System and method for electric field regulated additive manufacturing powder velocity based on visual feedback

Abstract

The application discloses a system and method for electric field regulation of additive manufacturing powder speed based on visual feedback, and relates to the technical field of additive manufacturing. The system comprises a laser head, a machine vision monitoring unit and a control unit, the laser head is coaxially arranged with a powder feeding nozzle, the powder feeding nozzle is connected with a powder feeder, a high-voltage electrode plate is installed in the powder feeder, and the high-voltage electrode plate is connected with a high-voltage power supply. The machine vision monitoring unit comprises a high-speed camera and an infrared thermal imager, the high-speed camera is used for collecting powder flow information, and the infrared thermal imager is used for monitoring molten pool information. The control unit is used for processing information collected by the high-speed camera and the infrared thermal imager in real time, transmitting the processed information to the high-voltage power supply, and changing the powder speed by adjusting the output voltage. The application can realize intelligent closed-loop control of the powder speed by capturing the powder flow form and the molten pool state in real time through the machine vision system, generating a control signal based on image processing to dynamically adjust the electric field intensity, effectively suppressing splashing, and improving the forming quality and the powder utilization rate.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of additive manufacturing technology, and in particular to a system and method for electric field regulation of powder velocity in additive manufacturing based on visual feedback. BACKGROUND

[0002] In the directed energy deposition (DED) process, the stability of the powder flow is the core, although the concept of using electric field to regulate powder velocity has been proposed, the control strategy of the existing scheme is mostly limited to PID regulation or open-loop control, and the following problems exist:

[0003] The existing powder feeding system generally adopts an open-loop control mode, which can meet the manufacturing scene of general precision requirements, but has obvious limitations in high-precision and high-stability additive manufacturing applications, and must rely on closed-loop control to achieve accurate regulation. However, there are still many technical challenges in realizing high-performance closed-loop control: first, in terms of perception, there is a certain feedback delay in real-time monitoring of the powder flow and the molten pool, which is difficult to cope with the transient changes in the working conditions in the high-speed manufacturing process; second, in terms of decision-making, the process has complex characteristics such as strong nonlinearity and multivariable coupling, and traditional control methods are difficult to achieve multi-objective coordination and dynamic optimization. SUMMARY

[0004] In view of the deficiencies of the prior art, the purpose of the present application is to provide a system and method for electric field regulation of powder velocity in additive manufacturing based on visual feedback, which can realize intelligent closed-loop control of powder velocity by capturing the powder flow pattern and molten pool state in real time through a machine vision system, generating a control signal based on image processing, and dynamically adjusting the electric field intensity, thereby effectively suppressing splashing and improving the forming quality and powder utilization rate.

[0005] In order to achieve the above-mentioned purpose, the present application is realized by the following technical scheme:

[0006] In a first aspect, embodiments of the present application provide a system for electric field regulation of powder velocity in additive manufacturing based on visual feedback, comprising:

[0007] A laser head is coaxially arranged with a powder feeding nozzle, the powder feeding nozzle is connected to a powder feeder, a pair of high-voltage electrode plates are installed in the powder feeder, and the high-voltage electrode plates are connected to a high-voltage power supply;

[0008] A machine vision monitoring unit includes a high-speed camera and an infrared thermal imager, the high-speed camera is used to collect powder flow information, and the infrared thermal imager is used to monitor molten pool information;

[0009] A control unit is used to process the information collected by the high-speed camera and the infrared thermal imager in real time, and transmit the processed information to the high-voltage power supply to change the powder velocity by adjusting the output voltage.

[0010] As a further implementation, the high-speed camera is configured with a backlight source.

[0011] As a further implementation, the powder flow information includes powder flow profile, concentration and motion trajectory; the molten pool information includes molten pool temperature field distribution and spatter generation condition.

[0012] As a further implementation, the control unit includes an image processing module, an intelligent decision module and a control output module, the image processing module is used to process image data and extract powder flow and molten pool key characteristic parameters;

[0013] The intelligent decision module generates electric field intensity control instructions based on comparison of powder flow key characteristic parameters with preset ideal process window; the control output module is used to send electric field intensity control instructions to high-voltage power supply.

[0014] In a second aspect, embodiments of the present application also provide a method for adjusting powder speed in additive manufacturing based on visual feedback, which adopts the system and includes:

[0015] Obtaining powder flow visible light image and molten pool infrared thermal image, and extracting powder flow and molten pool key characteristic parameters;

[0016] Comparing key characteristic parameters with preset ideal process window to generate optimal electric field intensity control instructions;

[0017] Outputting electric field intensity control instructions to change electric field intensity applied to powder.

