OPERATING PROCEDURE FOR A HEATING DEVICE FOR TEMPERATURE CONDITIONING OF PREFORMS IN A STARTUP PHASE, HEATING DEVICE AND MACHINE

Description

[0001] The present invention relates to a method for operating a heating device for the temperature conditioning of preforms. Furthermore, the present disclosure relates to a heating device for the temperature conditioning of preforms and a machine for the production of containers from preforms, including a heating device for the temperature conditioning of the preforms.

[0002] The production of containers by blow molding from preforms made of a thermoplastic material, for example, from PET (polyethylene terephthalate) preforms, is known, wherein the preforms are fed to different processing stations within a blow molding machine (DE 43 40 291 A1). Typically, a blow molding machine has a heating device for tempering or thermally conditioning the preforms and a blow molding unit with at least one blowing station, in which the previously temperature-conditioned preform is expanded into a container. The expansion is carried out using a pressurized gas (compressed air) as the pressure medium, which is introduced into the preform to be expanded with a molding pressure. The process engineering sequence for such expansion of the preform is explained in DE 43 40 291 A1. The basic structure of a blow molding station is described in DE 42 12 583 A1.Methods for temperature control of the preforms are explained in DE 23 52 926 A1. Temperature control or thermal conditioning in this context means that the preform is heated to a temperature suitable for blow forming and, if necessary, a temperature profile is applied to the preform. Blow forming of containers from preforms using an additional stretching bar is also known.

[0003] In a typical downstream processing method, the containers produced by blow molding are fed to a subsequent filling unit and filled with the intended product or filler material. This involves the use of separate blow molding machines and separate filling machines. It is also known to combine the separate blow molding machines and the separate filling machines into a single machine unit, i.e., a combined blow molding and filling unit, whereby the blow molding and filling processes still take place on separate machine components and sequentially.

[0004] It has also been proposed to manufacture containers, particularly in the form of bottles, from thermally conditioned or tempered preforms and simultaneously fill them with a liquid material. This liquid is supplied as a hydraulic pressure medium to expand the preform or to shape the container under forming and filling pressure, so that the preform is transformed within the container at the same time as it is filled. Such processes, in which the container is formed and filled simultaneously, can also be referred to as hydraulic forming processes or hydraulic container forming. Here, too, it is known to assist this forming process by using a stretching bar. Here, too, the preform is first temperature-conditioned before the forming and filling process.

[0005] When forming containers from preforms using the fill material itself, i.e., using the fill material as a hydraulic pressure medium, only one machine is required for forming and filling the containers, although this machine is more complex. US Patent 7,914,726 B2 provides an example of such a machine. DE 10 2010 007 541 A1 provides another example.

[0006] It is generally known to monitor the forming process and / or the temperature conditioning of the preforms using control and / or regulation technology, e.g. from US 2012 / 226376 A1, DE 10 2014 119 563.9, EP 1 383 636 B1 or US 2021 / 0101315 A1.

[0007] Regarding the temperature conditioning of the preforms, the requirements are essentially identical regardless of whether, in a subsequent step, the forming of the preform, which has a suitable temperature profile, is carried out by introducing a gas under pressure or a liquid under pressure. The heating device to be provided for the thermal conditioning of the preforms and the method to be used for operating such a heating device are therefore the same for both known forming processes.

[0008] The invention described below relates equally to both forming processes described. Heating devices known in the prior art consist, for example, of several so-called heating boxes. These heating boxes are usually arranged stationary along a heating section, and preforms are moved through these heating boxes by means of suitable transport devices and thereby heated. Typical transport devices consist, for example, of a circulating transport chain. The chain links are formed, for example, by transport mandrels, each of which holds a preform by clamping into the mouth section of a preform and guides it on its circulating movement along the heating section and through the heating boxes.

[0009] The heating device is usually modular in design, meaning that several such heating boxes are arranged as heating modules along the heating path. These can be identical heating boxes or heating boxes of different designs.

[0010] Heating elements are arranged within the heating boxes. In the prior art, near-infrared (NIR) emitters are preferably used as heating elements; for example, several near-infrared emitters can be arranged one above the other as heating elements in the longitudinal direction of a preform. An example of such a heating device and an example of the typical structure of a heating module referred to above as a heating box are shown in EP 2 749 397 A1 or WO 2011 / 063784 A2.

[0011] It is known in the prior art that these heating devices are connected to a control unit. This control unit is generally designed such that the preforms are heated within the heating device so that they exit the heating device with a desired temperature profile.

[0012] This means that a specific temperature is achieved within the preform, as well as a specific temperature profile in the longitudinal direction of the preform and, if applicable, also in the circumferential direction. It is also known in the prior art that, in addition to the heating elements mentioned above, devices for cooling the surface of the preforms may be provided, for example, devices for selectively applying a cooling airflow to the preform surface. These additional cooling devices may also be integrated into the aforementioned control device of the heating system. The terms "control device" and "control method" encompass devices and methods with which control in the sense of the English term "open-loop control" is implemented, with which regulation in the sense of the English term "closed-loop control" is implemented, and hybrid forms thereof.

[0013] To control the heating device so that the preforms are temperature-conditioned at the output of the heating device in the desired manner, i.e., exhibiting the desired temperature and temperature profile, it is known in the prior art to arrange a measuring sensor, e.g., a pyrometer, at the output of the heating device. This sensor measures the surface temperature of preforms passing by the sensor. In such an embodiment, the reference value for the control system would be the surface temperature of the preforms. This measured value can, for example, be compared with a setpoint, and the heating device control system can thus be set to regulate the surface temperature of the preforms according to a setpoint.

[0014] In some known heating devices, a distinction is made between heating elements arranged one above the other in the longitudinal direction of the preforms. For example, a separate heating power is defined for each stacked heating element, which is regulated and / or controlled by the control unit. A preset setting in the control unit can be made, for example by an operator, to determine whether and how heating elements arranged at different heights should heat differently. The control unit can, for example, provide a height-specific parameter for this purpose. It is also known that a higher-level power parameter is set, which applies to all heating elements.The actual heating power of a radiant level, i.e., all heating elements arranged at the same height, as specified by the control device, is then obtained by multiplying both parameters.

