PI control method and device based on observation compensation for laser soldering, controller and program product

Abstract

The invention provides a PI control method and device for laser soldering based on observation compensation, a controller and a program product, and the method comprises the steps: building a laser soldering thermodynamic model containing a thermal disturbance term based on a lumped parameter method, and constructing a state-space equation; designing a state observer based on the state-space equation, and estimating a state variable of the state-space equation and external disturbance acting on the state variable in real time; calculating a feedforward control quantity according to a target temperature curve and the thermodynamic model, calculating a compensation control quantity according to a disturbance value estimated by an observer, and calculating a PI control quantity according to the deviation between the output temperature and the target temperature to obtain a total control quantity; and in each sampling period, the total control quantity is dynamically adjusted according to the deviation between the current welding spot temperature and the target temperature, so that the temperature error tends to zero. According to the method, the disturbance observation technology and the feedforward-PI control are combined, and high-precision and high-robustness control over the welding temperature is achieved.

Description

Technical Field

[0001] This application relates to the field of welding control technology, and in particular to a PI control method, device, central controller, and computer program product based on observation compensation for laser soldering. Background Technology

[0002] Laser soldering technology, due to its characteristics of localized heating, rapid response, and small heat-affected zone, has become a key process in the field of microelectronic packaging. This technology uses a high-energy laser beam to precisely heat the solder joint, melting the solder and forming a reliable connection, offering irreplaceable advantages in the manufacture of precision devices such as integrated circuits and sensors. However, temperature control faces significant challenges in actual soldering processes: First, the thermal dynamics of the soldering system are complex, influenced by a combination of factors including solder paste material properties (such as absorptivity and specific heat capacity), environmental conditions (such as air convection and radiative heat dissipation), and process parameters (such as laser power and spot size). Second, significant time-varying disturbances exist during soldering, particularly the dynamic heat absorption effect of the ground plane, which introduces unpredictable temperature fluctuations. While traditional PID control methods are simple in structure, they struggle to handle these complex dynamic characteristics, often exhibiting problems such as large overshoot and long settling times, failing to meet the process requirements of high-precision soldering.

[0003] To improve control performance, existing technologies mainly employ two types of improvement schemes: one is model-based feedforward control, which predicts the required laser power by establishing a thermodynamic model. However, its control effect is heavily dependent on the accuracy of the model, and in practical applications, performance often degrades due to time-varying parameters or lack of dynamic modeling. The other is adaptive control, which can adjust controller parameters online to adapt to system changes, but its response speed to sudden disturbances is insufficient. More importantly, these methods do not systematically consider the influence of external disturbances such as heat absorption by the ground plane, leading to a significant increase in temperature control deviation under long-term welding or high-power conditions. Therefore, there is an urgent need for a new control method that can observe and compensate for external disturbances in real time, while taking into account both dynamic response speed and steady-state accuracy. This is precisely the core problem that this invention aims to solve. Summary of the Invention

[0004] The purpose of this application is to provide a PI control method, device, central controller, and computer program product based on observation compensation for laser soldering, thereby solving the aforementioned problems existing in the prior art.

[0005] To achieve the above objectives, the technical solution adopted in this application is as follows: This application provides, in one aspect, an observation-compensated PI control method for laser soldering, the method comprising: A thermodynamic model for laser soldering, including thermal disturbance terms, is established based on the lumped parameter method. Construct the state-space equations of the thermodynamic model; A state observer is designed based on the state space equation, and the state variables of the state space equation and the external disturbances acting on them are estimated in real time by configuring the observer gain matrix. The feedforward control quantity is calculated based on the target temperature curve and the thermodynamic model. The compensation control quantity is calculated based on the disturbance value estimated by the observer. The PI control quantity is calculated based on the deviation between the output temperature and the target temperature. The three are summed to obtain the total control quantity. In each sampling cycle, the total control quantity is dynamically adjusted based on the deviation between the current solder joint temperature and the target temperature, so that the solder joint temperature tracks the target temperature and the temperature error approaches zero.

[0006] Optionally, within each sampling period k, first calculate the feedforward control quantity and the compensation control quantity at time k+1; then calculate the PI control quantity at time k+1 based on the temperature error at time k; finally, sum the three to obtain the total control quantity at time k+1.

