TEMPERATURE CONTROL DEVICE FOR THE THERMAL CONDITIONING OF PREFORMS AND METHOD FOR OPERATING SUCH A TEMPERATURE CONTROL DEVICE

Abstract

The invention relates to a method for operating a temperature control device (116) for the thermal conditioning of preforms (14) made of a thermoplastic material in the temperature control device (116), wherein the respective preform (14) is prepared by the thermal conditioning in the temperature control device (116) for a subsequent forming procedure, in which the preform (14) is formed into a container (12) using a forming fluid supplied under a pressure into the preform (14) and in which the preform (14) is stretched in its axial direction by a stretching unit (11), wherein the temperature control device (116) is regulated in its heating power by a heating regulator (400, B) on the basis of a metrologically determined guide value, and is characterized in that a guide value is metrologically detected, from which the stretching force exerted on the preform (14) is derivable. Furthermore, the invention relates to a temperature control device (116) for the thermal conditioning of preforms (14) made of a thermoplastic material which is regulated on the basis of the guide value, wherein the guide value is derived from the stretching force exerted by the stretching unit (11). Finally, the invention relates to a container production machine having a temperature control device as defined above.

Claims

1-13. (canceled)

14: A method for operating a temperature control device to thermally condition preforms made of thermoplastic material in the temperature control device for a forming procedure in which the preforms are stretched axially using a stretching unit and formed into containers using a forming fluid supplied under a pressure into the preforms, the method comprising: regulating heating power of the temperature control device with a heating regulator based on a metrologically determined guide value, said guide value being a metrologically detected value from which a stretching force exerted on the preform by the stretching unit is derivable.

15: The method according to claim 14, wherein the stretching unit is a stretching rod driven by an electrically operated stretching rod drive, and wherein current consumption of the electrically operated stretching rod drive is the metrologically detected value.

16: The method according to claim 15, wherein the electrically operated stretching rod drive is a linear motor.

17: The method according to claim 14, wherein the guide value is determined based on a defined range of or defined characteristic points of the metrologically detected value.

18: The method according to claim 15, wherein a value for a friction force of stretching rod movement is metrologically detected and taken into consideration in the determination of the guide value.

19: The method according to claim 14, wherein an external temperature of the preforms is metrologically detected and supplied to the heating regulator as a second guide value, wherein the temperature control device comprises heating units for heating the preforms and cooling units for applying a coolant medium to the preforms, wherein the cooling units are regulated by the heating regulator on the basis of the second guide value, and wherein the heating units are regulated by the heating regulator on the basis of the guide value determined from the metrologically detected value from which the stretching force exerted on the preform by the stretching unit is derivable.

20: The method according to claim 19, wherein the heating regulator is configured to prioritize the guide value determined from the metrologically detected value from which the stretching force exerted on the preform by the stretching unit is derivable over the second guide value.

21: A method for producing containers from preforms by forming the preforms into the containers using a forming fluid supplied under a pressure into the preforms after thermal conditioning of the preforms in a temperature control device, the method comprising operating the temperature control device according to the method of claim 14.

22: A temperature control device for thermally conditioning preforms made of a thermoplastic material for a subsequent forming procedure in which the preforms are formed into containers using a forming fluid supplied under a pressure into the preforms and in which the preforms are stretched axially by a stretching unit, the temperature control device comprising: a heating regulator; and a measuring unit; wherein the heating regulator is arranged in a control loop with the measuring unit, wherein the measuring unit is configured to metrologically detect a value from which a stretching force exerted on the preforms by the stretching unit is derivable, and wherein the regulator is configured to regulate heating power of the temperature control device on the basis of the metrologically detected value.

23: The temperature control device according to claim 22, wherein the stretching unit is a stretching rod and comprises an electrically operated stretching rod drive, and wherein the measuring unit is configured to detect current consumption of the electrical stretching rod drive as the value.

24: The temperature control device according to claim 23, wherein the electrically operated stretching rod drive is a linear motor.

25: The temperature control device according to claim 22, wherein the heating regulator is configured to regulate according to an integral over a defined range or according to defined characteristic points of the metrologically detected value.

26: The temperature control device according to claim 22, further comprising a sensor for detecting an external temperature of the preforms and supplying measured values to the heating regulator as a second guide value, wherein the temperature control device comprises heating units for heating the preforms and cooling units for applying a coolant medium to the preforms, wherein the heating regulator is configured to regulate the cooling units on the basis of the second guide value, and wherein the heating regulator is configured to regulate the heating units on the basis of the metrologically detected value from which the stretching force exerted on the preforms by the stretching unit is derivable.

27: The temperature control device according to claim 26, wherein the heating regulator is configured to prioritize the guide value determined from the metrologically detected value from which the stretching force exerted on the preform by the stretching unit is derivable over the second guide value.

