An automatic screen changer adaptive control method and system

Abstract

The application relates to the technical field of extrusion screen changing control, in particular to an automatic screen changer adaptive control method and system, which comprises the following steps: acquiring an inlet pressure and an inlet temperature of an automatic screen changer; when a pressure integral determined based on the inlet pressure is greater than a preset pressure threshold value, heating of a preheating area of the automatic screen changer is controlled according to the inlet temperature; when the temperature of the preheating area reaches a preset target temperature, an absolute displacement amount of a screen plate of the automatic screen changer is acquired; during a preset transition period of the absolute displacement amount, a current when the screen plate is driven is acquired, and a pressure gradient of the inlet pressure and a current gradient of the current are extracted; during maintenance of a reduced speed, the temperature of the preset transition period is acquired; when the temperature of the preset transition period reaches a preset melting temperature, and the time length of the pressure gradient in a preset stable band exceeds a preset relaxation time, pulse heating is stopped and the speed is restored to a preset speed. The application can solve thermal degradation caused by shear heat generation and realize smooth screen changing.

Description

Technical Field

[0001] This application relates to the technical field of extrusion screen changing control, and in particular to an adaptive control method and system for an automatic screen changer. Background Technology

[0002] In continuous extrusion molding of polymer materials, screen changing equipment is usually connected in series in the melt pipeline to intercept and clean fluid impurities. Under conventional continuous extrusion conditions, the screen changing operation requires the room-temperature metal filter block to overcome the fluid resistance inside the pipeline and cut into the high-temperature, high-pressure melt flow channel. When the room-temperature metal block comes into physical contact with the high-temperature melt, the transient heat conduction imbalance at the hot-cold interface will cause a rapid local phase change in the melt in the contact area, thereby generating a solid-liquid phase change condensation layer with a clear shear yield stress on the surface of the metal block. The rheological properties of non-Newtonian fluids at such phase change boundaries are highly sensitive, and their physical state and internal stress distribution are directly constrained by both the external mechanical shear rate and the thermal field distribution of the flow channel.

[0003] Chinese invention patent application CN115071105A discloses a fully automatic screen changing method for a melt filter device. This technical solution involves configuring a pressure sensor within the melt flow channel of the screen changer to monitor the pipeline pressure and transmit the signal to a controller. Its basic control logic is set as follows: when the pipeline pressure exceeds a preset value, the controller sends a signal to start the drive mechanism, causing the annular filter screen to move from the inlet to the outlet; when the pipeline pressure drops to within the preset range, the controller sends a signal to stop the drive mechanism, and the annular filter screen stops moving. This solution establishes an operational mechanism that relies solely on the over-limit and under-limit signals of the pipeline pressure amplitude to implement the start-stop scheduling of the filter screen.

[0004] The aforementioned scheme relies on a single pressure amplitude exceeding the limit as the trigger condition, causing the drive mechanism to only execute continuous feed displacement at the system's inherent predetermined speed after receiving the start signal. When the room-temperature filter cuts into the high-temperature flow channel and touches the aforementioned solid-liquid phase change condensation layer, the continuous mechanical feed action without deceleration will directly and forcibly tear apart the condensation layer structure that has not yet absorbed heat and melted. The mechanical friction work done by the actuator to overcome the yield stress of the condensation layer is rapidly converted into concentrated shear heat within the confined physical space. When the polymer material is subjected to this direct mechanical shear work, the local temperature at the interface instantaneously exceeds the thermal stability physical boundary of the material itself, triggering an irreversible thermal degradation reaction in the polymer, resulting in severe shear heat generation defects in the mechanism under forced cutting conditions. Summary of the Invention

[0005] To address the thermal degradation caused by shear heating and achieve smooth screen switching, this application provides an adaptive control method and system for an automatic screen switcher.

[0006] Firstly, this application provides an adaptive control method for an automatic network switcher, employing the following technical solution: An adaptive control method for an automatic network switcher, comprising:

[0007] Obtain the inlet pressure and inlet temperature of the automatic screen changer;

[0008] When the pressure integral determined based on the inlet pressure is greater than the preset pressure threshold, the preheating zone of the automatic screen changer is heated according to the inlet temperature.

[0009] When the temperature of the preheating zone reaches the preset target temperature, the absolute displacement of the screen plate of the automatic screen changer is obtained, and when the absolute displacement enters the preset transition zone of the automatic screen changer, the screen plate is driven at a preset speed.

[0010] During the period when the absolute displacement is in the preset transition zone, the current driving the mesh plate is acquired, and the pressure gradient of the inlet pressure and the current gradient of the current are extracted.

[0011] When the pressure gradient is greater than a preset resistance threshold and the current gradient is greater than a preset current threshold, the mesh is driven at a derating speed, and the duty cycle is determined based on the pressure gradient to control the pulse heating in the preset transition zone, wherein the derating speed is lower than the preset speed.

[0012] During the derating rate, the temperature of the preset transition zone is obtained. When the temperature of the preset transition zone reaches the preset melting temperature and the pressure gradient is in the preset steady zone for a period of time exceeding the preset relaxation time, the pulse heating is stopped and the speed is restored to the preset rate.

[0013] Optionally, the integral of the variation of the inlet pressure within a preset time window is calculated as the pressure integral. When the pressure integral is greater than the preset pressure threshold, it is determined that the trigger condition is met.

[0014] If the triggering condition is met, the inlet temperature is locked as the reference temperature and the preheating zone is heated with a preset power. The reference temperature is then summed with a preset compensation constant to determine the preset target temperature.

[0015] The feedback temperature of the preheating zone is obtained. When the feedback temperature reaches the preset target temperature, a transition signal is generated to trigger the acquisition of the absolute displacement of the screen plate of the automatic screen changer.