[0015] By individually adjusting the heating power for each heating element level, a specific heating profile can be set. For example, the heating power in each level can be adjusted so that certain areas of the preform are heated more intensely. Simultaneously, the overall heating power can be set via the overarching power parameter common to all heating elements. In the prior art, the heating device is controlled by adjusting the overarching power parameter based on the pyrometer reading. The pyrometer reading serves as the control variable, for example, the surface temperature of the preforms. The height-specific parameter is not controlled in the prior art but results from the desired temperature profile along the axis of the preform. It is typically set during machine setup or commissioning and can be changed by an operator as needed.during a production changeover to other preforms.

[0016] Known heating devices and their control systems and methods perform well when the heating device has reached its equilibrium temperature in a thermodynamically stable state and is operated continuously in this state. This thermodynamically stable equilibrium exists when, after a certain operating period, the elements forming the heating device, such as heating elements, reflectors, etc., have reached a temperature that remains essentially constant during continued operation. However, such a thermodynamically stable equilibrium does not yet exist when the heating system is put into operation or when it is transferred from so-called inline operation back into production operation."Inline operation" refers to an operating state in which the regular container manufacturing process, and therefore also the regular heating process, is interrupted, for example, due to malfunctions. In the event of malfunctions, the supply of preforms to the heating device is typically interrupted, and the heating device continues to operate at a low heating power setting. Only in the case of prolonged malfunctions is the heating device switched off completely. During such startup phases, i.e., operating phases outside of continuous operation, heating devices exhibit unsteady heat radiation and heating behavior. This unsteady behavior results primarily from two effects. At the time the heating device starts up, the components of the device itself have not yet reached their final operating temperature. Therefore, stable thermal conditions do not yet exist.The thermal radiation striking the preforms passing through the heating device is not yet in thermodynamic equilibrium during the startup phase because reflectors or other components within the heating device have not yet reached their equilibrium temperature. These reflectors or other components of the heating device act as secondary radiators. Furthermore, the glass bulbs of the radiators or any filters may not yet have reached their equilibrium state, resulting in additional effects on the radiation intensity acting on the preforms, for example, on the wavelength spectrum of the radiation incident on the preforms.

[0017] Another aspect is that no preforms are initially fed into the heating device during its startup phase. In the prior art, it is common practice to introduce preforms only after a specific heating device temperature has been reached. With the introduction of the first preforms, the ratio between radiating and absorbing surfaces changes continuously.

[0018] During these startup phases of the heating device, the preforms are heated to varying degrees. Consequently, the containers produced from these preforms exhibit variations in their properties.

[0019] In the prior art, the temperature within the heating device is measured, for example, by temperature sensors, which may be located in a reflector of the heating device. Such a temperature measurement can be used, for example, to determine whether the heating device has reached a specific target temperature at which the feeding of the preforms into the heating device begins. It is also possible to provide several such temperature sensors.

[0020] While satisfactory results regarding container quality can be achieved during continuous operation of known heating devices, for example, after the start-up phase, because the control devices known in the prior art function adequately, problems arise regarding container quality before continuous operation, namely before reaching at least an approximately thermodynamically stable equilibrium state. In principle, it would of course be possible to design the start-up time of the heating device in such a way that an approximately thermodynamically stable equilibrium state is reached with good reliability; that is, for example, the components of the heating device should have reached their thermal equilibrium state or a state close to their thermal equilibrium before the preforms are fed into the heating device.This would also mean, however, that some time would pass before container production could begin. Typical startup times are in the range of minutes and can, for example, be 5 minutes. For more effective utilization of the existing machinery and for more efficient use of heating energy, however, starting production as early as possible is desirable. Therefore, in the prior art, container production already begins well before the heating system has reached its continuous operating state, i.e., still within the startup phase.

[0021] It is known that during this startup phase, the heating device is regulated and controlled differently than during continuous operation. The control described above, based on a temperature measurement of the preforms, and the transition to continuous operation are only possible once the first preforms leave the heating device, as a reference value can only be generated at this point by measuring the preform temperature. Therefore, it is known that, for example, after reaching an initial target temperature in the heating device, the device operates differently than at the time of the first temperature measurement of the preforms. From then on, the control of the heating device described above for continuous operation takes effect. Before this, the heating device is operated according to a different method.

[0022] Before the heating device reaches its thermodynamically stable equilibrium at full production capacity, there is a tendency for too little heat energy to be introduced into the preforms. This is because, until the components reach their steady-state thermal equilibrium, they absorb more radiant energy than they emit, which is then lacking in the preforms. Furthermore, the heated components of the device act as secondary radiators, emitting more long-wave radiation as the temperature increases, which is particularly well absorbed by materials such as PET.

[0023] Before reaching thermodynamically stable equilibrium, this long-wave radiation component is lower due to secondary radiators. For this reason, it is known in the prior art that when the heating device is loaded with preforms before reaching continuous operation and thus also significantly before reaching thermodynamically stable equilibrium, the total heating power of the heating device is set to a higher value than corresponds to a base value for continuous operation. This higher heating power value for the heating device is initially kept constant until the heating device is fully loaded. Only then does the control for continuous operation intervene as described above, since temperature measurements on the preforms are only possible at that point.

[0024] The heating devices described above, representing the state of the art, are initially started, and the heating elements are operated at a specific, preset starting power. Upon reaching a certain initial temperature within the heating device, the first preforms enter the device, and the heating device, or rather its heating elements, are operated at a predetermined power level. The heating device is controlled according to this constant power setting. Only after a specific, predetermined event is reached does the heating device's control system engage for continuous operation. This predetermined event could, for example, be the detection of the first surface temperatures of preforms.