28: A machine for producing containers from preforms by stretching the preforms axially with a stretching unit and introducing a forming fluid under pressure into the preforms to form the containers, the machine comprising a temperature control device according to claim 22.

Description

[0031] Further advantages, features, and details of the invention result from the exemplary embodiments described hereafter with reference to schematic drawings. In the figures:

[0032] FIG. 1 shows a very schematic illustration of a forming machine or a machine for forming containers from preforms,

[0033] FIG. 2 shows a schematic illustration of a heater box of a temperature control device,

[0034] FIG. 3 shows a schematic illustration of a thermally-conditioned preform having temperature profiling,

[0035] FIG. 4 shows a schematic illustration of a possible control architecture of a forming machine,

[0036] FIG. 5 shows a known regulation scheme for the regulation of a temperature control device,

[0037] FIG. 6 shows a regulation scheme according to the invention for the regulation of a temperature control device,

[0038] FIG. 7 shows a schematic illustration of a stretching force curve in dependence on the stretching travel,

[0039] FIG. 8 shows a schematic illustration of the relationship between heating power of the temperature control device and detected external temperature of the preform, on the one hand, and between heating power of the temperature control device and detected stretching force, on the other hand,

[0040] FIG. 9 shows an example of a filtered stretching force curve during a no-load stroke of the stretching rod,

[0041] FIG. 10 shows a block diagram of regulation relationships during the regulation of a temperature control device including an interfering variable compensation,

[0042] FIG. 11 shows a block diagram of a PT-n element,

[0043] FIG. 12 shows a schematic illustration of a temperature control device to explain regulation variables,

[0044] FIG. 13 shows a block diagram of a simplified control loop for a temperature control device which corresponds to FIG. 10 without interfering variable compensation, and

[0045] FIG. 14 shows a perspective side view of a blowing station as an example of a forming station, in which a stretching rod is positioned by an electrical drive.

[0046] The fundamental structure known from the prior art of a forming machine 10 is shown in FIG. 1. The illustration shows the preferred design of such a forming machine 10 as a type of a rotation machine having a rotating working wheel 110 supporting multiple forming stations 16. However, only one such forming station 16 is shown to simplify the drawing. Schematically shown preforms 14, which are also referred to as blanks, are continuously supplied by a supply unit 112 to a temperature control device 116 using a transfer wheel 114. In the region of the temperature control device 116, which is also referred to as a furnace and in which the preforms 14 are transported along a heating line and thermally conditioned at the same time, the preforms 14 can be transported depending on the application, for example, having the mouth sections 22 thereof upward in the vertical direction or downward in the vertical direction. The temperature control device 116 is equipped, for example, with heating units 118, which are arranged along a transport unit 120 to form the heating line. For example, a circulating chain having transport mandrels for holding the preforms 14 can be used as the transport unit 120. For example, heater boxes having IR radiators or light emitting diodes or NIR radiators are suitable as heating units 118. Since such temperature control devices are known in manifold types in the prior art, and since the design details of the heating units are not essential for the present invention, a more detailed description going beyond the description of FIG. 2 and FIG. 12 can be omitted and reference can be made to the prior art, in particular to the prior art for temperature control devices of blowing and stretch-blowing machines and for temperature control devices of forming and filling machines which are all comprised by the term forming machines.

[0047] After sufficient thermal conditioning, the preforms 14 are transferred by a transfer wheel 122 to a drivable working wheel 110, which is arranged so it is capable of rotation, i.e., revolving around a vertical machine axis MA, or to forming stations 16 which are arranged distributed around the circumference on the working wheel 110. The working wheel 110 is equipped with a plurality of such forming stations 16, in the region of which both forming of the preforms 14 into the schematically illustrated containers 12 and also filling of the containers 12 with the provided filling material take place. The forming of each container 12 takes place simultaneously with the filling in this case, wherein the filling material is used as a pressure medium during the forming. In blowing machines, in contrast, no filling takes place on this working wheel 110, but rather at a later point in time on a filling wheel having filling stations.

[0048] After the forming and filling, the finished formed and filled containers 12 are removed by a removal wheel 124 from the working wheel 110, transported further, and supplied to an output line 126. The working wheel 110 revolves continuously in the production operation at a desired revolution speed. During one revolution, the insertion of a preform 14 into a forming station 16, the expansion of the preform 14 to form a container 12 including filling with a filling material and possibly including stretching, if a stretching rod is provided, and the removal of the container 12 from the forming station 16 take place. A stretching unit, for example, a stretching rod, is provided for executing the present invention.

[0049] According to the embodiment in FIG. 1 it is furthermore provided that schematically shown closure caps 130 are supplied to the working wheel 110 via an input unit 128. In this way, it is possible also to already carry out closing of the containers 12 on the working wheel 110 and to handle finished formed, filled, and closed containers 12 using the removal wheel 124.