[0016] Optionally, the stroke of the absolute displacement includes a first stroke region, the preset transition region, and a second stroke region connected sequentially, and before obtaining the absolute displacement, it further includes:

[0017] Obtain the initial coordinates, preset gap, and inner diameter of the flow channel of the automatic screen changer;

[0018] The sum of the initial coordinates and the preset gap is determined as the first boundary marker at the intersection of the first travel area and the preset transition area;

[0019] The sum of the first boundary marker and the inner diameter of the flow channel of the automatic screen changer is determined as the second boundary marker at the junction of the preset transition zone and the second travel zone;

[0020] When the absolute displacement is within the first travel zone, the mesh plate is driven at a preset first speed greater than the preset speed;

[0021] When the absolute displacement is in the second stroke zone, the mesh plate is driven at a preset second speed.

[0022] Optionally, determining the duty cycle based on the pressure gradient to control the pulse heating in the preset transition zone includes:

[0023] Calculate the difference between the pressure gradient and the preset resistance threshold;

[0024] Multiply the difference by the preset gain to obtain the base duty cycle;

[0025] The basic duty cycle is limited to a preset ratio range and used as the duty cycle.

[0026] A modulation signal is generated based on the duty cycle, and the modulation signal is injected into the preset transition zone via a preset solid-state relay in a zero-crossing trigger mode to perform the pulse heating.

[0027] Optionally, after extracting the pressure gradient and the current gradient, the method further includes:

[0028] When the pressure gradient is greater than the preset resistance threshold and the current gradient is not greater than the preset current threshold, cavitation noise is determined to be generated.

[0029] Skip driving the stencil at the derating speed and control the pulse heating in the preset transition zone, and maintain driving the stencil at the preset speed.

[0030] Optionally, while maintaining the derating rate, the method further includes:

[0031] The cumulative duration for which the rate of decrease is maintained is timed;

[0032] When the accumulated time exceeds the preset tolerance period and the condition for recovery to the preset speed is not met, the mesh plate is controlled to move in the opposite direction by a preset distance;

[0033] Position locking is performed at the coordinates where the mesh plate completes the reverse movement to stop the displacement.

[0034] Optional, also includes:

[0035] When the position locking is maintained for a preset duration, the position locking is released;

[0036] Re-drive the stencil at the stated derating speed and reset the accumulated duration to zero.

[0037] Optionally, while maintaining the derating rate, the method further includes:

[0038] Calculate the time derivative of the absolute displacement as the actual velocity, and obtain the velocity difference between the preset velocity and the actual velocity;

[0039] The velocity difference is multiplied by the preset cross-sectional area of ​​the mesh to determine the volume difference, and feedforward signaling is generated based on the volume difference.

[0040] Optionally, generating the feedforward signaling based on the volume difference includes:

[0041] Obtain the current rotational speed and preset displacement coefficient of the preset extruder upstream of the automatic screen changer;

[0042] The derated speed is determined by dividing the volume difference by the preset displacement coefficient;

[0043] The target speed is obtained by subtracting the current speed from the drated speed.

[0044] The feedforward signal is generated based on the target rotational speed to control the preset extruder to operate at the target rotational speed.

[0045] Secondly, the automatic screen changer adaptive control system provided in this application adopts the following technical solution: an automatic screen changer adaptive control system, comprising:

[0046] The parameter acquisition module is used to acquire the inlet pressure and inlet temperature of the automatic screen changer;

[0047] The preheating control module is used to control the heating of the preheating zone of the automatic screen changer according to the inlet temperature when the pressure integral determined based on the inlet pressure is greater than a preset pressure threshold.

[0048] The displacement drive module is used to obtain the absolute displacement of the screen plate of the automatic screen changer when the temperature of the preheating zone reaches the preset target temperature, and drive the screen plate at a preset speed when the absolute displacement enters the preset transition zone of the automatic screen changer.

[0049] The derating heating module is used to acquire the current driving the mesh plate during the period when the absolute displacement is in the preset transition zone, and to extract the pressure gradient of the inlet pressure and the current gradient of the current; when the pressure gradient is greater than a preset resistance threshold and the current gradient is greater than a preset current threshold, the mesh plate is driven at a derating speed, and the duty cycle is determined based on the pressure gradient to control the pulse heating in the preset transition zone, wherein the derating speed is lower than the preset speed.

[0050] The state recovery module is used to acquire the temperature of the preset transition zone during the derating rate. When the temperature of the preset transition zone reaches the preset melting temperature and the pressure gradient is in the preset stable zone for a period of time exceeding the preset relaxation time, the pulse heating is stopped and the system returns to the preset rate.

[0051] In summary, this application includes the following beneficial technical effects:

[0052] 1. By acquiring the inlet pressure of the automatic screen changer and triggering preheating zone heating based on the inlet temperature when the pressure integral exceeds the threshold, and by simultaneously extracting the pressure gradient of the inlet pressure and the current gradient of the current driving the screen after the screen enters the preset transition zone, and only executing derating speed drive and pulse heating when both the pressure gradient and the current gradient exceed the threshold, until the preset transition zone temperature reaches the preset melting temperature and the pressure gradient continues to exceed the preset relaxation time within the preset stable zone, the preset speed is restored. This achieves the identification of the true solid phase condensation resistance by the joint constraint of the pressure gradient and the current gradient, avoiding the misjudgment of bubble rupture or pressure burrs as condensation layer yielding. Furthermore, by using the derating speed to reduce mechanical shear work and using pulse heating to supplement melting heat, thermal degradation caused by shear heat generation is avoided, thus achieving smooth screen changing.

[0053] 2. By defining the stroke of the absolute displacement in sequence as the first stroke zone, the preset transition zone and the second stroke zone, and driving the screen plate to quickly pass through the non-cutting zone at a first speed greater than the preset speed according to the stroke zone where the absolute displacement is located, entering the preset transition zone at the preset speed for condensation layer identification, and driving the screen plate to complete the screen-out side switching at the preset second speed, segmented speed planning for the entire stroke of the screen plate is realized, reducing the invalid screen-changing time in the non-cutting zone and reducing the pressure fluctuation on the screen-out side.

