Electrostatic powder coating airflow stability real-time compensation method

Abstract

The application provides a static powder coating airflow stability real-time compensation method, relates to the powder coating control technical field, and is realized based on a static powder coating airflow stability real-time compensation device. The device comprises a main control MCU, a gas control valve, a stepping motor driver for driving the gas control valve, a current sampling circuit coupled to the stepping motor driver and used for collecting the winding current of the stepping motor in real time. The method comprises the following steps: after the gas control valve is opened to the target opening degree and enters the holding state, the static holding current value is obtained; the static holding current value is compared with the preset reference holding current value, the preset reference holding current value corresponds to the holding current required by the target opening degree under the unobstructed state of the airflow channel; whether the airflow channel has the blocking trend is judged according to the offset of the static holding current value relative to the reference holding current value; if not, the current target opening degree of the gas control valve is maintained, the airflow state change can be directly sensed, and real-time active compensation can be performed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of powder coating control, in particular to a static powder coating airflow stability real-time compensation method. BACKGROUND

[0002] Static powder spraying is to use the force of the electrostatic field on charged particles to make the charged coating powder firmly adhere to the surface of the workpiece. After the powder layer is baked, melted, leveled and solidified at low temperature, a solid coating is formed on the surface of the workpiece. The static powder spraying control device, as a key equipment for static powder coating, often realizes the formula calling and management of spraying parameters through the master control MCU, storage module and various control components, which improves the convenience of control to a certain extent.

[0003] In the prior art, such as the static powder coating control device and method disclosed in the authorized announcement CN112650127B, there are technical defects of airflow monitoring means lagging behind and being indirect, which are specifically embodied in that the air control module mainly monitors the inlet air pressure through the air pressure acquisition module and alarms and stops when the pressure is lower than the set threshold. This will lead to: first, air pressure is the result of airflow rather than the cause. When the air pressure is monitored to decrease, the insufficient airflow has already occurred, and the spraying quality may have been damaged, so the response has a lag; second, in powder coating, the slight accumulation or formation of "soft blockage" of powder will cause the change of airflow passage resistance, but it does not necessarily cause significant fluctuation of inlet air pressure in the early stage, so this scheme cannot effectively perceive such gradual and local blockage trend and lacks predictability. SUMMARY

[0004] In view of the above defects or deficiencies in the prior art, the present application aims to provide a static powder coating airflow stability real-time compensation method, which is realized based on a static powder coating airflow stability real-time compensation device. The device includes a master control MCU, an air control valve, a stepper motor driver driving the air control valve, and a current sampling circuit coupled to the stepper motor driver for real-time acquisition of winding current of the stepper motor. The method includes the following steps:

[0005] After the air control valve is opened to the target opening degree and enters the holding state, the static holding current value is obtained through the current sampling circuit;

[0006] The static holding current value is compared with a preset reference holding current value, and the preset reference holding current value corresponds to the holding current required for the target opening degree under the unobstructed state of the airflow passage;

[0007] According to the offset of the static holding current value relative to the reference holding current value, it is judged whether the airflow passage has a blockage trend;

[0008] If not, maintain the current target opening degree of the pneumatic control valve;

[0009] If so, a corresponding opening compensation signal is generated based on the offset, and the stepper motor driver is controlled to increase the actual target opening of the pneumatic valve to counteract the decrease in airflow caused by the blockage trend.

[0010] According to the technical solution provided in this application, determining whether the airflow channel shows a tendency to blockage includes the following steps:

[0011] When the offset exceeds a preset threshold, it is determined that the airflow channel is showing signs of blockage.

[0012] Before determining whether the airflow channel shows signs of blockage, the following steps are also included:

[0013] Determine the type of airflow currently being controlled, whereby the airflow type includes powder distribution gas and powder delivery gas;

[0014] Based on the airflow type, match the preset threshold corresponding to the airflow type;

[0015] Wherein, the preset threshold corresponding to the powder dispensing gas is lower than the preset threshold corresponding to the powder delivery gas.

[0016] According to the technical solution provided in this application, before comparing the static holding current value with the preset reference holding current value, the method further includes the following steps:

[0017] Obtain the preset reference holding current value;

[0018] The process of obtaining the preset reference holding current value includes the following steps:

[0019] The historical operating condition database is retrieved to obtain a target stage set, which includes multiple historical stable spraying stages with a determined non-blocking trend, and the static holding current value corresponding to each historical stable spraying stage.

[0020] The preset reference holding current value is obtained based on the target stage set.

[0021] According to the technical solution provided in this application, before retrieving the historical operating condition database, the following steps are also included:

[0022] Real-time acquisition of current ambient temperature and humidity;

[0023] The process of retrieving the historical operating condition database to obtain the target stage set includes the following steps:

[0024] screening, from the historical working condition database, a historical stable spraying phase in which a difference between a historical ambient temperature and the current ambient temperature and a difference between a historical ambient humidity and the current ambient humidity are both within respective preset tolerance ranges;

[0025] If the number of the screened historical stable spraying phases is higher than a preset number threshold, all the historical stable spraying phases form the target phase set.

[0026] According to the technical scheme provided in the application, obtaining the preset reference holding current value according to the target phase set comprises the following steps:

[0027] Performing clustering analysis on the plurality of static holding current values in the target phase set to identify a current value cluster with the most concentrated distribution;

[0028] Performing weighted calculation on data in the current value cluster based on a time decay factor, in which a weight of recent data is higher than a weight of early data;

[0029] Multiplying a result of the weighted calculation by a life compensation coefficient corresponding to a cumulative running time of the equipment to obtain the preset reference holding current value.

