JP7559632B2 - Preform heating device and control method thereof - Google Patents

Description

The present disclosure relates to a preform heating device that heats preforms for thermoplastic containers, and to a method for controlling such a preform heating device.

Thermoplastic containers such as PET (polyethylene terephthalate) bottles are manufactured by first injection molding a small container shaped like a test tube called a preform, then heating the preform and blowing air into the heated preform to expand it (blow molding). For example, Patent Document 1 discloses a preform heating method used when biaxially stretching and blow molding a PET resin preform.

Patent No. 5692648

When manufacturing a preform, if there is a large temperature difference between the outer and inner surfaces of the heated preform, defects such as variations in the thickness and strength of the container will occur. For this reason, it is necessary to heat the preform so that the temperature difference between the outer and inner surfaces of the preform is kept within a desired range, preferably so that the inner surface temperature is made to match the outer surface temperature.

However, because the preform heating device heats the outer surface of the preform and the inner surface of the preform is not directly heated, it is difficult to achieve the desired temperature at the inner surface of the preform.

In addition, since the preform is generally transported while rotating inside the heating device, it is difficult to use a wired contact-type temperature sensor to measure the temperature of the inner surface of the preform. Even if a non-contact type temperature sensor such as an infrared temperature sensor is used, it is possible to measure the temperature of the outer surface of the preform, but it is not possible to measure the temperature of the inner surface of the preform.

As such, since the inner surface of the preform cannot be heated directly, the temperature of the heating device must be adjusted by trial and error while observing the quality of the final molded product, and temperature adjustment requires a great deal of work. In addition, since the inner surface temperature of the preform is unknown, the temperature of the heating device cannot be optimally adjusted, and there is a risk of defective products being produced due to small environmental changes, etc. Therefore, there is a need for a method of controlling a preform heating device that can heat the preform so that the inner surface temperature of the preform approaches the desired target value without the need for significant effort in temperature adjustment.

The object of the present disclosure is to provide a method for controlling a preform heating device that can heat a preform so that the inner surface temperature of the preform approaches a desired target value without requiring significant effort in temperature adjustment. Another object of the present disclosure is to provide such a preform heating device.

According to a method for controlling a preform heating apparatus according to one aspect of the present disclosure,
1. A method for controlling a preform heating device for heating a preform for a thermoplastic container, comprising:
the preform heating device includes at least one furnace that receives the preform and heats it at a predetermined furnace temperature;
The control method includes:
obtaining a first temperature model indicating a relationship between the furnace temperature and an outer surface temperature of the preform;
obtaining a second temperature model indicating a relationship between an outer surface temperature of the preform and an inner surface temperature of the preform;
calculating a first temperature function indicative of a change in temperature of an outer surface of the preform over time based on the first temperature model;
calculating a second temperature function indicative of a change in temperature of the inner surface of the preform over time based on the second temperature model;
calculating a setpoint for the furnace temperature based on the first and second temperature functions to reduce an error between the inner surface temperature of the preform and a predetermined inner surface temperature target below a predetermined threshold;
setting the calculated furnace temperature set point in the furnace.

This allows the preform to be heated so that its inner surface temperature approaches the desired target value without the need for significant effort in adjusting the temperature.

According to a method for controlling a preform heating apparatus according to one aspect of the present disclosure,
The second temperature model is represented by a transfer function from the outer surface temperature of the preform to the inner surface temperature of the preform.

This allows the furnace temperature setting to be calculated taking into account the inner surface temperature of the preform.

According to a method for controlling a preform heating apparatus according to one aspect of the present disclosure,
The second temperature model is represented by a transfer function of first or second order lag form including parameters of gain and time constant in the domain of Laplace transformed functions.

This allows the temperature model, including the inner surface temperature of the preform, to be properly represented.

According to a method for controlling a preform heating apparatus according to one aspect of the present disclosure,
The step of obtaining the second temperature model includes:
acquiring first time-series data indicating a change over time in an outer surface temperature of the preform;
acquiring second time series data indicating a change over time in an inner surface temperature of the preform;
and calculating a transfer function of the second temperature model based on the first and second time series data.

This allows for proper calculation of a temperature model that includes the inner surface temperature of the preform.

According to a method for controlling a preform heating apparatus according to one aspect of the present disclosure,
the step of acquiring the first time-series data includes a step of acquiring an outer surface temperature of the preform from a first temperature sensor provided on the outer surface of the preform when the outer surface of the preform is heated with a step-like temperature profile;
The step of acquiring the second time series data includes a step of acquiring the inner surface temperature of the preform from a second temperature sensor provided on the inner surface of the preform when the outer surface of the preform is heated with the step-like temperature profile.

This allows for proper calculation of a temperature model that includes the inner surface temperature of the preform.

According to a method for controlling a preform heating apparatus according to one aspect of the present disclosure,
The first temperature model is represented by a transfer function from the furnace temperature to the outer surface temperature of the preform.

This allows the furnace temperature setting to be calculated taking into account the temperature inside the furnace.

According to a method for controlling a preform heating apparatus according to one aspect of the present disclosure,
The first temperature model is represented by a transfer function of first or second order lag form including parameters of gain and time constant in the domain of Laplace transformed functions.

This allows for an appropriate representation of the temperature model, including the temperature inside the furnace.

According to a method for controlling a preform heating apparatus according to one aspect of the present disclosure,
The step of obtaining the first temperature model includes:
acquiring third time series data indicating a change in the furnace temperature over time;
acquiring fourth time-series data indicating a change over time in an outer surface temperature of the preform;
and calculating a transfer function of the first temperature model based on the third and fourth time series data.

This allows for proper calculation of the temperature model, including the temperature inside the furnace.

According to a method for controlling a preform heating apparatus according to one aspect of the present disclosure,
The step of calculating the furnace temperature set point includes the step of iteratively varying the furnace temperature set point to reduce an error between the inner surface temperature of the preform and the inner surface temperature target value.

This allows the furnace temperature setting to be calculated appropriately.

According to a method for controlling a preform heating apparatus according to one aspect of the present disclosure,
The step of calculating the set value of the furnace temperature includes a step of calculating the set value of the furnace temperature based on the first and second temperature functions so as to reduce an error between the inner surface temperature of the preform and the inner surface temperature target value below the threshold value, and so as to reduce an error between the outer surface temperature of the preform and a predetermined outer surface temperature target value below the threshold value.

This allows the preform to be heated so that the outer surface temperature of the preform approaches the desired target value without the need for significant effort in temperature adjustment.

According to a method for controlling a preform heating apparatus according to one aspect of the present disclosure,
The step of calculating the furnace temperature set value includes a step of iteratively changing the furnace temperature set value so as to reduce an error between the inner surface temperature of the preform and the inner surface temperature target value, and to reduce an error between the outer surface temperature of the preform and the outer surface temperature target value.

This allows the furnace temperature setting to be calculated appropriately.

According to a method for controlling a preform heating apparatus according to one aspect of the present disclosure,
The inner surface temperature target value is set to the same value as the outer surface temperature target value.

This reduces the difference between the outer and inner temperatures of the preform.