[0054] 3. By calculating the difference between the pressure gradient and the preset resistance threshold, the difference is multiplied by the preset gain to obtain the base duty cycle, which is then limited to a preset ratio range as the duty cycle. The solid-state relay then performs pulse heating to the preset transition zone in a zero-crossing trigger mode, realizing adaptive heat injection with dynamic adjustment of the duty cycle according to the actual resistance deviation. This not only automatically increases the heating duty cycle to accelerate melting when the resistance of the condensation layer increases, but also limits the maximum duty cycle through the preset ratio range to avoid overheating and degradation of the melt caused by prolonged full load of the pulse heating rod, thereby improving the adaptive capability of heat injection to operating condition fluctuations. Attached Figure Description

[0055] Figure 1 A flowchart illustrating an adaptive control method for an automatic screen changer provided in an embodiment of this application;

[0056] Figure 2 This is a schematic diagram of the control topology of an adaptive control system for an automatic network switcher provided in an embodiment of this application. Detailed Implementation

[0057] The following combination Figures 1-2 This application will be described in further detail.

[0058] This application discloses an adaptive control method for an automatic screen changer, which is applied to an automatic screen changer in a continuous extrusion molding process of polymer materials. The automatic screen changer is connected in series in the melt pipeline downstream of a preset extruder. The automatic screen changer includes a screen plate, an inlet flow channel, a preheating zone, a preset transition zone, a screen exit side stroke structure corresponding to the second stroke zone, a servo hydraulic actuator, an absolute displacement sensor, a pressure transmitter, a thermocouple, an array-type heating base, and an edge master control PLC.

[0059] The edge master PLC uses a controller supporting the EtherCAT hard real-time industrial Ethernet protocol, such as Beckhoff CX series controllers or Siemens S7-1500 series controllers. The control task cycle is configured to be no more than 2ms to meet the real-time requirements of synchronous sampling of pressure gradient, current gradient, and absolute displacement. The servo hydraulic actuator includes a servo driver, a proportional directional valve, and a bidirectional piston drive cylinder. The servo driver feeds back the current when driving the mesh board to the edge master PLC. The absolute displacement sensor is physically connected to the main shaft of the bidirectional piston drive cylinder to provide feedback on the absolute displacement of the mesh board. The absolute displacement sensor can be a magnetostrictive displacement sensor, with a range of 100mm to 500mm selected according to the mesh changer stroke, and a resolution no greater than 0.01mm; a high-resolution grating ruler can also be used, with a resolution no greater than... A pressure transmitter is installed on the inlet flow channel side of the automatic screen changer to obtain the inlet pressure. A thermocouple is also installed on the inlet flow channel side to obtain the inlet temperature. The thermocouples are either type K or type J conforming to IEC 60584. The sampled values ​​are input to the analog module of the edge control PLC after cold junction compensation. The array-type heating base is divided into a preheating zone, a preset transition zone, and a main flow channel center zone along the screen cutting direction. Each zone is equipped with an independent temperature probe and a pulse heating rod. The pulse heating rod is connected to the AC power supply via a preset solid-state relay. The preset solid-state relay uses an SSR with zero-crossing triggering function to reduce electromagnetic interference and contact erosion risks caused by phase switching.

[0060] The pressure transmitter acquires the inlet pressure of the automatic screen changer at a preset sampling period and outputs it to the edge control PLC. The thermocouple acquires the inlet temperature of the automatic screen changer at the same preset sampling period and outputs it to the edge control PLC. The inlet pressure is the sole input for calculating the pressure integral, and the inlet temperature is the sole temperature reference input for the preset target temperature. To avoid single-point pressure noise triggering the screen change, the edge control PLC calculates the integral of the inlet pressure variation within a preset time window as the pressure integral, which can be expressed as: The integration interval is a preset time window extending forward from the current moment. For inlet pressure, The preset sampling period is set. The preset time window can be 0.5s to 5s; for PC materials with a melt flow index (MFI) of 10, the preset time window can be 1s to 2s. When the pressure integral exceeds the preset pressure threshold, the edge control PLC determines that the upstream filter blockage of the automatic screen changer has formed a continuous accumulation trend, rather than a single pressure spike. As an optional implementation, the inlet pressure can be processed by a second-order low-pass filter before entering the variation integral, with the cutoff frequency set to 5Hz to 20Hz. This retains the low-frequency pressure rise corresponding to the screen changing resistance change while suppressing the high-frequency noise generated by the mechanical vibration of the pressure transmitter diaphragm.

[0061] The trigger condition, where the pressure integral exceeds a preset pressure threshold, serves as the input condition for preheating control. The edge master PLC locks the inlet temperature as the reference temperature during the sampling cycle that meets the trigger condition, and controls the preheating zone heating of the automatic screen changer with a preset power. The preset power can be 70% to 100% of the rated power of the preheating zone, used to increase the initial enthalpy of the metal contact area before the screen cuts into the melt flow channel. The edge master PLC sums the reference temperature with a preset compensation constant to determine the preset target temperature, which can be expressed as... , Inlet temperature, A preset compensation constant is set based on the heat capacity of the metal mesh, the thermal conductivity of the melt, and the heat dissipation intensity of the screen changer slide rail. Common values ​​range from 5°C to 30°C. For PET processing, when the inlet temperature is 275°C, a preset compensation constant of 10°C to 15°C can be used; for PC processing, when the inlet temperature is 290°C, a preset compensation constant of 15°C to 25°C can be used. The physical basis of this compensation setting follows the logic of transient heat conduction, that is, the heat conducted per unit time is positively correlated with the actual temperature gradient of the contact surface. Preheating the zone by storing heat in advance can effectively reduce the temperature difference between the room-temperature metal mesh and the high-temperature melt, directly weakening the thickness of the solid-liquid phase change condensation layer at the interface from the perspective of physical thermal field exchange, and improving the thermal environment inclusiveness before entering the transition zone.