[0025] A disadvantage of the heating device control described above during startup is that the preforms exiting the heating device cannot yet have a very uniform temperature or temperature profile, since a fixed power setting for the heating elements can only represent a suitable average value for the startup phase. The containers produced from these preforms therefore still exhibit a relatively large variation in their properties. Furthermore, process fluctuations can occur during the startup phase described above, and also afterward. Causes of such fluctuations include disturbances affecting the heating device, such as a changing ambient temperature, a design modification to the heating device after a malfunction, or different temperatures of the preforms when they are fed into the heating device.

[0026] It is known that during the startup phase of the heating device, a higher heating output is determined, for example, from a so-called trend curve, which contains empirically determined relationships between the heating device's output and its temperature. The control of the heating device, or rather its heating output, during this startup phase is thus based on a fixed output value from such a predefined trend curve. It is also known in the prior art to take a measured ambient temperature into account by shifting the empirically derived trend curve according to the recorded ambient temperature.In summary, it is known in the prior art that, before reaching the continuous operating state of the heating device, the heating device is not controlled by, for example, a temperature measurement of the preform, but rather that the heating elements are operated with a constant power output over time, whereby the power value to be set is taken from a trend curve. Using such trend curves to control a heating device is therefore generally known, for example from WO 2019 / 048419 A1.

[0027] The established trend curves from the prior art are created manually and stored in the heating device's control system. Creating a trend curve relies heavily on the experience of the machine or heating device operator. Therefore, the trend curves are subject to the operator's subjective experience. Furthermore, in practice, operators are sometimes hesitant to create and use trend curves due to their complexity. In such cases, process fluctuations are accepted, or the heating device is heated until a near-thermally stable equilibrium is reached. It goes without saying that this is detrimental to optimal machine utilization.Furthermore, incorrectly set trend lines by the operators could lead to high thermal stress and even overload of components of the heating device, such as thermal overload of the transport mandrels or the heating radiant heaters.

[0028] The object of the present invention is therefore to address one of the aforementioned problems, to improve the general state of the art, or to provide an alternative to what is known. In particular, a solution is to be provided that achieves optimized operation of a heating device during a startup phase.

[0029] This problem is solved by a method according to claim 1.

[0030] According to the invention, a method for operating a heating device for the temperature conditioning of preforms made of a thermoplastic material within the heating device is proposed. In this process, the respective preform is prepared for a subsequent forming operation by thermal conditioning in the heating device. During this subsequent forming operation, the preform is formed into a container using a forming fluid supplied to the preform under pressure. It is therefore proposed to heat the preform using a heating device in order to subsequently form it into a container, for example, in a blow molding machine. PET (polyethylene terephthalate) or the like is preferably proposed as the thermoplastic material. The thermal conditioning thus refers to a heating process of the preform.As previously described, it is known to shape the temperature-conditioned preform using a pressurized gas (compressed air) as the pressure medium and then fill it, or to simultaneously fill it with a liquid material using a hydraulic pressure medium. Conditioning can therefore also be understood as preparation. Thermal conditioning is thus a thermal preparation of the respective preform for subsequent shaping into a container. A container is, for example, a bottle or the like.

[0031] It is further proposed that the heating device be operated in several operating states, namely at least in a first and a second operating state. The second operating state serves as a startup phase during which the device's temperature approaches an equilibrium temperature of a thermodynamically stable state. The first operating state serves as the continuous operating state following the startup phase. Thus, it is proposed that the heating device be operable in at least a first and a second operating state.The second operating state is one in which a thermodynamically stable equilibrium has not yet been reached; that is, the heating elements and other components of the heating device have not yet reached their thermodynamic equilibrium. In this second operating state, the heating elements and other components are still moving towards thermal equilibrium. Relative to typical cycle times of a forming process, from thermal conditioning to the finished container, their temperatures and radiation behavior continue to change towards a dynamic equilibrium. Typical cycle times are in the range of 10 seconds, and these changes, for example, with regard to the heating device temperature, are in the range of a few degrees Celsius within this timeframe.The second operating state can also be understood as the start-up state of the heating device, when the heating device is not yet in thermal equilibrium. This second operating state can be, for example, a cold start or a warm start.

[0032] The terms continuous operating state and first operating state, and the terms startup state / startup phase and second operating state are used synonymously.

[0033] The first operating state is a state of operation of the heating device in which a thermodynamically stable equilibrium is reached. This first operating state can also be understood as continuous operation, in which the heating device has reached its equilibrium temperature in this thermodynamically stable state and operates in this state. This thermodynamically stable equilibrium exists when, after a certain operating period, the elements forming the heating device, such as heating elements, reflectors, etc., have reached a temperature that remains essentially constant during continuous operation. In the prior art, in the first operating state, the heating power is controlled within a control loop according to a reference value detected by a sensor, where the reference value or control variable is, for example, a measured temperature of the preform ϑPreform,.

[0034] It is particularly proposed that in the second operating state a setpoint characteristic curve for future control of the heating device be created by determining support points of the setpoint characteristic curve at predetermined times depending on a detected deviation between a reference value and a control actual value of a controlled variable.

[0035] It is therefore proposed that a setpoint characteristic curve be created during the startup phase or the second operating state. This setpoint characteristic curve can also be understood as the trend curve described previously. The setpoint characteristic curve is a characteristic curve for a setpoint, for example, a setpoint characteristic curve for controlling the heating output of radiant heaters in the heating device. The setpoint characteristic curve outputs a setpoint for controlling the heating device as a function of an input variable, where the input variable is preferably a measured temperature at the heating device. The setpoint characteristic curve is created for future control of the heating device; that is, it is proposed that the setpoint characteristic curve can be used to control the heating device after its creation. For this purpose, the setpoint characteristic curve is first determined and then stored in the control system of the heating device in a way that allows it to be accessed.It goes without saying that a storage unit is required for this purpose. The storage unit is, for example, part of the control system of the heating device or the forming machine, or it can be an external storage unit, such as one located on an external server. The external storage unit can also be referred to as online storage.