[0030] According to the technical scheme provided in the application, after screening, from the historical working condition database, a historical stable spraying phase in which a difference between a historical ambient temperature and the current ambient temperature and a difference between a historical ambient humidity and the current ambient humidity are both within respective preset tolerance ranges, the following steps are further included:

[0031] If the number of the screened historical stable spraying phases is lower than or equal to the preset number threshold, a current working condition vector is calculated, the current working condition vector including a current ambient temperature, a current ambient humidity and a current target opening degree;

[0032] Calculating a historical working condition vector corresponding to each of the historical stable spraying phases in the historical working condition database, the historical working condition vector including a historical ambient temperature, a historical ambient humidity and a historical target opening degree;

[0033] Calculating a multidimensional Euclidean distance between the current working condition vector and each of the historical working condition vectors, and screening the first K historical stable spraying phases with the smallest distance to form the target phase set.

[0034] According to the technical scheme provided in the application, the following steps are further included:

[0035] Recording and constructing a compensation event sequence, the compensation event sequence including a plurality of compensation events, each of the compensation events including a compensation time, a static holding current offset before compensation, and a compensation opening degree value applied to eliminate the offset;

[0036] performing time sequence pattern analysis on the compensation event sequence within the first preset time window, identifying a compensation event occurrence frequency and / or a compensation opening degree value change trend over time as a blockage development pattern;

[0037] based on the blockage development pattern, predicting a remaining time or a remaining spraying workload required for the gas path system to reach a critical state requiring cleaning and maintenance;

[0038] when the remaining time is lower than a first preset time length or the remaining spraying workload is lower than a first preset workload, generating a predictive maintenance prompt.

[0039] According to the technical scheme provided in the application, after the step of controlling the stepper motor driver to increase the actual target opening degree of the pneumatic control valve, the following steps are further included:

[0040] continuously monitoring the static holding current value within a second preset time window;

[0041] if the offset of the static holding current value does not decrease or continues to increase, it is determined that the blockage is not recoverable, and a system alarm is triggered and a safety shutdown process is executed.

[0042] According to the technical scheme provided in the application, after completing a spraying cycle, the coating quality detection result of the workpiece in the cycle is obtained, and the coating quality detection result includes a coating thickness uniformity index;

[0043] correlation analysis is performed between the coating quality detection result and the fluctuation of the static holding current value recorded in the same cycle;

[0044] if the coating thickness uniformity index does not meet the standard and analysis shows that it has a strong correlation with the static holding current fluctuation at a specific target opening degree, the value corresponding to the target opening degree in the preset reference holding current value is adjusted to make the static holding current fluctuation at the target opening degree tend to be stable in subsequent spraying.

[0045] Compared with the prior art, the application has the following beneficial effects:

[0046] I. Early, direct and non-contact diagnosis of airflow blockage is achieved: the monitoring object is changed from air pressure to the static holding current value of the stepper motor driving the pneumatic control valve. The current value directly reflects the resistance torque required to maintain the opening degree of the pneumatic control valve. When the airflow passage is slightly blocked, the increase in resistance will immediately be reflected in the increase in holding current. This change is earlier than the change in the monitorable air pressure, and the sensing method is non-contact and without additional sensors, realizing early and accurate diagnosis of the blockage trend.

[0047] Secondly, the passive alarm is changed into active compensation, and the airflow stability is significantly improved: by comparing the offset of the static holding current value and the reference value in real time, the system can make a judgment when the blockage just has a sign, and immediately generate a compensation signal to actively increase the opening of the air control valve to offset the decrease of airflow caused by the increase of channel resistance, so as to eliminate the problem in the embryonic state and ensure that the actual airflow can be dynamically maintained at a stable level corresponding to the target opening during the entire spraying process.

[0048] Thirdly, the spraying quality and consistency are fundamentally improved: the stability of the airflow is the key to ensure the shape of the powder cloud and the powder adhesion rate. The above-mentioned active compensation mechanism ensures the continuous stability of the spraying parameters, thereby directly contributing to the significant improvement of the uniformity of coating thickness, appearance quality and product yield, and meeting higher process requirements.

[0049] Fourthly, the system reliability is enhanced and the maintenance cost is reduced: since the blockage trend can be found and compensated early, sudden stop and production interruption caused by serious blockage are avoided. At the same time, the non-contact current monitoring scheme avoids the installation of additional sensors in the complex air circuit, simplifies the system structure, improves the reliability, and reduces the potential failure points and maintenance cost. BRIEF DESCRIPTION OF DRAWINGS

[0050] Figure 1 The step flow chart of the electrostatic powder coating airflow stability real-time compensation method provided in the present application is shown. DETAILED DESCRIPTION

[0051] The present application will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific examples described herein are only used to explain the related application, and not to limit the application. In addition, it should be noted that only the parts related to the application are shown in the drawings for ease of description.

[0052] It should be noted that the examples in the present application and the features in the examples can be combined with each other without conflict. The present application will be described in detail below with reference to the accompanying drawings and examples.

[0053] Example 1

[0054] As mentioned in the background, in view of the problems in the prior art, the present application proposes an electrostatic powder coating airflow stability real-time compensation method, which is realized based on an electrostatic powder coating airflow stability real-time compensation device. The device includes a main control MCU, an air control valve, a stepper motor driver for driving the air control valve, and a current sampling circuit coupled to the stepper motor driver for real-time acquisition of the winding current of the stepper motor; as shown in the figure, the method includes the following steps: Figure 1

[0055] ​S1, after the pneumatic control valve is opened to the target opening degree and enters the holding state, the static holding current value is obtained through the current sampling circuit;

[0056] S2, the static holding current value is compared with the preset reference holding current value, and the preset reference holding current value corresponds to the holding current required by the target opening degree in the unobstructed state of the airflow channel;

[0057] S3, according to the offset of the static holding current value relative to the reference holding current value, whether the airflow channel has an obstruction trend is judged;

[0058] S41, if not, the current target opening degree of the pneumatic control valve is maintained;

[0059] S42, if yes, a corresponding opening degree compensation signal is generated based on the offset, and the actual target opening degree of the pneumatic control valve is controlled to be increased by the stepper motor driver to offset the airflow drop caused by the obstruction trend.