[0007] Optionally, the thermodynamic model for laser soldering is:

[0008] in, ρ For solder paste density, c This refers to the specific heat capacity of the solder paste. V Where P is the volume of solder paste and P is the laser power. α The absorption rate of the solder paste to the laser. A The surface area of ​​the solder paste. h The surface heat transfer coefficient, T 0 represents the ambient temperature. T p The ground temperature. c p The specific heat capacity of the grounding plate. m p For the quality of the flooring, T The temperature of the solder joint; To simplify the subsequent formula expression, define , , The grounding model is then rewritten as: .

[0009] Optionally, constructing the state-space equations of the thermodynamic model includes: rewriting the rewritten grounded model into state-space equations, expressed as:

[0010] in, x ( t )= T- T 0 is a state variable. u ( t )= P For laser control quantity, This indicates the impact of grounding disturbance.

[0011] Optionally, the expression for the observer is:

[0012] in, It is a state variable x ( t The estimated value of ); L It is the observer gain matrix, used to adjust the convergence speed of the estimation error; It is the state estimation error, which is corrected by feedback of the observer's output; It is the rate of change of disturbance. The estimated value.

[0013] Optionally, the formula for calculating the total control quantity is as follows: u = u ff + u pi + u c in, u The overall control formula for the system is as follows: u ff This is the feedforward control quantity. u pi For PI control, u c It is an observer-based compensation control quantity; Feedforward control quantity u ff ( k The expression is as follows:

[0014] in, , To identify parameters for the model, A The surface area of ​​the solder paste. m For solder paste quality, T s The sampling period is T0, where T0 is the ambient temperature. T tar ( k )for k The target temperature at any given time; PI control quantity u pi ( kThe expression is as follows:

[0015] in, e ( k )= T tar ( k )- T ( k The current temperature error is represented by ( ). k p and k I These are the proportional and integral gains, respectively. It is the cumulative term of the error; Compensation control quantity of the observer u c The expression is as follows:

[0016] in, α The absorption rate of the solder paste to the laser. T p The ground temperature. c p The specific heat capacity of the grounding plate. m p For the quality of the flooring.

[0017] Optional, the observer's compensation control quantity u c The derivation of the expression is as follows: According to the state-space equations of the thermodynamic model, the disturbance compensation term is used to offset the grounding disturbance. T p ( t The impact on the system, and the expression for the disturbance cancellation condition are as follows:

[0018] in, u c ( t ) indicates the compensation control quantity; according to , Derive the compensation control quantity u c The expression is as follows:

[0019] The discretized expression for the compensation control quantity obtained by discretization is as follows:

[0020] in, T p (k ) is the current time disturbance value estimated by the observer.

[0021] This application also provides an observation-compensated PI control device for laser soldering, the device comprising: The model building module is used to establish a laser soldering thermodynamic model that includes thermal disturbance terms based on the lumped parameter method. The space equation construction module is used to construct the state-space equations of the thermodynamic model. The observer design module is used to design a state observer based on the state space equation, and to estimate the state variables of the state space equation and the external disturbances acting on them in real time by configuring the observer gain matrix; The total control quantity calculation module is used to calculate the feedforward control quantity based on the target temperature curve and the thermodynamic model, calculate the compensation control quantity based on the disturbance value estimated by the observer, calculate the PI control quantity based on the deviation between the output temperature and the target temperature, and sum the three to obtain the total control quantity. The adjustment module is used to dynamically adjust the total control quantity in each sampling cycle based on the deviation between the current solder joint temperature and the target temperature, so that the solder joint temperature tracks the target temperature and the temperature error tends to zero.

[0022] This application also provides a central controller, which includes: a feedforward controller, a PI controller, an observer equipped with a compensator, and a summing controller. The feedforward controller is used to calculate a feedforward control quantity based on the target temperature curve and the thermodynamic model. The observer is used to calculate a compensation control quantity based on the disturbance value estimated by the observer. The PI controller is used to calculate a PI control quantity based on the deviation between the output temperature and the target temperature. The summing controller sums the three to obtain a total control quantity.

[0023] In another aspect, this application provides a computer program product, including a computer program that, when executed by a processor, implements the steps of the method described above.