According to a method for controlling a preform heating apparatus according to one aspect of the present disclosure,
The inner surface temperature target value is set to a value having a predetermined temperature difference with respect to the outer surface temperature target value.

This allows the preform to be heated so that the outer surface temperature and inner surface temperature of the preform approach their desired target values, even if the outer surface temperature and inner surface temperature of the preform are different from each other.

According to a method for controlling a preform heating apparatus according to one aspect of the present disclosure,
the preform heating device includes a plurality of furnaces arranged adjacent to each other so that the preforms pass through them sequentially;
For each of the plurality of furnaces, the furnace temperature setpoint is constant over time.

This allows the preforms to be heated using a continuous furnace that includes multiple furnaces.

According to a method for controlling a preform heating apparatus according to one aspect of the present disclosure,
A preform heating apparatus for heating a preform for a thermoplastic container, the preform heating apparatus comprising:
at least one furnace for receiving and heating the preform at a predetermined furnace temperature;
a control device for controlling a set value of the furnace temperature,
The control device includes:
obtaining a first temperature model indicating a relationship between the furnace temperature and an outer surface temperature of the preform;
obtaining a second temperature model indicating a relationship between an outer surface temperature of the preform and an inner surface temperature of the preform;
calculating a first temperature function indicative of a change in temperature of an outer surface of the preform over time based on the first temperature model;
calculating a second temperature function indicative of a change in the temperature of the inner surface of the preform over time based on the second temperature model;
calculating a setpoint for the furnace temperature based on the first and second temperature functions so as to reduce an error between the inner surface temperature of the preform and a predetermined inner surface temperature target value;
The calculated furnace temperature set point is configured to be set in the furnace.

This allows the preform to be heated so that its inner surface temperature approaches the desired target value without the need for significant effort in adjusting the temperature.

According to a method for controlling a preform heating device according to one aspect of the present disclosure, the preform can be heated so that the inner surface temperature of the preform approaches a desired target value without requiring significant effort in adjusting the temperature.

FIG. 1 is a block diagram showing a configuration of a preform heating device 100 according to a first embodiment. FIG. 2 is a perspective view showing the configuration of the preform 10 of FIG. 1. 2 is a diagram illustrating a process for manufacturing a bottle 11 by blow molding a preform 10 heated by the preform heating device 100 of FIG. 1. FIG. FIG. 2 is a block diagram showing the configuration of the furnace 2 in FIG. 1 . 2 is a flowchart showing a set value calculation process executed by the control device 1 of FIG. 1 . FIG. 2 is a block diagram showing a configuration for acquiring a temperature model of a furnace 2 in the preform heating apparatus 100 of FIG. 1 . 7 is a graph showing an example of a temperature model of the furnace 2 acquired by the measuring device 41 of FIG. 6 . FIG. 2 is a schematic diagram showing a configuration for acquiring a temperature model of the preform 10 of FIG. 1 . 9 is a graph showing an example of a temperature model of the preform 10 acquired by the measuring device 51 of FIG. 8 . 6 is a graph showing an example of the outer surface temperature and the inner surface temperature of the preform 10 when the initial value of the furnace temperature set in step S5 of FIG. 5 is used. 6 is a graph showing an example of the outer surface temperature and the inner surface temperature of the preform 10 when the set value of the furnace temperature set in step S9 of FIG. 5 is used. FIG. 11 is a block diagram showing a configuration of a preform heating device 110 according to a second embodiment.

Below, an embodiment of one aspect of the present disclosure will be described with reference to the drawings. In each drawing, the same reference numerals indicate similar components.

[Application example]
1 is a block diagram showing the configuration of a preform heating apparatus 100 according to the first embodiment. The preform heating apparatus 100 heats a preform 10 for a thermoplastic container such as a PET bottle. The preform heating apparatus 100 includes at least one furnace 2-1 to 2-3 that houses the preform 10 and heats it at a predetermined furnace temperature, and a control device 1 that controls the set value of the furnace temperature.

In the example of FIG. 1, the preform heating device 100 includes multiple furnaces 2-1 to 2-3 arranged adjacent to each other so that the preform 10 passes through them sequentially. The preform 10 is transported by a belt conveyor 3 so that it passes through the furnaces 2-1, 2-2, and 2-3 in that order.

In this specification, furnaces 2-2 and 2-3 are collectively referred to as "furnace 2."

Figure 2 is a perspective view showing the configuration of the preform 10 in Figure 1. The preform 10 is injection molded to have a shape like a test tube. The preform 10 has an outer surface 10a and an inner surface 10b. As described above, when manufacturing the preform 10, if there is a large temperature difference between the outer surface 10a and the inner surface 10b of the heated preform 10, defects such as variations in the thickness and strength of the container will occur. For this reason, it is required to heat the preform 10 so that the temperature difference between the outer surface 10a and the inner surface 10b of the preform 10 is kept within a desired range, preferably so that the inner surface temperature is made to match the outer surface temperature. Below, a method of controlling the preform heating device 100 for heating the preform 10 so that the inner surface temperature of the preform 10 approaches a desired target value without requiring a lot of effort in temperature adjustment will be described.

The control device 1 acquires a temperature model of the furnace 2, i.e., a first temperature model F1(s) showing the relationship between the furnace temperature and the outer surface temperature of the preform 10. The control device 1 further acquires a temperature model of the preform 10, i.e., a second temperature model F2(s) showing the relationship between the outer surface temperature of the preform 10 and the inner surface temperature of the preform 10. The control device 1 further calculates a first temperature function Tout(t) showing the temporal change in the outer surface temperature of the preform 10 based on the first temperature model F1(s). The control device 1 further calculates a second temperature function Tin(t) showing the temporal change in the inner surface temperature of the preform 10 based on the second temperature model F2(s). The control device 1 further calculates the set values Tr1, Tr2, Tr3 of the furnace temperature based on the first temperature function Tout(t) and the second temperature function Tin(t) so as to reduce the error between the inner surface temperature Tin(t) of the preform 10 and a predetermined inner surface temperature target value Tin_tgt(t) to less than a predetermined threshold value Δfe. The control device 1 further sets the calculated furnace temperature set values Tr1, Tr2, and Tr3 in the furnace 2.

According to the preform heating device 100 of FIG. 1, by using the temperature model F2(s) showing the relationship between the outer surface temperature and the inner surface temperature of the preform 10, it is possible to heat the preform 10 so that the inner surface temperature of the preform 10 approaches the desired target value, for example, without the need to adjust the temperature of each furnace 2 and/or the speed of the belt conveyor 3 by trial and error, and without measuring the inner surface temperature of the preform 10 during heating. Therefore, according to the preform heating device 100 of FIG. 1, it is possible to heat the preform 10 so that the inner surface temperature of the preform 10 approaches the desired target value, without the need to spend a lot of time adjusting the temperature.