[0050] Different thermoplastic materials can be used as the material for the preforms 14. Polyethylene terephthalate (PET), polyethylene (PE), polyethylene naphthalate (PEN), or polypropylene (PP) are mentioned by way of example. The dimensioning and the weight of the preforms 14 are adapted to the size, the weight, and/or to the design of the containers 12 to be produced.

[0051] A variety of electrical and electronic components are typically arranged in the region of the temperature control device 116. In addition, the heating units 118 are provided with moisture-sensitive reflectors. Since filling and forming of the containers 12 using the liquid filling material takes place in the region of the working wheel 110, it is preferably to be ensured to avoid electrical problems that an inadvertent introduction of moisture into the region of the temperature control device 116 is avoided. This can be performed, for example, by a partition unit 132, which offers at least a spray protection. In addition, it is also possible to temperature control transport elements used in the region of the transfer wheel 122 for the preforms 14 suitably or to apply pressurized gas bursts to them in such a way that adhering moisture cannot reach the region of the temperature control device 116.

[0052] Handling of the preforms 14 and/or the containers 12 is preferably carried out using tongs and/or clamping spikes or mandrels to be applied at least in regions from the inside or from the outside to the mouth section 22 with a retaining force. Such handling means are also well-known from the prior art.

[0053] The forming machine 10 is equipped with measurement sensors for the purpose of its control and/or for the purpose of its regulation. It is thus typical, for example, for a temperature sensor 160 to be arranged in the temperature control device 116 in order to be able to measure a temperature of the temperature control device 116. Furthermore, it is known in the prior art that on the outlet side of the transport unit 120, which revolves clockwise, a temperature sensor 162 is arranged, which is designed, for example, as a pyrometer and detects a surface temperature, for example, on thermally-conditioned preforms 14 running past. Finally, performing measurements on finished containers 12 using measurement sensors is also known in the prior art. Thus, for example, a wall thickness measurement sensor 164 can be arranged on the output line 126 to detect the wall thickness of a container guided past it. The above-mentioned sensors can also be formed in this case by multiple sensors arranged vertically offset, for example, to carry out a temperature measurement along the preform longitudinal axis or, for example, to execute a wall thickness measurement along the container longitudinal axis. Multiple temperature sensors 160 can also be arranged in the temperature control device 116.

[0054] The heating unit 118 illustrated by way of example in FIG. 1 could appear, for example, as shown in greater detail in a schematic sectional view in FIG. 2. Such heating units are also referred to as heater boxes. In general, multiple of these heater boxes 118 are arranged adjacent to one another along the heating line to form a heating tunnel, through which the preforms 14 are guided.

[0055] The heater box 118 shown in a schematic sectional view in FIG. 2 comprises multiple near-infrared radiators 209, in the illustrated exemplary embodiment, nine near infrared radiators 209 are arranged one over another in the vertical direction and each of these near-infrared radiators 209 defines a heating level. These NIR radiators 209 can if needed all be operated at the same power or also at different powers individually or grouped in multiples. Depending on the axial extension of the preform 14, lower-lying radiator levels in the vertical direction can also be switched off. To achieve a temperature profile in the preforms 14, it is generally necessary for near infrared radiators 209 on different radiator levels to be operated at different heating powers.

[0056] A counter reflector 207, which reflects thermal radiation incident thereon back in the direction toward the preform 14 and thus back into the heating tunnel 211, is arranged opposite to the near-infrared radiators 209. The heating tunnel 211 is terminated on the bottom by a bottom reflector 212. The preform 14 is protected against thermal radiation on the mouth side by a support ring shield 205, since the mouth region having thread formed thereon is supposed to be protected from unnecessary heating. The support ring shield 205 is arranged in this case on the handling unit 203, which can be part of a circulating chain as explained with respect to FIG. 1. The handling unit 203 furthermore comprises a clamping mandrel 202, which engages in a clamping manner in the mouth section of the preform 14. Such clamping mandrels 202 and such handling units 203 are well-known from the prior art and do not require further explanation. The fundamental structure of this above-described heater box 118 is also known from the prior art.

[0057] The temperature sensor 160 schematically shown in FIG. 1 is also shown in the heater box 118 of FIG. 2, wherein this temperature sensor 160 is generally arranged behind a reflector, for example, behind the rear reflector 207. This temperature sensor 160 detects a temperature of the heater box 118. In principle, it would also be possible to detect a temperature inside the heating tunnel 211 or to perform a temperature measurement on the preform 14 inside the heating tunnel 211.