[0036] The setpoint characteristic curve is formed from a multitude of support points that represent the curve's progression. Support points are fundamentally a mathematical concept. They can also be understood as discrete function values ​​of the setpoint characteristic curve. Essentially, the support points define the discrete progression of the setpoint characteristic curve.

[0037] The support points are determined by identifying them at predetermined times based on a measured deviation between a reference value and a measured actual control value. It is therefore proposed to determine the support points at different times, for example, at fixed times and / or at predetermined temperature-dependent increments. In a preferred embodiment, the predetermined times correspond to the x-coordinates of the determined setpoint characteristic curve.

[0038] Furthermore, it is proposed that the support points be determined based on a detected deviation between a reference value and a detected actual control value. A reference value can be, for example, a predefined setpoint or a predefined comparison value, such as a constant value. The actual control value corresponds to a current value—a quantity used in the control of the heating device. For example, an actual control value is a detected controlled variable, such as the measured temperature of the preform at the end of thermal conditioning. The actual control value can also be an output variable from a controller of the heating device. Additionally, the actual control value can be a temperature measured at the heating device.The actual control value therefore refers not only to the controlled variable that is output at the control of the heating device, but also to an instantaneous value of a quantity that is used in the control of the heating device.

[0039] The above method can also be understood and described as a method for determining a setpoint characteristic curve for the future control of a heating device for the temperature conditioning of preforms made of a thermoplastic material.

[0040] It has been established that a trend curve can be automatically generated based on the current deviation between a control setpoint and a reference value. This is based on the understanding that the detected deviations in the heating device's control system allow conclusions to be drawn about the thermal state of the heating direction. For example, a large deviation indicates that the heating device is not yet in a thermally stable state. Small deviations indicate that the heating device is closer to a thermally stable state. The course of the detected deviations can therefore be used to create the setpoint characteristic curve or the trend curve.

[0041] In contrast to conventional methods where trend curves are manually and empirically defined, this approach proposes automated trend curve generation. This offers several advantages. Firstly, incorrectly configured trend curves and setpoint curves are reduced, resulting in optimized heating operation. Secondly, operators no longer need to understand how to create complex trend curves, as the curve is generated automatically. This significantly simplifies the operation of the heating system. Furthermore, the trend curves can be saved and used for future operating conditions.

[0042] Preferably, the setpoint characteristic is a heating power setpoint characteristic for controlling the heating device. It is therefore proposed that the setpoint characteristic outputs a setpoint for the heating power of the heating device. This heating power setpoint is then, for example, specified as a control variable for the heating radiant heaters of the heating device.

[0043] Preferably, a heating power setpoint for controlling the heating device is generated using the heating power setpoint characteristic curve as a function of a measured actual temperature value of the heating device. It is therefore proposed that the setpoint characteristic curve outputs a setpoint for controlling the heating device as a function of an input variable, where the input variable is a measured actual temperature value at the heating device. The setpoint characteristic curve thus outputs a setpoint for controlling the heating device as a function of a measured actual temperature value of the heating device. The actual temperature value can be measured, for example, with at least one temperature sensor. It is also possible to provide several such temperature sensors. Preferably, the determination of the support points is implemented such that a function value at a support point decreases with decreasing deviation.It is therefore proposed that the greater the detected deviation, the larger the generated target value. Thus, it is proposed that the output or generated target value follows the trend of the detected deviation. A large deviation, for example, results in a larger generated target value. Conversely, a smaller deviation results in a smaller generated target value.

[0044] Preferably, the future control method is to control the heating device in the first operating state using the setpoint curve after the setpoint curve has been determined, and / or the future control method is to control the heating device in a second operating state using the setpoint curve after the setpoint curve has been created. It is therefore proposed that the determined setpoint curve be used in continuous operation following the second operating state and / or in another second operating state following the initial second operating state.

[0045] Using the setpoint characteristic curve for future control in both operating modes is advantageous because such a curve can account for different environmental conditions. For example, machines of the same design may be used in different countries with varying temperatures or humidity levels. If a machine is then operated with a suitable characteristic curve, for example, during a second start-up phase or in continuous operation, it can be repeatedly started up with this curve and later transitioned to the desired continuous operation. It is therefore suggested that a characteristic curve be plotted once and then reused in subsequent operation. Thus, the characteristic curve can be determined once or, if necessary, multiple times.

[0046] Preferably, the predetermined times are fixed, for example, fixed times in the range of seconds. These fixed times can also be interpreted as fixed time intervals. For example, a data point is determined every second.

[0047] Additionally or alternatively, the predetermined time points are predetermined temperature-dependent time points. It is therefore proposed to create the time points based on a temperature profile. For example, threshold values ​​of 0%, 5%, 10%, ... 95%, 100% can be defined for a measured temperature of a preform or the heating device. A predetermined time point then corresponds to the time at which the threshold value is reached. The temperature-dependent time points are thus times that occur at predetermined and recorded temperature values ​​of the preform or at predetermined and recorded temperature values ​​of the heating device in the second operating state. It is understood that the temperature of the preform and / or the heating device is measured accordingly with a temperature sensor.

[0048] Preferably, the recorded data points are interpolated as a trend curve, in particular linearly or quadratically. This is advantageous because the interpolated trend curve can be used for continuous control, and the trend is also more clearly recognizable when, for example, it is displayed as a curve.

[0049] Preferably, the generated setpoint curve or the interpolated trend curve is displayed on a screen of the heating device. It is therefore proposed that the heating device have a display to show the setpoint curve. This allows the setpoint curve to be monitored and tracked externally.

[0050] Preferably, the generated setpoint characteristic curve is stored in a storage unit of the heating device and / or in online storage and / or in a storage unit of the forming machine after its creation and is made available for future control of the heating device. The storage unit can also be considered a storage module or data storage device. The storage unit is, for example, part of the control system of the heating device. The storage unit is, for example, non-volatile memory. By storing the determined setpoint characteristic curve in online storage or on an external server, the determined characteristic curves can be made available for download by other machines that, for example, have the same design.