[0062] The temperature probe in the preheating zone acquires the feedback temperature and outputs it to the edge master control PLC. When the feedback temperature reaches the preset target temperature, the edge master control PLC generates a transition signal. This transition signal serves as the trigger input for acquiring the absolute displacement of the screen plate in the automatic screen changer. Before acquiring the absolute displacement of the screen plate, the edge master control PLC reads the initial coordinates of the screen plate, the preset gap, and the inner diameter of the flow channel of the automatic screen changer from the feedback of the absolute displacement sensor. The initial coordinates are set as follows: The preset gap is denoted as The inner diameter of the flow channel is denoted as The edge control PLC determines the sum of the initial coordinates and the preset gap as the first boundary marker at the intersection of the first travel zone and the preset transition zone. The first boundary marker is calculated as follows: The edge control PLC determines the sum of the first boundary marker and the inner diameter of the flow channel as the second boundary marker at the intersection of the preset transition zone and the second stroke zone. The second boundary marker is calculated as follows: Constructing incremental and continuous coordinate markers ensures that the displacement drive module accurately judges the spatial position of the stencil, preventing the servo system from experiencing feed back or stroke errors during stencil changing.

[0063] The absolute displacement stroke includes a first stroke zone, a preset transition zone, and a second stroke zone connected in sequence. The first stroke zone corresponds to the area where the screen plate is close to the melt flow channel but has not yet formed the main cutting contact. The preset transition zone corresponds to the area where the leading edge of the new screen plate crosses the inlet flow channel and forms a hot-cold interface with the high-temperature melt. The second stroke zone corresponds to the area where the screen plate crosses the center of the main flow channel and completes the effective screen switching.

[0064] After acquiring the absolute displacement of the screen plate in the automatic screen changer, the absolute displacement sensor continuously acquires the absolute displacement and outputs it to the edge control PLC. The edge control PLC generates speed commands based on the absolute displacement, the first boundary marker, and the second boundary marker as input conditions. When the absolute displacement is in the first stroke zone, the edge control PLC drives the screen plate at a preset first speed greater than the preset speed, causing the screen plate to quickly approach the melt flow channel and reduce the invalid screen changing time in the non-cutting zone; the preset first speed can be 1.2 to 3 times the preset speed. When the absolute displacement enters the preset transition zone of the automatic screen changer, the edge control PLC drives the screen plate at a preset speed, which serves as the reference feed speed before condensation layer identification; the preset speed can be 0.5 mm / s to 10 mm / s, specifically set according to the melt viscosity, flow channel inner diameter, and filter screen area. When the absolute displacement is in the second stroke zone, the edge control PLC drives the screen plate at a preset second speed, which can be equal to or lower than the preset speed to reduce pressure fluctuations on the screen exit side.

[0065] like Figure 1 As shown, after the control system establishes continuous feeding action at a preset speed in the preset transition zone, it constructs a bottom-up cyclic detection loop. When the pressure gradient is determined to be less than the preset resistance threshold or the current gradient is determined to be less than the preset current threshold, the preset speed is directly maintained and the system returns to the previous pressure gradient determination node along the command link. During the triggering of derating speed drive and pulse heating action, if the temperature in the preset transition zone does not reach the preset melting temperature and the cumulative duration does not reach the preset tolerance period threshold, the logic flow will backtrack to the temperature determination node, forming an independent polling waiting inner loop. During the period when the absolute displacement is in the preset transition zone, the inlet pressure and the current when driving the mesh plate together constitute the data input for solid-liquid phase change condensation layer identification.

[0066] During the preset transition zone, the inlet pressure and the current during the drive of the mesh plate together constitute the data input for solid-liquid phase change condensation layer identification. The edge control PLC acquires the current during the drive of the mesh plate and extracts the pressure gradient of the inlet pressure and the current gradient of the current. The pressure gradient can be calculated according to... The current gradient can be calculated as follows: calculate, The current inlet pressure of the sampling point. This represents the current driving the stencil at the current sampling point. The differential span can be 2 to 10 sampling periods to reduce single-point noise amplification. The pressure gradient characterizes the rate of change of melt flow channel resistance, and the current gradient characterizes the rate of change of change of the actual load on the servo hydraulic actuator.

[0067] While transient increases in inlet pressure can also occur due to bubble bursting, localized cavitation, or pressure transmitter diaphragm impact, these disturbances do not synchronously cause a sudden increase in load on the servo hydraulic actuator. The combined logical constraints of the pressure and current gradients can filter out gas-phase cavitation noise. For PC materials with a melt flow index (MFI) of 10, the preset resistance threshold can be 5 MPa / s, the preset current threshold can be 15 A / s, and the preset relaxation time can be 800 ms. For PET materials, the preset resistance threshold can be 3 MPa / s to 6 MPa / s, and the preset current threshold can be 10 A / s to 20 A / s.

[0068] When both the pressure gradient and the current gradient exceed a preset resistance threshold, the edge controller PLC determines that the stencil encounters real solid-phase condensation resistance in a preset transition zone. This determination output serves as the input condition for both mechanical derating and heat injection. The edge controller PLC drives the stencil according to the derating rate, which is lower than a preset rate. The derating rate can be expressed as... , For preset speed, This is the derating factor. The derating factor can be taken as 0.02 to 0.1, causing the stencil to transition from continuous cutting to a near-stagnant, slow-moving state. In this state, the mechanical shear rate decreases significantly, and the shear heat converted from mechanical friction at the non-Newtonian melt interface decreases with decreasing velocity. For the approximation of flat plate shearing, the shear rate can be calculated as follows: Estimate, For the stencil feed speed, The equivalent thickness of the condensation layer; the derating rate will After compression, the viscous dissipation power per unit volume Synchronous reduction, among which To characterize the shear stress generated in the melt by mechanical action, the definitions of the parameters in the above formula provide a theoretical basis for the precise quantification of viscous dissipation power, effectively blocking the path of thermal degradation caused by local temperatures exceeding the material's thermal stability boundary.

