System and method for adjusting a closed-loop controller of a high-temperature molten liquid dispensing system

Abstract

A system and method for adjusting a closed-loop controller for a high-temperature molten liquid dispensing system is disclosed. In an exemplary method, based on a set temperature setpoint, the high-temperature molten liquid dispensing system is maintained in a steady state with respect to a temperature process variable and a heater duty cycle control variable. The heater duty cycle control variable is brought into a sustained oscillation. An amplitude and a limit period are determined. A limit gain is determined based on the step value and the amplitude. A proportionality constant, an integral constant, or a derivative constant is determined based on the limit period and / or the limit gain. An open-loop controller is implemented using the proportionality constant, the integral constant, or the derivative constant.

Description

[Background technology]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims priority to U.S. Provisional Patent Application No. 62 / 901,1198, filed September 16, 2019, which is incorporated by reference in its entirety.

[0002] [Technical field] The present invention relates generally to fluid dispensing, and more particularly to adjusting a closed-loop controller for a high temperature melt (hot melt) fluid dispensing system.

[0003] [background] Hot melt liquid dispensing systems are used in a variety of applications. For example, such systems may apply hot melt adhesives during the manufacture of disposable hygiene products. As another example, hot melt liquid dispensing systems may apply hot melt adhesives to assemble various types of packaging, such as paper-based packaging for food and beverages. Hot melt adhesives used in such applications may include moisture-curing hot melt polyurethane adhesives ("hot melt PURs"), which are often used where stable inter-surface bonds must be formed. Other conventional hot melt adhesives may be used to secure a variety of both similar and dissimilar materials together in mating relationships, such as wood, plastic, corrugated film, paper, carton stock, metal, rigid polyvinyl chloride (PVC), fabric, leather, and the like. Hot melt adhesives may be particularly useful in applications where it is desirable for the adhesive to solidify rapidly after melting and dispensing.

[0004] In an exemplary configuration of a hot melt liquid dispensing system, a hot melt adhesive in solid form is fed into a melter containing a heated tank and / or a heated grid to produce a molten hot melt adhesive. After heating, the molten adhesive is pumped through a heated hose to an applicator. The applicator, equipped with a valve and a nozzle, is sometimes referred to as a dispensing "gun" or gun module. The applicator then dispenses the molten adhesive, often as a series of dots or lines, onto the desired surface or substrate. It is always paramount that the adhesive be applied in the correct location, timing, and amount. For example, dispensing an insufficient amount of adhesive can result in an ineffective bond, while excessive adhesive not only wastes material but can also result in undesirable flow as the adhesive is applied to the surface. In addition to parameters that directly control the applicator, other process variables within the dispensing system also affect how effectively the adhesive is applied to the surface. For example, the amount and placement of adhesive dispensed can be affected by the viscosity of the molten adhesive, which is a function of the temperature of the molten adhesive.

[0005] Various control methods have been developed to adjust various parameters of hot melt adhesive dispensing systems to achieve desired adhesive application results. One common mechanism for controlling dispensing systems is to use a control loop system, such as a proportional-integral-derivative (PID) controller. However, implementing an effective control loop system presents several challenges. For example, the values ​​of the constants used in the control loop system must be carefully set (e.g., tuned) to achieve optimal results. For example, with respect to temperature, an untuned control loop may oscillate, thereby causing the adhesive temperature to vary in a manner similar to a sinusoidal wave. While these constants may be preset to default values, they are often not optimal for a particular installation of the dispensing system. For example, a dispensing system may be installed according to any one of a number of possible configurations, each containing an equally wide variety of equipment. For example, various types and quantities (capacities) of hoses and guns may be attached to a melter. However, melters (or other equipment) may be sold by manufacturers or suppliers without prior knowledge of what other equipment the melter will be used with when placed in service. Furthermore, the original equipment used with the melter may be reconfigured or replaced with different equipment entirely. Furthermore, even if it is possible to adjust the constant values ​​of the control loops, this often requires specialized knowledge and is a very time-consuming trial-and-error approach.

[0006] These and other shortcomings are addressed in the present invention. Summary of the Invention

[0007] Disclosed herein are systems and methods for adjusting a closed-loop controller of a high-temperature molten liquid dispensing system. In an exemplary method of the present invention, the high-temperature molten liquid dispensing system includes an applicator configured to dispense a high-temperature molten liquid and a high-temperature molten liquid heater associated with the applicator. The closed-loop controller is configured to receive a temperature setpoint for the high-temperature molten liquid and a measured temperature process variable for the high-temperature molten liquid, and to output a duty cycle control variable for controlling the high-temperature molten liquid heater. The method includes setting the temperature setpoint and maintaining the high-temperature molten liquid dispensing system in a steady state with respect to the temperature process variable and the duty cycle control variable based on the temperature setpoint. The duty cycle control variable is adjusted by alternating positive and negative step values ​​to induce sustained oscillation of the temperature process variable. An amplitude of the sustained oscillation and a limit period associated with the sustained oscillation are determined. A limit gain is determined based on the step value and the amplitude of the sustained oscillation. At least one of a proportional constant, an integral constant, and a derivative constant is determined based on at least one of the limit period and the limit gain, and an open-loop controller is implemented using the at least one of the proportional constant, the integral constant, and the derivative constant.

[0008] An exemplary hot molten liquid dispensing system includes an applicator, a hot molten liquid heater associated with the applicator, and a control system configured to implement a closed-loop controller. The closed-loop controller is configured to receive a temperature setpoint for the hot molten liquid and a measured temperature process variable for the hot molten liquid, and to output a duty cycle control variable for controlling the hot molten liquid heater. The control system is further configured to set the temperature setpoint. Based on the temperature setpoint, the hot molten liquid dispensing system is maintained in a steady state with respect to the temperature process variable and the duty cycle control variable. Positive and negative step values ​​alternately adjust the duty cycle control variable to induce sustained oscillation of the temperature process variable. A limiting gain is determined based on the step value and the amplitude of the sustained oscillation. At least one of a proportional constant, an integral constant, and a derivative constant is determined based on at least one of the limiting period and the limiting gain. The control device implements an open-loop controller using at least one of the proportional constant, the integral constant, and the derivative constant.

