Optical crystal oil bath annealing furnace regulation system and method

Abstract

This invention discloses a control system and method for an optical crystal oil bath annealing furnace, belonging to the technical field of optical crystal preparation equipment. The control system includes a stirring mechanism and an external circulation system, and further includes: a crystal rotation mechanism, comprising a crystal support and a rotation drive unit. The crystal support is disposed within the furnace cavity and rotates around the axial direction of the inner furnace cylinder under the drive of the rotation drive unit; a spiral guide rib divides the space between the outer wall of the inner furnace cylinder and the inner wall of the outer furnace cylinder into a spiral flow channel; a sensing module is used to detect real-time parameters including the real-time oil temperature and level of the heat transfer oil in the furnace cavity, the real-time flow rate of the heat transfer oil in the spiral flow channel, and the real-time rotational speed of the stirring paddle and the crystal support; a controller is used to control the operation of the stirring mechanism, the rotation drive unit, the external circulation system, and the heating unit based on the real-time parameters. The optical crystal oil bath annealing furnace control system of this invention significantly improves the uniformity of the temperature field throughout the furnace cavity.

Description

Technical Field

[0001] This invention relates to the field of optical crystal preparation equipment technology, specifically to an optical crystal oil bath annealing furnace control system and method. Background Technology

[0002] With the rapid development of laser and high-power optics systems, large-size optical crystals such as KDP, LBO, and BBO have become core components of high-end optical equipment. These crystals are anisotropic, water-soluble, nonlinear optical crystals, and their optical performance and yield are entirely determined by the uniformity of the temperature field within the furnace cavity during the oil bath annealing process. The industry has stringent requirements for the annealing process: the uniformity of the temperature field across the entire furnace cavity must be ≤±0.5℃, and the temperature control accuracy must reach ±0.1℃. If the temperature difference between the inside and outside of the crystal exceeds 0.5℃, the resulting thermal stress will exceed the crystal's yield limit, causing internal microcracks or even overall fragmentation, directly resulting in the crystal being scrapped. Currently, the industry mainstream uses oil bath annealing furnaces to complete crystal heat treatment, and the temperature uniformity within the furnace cavity is entirely achieved through the control of the flow of the heat-conducting oil.

[0003] Existing optical crystal oil bath annealing furnaces generally consist of a stirring mechanism, a circulating oil pump, a furnace body, and a single-point temperature probe. During the annealing process, the heat transfer oil is stirred by the stirring paddle and the oil is transported by the circulating pump to complete the heat exchange in the furnace cavity. By collecting the temperature of the heat transfer oil and adjusting the heating power and the circulation flow rate of the heat transfer oil in conjunction with a fixed parameter PID program, isothermal annealing of the crystal can be achieved.

[0004] However, under the conditions of large-volume furnace cavity and 200℃ high-temperature annealing, the existing oil bath annealing furnace with single stirring and single-sided oil path arrangement is prone to forming a viscous boundary layer with low heat transfer efficiency on the crystal surface. At the same time, flow dead zones are prone to appear at the corners of the furnace cavity and the back of the crystal. The heat transfer oil will also show temperature stratification due to density differences, forming an obvious temperature field gradient. Under high temperature environment, the physical properties of heat transfer oil such as viscosity and thermal conductivity change significantly, thereby greatly increasing the temperature difference in the furnace cavity. This can easily cause thermal stress cracks in optical crystals, reduce crystal yield, and make it difficult to meet the mass production annealing requirements of large-size optical crystals. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems in the prior art and provide an optical crystal oil bath annealing furnace control system that eliminates flow dead zones and temperature stratification in the furnace cavity during the annealing process, efficiently breaks the viscous boundary layer on the crystal surface, and significantly improves the uniformity of the temperature field throughout the furnace cavity.

[0006] This invention provides a control system for an optical crystal oil bath annealing furnace, including a stirring mechanism and an external circulation system. The stirring paddle of the stirring mechanism is disposed inside the furnace cavity of the inner furnace cylinder of the oil bath annealing furnace and rotates axially around the inner furnace cylinder. The external circulation system is used to supply heat transfer oil into the furnace cavity. The system also includes: The crystal rotation mechanism includes a crystal support and a rotation drive unit. The crystal support is disposed inside the furnace cavity and is used to support an optical crystal. The rotation drive unit is connected to the crystal support and is used to drive the crystal support to rotate synchronously with the stirring paddle. Under the drive of the rotation drive unit, the crystal support rotates around the axial direction of the inner furnace cylinder. A spiral guide rib is disposed between the outer wall of the inner furnace cylinder and the inner wall of the outer furnace cylinder. The spiral guide rib divides the space between the outer wall of the inner furnace cylinder and the inner wall of the outer furnace cylinder into a spiral flow channel. The liquid inlet end of the spiral flow channel is connected to the oil supply end of the external circulation system, the liquid outlet end of the spiral flow channel is connected to the furnace cavity, and the furnace cavity is connected to the oil return end of the external circulation system. The sensing and detection module is used to detect real-time parameters including the real-time oil temperature and real-time liquid level of the heat transfer oil in the furnace cavity, the real-time flow rate of the heat transfer oil in the spiral flow channel, and the real-time rotation speed of the agitator and crystal support. The controller is electrically connected to the sensing and detection module, the stirring mechanism, the rotary drive unit, the external circulation system, and the heating unit of the annealing furnace. The controller controls the operation of the stirring mechanism, the rotary drive unit, the external circulation system, and the heating unit according to the real-time parameters through a PID control algorithm.