[0018] As a further implementation, according to input key characteristic parameters, switching between spatter suppression mode, flow speed compensation mode and steady state maintenance mode.

[0019] As a further implementation, when the number of spatter particles extracted from the molten pool infrared thermal image continuously exceeds the dynamic safety threshold within a continuous set control period, switching to the spatter suppression mode;

[0020] Or, when the aspect ratio of the molten pool suddenly increases and exceeds the threshold, switching to the spatter suppression mode.

[0021] As a further implementation, the control process in the spatter suppression mode is divided into a first stage and a second stage, wherein the first stage is emergency braking and the second stage is proportional regulation steady flow.

[0022] As a further implementation, when the difference between actual average speed of powder flow and target speed continuously exceeds the tolerance range, switching to the flow speed compensation mode;

[0023] Or, when the divergence angle of powder flow is greater than the allowed maximum divergence angle, switching to the flow speed compensation mode;

[0024] Alternatively, when the instantaneous mass flow estimated based on the velocity and flow density is lower than the process required value, switch to the flow rate compensation mode.

[0025] As a further implementation, when the velocity deviation is less than a set value, the flow beam shape is ideal, there is no splashing, and the molten pool area and temperature fluctuation are within the allowed range, switch to the steady state maintenance mode.

[0026] The beneficial effects of the present application are as follows:

[0027] (1) The machine vision monitoring unit of the present application includes a high-speed camera and an infrared thermal imager, and the control unit can receive and process the image information collected by the high-speed camera and the infrared thermal imager in real time, and transmit the processed information to the high-voltage power supply to change the powder speed by adjusting the output voltage; it realizes simultaneous monitoring of powder flow and molten pool, not only can control the speed, but also can indirectly guarantee the quality of the molten pool, realize the collaborative optimization of multiple process parameters; through machine vision real-time capture of powder flow shape and molten pool state, based on image processing to generate control signal, dynamically adjust the electric field intensity, so as to realize intelligent closed-loop control of powder speed, effectively suppress splashing, improve forming quality and powder utilization rate.

[0028] (2) According to the input characteristic parameters, the present application switches between the three modes of splashing suppression, flow rate compensation and steady state maintenance, and adopts different control strategies to output control instructions, forming a control scheme of multi-modal input, multi-objective optimization and multi-priority decision. Through intelligent state switching, the safety target of splashing suppression is prioritized, and then the flow rate control is dynamically optimized, effectively solving the contradiction of multi-objective control; at the same time, the system automatically reduces the control output under steady state conditions, significantly reducing energy consumption and actuator wear while maintaining accuracy, and can realize adaptive, high-precision and strong robustness control of powder speed. BRIEF DESCRIPTION OF DRAWINGS

[0029] The drawings accompanying the specification of the present application form a part thereof, serve to provide further understanding of the present application, and together with the description of the exemplary embodiments of the present application and their description serve to explain the present application, and do not constitute an improper limitation of the present application.

[0030] Figure 1 is a schematic diagram of the system structure of the present application according to one or more embodiments;

[0031] Figure 2 is a flow chart of the method of the present application according to one or more embodiments.

[0032] 1, powder storage bin, 2, powder feeder, 3, control unit, 4, powder feeding nozzle, 5, high-voltage electrode plate, 6, high-voltage power supply, 7, laser head, 8, laser, 9, molten pool, 10, substrate, 11, high-speed camera, 12, backlight, 13, infrared thermal imager. Detailed Implementation

[0033] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0034] Example 1:

[0035] This embodiment provides a system for controlling the speed of additive manufacturing powder using an electric field based on visual feedback, such as... Figure 1 As shown, it mainly includes a laser head 7, a powder feeding nozzle 4, a high-voltage electrode plate 5, a high-voltage power supply 6, a machine vision monitoring unit, and a control unit 3. The powder feeding nozzle 4 is coaxially mounted on the outside of the laser head 7. The powder feeding nozzle 4 is connected to the powder feeder 2 through a powder feeding pipe. The powder feeder 2 is connected to the powder storage bin 1. The powder feeding nozzle 4 provides the powder required in the additive manufacturing process of the substrate. The laser head 7 is used to emit a laser 8 to the substrate 10 and form a molten pool 9 on the surface of the substrate.