[0069] While driving the mesh at the derating speed, the edge controller PLC determines the duty cycle based on the pressure gradient to control pulse heating in the preset transition zone. The edge controller PLC calculates the difference between the pressure gradient and the preset resistance threshold, multiplies this difference by the preset gain to obtain the base duty cycle, and limits the base duty cycle within a preset proportional range. The duty cycle can be expressed as: , Preset gain, To preset the resistance threshold, and These are the lower and upper limits of the preset ratio range. Preset gain. The value can be selected from 0.5 to 2.0, and the preset ratio range can be from 10% to 80%. The lower limit ensures a minimum heat flow injection in the preset transition zone, while the upper limit prevents the pulse heating rod from being fully loaded for a long time, which could lead to thermal and oxidative degradation of the melt. The edge master control PLC generates a modulation signal based on the duty cycle and injects the modulation signal into the preset transition zone through a preset solid-state relay in zero-crossing trigger mode to execute pulse heating. The modulation signal period can be selected from 0.5s to 2s. When using 50Hz AC power supply, the zero-crossing trigger SSR has a minimum on / off unit of half a cycle, and the edge master control PLC can output a pulse sequence in an integer cycle control mode.

[0070] As an optional implementation, the preset transition zone can be arranged with two sets of independent pulse heating rods. The duty cycle of the heating rod near the inlet pressure side is Duty, and the duty cycle of the heating rod near the outlet side is 0.5Duty to 0.8Duty, so as to match the temperature gradient in the melt flow direction and avoid local overheating on the outlet side.

[0071] During the derating rate maintenance, the temperature probe in the preset transition zone acquires the temperature of the preset transition zone, while the pressure transmitter continues to acquire the inlet pressure, and the edge master PLC calculates the pressure gradient. When the temperature of the preset transition zone reaches the preset melting temperature, and the pressure gradient remains in the preset stable zone for longer than the preset relaxation time, the edge master PLC stops pulse heating and returns to the preset rate. The preset melting temperature is set according to the melting or softening characteristics of the material. For PC, it can be a process temperature range above the glass transition temperature and below the thermal degradation initiation temperature, such as 280℃ to 310℃; for PET, it can be 260℃ to 290℃. The preset stable zone can be set to [-0.5MPa / s, 0.5MPa / s] or [-1MPa / s, 1MPa / s] to confirm that the condensation layer resistance has returned from the abrupt state to a flowable state. The preset relaxation time corresponds to the stress decay time of the material chain segment after shear disturbance, conforming to the Maxwell model. middle The physical meaning of which, The initial stress induced by shear disturbance. The time variable represents the stress decay process. The physical meaning of the parameters in the above formula establishes the scientific calculation rules for relaxation time, enabling the control system to accurately determine whether the residual elastic stress at the interface has been fully released, thereby avoiding the risk of inducing pressure oscillations again when returning to the preset speed. As an optional implementation method, the preset relaxation time can be written into the edge control PLC from the material grade table, or it can be obtained by fitting the pressure pulse decay curve of the previous batch of stable extrusion section. The fitting model adopts a single exponential or double exponential decay model.

[0072] After extracting the pressure and current gradients, when the pressure gradient exceeds a preset resistance threshold and the current gradient does not exceed a preset current threshold, the edge master control PLC determines that cavitation noise has been generated. This determination output serves as a bypass input, allowing the edge master control PLC to skip driving the stencil at the derating speed and controlling the pulse heating in the preset transition zone, while maintaining the stencil drive at the preset speed. This branch avoids mistaking short-term pressure spikes formed by bubble rupture as yield resistance of the condensation layer, preventing ineffective derating from lengthening the stencil replacement cycle and also preventing ineffective pulse heating from increasing the melt residence time. When the inlet pressure exhibits an isolated transient spike and the current gradient does not show a synchronous jump, the control channel maintains the initial duty cycle and locks the preset speed level. When the inlet pressure and current gradient synchronously exceed the limits, triggering derating speed drive and pulse heating, the temperature in the preset transition zone rises in a controlled manner. Before the reset condition is met, the pressure gradient converges within a preset relaxation time and is controlled and constrained within the upper and lower limits of the preset stable band. Subsequently, the system triggers a zeroing of the duty cycle level and restoration of the feed speed reference. As an optional implementation, cavitation noise determination can also introduce an inlet pressure peak width constraint. When the pressure gradient exceeds the limit for less than 20ms to 100ms and the current gradient does not exceed the limit, the edge master control PLC marks the event as a cavitation noise event and writes it into the fault trend record.

[0073] During the derating speed maintenance, the edge controller PLC timers the cumulative duration of the derating speed maintenance. If the cumulative duration exceeds the preset tolerance period and the conditions for returning to the preset speed are not met, the edge controller PLC controls the stencil to move in the reverse direction a preset distance. The preset tolerance period can be 2s to 10s, and the preset distance can be 0.2mm to 2mm. The reverse movement is used to release the compressive stress between the condensation layer and the leading edge of the stencil, allowing the molten heat to re-enter the contact gap and reducing the coating friction of the condensation layer on the stencil. The coordinates of the stencil completing the reverse movement are fed back to the edge controller PLC by the absolute displacement sensor, and the edge controller PLC performs position locking at that coordinate to stop the displacement. Position locking can be achieved through the servo drive position holding function, or through a combination of proportional directional valve neutral locking and hydraulic lock. When the position locking duration reaches the preset duration, the edge controller PLC releases the position locking, restarts the stencil at the derating speed, and resets the cumulative duration to zero. The preset duration can be set from 0.5s to 3s, which serves as the waiting time for the condensation layer to absorb heat and soften.

[0074] During the derating period, the edge controller PLC calculates the time derivative of the absolute displacement as the actual speed and obtains the speed difference between the preset speed and the actual speed. The actual speed can be expressed as... , where variables Specifically, it refers to the absolute displacement of the stencil sampled in real time. By clearly calculating the actual velocity by taking the time derivative of the absolute displacement, it ensures that the calculation benchmark for subsequent volume compensation is closely synchronized with the actual physical movement of the stencil, thus avoiding distortion in the volume difference measurement.