[0007] Preferably, the sensing module includes a temperature sensor, a flow sensor, a speed sensor, and a level sensor. The temperature sensor is located inside the furnace cavity and is used to detect the oil temperature of the heat transfer oil at different locations within the furnace cavity. The flow sensor is located between the circulation system and the spiral flow channel and is used to detect the real-time flow rate of the heat transfer oil entering the spiral flow channel. The speed sensor is used to detect the real-time speed of the agitator and the crystal support. The level sensor is located inside the furnace cavity and is used to detect the real-time level of the liquid within the furnace cavity. The controller has a preset flow field-temperature field coupling model and preset parameters including a set temperature value, a set flow rate value, a set level value, and a set speed value for the agitator and the crystal support. Based on the relationship between the real-time parameters and the corresponding preset parameters, the controller uses a PID control algorithm and the flow field-temperature field coupling model to control the operation of the heating unit, the external circulation system, the stirring mechanism, and the rotary drive unit.

[0008] Preferably, the temperature sensor is a multi-point K-type thermocouple, which is distributed at the liquid inlet end of the spiral flow channel and at the top, middle and bottom of the furnace cavity. The multi-point K-type thermocouple detects the real-time temperature values ​​of the heat transfer oil at the liquid inlet end of the spiral flow channel and at the top, middle and bottom of the furnace cavity.

[0009] Preferably, the stirring mechanism further includes a stirring motor, a stirring shaft, and an oil baffle. The stirring shaft is vertically arranged inside the furnace cavity of the inner furnace cylinder. The top of the stirring shaft is connected to the stirring motor. The oil baffle is disposed on the shaft body of the stirring shaft and is used to reduce the flow rate of the heat transfer oil. The stirring paddle is disposed at the bottom end of the stirring shaft. The rotation drive unit includes a rotation motor and a rotation shaft. The rotation shaft is coaxially arranged with the stirring shaft. The top end of the rotation shaft is connected to the rotation motor, and the bottom end of the rotation shaft is fixedly connected to the crystal support. Under the drive of the stirring motor and the rotation motor, the stirring shaft and the rotation shaft rotate synchronously.

[0010] Preferably, an oil return structure is also provided between the furnace cavity and the external circulation system. The furnace cavity is connected to the external circulation system through the oil return structure. The oil return structure is connected to a predetermined height position at the top of the furnace cavity. The furnace cavity oil return structure is used to recover the heat transfer oil in the furnace cavity that is higher than the predetermined liquid level to the external circulation system.

[0011] Preferably, the furnace cavity oil return structure includes a top overflow orifice plate, an annular oil return corridor, and an oil collection chamber. The top overflow orifice plate is located at a predetermined height at the top of the furnace cavity, and multiple circular overflow holes are provided on the top overflow orifice plate. The annular oil return corridor is located around the top overflow orifice plate. The heat transfer oil in the furnace cavity that is higher than the top overflow orifice plate overflows from the circular overflow holes and flows into the annular oil return corridor. The oil collection chamber is connected to the annular oil return corridor and is used to collect the oil in the annular oil return corridor. The oil collection chamber is connected to the external circulation system through an oil return pipeline.

[0012] Preferably, the external circulation system includes a circulation pump, a filter device, and a pressure transmitter. The return oil line is connected to the filter device, the filter device is connected to the circulation pump, and the circulation pump is connected to the inlet end of the spiral flow channel through a buffer joint.

[0013] Preferably, a pressure transmitter is also provided between the buffer joint and the inlet end of the spiral flow channel. The pressure transmitter is used to detect the real-time hydraulic value in the return oil line. The pressure transmitter is electrically connected to the controller, and the controller is electrically connected to the circulating pump. The controller has a preset pressure threshold. The controller controls the power of the circulating pump according to the pressure threshold, so that the real-time hydraulic value in the return oil line is maintained within the pressure threshold.

[0014] This invention also provides a method for controlling an optical crystal oil bath annealing furnace, which employs an optical crystal oil bath annealing furnace control system and includes the following steps: The optical crystal is fixed to the crystal holder, the annealing process parameters are set, the matching PID parameter library is retrieved, and the pressure monitoring and protection module, stirring mechanism and crystal rotation mechanism are simultaneously verified to complete the self-test of the whole machine. When the external circulation system is turned on, the heat transfer oil is sent into the spiral flow channel and transported from bottom to top into the furnace cavity to form an axial flow field. The furnace cavity oil return structure recovers the overflowing heat transfer oil, forming a closed loop circulation. The stirring mechanism and the crystal rotation mechanism are started simultaneously, and the stirring paddle and the crystal support rotate synchronously to form a coaxial turbulence at the top. Real-time hydraulic values ​​in the pipeline are collected, and the power of the external circulation system is dynamically adjusted to keep the real-time hydraulic values ​​in the pipeline within the preset pressure threshold and stabilize the oil supply pressure. By collecting real-time temperature in the furnace cavity, real-time speed of the agitator, real-time speed of the crystal support, and real-time circulation flow data, the heating power, agitator speed, crystal support speed, and circulation flow are adjusted in real time to adapt to the changes in the physical properties of the high-temperature heat transfer oil. Real-time acquisition of crystal surface temperature ensures a temperature difference of ≤±0.5℃ across the entire range. Automatic pressure adjustment or shutdown protection is triggered when real-time hydraulic value or temperature exceeds the limit. After annealing is completed, the heating system, stirring system and external circulation system are shut down in sequence, the heat transfer oil in the furnace cavity is drained and the pipelines and furnace cavity are cleaned, and the parameters are reset to wait for the next operation.