[0051] Preferably, the specified support points are manually adjustable and stored in a memory unit of the heating device, and can be individually adapted via an input interface of the heating device. It is therefore proposed that manual adjustment of the setpoint curve be provided after the curve has been automatically generated and stored in the memory unit. This allows the operator of the heating device to subsequently make adjustments to the trend curve. The input interface is, for example, an operating terminal on the heating device where the setpoint curve can be modified by manual input.

[0052] Preferably, the detected deviation is a deviation between a target temperature of a preform and a measured actual temperature of a preform. In a particularly preferred embodiment, the measured actual temperature is detected by a temperature sensor at the end of the thermal conditioning of the preform, and the target temperature is a target temperature of a preform at the end of the thermal conditioning.

[0053] Preferably, the detected deviation is a deviation between a reference value and a control variable of a heating device controller. In a particularly preferred embodiment, the reference value is zero in order to detect a deviation of the control variable from zero.

[0054] Preferably, the detected deviation is a deviation between a reference value and a sum control variable for controlling the heating device, wherein the sum control variable is formed from a control variable of a controller of the heating device and at least one detected disturbance variable. In a particularly preferred embodiment, the reference value is equal to zero in order to detect a deviation of the sum control variable from zero.

[0055] Preferably, the detected deviation is a deviation between a reference value and a measured actual temperature value of the heating device. In a particularly preferred embodiment, the reference value is a setpoint temperature of the heating device.

[0056] As a further aspect, a heating device for the temperature conditioning of preforms made of a thermoplastic material in the heating device is disclosed, wherein the respective preform is prepared by thermal conditioning in the heating device for a subsequent forming process in which the preform can be formed into a container with a forming fluid supplied to the preform under pressure, wherein the heating device has a control device that operates the heating device at least in a first operating state and in a second operating state, wherein the operation of the heating device in the second operating state is a startup state of the heating device in which a temperature of the heating device approaches an equilibrium temperature of a thermodynamically stable equilibrium state of the heating device.The operation of the heating device in the first operating state is a continuous operation of the heating device following the startup state. The control unit for executing the operating procedure is designed according to one of the aforementioned embodiments. The advantages, explanations, and definitions described above for the aforementioned procedure apply analogously to the heating device described above, and vice versa.

[0057] As a further aspect, a machine is disclosed for the production of containers from preforms by forming them using a forming fluid introduced under pressure into the preform and with a heating device for temperature conditioning the preforms, wherein the heating device is designed according to one of the preceding embodiments. The advantages, explanations, and definitions described above for the preceding method and the heating device apply analogously to the machine described above, and vice versa.

[0058] It is advantageously proposed, for example, that a temperature sensor be installed in the heating device. This temperature sensor serves to detect the temperature of the heating device and can, for example, be arranged and designed in a manner generally known from the prior art.

[0059] Further advantages, features, and details of the invention will become apparent from the exemplary embodiments described below with reference to schematic drawings. These show: Fig. 1 a highly schematic representation of a forming machine or a machine for forming containers from preforms, Fig. 2 a schematic representation of a heating box of a heating device, Fig. 3 a schematic representation of a temperature-conditioned preform with temperature profiling, Fig. 4 a schematic representation of a possible control architecture of a forming machine, Fig. 5 a known control scheme for controlling a heating device, Fig. 6 a control scheme according to the invention for controlling a heating device.

[0060] The basic structure of a forming machine 10, known from the prior art, is in Figure 1The illustration shows the preferred embodiment of such a forming machine 10 in the form of a rotary machine with a rotating work wheel 110 carrying several forming stations 16. For the sake of graphical simplification, however, only one such forming station 16 is shown. From a feeding device 112, preforms 14, also referred to as preforms, are continuously fed to a heating device 116 using a transfer wheel 114. In the area of ​​the heating device 116, which is also referred to as a furnace, and in which the preforms 14 are transported along a heating section and thermally conditioned, the preforms 14 can be transported, depending on the application, for example, vertically upwards or vertically downwards with their end sections 22.The heating device 116 is, for example, equipped with heating elements 118 arranged along a transport device 120 to form the heating section. A circulating chain with transport mandrels for holding the preforms 14 can be used, for example, as the transport device 120. Suitable heating elements 118 include, for example, heating boxes with IR emitters, light-emitting diodes, or NIR emitters. Since such heating devices are known in various forms in the prior art, and since the design details of the heating elements are not essential for the present invention, reference can be made to a description beyond the one already provided. Figure 2A more detailed description is omitted, and reference is made to the state of the art, in particular to the state of the art concerning heating devices for blow molding and stretch blow molding machines and for heating devices for forming and filling machines, all of which are encompassed by the term forming machines.

[0061] After sufficient temperature conditioning, the preforms 14 are transferred from a transfer wheel 122 to a rotating working wheel 110, which is driven around a vertical machine axis MA, or to forming stations 16 arranged circumferentially around the working wheel 110. The working wheel 110 is equipped with a plurality of such forming stations 16, in which the preforms 14 are formed into the schematically depicted containers 12, and the containers 12 are filled with the intended material. The forming of each container 12 takes place simultaneously with the filling, with the material serving as the pressure medium during the forming process. In contrast, blow molding machines do not fill the containers on this working wheel 110, but rather at a later time on a filling wheel with filling stations.

[0062] After forming and filling, the finished and filled containers 12 are removed from the working wheel 110 by a removal wheel 124, conveyed further, and fed to an output section 126. The working wheel 110 rotates continuously at a desired speed during production. During one revolution, a preform 14 is inserted into a forming station 16, the preform 14 expands into a container 12, including filling with a product and, if a stretching bar is provided, stretching, and the container 12 is removed from the forming station 16.

[0063] According to the embodiment in Figure 1It is further provided that the working wheel 110 is supplied with schematically depicted closure caps 130 via an input device 128. This makes it possible to also perform the sealing of the containers 12 on the working wheel 110 and to handle finished, filled and sealed containers 12 using the removal wheel 124.