[0009] An exemplary control system is provided for adjusting a closed-loop controller for a hot molten liquid dispensing system having an applicator configured to dispense a hot molten liquid and a hot molten liquid heater associated with the applicator. The closed-loop controller is configured to receive a temperature setpoint for the hot molten liquid and a measured temperature process variable for the hot molten liquid, and to output a duty cycle control variable for controlling the hot molten liquid heater. The control system includes one or more processors and a memory storing instructions that, when executed by the one or more processors, cause the control system to perform the following operations: A temperature setpoint is set, and based on the temperature setpoint, the hot molten liquid dispensing system is maintained in a steady state with respect to the temperature process variable and the duty cycle control variable. The duty cycle control variable is adjusted by alternating positive and negative step values ​​to cause sustained oscillation of the temperature process variable. An amplitude of the sustained oscillation and a limit period associated with the sustained oscillation are determined. A limit gain is determined based on the step value and the amplitude of the sustained oscillation. At least one of a proportional constant, an integral constant, and a derivative constant is determined based on at least one of the limit period and the limit gain, and an open-loop controller is implemented using the at least one of the proportional constant, the integral constant, and the derivative constant.

[0010] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments and, together with the following detailed description, serve to explain the principles of the method and system of the present invention. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 illustrates an exemplary dispensing system according to one embodiment of the present invention.

[0012] [Figure 2]FIG. 2 shows an exemplary schematic diagram according to one embodiment of the present invention.

[0013] [Figure 3] FIG. 3 shows an exemplary schematic diagram according to one embodiment of the present invention.

[0014] [Figure 4] FIG. 4 shows a flowchart of an exemplary method according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] Aspects of the present invention will now be described in detail with reference to the drawings, in which like reference numerals refer to the same elements throughout unless otherwise specified.

[0016] The disclosed systems and methods relate to tuning a closed-loop controller, such as a PID controller, of a hot melt liquid dispensing system. The closed-loop controller may be implemented in a hot melt adhesive dispensing system. While reference is made primarily to hot melt adhesives, the techniques described herein may be applicable to any type of hot melt liquid, including non-adhesives. Similarly, the techniques described herein are typically described with respect to tuning a closed-loop controller of a hot melt liquid dispensing system for a temperature control loop. However, such techniques are equally applicable to tuning a closed-loop controller of a hot molten liquid dispensing system for a pressure control loop, a flow rate control loop, a bubble density control loop, and control loops for other process variables of the hot molten liquid dispensing system. The closed-loop controller may be (or may include) a PID controller. Tuning a PID controller may include determining the proportional (P), integral (I), and derivative (D) terms of the controller and their respective constants (e.g., gain, integral time, derivative time). The techniques described herein may also be applied to tuning a P controller, a PI controller, or a PD controller.

[0017] FIG. 1 illustrates an exemplary hot melt adhesive system 10 (e.g., a hot melt adhesive dispensing system or other type of hot melt liquid dispensing system) in which the technology described herein may be implemented. The hot melt adhesive system 10 includes an adhesive supply 22 for receiving and melting solid or semi-solid hot melt adhesive 24a, such as pellets, a manifold 26 connected to the adhesive supply 22, a controller 28, and a user interface 29. The adhesive supply 22 may be, among other things, a tank-type melter or a grid and reservoir melter. Upon melting, the solid or semi-solid hot melt adhesive 24a stored in the adhesive supply 22 transforms into liquid hot melt adhesive 24. The adhesive supply 22 includes a sidewall 30, a removable cover 31, and a base 32 that includes one or more adhesive supply heaters 34 for melting and heating the hot melt adhesive 24a and liquid hot melt adhesive 24 in the adhesive supply 22. An adhesive supply outlet 36 adjacent the base 32 is coupled to a passage 38 which connects to an inlet 40 in the manifold 26 .

[0018] A pump 58, such as a vertically oriented piston pump (as shown) or a gear pump, is coupled to the manifold 26 for pumping the liquid hot melt adhesive 24 from the adhesive supply 22 into the manifold 26, where it is split into separate streams. A pump motor 59 drives the pump 58. Operation of the pump 58 (and thus, as a function of the pump motor 59) supplies the hot melt adhesive under pressure to the manifold 26 and the applicators 48, 50. Such pressure can affect the amount of hot melt adhesive dispensed in one applicator cycle (also called a gun cycle) of the adhesive dispensing module 54, as well as generally affect the flow rate and velocity of the hot melt adhesive into, through, and / or out of the manifold 26.

[0019] The manifold 26 is attached to the sidewall 30 of the adhesive supply 22 with spacers 41 and is spaced from the adhesive supply 22 by a distance 42 sufficient to provide thermal isolation of the adhesive supply 22 from the manifold 26. The manifold 26 includes multiple outlet ports 44 that may be fitted with heated hoses 46 attached to one or more adhesive applicators 48, 50 to supply liquid adhesive 24 to the applicators 48, 50. The manifold 26 may include a manifold heater 56 that is separate from the adhesive supply heater 34 and may be independently controlled by the controller 28. In some embodiments, a single heater may be used to heat the adhesive supply 22 and the manifold 26. While FIG. 1 shows the adhesive supply 22 physically proximate to the manifold 26, other arrangements are possible in which the source of hot melt adhesive is physically separate from the manifold. In such arrangements, multiple pumps may be used to move the hot melt adhesive from the adhesive supply 22 toward the final application point.

[0020] The manifold 26 may generate multiple streams that are carried by corresponding heated hoses 46 to the applicators 48, 50. The hoses 46 are electrically coupled to the controller 28 by cord sets 62 associated with each hose 46. The applicators 48, 50 include one or more adhesive dispensing modules 54 configured to dispense / apply the liquid hot melt adhesive 24 to products, such as cartons, packages, or other objects. The adhesive dispensing modules 54 are attached to an applicator body 51 having an applicator heater 53 and supported on a frame 52. The hot melt adhesive system 10 includes two applicators 48, 50, one on each side of the dispensing unit 20, as shown in FIG. 1 . However, other implementations of the hot melt adhesive system 10 may use different numbers of applicators, dispensing modules, and other configurations. For example, the applicators 48, 50 may each be configured with a single adhesive dispensing module 54, or each may be configured with a pair of adhesive dispensing modules 54. The adhesive dispensing modules 54 of the applicators 48, 50 may generally be monitored, controlled, and activated by a common air supply. Alternatively, the adhesive dispensing modules 54 of the applicators 48, 50 may be independently monitored, controlled, and activated by separate air supplies. The applicators 48, 50 and / or the adhesive dispensing modules 54 may variously be referred to as applicators or dispensers.