[0036] The powder feeder 2 is equipped with a pair of high-voltage electrode plates 5, according to Figure 1 In the center view, two high-voltage electrode plates 5 are arranged vertically in sequence, i.e., along the powder feeding direction. One high-voltage electrode plate 5 is connected to the positive terminal of the high-voltage power supply 6 via a wire, and the other high-voltage electrode plate 5 is connected to the negative terminal of the high-voltage power supply 6 via a wire. The powder feeding speed is adjusted by changing the output voltage of the high-voltage power supply 6. In this embodiment, the high-voltage power supply 6 is a programmable high-voltage power supply 6, capable of generating a uniform electrostatic field with adjustable intensity; the output voltage range of the high-voltage power supply 6 is -30kV to +30kV.

[0037] In this embodiment, the high-voltage electrode plate 5 is an annular copper electrode plate, which is sleeved on the outer wall of the powder feeding pipe so that the powder flow can pass through the center of the electrode plate; the distance between the two high-voltage electrode plates 5 is 10mm.

[0038] The machine vision monitoring unit in this embodiment includes a high-speed camera 11 and an infrared thermal imager 13. The high-speed camera 11 is used to acquire powder flow information, and the infrared thermal imager 13 is used to monitor the information of the molten pool 9. The high-speed camera 11 is equipped with a backlight 12 (LED) so that it can clearly capture the contour, concentration, and trajectory of the powder flow. The information of the molten pool 9 monitored by the infrared thermal imager 13 includes the temperature field distribution of the molten pool 9 and the generation of spatter.

[0039] like Figure 1As shown, the high-speed camera 11, the infrared thermal imager 13 and the high-voltage power supply 6 are all connected to the control unit 3, which includes an image processing module, an intelligent decision-making module and a control output module. The image processing module can process the image data of the high-speed camera 11 and the infrared thermal imager 13 in real time, extract the key characteristic parameters of the powder flow and the molten pool 9 through background subtraction, threshold segmentation, optical flow algorithm, etc. Among them, the key characteristic parameters of the powder flow include the velocity distribution and divergence angle of the powder flow, and the key characteristic parameters of the molten pool 9 include the number of splashing particles in the molten pool 9 area and the trajectory of the splashing particles.

[0040] The intelligent decision-making module has an expert database and optimization algorithms (such as PID controller, fuzzy logic or machine learning model) built in, which can compare the extracted key characteristic parameters with the preset ideal process window and generate the optimal electric field strength control instruction. Further, when the splashing is identified to be intensified, a negative voltage instruction is output to slow down the powder; when the powder flow is identified to be divergent or the energy is insufficient, a positive voltage instruction is output to accelerate and focus the powder flow.

[0041] The control output module is used to send the electric field strength control instruction to the high-voltage power supply 6 in real time, adjust the output voltage of the high-voltage power supply 6, thereby changing the electric field strength, and completing a closed-loop control cycle.

[0042] This embodiment dynamically adjusts the electric field strength through the acquired image data, thereby realizing intelligent closed-loop control of the powder speed, effectively suppressing splashing and improving the forming quality and powder utilization rate.

[0043] Embodiment 2:

[0044] The embodiment provides a method for electric field regulation and control of powder speed in additive manufacturing based on visual feedback, which adopts the system of embodiment 1, and comprises the following steps:

[0045] Obtaining a visible light image of the powder flow and an infrared thermal image of the molten pool 9, and extracting key characteristic parameters of the powder flow and the molten pool 9;

[0046] Comparing the key characteristic parameters with a preset ideal process window to generate an optimal electric field strength control instruction;

[0047] Outputting the electric field strength control instruction to change the electric field strength applied to the powder.

[0048] Specifically, as shown in the figure, the method comprises the following steps: Figure 2

[0049] Step 1: setting process parameters, including target powder speed, splashing tolerance threshold, ideal temperature range of the molten pool 9, etc.

[0050] ​Step 2: Start the high-speed camera 11 and the infrared thermal imager 13 to simultaneously acquire visible-light images of the powder flow and infrared thermal images of the molten pool 9.

[0051] Step 3: The image processing module processes the image data in real time. Through algorithms such as background subtraction, threshold segmentation, and optical flow, it extracts key feature parameters such as powder flow velocity distribution, powder flow divergence angle, number and trajectory of splashed particles in the molten pool 9 region, and quantifies the powder flow state and the stability of the molten pool 9.

[0052] Step 4: The intelligent decision-making module switches between splash suppression mode, flow rate compensation mode and steady-state maintenance mode based on the input key characteristic parameters, and generates output instructions using different control strategies.

[0053] like Figure 2 As shown, the triggering conditions for splash suppression mode, flow rate compensation mode and steady-state maintenance mode are determined sequentially.