[0058] FIG. 3 shows a sectional view of a typical preform 14 having a closed bottom region 301 and an open mouth region 302. An external thread 303 and a support ring 304 are formed in the region of the mouth section 302. After completed thermal conditioning, a defined temperature distribution results in the preform 14. Thus, for example, a temperature profile as shown on the left side of the preform 14 can be generated by corresponding heating in the axial direction of the preform 14. It can be seen therein that a higher temperature is implemented in the bottom region and in a region below the support ring than in a region lying in between. However, it is also possible to heat the preform homogeneously in the axial direction. It is obvious from the enlarged portion of the wall region 305 that a temperature curve can also be set or is intentionally settable inside the preform wall. This is because, inter alia, the absorption of the thermal radiation results in stronger heating on the radial outside than on the radial inside. Temperature differences in the preform wall do cancel out with time due to thermal equalization processes. These temperature equalization processes are, however, relatively slow in the preforms, which typically consist of PET.

[0059] In addition, the preforms 14 can also be provided with a temperature profile in the circumferential direction. This is known, for example, for preforms which are subsequently to be shaped into non-round containers, for example, into oval containers.

[0060] FIG. 4 shows the schematic illustration of a possible modular control architecture of a control unit 400 for a forming machine 10. A master controller is identified by the letter A, letter B identifies a control unit for the control and/or regulation of a temperature control device, letter C identifies a controller for the drive, for example, of the working wheel 110, letter D identifies safety units, for example, emergency stop switch, and letter E identifies, for example, a control unit for the forming process, i.e., for example, for the possible drive of a stretching rod, for switching valves for switching on and off a forming fluid, etc. Control-relevant data can be displayed on a display screen 401 and the display screen 401 is supplied with values to be displayed by the master controller via a data line 405. The display screen 401 can also function as an input unit and values input via this input unit can be transferred via the connecting line 405 to the master controller A. The further data lines 402, 403, and 404 and data line 405 can be embodied, for example, as a data bus and are used, for example, for transferring data between the master controller A and the further control modules or mutually between the control modules.

[0061] FIG. 5 shows the schematic structure of a control unit B, which is fundamentally known in the prior art, for the heating regulator, wherein the surface temperature T.sub.exterior of a preform is selected as a guide value. The temperature control device regulated by this illustrated regulation operates using heating units 118 and using cooling units 119 in the form of a fan. The regulation receives a starting heating power P.sub.beat0 and a starting fan power P.sub.fan0 as operating points, since cooling of the preform surface is provided in the present case in addition to thermal radiators. The regulation of the temperature conditioning is to be carried out in this case on the basis of the measurement of a surface temperature of the preforms 14, and for this purpose, as explained with respect to FIG. 1, a pyrometer 162 is arranged at the end of the heating line. On the basis of the surface temperature T.sub.exterior, ACTUAL of the preforms 14 measured using the pyrometer 162, the regulator adjusts the heating power of the heating units 118. Furthermore, it can be provided that an ambient temperature is detected and this ambient temperature is also incorporated into the regulation of the temperature control device. It is provided in the illustrated exemplary embodiment that sinking of the heating power is detected. To prevent excessively strong sinking of the heating power, if the power □S.sub.U is undershot, the power of the surface cooling by the cooling units 119 is changed. Upon sinking of the heating power, for example, the power of the surface cooling is increased until the heating regulator establishes sinking of the surface temperature of the preforms and increases the heating power again.

[0062] FIG. 6 schematically shows an example of a heating controller according to the invention having a control unit B for the heating regulation using two guide variables and using two manipulated variables. A variable F.sub.stretch, ACTUAL/F.sub.stretch, TARGET is selected as the first guide variable, namely the stretching force or a variable from which the stretching force is derivable, or a variable determined therefrom, for example, the deformation work. A variable T.sub.surface, ACTUAL/T.sub.surface, TARGET is selected as the second guide variable, i.e., the surface temperature of a preform. On the one hand, the heating power P.sub.heat of the heating units 118 of the temperature control device and, on the other hand, the cooling power P.sub.fan of the cooling units 119 are selected as manipulated variables. To enhance the robustness of the regulation, the regulation architecture shown in FIG. 6 is designed as a decentralized multivariable regulator.