[0024] The beneficial effects of this application are: This application's observation-compensated PI control method addresses the problem of insufficient temperature control accuracy caused by external thermal disturbances, particularly dynamic heat absorption by the ground plane; control mismatch resulting from time-varying model parameters such as absorptivity and heat transfer coefficient varying with temperature in traditional feedforward control; and the difficulty of simultaneously meeting the contradictory requirements of rapid dynamic response and high steady-state accuracy in existing control methods. This application's method innovatively combines disturbance observation technology with feedforward-PI control, effectively solving the above problems and achieving high-precision, robust control of welding temperature. Attached Figure Description

[0025] Figure 1This is a schematic diagram of a PI control method based on observation compensation for laser soldering provided in this application; Figure 2 This is a schematic diagram of the calculation process of the total control quantity in a PI control method based on observation compensation for laser soldering provided in this application; Figure 3 After adopting the observation-compensated PI control method of this application, the pad radius is 2×10. -3 Comparison of the target temperature curve and the simulation curve for m; Figure 4 The pad radius is 2×10 -3 Power comparison curves of the PI control method with observation compensation proposed in this application and the adaptive backstepping sliding control method (ABSMC-NDO) based on nonlinear disturbance observer at m; Figure 5 The pad radius is 2×10 -3 Temperature error comparison curves between the PI control method with observation compensation proposed in this application and the adaptive backstepping sliding control method (ABSMC-NDO) based on nonlinear disturbance observer at m; Figure 6 This is a schematic diagram of a PI control device based on observation compensation for laser soldering provided in this application; Figure 7 This is a schematic diagram of the method flow for the central controller provided in this application. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0027] This application addresses three key issues in laser soldering temperature control: first, insufficient temperature control accuracy due to external thermal disturbances (especially dynamic heat absorption by the ground plane); second, control mismatch caused by time-varying model parameters (such as absorptivity and heat transfer coefficient changing with temperature) in traditional feedforward control; and third, the inability of existing control methods to simultaneously meet the contradictory requirements of rapid dynamic response and high steady-state accuracy. This application innovatively combines disturbance observation technology with feedforward-PI control, effectively solving these problems and achieving high-precision, robust control of the soldering temperature.

[0028] like Figure 1 As shown, this application proposes an observation-compensated PI control method for laser soldering, the method comprising: Step S100: Establish a laser soldering thermodynamic model that includes thermal disturbance terms based on the lumped parameter method.

[0029] In step S100 of this application, when the solder paste is heated by laser, the internal thermal resistance of the solder paste is much smaller than the surface thermal resistance. Therefore, the internal temperature of the solder paste tends to be uniform at any given moment, so that the entire soldering material can be considered to be at the same temperature at the same instant. The temperature to be solved is then a univariate function of time t and is independent of spatial coordinates. It is assumed that the previously continuously distributed mass and heat capacity of the material are concentrated at a single point, resulting in only one temperature value. Based on this simplified analysis that ignores the internal thermal resistance of the object—the lumped parameter method—a thermodynamic model is established for the laser heating process. Based on the lumped parameter method, a thermodynamic model including a grounding thermal disturbance term is established, also known in the art as a grounding model. The grounding model uses laser power as input and solder joint temperature as output, establishing an input-output relationship.

[0030] Based on the grounding model: (1) in, ρ For solder paste density, c This refers to the specific heat capacity of the solder paste. V Where P is the volume of solder paste and P is the laser power. α The absorption rate of the solder paste to the laser. A The surface area of ​​the solder paste. h The surface heat transfer coefficient, T 0 represents the ambient temperature. T p The ground temperature. c p The specific heat capacity of the grounding plate. m p For the quality of the flooring, T Let be the solder joint temperature. To simplify subsequent formula expressions, define . , , The grounding model is then rewritten as: (2) Step S200: Construct the state-space equations of the thermodynamic model.

[0031] Construct the state-space equations of the system, transform the thermodynamic model into a state-space expression, and construct the state-space equations of the thermodynamic model.