[0060] Specifically, the main control MCU (Microcontroller Unit): as the brain of the system, for example, can be used in the STM32F107VCT6 chip of STMicroelectronics. It is responsible for executing control logic, performing data operations, and communicating with each module. The air control valve is a valve that can accurately control the opening degree, used to adjust the compressed air flow to the spray gun. In this embodiment, the air control valve is preferably a proportional valve or an electronic expansion valve driven by a stepper motor, and its opening degree can be accurately controlled and maintained. Stepper motor driver: connected with the main control MCU, receives the pulse and direction signal issued by it, used to drive the stepper motor to rotate accurately, so as to drive the air control valve core to move to the specified position and keep. For example, common stepper motor drive chip such as DRV8825 can be used. Current sampling circuit: this is a key sensing module, which is coupled (i.e. electrically connected) to the power output of the stepper motor driver or the motor winding loop. It can be a circuit composed of a sampling resistor, an operational amplifier and an analog-to-digital converter (ADC) for high-precision, real-time acquisition of current signals flowing through the stepper motor winding. Its acquisition is the analog value of the current, which is converted into a digital signal for the main control MCU to read. Static holding current value: after the stepper motor drives the air control valve to a certain target opening degree (i.e. the desired valve opening degree, usually set by the main control MCU according to the formula parameters) under the action of the driver, the motor needs to be continuously powered to generate a holding torque to resist the impact force of the airflow on the valve core and other external disturbances, and to stabilize the valve core at this position. At this time, the motor no longer rotates, and the stable current flowing through the winding for maintaining this holding torque is the static holding current value. It is a physical quantity that directly reflects the size of the motor load. Pre-set reference holding current value: this is a reference value stored in the memory (such as the Flash of the main control MCU or the external EEPROM). It represents the normal and standard static holding current value corresponding to the air control valve at a certain specific target opening degree in the ideal state of unobstructed airflow passage. This reference value is measured and stored in advance by experiment or self-learning when the system is healthy and the airflow is unobstructed, providing a comparison standard for subsequent judgment.

[0061] The following describes the implementation:

[0062] First, the main control MCU sends instructions to the stepper motor driver according to the spraying formula, and opens the air control valve to a preset target opening degree. When the valve core reaches the specified position and enters the stable holding state, the current sampling circuit starts to work, which continuously monitors the current of the motor winding and sends the stable current reading (i.e. the static holding current value) to the main control MCU.

[0063] Then, the host MCU calls out the preset reference holding current value corresponding to the current target opening degree from the memory. It compares the real-time collected static holding current value with this reference value, and calculates the offset between them (usually the absolute value or difference of the real-time value minus the reference value).

[0064] Then, the host MCU makes a logical judgment according to this offset. If the offset is very small (for example, within the allowed error range), it indicates that the current airflow passage resistance is normal, and there is no obvious tendency of blockage. At this time, the host MCU does not take additional action, maintains the current target opening degree of the air control valve, and the spraying operation proceeds normally.

[0065] The present embodiment realizes early and forward diagnosis of airflow blockage. Its technical principle lies in that when the powder starts to accumulate in the airflow passage and forms soft blockage, it will cause the cross-sectional area of the passage to become smaller and the airflow resistance to increase. This increased resistance will act on the valve core of the air control valve, trying to change its position. In order to resist this increased resistance and stabilize the valve core at the given target opening degree, the stepper motor needs to output a larger holding torque, and the larger holding torque directly manifests as the increase of the winding static holding current value. Therefore, the offset of the static holding current value becomes a direct and sensitive indicator of the change of airflow resistance. Compared with the prior art scheme of monitoring air pressure (a result-oriented parameter), the present scheme monitors the direct reflection of the cause (resistance change) of air pressure change on the driving element, so the response is faster and more sensitive, and it can perceive the sign of blockage in advance when the airflow flow has not yet decreased significantly and the air pressure has not yet fluctuated significantly, thus gaining valuable time for subsequent compensation action, and fundamentally improving the timeliness and accuracy of control.

[0066] Specifically, the opening compensation signal: this is a control instruction generated by the master MCU after determining that compensation is needed. This signal is essentially a new target position instruction, indicating that the stepper motor driver needs to increase the opening of the pneumatic control valve by a certain amount based on the original target opening. This signal can be a digital quantity or an analog quantity instruction implemented through PWM (pulse width modulation) or other methods. Actual target opening: this is the new control target obtained after compensation calculation. Its value is the sum of the initial target opening and the compensation opening value. The master MCU will use this actual target opening as the new set value to control the stepper motor action. When the master MCU determines that there is a tendency for the airflow passage to be blocked (i.e., the offset exceeds a certain judgment threshold), the master MCU will generate a corresponding opening compensation signal based on the calculated current offset through a certain control algorithm (e.g., proportional control, lookup table method, or fuzzy control). The meaning of this compensation signal is: how much does the pneumatic control valve opening need to be increased to offset the increased airflow resistance due to the blockage, so that the actual airflow flow rate returns to the desired value. Subsequently, the master MCU converts the compensation signal into a driving instruction to control the stepper motor driver to drive the stepper motor, which drives the valve core of the pneumatic control valve to move, increasing the actual target opening of the pneumatic control valve. By increasing the valve opening, the flow area is equivalent to being increased, thereby compensating for the pressure loss caused by the blockage point, so that the airflow flow rate reaching the spray gun can be maintained stable.