Figure 3 is a diagram illustrating the process of manufacturing a bottle 11 by blow molding the preform 10 heated by the preform heating device 100 of Figure 1. The preform 10 heated by the preform heating device 100 is inserted into a mold 31 for the bottle 11 as shown in Figure 3 (a). Figures 3 (a) to 3 (c) show cutaway views of the mold 31. A pipe 32 connected to a high-pressure air source is inserted inside the preform 10. As shown in Figure 3 (b), the preform 10 expands by blowing air into the preform 10 through the pipe 32. Finally, as shown in Figure 3 (c), the preform 10 is molded into the shape of the bottle 11. Thereafter, as shown in Figure 3 (d), the molded bottle 11 is removed from the mold 31. By preheating the preform 10 by the preform heating device 100, a high-quality bottle 11 can be manufactured without defects such as variations in thickness and strength.

[First embodiment]
Hereinafter, the preform heating apparatus 100 according to the first embodiment will be further described with reference to the drawings.

[Configuration Example of First Embodiment]
With further reference to FIG. 1, the furnaces 2-1 to 2-3 are equipped with temperature controllers 21-1 to 21-3, heaters 22-1 to 22-3, and temperature sensors 23-1 to 23-3, respectively.

In this specification, the temperature regulators 21-1 to 21-3 are also collectively referred to as "temperature regulators 21." Also, in this specification, the heaters 22-1 to 22-3 are also collectively referred to as "heaters 22." Also, in this specification, the temperature sensors 23-1 to 23-3 are also collectively referred to as "temperature sensors 23."

Figure 4 is a block diagram showing the configuration of the furnace 2 in Figure 1. All of the furnaces 2-1 to 2-3 in Figure 1 are configured in the same way as the furnace 2 in Figure 4. The set value of the furnace temperature is input from the control device 1 to the temperature regulator 21. The temperature regulator 21 operates the heater 22 according to the set value of the furnace temperature. The heater 22 is, for example, an infrared heater. The temperature sensor 23 measures the actual furnace temperature, for example, the temperature inside the furnace 2, near the position where the preform 10 passes, and notifies the temperature regulator 21. Therefore, the temperature regulator 21 feedback controls the heater 22 so that the temperature inside the furnace 2 approaches the set value.

The preform 10 may be transported by the belt conveyor 3 while rotating around its longitudinal axis. In addition, in each furnace 2, the heater 22 may be arranged to surround the preform 10. This allows the entire preform 10 to be heated substantially uniformly.

Referring further to FIG. 1, the preform heating device 100 may further include a belt conveyor 3, a drive device 4, a temperature sensor 5, an input device 6, and a display device 7.

The drive device 4 drives the belt conveyor 3 at a predetermined speed under the control of the control device 1. The heating time of the preforms 10 in each furnace 2 can be determined by dividing the length of each furnace 2 along the belt conveyor 3 by the speed of the belt conveyor 3.

The temperature sensor 5 measures the temperature outside the furnace 2, for example, the air temperature near the preform heating device 100, and notifies the control device 1. The air temperature is equal to the temperature of the preform 10 before heating.

The input device 6 receives user input to set the state of the preform heating device 100 and inputs it to the control device 1. The input device 6 may include a keyboard and a pointing device.

The display device 7 receives data indicating the status of the preform heating device 100 from the control device 1 and displays it.

The control device 1 controls the overall operation of the preform heating device 100. In particular, the control device 1 executes a set value calculation process described later with reference to FIG. 5, calculates the set value of the furnace temperature for heating the preform 10, and sets it in each furnace 2. For this purpose, the control device 1 acquires a temperature model F1(s) showing the relationship between the furnace temperature and the outer surface temperature of the preform 10 from a measuring device 41 described later with reference to FIG. 6. The control device 1 also acquires a temperature model F2(s) showing the relationship between the outer surface temperature and the inner surface temperature of the preform 10 from a measuring device 51 described later with reference to FIG. 8. The control device 1 may include a communication interface such as a wired or wireless LAN (Local Area Network) in order to acquire the temperature models F1(s) and F2(s) from the measuring devices 41 and 51, and may also be provided with another interface such as a USB (Universal Serial Bus).

The control device 1 includes a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), etc., and controls each component of the preform heating device 100 in response to information processing. The control device 1 further includes an auxiliary storage device, such as a hard disk drive or solid state drive, and stores programs executed by the control device 1, data acquired by the control device 1, etc.

[Operation Example of First Embodiment]
The preform heating device 100 acquires a temperature model F1(s) of the furnace 2 that is generated in advance based on the measured temperature of the furnace 2, and also acquires a temperature model F2(s) of the preform 10 that is generated in advance based on the measured temperature of the preform 10. Next, the preform heating device 100 performs a simulation based on the temperature model F1(s) of the furnace 2 and the temperature model F2(s) of the preform 10 to calculate the outer surface temperature Tout(t) and the inner surface temperature Tin(t) of the preform 10, and calculates set values Tr1, Tr2, and Tr3 of the furnace temperatures so that the outer surface temperature Tout(t) and the inner surface temperature Tin(t) approach their target values Tout_tgt(t) and Tin_tgt(t), respectively. The preform heating apparatus 100 can heat the preform 10 so that the outer surface temperature Tout(t) and inner surface temperature Tin(t) of the preform 10 approach their target values Tout_tgt(t) and Tin_tgt(t), respectively, by setting the calculated furnace temperature set values Tr1, Tr2, and Tr3 in the furnace 2.

Figure 5 is a flowchart showing the setting value calculation process executed by the control device 1 of Figure 1.

In step S1, the control device 1 acquires a temperature model of the furnace 2, i.e., a temperature model F1(s) that indicates the relationship between the furnace temperature and the outer surface temperature of the preform 10, as described below with reference to Figures 6 and 7.

In step S2, the control device 1 acquires a temperature model of the preform 10, i.e., a temperature model F2(s) that indicates the relationship between the outer surface temperature of the preform 10 and the inner surface temperature of the preform 10, as described below with reference to Figures 8 and 9.

In step S3, the control device 1 sets each parameter of the preform heating device 100. The parameters of the preform heating device 100 include, for example, the following:

N: The maximum number of iterations, for example, N=1000.
- Δfe: Threshold value for convergence condition. For example, Δfe = 0.001.
tz1, tz2, tz3: the time lengths during which the preforms 10 transported by the belt conveyor 3 pass through the furnaces 2-1 to 2-3, respectively. For example, tz1=tz2=tz3=30 seconds.
Tend: the time length of a function indicating the change in temperature over time (such as the outer surface temperature Tout(t) and the inner surface temperature Tin(t)). That is, tend = tz1 + tz2 + tz3.
Δt: Sampling time width of the function (such as the outer surface temperature Tout(t) and the inner surface temperature Tin(t)) that indicates the change over time of the calculated temperature. For example, Δt = 0.1 [seconds].
Tout1_tgt, Tout2_tgt, Tout3_tgt: final outer surface temperature target values of the preforms 10 when they are output from the furnaces 2-1 to 2-3, respectively. For example, Tout1_tgt=100, Tout2_tgt=200, Tout3_tgt=220° C.
Tin1_tgt, Tin2_tgt, Tin3_tgt: final inner surface temperature target values of the preforms 10 when they are output from the furnaces 2-1 to 2-3, respectively. For example, Tin1_tgt=Tout1_tgt, Tin2_tgt=Tout2_tgt, Tin3_tgt=Tout3_tgt.
Tout_tgt(t): a temperature function indicating a temporal change in the target value of the outer surface temperature of the preform 10. That is, over the first time length tz1, Tout_tgt(t) = Tout1_tgt, over the next time length tz2, Tout_tgt(t) = Tout2_tgt, and over the final time length tz3, Tout_tgt(t) = Tout3_tgt.
Tin_tgt(t): a temperature function indicating the change over time of the target value of the inner surface temperature of the preform 10. That is, over the first time length tz1, Tin_tgt(t) = Tin1_tgt, over the next time length tz2, Tin_tgt(t) = Tin2_tgt, and over the final time length tz3, Tin_tgt(t) = Tin3_tgt.
a, b: weighting coefficients used in the calculation of the evaluation function value. For example, a=1, b=1.
Tref: air temperature in the vicinity of the preform heating device 100. For example, Tref=25° C. (fixed value).