[0021] The pump 58 is located external to the adhesive supply 22 and is connected to an air pressure regulator 70 that receives air from the air supply 61. If the pump 58 includes a gear pump, the pump 58 can typically operate without air from the air supply 61. More specifically, the air pressure regulator 70 is attached to the dispensing unit 20 and connected to the air supply 61. In some implementations, the pump 58 can be attached to the manifold 26 and heated by the manifold heater 56. This arrangement allows for a larger tank opening 60, increasing tank capacity and reducing the time required to heat the pump 58. Additionally, a flow meter 80 can be attached to the manifold 26 to measure the flow of hot melt adhesive therethrough. The flow meter 80 has a pair of sensors that are electrically coupled to the controller 28 by respective cords 63 a, 63 b associated with each sensor. At least one product detector 90, such as an optical sensor, is also electrically coupled to the controller 28.

[0022] The dispensing unit 20 includes a controller 28 that may implement a PID controller (or other type of closed-loop controller) and the associated regulation techniques described herein. The controller 28 houses the power and electronic controls for the hot melt adhesive system 10. The controller 28 may be configured with one or more processors and a memory configured to store instructions that, when executed by the one or more processors, cause the controller 28 to perform various operations described herein, including the PID controller and associated regulation techniques. The controller 28 may be configured to monitor and store various measured process variables of the hot melt adhesive system 10, such as hot melt adhesive temperature, hot melt adhesive pressure, hot melt adhesive density (e.g., bubble density), and hot melt adhesive flow (e.g., flow rate). The controller 28 may be configured to set, regulate, and store various input operating parameters (e.g., setpoints) of the hot melt adhesive system 10, such as heater duty cycle, hot melt adhesive temperature setpoint, pressure of air supplied to the pump 58, and speed of the pump 58.

[0023] With respect to the heating functions of the hot melt adhesive system 10, the controller 28 is electrically coupled to the heaters, including the adhesive supply heater 34, the manifold heater 56, and the applicator heater 53, as well as any hose heaters. The controller 28 may also be coupled to various temperature sensors in the hot melt adhesive system 10, which may be associated with or included in the adhesive supply heater 34, the manifold heater 56, the applicator heater 53, and any hose heaters. The controller 28 independently monitors and regulates the adhesive supply heater 34, the manifold heater 56, the applicator heater 53, and any hose heaters to melt the solid or semi-solid hot melt adhesive 24a received in the adhesive supply 22, maintain the temperature of the (molten) hot melt adhesive 24, and ensure the proper viscosity of the hot melt adhesive 24 supplied to the applicators 48, 50 and dispensed by the adhesive dispensing module 54. For example, the controller 28 receives temperature information (measured temperature process values) from temperature sensors and sends heater control commands (e.g., duty cycle control signals or control variables) to each heater to regulate the temperature to a temperature value setpoint. Such heater control commands may increase or decrease the temperature of any or all of the heaters in the hot melt adhesive system 10.

[0024] In addition to the foregoing, the controller 28 may monitor, store, and set various operating parameter values ​​related to the temperature of the hot melt adhesive within the hot melt adhesive system 10. In addition to the current and setpoint temperature values ​​for the adhesive supply heater 34, manifold heater 56, applicator heater 53, and hose 46, the controller 28 may also monitor, store, and set duty cycle control information for any or all of these heaters. For example, the controller 28 may monitor, store, and set duty cycle control information for the adhesive supply heater 34. The duty cycle of a heater may refer to the percentage or proportion of time that the heater is activated (i.e., the time it heats the associated hot melt adhesive) within a time interval (i.e., control period).

[0025] FIG. 2 shows a schematic diagram 200 including a PID controller associated with closed-loop temperature control of a hot melt adhesive in a hot melt adhesive dispensing system (e.g., hot melt adhesive system 10 of FIG. 1). The PID controller may be implemented by a hot melt adhesive dispensing system controller (e.g., controller 28 of FIG. 1). The PID controller may be implemented in software associated with the controller, hardware associated with the controller, or a combination thereof. The controller may be configured to receive a temperature setpoint (target value) at which the hot melt adhesive in the system should be maintained and a currently measured temperature of the hot melt adhesive. In particular, the temperature setpoint may be the temperature at which the hot melt adhesive should be dispensed from an applicator in the system. The controller may further be configured to determine and generate duty cycle control signals to one or more heaters (e.g., adhesive supply heater 34, manifold heater 56, applicator heater 53, and / or hose heaters of FIG. 1). The duty cycle control signal may indicate a duty cycle control variable (e.g., a duty cycle process variable or gain) according to which the heater should operate. FIG. 2 illustrates a system with a single channel. Systems often include multiple such channels. For example, a system may include multiple heaters. In this case, the system may implement multiple PID controllers, each controlling a separate one of the heaters. The same is true for other components and / or processes of the system.

[0026] Initially, the controller receives a temperature setpoint (target value) 210 for the hot melt adhesive in the system. The controller also receives a current or approximately current measured temperature value 224 of the hot melt adhesive via a temperature sensor. The temperature setpoint 210 may be considered a setpoint (SP) or a function r(t) according to some common control loop nomenclature. The measured temperature 224 may be considered a process variable (PV) or a function y(t) according to some common control loop nomenclature. The controller then determines a difference between the temperature setpoint 210 and the measured temperature value 224 to determine a temperature error 212. The temperature error 212 may be considered an error function e(t) according to some common control loop nomenclature. The controller applies one or more of a proportional (P) term 214, an integral (I) term 216, and a derivative (D) term 218 to the temperature error 212 to determine a modified duty cycle control signal 220 for the heater(s) of the system. Duty cycle control signal 220 can be viewed as a function u(t), following some common control loop nomenclature. In a strict PID controller, a proportional term 214, an integral term 216, and a derivative term 218 are each applied to temperature error 212. In a PI controller, only the proportional term 214 and the integral term 216 are applied to temperature error 212. In a PD controller, only the proportional term 214 and the derivative term 218 are applied to temperature error 212. In a P controller, only the proportional term 214 is applied to temperature error 212.