[0054] Traditional single control modes cannot simultaneously handle different types of operating conditions. For example, suppressing splash requires rapid deceleration, while improving efficiency requires precise acceleration. These two objectives will seriously conflict in a single control loop. Therefore, this embodiment provides an intelligent mechanism with priority judgment capabilities, which dynamically switches the most suitable control strategy based on real-time process status (such as whether splash occurs, whether the speed deviates, and whether the operation is stable), thereby realizing the leap from "passive reaction" to "active decision-making".

[0055] The triggering conditions for splash suppression mode include:

[0056] Primary trigger condition: Number of splash particles extracted from the Molten Pool 9 image ( If the dynamic safety threshold is exceeded continuously for M consecutive control cycles (e.g., M=3), This means switching to splash suppression mode. The continuous triggering mechanism effectively avoids misjudgments caused by noise in a single frame of image. Auxiliary triggering conditions: Switching to splash suppression mode occurs when the aspect ratio of the molten pool 9 suddenly increases and exceeds a threshold (indicating instability in the molten pool 9 and impending splashing), or when an extra-large (greater than 200µm) splash particle is detected. The triggering condition for splash suppression mode has the highest priority; once the condition is met, the system immediately interrupts other current control modes and forces entry into splash suppression mode.

[0057] The control strategy for splash suppression mode is as follows:

[0058] Control objective: Suppress splash as quickly as possible, with priority over speed tracking.

[0059] The control target of the splashing suppression mode is a hybrid algorithm combining nonlinear Bang-Bang control (also known as hysteresis control or ripple regulator control) and proportional control (P), which can provide suppression force that accurately matches real-time deviation and achieve fine adjustment with controllable force, including: the first stage (Bang-Bang emergency braking): once entered, the control unit 3 immediately outputs a pre-labeled fixed maximum deceleration voltage command, which is sufficient to generate a strong reverse electric field force in the shortest time to sharply decelerate the powder flow; this stage lasts for K control cycles (such as K=2), the purpose is to quickly curb the splashing trend.

[0060] The second stage (proportional regulation stable flow): after emergency braking, the controller switches to proportional control; its input is the deviation of the number of splashes and the threshold ( ), and the output is . Among them, is the proportional gain, which is usually large to ensure strong suppression of splashing. At this time, the goal of the controller is to make tend to zero, not the speed deviation.

[0061] The exit condition of the splashing suppression mode is: when (the safety recovery threshold is lower than ) and the aspect ratio of the molten pool 9 returns to the normal range and lasts for a period of time (such as 5 control cycles), it can be exited. After exiting, the control unit 3 does not immediately return to the original target speed, but enters the "speed ramp recovery" process, gradually increasing the target speed from the current lower value to the original set value at a pre-set slow slope, avoiding sudden changes in speed impacting the molten pool 9 again.

[0062] For the flow rate compensation mode, the triggering condition is:

[0063] Condition B1 (insufficient speed): the difference between the actual average speed of the powder flow ( ) and the target speed ( ) exceeds the tolerance range;

[0064] Condition B2 (flow beam divergence): the divergence angle of the powder flow ( ) is greater than the allowed maximum divergence angle ( ), indicating poor powder focusing and decreased utilization;

[0065] Condition B3 (insufficient flow estimation): the instantaneous mass flow estimated based on speed and flow density is lower than the process requirement value.

[0066] The control strategy of the flow rate compensation mode is:

[0067] Control target: make the actual speed accurately track the target speed and keep the flow beam concentrated.

[0068] Control algorithm: The system adopts parameter self-tuning PID control, which has parameter self-tuning function and meets the requirements of accurate and stable tracking of target speed in flow rate compensation mode.

[0069] For condition B1: the input is the speed deviation. The output is .

[0070] For condition B2: the input is the divergence angle deviation. The output is Increasing the voltage can usually both accelerate and focus the signal, so the two outputs are usually positively correlated.

[0071] Synthesized Output: The final voltage command is a weighted sum of the two: , where w is the weighting coefficient.

[0072] PID parameters ( The flow rate is not fixed and is adjusted online based on the real-time quality flow rate. The higher the flow rate, the greater the system inertia, therefore the flow rate is automatically increased. (Differential gain) is adjusted to suppress overshoot. (Proportional gain) to avoid oscillation.

[0073] For the steady-state maintenance mode, both the triggering and maintenance conditions must be met simultaneously:

[0074] (Speed ​​deviation is extremely small); This indicates a speed deviation, typically 0.15.

[0075] (Ideal stream shape); This indicates the stream divergence angle, typically 0.5°.

[0076] (Almost no splashing);

[0077] The area and temperature fluctuation of the molten pool 9 are within the allowable range.

[0078] The control strategy for maintaining steady-state mode is as follows:

[0079] Control objectives: Maintain the current excellent state while reducing control actions, saving energy and extending the life of the high-voltage power supply.