[0064] Various thermoplastic materials can be used as material for the preforms 14. Examples include polyethylene terephthalate (PET), polyethylene (PE), polyethylene naphthalate (PEN), or polypropylene (PP). The dimensions and weight of the preforms 14 are adapted to the size, weight, and / or design of the containers 12 to be manufactured.

[0065] A large number of electrical and electronic components are typically arranged in the area of ​​the heating device 116. Furthermore, the heating elements 118 are equipped with moisture-sensitive reflectors. Since the containers 12 are filled and shaped using the liquid material in the area of ​​the working wheel 110, it is preferable to prevent unintentional moisture ingress into the area of ​​the heating device 116 in order to avoid electrical problems. This can be achieved, for example, by a barrier device 132 that provides at least splash protection. In addition, it is also possible to appropriately temperature-controlled or pressurized the transport elements used for the preforms 14 in the area of ​​the transfer wheel 122 so that any adhering moisture cannot enter the area of ​​the heating device 116.

[0066] The preforms 14 and / or the containers 12 are preferably handled using tongs and / or the mouth section 22 with clamping or locking mandrels that exert a holding force at least partially from the inside or outside. Such handling devices are also well known from the prior art.

[0067] The forming machine 10 is equipped with measuring sensors for the purpose of its control and regulation. For example, it is common practice to arrange a temperature sensor 160 in the heating device 116 to measure its temperature. Furthermore, it is known in the prior art that a temperature sensor 162, which is designed, for example, as a pyrometer, is arranged on the outlet side of the clockwise rotating transport device 120 and detects the surface temperature of temperature-conditioned preforms 14 passing by it. The temperature sensor 162 is thus located at the end of the thermal conditioning process. Finally, it is also known in the prior art to use measuring sensors to take measurements on finished containers 12. For example, a wall thickness measuring sensor 164 can be arranged on the discharge section 126 to detect the wall thickness of a container passing by it.The aforementioned sensors can also be configured as several sensors arranged at different heights, for example to perform a temperature measurement along the longitudinal axis of the preform or to measure the wall thickness along the longitudinal axis of the container. Several temperature sensors 160 can also be arranged in the heating device 116.

[0068] The area where the preforms are fed into the heating device 116, i.e. e.g. the local area following the feed device 112 and the transfer wheel 114, corresponds to the beginning of the thermal conditioning of the preforms.

[0069] The area where the preforms are produced from the heating device 116, i.e. e.g. the local area in front of the transfer wheel 122, corresponds to an end of the thermal conditioning.

[0070] The in Figure 1The heating device 118, shown as an example and which is part of the heating device 116, could, for example, be configured as shown in Figure 2 a more detailed schematic sectional view illustrates this. Such heating devices are also called heating boxes. Typically, several of these heating boxes 118 are arranged side by side along the heating section to form a heating tunnel through which the preforms 14 are passed, as shown in the Figure 1 This is an example.

[0071] In the Figure 1 Furthermore, an exemplary path of the preforms 14 through the forming machine 10 is shown with arrows.

[0072] The in Figure 2The heating box 118, shown in a schematic sectional view, has several near-infrared emitters 209. In the illustrated embodiment, nine near-infrared emitters 209 are arranged vertically one above the other, and each of these near-infrared emitters 209 defines a heating level. These NIR emitters 209 can all be operated at the same power as required, or individually or in groups at different power levels. Depending on the axial extent of the preform 14, lower emitter levels in the vertical direction can also be switched off. To achieve a temperature profile in the preforms 14, it is generally necessary to operate near-infrared emitters 209 at different heating levels with different heating power.

[0073] Opposite the near-infrared emitters 209 is a counter-reflector 207, which reflects incident heating radiation back towards the preform 14 and thus back into the heating tunnel 211. The heating tunnel 211 is closed at the bottom by a bottom reflector 212. The preform 14 is protected against heating radiation at its opening by a support ring shield 205, as the opening area with its integrated thread is to be protected from unnecessary heating. The support ring shield 205 is arranged on the handling device 203, which, as described above, Figure 1It is explained that the handling device 203 can be part of a circulating chain. The handling device 203 also has a clamping mandrel 202 that clamps into the opening section of the preform 14. Such clamping mandrels 202 and such handling devices 203 are well known from the prior art and require no further explanation. The basic structure of this heating box 118 described above is also known from the prior art.

[0074] The in Figure 1 The temperature sensor 160, shown in principle, is located in the heating box 118 of the Figure 2also shown, whereby this temperature sensor 160 is usually arranged behind a reflector, for example behind the counter-reflector 207. This temperature sensor 160 detects a temperature of the heating box 118. In principle, it would also be possible to detect a temperature inside the heating tunnel 211 or to take a temperature measurement on the preform 14 inside the heating tunnel 211.

[0075] Figure 3Figure 14 shows a typical preform 14 in a sectional view, featuring a closed base 301 and an open mouth section 302. An external thread 303 and a support ring 304 are formed in the mouth section 302. After temperature conditioning, a specific temperature distribution results within the preform 14. For example, a temperature profile can be generated by heating the preform 14 axially, as shown on the left side of the preform 14. It can be seen that a higher temperature is achieved in the base and in an area below the support ring than in the intervening area. However, it is also possible to heat the preform homogeneously in the axial direction. The enlarged section of the wall area 305 shows that a temperature profile can also be set within the preform wall.This is partly due to the fact that the absorption of heating radiation leads to greater heating on the radial outer surface than on the radial inner surface. While temperature differences in the preform wall do eventually equalize through thermal equalization processes, these processes are relatively slow in preforms typically made of PET. Additionally, the preform 14 can also be provided with a circumferential temperature profile. This is known, for example, for preforms that are subsequently to be formed into non-circular containers, such as oval containers.