[0015] Preferably, when adjusting the heating power, impeller speed, crystal support speed and circulation flow rate in real time, the heating power, impeller speed, crystal support speed and circulation flow rate are adjusted in a coordinated manner using a PID control algorithm and a flow field-temperature field coupling model.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: The optical crystal oil bath annealing furnace control system of the present invention fixes the optical crystal to the crystal support and seals the furnace body, and starts the external circulation system to transport heat transfer oil. The heat transfer oil enters the liquid outlet of the spiral flow channel from the oil supply end, flows from bottom to top along the spiral flow channel formed by the spiral guide ribs, and fills the furnace cavity through the liquid inlet at the top of the flow channel; after the liquid level reaches the target, the furnace cavity return oil structure at the top of the furnace cavity collects the overflow heat transfer oil and sends it back to the return oil end of the external circulation system, forming a bottom double-sided jacketed downward circulation oil path, and constructing a stable and uniform axial flow field. The stirring mechanism and the crystal rotation mechanism are started simultaneously. The stirring paddle rotates axially along the inner furnace cylinder to generate radial turbulence, and the rotation drive unit drives the crystal support to rotate synchronously, forming a coaxial turbulence system of the top stirring crystal. The two work together to form a dual-drive composite flow field with the bottom axial oil flow; the spiral guide ribs evenly distribute the oil flow and reduce oil temperature fluctuations, the synchronous rotation structure continuously scours the viscous boundary layer on the crystal surface, and the furnace cavity return oil structure eliminates oil stratification and flow dead zones. The system relies on a dual-drive composite flow field to form stable forced turbulence across the entire domain, effectively breaking down the insulating oil film on the crystal surface and reducing the temperature difference within the furnace cavity. The entire flow field provides gentle scouring without scratching the crystal. This synergistic flow field can eliminate temperature stratification and flow dead zones within the furnace cavity, reduce the probability of microcracks caused by thermal stress in the crystal, and stably achieve high-precision temperature field uniformity. This meets the stringent annealing process requirements for large-size optical crystals, improving crystal yield and optical performance. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the liquid phase flow circulation model of the present invention; Figure 2 This is a schematic diagram of the crystal scaffold structure of the present invention; Figure 3 This is a schematic diagram of the structure of the folded turbine impeller of the present invention; Figure 4 This is a schematic diagram of the structure of the rotary stirring unit of the present invention; Figure 5 This is a schematic diagram of the structure of the folded turbine impeller of the present invention; Figure 6 This is a schematic diagram of the flow field path inside the furnace cavity of the present invention; Figure 7 This is the control logic diagram of the PLC module and sensing unit of the present invention; Figure 8 This is a schematic diagram of the structural steps of the control method of the present invention.

[0018] Explanation of reference numerals in the attached figures: 101. Stirring paddle; 102. Inner furnace cylinder; 103. Furnace cavity; 104. Stirring paddle; 105. Crystal support; 106. Spiral flow channel; 107. Spiral guide rib; 108. Outer furnace cylinder; 201. Stirring motor; 202. Stirring shaft; 204. Oil baffle plate; 205. Rotary motor; 206. Rotary shaft. Detailed Implementation

[0019] The following is in conjunction with the appendix Figures 1-8 The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0020] like Figures 1-8As shown, the present invention provides an optical crystal oil bath annealing furnace control system, including a stirring mechanism and an external circulation system. The stirring paddle 101 of the stirring mechanism is disposed in the furnace cavity 103 of the inner furnace cylinder 102 of the oil bath annealing furnace and rotates around the axial direction of the inner furnace cylinder 102. The external circulation system is used to supply heat transfer oil into the furnace cavity 103. It also includes: a crystal rotation mechanism, a spiral guide rib 107, a sensing and detection module and a controller. The crystal rotation mechanism includes a crystal support 105 and a rotation drive unit (rotary motor 205, rotation shaft 206). The crystal support 105 is disposed in the furnace cavity 103 and is used to support the optical crystal. The rotation drive unit is connected to the crystal support 105 and is used to drive the crystal support 105 and the stirring paddle 101 to rotate synchronously. Under the drive of the rotation drive unit, the crystal support 105 rotates around the axial direction of the inner furnace cylinder 102. A spiral guide rib 107 is disposed between the outer wall of the inner furnace cylinder 102 and the inner wall of the outer furnace cylinder 108. The spiral guide rib 107 divides the space between the outer wall of the inner furnace cylinder 102 and the inner wall of the outer furnace cylinder 108 into a spiral flow channel 106. The liquid inlet end of the spiral flow channel 106 is connected to the oil supply end of the external circulation system, and the liquid outlet end of the spiral flow channel 106 is connected to the furnace cavity 103. The furnace cavity 103 is connected to the oil return end of the external circulation system. The sensing module is used to detect real-time parameters including the real-time oil temperature and real-time liquid level of the heat transfer oil in the furnace cavity 103, the real-time flow rate of the heat transfer oil in the spiral flow channel 106, and the real-time rotation speed of the stirring paddle 101 and the crystal support 105. The controller is electrically connected to the sensing module, the stirring mechanism (stirring motor 201, stirring shaft 202, oil baffle 204, stirring paddle 101), the rotary drive unit, the external circulation system, and the heating unit of the annealing furnace. The controller is used to control the operation of the stirring mechanism, the rotary drive unit, the external circulation system, and the heating unit according to the real-time parameters.

[0021] The working principle of the above embodiments is briefly described below: When using this optical crystal oil bath annealing furnace control system, the optical crystal is first clamped and fixed on the crystal support 105, the furnace body is closed to complete the seal, the external circulation system is started to output heat transfer oil, the heat transfer oil is sent from the oil supply end to the liquid outlet end of the spiral flow channel 106, and flows from bottom to top along the spiral flow channel 106 formed by the spiral guide ribs 107. It is sent into the furnace cavity 103 from the liquid inlet end at the top of the spiral flow channel 106, continuously filling the furnace cavity 103. When the heat transfer oil level in the furnace cavity 103 reaches the predetermined height, the heat transfer oil at the top of the furnace cavity 103 is recovered and transported to the oil return end of the external circulation system, forming a continuously flowing bottom double-sided jacketed downward circulation oil path, maintaining a stable heat transfer oil level and a uniform axial flow field from bottom to top in the furnace cavity 103.