[0032] The rewritten grounding model is converted into a state-space equation, expressed as follows:

[0033] in, x ( t )=T - T 0 represents a state variable, indicating the degree of overheating of the solder joint temperature relative to the ambient temperature. u ( t )= P For laser control quantity, This indicates the impact of grounding disturbance.

[0034] Step S300: Design a state observer based on the state space equation, and estimate the state variables of the state space equation and the external disturbances acting on it in real time by configuring the observer gain matrix.

[0035] It should be noted that in step S300, a state observer is designed, and the real-time estimation of the state variables of the state-space equation system and the external disturbances acting upon them is achieved by configuring the observer gain matrix. That is, the real-time estimation of the solder joint temperature state and external thermal disturbances. The external disturbances are the effects caused by changes in the ground plane temperature.

[0036] The derivative of the output state estimate of the observer design as follows: (4) in, It is a state variable x ( t The estimated value of ); L It is the observer gain matrix, used to adjust the convergence speed of the estimation error; It is the true rate of change; It is the state estimation error, which is corrected by feedback of the observer's output; It is the rate of change of disturbance. The estimated value. Gain matrix. L The design method is based on Lyapunov stability theory. The core principle is to ensure that the dynamic system with state estimation error can quickly and globally asymptotically converge to zero.

[0037] Step S400: Calculate the feedforward control quantity based on the target temperature curve and the thermodynamic model, calculate the compensation control quantity based on the disturbance value estimated by the observer, calculate the PI control quantity based on the deviation between the output temperature and the target temperature, and sum the three to obtain the total control quantity.

[0038] It should be noted that the feedforward control, compensation control, and PI control are obtained through corresponding calculation formulas. Specifically, the feedforward control formula is derived based on a thermodynamic model, the PI control formula is obtained based on the error signal, and the compensation control formula is obtained through a state observer. The sum of these three control formulas is the total control formula of the system, which is used to control the actual temperature to track the target temperature. Among these, observation compensation is the core innovation: this is not a simple feedback correction. It uses a state observer to estimate in real time the unmeasurable internal state (solder joint temperature) and the impact of external disturbances (grounding plate temperature changes) from the measurable laser power and output temperature. This is a form of "soft measurement" and "disturbance prediction," providing crucial information for subsequent feedforward compensation.

[0039] like Figure 2 As shown, within each sampling period k, the feedforward control quantity and the compensation control quantity at time k+1 are first calculated; then the PI control quantity at time k+1 is calculated based on the temperature error at time k; finally, the three are summed to obtain the total control quantity at time k+1.

[0040] The grounding model for laser soldering is implemented using observation-compensated PI control, based on the objective function. T tar Find k Output power of the time feedforward controller u ff ( k Then, based on the deviation between the output and the target... e ( k )beg k Output power of the PI controller at any time u pi ( k ), by observing the disturbance T p ( k Design compensation control quantity u c ( k Completely negate its interference with the system. u pi ( k ), u ff ( k )and u c ( k Summing up yields the total control input:

[0041]

[0042]

[0043] in, , To identify parameters for the model, A The surface area of ​​the solder paste. m For solder paste quality, T s The sampling period is T0, where T0 is the ambient temperature. u pi ( k )for k The output power (W) of the PI controller at any given time. u ff ( k Let be the output power (W) of the feedforward controller at time k. u c ( k )for k The output power (W) of the constant compensation controller is adjusted. e ( k (This is for heating) k Temperature error at any given time (°C) k p , k I These are the proportional coefficient and the integral coefficient, respectively.

[0044] The formula for calculating the total control quantity in this application consists of three parts, as follows: u = u ff + u pi + u c (5) in, u The overall control formula for the system is as follows: u ff This is the feedforward control quantity. u pi For PI control, u c This is the observer-based compensation control variable. The target temperature is defined as... T tar , in equation (2) T Replace with target temperature T tar If we disregard grounding disturbance, then Equation 2 becomes: From this, we can derive Formula 6, and the calculation formula for the feedforward control quantity can be recursively derived as follows: (6) Equation (6) is discretized to obtain the discrete expression of the feedforward control quantity:

[0045] PI control is used to eliminate steady-state errors and ensure that the temperature accurately tracks the target value. The PI control variable consists of a proportional term and an integral term. (7) in, e ( k )= T tar ( k )- T ( k The current temperature error is represented by ( ). k p and k I These are the proportional and integral gains, respectively. It is the cumulative term of the error, used to eliminate static error.