[0076] Figure 4Figure 1 shows a schematic representation of a possible modular control architecture for a control unit 400 for a forming machine 10. Letter A designates a master controller, letter B designates a control unit for controlling or regulating a heating device, letter C designates a control unit for the drive, for example, of the working wheel 110, letter D designates safety devices, such as emergency stop switches, and letter E designates, for example, a control unit for the forming process, i.e., for the possible drive of a drawing bar, for switching valves for switching on or off a forming fluid, etc. Control-relevant data can be displayed on a display 401, and the master controller supplies the display 401 with values ​​to be displayed via a data line 405.Display 401 can also function as an input unit, and values ​​entered via this input unit can be transmitted to the master controller A via connection line 405. The other data lines 402, 403, and 404, as well as data line 405, can, for example, be configured as a data bus and serve, for instance, to transmit data between the master controller A and the other control modules, or between the control modules themselves.

[0077] Figure 5Figure 1 shows the schematic structure of a control unit B for heating control, where the surface temperature ϑPreform,ist of a preform is chosen as the reference value. The heating device controlled by this unit operates with heating elements and cooling elements in the form of a fan. The control unit receives a starting heating power PHeating,0 and a starting fan power PFan,0 as operating points, since cooling of the preform surface is provided in addition to heating elements. The heating control is to be carried out based on the measurement of the surface temperature of the preforms 14, and for this purpose, as shown in Figure 2, the following applies: Figure 1As explained, a pyrometer 162 is arranged at the end of the heating section. Based on the surface temperature ϑ of the preforms 14 measured by the pyrometer 162, the control system adjusts the heating power. Furthermore, it can be provided that an ambient temperature is detected and also incorporated into the control of the heating device. In the illustrated embodiment, a drop in heating power is detected. To prevent an excessive drop in heating power, the surface cooling power via the ventilation is adjusted if the power falls below the threshold ΔSu. For example, if the heating power drops, the surface cooling power is increased until the heating controller detects a drop in the surface temperature of the preforms and increases the heating power again.

[0078] Figure 6shows a control scheme for regulating a heating device, as in the basic principle in the Figure 5 shown. The Figure 6 This illustrates how a setpoint characteristic is acquired in the second operating state. The control unit B has a controller, for example, a PI controller. The actual surface temperature ϑPreform,ist of the preform is supplied to the controller as a reference input, measured, for example, with the temperature sensor 162 or a pyrometer. The surface temperature ϑPreform,ist of the preform is preferably filtered. The setpoint for the controller is the desired surface temperature ϑPreform,set of the preform.

[0079] The control error, calculated from the preform,set and preform,actual values, is fed into the controller. This control error is also known as the control deviation. Based on this control error, the controller generates a manipulated variable, Pcontrol, which is fed into the controlled system, represented as a heater and heating process.

[0080] The Figure 6 This illustrates how, in the second operating state, a setpoint characteristic curve P Trend is created for the future control of the heating device 116. Support points f 1 to f 4 of the setpoint characteristic curve P Trend are determined at predetermined times t 1 to t 4 as a function of a detected deviation Δx i between a reference value and a controlled variable's actual value. Figure 6Four different recorded deviations, Δx 1 to Δx 4, are shown, which are fed into the CALC block. These recorded deviations, Δx 1 to Δx 4, are abbreviated as Δx i. The CALC block, which illustrates a calculation unit of the control unit, contains a function or algorithm to generate the function values ​​based on the recorded deviations Δx i.

[0081] The detected deviation Δx 1 is a deviation between the temperature setpoint ϑ pre-form,set of a preform and the measured actual temperature ϑ preform,ist of a preform 14, where the measured actual temperature is detected by a temperature sensor 162 at the end of the thermal conditioning of the preform 14. The temperature setpoint ϑ preform,set is a temperature setpoint of a preform 14 at the end of the thermal conditioning. In this case, the detected deviation Δx 1 corresponds to the control deviation or control difference of a controller of the heating device 116. The reference value is therefore a temperature setpoint and the controlled actual value corresponds to an actual temperature.

[0082] The detected deviation Δx 2 is a deviation between a reference value V 2 and a control variable P Steu of a controller of the heating device 116, where the reference value V 2 is, for example, equal to zero in order to detect a deviation of the control variable P Steu from zero. In this example, the detected deviation Δx 2 therefore corresponds to the control variable deviation P Steu of the controller from zero. The reference value is thus a predefined reference value V 2, and the actual controlled value of a controlled variable corresponds to the current value of the control variable P Steu.

[0083] The detected deviation Δx3 is a deviation between a reference value V3 and a sum control variable PSum for controlling the heating device 116, wherein the sum control variable is formed from a control variable PSteu of a controller of the heating device 116 and at least one detected disturbance variable PStartup, PInput, PHeating,0, wherein preferably the reference value V3 is equal to zero in order to detect a deviation of the sum control variable PSum from zero. In this example, the detected deviation Δx3 corresponds to the deviation of the sum control variable PSum of the controller from zero. The reference value is therefore a predetermined reference value V3, and the actual value of a controlled variable corresponds to the current value of the sum control variable PSum.

[0084] The detected deviation Δx4 is a deviation between a reference value V4 and a measured actual temperature ϑH,ist of the heating device 116, where preferably the reference value V4 is a setpoint temperature ϑH,set of the heating device 116. In this example, the detected deviation Δx4 corresponds to the deviation of the measured actual temperature ϑH,ist of the controller from the reference value V4. The reference value is therefore a predetermined reference value V4, and the controlled variable's actual value corresponds to the current actual temperature ϑH,ist. The reference value V4 is, for example, a setpoint temperature ϑH,set of the heating device 116.

[0085] The four deviations recorded above, Δx 1 to Δx 4 and Δx i, are used to determine the function values ​​of the support points for f 1 to f 4. A maximum drive power P max can also be taken into account to determine the setpoint characteristic curve.

[0086] The Figure 6 Furthermore, it shows that the setpoint characteristic P Trend is a heating power setpoint characteristic for controlling the heating device 116, since in the diagram shown a heating power P Heiz is output, which is applied as a disturbance variable.