[0067] The present embodiment changes passive alarm to active maintenance, realizing real-time closed-loop control of airflow stability. The technical principle is based on the feedforward control idea of disturbance compensation. The system takes the detected current offset (representing airflow resistance disturbance) as input, calculates the control amount (valve opening compensation amount) required to eliminate the disturbance through a pre-set or self-learning controller, and executes it immediately. This forms a fast local closed loop. Unlike the prior art, the entire system no longer waits until the airflow is abnormal before stopping and alarming, but actively attacks and suppresses the disturbance as soon as it appears, so that the controlled quantity (airflow) is always maintained near the set value. This greatly improves the stability and continuity of the spraying process, avoids quality defects such as uneven coating, orange peel, and non-compliance of thickness caused by airflow fluctuations, and reduces the loss of production efficiency caused by frequent stoppage to handle blockage.

[0068] In a preferred embodiment, the step of determining whether the airflow passage has a tendency to be blocked includes the following steps:

[0069] When the offset exceeds the pre-set threshold, it is determined that the airflow passage has a tendency to be blocked;

[0070] Before the step of determining whether the airflow passage has a tendency to be blocked, the following steps are further included:

[0071] Determine the type of airflow currently being controlled, including powder mixing gas and powder feeding gas;

[0072] According to the airflow type, the preset threshold corresponding to the airflow type is matched;

[0073] The preset threshold corresponding to the powder distribution airflow is lower than the preset threshold corresponding to the powder feeding airflow.

[0074] Specifically, airflow types: In electrostatic powder coating, there are at least two functionally different airflows: powder distribution airflow (or atomization airflow): its main function is to fluidize and transport powder from the powder supply bucket to the spray gun, and to preliminarily atomize the powder. This airflow requires stability and gentleness, and excessive fluctuations will directly lead to uneven powder output. Powder feeding airflow (or shaping airflow): its main function is to form a specific shaped powder cloud from the powder reaching the spray gun and push it towards the workpiece. The pressure and flow of this airflow are usually high and are allowed to be adjusted within a certain range to change the shape of the powder cloud and the spraying speed, and its own fluctuation is relatively large. Preset threshold: this is the critical value for determining whether the offset constitutes a "blocking trend". This threshold is not fixed, but is dynamically selected according to the current controlled airflow type.

[0075] Specifically, before making the blocking trend judgment, the main control MCU first needs to determine the current controlled airflow type. This can be determined by querying the current spraying formula parameters being executed, for example, the formula will specify which air path electromagnetic valve or proportional valve leading to the spray gun is currently controlled. Then, the main control MCU matches the preset threshold corresponding to the determined airflow type from a preset reference table or rule. Specifically, the preset threshold corresponding to the powder distribution airflow is set to be lower than the preset threshold corresponding to the powder feeding airflow. Finally, the main control MCU compares the calculated current offset with this matched specific threshold. Only when the offset exceeds this targeted threshold, it is determined that a blocking trend has occurred.

[0076] The embodiment significantly improves the accuracy and reliability of the blockage trend judgment and effectively reduces the false alarm rate. Different air flow circuit processes have different sensitivity and inherent fluctuation characteristics. The powder distribution circuit has very high stability requirements, and a small abnormal fluctuation in its current may mean that the powder is not flowing smoothly, which will affect the coating quality, so a lower and more sensitive threshold is needed to detect abnormalities early. The powder feeding circuit itself has high pressure and flow, and when the gun is switched or the powder block passes through, it will produce inherent and large instantaneous fluctuations, and the current itself has a wider normal fluctuation range. If the same sensitive threshold as the powder distribution gas is used, it will cause the system to frequently false alarm. Therefore, a higher and more relaxed threshold is set for it, which can effectively filter out these inherent normal fluctuations and trigger an alarm only when a truly serious and continuous blockage occurs. This differentiated threshold management strategy makes the blockage diagnosis logic more in line with physical reality and process requirements, and is a key step to achieve intelligent and fine control.

[0077] In a preferred embodiment, before comparing the static holding current value with the preset reference holding current value, the following steps are further included:

[0078] obtaining a preset reference holding current value;

[0079] The step of obtaining a preset reference holding current value includes the following steps:

[0080] Accessing a historical working condition database to obtain a target stage set, the target stage set including a plurality of historical stable spraying stages determined to have no blockage trend, and a static holding current value corresponding to each of the historical stable spraying stages;

[0081] According to the target stage set, the preset reference holding current value is obtained.

[0082] In particular, the historical working condition database: this is a structured data set stored in a non-volatile memory (such as an SD card, EEPROM or MCU built-in Flash). It records the key parameters of the system in the past running time, and each record unit is called a historical stable spraying phase. Each record in the database contains at least: time stamp, ambient temperature, ambient humidity, air control valve target opening degree, and static holding current value collected at this opening degree. In addition, the record is also attached with a "health status" label, marking whether this phase is a stable state judged by the system as "no blocking trend". Target phase set: this is a data subset retrieved from the historical working condition database when performing the benchmark value acquisition task. The set contains a plurality of "historical stable spraying phase" records that meet certain screening conditions, which will be used to calculate the preset benchmark holding current value currently required. Historical stable spraying phase: this refers to the state of the system in the past for a certain period of time, which is in a continuous and stable spraying operation state, and the system self-diagnosis has not found any blocking trend. The data collected in this phase is considered to be a reliable sample of the system in the "healthy" state.