[0063] To improve the transient behavior of the temperature control device, a feedforward control k.sub.2 is integrated into the regulator according to FIG. 6. This adds, in dependence on the difference between the ACTUAL furnace temperature T.sub.furnace, ACTUAL and the stable furnace temperature T.sub.furnace, stable, i.e., the furnace temperature after reaching the thermal equilibrium state after a defined operating duration, an additional percentage power with a factor to the equilibrium heating power P.sub.heat0, P.sub.heat0 represents a base value. Before reaching the equilibrium state of the temperature control device or the furnace, a higher heating power thus results, to nonetheless bring the preforms to the desired temperature. The block diagram shown in FIG. 6 furthermore provides a decoupling branch k.sub.1 to attenuate internal couplings. In the illustrated exemplary embodiment, the guide variable F.sub.stretch, ACTUAL/F.sub.stretch, TARGET is prioritized over the guide variable F.sub.surface, ACTUAL/F.sub.surface, TARGET. The feedforward control is shown in the block diagram as interference k.sub.2, which is made dependent on the difference between the temperature of the temperature control device T.sub.furnace, stable upon the presence of equilibrium conditions in relation to the actual temperature of the temperature control device T.sub.furnace, ACTUAL. The greater this temperature difference is, the greater the interference effect is to be formed and therefore the higher the factor should be selected to increase the heating power in relation to the base heating power.

[0064] The heating power P.sub.heat0 and the fan power P.sub.fan0 represent set powers for these actuators and describe an operating point or a base point. These powers are changed in dependence on the guide variables.

[0065] According to the invention, a regulation on the basis of a metrologically detected variable is provided, which is derivable from a stretching force or is the stretching force itself. A regulation according to variables determined therefrom can also be provided, for example, on the basis of the stretching force. Therefore, it is to be explained hereafter on the basis of an example how this variable can be respectively provided for the regulation.

[0066] FIG. 7 shows a metrologically detected stretching force curve, which was derived from the current consumption of the stretching rod drive, namely a servo motor. The stretching force is plotted over the stretching travel of the stretching rod, wherein stretching force is not yet exerted on the preform until the preform cup is reached by the stretching rod. Stretching thus does not yet take place on this travel section. Because of the mass inertia of the motor armature of the servo motor, the gearing, and the stretching rod, the acceleration and deceleration are also visible in the illustrated force curve. At the beginning of the stretching travel, the mass of the stretching system is accelerated. If the stretching rod has reached constant speed, in the illustrated case at approximately 50 mm, friction forces become visible. These results, on the one hand, from the gearing of the drive, on the other hand, from the friction forces of the stretching rod surface on seals. These seals seal off the part of the forming station to which pressure is applied from the surroundings. If the stretching rod contacts the cup, the stretching force increases. This takes place at a stretching travel of approximately 140 mm in FIG. 7. After the P1 valve has been switched, the stretching force drops again, since the internal pressure in the preform also generates an axial force, recognizable at the stretching force drop at a stretching travel just below 200 mm at the point peak1. With progression of the container bubble development, the strain hardening of the preform material appears as a rise of the drive force curve toward a second local maximum in the stretching force curve at peak2. So as not to collide with the base mold of the forming station, the stretching rod has to decelerate at the end of the P1 phase. The braking force required for this purpose is overlaid with the force which is to be applied for the actual stretching.

[0067] For example, the first and/or the second peak (peak1 and/or peak2) or also an integral over a range of the stretching force curve, for example, arranged essentially between these two peaks, is suitable for the use as a guide value. Such an integral represents stretching work. The forming process during the forming of a preform into a container is, in simplified form, the introduction of forming energy into a preform to produce a container. This forming energy is divided into thermal energy (temperature control of the preform) and into mechanical energy (radial and axial expansion of the preform). If one introduces more thermal energy, less mechanical work is necessary for the forming.

[0068] The mechanical forming work is composed of the application of a forming fluid to the preform at a defined forming pressure and/or having a defined volume flow and of the force applied by the stretching rod. The force applied by the stretching rod can be determined as stated above by metrological detection of the motor current.

[0069] The suitability of the second peak as a guide value is illustrated and explained hereafter. The measurement results compiled in FIG. 8 were achieved in studies using this second peak as the guide value. For example, the relationship of the second peak to the heating power during the thermal conditioning was studied, i.e., the change in peak2 with changed heating power. It is also indicated for comparison in FIG. 8 how the surface temperature of the preform is dependent on the changed heating power. FIG. 8 shows in the case of this comparison that the stretching force reflects the heating power introduced into the preform, i.e., the thermally introduced energy content, with higher accuracy than the previously used surface temperature detected by a pyrometer. With rising surface temperature and/or with rising heating power, the stretching force sinks as expected. While the stretching force sinks by 42% (by 55 N) upon the performed change in the heating power, the surface temperature only decreases upon the same change by 3.5% (by 3.8° C.). The stretching force thus proved to be more sensitive with respect to the heating power than the surface temperature.