In step S4, the control device 1 initializes the number of process iterations i to zero.

In step S5, the control device 1 sets the initial values (i.e., the values when i = 0) of the furnace temperature setting values Tr1(i), Tr2(i), and Tr3(i) of the furnaces 2-1 to 2-3. The initial values are set, for example, as Tr1(0) = Tr2(0) = Tr3(0) = 200°C.

In step S6, the control device 1 estimates a temperature function Tout(t) indicating the change over time of the outer surface temperature of the preform 10 based on the temperature model F1(s) of the furnace 2 by simulation. Also, in step S6, the control device 1 estimates a temperature function Tin(t) indicating the change over time of the inner surface temperature of the preform 10 based on the temperature model F2(s) of the preform 10. The temperature function Tout(t) indicates the outer surface temperature of the preform 10 when heated by the furnace 2-1 over the first time length tz1, the outer surface temperature of the preform 10 when heated by the furnace 2-2 over the next time length tz2, and the outer surface temperature of the preform 10 when heated by the furnace 2-3 over the final time length tz3. Similarly, the temperature function Tin(t) represents the inner surface temperature of the preform 10 when it is heated by furnace 2-1 over the first time length tz1, the inner surface temperature of the preform 10 when it is heated by furnace 2-2 over the next time length tz2, and the inner surface temperature of the preform 10 when it is heated by furnace 2-3 over the final time length tz3.

In step S7, the control device 1 calculates an evaluation function value fe(i) that indicates the error between the estimated outer surface temperature Tout(t) and inner surface temperature Tin(t) of the preform 10 and their target values Tout_tgt(t) and Tin_tgt(t).

In step S8, the control device 1 determines whether the evaluation function value fe(i) has converged. If YES, the control device 1 proceeds to step S9. If NO, the control device 1 proceeds to step S10.

In step S9, the control device 1 sets the current furnace temperature setting values Tr1(i), Tr2(i), and Tr3(i) as setting values Tr1, Tr2, and Tr3 for furnaces 2-1 to 2-3, respectively, and ends the process.

In step S10, the control device 1 determines whether the number of iterations i has reached the maximum value N, and if YES, proceeds to step S11, and if NO, proceeds to step S12.

In step S11, the control device 1 displays an error message on the display device 7 indicating that the set value for the furnace temperature could not be determined, and ends the process.

In step S12, the control device 1 increments the number of iterations i by 1.

In step S13, the control device 1 changes the furnace temperature set values Tr1(i), Tr2(i), and Tr3(i) and repeats the processes of steps S6 to S8. Using a known hill-climbing method, genetic algorithm, simulated annealing, or the like, the control device 1 iteratively changes the furnace temperature set values Tr1(i), Tr2(i), and Tr3(i) so as to reduce the error between the inner surface temperature Tin(t) of the preform 10 and the inner surface temperature target value Tin_tgt(t) and to reduce the error between the outer surface temperature Tout(t) of the preform 10 and the outer surface temperature target value Tout_tgt(t).

In step S9, the furnace temperature set values Tr1, Tr2, and Tr3 are set for the furnaces 2-1 to 2-3, respectively, and then the control device 1 controls each furnace 2 and the driving device 4 to heat the preform 10.

[Generation of furnace 2 temperature model]
Next, a method for generating the temperature model of the furnace 2 acquired in step S1 of FIG. 5 will be described.

Figure 6 is a block diagram showing a configuration for acquiring a temperature model of the furnace 2 in the preform heating device 100 of Figure 1. A measuring device 41 and at least one temperature sensor 42 are used to generate and acquire a temperature model of the furnace 2. In Figure 6, components other than the measuring device 41 and the temperature sensor 42 are configured in the same manner as the corresponding components in Figure 1 or Figure 4. The temperature sensor 42 is a non-contact temperature sensor, for example, an infrared temperature sensor. The temperature sensor 42 is provided inside or outside the furnace 2 so that the outer surface temperature of the preform 10 can be measured without receiving heat generated by the heater 22 when the preform 10 is heated by the furnace 2. The measuring device 41 acquires time series data indicating the time change of the furnace temperature from the temperature sensor 23, and also acquires time series data indicating the time change of the outer surface temperature of the preform 10 from the temperature sensor 42, and sends the acquired time series data to the control device 1.

At least one temperature sensor 42 is provided for each of the furnaces 2-1 to 2-3 in FIG. 1. Each temperature sensor 42 is provided so as to track the preforms 10 transported by the belt conveyor 3 and measure the change in the outer surface temperature of the preforms 10 over time.

Figure 7 is a graph showing an example of the temperature model of the furnace 2 acquired by the measuring device 41 of Figure 6. Time t0 indicates the moment when the preform 10 conveyed by the belt conveyor 3 enters the furnace 2-1, time t1 indicates the moment when the preform 10 leaves the furnace 2-1 and enters the furnace 2-2, time t2 indicates the moment when the preform 10 leaves the furnace 2-2 and enters the furnace 2-3, and time t3 indicates the moment when the preform 10 leaves the furnace 2-3. As described above, the time length from time t0 to t1, the time length from time t1 to t2, and the time length from time t2 to t3 are represented by the time lengths tz1, tz2, and tz3, respectively. When a sufficiently long time has passed since the furnaces 2-1 to 2-3 were turned on and the temperature has reached a steady state, the actual furnace temperature of each furnace 2-1 to 2-3 is considered to be consistent with its set value Tr1, Tr2, or Tr3. As a result, the outer surface of the preform 10 is heated with a step-like temperature profile. As shown in FIG. 7, by heating the preform 10 in each of the furnaces 2-1 to 2-3, the outer surface temperature of the preform 10 gradually approaches the set values Tr1, Tr2, and Tr3 of the furnace temperature.

The control device 1 calculates a temperature model of the furnace 2 that indicates the relationship between the furnace temperature and the outer surface temperature of the preform 10 based on the time series data of the furnace temperature and the time series data of the outer surface temperature of the preform 10. The temperature model of the furnace 2 is represented by a transfer function from the furnace temperature to the outer surface temperature of the preform 10. The temperature model of the furnace 2 is represented by a first-order lag transfer function including parameters of gain and time constant in the domain of the Laplace transformed function, for example, as shown in the following equation.

F1(s)=k1/(T1・s+1) (1)

Here, k1 represents the gain and T1 represents the time constant.