[0027] The proportional term 214 may be applied to the temperature error 212 according to a proportionality constant, which in the parallel (ideal) form of the PID controller is the proportional gain K p The description and equations provided herein relate primarily to the parallel form of the PID controller. The same or similar techniques or principles may be implemented in other forms, such as the standard form, with slightly different equations. The proportional term 214 may be determined according to the following equation (1): Formula (1): TIFF0007770310000001.tif6150

[0028] Integral term 216 may additionally or alternatively be applied to temperature error 212 according to an integral constant, which in a parallel form of a PID controller is the integral gain K i (shown in FIG. 2). The integral term 216 may be determined according to the following equation (2): Formula (2): TIFF0007770310000002.tif14150

[0029] The derivative term 218 may additionally or alternatively be applied to the temperature error 212 according to a derivative constant, which in parallel form is the derivative gain K d The derivative term 218 may be determined according to equation (3) below: Formula (3): TIFF0007770310000003.tif9150

[0030] In the parallel form of the PID controller, a proportional term 214, an integral term 216, and a derivative term 218 may be applied to the temperature error 212 according to equation (4) below to determine a duty cycle control signal 220 (i.e., function u(t)). Formula (4): TIFF0007770310000004.tif11150

[0031] In other words, the duty cycle control signal 220 (ie, the function u(t)) may be equal to the proportional term 214 plus the integral term 216 plus the derivative term 218 .

[0032] In the standard form of a PID controller, a proportional term 214, an integral term 216, and a derivative term 218 may be applied to the temperature error 212 according to equation (5) to determine a duty cycle control signal 220 (i.e., function u(t)). Formula (5): TIFF0007770310000005.tif13150

[0033] In equation (5), T idenotes the integration time, and K p denotes the proportional gain, and T d denotes the differential time. In the standard form, according to some nomenclature, K p Instead of K c The standard and parallel forms are sometimes called i =K p / T i and K d =K p PT d Or, in some cases, K i =1 / T i and K d =T pd is.

[0034] The heater 222 (or possibly multiple heaters) operates according to the generated duty cycle control signal 220. In some cases, another component or process in the system may operate according to a control signal similar to the duty cycle control signal 220. The duty cycle control signal 220 may cause the heater 222 to increase its duty cycle, decrease its duty cycle, or maintain its current duty cycle. This may increase, decrease, or maintain the temperature of the hot melt adhesive. A newly measured temperature value 224 reflects the operation of the heater 222 based on the duty cycle control signal 220. Because there is often a delay between when the heater's duty cycle is adjusted and when the resulting temperature change occurs, the measured temperature value 224 may be captured a predetermined time after the duty cycle is adjusted by the duty cycle control signal 220. It is further noted that following heater duty cycle adjustments, the temperature change may occur gradually until a temperature is reached that ultimately reflects the duty cycle adjustment as dictated by duty cycle control signal 220. Further iterations of the control loop may be performed, such as with new measured temperature values ​​224, to implement temperature control of the hot melt adhesive dispensing system. For example, the control loop may be continuously executed to repeat each control period or each control interval.

[0035] The controller may also be applied to other process variables or features of a hot melt adhesive dispensing system. For example, the controller may be applied to the pressure at which the hot melt adhesive is delivered to the applicator. In this exemplary pressure control loop, the pressure setpoint may include (or may be) the controller's setpoint (SP), i.e., function r(t), and the measured pressure value may include (or may be) the controller's process variable (PV), i.e., function y(t). A control signal to a pump (and / or pump motor) in a hot melt adhesive dispensing system may include (or may be) the controller's manipulated variable (MV), i.e., function u(t). For example, the control signal to a pump may adjust the pump's speed (e.g., revolutions per minute or cycles). As another example, a controller may be applied to the flow rate at which the hot melt adhesive is delivered to the applicator. In this exemplary flow rate control loop, the flow rate setpoint may include (or may be) the setpoint (SP), i.e., function r(t), and the measured flow rate value may include (or may be) the process variable (PV), i.e., function y(t). The control signal to the pump (and / or pump motor) may (can) include a manipulated variable (MV) or function u(t), such as to adjust the speed of the pump. As another example, the controller may apply a bubble density to the hot melt adhesive being delivered to the applicator. Bubble density may indicate the relationship between the liquid hot melt (in terms of mass or volume) and the gas in the bubble. Bubble density may be measured and / or adjusted in several ways. For example, bubble density may be reduced by mixing more gas into the liquid stream.

[0036] FIG. 3 shows a schematic diagram 300 of a control system including an autotune function 330 and a PID controller 332 (or other closed-loop controller, including a P controller, a PI controller, or a PD controller). The control system may generally be used to autotune the PID controller 332. The control system may be switched between an operational mode (using the PID controller 332) and an autotune mode (using the autotune function 330). An operator may selectively cause the control system to switch between the operational mode and the autotune mode. Additionally or alternatively, the control system may automatically switch between the operational mode and the autotune mode upon determining that the hot melt adhesive dispensing system is operating outside of required tolerances (e.g., with respect to dispensed volume, placement, timing, etc.). The autotune mode may be activated while the hot melt adhesive dispensing system is applying hot melt adhesive to an actual product (i.e., online). Alternatively, and preferably, the autotune mode may be activated while the hot melt adhesive dispensing system is not dispensing hot melt adhesive to an actual product (i.e., offline). In the operational mode, the hot melt adhesive dispensing system applies (applies) hot melt adhesive to an actual product, preferably according to the required tolerances.