[0022] Based on this, the stirring mechanism and the crystal rotation mechanism are started simultaneously. The stirring mechanism drives the stirring paddle 101 in the furnace cavity 103 to rotate axially along the inner furnace cylinder 102, stirring the heat transfer oil and forming radial turbulence. The rotation drive of the crystal rotation mechanism drives the crystal support 105 carrying the optical crystal to rotate axially along the inner furnace cylinder 102, realizing that the stirring paddle 101 and the optical crystal rotate synchronously and coaxially, forming a top stirring crystal coaxial turbulence system. Under the combined action of the axial flow of the heat transfer oil being pushed upward uniformly in the bottom spiral flow channel, the radial stirring of the top stirring paddle 101, and the rotation and scouring of the crystal itself, a complete dual-drive composite flow field is formed throughout the furnace cavity 103. The spiral guide rib 107 can evenly distribute the medium flow of the spiral flow channel 106, avoid the flow field deviation in the furnace cavity 103, extend the heat transfer oil's heat exchange path in the jacket, and reduce the oil temperature fluctuation entering the furnace cavity 103. The stirring paddle 101 and the crystal rotate synchronously to continuously scour the viscous boundary layer on the surface of the optical crystal, eliminating the heat exchange dead angle on the front and back of the crystal.

[0023] Under the combined effect of the "bottom double-sided jacketed circulation and top stirring crystal coaxial turbulence" dual-drive composite flow field, the heat transfer oil forms a stable and sufficient forced turbulence throughout the entire area, which greatly improves the heat transfer uniformity in the furnace cavity 103, effectively destroys the heat insulation oil film on the crystal surface, and eliminates temperature stratification and flow dead zones in the furnace cavity 103. The spiral guide structure, flexible synchronous disturbance structure and continuous overflow return oil design extend the entire flow path of the heat transfer oil, further reducing the temperature difference throughout the furnace cavity 103. At the same time, the uniform and gentle fluid flushing method will not scratch the surface of the optical crystal, and can stably achieve high-precision temperature field uniformity, meeting the stringent process requirements of annealing large-size optical crystals.

[0024] Throughout the process, the sensing module detects real-time parameters including the real-time oil temperature and level of the heat transfer oil in the furnace cavity 103, the real-time flow rate of the heat transfer oil in the spiral flow channel 106, and the real-time rotational speed of the agitator 101 and the crystal support 105. The controller then uses these real-time parameters to make auxiliary real-time adjustments to the operating status of the stirring mechanism, the rotary drive unit, the external circulation system, and the heating unit, further ensuring a uniform temperature field within the furnace cavity 103.

[0025] The optical crystal oil bath annealing furnace control system of the present invention relies on the synergistic effect of the bottom double-sided jacketed circulation and the top stirring crystal coaxial turbulence dual-drive composite flow field to eliminate the flow dead zone and temperature stratification in the furnace cavity 103 during the annealing process, efficiently break the viscous boundary layer on the crystal surface, greatly improve the uniformity of the temperature field throughout the furnace cavity 103, and the gentle heat exchange throughout the process can avoid the generation of thermal stress microcracks and surface scratches in the optical crystal, ensuring the yield and optical performance of the optical crystal after annealing.

[0026] Based on the above embodiments, in order to continuously ensure that the temperature difference throughout the furnace cavity 103 is ≤ ±0.5℃ and prevent the crystal from developing thermal cracks.

[0027] like Figure 7 and Figure 8 As shown, the sensing and detection module includes a temperature sensor, a flow sensor (turbine flow sensor), a speed sensor (photoelectric speed sensor), and a liquid level sensor. The temperature sensor is located inside the furnace cavity 103 and is used to detect the oil temperature of the heat transfer oil at different locations within the furnace cavity 103. The flow sensor is located between the circulation system and the spiral flow channel 106 and is used to detect the real-time flow rate of the heat transfer oil entering the spiral flow channel 106. The speed sensor is used to detect the real-time speed of the agitator 101 and the crystal support 105. The liquid level sensor is located inside the furnace cavity 103 and is used to detect the real-time liquid level within the furnace cavity 103. The controller has a preset flow field-temperature field coupling model and preset parameters including a set temperature value, a set flow rate value, a set liquid level value, and a set speed value for the agitator 101 and the crystal support 105. Based on the relationship between the real-time parameters and the corresponding preset parameters, the controller uses a PID control algorithm and the flow field-temperature field coupling model to control the operation of the heating unit, the external circulation system, the stirring mechanism, and the rotary drive unit.