[0087] The determination of the support points is carried out such that a function value fi (ti ) at a support point decreases with decreasing deviation Δxi. As can be seen, the output heating power PHeiz decreases with increasing actual temperature ϑH,ist.

[0088] In the illustrated embodiment, the predetermined times are fixed, predefined times.

[0089] The additional parts of the block diagram illustrate further disturbance variables that are preferably taken into account in the control unit, such as the initial heating power PHeat,0, the startup heating power PStartup, and the additional power PInput to compensate for different input temperatures ϑInput of the preforms. ϑRef denotes a reference temperature of the preforms at the input of the thermal conditioning system.

[0090] The lower dashed control loop corresponds to a parallel control of the ventilation of the heating device 116. In addition to radiant heaters, cooling of the preform surface is therefore provided, for example, for... Figure 5 described. Reference sign

[0091] 10 Forming machine 12 Container 14 Preforms 16 Forming stations 22 Discharge section 110 Working wheel 112 Feeding device 114 Transfer wheel 116 Heating device 118 Heating device 120 Transport device 122 Transfer wheel 124 Removal wheel 126 Output section 128 Input device 130 Sealing caps 132 Sealing device 160 Temperature sensor 162 Temperature sensor, in particular pyrometer 164 Wall thickness measuring sensor 202 Clamping mandrel 203 Handling device 205 Support ring shield 207 Counter reflector 209 Near-infrared emitter 211 Heating tunnel 212 Bottom reflector 301 Bottom area 302 Discharge section 303 External thread 304 Support ring 305 Wall area 400 Control unit 401 Display 402, 403, 404 Data lines 405 Connecting line A Master control B Control unit for the heating device C Control unit for the drive D Safety device E Control unit for the forming process

Claims

1. The method for operating a heating device (116) for the temperature conditioning of preforms (14) of a thermoplastic material in the heating device (116), wherein the respective preform (14) is prepared by thermal conditioning in the heating device (116) for a subsequent forming process, wherein the preform (14) is formed into a container (12) by means of a forming fluid fed into the preform (14) under pressure, wherein the heating device (116) is operated in a plurality of operating states, namely at least in a first and in a second operating state, wherein the heating device (116) is operated in the second operating state for a start-up phase of the heating device (116) in which a temperature of the heating device (116) approaches an equilibrium temperature of a thermodynamically stable equilibrium state of the heating device (116), wherein the operation of the heating device (116) takes place in the first operating state for continuous operation of the heating device (116) following the start-up phase, characterized in that, in the second operating state, a setpoint characteristic curve (PTrend) is created for the future control of the heating device (116) by determining support points of the setpoint characteristic curve at predetermined points in time depending on a recorded deviation (Δxi) between a reference value and a control actual value of a control variable.

2. The method according to Claim 1, wherein the setpoint characteristic curve is a heating power setpoint characteristic (PTrend) for controlling the heating device (116), and preferably, along with the heating power setpoint characteristic curve, a heating power setpoint (PHeattrend) is generated for the control of the heating device depending on a measured temperature actual value (ϑH,actual) of the heating device.

3. The method according to Claim 1 or 2, wherein the determination of the support points is carried out in such a way that a function value of a support point decreases with decreasing deviation (ΔXi).

4. The method according to any one of the preceding claims, wherein the future control is a control of the heating device in the first operating state with the setpoint characteristic curve after the setpoint characteristic curve has been determined, and / or the future control is a control of the heating device in a second operating state with the setpoint characteristic curve after the setpoint characteristic curve has been established.

5. The method according to any of the preceding claims, wherein the predetermined points in time - are fixed points in time, and / or - are temperature-dependent points in time which are present at predetermined and detected temperature values of the preform (14) or which are present at predetermined and recorded temperature values of the heating device (116) in the second operating state.

6. The method according to any one of the preceding claims, wherein the detected support points are interpolated as a trend curve, in particular, linearly or quadratically interpolated.

7. The method according to any one of the preceding claims, wherein the established setpoint characteristic curve or the interpolated trend curve is indicated on a display of the heating device (116).

8. The method according to any one of the preceding claims, wherein the established setpoint characteristic curve is stored in a memory unit of the heating device (116) and / or in an online memory and / or in a memory unit of a forming machine after creation and is stored in a retrievable manner for future control of the heating device (116).

9. The method according to any one of the preceding claims, wherein the specific support points are manually stored in a memory unit of the heating device (116) in a manually variable manner and are stored in an individually adaptable manner via an input interface of the heating device.

10. The method according to any one of the preceding claims, wherein the detected deviation (ΔXi) is a deviation (ΔX1) between a temperature setpoint (ϑpreform,setpoint) of a preform (14) and a measured actual temperature value (ϑpreform,actual) of a preform (14), wherein, preferably, the measured actual temperature value is detected by a temperature sensor at the end of the thermal conditioning of the preform (14), and the temperature setpoint is a temperature set-point of a preform (14) at the end of the thermal conditioning.

11. The method according to any one of the preceding claims, wherein the deviation (ΔXi) covered is a deviation (ΔX2) between a reference value (V2) and a control variable (Pcontrol) of a controller of the heating device (116), wherein, preferably, the reference value (V2) is equal to zero in order to establish a deviation of the control variable (PControl) from zero.

12. The method according to any one of the preceding claims, wherein the measured deviation (ΔXi) is a deviation (ΔX3) between a reference value (V3) and a total control variable (PSum) for controlling the heating device (116), wherein the total control variable is formed from a control variable (PControl) of a controller of the heating device (116) and at least one recorded disturbance variable, wherein, preferably, the reference value is equal to zero in order to determine a deviation of the total control variable (PSum) from zero.

13. The method according to any one of the preceding claims, wherein the deviation (ΔXi) is a deviation (ΔX4) between a reference value (V4) and a measured actual temperature value (ϑH,actual) of the heating device (116), wherein preferably the reference value (V4) is a temperature set-point (ϑH,setpoint) of the heating device (116).