[0046] The disturbance compensation term is used to offset grounding disturbances. T p ( t The disturbance cancellation condition expression for the influence on the temperature control system of laser soldering equipment is as follows: (8) in, u c ( t ) represents the compensation control quantity over continuous time.

[0047] According to formula (8) and , The compensation control quantity can be derived. u c The expression: (9) Equation (9) is discretized to obtain the discrete expression of the compensation control quantity: (10) in, T p ( k ) is the current time disturbance value estimated by the observer.

[0048] The feedforward control is used to provide the main laser power in advance according to the target temperature curve, improving the system's dynamic response. The PI control is used to adjust according to the real-time temperature error signal to eliminate steady-state error and ensure control accuracy. The disturbance compensation control is used to generate a control quantity based on the disturbance value estimated by the state observer to actively counteract the effects of external thermal disturbances.

[0049] like Figure 2As shown, the feedforward control quantity, compensation control quantity, and PI control quantity are respectively generated by the feedforward controller, the observer-based compensator, and the PI controller. The PI controller calculates the PI control quantity based on the deviation between the target temperature and the output temperature; the feedforward PI controller calculates the feedforward control quantity based on the target temperature function; the observer calculates the compensation control quantity based on the thermal disturbance of the ground plane. Specifically, the observer, based on the laser power and the measured solder joint temperature, estimates in real time those quantities that cannot be directly measured or disturbed, namely the state variables and the total external disturbance, through the internally embedded state-space equation, and calculates the compensation control quantity accordingly. The three control quantities are then combined and input to the output solder joint temperature of the laser welding system. The laser welding system includes: optical lenses and fiber optic lamps, a PCB board with solder paste and a ground plane, etc. The thermal disturbance of the ground plane is the main external disturbance affecting the output of this system. The standard configuration in the field of laser soldering is: a laser generates a beam that is precisely irradiated onto the solder paste area on the PCB board through a transmission path composed of optical lenses and fiber optic lamps, while the ground plane is a common basic component in PCB assembly used to provide electrical reference ground and heat dissipation. This overall framework is a common and mature technology platform in the industry, and its core components (such as the laser generation and focusing system, the worktable, and the temperature monitoring unit) have been widely adopted in existing technologies and commercial equipment.

[0050] Step S500: In each sampling period, the total control quantity is dynamically adjusted according to the deviation between the current solder joint temperature and the target temperature, so that the solder joint temperature tracks the target temperature and the temperature error approaches zero.

[0051] In each sampling cycle, based on the target temperature and the solder joint temperature measured in the current cycle, the control input value for the current cycle is calculated using the total control quantity calculation formula in step S400. This is used to control the error between the solder joint temperature and the target temperature, so that the temperature error eventually tends to 0. All three variables are adjusted, but with different change mechanisms: the feedforward control quantity changes only with the target temperature curve; the PI control quantity changes only with the current temperature error, aiming to eliminate steady-state error; the compensation control quantity changes with the disturbance value estimated by the observer; and the total control quantity changes dynamically in each cycle.

[0052] The temperature control method for laser soldering equipment in this application adopts a PI control strategy based on observation compensation. It establishes a thermodynamic state-space model including thermal disturbance terms, designs a state observer to estimate unmeasurable thermal disturbances of the solder pads in real time, and constructs a composite control quantity based on this estimate. The control method consists of three parts: feedforward control, PI feedback control, and disturbance compensation control. Feedforward control predicts the required laser power based on the target temperature curve; PI feedback control eliminates steady-state errors; and disturbance compensation control actively counteracts the influence of thermal disturbances of the solder pads. Through real-time estimation and compensation of the state and disturbances of the laser soldering temperature control system by the observer, the model's description accuracy and the control system's anti-interference capability are significantly improved. While ensuring control accuracy, the method exhibits strong robustness to system parameter changes and unknown disturbances, effectively reducing the error between the solder joint temperature and the target temperature. It is also simple to implement, has a fast response, and is suitable for precise temperature control of laser soldering equipment.