Here, the temperature function showing the change in furnace temperature over time is represented by Tr(t). That is, Tr(t) = Tr1 over the first time length tz1, Tr(t) = Tr2 over the next time length tz2, and Tr(t) = Tr3 over the final time length tz3. In this case, in the domain of the Laplace transformed function, the system in which the furnace temperature Tr(s) is the input and the outer surface temperature Tout(s) of the preform 10 is the output is expressed by the following equation.

Tout(s)=F1(s)・Tr(s) (2)

Since the furnace temperatures Tr1, Tr2, and Tr3 are constant in each of the furnaces 2-1 to 2-3, each of the furnace temperatures Tr1, Tr2, and Tr3 is represented by a step function A1·u(t) having an amplitude A1. Here, A1 indicates the difference between the outer surface temperature of the preform 10 and the furnace temperature when the preform 10 enters each of the furnaces 2-1 to 2-3. The Laplace transform of the step function A1·u(t) is represented by A1/s. In this case, by substituting Tr(s)=A1/s into equation (2) and performing an inverse Laplace transform, the time domain temperature function Tout(t) indicating the temporal change in the outer surface temperature of the preform 10 can be obtained as shown in the following equation.

Tout(t)=A1・k1(1-exp(-t/T1))+B1 (3)

Here, B1 indicates the outer surface temperature of the preform 10 when the preform 10 enters each of the furnaces 2-1 to 2-3.

Equation (3) represents the step response to the step function A1·u(t). The gain k1 and time constant T1 of equation (1) are calculated by applying the time series data of the outer surface temperature of the preform 10 to equation (3) using a known least squares method or the like. This makes it possible to identify the transfer function F1(s) of the temperature model of the furnace 2.

The control device 1 may acquire time series data of the corresponding set values of each parameter of the preform heating device 100, together with time series data of the furnace temperature and the outer surface temperature of the preform 10. This allows the preform heating device 100 to operate so as to reproduce a predetermined change over time in the furnace temperature and a predetermined change over time in the outer surface temperature of the preform 10.

The temperature model F1(s) of the furnace 2 may be calculated by the measuring device 41 based on the time series data of the furnace temperature and the time series data of the outer surface temperature of the preform 10, and may be sent from the measuring device 41 to the control device 1.

[Generation of Temperature Model of Preform 10]
Next, a method for generating the temperature model of the preform 10 acquired in step S2 of FIG. 5 will be described.

Figure 8 is a schematic diagram showing a configuration for acquiring a temperature model of the preform 10 in Figure 1. In order to generate and acquire a temperature model of the preform 10, a measuring device 51, temperature sensors 52 and 53, a thermal insulation container 54, and hot water 55 are used. The temperature sensors 52 and 53 are, for example, thermocouples. The temperature sensor 52 is provided on the outer surface of the preform 10, and the temperature sensor 53 is provided on the inner surface of the preform 10. The temperature sensors 52 and 53 are fixed to the outer surface and inner surface of the preform 10, respectively, by, for example, gluing or embedding. Hot water 55 is poured into the thermal insulation container 54, and almost the entire preform 10 is immersed in the hot water 55. However, the preform 10 is held so that the hot water 55 does not flow into its interior. The measuring device 41 acquires time series data indicating the temporal change in the temperature of the outer surface of the preform 10 from the temperature sensor 52, and also acquires time series data indicating the temporal change in the temperature of the inner surface of the preform 10 from the temperature sensor 53, and sends the acquired time series data to the control device 1.

Figure 9 is a graph showing an example of a temperature model of the preform 10 acquired by the measuring device 51 of Figure 8. Time t10 indicates the moment when the preform 10 is immersed in the hot water 55. Time t11 indicates the moment when the inner surface temperature of the preform 10 reaches a value that is a predetermined ratio of the temperature Tref+A2 of the hot water 55, for example, Tref+A2a=Tref+A2×0.632. As shown in Figure 7, by immersing the preform 10 in the hot water 55, the outer surface temperature of the preform 10 has a step-like temperature profile, and the inner surface temperature of the preform 10 gradually approaches the outer surface temperature.

The control device 1 calculates a temperature model of the preform 10 that indicates the relationship between the outer surface temperature and the inner surface temperature of the preform 10 based on the time series data of the outer surface temperature and the inner surface temperature of the preform 10. The temperature model of the preform 10 is represented by a transfer function from the outer surface temperature to the inner surface temperature of the preform 10. The temperature model of the preform 10 is represented by a first-order lag transfer function including parameters of gain and time constant in the domain of the Laplace transformed function, for example, as shown in the following equation.

F2(s)=k2/(T2・s+1) (4)

Here, k2 is the gain and T2 is the time constant.

Here, in the domain of the Laplace transformed function, the system in which the outer surface temperature Tout(s) of the preform 10 is the input and the inner surface temperature Tin(s) of the preform 10 is the output is expressed by the following equation.

Tin(s)=F2(s)・Tout(s) (5)

In the example of FIG. 9, the outer surface temperature of the preform 10 is represented by a step function A2·u(t) having an amplitude A2. The Laplace transform of the step function A2·u(t) is represented by A2/s. In this case, by substituting Tout(s)=A2/s into equation (5) and performing an inverse Laplace transform, the time domain temperature function Tout(t) that indicates the temporal change in the inner surface temperature of the preform 10 can be obtained as shown in the following equation.

Tin(t)=A2・k2(1-exp(-t/T2))+Tref (6)

Equation (6) represents the step response to the step function A2·u(t). The gain k2 and time constant T2 of equation (4) are calculated by applying the time series data of the inner surface temperature of the preform 10 to equation (6) using a known least squares method or the like. This makes it possible to identify the transfer function F2(s) of the temperature model of the preform 10.

The temperature model F2(s) of the preform 10 may be calculated by the measuring device 51 based on time series data of the outer surface temperature and inner surface temperature of the preform 10, and sent from the measuring device 51 to the control device 1.

[Estimation of outer surface temperature Tout(t) and inner surface temperature Tin(t) of preform 10]
Next, a method for estimating the outer surface temperature Tout(t) and the inner surface temperature Tin(t) of the preform 10 by simulation in step S6 of FIG. 5 will be described.

In the processing of step S6, the time t is discretized by the sampling time interval Δt. The control device 1 executes the processing of the following steps (i) to (iv) from time t = 0 to tend, and calculates the values of the outer surface temperature Tout(t) and the inner surface temperature Tin(t) for each sampling time interval Δt.

Step (i)
At time t=0, initial values are set for the outer surface temperature Tout(t) and the inner surface temperature Tin(t) of the preform 10 at the start of heating the preform 10. The initial values of the outer surface temperature Tout(t) and the inner surface temperature Tin(t) of the preform 10 are set to, for example, Tout(0)=Tin(0)=Tref=25° C.