[0028] Throughout the entire operation of the equipment, the sensing and detection module continuously collects multi-dimensional real-time parameters: temperature sensors arranged in the furnace cavity 103 and the flow channel collect the temperature of the heat transfer oil at various points; turbine flow sensors monitor the flow rate of heat transfer oil flowing into the spiral flow channel 106; photoelectric speed sensors capture the rotational speed of the agitator 104 and the crystal support 105; and liquid level sensors detect the liquid level of the heat transfer oil inside the furnace cavity 103. All real-time parameters are uploaded to the controller. The controller is pre-set with a flow field-temperature field coupling model, an improved PID control algorithm with a feedforward element, and standard process parameters such as set temperature, set flow rate, set speed, and set liquid level. The flow-temperature coupling model handles operating condition analysis and disturbance prediction, while the PID control algorithm is responsible for closed-loop deviation correction and actuator output. Together, they achieve regulation: the controller compares and calculates the real-time parameters returned by the sensors with the set parameters. The flow-temperature coupling model distinguishes the causes of temperature deviations, identifying whether the deviation stems from insufficient heat input, changes in the heat transfer oil properties, or abnormal heat transfer caused by flow field disturbances. It then outputs a feedforward compensation to the PID controller. The PID controller, combining the feedback deviation and the model's feedforward compensation, synchronously sends control signals to the heating unit, external circulation system, stirring mechanism, and rotary drive unit, dynamically correcting the operating status of the circulating oil circuit, stirring, and crystal rotation. When the furnace temperature reaches 200℃, the viscosity and thermal conductivity of the heat transfer oil change. The flow-temperature coupling model identifies fluctuations in oil properties and outputs a compensation signal. Based on this, the PID controller adjusts the external circulation pump flow rate and the stirring mechanism speed, maintaining the forced convection velocity in the furnace at 510 times the natural convection velocity. This suppresses oil flow turbulence and temperature stratification caused by natural convection, eliminates dead zones in the furnace flow, and ensures uniform heat transfer. For the low-speed heating process of 6℃ / h, the system has high thermal inertia. The flow-temperature coupling model predicts the temperature change trend and outputs a feedforward quantity. The differential component of the PID controller, in conjunction with the feedforward signal, adjusts the heating power and circulation flow rate in advance to offset the overshoot and oscillation caused by temperature inertia. After adjustment, the sensing module continuously collects data to form a complete closed loop, ensuring that the temperature difference throughout the furnace is ≤±0.5℃, avoiding thermal stress cracks in the optical crystal, and achieving the high-precision uniform temperature environment required for annealing large-size crystals.

[0029] As a preferred option, such as Figure 7As shown, the temperature sensor is a multi-point K-type thermocouple, which is distributed at the liquid inlet end of the spiral flow channel 106 and the top, middle and bottom of the furnace cavity 103. The multi-point K-type thermocouple detects the real-time temperature value of the heat transfer oil at the liquid inlet end of the spiral flow channel 106 and the top, middle and bottom of the furnace cavity 103. Multiple K-type thermocouples are installed at various locations, including the liquid inlet of the spiral flow channel 106, the top of the furnace cavity 103, the middle of the furnace cavity 103, and the bottom of the furnace cavity 103. These thermocouples can simultaneously collect the independent real-time temperatures of the heat transfer oil in the jacketed oil inlet and the upper, middle, and lower multi-layer areas of the furnace cavity 103. Compared with single-point temperature measurement, this method can completely capture the stratified temperature differences of the spiral flow channel oil supply and the axial upper and lower oil flow in the furnace cavity 103 in the basic scheme. The multi-layer temperature data are simultaneously sent to the flow field-temperature field coupling model of the controller. The model can accurately identify problems such as upper and lower temperature stratification in the furnace and temperature differences in oil supply on one side. It can then adjust the external circulation flow rate and stirring speed accordingly. This helps the double-sided spiral flow channel and dual-drive stirring structure of the basic scheme to eliminate the global temperature gradient, further reduce the temperature difference in various parts of the furnace, and stabilize the uniform temperature environment for optical crystal annealing.

[0030] As a preferred option, such as Figures 1-5As shown, the stirring mechanism further includes a stirring motor 201, a stirring shaft 202, and an oil baffle 204. The stirring shaft 202 is vertically arranged inside the furnace cavity 103 of the inner furnace cylinder 102. The top of the stirring shaft 202 is connected to the stirring motor 201. The oil baffle 204 is disposed on the shaft of the stirring shaft 202 and is used to reduce the flow rate of the heat transfer oil. The stirring paddle 101 is disposed at the bottom end of the stirring shaft 202. The rotation drive unit includes a rotary motor 205 and a rotary shaft 206. The rotary shaft 206 is coaxially arranged with the stirring shaft 202. The top end of the rotary shaft 206 is connected to the rotary motor 205, and the bottom end of the rotary shaft 206 is fixedly connected to the crystal support 105. Under the drive of the stirring motor 201 and the rotary motor 205, the stirring shaft 202 and the rotary shaft 206 rotate synchronously. The stirring mechanism consists of a stirring motor 201, a stirring shaft 202, a folded turbine-type stirring paddle 101, and an oil baffle 204. The stirring motor 201 is connected to the top of the vertical stirring shaft 202, and the stirring paddle 101 is mounted at the bottom. The stirring shaft 202 adopts a multi-axial and radial sealing structure to isolate the high-temperature heat transfer oil and prevent oil leakage from disrupting the stable circulation inside the furnace. An oil baffle 204 is installed on the shaft of the stirring shaft 202. When the heat transfer oil from the external circulation system enters the furnace cavity 103 through the spiral flow channel, the high-speed oil flow will directly impact the original convection field inside the furnace. The oil baffle 204 can buffer and reduce the impact flow velocity of the oil, allowing the axial downward oil inlet and the top stirring radial convection to form a smooth and stable composite flow field, avoiding the impact eddies that cause local heat accumulation. The crystal rotation drive unit is equipped with an independent rotary motor 205 and a rotary shaft 206. The rotary shaft 206 is coaxially arranged with the stirring shaft 202, and the crystal support 105 is fixed at the bottom. The stirring motor 201 and the rotary motor 205 can drive the stirring shaft 202 and the rotary shaft 206 to rotate synchronously, which can maintain the core functions of the stirring paddle 101 in turbulence and crystal rotation scouring, and can independently fine-tune the two sets of speeds of stirring and crystal rotation. With the help of controller parameter adjustment, the efficiency of breaking the viscous boundary layer on the crystal surface can be flexibly adjusted to continuously ensure uniform heat exchange on the outer wall of the crystal and avoid the generation of temperature difference cracks.