[0080] Control algorithm: Integral separation PID control with dead zone is adopted.

[0081] Dead Zone: Set a dead zone near the steady state, when the speed deviation is in the range of the dead zone, the controller output is zero, to avoid unnecessary, small voltage adjustment, so as to eliminate high frequency oscillation. Integral separation: When entering the steady state mode, the integral term (I term) is zeroed, which can prevent the integral value accumulated before entering the steady state from causing overshoot during the steady state. At this time, the controller actually only works in a small proportional band (P), keeping the system running smoothly and stably.

[0082] The goal of the steady state maintenance mode is to maximize the stability, energy saving and consumption reduction when the system has reached the optimal working condition. The integral separation PID with dead zone is used to achieve the goal of energy saving, consumption reduction and prolonging the service life of the equipment by actively reducing intervention.

[0083] Step 5: Loop execution: repeat steps 2 to 4 to realize real-time, self-adaptive closed-loop control of the whole manufacturing process.

[0084] The embodiment can not only control the speed, but also indirectly ensure the quality of the molten pool 9 by monitoring the powder flow and the molten pool 9 at the same time, realizing the collaborative optimization of multiple process parameters; and the image-based processing and decision-making are completed within milliseconds, which can timely suppress splashing and compensate for flow rate fluctuations, significantly improving the surface quality and internal density of the deposited layer.

[0085] The embodiment forms an intelligent control strategy of multi-modal input, multi-target optimization and multi-priority decision, realizing self-adaptive, high-precision and strong robustness control of the powder speed.

[0086] The above only describes the preferred embodiments of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method of electric field regulated additive manufacturing powder velocity based on visual feedback, characterized in that, The method comprises the following steps: acquiring visible light images of the powder flow and infrared thermal images of the molten pool, and extracting key characteristic parameters of the powder flow and the molten pool; comparing the key characteristic parameters with a preset ideal process window to generate optimal electric field intensity control instructions; switching among three modes of splash suppression, flow rate compensation and steady state maintenance according to the input key characteristic parameters; switching to the splash suppression mode when the number of splash particles extracted from the infrared thermal images of the molten pool continuously exceeds a dynamic safety threshold within a continuous set control period, or when the aspect ratio of the molten pool suddenly increases and exceeds a threshold; switching to the flow rate compensation mode when the difference between the actual average speed of the powder flow and the target speed continuously exceeds a tolerance range, or when the divergence angle of the powder flow is greater than the maximum allowed divergence angle, or when the instantaneous mass flow estimated based on the speed and flow density is lower than the process requirement value; switching to the steady state maintenance mode when the speed deviation is less than a set value, the flow beam shape is ideal, there is no splash, and the molten pool area and temperature fluctuation are within the allowed range; outputting the electric field intensity control instructions to change the electric field intensity applied to the powder; The system used in the method comprises: a laser head coaxially arranged with a powder feeding nozzle, the powder feeding nozzle being connected to a powder feeder, a pair of high-voltage electrode plates being installed in the powder feeder, and the high-voltage electrode plates being connected to a high-voltage power supply; a machine vision monitoring unit comprising a high-speed camera and an infrared thermal imager, the high-speed camera being used to collect powder flow information, and the infrared thermal imager being used to monitor molten pool information; a control unit used to process the information collected by the high-speed camera and the infrared thermal imager in real time, and transmit the processed information to the high-voltage power supply to change the powder speed by adjusting the output voltage.

2. The method of claim 1, wherein the method is based on visual feedback of the electric field modulated additive manufacturing powder velocity. The high-speed camera is provided with a backlight source.

3. The method of claim 1, wherein the method is based on visual feedback of the electric field modulated additive manufacturing powder velocity, and The powder flow information includes powder flow profile, concentration and motion trajectory; and the molten pool information includes molten pool temperature field distribution and splash generation condition.

4. The method of claim 1, wherein the method is based on visual feedback of the electric field modulated additive manufacturing powder velocity. The control unit comprises an image processing module, an intelligent decision-making module and a control output module, the image processing module being used to process image data and extract key characteristic parameters of the powder flow and the molten pool; The intelligent decision-making module generates electric field intensity control instructions based on the comparison between the key characteristic parameters of the powder flow and the preset ideal process window; and the control output module is used to send the electric field intensity control instructions to the high-voltage power supply.

5. The method of claim 1, wherein the method is based on visual feedback of the electric field modulated additive manufacturing powder velocity. The control process in the splash suppression mode is divided into a first stage and a second stage, wherein the first stage is emergency braking, and the second stage is proportional regulation and flow stabilization.

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