[0037] In the operational mode, the control process generally proceeds in the manner described in connection with FIG. 2. That is, a hot melt adhesive temperature setpoint 310 is input and compared to a measured hot melt adhesive temperature value 324 to determine a temperature error 312. The temperature setpoint 310 may be input, for example, by an operator. The temperature error 312 is input to a PID controller 332. The PID controller 332 may be the same as or similar to the PID controller described in connection with FIG. 2. The PID controller 332 may include one or more proportional, integral, and derivative terms (e.g., proportional term 214, integral term 216, and derivative term 218, respectively, of FIG. 2) and respective constants (e.g., gain, integral time, and / or derivative time). Based on the temperature error 312 and the proportional, integral, and / or derivative terms (and their respective constants) of the PID controller 332, the PID controller 332 determines a duty cycle control signal 320 for operation of the hot melt adhesive heater(s) 322 (or other components or processes of the system). New measured temperature values ​​324 can be obtained and further iterations of the control process performed in a similar manner to effect temperature control.

[0038] In autotune mode, a temperature setpoint 310 is also input and compared to a measured temperature value 324 to determine a temperature error 312. The temperature setpoint 310 may be input, for example, by an operator. The temperature error 312 is input to an autotune function 330. The autotune function 330 may include a relay autotune function, which introduces a relay into the feedback control loop of the control system. Generally, the autotune function 330 extracts a step value and a frequency (i.e., period) near a critical point (i.e., oscillation point). The autotune function 330 uses the determined step value and frequency to calculate the respective constants (e.g., K in parallel form) for the proportional, integral, and derivative terms of a PID controller 332. p , K. i and K. d) is determined. More specifically, a step value (for the duty cycle control signal 320) is selected to achieve (e.g., gradually increase) a sustained oscillation (for the measured temperature value 324). A limit period and amplitude of the sustained oscillation are determined. A limit gain is then determined based on the amplitude of the oscillation. Constants for each of the proportional, integral, and derivative terms are determined based on one or more of the limit period and limit gain. The autotuning process is described in further detail in conjunction with the data flow diagram of FIG. 4. In an operational mode, the PID controller 332 applies such constants to implement temperature control of the hot melt adhesive dispensing system.

[0039] FIG. 4 shows a data flow diagram of a method 400 for tuning (e.g., autotuning) a closed-loop controller for a hot melt adhesive dispensing system (e.g., hot melt adhesive system 10 of FIG. 1). The closed-loop controller may include a PID controller, a P controller, a PI controller, or a PD controller (e.g., the PID controller described in connection with FIG. 2 or PID controller 332 of FIG. 3). The closed-loop controller may be implemented by controller 28 of FIG. 1. The hot melt adhesive dispensing system may include an applicator configured to dispense hot melt adhesive and a hot melt adhesive heater associated with the applicator. The applicator may be implemented in accordance with one or more of applicators 48, 50 and adhesive dispensing module 54 of FIG. 1. The hot melt adhesive heater may be implemented in accordance with one or more of adhesive supply heater 34, manifold heater 56, applicator heater 53, and hose heater of FIG. 1.

[0040] The closed-loop controller may be configured to receive an adhesive temperature set point (e.g., temperature set points 210, 310 of FIGS. 2 and 3, respectively) and a measured adhesive temperature process variable (e.g., measured temperature values ​​224, 324 of FIGS. 2 and 3, respectively). The closed-loop controller may further be configured to output a duty cycle control variable (e.g., duty cycle control signals 220, 320 of FIGS. 2 and 3, respectively) for controlling the hot melt adhesive heater. Although method 400 is described with respect to a hot melt adhesive and a hot melt adhesive dispensing system, the techniques described herein apply equally to other types of hot melt liquids and hot melt liquid dispensing systems.

[0041] Method 400 may be initiated by an operator. Additionally or alternatively, method 400 may be initiated (automatically) by the hot melt adhesive dispensing system or closed-loop controller. For example, the hot melt adhesive dispensing system may determine that hot melt adhesive is being applied outside of acceptable tolerances (e.g., with respect to dispensed volume, placement, timing, etc.). Initiating the method may include switching the hot melt adhesive dispensing system from an operational mode (see discussion of PID controller 332 in FIG. 3 ) to an autotune mode (see discussion of autotune function 330 in FIG. 3 ).

[0042] In step 402, an adhesive temperature setpoint is set and the hot melt adhesive dispensing system is brought to and maintained at a steady state. The steady state may be in terms of the hot melt adhesive temperature (e.g., the measured adhesive temperature process variable) and the duty cycle process control variable. At the steady state, the measured adhesive temperature process variable may fluctuate (e.g., oscillate) around the adhesive temperature setpoint. Such fluctuations or oscillations may be due to an unregulated state of the open-loop controller. An average of the duty cycle control variable over a period (e.g., a predetermined cycle time) at the steady state may be determined. The closed-loop controller may be tuned for the adhesive temperature setpoint based on the average of the duty cycle control variable. Furthermore, an average of the measured adhesive temperature process variable over the period at the steady state may be determined. The period may be measured from the time the measured adhesive temperature process variable reaches the adhesive temperature setpoint. The period may be determined to minimize offsets due to imperfect swings of the measured adhesive temperature process variable above and below the adhesive temperature setpoint. Rather than a period of time, the average of the duty cycle control variable and / or the measured adhesive temperature process variable may be determined over a number (e.g., a predefined number) of data points (e.g., 200 data points). In some cases, an initial wait period may be beneficial before beginning to determine the average of the duty cycle control variable and / or the measured adhesive temperature process variable. For example, the method 400 may be initiated while the hot melt adhesive dispensing system is cold or well below the adhesive temperature setpoint. In such cases, an initial warm-up period may be beneficial. The initial wait period or warm-up period may end once the measured adhesive temperature process variable reaches the adhesive temperature setpoint.