Step (ii)
At iteration 1 of the simulation, ie, time t=Δt, the controller 1 reads the furnace temperature Tr(0) and calculates the following:

Tout'(1)=-aout・Tout(0)+bout・Tr(0)
Tout(1)=Tout(0)+Tout'(1)・Δt
Tin'(1)=-ain・Tin(0)+bin・Tout(0)
Tin (1) = Tin (0) + Tin' (1) Δt

Here, aout, bout, ain, and bin are expressed by the following formula.

aout=1/T1
bout=k1/T1
ain=1/T2
bin=k2/T2

Furthermore, Tout'(1) denotes the differential coefficient of the temperature function Tout(t) at t=1, and Tin'(1) denotes the differential coefficient of the temperature function Tin(t) at t=1.

Step (iii)
At simulation iteration j, ie, time t=j·Δt, the controller 1 reads the furnace temperature Tr(1) and calculates the following values:

Tout'(j)=-aout・Tout(j-1)+bout・Tr(j-1)
Tout(j)=Tout(j-1)+Tout'(j)・Δt
Tin'(j)=-ain・Tin(j-1)+bin・Tout(j-1)
Tin(j)=Tin(j-1)+Tin'(j)・Δt

Step (iv)
If the time t=j·Δt reaches tend, the process ends and proceeds to step S7 in FIG. 5; otherwise, the number of iterations j is incremented (j=j+1) and the process returns to step (iii).

In this way, by processing step S6, the outer surface temperature Tout(t) can be estimated based on the temperature model F1(s) of the furnace 2, and the inner surface temperature Tin(t) can be estimated based on the temperature model F2(s) of the preform 10.

[Calculation of evaluation function value fe(i)]
The evaluation function value fe(i) used in step S7 of FIG. 5 is calculated, for example, as follows.

Here, a indicates the weighting coefficient of the outer surface temperature error eout(t), and b indicates the weighting coefficient of the inner surface temperature error ein(t). Furthermore, eout(t) indicates the error between the inner surface temperature Tin(t) of the preform 10 and the inner surface temperature target value Tin_tgt(t) as shown in the following formula, and ein(t) indicates the error between the inner surface temperature Tin(t) of the preform 10 and the predetermined inner surface temperature target value Tin_tgt(t) as shown in the following formula.

eout(t)=|Tout(t)−Tout_tgt(t)|
ein(t)=|Tin(t)−Tin_tgt(t)|

Here, |x| represents the absolute value of x.

In step S8 of FIG. 5, in order to determine whether the evaluation function value fe(i) has converged, the control device 1 may determine whether the difference between the latest calculated evaluation function value and the evaluation function value calculated in the immediately previous iteration of the processing is equal to or less than a threshold value Δfe. In addition, in order to more reliably determine whether the evaluation function value fe(i) has converged, the control device 1 may determine whether the difference between the latest calculated evaluation function value and the evaluation function value calculated in the previous iteration of the processing, for example, the 10th iteration, is equal to or less than a threshold value Δfe, as shown in the following formula.

|fe(i-10)−fe(i)|<Δfe (8)

[Effects of the First Embodiment]
10 is a graph showing an example of the outer surface temperature and the inner surface temperature of the preform 10 when the initial value of the set value of the furnace temperature set in step S5 of FIG. 5 is used. FIG. 11 is a graph showing an example of the outer surface temperature and the inner surface temperature of the preform 10 when the set value of the furnace temperature set in step S9 of FIG. 5 is used. In the above example, the initial values of the set values Tr1(i), Tr2(i), and Tr3(i) of the furnace temperature are set to equal values Tr1(0)=Tr2(0)=Tr3(0)=200°C. In this case, as shown in FIG. 10, even when time t3 is reached, the difference between the outer surface temperature and the inner surface temperature of the preform 10 may remain. On the other hand, by appropriately calculating the set values Tr1, Tr2, and Tr3 of the furnace temperature by executing the set value calculation process of FIG. 5, the difference between the outer surface temperature and the inner surface temperature of the preform 10 can be reduced.

According to the preform heating device 100 of the first embodiment, the control device 1 generates and acquires a temperature model indicating the inner surface temperature of the preform 10 in advance. Also, according to the preform heating device 100 of the first embodiment, the control device 1 can estimate the inner surface temperature of the preform 10 by applying the outer surface temperature of the preform 10 measured by the non-contact temperature sensor 42 to the temperature model of the preform 10. Also, according to the preform heating device 100 of the first embodiment, the control device 1 can reduce, preferably minimize, the error between the inner surface temperature Tin(t) of the preform 10 and the inner surface temperature target value Tin_tgt(t) by iteratively calculating the furnace temperature set values Tr1, Tr2, and Tr3 by a simulation including feedback control, and can reduce, preferably minimize, the error between the outer surface temperature Tout(t) of the preform 10 and the outer surface temperature target value Tout_tgt(t). Furthermore, according to the preform heating device 100 of the first embodiment, the control device 1 can set the calculated furnace temperature set values Tr1, Tr2, and Tr3 for the furnaces 2-1 to 2-3, respectively, and heat the preform 10 so that the inner surface temperature of the preform 10 approaches the desired target value.

The preform heating device 100 according to the first embodiment can heat the preform 10 so that the inner surface temperature of the preform 10 approaches the desired target value without requiring significant effort in adjusting the temperature.

Second Embodiment
FIG. 12 is a block diagram showing the configuration of a preform heating apparatus 110 according to the second embodiment. The preform heating apparatus 110 in FIG. 12 includes a control device 1A, one furnace 2A, and a temperature sensor 5. The preform heating apparatus according to the embodiment is not limited to the one including a plurality of furnaces 2-1 to 2-3 and a belt conveyor 3 as shown in FIG. 1. The furnace 2A is configured similarly to the furnace 2 in FIG. 4, except that the preform 10 is not transported by the belt conveyor 3, but is housed therein. The control device 1A operates substantially similarly to the control device 1 in FIG. 1, except that it controls one furnace 2A instead of the three furnaces 2-1 to 2-3 and the drive device 4 in FIG. 1. However, the control device 1A may change the set value of the furnace temperature of the furnace 2A over time, for example, as shown in FIG. 11. According to the preform heating apparatus 110 of FIG. 12, similar to the preform heating apparatus 100 of FIG. 1, the preform 10 can be heated so as to bring the inner surface temperature of the preform 10 close to the desired target value without requiring significant effort in temperature adjustment.

[Other Modifications]
Although the embodiment of the present disclosure has been described in detail above, the above description is merely an example of the present disclosure in every respect. It goes without saying that various improvements and modifications can be made without departing from the scope of the present disclosure. For example, the following modifications are possible. In the following, the same reference numerals are used for the same components as in the above embodiment, and the description of the same points as in the above embodiment is omitted as appropriate. The following modifications can be combined as appropriate.

In the above example, the temperature model F1(s) of the furnace 2 temperature model and the temperature model F2(s) of the preform 10 are represented by a first-order lag transfer function, but they may be represented by other transfer functions, for example, the following equation.

F1(s)=k10/((T11・s+1)(T12・s+1)) (9)
F2(s)=k20/((T21・s+1)(T22・s+1)) (10)

Here, k10 and k20 indicate gains, and T11 to T22 indicate time constants. Equations (9) and (10) are second-order lag transfer functions. The temperature model F1(s) of the furnace 2 temperature model and the temperature model F2(s) of the preform 10 are not limited to the first-order lag type and the second-order lag type, and may be expressed by other transfer functions.