[0075] The edge controller PLC multiplies the speed difference by the preset cross-sectional area of ​​the mesh plate to determine the volume difference, which can be expressed as: , This represents the preset cross-sectional area of ​​the stencil. The volume difference indicates the amount of transient effective volume replacement caused by stencil derating or reverse unloading. The edge master PLC generates feedforward signaling based on the volume difference to prevent the upstream preset extruder from continuing to push melt at the original flow rate, thus avoiding secondary accumulation of inlet pressure.

[0076] The edge PLC acquires the current speed and preset displacement coefficient of the upstream extruder of the automatic screen changer. It divides the volume difference by the preset displacement coefficient to determine the derating speed, and calculates the difference between the current speed and the derating speed to obtain the target speed. Based on the target speed, it generates feedforward signals to control the extruder to operate at the target speed. The preset displacement coefficient can be obtained from the theoretical conveying volume per screw revolution or the displacement per revolution of the melt gear pump, and the unit can be... As an optional implementation, when a melt gear pump is configured upstream of the automatic screen changer, the feedforward signaling is sent to the melt gear pump servo drive; when no melt gear pump is configured upstream of the automatic screen changer, the feedforward signaling is sent to the extruder main screw inverter or drive, and the target speed is transmitted via Modbus TCP, PROFINET, or EtherCAT process data objects.

[0077] As an alternative implementation, the servo hydraulic actuator can be replaced by a servo motor and ball screw mechanism. In this alternative structure, the servo motor drives the ball screw to push the mesh plate via a coupling. The current driving the mesh plate is fed back by the servo motor driver, and the current gradient is calculated based on the torque current component of the servo motor. Axis current. The shaft current and output torque approximately satisfy , Since it is the motor torque constant, therefore The axial current gradient can serve as an equivalent input to sudden changes in the stencil load. This alternative structure still uses the pressure gradient of the inlet pressure and the current gradient when driving the stencil to identify the true solid-phase condensation resistance, and maintains coordinated control of derating rate and pulse heating.

[0078] When processing PET using the above method, traditional constant-speed screen changers can experience a localized temperature drop of approximately 15°C at the moment the screen cuts in, with the inlet pressure peak reaching 25 MPa, resulting in approximately 3 to 5 carbonized black spots per square meter on the product surface. With this implementation method, pressure integral first triggers preheating zone heating. After the absolute displacement enters the preset transition zone, the solid-liquid phase change condensation layer is identified by both the pressure and current gradients. The derating rate reduces mechanical shear work, and pulse heating replenishes the melting heat to the condensation layer. The preset melting temperature, preset stable zone, and preset relaxation time jointly constrain the recovery to the preset speed. The inlet pressure peak can be suppressed to within 18 MPa, and temperature fluctuations during screen changing can be controlled within... Within a certain range, the carbonization black spot can be reduced to 0.

[0079] This application discloses an adaptive control system for an automatic network switcher, used to implement an adaptive control method for an automatic network switcher. The adaptive control system for the automatic network switcher includes a virtual functional module architecture and a physical hardware architecture.

[0080] The virtual functional module architecture includes a parameter acquisition module, a preheating control module, a displacement drive module, a derating heating module, and a state recovery module. Each virtual functional module forms a static input-output relationship based on inlet pressure, inlet temperature, pressure integral, preset target temperature, absolute displacement, pressure gradient, current gradient, duty cycle, derating rate, preset transition zone temperature, preset smooth band, and preset relaxation time.

[0081] The parameter acquisition module is used to acquire the inlet pressure and inlet temperature of the automatic screen changer. The input terminals of the parameter acquisition module connect to a pressure transmitter and a thermocouple, while the output terminals provide the inlet pressure and inlet temperature. The inlet pressure data format can be in MPa (engineering quantity), and the inlet temperature data format can be in °C (engineering quantity). The parameter acquisition module also has a sampling timestamp field, which is generated according to the task cycle of the edge control PLC and is used to provide a unified time reference for pressure integration, pressure gradient, and current gradient.

[0082] The preheating control module controls the heating of the preheating zone of the automatic screen changer based on the inlet temperature when the pressure integral determined based on the inlet pressure exceeds a preset pressure threshold. The input of the preheating control module receives the inlet pressure and inlet temperature output by the module. The internal data of the preheating control module includes a preset time window, a preset pressure threshold, a reference temperature, a preset compensation constant, a preset power, a feedback temperature, and a preset target temperature. The output of the preheating control module provides the preset target temperature and a transition signal. The pressure integral is composed of the integral of the inlet pressure variation within the preset time window. The preset target temperature is the sum of the reference temperature and the preset compensation constant. The transition signal is valid when the feedback temperature reaches the preset target temperature.

[0083] The displacement drive module is used to acquire the absolute displacement of the screen plate of the automatic screen changer when the temperature of the preheating zone reaches the preset target temperature, and to drive the screen plate at a preset speed when the absolute displacement enters the preset transition zone of the automatic screen changer. The input of the displacement drive module receives the transition signal and preset target temperature output from the preheating control module, and also receives the absolute displacement output from the absolute displacement sensor. The internal data of the displacement drive module includes initial coordinates, preset gap, flow channel inner diameter, first marker, second marker, first stroke zone, preset transition zone, second stroke zone, preset first speed, preset speed, and preset second speed. The first marker is composed of the sum of the initial coordinates and the preset gap, and the second marker is composed of the sum of the first marker and the flow channel inner diameter. The output of the displacement drive module provides the speed command for driving the screen plate and provides the derating heating module with the spatial state of the absolute displacement within the preset transition zone.

[0084] The derating heating module is used to acquire the current driving the mesh plate during the period when the absolute displacement is within a preset transition zone, and to extract the pressure gradient of the inlet pressure and the current gradient of the current. When the pressure gradient is greater than a preset resistance threshold and the current gradient is greater than a preset current threshold, the mesh plate is driven at a derating speed, and the duty cycle is determined based on the pressure gradient to control pulse heating in the preset transition zone, wherein the derating speed is lower than a preset speed. The input of the derating heating module receives the spatial state of the absolute displacement in the preset transition zone output by the displacement driving module, the inlet pressure output by the parameter acquisition module, the current driving the mesh plate output by the servo driver, and the preset speed output by the displacement driving module. The internal data of the derating heating module includes pressure gradient, preset resistance threshold, current gradient, preset current threshold, derating speed, preset gain, base duty cycle, preset ratio range, duty cycle, modulation signal, preset solid-state relay, and cavitation noise flag. The output of the derating heating module provides derating speed, duty cycle, modulation signal, and cavitation noise flag. The cavitation noise flag corresponds to a static state where the pressure gradient is greater than a preset resistance threshold and the current gradient is not greater than a preset current threshold. This state is associated with maintaining the output of the stencil driven at a preset speed.

