (A), a zoom motor (B), a zoom position sensor (C), a focus motor (D), a focus position sensor (E), a temperature sensor (I), a microcomputer controller (H), an optical lens assembly, and a sealed chamber; The sealed chamber is a ball table structure sealed shell, which houses the optical lens assembly, Zoom motor (B), Zoom position sensor (C), Focus motor (D), Focus position sensor (E), temperature sensor (I), and microcomputer controller (H). The optical lens assembly includes a lens barrel, a zoom curve barrel, a focus curve barrel, and a lens group; The heat-insulating plane mirror window (A) is located at the front opening of the sealed chamber; The temperature sensor (I) is mounted on the lens barrel; The microcomputer controller (H) has a built-in PID position closed-loop control algorithm and stores the Focus sharp point position data at each focal length and temperature. The microcomputer controller (H) is connected to the temperature sensor (I), the zoom motor (B), the focus motor (D), the zoom position sensor (C), and the focus position sensor (E).

2. The active calorimetry device for infrared thermal imagers according to claim 1, characterized in that, Both the Zoom motor (B) and the Focus motor (D) adopt a brushless motor structure, including a motor winding (F) and a motor permanent magnet (G); the motor winding (F) is the stator, and the motor permanent magnet (G) is the rotor; the motor permanent magnet (G) is directly fixed to the surface of the Zoom and Focus curved cylinders.

3. The active calorimetry device for infrared thermal imagers according to claim 1, characterized in that, Both the Zoom position sensor (C) and the Focus position sensor (E) adopt a grating ruler structure, including a grating ruler and a reading head; the grating ruler is directly attached to the surface of the Zoom curve cylinder and the Focus curve cylinder.

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