[0031] As a preferred option, such as Figure 3 and Figure 5 As shown, the stirring paddle 101 employs four folded blades, and the angle between the blades and the horizontal plane, as well as the blade width and diameter, are all adjustable. The stirring motor 201 drives the folded turbine impeller to rotate synchronously, and the four folded blades agitate the heat transfer oil in the upper part of the furnace cavity 103, creating radial turbulence. Operators can adjust the blade angle and size based on the current furnace cavity 103 dimensions, crystal specifications, and heat transfer oil viscosity simulation data. This matches the axial oil flow from bottom to top through the double-sided spiral flow channels of the basic scheme, allowing the axial oil flow and radial stirring flow field to fully merge, eliminating local flow blind spots, enhancing the overall oil exchange capacity, stabilizing the temperature field uniformity within the furnace, and reducing the temperature difference on the crystal surface.

[0032] As a preferred option, such as Figure 1 and Figure 2 As shown, the spiral guide rib 107 includes a vertical part and a horizontal part. The vertical part and the horizontal part together form a complete spiral guide channel, which can constrain the flow direction of the heat transfer oil in the jacket in layers, evenly disperse the flow rate of the heat transfer oil sent into the jacket by the external circulation, avoid the problem of excessive oil flow rate on one side and insufficient oil supply on one side, ensure that the temperature and flow rate of the heat transfer oil sent into the furnace cavity 103 from bottom to top of the spiral flow channel are completely consistent, stabilize the axial uniform oil supply system of the basic scheme, reduce the temperature difference between the upper and lower and left and right sides of the furnace from the oil supply source, and protect the optical crystal.

[0033] An oil return structure is also provided between the furnace cavity 103 and the external circulation system. The furnace cavity 103 is connected to the external circulation system through the oil return structure, which is located at a predetermined height at the top of the furnace cavity 103. The oil return structure of the furnace cavity 103 is used to recover the heat transfer oil in the furnace cavity 103 that is higher than the predetermined liquid level to the external circulation system. The oil return structure at the predetermined height at the top of the furnace cavity 103 simultaneously collects the overflow heat transfer oil, which can keep the height of the heat transfer oil in the furnace cavity 103 relatively constant and avoid temperature stratification of the heat transfer oil at the top and bottom and dead flow zones at the corners of the furnace cavity 103.

[0034] As a preferred embodiment, the oil return structure includes a top overflow orifice plate, an annular oil return corridor, and an oil collection chamber. The top overflow orifice plate is located at a predetermined height at the top of the furnace cavity 103, and multiple circular overflow holes are provided on the top overflow orifice plate. The annular oil return corridor is located around the top overflow orifice plate. The heat transfer oil in the furnace cavity 103 that is higher than the top overflow orifice plate overflows from the circular overflow holes and flows into the annular oil return corridor. The oil collection chamber is connected to the annular oil return corridor and is used to collect the oil in the annular oil return corridor. The oil collection chamber is connected to the external circulation system through an oil return pipeline. A top overflow orifice plate with multiple sets of circular overflow holes is installed at a preset height at the top of furnace cavity 103. When the heat transfer oil level in the furnace exceeds the height of the overflow orifice plate, the hot oil overflows evenly from the circular overflow holes and flows into the outer annular oil return corridor. The annular oil return corridor is designed according to hydrostatics, with uniform annular cross-sectional dimensions, allowing the oil to flow smoothly within the corridor without dead zones, preventing localized oil and heat accumulation. The annular oil return corridor connects to the oil collection chamber, which collects all overflowing heat transfer oil and then transports it to the external circulation system through the oil return pipeline, completing the closed-loop flow path of the external circulation system - spiral flow channel 106 - furnace cavity 103 - oil return structure - external circulation system. The entire layered oil return structure can evenly and continuously replace the high-temperature heat transfer oil in the furnace, avoiding oil stagnation at the top of the furnace and the generation of localized high temperatures. It continuously works with the dual-drive convection system of the basic scheme to refresh the oil throughout the entire area, stabilizing the temperature uniformity inside the furnace.

[0035] As a preferred embodiment, the external circulation system includes a circulation pump, a filter device, and a pressure transmitter. The return oil pipeline is connected to the filter device, which is connected to the circulation pump. The circulation pump is connected to the inlet end of the spiral flow channel 106 via a buffer joint. The oil collection chamber of the return oil structure is connected to a secondary filter device via the return oil pipeline. When the heat transfer oil flows back, it first passes through two-stage filters to intercept impurities and crystal debris, completing secondary purification. The filtered clean heat transfer oil is sent to the circulation pump, and the heat transfer oil output by the circulation pump is sent to the inlet end of the double-sided jacketed spiral flow channel 106 via a buffer joint. The secondary filtration can prevent impurities from clogging the spiral guide ribs, overflow holes, and pipelines, preventing oil circuit blockage from causing unilateral oil supply interruption and flow field imbalance, maintaining a complete and uniform oil circulation in the basic scheme for a long time, and continuously stabilizing the temperature field throughout the furnace.