[0083] In particular, when the system needs to obtain the preset benchmark holding current value (for example, after replacing the powder type or periodically calibrating), the host MCU will start the process. First, the host MCU calls the historical working condition database. It initiates a query request to the database, and according to certain screening rules (described later), finds out from the historical data those historical stable spraying phases marked as "no blocking trend". These selected phases make up the target phase set. Then, the host MCU obtains the preset benchmark holding current value according to the target phase set. The specific calculation method can be various, for example, the arithmetic mean, median, or more complex statistical methods (such as the subsequent clustering weighting method) can be taken to all the static holding current values corresponding to the same target opening degree in the set. The value calculated in this way is taken as the preset benchmark holding current value of the current system at the target opening degree, for real-time comparison.

[0084] In a preferred embodiment, before the historical working condition database is called, the following steps are further included:

[0085] Real-time acquisition of the current ambient temperature and the current ambient humidity;

[0086] The step of calling the historical working condition database to obtain the target phase set includes the following steps:

[0087] In the historical working condition database, the historical stable spraying phases whose difference between the historical ambient temperature and the current ambient temperature, and the difference between the historical ambient humidity and the current ambient humidity are within the respective preset tolerance range are screened out;

[0088] If the number of the screened historical stable spraying phases is higher than the preset number threshold, all the historical stable spraying phases are taken as the target phase set.

[0089] Specifically, first, the system acquires the current ambient temperature and the current ambient humidity in real time through the temperature and humidity sensor installed in the control cabinet. The sensor is connected with the main control MCU through the I2C interface. Before calling the historical working condition database, the main control MCU reads the current temperature value (such as 25.3°C) and the humidity value (such as 58%RH). Then, the system sets the preset tolerance range for the temperature and the humidity, respectively. Usually, the temperature tolerance is set to ±1.5°C, and the humidity tolerance is set to ±5%RH. This means that the system will find the historical records in the historical database whose ambient temperature is between 23.8°C and 26.8°C and whose ambient humidity is between 53%RH and 63%RH. The historical working condition database is stored in the W25Q128 Flash chip in a paging storage structure, and each record contains a timestamp, an ambient temperature, an ambient humidity, a target opening, a static holding current value, and a health status flag. The system quickly queries the database through the SPI interface to screen the historical stable spraying phases that meet the conditions. The system sets the preset number threshold to 25. If the number of the screened records that meet the conditions reaches 30, which is higher than the threshold, the system will include all these records in the target phase set. This set will serve as the data basis for the subsequent reference value calculation.

[0090] The present embodiment significantly improves the adaptability of the reference value to environmental changes. Its technical principle is based on the aerodynamic characteristics: the density and viscosity of air will change with the change of temperature and humidity, which directly affects the flow resistance and state of airflow in the pipeline. At a higher temperature, the air density decreases, and the viscosity increases, which will cause the airflow characteristics to change at the same valve opening. Accordingly, the motor holding current required to maintain the opening will also change. By introducing the environmental parameter matching mechanism, the system can automatically select the historical data collected under the most similar current environmental conditions, so that the calculated reference value contains the influence of the actual environmental factors. This method overcomes the defect that the fixed reference value cannot adapt to the influence of seasonal changes, weather changes and other environmental factors. For example, in different environments of high temperature and high humidity in summer and low temperature and dryness in winter, the system will automatically adopt different reference values, ensuring the accuracy of the blockage judgment is not affected by environmental fluctuations.

[0091] In a preferred embodiment, the obtaining of the preset reference holding current value according to the target phase set comprises the following steps:

[0092] Performing cluster analysis on the static holding current values in the target phase set to identify the current value cluster with the most concentrated distribution;

[0093] weighting calculation is performed on data in the current value cluster based on a time decay factor, in which a weight of recent data is higher than a weight of early data;

[0094] multiplying the result of the weighting calculation by a life compensation coefficient corresponding to a cumulative running time of the equipment to obtain the preset reference holding current value.

[0095] Specifically, after obtaining the target stage set, the system first performs clustering analysis on the static holding current values in the set. A DBSCAN algorithm based on density is adopted, and the neighborhood radius is set to 0.5 mA and the minimum sample number is 5. The algorithm can automatically identify the region with the densest data distribution, while excluding outliers caused by measurement noise or transient interference. After identifying the main current value cluster, the system performs time weighting calculation. The time decay factor is set according to an exponential decay law: the data weight within 24 hours is 1.0, the data weight within 24-72 hours is 0.8, the data weight within 72-168 hours is 0.6, and the data weight beyond one week is 0.4. The system performs weighted average calculation on each data point in the cluster according to its time weight to obtain a preliminary reference current value. Finally, the system introduces a life compensation coefficient. The coefficient is calculated according to the cumulative running time of the equipment and stored in the Flash memory of the main control MCU. The calculation formula of the coefficient is: 1 + 0.00001 × running hours. For example, after the equipment runs for 10,000 hours, the life compensation coefficient is 1.1. The system multiplies the weighted average result by the coefficient to obtain the final preset reference holding current value.

[0096] The clustering analysis stage of the embodiment adopts a density-based spatial clustering method, which can effectively identify the internal distribution structure of the data, automatically exclude abnormal data points caused by electromagnetic interference, power fluctuations, etc., and ensure the robustness of the reference value calculation. The time weighting mechanism is based on the principle that "recent data has more reference value", and gives different weights to data at different times through an exponential decay function. This reflects the time-varying nature of the system state, enabling the reference value to track slow changes in the equipment, such as slight deposition of powder in the pipeline, slow wear of mechanical parts, etc. The life compensation coefficient takes into account the overall aging trend of the equipment from a macro perspective. As the running time of the equipment increases, mechanical parts will wear out and electrical characteristics will drift, which will cause changes in the basic parameters of the system. By introducing a compensation coefficient that is positively correlated with the running time, the system can automatically correct this long-term drift and maintain the accuracy of the reference value.