[0043] In step 404, the duty cycle control variable is alternately adjusted by positive and negative step values ​​to cause sustained oscillation of the glue temperature process variable. The duty cycle control variable may be alternately adjusted based on the determined average of the duty cycle control variable. Additionally or alternatively, the duty cycle control variable may be alternately adjusted based on the determined average of the measured glue temperature process variable. The duty cycle control variable adjusted first may be the determined average of the duty cycle control variable. The step value may be the amplitude of the drive function that causes oscillation of the glue temperature process variable. The oscillation may be sustained for a predetermined period of time. The step value may be determined based on a current duty cycle control variable (e.g., a current duty cycle setpoint). For example, the step value may be determined based on a current duty cycle control variable such that adjusting the current duty cycle control variable by the positive or negative step value will not cause the duty cycle control variable to go below 0% or above 100%. Inducing sustained oscillation of the glue temperature process variable may include adjusting the duty cycle control variable by the step value with a positive sign. In response to determining that the glue temperature process variable is above the glue temperature setpoint (e.g., crossing the glue temperature setpoint from below the glue temperature setpoint to above the glue temperature setpoint), the duty cycle control variable is adjusted by the step value with a negative sign. In response to determining that the glue temperature process variable is below the glue temperature setpoint (e.g., crossing the glue temperature setpoint from above the glue temperature setpoint to below the glue temperature setpoint), the duty cycle control variable is adjusted by the step value with a positive sign. Further similar iterations of alternatingly adjusting the duty cycle control variable by the step values ​​with a positive and negative sign may be performed until oscillation is sustained, such as for a predetermined period of time.

[0044] In one aspect, when generating a sustained oscillation of the glue temperature process variable, hysteresis can be applied to the glue temperature setpoint. For example, instead of a single glue temperature setpoint, a crossover threshold range can be used. The crossover threshold range can include a lower glue temperature threshold and an upper glue temperature threshold. After generating a sustained oscillation and adjusting the duty cycle control variable by a positive step value, the duty cycle control variable can be readjusted by a negative step value only if the glue temperature process variable crosses (rises above) the upper glue temperature threshold. Conversely, after adjusting the duty cycle control variable by a negative step value, the duty cycle control variable can be readjusted by a positive step value only after the glue temperature process variable crosses (falls below) the lower glue temperature threshold. A small amount of hysteresis can help improve the reliability of the autotuning process, for example, in the presence of A / D converter quantization or environmental electrical noise.

[0045] In step 406, the amplitude of the sustained oscillation and the critical period associated with the sustained oscillation are determined. According to some nomenclature, the critical period is P u The critical period can be calculated based on the observed period (P) of sustained oscillations. u ) may be determined to be equal to the period (P). The amplitude of the sustained oscillation may be referred to as amplitude A. In step 408, the limit gain K u is determined based on the step value and the amplitude of the sustained oscillation. u can be determined according to the following equation (6): In equation (6) below, the step value is designated as d and the amplitude of the sustained oscillation is designated as A. Formula (6): TIFF0007770310000006.tif10150

[0046] In one embodiment, the amplitude A and the limit period P ucan be determined based on a sample subset (e.g., multiple cycles) of oscillations in a sustained oscillation. u may be determined based on the average observed period (P) of the sample subset of vibrations. The amplitude A may be determined based on the average amplitude of the sample subset of vibrations.

[0047] In step 410, at least one of a proportional constant, an integral constant, and a derivative constant is determined based on at least one of a limit period and a limit gain. In the case of a PID controller, the proportional constant, the integral constant, and the derivative constant are each determined. The proportional constant may be determined based on at least the limit gain. The integral constant and the derivative constant may be determined based on at least the limit period. The proportional constant, the integral constant, and / or the derivative constant may be determined, for example, based on the Ziegler-Nichols method applied to the limit gain and the limit period. Other rules or methodologies may also be used to determine the proportional constant, the integral constant, and / or the derivative constant based on at least one of the limit period or the limit gain. The proportional constant (e.g., the proportional gain) may be determined according to the following equation (7): In equation (7), K p indicates the proportional gain, and K u indicates the marginal gain. Formula (7): TIFF0007770310000007.tif6150

[0048] The integral constant is the integral gain K i The integral gain K i can be determined according to the following equation (8): i indicates the integration time. Formula (8): TIFF0007770310000008.tif10150

[0049] In the standard form of a PID controller, the derivative constant is the derivative time T d In the parallel form of the PID controller, the derivative constant is the derivative gain K d, which can be determined according to the following equation (9): d is the derivative time T used in the standard form d It may be equal to . Formula (9): TIFF0007770310000009.tif9150

[0050] In step 412, the closed-loop controller is implemented with at least one of a proportional constant, an integral constant, and a derivative constant. That is, a proportional constant is applied to the proportional term, an integral constant is applied to the integral term, and / or a derivative constant is applied to the derivative term. If the closed-loop controller is a PID controller, the PID controller is implemented with each of a proportional constant, an integral constant, and a derivative constant. In a parallel form of a PID controller, the proportional constant is the proportional gain K p P, and the integral constant is the integral gain K i and the derivative constant is the differential gain K d In parallel form, the PID controller may be implemented according to equation (4).

[0051] After the closed-loop controller (e.g., a PID controller) is implemented in step 412, the hot melt adhesive dispensing system may be switched to an operational mode in which the hot melt adhesive heater heats the hot melt adhesive according to a duty cycle control variable, which is controlled via a closed-loop controller implemented (tuned) with at least one of a proportional constant, an integral constant, and a derivative constant.

[0052] After the open-loop controller is tuned, the quality of the tuning can be evaluated. In one example, an indicator of the quality of tuning can be determined based on the measured glue temperature process variable. The value of the indicator of the quality of tuning can be determined based on the difference between the mean of the measured glue temperature process variable and the glue temperature set point, and the variance or standard deviation of the measured glue temperature process variable. Optimal tuning may have occurred (or can be determined) when the mean of the measured glue temperature process variable is centered on the glue temperature set point and the values ​​of the measured glue temperature process variable are all close to the glue temperature set point. Other methods of evaluating the quality of tuning are also contemplated.

[0053] As mentioned above, method 400 may also be implemented with respect to the pressure of the hot melt adhesive supplied to the applicator, the flow rate of the hot melt adhesive supplied to the application and / or manifold, or the foam density as it is supplied to the applicator, rather than the temperature of the hot melt adhesive.