[0036] As a preferred option, such as Figure 7 As shown, a pressure transmitter is also provided between the buffer joint and the inlet end of the spiral flow channel 106. The pressure transmitter is used to detect the real-time hydraulic value in the return oil pipeline. The pressure transmitter is electrically connected to the controller, which is electrically connected to the circulating pump. The controller has a preset pressure threshold and controls the power of the circulating pump according to the pressure threshold, so that the real-time hydraulic value in the return oil pipeline is maintained within the pressure threshold. The pressure transmitter collects the hydraulic values ​​inside the return oil pipeline and the supply oil pipeline in real time and transmits the hydraulic signal to the controller. The controller has a preset safety pressure threshold and compares the actual hydraulic pressure in the pipeline with the threshold in real time. When the oil pressure is too high / too low, the controller automatically adjusts the output power of the circulating pump to stabilize and control the hydraulic pressure in the pipeline within the threshold range. Stable oil pressure can avoid the sudden increase or decrease in the oil supply velocity of the spiral flow channel caused by the pressure fluctuation of the circulating pump, prevent sudden changes in the oil supply flow of the jacket from destroying the axial uniform flow field of the basic scheme, eliminate the temperature fluctuation in the furnace caused by unstable oil supply, and continuously maintain the high-precision uniform temperature conditions required for optical crystal annealing.

[0037] This invention also provides a method for controlling an optical crystal oil bath annealing furnace, which employs an optical crystal oil bath annealing furnace control system and includes the following steps: The optical crystal is fixed to the crystal support 105, the annealing process parameters are set, the matching PID parameter library is retrieved, and the pressure monitoring and protection module, stirring mechanism, and crystal rotation mechanism are simultaneously verified to complete the machine self-test. The external circulation system is turned on, and the heat transfer oil is sent into the spiral flow channel 106, which is transported from bottom to top into the furnace cavity 103 to form an axial flow field. The oil return structure of the furnace cavity 103 recovers the overflowing heat transfer oil to form a closed loop circulation. The stirring mechanism and crystal rotation mechanism are started simultaneously, and the stirring paddle 101 and the crystal support 105 rotate synchronously to form a coaxial turbulence at the top. The real-time hydraulic value in the pipeline is collected in real time, and the power of the external circulation system is dynamically adjusted to keep the real-time hydraulic value in the pipeline within the preset pressure threshold and stabilize the oil supply pressure. By collecting the real-time temperature in the furnace cavity 103, the real-time rotation speed of the stirring paddle 101, the real-time rotation speed of the crystal support 105, and the real-time circulation flow rate data, the heating power, the rotation speed of the stirring paddle 101, the rotation speed of the crystal support 105, and the circulation flow rate are adjusted in real time to adapt to the changes in the physical properties of the high-temperature heat transfer oil. The crystal surface temperature is collected in real time to ensure that the temperature difference across the entire range is ≤ ±0.5℃. When the real-time hydraulic value or temperature exceeds the limit, the pressure is automatically adjusted or the shutdown protection is triggered. After annealing, the heating system, stirring system and external circulation system are shut down in sequence, the heat transfer oil in the furnace cavity 103 is drained and the pipeline and furnace cavity 103 are cleaned. The parameters are reset and ready for the next operation.

[0038] As a preferred embodiment, when adjusting the heating power, the rotation speed of the agitator 101, the rotation speed of the crystal support 105, and the circulation flow rate in real time, the heating power, the rotation speed of the agitator 101, the rotation speed of the crystal support 105, and the circulation flow rate are adjusted in a coordinated manner using a PID control algorithm and a flow field-temperature field coupling model.

[0039] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A control system for an optical crystal oil bath annealing furnace, comprising a stirring mechanism and an external circulation system, wherein the stirring paddle of the stirring mechanism is disposed within the furnace cavity of the inner furnace cylinder of the oil bath annealing furnace and rotates axially around the inner furnace cylinder, and the external circulation system is used to supply heat transfer oil into the furnace cavity, characterized in that, Also includes: The crystal rotation mechanism includes a crystal support and a rotation drive unit. The crystal support is disposed inside the furnace cavity and is used to support an optical crystal. The rotation drive unit is connected to the crystal support and is used to drive the crystal support to rotate synchronously with the stirring paddle. Under the drive of the rotation drive unit, the crystal support rotates around the axial direction of the inner furnace cylinder. A spiral guide rib is disposed between the outer wall of the inner furnace cylinder and the inner wall of the outer furnace cylinder. The spiral guide rib divides the space between the outer wall of the inner furnace cylinder and the inner wall of the outer furnace cylinder into a spiral flow channel. The liquid inlet end of the spiral flow channel is connected to the oil supply end of the external circulation system, the liquid outlet end of the spiral flow channel is connected to the furnace cavity, and the furnace cavity is connected to the oil return end of the external circulation system. The sensing and detection module is used to detect real-time parameters including the real-time oil temperature and real-time liquid level of the heat transfer oil in the furnace cavity, the real-time flow rate of the heat transfer oil in the spiral flow channel, and the real-time rotation speed of the agitator and crystal support. The controller is electrically connected to the sensing and detection module, the stirring mechanism, the rotary drive unit, the external circulation system, and the heating unit of the annealing furnace. The controller controls the operation of the stirring mechanism, the rotary drive unit, the external circulation system, and the heating unit according to the real-time parameters through a PID control algorithm.

2. The optical crystal oil bath annealing furnace control system as described in claim 1, characterized in that, The sensing and detection module includes a temperature sensor, a flow sensor, a speed sensor, and a level sensor. The temperature sensor is located inside the furnace cavity and is used to detect the oil temperature at different locations within the furnace cavity. The flow sensor is located between the circulation system and the spiral flow channel and is used to detect the real-time flow rate of the heat transfer oil entering the spiral flow channel. The speed sensor is used to detect the real-time speed of the agitator and crystal support. The level sensor is located inside the furnace cavity and is used to detect the real-time level of the liquid within the furnace cavity. The controller has a preset flow field-temperature field coupling model and preset parameters including set temperature, set flow rate, set level, and set speed of the agitator and crystal support. Based on the relationship between the real-time parameters and the corresponding preset parameters, the controller uses a PID control algorithm and the flow field-temperature field coupling model to control the operation of the heating unit, the external circulation system, the stirring mechanism, and the rotary drive unit.