[0097] In a preferred embodiment, after the historical stable spraying stages in which the difference between the historical environment temperature and the current environment temperature and the difference between the historical environment humidity and the current environment humidity are both within the respective preset tolerance ranges are screened out in the historical working condition database, the following steps are further included:

[0098] If the number of the screened historical stable spraying phases is less than or equal to the preset number threshold, a current working condition vector is calculated, the current working condition vector including a current ambient temperature, a current ambient humidity and a current target opening degree;

[0099] A historical working condition vector corresponding to each of the historical stable spraying phases in the historical working condition database is calculated, the historical working condition vector including a historical ambient temperature, a historical ambient humidity and a historical target opening degree;

[0100] A multi-dimensional Euclidean distance between the current working condition vector and each of the historical working condition vectors is calculated, and the first K historical stable spraying phases with the smallest distance are screened out to form the target phase set.

[0101] Specifically, when the system finds that the number of the screened historical stable spraying phases is insufficient (for example, only 15, less than the threshold of 25), the process is started. The system first constructs a current working condition vector, which is a three-dimensional vector containing the current ambient temperature (for example, 28.5°C), the current ambient humidity (for example, 65% RH) and the current target opening degree (for example, 40%). At the same time, the system constructs a corresponding historical working condition vector for each record in the historical database, each vector also containing three dimensions of historical ambient temperature, historical ambient humidity and historical target opening degree. The system uses the Min-Max normalization method to standardize each dimension, eliminating the influence of dimension. Then, the system calculates the multi-dimensional Euclidean distance between the current working condition vector and each historical working condition vector. The system selects the first K historical records (usually K=20) with the smallest Euclidean distance, which represent the historical data closest to the current condition in the comprehensive working condition, and forms a new target phase set from them, which is used for subsequent benchmark value calculation.

[0102] The traditional environment matching only considers two dimensions of temperature and humidity, while the present scheme innovatively introduces the target opening degree as the third dimension. This is because under different process requirements, the working point of the pneumatic valve is different, and the corresponding current characteristics also differ. The process parameters and the environmental parameters together form a feature vector, making the similarity matching more comprehensive and accurate. The Euclidean distance as a similarity measure can well reflect the overall closeness of two working conditions in the three-dimensional feature space. The smaller the distance, the more similar the two working conditions, and the closer the corresponding current characteristics. This method is more delicate and scientific than simple threshold judgment. Through this multi-dimensional similarity matching, the system can find the "most similar" reference data when there is no completely matched historical data, realizing the maximum utilization of data. Especially in the early stage of device operation or when encountering rare environmental conditions, this mechanism can ensure that the system can still provide reasonable benchmark values, greatly enhancing the applicability and robustness of the system.

[0103] In a preferred embodiment, the following steps are further included:

[0104] a compensation event sequence is recorded and constructed, the compensation event sequence comprising a plurality of compensation events, each of the compensation events comprising: a compensation time, a static holding current offset before compensation, and a compensation opening degree value applied to eliminate the offset;

[0105] a time series pattern analysis is performed on the compensation event sequence within a first preset time window, a compensation event occurrence frequency and / or a compensation opening degree value change trend over time are identified as a clogging development pattern;

[0106] based on the clogging development pattern, a remaining time or a remaining spraying work amount required for the gas path system to reach a critical state requiring cleaning and maintenance is predicted;

[0107] when the remaining time is lower than a first preset time length, or the remaining spraying work amount is lower than a first preset work amount, a predictive maintenance prompt is generated.

[0108] Specifically, the system records a compensation event each time the compensation operation is performed. Each event contains four elements: compensation time (time stamp accurate to milliseconds), static holding current offset before compensation, actual compensation opening degree value applied, and current target opening degree. These data are stored in the form of a structure in a circular buffer. The system sets the first preset time window to 8 hours, and performs a time series pattern analysis on the compensation event sequence within the window every 1 hour. The analysis mainly focuses on the change trends of two indicators: one is the compensation event occurrence frequency, i.e. the number of compensations per unit time; the other is the compensation strength, i.e. the opening degree value of each compensation on average. The system uses a linear regression algorithm to analyze the trends of these two indicators. For the compensation frequency, the slope of its change over time is calculated; for the compensation strength, the growth trend is also analyzed. Based on these trend analyses, the system establishes a simple prediction model to estimate the remaining time required for the gas path system to reach a critical state (such as the compensation opening degree reaching the maximum value or the compensation frequency exceeding the allowed upper limit). When the predicted remaining time is lower than the first preset time length (such as 2 hours), the system generates a three-level warning information through the human-machine interface, and sends a predictive maintenance request to the MES system through the industrial Ethernet, prompting the maintenance personnel to arrange the gas path system cleaning.

[0109] The embodiment considers that the compensation event sequence is essentially a quantitative record of the effort the system has to make to maintain normal function. When powder accumulation starts to occur in the pneumatic system, the system needs to maintain stable airflow by more and more frequent and large compensation. The change rule of this compensation behavior accurately reflects the degradation process of the system health state. Through time series pattern analysis, the system can capture early signals of this degradation. The increase in compensation frequency reflects the speed of clogging development, while the increase in compensation strength reflects the severity of clogging. These two indicators together depict the complete degradation trajectory of the system health state. Based on the trend extrapolation of historical data, the system can predict the time to reach the maintenance critical point, providing a scientific basis for planned maintenance. This predictive maintenance mode, compared with traditional regular maintenance or post-failure maintenance, not only avoids the waste of resources caused by over-maintenance, but also prevents production interruption caused by sudden failure, achieving the optimal balance between maintenance cost and production efficiency.