In the above example, the case was described where the inner surface temperature target values Tin1_tgt, Tin2_tgt, and Tin3_tgt of the preform 10 are equal to the outer surface temperature target values Tout1_tgt, Tout2_tgt, and Tout3_tgt of the preform 10, respectively, but these target values may be different from each other. The inner surface temperature target value Tin_tgt(t) may be set to a value that has a predetermined temperature difference from the outer surface temperature target value Tout_tgt(t).

In step S7 of FIG. 5, the following formula may be used instead of formula (7).

Since the error towards the end of the heating time is more important, the right-hand side of equation (11) is multiplied by the elapsed time t as a weighting factor.

In the above example, the case where the weighting coefficients in equation (7) are a = b = 1 has been described, but other values of the weighting coefficients a and b may be used. For example, by setting the weighting coefficients a = 0, b = 1, the outer surface temperature of the preform 10 can be ignored in step S7 of FIG. 5, and the furnace temperature setting values Tr1, Tr2, and Tr3 can be calculated so as to reduce the error between the inner surface temperature Tin(t) of the preform 10 and the inner surface temperature target value Tin_tgt(t) to less than a predetermined threshold value Δfe.

In the above example, the time lengths tz1, tz2, and tz3 during which the preforms 10 transported by the belt conveyor 3 pass through the furnaces 2-1 to 2-3 are equal to each other, but these time lengths may be different from each other.

[summary]
The preform heating apparatus and the control method thereof according to each aspect of the present disclosure may be expressed as follows.

According to a method for controlling a preform heating device according to one aspect of the present disclosure, a method for controlling a preform heating device for heating a preform 10 of a thermoplastic container is provided. The preform heating device includes at least one furnace 2 that accommodates the preform 10 and heats it at a predetermined furnace temperature. The control method includes a step of acquiring a first temperature model F1(s) indicating a relationship between the furnace temperature and the outer surface temperature of the preform 10. The control device further includes a step of acquiring a second temperature model F2(s) indicating a relationship between the outer surface temperature of the preform 10 and the inner surface temperature of the preform 10. The control device further includes a step of calculating a first temperature function Tout(t) indicating a change in the outer surface temperature of the preform 10 over time based on the first temperature model F1(s). The control device further includes a step of calculating a second temperature function Tin(t) indicating a change in the inner surface temperature of the preform 10 over time based on the second temperature model F2(s). The control device further includes a step of calculating furnace temperature set values Tr1, Tr2, and Tr3 based on the first temperature function Tout(t) and the second temperature function Tin(t) so as to reduce the error between the inner surface temperature Tin(t) of the preform 10 and a predetermined inner surface temperature target value Tin_tgt(t) to less than a predetermined threshold value Δfe. The control device further includes a step of setting the calculated furnace temperature set values Tr1, Tr2, and Tr3 in the furnace 2.

According to a method for controlling a preform heating device according to one aspect of the present disclosure, the second temperature model F2(s) is represented by a transfer function from the outer surface temperature of the preform 10 to the inner surface temperature of the preform 10.

According to a method for controlling a preform heating device according to one aspect of the present disclosure, the second temperature model F2(s) is represented by a first-order or second-order lag transfer function including gain and time constant parameters in the domain of the Laplace transformed function.

According to a method for controlling a preform heating device according to one aspect of the present disclosure, the step of acquiring the second temperature model F2(s) includes the steps of acquiring first time series data showing the change over time of the outer surface temperature of the preform 10, acquiring second time series data showing the change over time of the inner surface temperature of the preform 10, and calculating a transfer function of the second temperature model F2(s) based on the first and second time series data.

According to a method for controlling a preform heating device according to one aspect of the present disclosure, the step of acquiring first time series data includes a step of acquiring the outer surface temperature of the preform 10 from a first temperature sensor 52 provided on the outer surface of the preform 10 when the outer surface of the preform 10 is heated with a step-like temperature profile. The step of acquiring second time series data includes a step of acquiring the inner surface temperature of the preform 10 from a second temperature sensor 53 provided on the inner surface of the preform 10 when the outer surface of the preform 10 is heated with a step-like temperature profile.

According to a method for controlling a preform heating device according to one aspect of the present disclosure, the first temperature model F1(s) is represented by a transfer function from the furnace temperature to the outer surface temperature of the preform 10.

According to a method for controlling a preform heating device according to one aspect of the present disclosure, the first temperature model F1(s) is represented by a first-order or second-order lag transfer function in the domain of the Laplace transformed function, the transfer function including parameters of gain and time constant.

According to a method for controlling a preform heating device according to one aspect of the present disclosure, the step of acquiring the first temperature model F1(s) includes the steps of acquiring third time series data showing the change over time of the furnace temperature, acquiring fourth time series data showing the change over time of the outer surface temperature of the preform 10, and calculating a transfer function of the first temperature model F1(s) based on the third and fourth time series data.

According to a method for controlling a preform heating device according to one aspect of the present disclosure, the step of calculating the furnace temperature set values Tr1, Tr2, and Tr3 includes a step of repeatedly changing the furnace temperature set values Tr1, Tr2, and Tr3 so as to reduce the error between the inner surface temperature Tin(t) of the preform 10 and the inner surface temperature target value Tin_tgt(t).

According to a control method for a preform heating device according to one aspect of the present disclosure, the step of calculating the furnace temperature set values Tr1, Tr2, Tr3 includes a step of calculating the furnace temperature set values Tr1, Tr2, Tr3 based on the first temperature function Tout(t) and the second temperature function Tin(t) so as to reduce the error between the inner surface temperature Tin(t) of the preform 10 and the inner surface temperature target value Tin_tgt(t) below a threshold value Δfe, and so as to reduce the error between the outer surface temperature Tout(t) of the preform 10 and a predetermined outer surface temperature target value Tout_tgt(t) below a threshold value Δfe.

According to a method for controlling a preform heating device according to one aspect of the present disclosure, the step of calculating the furnace temperature set values Tr1, Tr2, Tr3 includes a step of repeatedly changing the furnace temperature set values Tr1, Tr2, Tr3 so as to reduce the error between the inner surface temperature Tin(t) of the preform 10 and the inner surface temperature target value Tin_tgt(t) and to reduce the error between the outer surface temperature Tout(t) of the preform 10 and the outer surface temperature target value Tout_tgt(t).

According to a method for controlling a preform heating device according to one aspect of the present disclosure, the target inner surface temperature Tin_tgt(t) is set to the same value as the target outer surface temperature Tout_tgt(t).

According to a method for controlling a preform heating device according to one aspect of the present disclosure, the target inner surface temperature Tin_tgt(t) is set to a value that has a predetermined temperature difference with respect to the target outer surface temperature Tout_tgt(t).

According to a method for controlling a preform heating device according to one aspect of the present disclosure, the preform heating device includes a plurality of furnaces 2 arranged adjacent to each other so that the preforms 10 pass through them sequentially. For each of the plurality of furnaces 2, the set values Tr1, Tr2, and Tr3 of the furnace temperatures are constant over time.