[0070] FIG. 10 shows a block diagram to illustrate essential regulation-theoretical regulation relationships in the thermal conditioning process. The attempt is intentionally made in this case to describe the guide variables F.sub.stretch and T.sub.surface separately. To avoid confusions between time constants and temperatures, ϑ is used hereafter for temperatures. The master value of the heating power P.sub.heat and the speed of the fan n.sub.fan (in % of the maximum speed) are used as inputs into the system. The surface temperature of the preform ϑ.sub.surface is measured by means of the pyrometer 162 at the end of the heating line. In the chronologically following blowing process, a stretching force F.sub.stretch is measured (or a variable from which the stretching force is derivable). It results from the amount of energy contained in the preform Q.sub.preform after the temperature conditioning process and the factor K.sub.QF. This factor is dependent on the settings of the blowing parameters. If one increases the blowing pressure, for example, the stretching rod guides the bubble less. It thus also becomes less sensitive to variations in the energy content in the preform as a result of the thermal conditioning.

[0071] The time between leaving the heating and measuring the stretching force is described from the aspect of the energy content as the dead time T.sub.f. An energy loss due to convection does occur during this time, however, the energy content only changes insignificantly and can therefore also be neglected in regulation.

[0072] The energy Q.sub.preform contained in the preform is decisively determined by the energy Q.sub.heat introduced by the temperature control device. The energy Q.sub.cool is removed by the surface cooling. If the temperature control device is in a steady operating state, which is achieved after a heating time, surrounding components are heated and emit longwave secondary radiation, which introduces the interference energy Q.sub.interference into the preform. This interference energy also acts on the surface temperature by way of the factor K.sub.Qϑ. Since the process is set to the steady state of the temperature control device, an absence of this energy results in deviations in the process, since the preform does not have the total energy required for the blowing process. The amount of secondary radiation which is emitted may be estimated by the temperature of the reflector plate ϑ.sub.PT100. However, since the relationship between energy Q.sub.interference and ϑ.sub.PT100 is not accurately known, it is described by the nonlinear relationship NL.sub.ϑQ. The temperature ϑ.sub.PT100 results with a PT-1 behavior in dependence on the heating power P.sub.heat. Due to the good absorption of the longwave secondary radiation, it has influence on the surface temperature of the preform. This is depicted by means of the factor K.sub.Qϑ. It describes how the surface temperature also changes due to the interference energy.

[0073] The entry temperature of the preform ϑ.sub.0 is a further source of interference. This can change depending on the storage of the preform. If it rises, the surface temperature and the energy content thus also increase.

[0074] Upon an increase of the heating power, the preform located in the last heating module receives less additional energy because of the short remaining dwell time in the temperature control device. A preform which is just at the beginning of the temperature control device at the point in time of the power increase, in contrast, will already have the full additional energy content. Since every preform can be viewed as an energy accumulator between these two cases, it is obvious that a higher-order transmission behavior without harmonics results.

[0075] Since this observation is also carried out for the surface cooling, the main dynamics of the temperature control device are represented by 4 PT-n elements having degree k.

[0076] FIG. 11 shows a block diagram of such a PT-n element. A PT-n consists in this case of a series circuit of n PT-1 elements having the time constant T.sub.uy. The transmission element has an amplification K.sub.uy in this case. The individual PT-n elements are coupled according to P-canonical form.

[0077] FIG. 12 illustrates the arrangement of heating units 118 and of cooling units 119 along the heating line 120 and the incorporation thereof into the regulation of the temperature control device 116 on the basis of the specified parameters for heating powers and for fan speeds. It is clear by way of example from this overview where and when which parameter has influence on the thermally-conditioning effect of the temperature control device. Qualitatively, it can be stated that the time behavior of the surface cooling will always be somewhat faster than the time behavior of the heating modules. Because of the shorter line, the dynamics decay faster after manipulated variable change of the surface cooling than those of the heating line. The time which a fan or a heating module requires after change of the speed with the heating power, respectively, to set it is assumed to be negligible.

[0078] A model of the control loop suitable for the regulator of the temperature control device has been described with respect to FIG. 10. FIG. 13 shows a base regulator without interference variable compensation, i.e., the interference variables mentioned with respect to FIG. 10 are neglected here. Furthermore, the dead time at the transfer T.sub.t and also the factor K.sub.QF are depicted by means of the four transmission elements in P-canonical form. The factors K.sub.PF(BP) and K.sub.nF(BP) are introduced for the effect of the heating power and the surface cooling. They are dependent on the blowing parameter vector BP. If the blowing parameters are constant, the factors are thus also constant.

[0079] Since the temperatures and forces are dependent on the energy state of the preform, it may additionally be established that the amplifications K.sub.uy in FIG. 13 are dependent on the dwell time in the temperature control device. This is defined by the production speed PG. If they are reduced, all factors increase, since the preform remains longer in each module. It can be presumed in a good approximation for regulation, for example, that this influence is linear around the operating point.

[0080] The base regulator is supposed to regulate the surface temperature and the stretching force as guide values. The heating units and the surface cooling still remain actuators. The use of a decentralized regulator enables a simple implementation.

[0081] Since the stretching force has a better correlation to the container quality than the surface temperature, it is preferably used as the manipulated variable for the temperature control device.