[0054] The control system and controller (e.g., PID controller) tuning techniques described herein realize many advantages when applied to hot melt adhesive dispensing systems or other types of hot melt liquid dispensing systems. For example, the closed-loop control techniques described herein avoid many of the drawbacks associated with non-optimized feedback control loops or open-loop control systems, such as allowing the feedback loop to slowly ("drift") or quickly ("runaway") cause the process to move away from the set point. As another example, the tuning techniques described herein can be implemented even while the associated hot melt adhesive dispensing system is operating. As another example, the control system and tuning techniques described herein are particularly well-suited for hot melt liquid dispensing systems, which often experience relatively long time constants or dead times due to the time delay between when a duty cycle control variable is adjusted and when a corresponding change in adhesive temperature is observed. As yet another example, the techniques described herein can be used to quickly and easily retune a controller (e.g., a PID controller) after one or more parts or components of a hot melt adhesive dispensing system are replaced, modified, or replaced, or when various other operating parameters of the hot melt adhesive dispensing system are changed.

[0055] Those skilled in the art will appreciate that the systems and methods disclosed herein may be implemented via a computing device that may include, but is not limited to, one or more processors, a system memory, and a system bus that couples various system components, including coupling the processors to the system memory. In the case of multiple processors, the system may utilize parallel computing.

[0056] For purposes of exemplary illustration, application programs and other executable program components, such as operating systems, are illustrated as separate blocks in the accompanying drawings herein. It is recognized, however, that such programs and components reside at various times in different storage components of the computing device and are executed by the computer's data processor(s). An implementation of the service software may be stored on or transmitted via some form of computer-readable media. Any of the disclosed methods may be performed by computer-readable instructions embodied on a computer-readable medium. A computer-readable medium may be any available medium that can be accessed by a computer. By way of example, and not limitation, computer-readable media may include "computer storage media" and "communications media." "Computer storage media" includes volatile and non-volatile, removable and non-removable media implemented in any method or technology for storage of information, such as computer-readable instructions, data structures, program modules, or other data. Examples of computer storage media include, but are not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disk (DVD) or other optical storage devices, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium usable to store desired information and accessible by a computer. Application programs, etc., and / or the storage media may be implemented at least in part on a remote system.

[0057] As used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Numerical ranges may be expressed as from "about" one particular value and / or to "about" another particular value. When a range is expressed in this manner, other embodiments include ranges from the one particular value and / or to the other particular value. Similarly, when a value is expressed as an approximation, by use of "about," it is to be understood that the one particular value also applies in other embodiments. Moreover, it is to be understood that each endpoint of such a range is valid both in relation to the other endpoint, and independently of the other endpoint.

[0058] Unless expressly stated otherwise, it is not intended that any method described herein be understood as requiring that its steps be performed in a particular order. Thus, if a method claim does not actually specify the order in which its steps must be followed, or if the claims or specification do not specifically state that the steps are limited to a particular order, no order is intended to be implied in any way. This applies to any possible implicit basis for interpretation, including matters of logic regarding the arrangement of steps or operational flow, the plain meaning derived from grammar or punctuation, and the number or type of embodiments described herein.

[0059] It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the scope or spirit of the present application. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice disclosed therein. It is intended that the specification and examples be considered as exemplary only, with the true scope and spirit being indicated by the following claims.

Claims

1. 1. A method for adjusting a closed-loop controller for a hot molten liquid dispensing system having an applicator configured to dispense a hot molten liquid and a hot molten liquid heater associated with the applicator, comprising: the closed-loop controller is configured to receive a high temperature molten liquid temperature setpoint and a measured high temperature molten liquid temperature process variable, and to output a duty cycle control variable for controlling the high temperature molten liquid heater; The method comprises: setting the temperature setpoint; maintaining the hot molten liquid dispensing system at a steady state with respect to the temperature process variable and the duty cycle control variable based on the temperature setpoint; adjusting the duty cycle control variable by alternating positive and negative step values ​​to cause sustained oscillation of the temperature process variable; determining an amplitude of the sustained vibration and a critical period associated with the sustained vibration; determining a threshold gain based on the step value and the amplitude of the sustained oscillation; determining each of a proportional constant, an integral constant, and a derivative constant based on at least one of the limit period and the limit gain; implementing an open loop controller using the proportional constant, the integral constant, and the derivative constant; A method comprising:

2. supplying the hot molten liquid to the applicator using a hot molten liquid pump; Further provided with causing a sustained oscillation of the temperature process variable adjusting the duty cycle control variable by the step value having a positive sign; adjusting the duty cycle control variable by a negative step value in response to determining that the temperature process variable is above the temperature setpoint; adjusting the duty cycle control variable by the step value having a positive sign in response to determining that the temperature process variable is below the temperature setpoint; adjusting the duty cycle control variable alternately by the step value of positive and negative sign until the oscillation is sustained; have 2. The method of claim 1 .

3. generating the duty cycle control variable for controlling the hot molten liquid heater implemented in at least one of an adhesive supply heater, a manifold heater, an applicator heater, and / or a hose heater; Further provided with the temperature setpoint includes a temperature setpoint threshold range defined by a lower temperature threshold and an upper temperature threshold; adjusting the duty cycle control variable by the negative sign of the step value in response to determining that the temperature process variable is above the upper temperature threshold; In response to determining that the temperature process variable is below the lower temperature threshold, the duty cycle control variable is adjusted by the positive sign step value.

3. The method of claim 2.

4. supplying the hot molten liquid to the applicator using a hot molten liquid pump; Further provided with The closed-loop controller includes a PID controller and is implemented using the proportional constant, the integral constant, and the derivative constant.

2. The method of claim 1 .

5. supplying the hot molten liquid to the applicator using a hot molten liquid pump; Further provided with The marginal gain is inversely proportional to the amplitude of the sustained oscillation 2. The method of claim 1 .

6. supplying the hot molten liquid to the applicator using a hot molten liquid pump; Further provided with The proportionality constant is based on the marginal gain and is proportional to the marginal gain.

2. The method of claim 1 .

7. generating the duty cycle control variable for controlling the hot molten liquid heater implemented in at least one of an adhesive supply heater, a manifold heater, an applicator heater, and / or a hose heater; Further provided with the closed loop controller comprises a parallel PID controller; the proportionality constant includes a proportional gain, the integral constant includes an integral gain; The derivative constant includes a derivative gain.