According to a preform heating device according to one aspect of the present disclosure, a preform heating device for heating a preform 10 of a thermoplastic container is provided. The preform heating device includes at least one furnace 2 that accommodates the preform 10 and heats it at a predetermined furnace temperature, and a control device 1 that controls the set values Tr1, Tr2, and Tr3 of the furnace temperature. The control device 1 acquires a first temperature model F1(s) that indicates the relationship between the furnace temperature and the outer surface temperature of the preform 10. The control device 1 further acquires a second temperature model F2(s) that indicates the relationship between the outer surface temperature of the preform 10 and the inner surface temperature of the preform 10. The control device 1 further calculates a first temperature function Tout(t) that indicates the change over time of the outer surface temperature of the preform 10 based on the first temperature model F1(s). The control device 1 further calculates a second temperature function Tin(t) that indicates the change over time of the inner surface temperature of the preform 10 based on the second temperature model F2(s). The control device 1 further calculates the furnace temperature set values Tr1, Tr2, and Tr3 based on the first temperature function Tout(t) and the second temperature function Tin(t) so as to reduce the error between the inner surface temperature of the preform 10 and a predetermined inner surface temperature target value Tin_tgt(t) to less than a predetermined threshold value Δfe. The control device 1 further sets the calculated furnace temperature set values Tr1, Tr2, and Tr3 in the furnace 2.

The present disclosure is applicable to a preform heating device that heats preforms for thermoplastic containers such as PET bottles for blow molding.

Reference Signs List 1, 1A Control device 2, 2-1 to 2-3, 2A Furnace 3 Belt conveyor 4 Driving device 5 Temperature sensor 6 Input device 7 Display device 10 Preform 10a Inner surface 10b Outer surface 11 Bottle 21, 21-1 to 21-3 Temperature regulator 22, 22-1 to 22-3 Heater 23, 23-1 to 23-3 Temperature sensor 31 Mold 32 Pipe 41 Measuring device 42 Temperature sensor 51 Measuring device 52, 53 Temperature sensor 54 Insulating container 55 Hot water 100, 110 Preform heating device

Claims (15)

1. A method for controlling a preform heating device for heating a preform for a thermoplastic container, comprising:
the preform heating device includes at least one furnace that receives the preform and heats it at a predetermined furnace temperature;
The control method includes:
obtaining a first temperature model indicating a relationship between the furnace temperature and an outer surface temperature of the preform;
obtaining a second temperature model indicating a relationship between an outer surface temperature of the preform and an inner surface temperature of the preform;
calculating a first temperature function indicative of a change in temperature of an outer surface of the preform over time based on the first temperature model;
calculating a second temperature function indicative of a change in temperature of the inner surface of the preform over time based on the second temperature model;
calculating a setpoint for the furnace temperature based on the first and second temperature functions to reduce an error between the inner surface temperature of the preform and a predetermined inner surface temperature target below a predetermined threshold;
setting the calculated furnace temperature set point in the furnace.
A method for controlling a preform heating device. The second temperature model is represented by a transfer function from an outer surface temperature of the preform to an inner surface temperature of the preform.
A method for controlling the preform heating apparatus according to claim 1. the second temperature model is represented by a transfer function of a first-order lag form or a second-order lag form including parameters of gain and time constant in a domain of a Laplace transformed function;
A method for controlling a preform heating apparatus according to claim 2. The step of obtaining the second temperature model includes:
acquiring first time-series data indicating a change over time in an outer surface temperature of the preform;
acquiring second time series data indicating a change over time in an inner surface temperature of the preform;
and calculating a transfer function of the second temperature model based on the first and second time series data.
A method for controlling a preform heating apparatus according to claim 3. the step of acquiring the first time-series data includes a step of acquiring an outer surface temperature of the preform from a first temperature sensor provided on the outer surface of the preform when the outer surface of the preform is heated with a step-like temperature profile;
The step of acquiring the second time-series data includes a step of acquiring an inner surface temperature of the preform from a second temperature sensor provided on the inner surface of the preform when the outer surface of the preform is heated with the step-like temperature profile.
A method for controlling a preform heating apparatus according to claim 4. The first temperature model is represented by a transfer function from the furnace temperature to an outer surface temperature of the preform.
A method for controlling a preform heating device according to any one of claims 1 to 5. the first temperature model is represented by a transfer function of a first-order lag form or a second-order lag form including parameters of gain and time constant in a domain of a Laplace transformed function;
A method for controlling a preform heating apparatus according to claim 6. The step of obtaining the first temperature model includes:
acquiring third time series data indicating a change in the furnace temperature over time;
acquiring fourth time-series data indicating a change over time in an outer surface temperature of the preform;
calculating a transfer function of the first temperature model based on the third and fourth time series data.
A method for controlling a preform heating apparatus according to claim 7. The step of calculating the furnace temperature set point includes the step of iteratively changing the furnace temperature set point so as to reduce an error between the inner surface temperature of the preform and the inner surface temperature target value.
A method for controlling a preform heating device according to any one of claims 1 to 8. the step of calculating the set value of the furnace temperature includes a step of calculating the set value of the furnace temperature based on the first and second temperature functions so as to reduce an error between the inner surface temperature of the preform and the inner surface temperature target value below the threshold value, and so as to reduce an error between the outer surface temperature of the preform and a predetermined outer surface temperature target value below the threshold value.
A method for controlling a preform heating device according to any one of claims 1 to 9. the step of calculating the furnace temperature set point includes the step of iteratively changing the furnace temperature set point so as to reduce an error between the inner surface temperature of the preform and the inner surface temperature target value and to reduce an error between the outer surface temperature of the preform and the outer surface temperature target value;
A method for controlling a preform heating apparatus according to claim 10. The inner surface temperature target value is set to the same value as the outer surface temperature target value.
A method for controlling a preform heating apparatus according to claim 10 or 11. The inner surface temperature target value is set to a value having a predetermined temperature difference with respect to the outer surface temperature target value.
A method for controlling a preform heating apparatus according to claim 10 or 11. the preform heating device comprises a plurality of furnaces arranged adjacent to each other so that the preforms pass through them in sequence;
for each of the plurality of furnaces, the furnace temperature set point is constant over time;
A method for controlling a preform heating device according to any one of claims 1 to 13. A preform heating apparatus for heating a preform for a thermoplastic container, the preform heating apparatus comprising:
at least one furnace for receiving and heating the preform at a predetermined furnace temperature;
a control device for controlling a set value of the furnace temperature,
The control device includes:
obtaining a first temperature model indicating a relationship between the furnace temperature and an outer surface temperature of the preform;
obtaining a second temperature model indicating a relationship between an outer surface temperature of the preform and an inner surface temperature of the preform;
calculating a first temperature function indicative of a change in temperature of an outer surface of the preform over time based on the first temperature model;
calculating a second temperature function indicative of a change in the temperature of the inner surface of the preform over time based on the second temperature model;
calculating a setpoint for the furnace temperature based on the first and second temperature functions so as to reduce an error between the inner surface temperature of the preform and a predetermined inner surface temperature target value;
configured to set the calculated furnace temperature set point to the furnace.
Preform heating device.

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