[0110] In a preferred embodiment, after the step of controlling the stepper motor driver to increase the actual target opening of the pneumatic control valve, the following steps are further included:

[0111] In the second preset time window, the static holding current value is continuously monitored;

[0112] If the offset of the static holding current value does not decrease or continues to increase, it is determined to be an irreversible clogging, and a system alarm is triggered and a safety shutdown process is executed.

[0113] Specifically, after performing the compensation operation, the system starts a second preset time window (usually set to 30 seconds). During this period, the main control MCU continuously monitors the static holding current value through the current sampling circuit, and the sampling frequency remains 1 kHz, ensuring that rapid changes in current can be captured. The system calculates the trend of current offset once every second. If it is found that the offset does not decrease or continues to increase after compensation, the system will make a second judgment. At the same time, the system will check whether the actual target opening of the pneumatic control valve has reached the maximum safety opening (usually 90% of the rated opening) preset by the system. When the following two conditions are met at the same time, the system determines that it is an irreversible clogging:

[0114] In the second preset time window, the offset of the static holding current value is reduced by less than 10% or continues to increase by more than 5% compared to before compensation;

[0115] The actual target opening of the pneumatic control valve has reached the maximum safety opening.

[0116] Once the un-recoverable blockage is determined, the system immediately triggers the highest level of fault alarm. The alarm signal is sent out through multiple channels simultaneously: the local audible and visual alarm emits continuous beeping and red flashing; the human-machine interface displays the warning information "serious blockage, stop immediately"; at the same time, an emergency stop signal is sent to the central monitoring system through the industrial Ethernet.

[0117] The safe shutdown process is executed according to the predetermined safety interlocking sequence: first, the total air inlet solenoid valve is cut off, then the high-voltage generator output is turned off within 100 ms, and finally all pumps and transmission devices are stopped. The entire shutdown process is completed within 500 ms, ensuring that the system quickly enters a safe state.

[0118] In a preferred embodiment, after completing a spraying cycle, the coating quality detection result of the workpiece in the cycle is obtained, and the coating quality detection result includes a coating thickness uniformity index;

[0119] The coating quality detection result is associated with the fluctuation of the recorded static holding current value in the same cycle for analysis;

[0120] If the coating thickness uniformity index does not meet the standard, and analysis shows that it has a strong correlation with the static holding current fluctuation at a specific target opening, the value corresponding to the target opening in the preset reference holding current value is adjusted to make the static holding current fluctuation at the target opening tend to be stable in subsequent spraying.

[0121] Specifically, after completing a spraying cycle (such as a shift or a batch of workpieces), the system obtains the coating quality detection result by the following way:

[0122] For online detection systems, coating thickness data is automatically collected by a thickness gauge installed at the end of the production line; for offline detection, after manual measurement using a handheld thickness gauge, the data is input into the system through an RS485 interface. The system calculates the coating thickness uniformity index, usually using the standard deviation or range of thickness distribution as the evaluation index. At the same time, the system extracts all static holding current values recorded during the same spraying period from the historical database, including characteristic parameters such as fluctuation range and frequency. The system uses correlation analysis (such as Pearson correlation coefficient calculation) to correlate the coating quality detection results with the fluctuation of static holding current. The analysis process focuses on the correlation between current fluctuation and coating uniformity within a specific target opening interval (such as the 30%-50% opening range). When the coating thickness uniformity index is found to be substandard (such as a thickness range exceeding the standard value of 15μm), and the correlation analysis shows a strong correlation between it and the static holding current fluctuation at a specific target opening (correlation coefficient greater than 0.7), the system initiates the reference value adjustment program. The adjustment method uses gradual optimization: first, calculate the deviation of the current reference value from the ideal value, then adjust the value corresponding to the target opening in the preset reference holding current value by no more than 5% each time. The adjusted reference value will be applied to subsequent spraying operations, and the system will continuously monitor the adjustment effect. If the effect is not ideal, continue to fine-tune until the current fluctuation stabilizes and the coating quality meets the standards.

[0123] Specifically, in the powder coating process, airflow stability is a key process parameter that affects coating quality, but it is not the only factor. Powder characteristics, environmental conditions, workpiece geometry, and other factors can affect the final coating quality. Traditional control methods only focus on the stability of process parameters, while this scheme innovatively takes the final product quality as the control target. Through correlation analysis, the system can automatically identify the key process parameters that have the greatest impact on product quality and their control range. When it is found that the current fluctuation at a specific target opening is highly correlated with coating uniformity, it indicates that this working point is a key control point that affects quality. By adjusting the reference current value at this point, the system is actually optimizing the most sensitive area of the entire control curve.

[0124] In this paper, specific examples are used to illustrate the principles and implementation of the application. The above examples are only used to help understand the method and its core idea. The above description is only the preferred embodiment of the application. It should be noted that due to the limitations of language expression, there are infinitely many specific structures, and for ordinary technical personnel in this technical field, without departing from the principles of the application, some improvements, refinements, or changes can be made, or the above technical features can be combined in an appropriate way; these improvements, refinements, changes, or combinations, or the application of the inventive concept and technical solution to other occasions without improvement, shall be regarded as the protection scope of the application.