[0082] It is indirectly possible using the guide variables stretching force and surface temperature to specify the radial temperature profile in the preform. If the energy content (stretching force) is kept constant, the temperature in the interior of the preform has to rise upon reduction of the surface temperature. The internal temperature may thus be specified or maintained indirectly using this mode of action of the regulator.

[0083] The control loop described with respect to FIG. 10 is shown as a block diagram in FIG. 6. Since the temperature control device also strongly influences the surface temperature, a static decoupling is provided with k.sub.1. A decoupling branch from surface temperature to temperature control device is avoided. The change of the surface temperature does have an effect on the stretching force, but the significance of the surface temperature with regard to the quality of the container is less. Therefore, control actions of the surface cooling are not supposed to be transferred directly to the heating power.

[0084] For example, the first or second peak and the stretching work can be selected as guide variables. Since all three variables describe the energy content in the preform after the thermal conditioning, in the above explanations, all three possible guide variables are described under the term “stretching force” and/or F.sub.stretch. The stretching work is considered to be preferable as the guide variable, since it takes into consideration the entire process sequence during the forming.

[0085] To approximately compensate for the transient state of the temperature control device, i.e., the state before reaching a thermal equilibrium, the deviation from the already known stable temperature is connected as power to the temperature control device by the factor k.sub.2. An improvement of the startup behavior can thus also be achieved using the base regulator explained with respect to FIG. 13 by means of empirical setting.

[0086] P.sub.heat0 and n.sub.fan0 represent the powers set in the formula for the actuators and therefore describe the operating point. The signs in the subtraction are exchanged in comparison to the standard controller. This results from the relationships described hereafter. Thus, a higher heating power reduces the stretching force, and a greater airflow cools the surface more strongly.

Δheating power˜−Δstretching force

Δairflow˜−ΔT.sub.surface

[0087] Since the essential interfering factors such as ambient temperature or soiling of the temperature control device only change very slowly, low dynamic requirements for the regulator result therefrom. The steady accuracy of the process, and thus a constant container quality in the course of the container production, has priority.

[0088] To achieve static accuracy, because of the non-integrating property of the main control loops, I components are provided in both regulators. To additionally achieve better dynamics of the closed-loop, PI regulators are used. The use of a PID regulator is precluded, since the D component can be selected to be very small because of the process noise, so as not to cause the control loop to oscillate.

[0089] Several main functions of the regulator are described hereafter, for example, how the guide variables stretching force can be generated.

[0090] Upon the start of the stretching, the stretching force, the stretching travel, and the bottle interior pressure are recorded. After ending the process, these measurements series are transmitted by means of an OPC interface to a computer for visualization. This computer processes the data, for example, for the export as a CSV file. The curve can thus be manually analyzed thereafter. However, the real-time analysis of the curve in the form of a guide value is necessary for the described regulator.

[0091] To ascertain the stretching force, the effective value of the current of the last millisecond is output in each case by the stretching rod drive. This is computed on a drive-internal FPGA, which also ensures the position regulation by means of a cascade regulation having guide variable generator. At a sampling rate of 1 ms, a large information loss thus does not result, since the entire time range is detected by effective value formation of the last millisecond. Due to the motor-internal effective value formation, noise caused by the converter is already filtered out. However, the generated stretching force curve is still subject to a substantial noise component. Therefore, filtering with a discrete PT1 filter is provided as the first, although optional step.

[0092] As explained with respect to FIG. 7, various ranges in the stretching force curve may be utilized for regulation. However, the range in which the friction occurs is also relevant. The two peaks and the stretching work are particularly relevant as possible guide values for the stretching-force-based part of the regulator. These values are sought out and/or determined in defined ranges. The ranges in which these are determined are set, for example, in dependence on the stretching travel.

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[0093] The above image shows the fundamental sequence of an exemplary algorithm. It is firstly identified in which ranges of the data the values to be ascertained and/or the friction are located. The noise is subsequently reduced by means of a discrete PT1 filter. The mean friction force is now determined. This occurs after the acceleration of the stretching rod during the constant travel up to the incidence on the cup of the preform. This force is subtracted as an offset from the curve, since it results from friction losses. The determination of the maxima and of the stretching force integral are now performed. To specify ranges in the stretching force curve for the respective variables, the travel of the stretching rod is used. This is also recorded with the same resolution as the stretching force. This travel is used as the x axis of the stretching force curve to define in which region the friction force occurs, the peaks are located, and the stretching work is to be determined. The regions can overlap in this case.

[0094] The algorithm passes through the array in which the travel is recorded and determines the index of the respective travel range limits. The stretching force curve is subsequently traversed value by value. If the value is located between the limits, the maximum deflection (in positive or negative direction) and the stretching work are determined for the peaks.