3. The optical crystal oil bath annealing furnace control system as described in claim 2, characterized in that, The temperature sensor is a multi-point K-type thermocouple, which is distributed at the liquid inlet end of the spiral flow channel and the top, middle and bottom of the furnace cavity. The multi-point K-type thermocouple detects the real-time temperature value of the heat transfer oil at the liquid inlet end of the spiral flow channel and the top, middle and bottom of the furnace cavity.

4. The optical crystal oil bath annealing furnace control system as described in claim 1, characterized in that, The stirring mechanism also includes a stirring motor, a stirring shaft, and an oil baffle. The stirring shaft is vertically installed inside the furnace cavity of the inner furnace cylinder. The top of the stirring shaft is connected to the stirring motor. The oil baffle is installed on the shaft of the stirring shaft and is used to reduce the flow rate of the heat transfer oil. The stirring paddle is installed at the bottom end of the stirring shaft. The rotation drive unit includes a rotation motor and a rotation shaft. The rotation shaft is coaxial with the stirring shaft. The top end of the rotation shaft is connected to the rotation motor, and the bottom end of the rotation shaft is fixedly connected to the crystal support. Under the drive of the stirring motor and the rotation motor, the stirring shaft and the rotation shaft rotate synchronously.

5. The optical crystal oil bath annealing furnace control system as described in claim 1, characterized in that, An oil return structure is also provided between the furnace cavity and the external circulation system. The furnace cavity is connected to the external circulation system through the oil return structure. The oil return structure is connected to a predetermined height position at the top of the furnace cavity. The furnace cavity oil return structure is used to recover the heat transfer oil in the furnace cavity that is higher than the predetermined liquid level to the external circulation system.

6. The optical crystal oil bath annealing furnace control system as described in claim 5, characterized in that, The furnace cavity oil return structure includes a top overflow orifice plate, an annular oil return corridor, and an oil collection chamber. The top overflow orifice plate is located at a predetermined height at the top of the furnace cavity, and multiple circular overflow holes are provided on the top overflow orifice plate. The annular oil return corridor is located around the top overflow orifice plate. The heat transfer oil in the furnace cavity that is higher than the top overflow orifice plate overflows from the circular overflow holes and flows into the annular oil return corridor. The oil collection chamber is connected to the annular oil return corridor and is used to collect the oil in the annular oil return corridor. The oil collection chamber is connected to the external circulation system through an oil return pipeline.

7. The optical crystal oil bath annealing furnace control system as described in claim 6, characterized in that, The external circulation system includes a circulation pump, a filter device, and a pressure transmitter. The return oil pipeline is connected to the filter device, and the filter device is connected to the circulation pump. The circulation pump is connected to the inlet end of the spiral flow channel through a buffer joint.

8. The optical crystal oil bath annealing furnace control system as described in claim 7, characterized in that, A pressure transmitter is also provided between the buffer joint and the inlet end of the spiral flow channel. The pressure transmitter is used to detect the real-time hydraulic value in the return oil line. The pressure transmitter is electrically connected to the controller, which is electrically connected to the circulation pump. The controller has a preset pressure threshold. The controller controls the power of the circulation pump according to the pressure threshold, so that the real-time hydraulic value in the return oil line is maintained within the pressure threshold.

9. A method for controlling an oil bath annealing furnace for optical crystals, characterized in that, The optical crystal oil bath annealing furnace control system as described in any one of claims 1-8 includes the following steps: The optical crystal is fixed to the crystal holder, the annealing process parameters are set, the matching PID parameter library is retrieved, and the pressure monitoring and protection module, stirring mechanism and crystal rotation mechanism are simultaneously verified to complete the self-test of the whole machine. When the external circulation system is turned on, the heat transfer oil is sent into the spiral flow channel and transported from bottom to top into the furnace cavity to form an axial flow field. The furnace cavity oil return structure recovers the overflowing heat transfer oil, forming a closed loop circulation. The stirring mechanism and the crystal rotation mechanism are started simultaneously, and the stirring paddle and the crystal support rotate synchronously to form a coaxial turbulence at the top. Real-time hydraulic values ​​in the pipeline are collected, and the power of the external circulation system is dynamically adjusted to keep the real-time hydraulic values ​​in the pipeline within the preset pressure threshold and stabilize the oil supply pressure. By collecting real-time temperature in the furnace cavity, real-time speed of the agitator, real-time speed of the crystal support, and real-time circulation flow data, the heating power, agitator speed, crystal support speed, and circulation flow are adjusted in real time to adapt to the changes in the physical properties of the high-temperature heat transfer oil. Real-time acquisition of crystal surface temperature ensures a temperature difference of ≤±0.5℃ across the entire range. Automatic pressure adjustment or shutdown protection is triggered when real-time hydraulic value or temperature exceeds the limit. After annealing is completed, the heating system, stirring system and external circulation system are shut down in sequence, the heat transfer oil in the furnace cavity is drained and the pipelines and furnace cavity are cleaned, and the parameters are reset to wait for the next operation.

10. The method for controlling an optical crystal oil bath annealing furnace as described in claim 9, characterized in that, When adjusting the heating power, agitator speed, crystal support speed and circulation flow rate in real time, the PID control algorithm and flow field-temperature field coupling model are used to adjust the heating power, agitator speed and crystal support speed and circulation flow rate in a coordinated manner.

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