[0085] The state recovery module is used to acquire the temperature of the preset transition zone while maintaining the derating rate. When the temperature of the preset transition zone reaches the preset melting temperature, and the pressure gradient remains in the preset stable zone for a duration exceeding the preset relaxation time, pulse heating is stopped and the speed is restored to the preset speed. The input of the state recovery module receives the derating rate, duty cycle, and pressure gradient output from the derating heating module, and also receives the temperature of the preset transition zone output from the preset transition zone temperature probe. The internal data of the state recovery module includes the preset melting temperature, preset stable zone, preset relaxation time, cumulative duration, preset tolerance period, preset distance, position lockout, preset duration, actual speed, speed difference, preset cross-sectional area of ​​the mesh, volume difference, current rotational speed, preset displacement coefficient, derating speed, target speed, and feedforward signaling. The output of the state recovery module provides the control quantity to stop pulse heating, the speed command to restore to the preset speed, the position command to move back a preset distance, the position lockout status, the target speed, and feedforward signaling. The actual speed is composed of the time derivative of the absolute displacement; the speed difference is composed of the difference between the preset speed and the actual speed; the volume difference is composed of the speed difference multiplied by the preset cross-sectional area of ​​the mesh plate; and the target rotational speed is composed of the difference between the current rotational speed and the derating rotational speed.

[0086] The physical hardware architecture includes a processor, memory, communication interface, pressure transmitter, thermocouple, absolute displacement sensor, servo driver, proportional directional valve, bidirectional piston drive cylinder, array-type heating base, preset solid-state relay, preset extruder interface, and human-machine interface. For example... Figure 2 As shown, the pressure transmitter, thermocouple, and absolute displacement sensor form a unidirectional data acquisition link with the edge master control PLC; the servo hydraulic actuator receives commands through the bidirectional interactive channel between the edge master control PLC and the servo driver, and relies on the internal proportional directional valve to guide the bidirectional piston to drive the cylinder to connect to the automatic screen changer in one direction; the heating level signal output by the edge master control PLC triggers the array heating base in one direction through the preset solid-state relay to complete the heat flow injection in the screen changing area.

[0087] The processor can be the central processing unit of an edge-controlled PLC, with models including Beckhoff CX series or Siemens S7-1500 series. The memory includes a non-volatile program memory area and a runtime data memory area. The non-volatile program memory area stores structured text programs, ladder diagram programs, or function block programs conforming to IEC 61131-3 standards. The runtime data memory area stores inlet pressure, inlet temperature, pressure integral, preset target temperature, absolute displacement, pressure gradient, current gradient, duty cycle, derating rate, preset transition zone temperature, and target speed. Communication interfaces include EtherCAT, PROFINET, analog input, analog output, digital output, and industrial Ethernet interfaces. The EtherCAT interface is used for data exchange with servo drives, remote I / O modules, and absolute displacement sensors; the analog input interface is used for pressure transmitter and thermocouple signal acquisition; the digital output interface is used for preset solid-state relay triggering; and the industrial Ethernet interface is used for preset extruder target speed and feedforward signal transmission.

[0088] The pressure transmitter is installed on the inlet flow channel side of the automatic screen changer, with a range of 0MPa to 40MPa and an output signal of 4mA to 20mA or a digital bus signal. Thermocouples are installed on the inlet flow channel side of the automatic screen changer, as well as in the preheating zone and preset transition zone. A cold junction compensation circuit is configured between the thermocouples and the temperature acquisition module. An absolute displacement sensor is installed on the main shaft of the bidirectional piston-driven cylinder or the screen slide, outputting the absolute displacement of the screen. The servo driver and proportional directional valve form the electro-hydraulic control link of the servo hydraulic actuator, and the bidirectional piston-driven cylinder is mechanically connected to the screen. An array-type heating base is fixed circumferentially or laterally to the slide rail of the automatic screen changer, with pulse heating rods embedded in the preheating zone and preset transition zone. A preset solid-state relay is located between the processor's digital output terminal and the pulse heating rod power supply circuit, with a zero-crossing trigger mode matched to the modulation signal corresponding to the duty cycle. The preset extruder interface can connect to a melt gear pump servo driver, an extruder main screw frequency converter, or an extruder main screw driver. The human-machine interface is used to configure preset pressure threshold, preset resistance threshold, preset current threshold, preset ratio range, preset melting temperature, preset stable band, preset relaxation time, preset tolerance period, preset distance, and preset duration.

[0089] The aforementioned virtual functional modules are implemented by the processor reading and executing computer programs from the memory. The processor, memory, and communication interface constitute the static computing platform of the edge master PLC. The parameter acquisition module, preheating control module, displacement drive module, derating heating module, and state recovery module are all stored in the memory in the form of computer program function blocks, and form data connections with pressure transmitters, thermocouples, absolute displacement sensors, servo drivers, preset solid-state relays, and preset extruder interfaces through the communication interface.