Claims

1. A method for real-time compensation of airflow stability in electrostatic powder coating, characterized in that: This method is based on a real-time compensation device for airflow stability in electrostatic powder coating. The device includes a main control MCU, a pneumatic control valve, a stepper motor driver that drives the pneumatic control valve, and a current sampling circuit coupled to the stepper motor driver for real-time acquisition of the stepper motor winding current. The method includes the following steps: After the pneumatic control valve opens to the target opening degree and enters the holding state, its static holding current value is obtained through the current sampling circuit; The static holding current value is compared with a preset reference holding current value, which corresponds to the holding current required for the target opening when the airflow channel is unobstructed. Based on the offset of the static holding current value relative to the reference holding current value, it is determined whether the airflow channel shows a tendency to become blocked; If not, maintain the current target opening degree of the pneumatic control valve; If so, a corresponding opening compensation signal is generated based on the offset, and the stepper motor driver is controlled to increase the actual target opening of the pneumatic valve to counteract the decrease in airflow caused by the blockage trend.

2. The real-time compensation method for airflow stability in electrostatic powder coating according to claim 1, characterized in that: The process of determining whether the airflow channel shows signs of blockage includes the following steps: When the offset exceeds a preset threshold, it is determined that the airflow channel is showing signs of blockage. Before determining whether the airflow channel shows signs of blockage, the following steps are also included: Determine the type of airflow currently being controlled, whereby the airflow type includes powder distribution gas and powder delivery gas; Based on the airflow type, match the preset threshold corresponding to the airflow type; Wherein, the preset threshold corresponding to the powder dispensing gas is lower than the preset threshold corresponding to the powder delivery gas.

3. The real-time compensation method for airflow stability in electrostatic powder coating according to claim 1, characterized in that: Before comparing the static holding current value with the preset reference holding current value, the following steps are also included: Obtain the preset reference holding current value; The process of obtaining the preset reference holding current value includes the following steps: The historical operating condition database is retrieved to obtain a target stage set, which includes multiple historical stable spraying stages with a determined non-blocking trend, and the static holding current value corresponding to each historical stable spraying stage. The preset reference holding current value is obtained based on the target stage set.

4. The real-time compensation method for airflow stability in electrostatic powder coating according to claim 3, characterized in that: Before retrieving the historical operating condition database, the following steps are also included: Real-time acquisition of current ambient temperature and humidity; The process of retrieving the historical operating condition database to obtain the target stage set includes the following steps: In the historical operating condition database, historical stable spraying stages are selected where the difference between the historical ambient temperature and the current ambient temperature, and the difference between the historical ambient humidity and the current ambient humidity are both within their respective preset tolerance ranges. If the number of the selected historical stable spraying stages is higher than a preset threshold, then all the historical stable spraying stages are combined to form the target stage set.

5. The real-time compensation method for airflow stability in electrostatic powder coating according to claim 3, characterized in that: The step of obtaining the preset reference holding current value based on the target stage set includes the following steps: Cluster analysis is performed on multiple static holding current values ​​in the target stage set to identify the most concentrated cluster of current values. The data in the current value cluster are weighted based on a time decay factor, wherein the weight of recent data is higher than that of earlier data. The weighted result is multiplied by the life compensation coefficient corresponding to the cumulative running time of the equipment to obtain the preset reference holding current value.

6. The real-time compensation method for airflow stability in electrostatic powder coating according to claim 4, characterized in that: After selecting historical stable spraying stages from the historical operating condition database where the difference between historical ambient temperature and current ambient temperature, and the difference between historical ambient humidity and current ambient humidity are all within their respective preset tolerance ranges, the process further includes the following steps: If the number of the selected historical stable spraying stages is less than or equal to the preset number threshold, then the current working condition vector is calculated, which includes the current ambient temperature, the current ambient humidity, and the current target opening. Calculate the historical operating condition vector corresponding to each historical stable spraying stage in the historical operating condition database. The historical operating condition vector includes historical ambient temperature, historical ambient humidity, and historical target opening. Calculate the multidimensional Euclidean distance between the current working condition vector and each of the historical working condition vectors, and select the top K historical stable spraying stages with the smallest distance to form the target stage set.

7. The real-time compensation method for airflow stability in electrostatic powder coating according to claim 1, characterized in that: It also includes the following steps: Record and construct a compensation event sequence, the compensation event sequence including multiple compensation events, each of the compensation events including: compensation time, static holding current offset before compensation, and compensation opening value applied to eliminate the offset; Time-series pattern analysis is performed on the sequence of compensation events within the first preset time window to identify the changing trends of the frequency of occurrence of compensation events and / or the compensation opening value over time, as a congestion development pattern. Based on the blockage development pattern, predict the remaining time or remaining spraying workload required for the gas system to reach a critical state requiring cleaning and maintenance. When the remaining time is less than the first preset duration, or the remaining spraying workload is less than the first preset workload, a predictive maintenance prompt is generated.

8. The method for real-time compensation of airflow stability in electrostatic powder coating according to claim 1, characterized in that: After controlling the stepper motor driver to increase the actual target opening degree of the pneumatic control valve, the following steps are also included: Within the second preset time window, the static holding current value is continuously monitored; If the offset of the static holding current value does not decrease or continues to increase, it is determined to be an irreversible blockage, triggering a system alarm and executing a safety shutdown procedure.

9. The method for real-time compensation of airflow stability in electrostatic powder coating according to claim 1, characterized in that: After completing a spraying cycle, the coating quality inspection results of the workpiece within that cycle are obtained, and the coating quality inspection results include coating thickness uniformity indicators. The coating quality test results are correlated with the fluctuation of the static holding current value recorded within the same period; If the coating thickness uniformity index fails to meet the standard, and analysis shows that it has a strong correlation with the static holding current fluctuation under a specific target opening, then the value of the preset reference holding current corresponding to the target opening is adjusted so that the static holding current fluctuation of subsequent spraying under the target opening tends to be stable.

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