[0095] The ranges can be set manually, for example, or an automated definition of the positions of the peaks can also be performed and ranges can be defined therefrom. Alternative methods for establishing the ranges are also possible.

[0096] All determined values of the function are subsequently output. Therefore, either the first or second process peak and the stretching work can then be linked as the guide variable “stretching force” to the input of the regulator. The value which best reflects the quality of the bottle can thus be selected depending on the process. Optionally, only one of these values can also be output and used as a guide variable, for example, only the stretching force.

[0097] It is possible to define a stretching force curve as a reference curve. This reference curve is provided, for example, in stored form and is subtracted, for example, from the presently detected curve. To eliminate influence of phase offset by way of the filter, the reference curve is filtered using the same filter constant, for example, before subtraction from the present curve. Furthermore, the resulting curve thus also remains free of noise. If the process and/or the stretching force curve is identical to the reference curve, the value 0 is output as the value for peak 1 and peak 2 and for the stretching work. It is thus not necessary upon use of the reference curve to explicitly specify a target value for the stretching force.

[0098] A change of the blowing pressure results in a change of the stretching force. It is therefore advantageous for a stable regulation if the regulator switches off upon change of the blowing pressure and the settings of the temperature control device are frozen. If one presumes that the temperature control of the preform has not changed in the time of the switching off, after the pressure change, the actual value for the stretching force can be assumed as the new target value and the regulation can be switched on again. This also applies for the change of another blowing parameter.

[0099] FIG. 9 shows the stretching force curve of a no-load stroke of a stretching rod. The readout algorithm has already subtracted the friction force during the constant travel. However a rising friction force remains on the travel section on which normally the stretching process takes place (see rising force in FIG. 9). Since the stations have different stiffnesses, the measured value for the stretching work varies. To avoid this behavior, no-load strokes can be used for referencing the measured system stretching drive. Subtracting a reference curve from a present stretching force curve can be implemented in the readout algorithm. This functionality can be utilized to subtract the no-load stroke curve of the respective station from the stretching force curve.

[0100] FIG. 14 shows a blowing station 3 in a perspective viewing direction from the front. It is recognizable from this illustration in particular that the stretching rod 11 is mounted by a stretching rod carrier 41. A forming station which forms and fills a preform simultaneously, could also be embodied in the same manner with respect to the stretching rod 11 and the stretching rod drive 49.

[0101] FIG. 14 also shows the arrangement of a pneumatic block 46 for the blowing pressure supply of the blowing station 3. The pneumatic block 42 is equipped with high pressure valves 43, which can be connected via fittings 44 to one or more pressure supplies. After blow molding of the container 12, blowing air to be discharged into an environment is firstly supplied to a silencer 45 via the pneumatic block 42.

[0102] The blowing procedure is typically carried out in such a manner that after the preform 14 is inserted into the blow mold 4, locking of the blowing station 3 occurs and firstly the stretching rod 11 is moved into the preform 14 with simultaneous blowing pressure assistance in such a way that the preform 14 does not shrink radially onto the stretching rod 11 due to the axial stretching. In this phase, a blowing pressure P1 is supplied. After the stretching procedure is completely carried out, the complete expansion of the container bubble into the final contour of the container 12 is performed by application of a higher blowing pressure P2. The maximum internal pressure P2 is maintained until the container 12 has reached a sufficient dimensional stability due to cooling. After reaching this dimensional stability, the blowing pressure supply is switched off and the stretching rod 11 is retracted again from the blow mold 4 and thus out of the blown container 12.

[0103] FIG. 14 also illustrates that the stretching rod carrier 41 is connected to a coupling element 46, which is guided at least in regions behind a cover 47. The coupling element 46 is positionable by a servo motor 49, for example, using a threaded rod (not recognizable in FIG. 14). The arrangement of the threaded rod, the mechanical positioning of the pneumatic block 42, and further details are explained, for example, in EP 2117806 B1 with respect to FIGS. 5 and 6 therein.

[0104] The threaded rod shown therein is connected via a coupling to a motor shaft of the servo motor 49. In the exemplary embodiment illustrated therein, the motor shaft and the threaded rod extend along a common longitudinal axis, so that the threaded rod is arranged as an extension of the motor shaft. In particular a gear-free connection of the motor shaft to the threaded rod is assisted in this way.

[0105] The coupling of the servo motor 49 via a threaded rod, a coupling element 46, and the stretching rod carrier 41 having the stretching rod 11 provides a system which is rigid in relation to external loads and nonetheless highly dynamic.

[0106] A present stretching force can be inferred in a simple manner from a metrological detection of the motor current of the servo motor 49. A regulation of the temperature control device can be performed, as explained above, in dependence on the stretching force metrologically detected by the detection of the motor current.