[0053] Based on a thermodynamic model of the laser soldering heating process established using the lumped parameter method, a state observer capable of estimating disturbances in real time is designed to address external disturbances such as thermal disturbances at the welding surface. The observation results are then used to calculate the compensation control quantity. The total control quantity is decomposed into three parts: a model-based feedforward control quantity, a PI control quantity for eliminating steady-state errors, and a compensation control quantity for offsetting external disturbances. The compensation control quantity is dynamically adjusted based on the disturbance estimate output by the observer. To further improve control accuracy, the observer gain parameter is designed based on Lyapunov stability theory to ensure rapid convergence of the disturbance estimation error. Experiments and simulations confirm that the control scheme can effectively compensate for the thermal disturbance effects during laser soldering. Compared with the adaptive backstepping sliding mode control algorithm (ABSMC-NDO) based on a nonlinear disturbance observer, the control method described in this application has higher control accuracy and performance.

[0054] like Figure 3 As shown, the simulated temperature curve of the method in this application highly overlaps with the target temperature curve, achieving accurate tracking in all stages of preheating, activation, reflux, and cooling, with minimal maximum deviation. This indicates that the method can effectively overcome the influence of model nonlinearity and external thermal disturbances, significantly improving temperature control accuracy.

[0055] like Figure 4 As shown, compared with the traditional ABSMC-NDO method, the laser power output curve of the method in this application is smoother and free of high-frequency jitter, indicating that its control quantity calculation is more robust, avoiding over-adjustment and actuator wear, while reducing energy loss and improving system operation stability and lifespan.

[0056] like Figure 5As shown, the temperature error curve of the method in this application fluctuates much less than that of the ABSMC-NDO method, and its absolute error value remains at a low level (close to 0°C) throughout the process, especially in the later stages of welding when disturbances are significant. This proves that its observer-based disturbance compensation mechanism can effectively estimate and offset external disturbances (such as changes in grounding plate temperature) in real time, and has strong robustness to unknown disturbances and changes in model parameters.

[0057] like Figure 6 As shown, this application also proposes an observation-compensated PI control device for laser soldering, the device comprising: Model building module 100 is used to establish a laser soldering thermodynamic model that includes thermal disturbance terms based on the lumped parameter method.

[0058] The space equation construction module 200 is used to construct the state-space equations of the thermodynamic model.

[0059] The observer design module 300 is used to design a state observer based on the state space equation and to estimate the state variables of the state space equation and the external disturbances acting on it in real time by configuring the observer gain matrix.

[0060] The total control quantity calculation module 400 is used to calculate the feedforward control quantity based on the target temperature curve and the thermodynamic model, calculate the compensation control quantity based on the disturbance value estimated by the observer, calculate the PI control quantity based on the deviation between the output temperature and the target temperature, and sum the three to obtain the total control quantity.

[0061] The adjustment module 500 is used to dynamically adjust the total control quantity in each sampling cycle according to the deviation between the current solder joint temperature and the target temperature, so that the solder joint temperature tracks the target temperature and the temperature error tends to zero.

[0062] In this embodiment, during the laser soldering heating process, the solder paste melts under the irradiation of the laser beam. An infrared temperature measurement system monitors the solder joint temperature in real time with a fixed sampling period, while an error detection system compares the measured temperature of the current period with the target temperature. If a deviation exists, the control system calculates the optimal laser power adjustment value based on an observation-compensated PI control algorithm, integrating the current temperature data, the target temperature curve, and the disturbance component estimated by the observer. This control quantity consists of three parts: feedforward compensation, PI feedback, and disturbance cancellation. The feedforward term pre-compensates the system inertia based on the target temperature change rate; the PI term dynamically corrects the steady-state error; and the compensation term cancels the thermal disturbance of the solder pads estimated by the state observer in real time. The control signal is output to the laser generator, adjusting the power while initiating the temperature acquisition for the next period. Within each control cycle, the system repeats the following process: temperature measurement → error detection → state observation → composite control quantity calculation → power adjustment → new round of monitoring. Through this closed-loop control mechanism, the system can quickly eliminate temperature deviations, ensuring that the solder joint temperature accurately tracks the target curve until soldering is complete. This method effectively improves anti-interference capability and dynamic response speed, and achieves high-precision laser brazing temperature control.