[0090] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. An adaptive control method for an automatic screen changer, characterized in that, include: Obtain the inlet pressure and inlet temperature of the automatic screen changer; When the pressure integral determined based on the inlet pressure is greater than the preset pressure threshold, the preheating zone of the automatic screen changer is heated according to the inlet temperature. When the temperature of the preheating zone reaches the preset target temperature, the absolute displacement of the screen plate of the automatic screen changer is obtained, and when the absolute displacement enters the preset transition zone of the automatic screen changer, the screen plate is driven at a preset speed. During the period when the absolute displacement is in the preset transition zone, the current driving the mesh plate is acquired, and the pressure gradient of the inlet pressure and the current gradient of the current are extracted. When the pressure gradient is greater than a preset resistance threshold and the current gradient is greater than a preset current threshold, the mesh is driven at a derating speed, and the duty cycle is determined based on the pressure gradient to control the pulse heating in the preset transition zone, wherein the derating speed is lower than the preset speed. During the derating rate, the temperature of the preset transition zone is obtained. When the temperature of the preset transition zone reaches the preset melting temperature and the pressure gradient is in the preset steady zone for a period of time exceeding the preset relaxation time, the pulse heating is stopped and the speed is restored to the preset rate.

2. The adaptive control method for an automatic network switcher according to claim 1, characterized in that: The integral of the variation of the inlet pressure within a preset time window is calculated as the pressure integral. When the pressure integral is greater than the preset pressure threshold, it is determined that the trigger condition is met. If the triggering condition is met, the inlet temperature is locked as the reference temperature and the preheating zone is heated with a preset power. The reference temperature is then summed with a preset compensation constant to determine the preset target temperature. The feedback temperature of the preheating zone is obtained. When the feedback temperature reaches the preset target temperature, a transition signal is generated to trigger the acquisition of the absolute displacement of the screen plate of the automatic screen changer.

3. The adaptive control method for an automatic network switcher according to claim 1, characterized in that, The absolute displacement travel includes a first travel area, the preset transition area, and a second travel area connected sequentially, and before obtaining the absolute displacement, it also includes: Obtain the initial coordinates, preset gap, and inner diameter of the flow channel of the automatic screen changer; The sum of the initial coordinates and the preset gap is determined as the first boundary marker at the intersection of the first travel area and the preset transition area; The sum of the first boundary marker and the inner diameter of the flow channel of the automatic screen changer is determined as the second boundary marker at the junction of the preset transition zone and the second travel zone; When the absolute displacement is within the first travel zone, the mesh plate is driven at a preset first speed greater than the preset speed; When the absolute displacement is in the second stroke zone, the mesh plate is driven at a preset second speed.

4. The adaptive control method for an automatic network switcher according to claim 1, characterized in that, The step of determining the duty cycle based on the pressure gradient to control the pulse heating in the preset transition zone includes: Calculate the difference between the pressure gradient and the preset resistance threshold; Multiply the difference by the preset gain to obtain the base duty cycle; The basic duty cycle is limited to a preset ratio range and used as the duty cycle. A modulation signal is generated based on the duty cycle, and the modulation signal is injected into the preset transition zone via a preset solid-state relay in a zero-crossing trigger mode to perform the pulse heating.

5. The adaptive control method for an automatic network switcher according to claim 1, characterized in that, After extracting the pressure gradient and the current gradient, the method further includes: When the pressure gradient is greater than the preset resistance threshold and the current gradient is not greater than the preset current threshold, cavitation noise is determined to be generated. Skip driving the stencil at the derating speed and control the pulse heating in the preset transition zone, and maintain driving the stencil at the preset speed.

6. The adaptive control method for an automatic network switcher according to claim 1, characterized in that, During the period of maintaining the aforementioned rate of depreciation, the following is also included: The cumulative duration for which the rate of decrease is maintained is timed; When the accumulated time exceeds the preset tolerance period and the condition for recovery to the preset speed is not met, the mesh plate is controlled to move in the opposite direction by a preset distance; Position locking is performed at the coordinates where the reverse movement of the mesh plate is completed to stop the displacement.

7. The adaptive control method for an automatic network switcher according to claim 6, characterized in that, Also includes: When the position locking is maintained for a preset duration, the position locking is released; Re-drive the stencil at the stated derating speed and reset the accumulated duration to zero.

8. The adaptive control method for an automatic network switcher according to claim 1, characterized in that, During the period of maintaining the aforementioned rate of depreciation, the following is also included: Calculate the time derivative of the absolute displacement as the actual velocity, and obtain the velocity difference between the preset velocity and the actual velocity; The velocity difference is multiplied by the preset cross-sectional area of ​​the mesh to determine the volume difference, and feedforward signaling is generated based on the volume difference.

9. The adaptive control method for an automatic network switcher according to claim 8, characterized in that, The generation of the feedforward signaling based on the volume difference includes: Obtain the current rotational speed and preset displacement coefficient of the preset extruder upstream of the automatic screen changer; The derated speed is determined by dividing the volume difference by the preset displacement coefficient; The target speed is obtained by subtracting the current speed from the drated speed. The feedforward signal is generated based on the target rotational speed to control the preset extruder to operate at the target rotational speed.

10. An adaptive control system for an automatic network switcher, used to implement the adaptive control method for an automatic network switcher as described in any one of claims 1-9, characterized in that, include: The parameter acquisition module is used to acquire the inlet pressure and inlet temperature of the automatic screen changer; The preheating control module is used to control the heating of the preheating zone of the automatic screen changer according to the inlet temperature when the pressure integral determined based on the inlet pressure is greater than a preset pressure threshold. The displacement drive module is used to obtain the absolute displacement of the screen plate of the automatic screen changer when the temperature of the preheating zone reaches the preset target temperature, and drive the screen plate at a preset speed when the absolute displacement enters the preset transition zone of the automatic screen changer. The derating heating module is used to acquire the current driving the mesh plate during the period when the absolute displacement is in the preset transition zone, and to extract the pressure gradient of the inlet pressure and the current gradient of the current; when the pressure gradient is greater than a preset resistance threshold and the current gradient is greater than a preset current threshold, the mesh plate is driven at a derating speed, and the duty cycle is determined based on the pressure gradient to control the pulse heating in the preset transition zone, wherein the derating speed is lower than the preset speed. The state recovery module is used to acquire the temperature of the preset transition zone during the derating rate. When the temperature of the preset transition zone reaches the preset melting temperature and the pressure gradient is in the preset stable zone for a period of time exceeding the preset relaxation time, the pulse heating is stopped and the system returns to the preset rate.

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