2. The method of claim 1 .

8. supplying the hot molten liquid to the applicator using a hot molten liquid pump; Further provided with The amplitude of the sustained vibration and the limit period are determined based on a subset of the periods of the sustained vibration.

2. The method of claim 1 .

9. generating the duty cycle control variable for controlling the hot molten liquid heater implemented in at least one of an adhesive supply heater, a manifold heater, an applicator heater, and / or a hose heater; Further provided with the amplitude of the sustained oscillation is the average amplitude of a subset of the periods; The limit period is the average period over a subset of the periods 9. The method of claim 8.

10. supplying the hot molten liquid to the applicator using a hot molten liquid pump; Further provided with maintaining a steady state of the hot molten liquid dispensing system for a period of time; The duty cycle control variable is adjusted by alternating positive and negative sign step values ​​based on an average of the duty cycle control variable over the period of time.

2. The method of claim 1 .

11. generating the duty cycle control variable for controlling the hot molten liquid heater implemented in at least one of an adhesive supply heater, a manifold heater, an applicator heater, and / or a hose heater; Further provided with The duty cycle control variable that is initially adjusted is the average of the duty cycle control variable over the period of time.

11. The method of claim 10.

12. an applicator configured to dispense a hot molten liquid; a high temperature molten liquid heater associated with said applicator; a control system configured to implement a closed-loop controller; A system comprising: the closed-loop controller is configured to receive a high temperature molten liquid temperature setpoint and a measured high temperature molten liquid temperature process variable, and to output a duty cycle control variable for controlling the high temperature molten liquid heater; The control system further comprises: setting the temperature setpoint; maintaining the system at a steady state with respect to the temperature process variable and the duty cycle control variable based on the temperature setpoint; adjusting the duty cycle control variable by alternating positive and negative step values ​​to cause sustained oscillation of the temperature process variable; determining an amplitude of the sustained vibration and a critical period associated with the sustained vibration; determining a threshold gain based on the step value and the amplitude of the sustained oscillation; determining each of a proportional constant, an integral constant, and a derivative constant based on at least one of the limit period and the limit gain; implementing an open loop controller using the proportional constant, the integral constant, and the derivative constant; and configured to adjust the closed-loop controller by A system characterized by:

13. a hot molten liquid pump configured to supply the hot molten liquid to the applicator; Further provided with causing a sustained oscillation of the temperature process variable adjusting the duty cycle control variable by the step value having a positive sign; adjusting the duty cycle control variable by a negative step value in response to determining that the temperature process variable is above the temperature setpoint; adjusting the duty cycle control variable by the step value having a positive sign in response to determining that the temperature process variable is below the temperature setpoint; adjusting the duty cycle control variable alternately by the step value of positive and negative sign until the oscillation is sustained; have 13. The system of claim 12.

14. the temperature setpoint includes a temperature setpoint threshold range defined by a lower temperature threshold and an upper temperature threshold; adjusting the duty cycle control variable by the negative sign of the step value in response to determining that the temperature process variable is above the upper temperature threshold; adjusting the duty cycle control variable by the positive step value in response to determining that the temperature process variable is below the lower temperature threshold; The control system further comprises: generating the duty cycle control variable for controlling a hot molten liquid heater implemented in at least one of an adhesive supply heater, a manifold heater, an applicator heater, and / or a hose heater; It is configured as follows:

14. The system of claim 13.

15. a hot molten liquid pump configured to supply the hot molten liquid to the applicator; Further provided with the closed-loop controller includes a PID controller and is implemented using the proportional constant, the integral constant, and the derivative constant; The control system further comprises: generating the duty cycle control variable for controlling a hot molten liquid heater implemented in at least one of an adhesive supply heater, a manifold heater, an applicator heater, and / or a hose heater; It is configured as follows:

13. The system of claim 12.

16. a hot molten liquid pump configured to supply the hot molten liquid to the applicator; Further provided with The amplitude of the sustained vibration and the limit period are determined based on a subset of the periods of the sustained vibration.

13. The system of claim 12.

17. the amplitude of the sustained oscillation is the average amplitude of a subset of the periods; the limit period is an average period over a subset of the periods; The control system further comprises: generating the duty cycle control variable for controlling a hot molten liquid heater implemented in at least one of an adhesive supply heater, a manifold heater, an applicator heater, and / or a hose heater; It is configured as follows:

17. The system of claim 16.

18. a hot molten liquid pump configured to supply the hot molten liquid to the applicator; Further provided with a steady state of the system is maintained for a period of time; The duty cycle control variable is adjusted by alternating positive and negative sign step values ​​based on an average of the duty cycle control variable over the period of time.

13. The system of claim 12.

19. the duty cycle control variable that is initially adjusted is the average of the duty cycle control variable over the period of time; The control system further comprises: generating the duty cycle control variable for controlling a hot molten liquid heater implemented in at least one of an adhesive supply heater, a manifold heater, an applicator heater, and / or a hose heater; It is configured as follows:

20. The system of claim 18.

20. 1. A control system for coordinating a closed-loop controller for a hot molten liquid dispensing system having an applicator configured to dispense a hot molten liquid and a hot molten liquid heater associated with the applicator, the control system comprising: the closed-loop controller is configured to receive a high temperature molten liquid temperature setpoint and a measured high temperature molten liquid temperature process variable, and to output a duty cycle control variable for controlling the high temperature molten liquid heater; The control system one or more processors; a memory for storing instructions; Equipped with The instructions, when executed by the one or more processors, cause the control system to: Setting the temperature setpoint; maintaining the hot molten liquid dispensing system in a steady state with respect to the temperature process variable and the duty cycle control variable based on the temperature setpoint; adjusting the duty cycle control variable by alternating positive and negative step values ​​to cause sustained oscillation of the temperature process variable; determining an amplitude of the sustained vibration and a limit period associated with the sustained vibration; determining a threshold gain based on the step value and the amplitude of the sustained oscillation; determining each of a proportional constant, an integral constant, and a derivative constant based on at least one of the limit period and the limit gain; implementing an open-loop controller using the proportional constant, the integral constant, and the derivative constant; A control system comprising:

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