[0063] The laser soldering system applicable to this application comprises multiple functional modules, including a laser generator, a temperature monitoring unit, a position correction component, a central control module, a vision monitoring unit, and a beam adjustment device. The system's workflow is as follows: First, the motion control unit drives the work platform to position the area to be soldered at the vertical projection position of the laser beam. Then, the focus is adjusted and the laser source is activated, allowing the semiconductor laser beam to precisely irradiate the soldering area via optical fibers and a focusing device. The temperature monitoring unit uses non-contact infrared detection technology to periodically collect the temperature of the solder joint. The central control module adjusts the laser output power in real time by comparing the deviation between the measured temperature and the preset temperature, thereby ensuring the solder reaches the optimal melting temperature. After the solder has fully melted, the soldering process is completed. The work platform moves the sample to the inspection area, where infrared scanning technology is used to perform a comprehensive quality inspection of the solder pad surface. The entire system's data acquisition, motion positioning, and image processing functions are all uniformly coordinated by the host computer, forming an intelligent soldering solution.

[0064] like Figure 7 As shown, this application also provides a central controller, which includes: a feedforward controller, a PI controller, an observer equipped with a compensator, and a summing controller. The feedforward controller is used to calculate the feedforward control quantity based on the target temperature curve and the thermodynamic model. The observer is used to calculate the compensation control quantity based on the disturbance value estimated by the observer. The PI controller is used to calculate the PI control quantity based on the deviation between the output temperature and the target temperature. The summing controller sums the three to obtain the total control quantity.

[0065] The central controller further includes a regulator, used to dynamically adjust the total control quantity in each sampling cycle based on the deviation between the current solder joint temperature and the target temperature, so that the solder joint temperature tracks the target temperature and the temperature error approaches zero. The central controller outputs the total control quantity to the laser soldering system to adjust the output welding temperature.

[0066] In another aspect, this application provides a computer program product, including a computer program that, when executed by a processor, implements the steps of the method described above.

[0067] Compared with the prior art, the PI control method based on observation compensation in the welding process of laser soldering equipment provided in this application has the following beneficial effects: 1. This control method introduces a disturbance observer to estimate and compensate for external thermal disturbances such as ground plane heat absorption in real time. Combined with a feedforward-PI-compensation three-channel coordinated control strategy, it significantly improves temperature control accuracy. Compared with the traditional PID control method, the temperature error is greatly reduced, effectively solving the control deviation problem caused by external disturbances and model mismatch. This method maintains stable control performance under different power conditions and solder paste materials, significantly improving the consistency of soldering quality.

[0068] 2. The dynamic weight allocation strategy of this method can automatically adjust the contribution weight of each control channel according to different stages of the welding process, ensuring both rapid dynamic response and steady-state accuracy. Simultaneously, the synergistic effect of feedforward and compensation control reduces unnecessary power oscillations. Furthermore, this method exhibits strong robustness to model parameter changes and external disturbances, providing a reliable temperature control solution for high-precision laser welding.

[0069] The above description is only a preferred embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A PI control method based on observation compensation for laser soldering, characterized in that, The method includes: A thermodynamic model for laser soldering, including thermal disturbance terms, is established based on the lumped parameter method. Construct the state-space equations of the thermodynamic model; A state observer is designed based on the state space equation, and the state variables of the state space equation and the external disturbances acting on them are estimated in real time by configuring the observer gain matrix. The feedforward control quantity is calculated based on the target temperature curve and the thermodynamic model. The compensation control quantity is calculated based on the disturbance value estimated by the observer. The PI control quantity is calculated based on the deviation between the output temperature and the target temperature. The three are summed to obtain the total control quantity. In each sampling cycle, the total control quantity is dynamically adjusted based on the deviation between the current solder joint temperature and the target temperature, so that the solder joint temperature tracks the target temperature and the temperature error approaches zero.

2. The method according to claim 1, characterized in that, Within each sampling period k, the feedforward control quantity and the compensation control quantity at time k+1 are first calculated; then the PI control quantity at time k+1 is calculated based on the temperature error at time k; finally, the three are summed to obtain the total control quantity at time k+1.

3. The method according to claim 1, characterized in that, The thermodynamic model for laser soldering is as follows: in, ρ For solder paste density, c This refers to the specific heat capacity of the solder paste. V Where P is the volume of solder paste and P is the laser power. α The absorption rate of the solder paste to the laser. A The surface area of ​​the solder paste. h The surface heat transfer coefficient, T 0 represents the ambient temperature. T p The ground temperature. c p The specific heat capacity of the grounding plate. m p For the quality of the flooring, T The temperature of the solder joint; To simplify the subsequent formula expression, define , , The grounding model is then rewritten as: 。 4. The method according to claim 3, characterized in that, The construction of the state-space equations for the thermodynamic model includes: rewriting the rewritten grounded model into state-space equations, expressed as: in, x ( t )= T - T 0 is a state variable. u ( t )= P For laser control quantity, This indicates the impact of grounding disturbance.

5. The method according to any one of claims 1 to 4, characterized in that, The expression for the observer is: in, It is a state variable x ( t The estimated value of ); L It is the observer gain matrix, used to adjust the convergence speed of the estimation error; It is the state estimation error, which is corrected by feedback of the observer's output; It is the rate of change of disturbance. The estimated value.

6. The method according to any one of claims 1 to 5, characterized in that, The formula for calculating the total control quantity is as follows: u = u ff + u pi + u c in, u The overall control formula for the system is as follows: u ff This is the feedforward control variable. u pi For PI control, u c For observer-based compensation control variables; Feedforward control quantity u ff ( k The expression is as follows: in, , To identify parameters for the model, A The surface area of ​​the solder paste. m For solder paste quality, T s The sampling period is T0, where T0 is the ambient temperature. T tar ( k )for k The target temperature at any given time; PI control quantity u pi ( k The expression is as follows: in, e ( k )= T tar ( k )- T ( k The current temperature error is represented by ( ). k p and k I These are the proportional and integral gains, respectively. It is the cumulative term of the error; Compensation control quantity of the observer u c The expression is as follows: in, α The absorption rate of the solder paste to the laser. T p The ground temperature. c p The specific heat capacity of the grounding plate. m p For the quality of the flooring.

7. The method according to claim 6, characterized in that, Compensation control quantity of the observer u c The derivation of the expression is as follows: According to the state-space equations of the thermodynamic model, the disturbance compensation term is used to offset the grounding disturbance. T p ( t The impact on the system, and the expression for the disturbance cancellation condition are as follows: in, u c ( t ) indicates the compensation control quantity; according to , Derive the compensation control quantity u c The expression is as follows: The discretized expression for the compensation control quantity obtained by discretization is as follows: in, T p ( k ) is the current time disturbance value estimated by the observer.

8. A PI control device based on observation compensation for laser soldering, characterized in that, The device includes: The model building module is used to establish a laser soldering thermodynamic model that includes thermal disturbance terms based on the lumped parameter method. The space equation construction module is used to construct the state-space equations of the thermodynamic model. The observer design module is used to design a state observer based on the state space equation, and to estimate the state variables of the state space equation and the external disturbances acting on them in real time by configuring the observer gain matrix; The total control quantity calculation module is used to calculate the feedforward control quantity based on the target temperature curve and the thermodynamic model, calculate the compensation control quantity based on the disturbance value estimated by the observer, calculate the PI control quantity based on the deviation between the output temperature and the target temperature, and sum the three to obtain the total control quantity. The adjustment module is used to dynamically adjust the total control quantity in each sampling cycle based on the deviation between the current solder joint temperature and the target temperature, so that the solder joint temperature tracks the target temperature and the temperature error tends to zero.

9. A central controller, characterized in that, The central controller includes: a feedforward controller, a PI controller, an observer equipped with a compensator, and a summing controller. The feedforward controller is used to calculate the feedforward control quantity based on the target temperature curve and the thermodynamic model. The observer is used to calculate the compensation control quantity based on the disturbance value estimated by the observer. The PI controller is used to calculate the PI control quantity based on the deviation between the output temperature and the target temperature. The summing controller sums the three to obtain the total control quantity.

10. A computer program product, comprising a computer program, characterized in that, When executed by a processor, the computer program implements the steps of the method described in any one of claims 1 to 7.

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