Thermoforming apparatus and thermoforming method

Abstract

To provide a thermoforming apparatus capable of satisfying the optimum heating condition of a resin sheet.SOLUTION: The thermal forming device 100 having a heater unit 10 for heating a sheet S1 part which is an object to be heated includes a radiation thermometer 33 for measuring the sheet surface temperature Dss of the sheet S1 part, a PLC31 for controlling the power of the heater unit 10, and a power measuring means for measuring the power of the heater unit 10. A PLC31 includes a first temperature control means 312 for controlling an output of a heater unit 10 so that a sheet surface temperature Dss measured by a radiation thermometer 33 is sequentially lowered from an initial temperature, and starts feedback control for performing control according to a comparison result between the sheet surface temperature Dss and a target temperature Td after the sheet surface temperature Dss reaches the target temperature Td by control by the first temperature control means 312. The fixing device includes a second temperature control means 313, and a calorific value evaluation means 315 for linearly approximating the change of the power value given to the sheet S1 part by the heater unit 10 based on the power value of the power measuring means and evaluating it as an inclination I.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a technology that contributes to improving the productivity of a thermoforming device, and more particularly to controlling the temperature of a heater. [Background technology]

[0002] The thermoforming device uses a heater to heat an object such as a resin sheet and then forms it. The heater of this thermoforming device is controlled by a computer-based control device, and heats the object to a predetermined temperature.

[0003] Patent Document 1 discloses inventions relating to a thermoforming device, a thermoforming method, a heater temperature control method, and a heating device. The heater temperature control method raises the heater temperature to a predetermined temperature, and then controls the heater temperature to gradually decrease based on the measured surface temperature of the heated object. Then, when the surface temperature reaches a target temperature, the heater temperature is feedback-controlled to bring the surface temperature close to the target temperature. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6472213 Summary of the Invention [Problem to be solved by the invention]

[0005] The technology described in Patent Document 1 uses a first temperature control means (heating control) to gradually lower the heater's set temperature, and a second temperature control means (temperature maintenance control) to perform feedback control while measuring the surface temperature of the heated object, and maintains this feedback control for a predetermined period of time to increase the internal temperature of the heated object, but the termination condition of this second temperature control means is determined by the characteristics of the sheet.

[0006] However, these termination conditions are determined empirically or experimentally, and are often set longer in the field to allow for a margin of error. However, setting the temperature holding control time too long can result in a deterioration in cycle time, while setting it too short can affect the defect rate of thermoformed products. Furthermore, since it is known that this holding time is influenced by factors such as the ambient temperature, it is difficult to set optimal conditions. Furthermore, extending the temperature holding control time to allow for a margin of error can lead to drawdown and other problems, which can lead to defective thermoformed products. For this reason, the applicant has discovered a method for determining termination conditions by satisfying certain conditions.

[0007] An object of the present invention is to provide a thermoforming apparatus that can satisfy optimal heating conditions for a resin sheet when thermoforming the resin sheet. [Means for solving the problem]

[0008] In order to achieve the above object, a thermoforming apparatus according to one aspect of the present invention has the following features.

[0009] (1) A thermoforming device having a heater for heating a resin sheet, which is an object to be heated, a temperature measuring unit that measures the surface temperature of the resin sheet; an output control unit that controls the output of the heater; an output measuring means for measuring the output of the heater, The output control unit a first temperature control means for controlling an output of the heater based on the surface temperature measured by the temperature measurement unit; a second temperature control means that starts a feedback control according to a comparison result between the surface temperature and the target temperature after the surface temperature reaches the target temperature under the control of the first temperature control means; a heat quantity evaluation means for evaluating a change in the output value applied by the heater to the resin sheet as a slope by linear approximation based on the output value of the output measurement means; It is characterized by:

[0010] The aspect described in (1) above allows optimal heating of the resin sheet, thereby improving the productivity of the thermoforming device. In order to properly manage the heating time of the resin sheet, the heat quantity evaluation means determines whether to end the heating process based on the change in the heat quantity of the heater.

[0011] Specifically, the heater output is controlled by a first temperature control means, and feedback control is performed by a second temperature control means, thereby reducing the rate of temperature change of the heater itself. This rate of temperature change is monitored by a heat quantity evaluation means, and when the slope of the rate of change of the heater output value reaches zero, the heat retention control by the second temperature control means is terminated. Here, the slope of the heater output value is a value obtained, for example, by integrating the change curve of the current value supplied to the heater, and is preferably obtained using a calculation method for finding a regression line, such as the least squares method.

[0012] It has been experimentally confirmed that the internal and external temperatures of the resin sheet are equal when this gradient reaches zero, so if this is set as the end condition, it will be possible to respond to changes in the external temperature, etc. In other words, heating that satisfies the optimal heating conditions for the resin sheet can be performed for thermoforming, which ultimately shortens the cycle time and improves productivity.

[0013] Regarding temperature control, when the surface temperature reaches temperature information indicating a predetermined temperature lower than the target temperature, the first temperature control means changes the control to lower the heater temperature to a temperature higher than the temperature information and repeats it, the second temperature control means continues the feedback control until the internal temperature of the resin sheet reaches a temperature close to the target temperature, and the heat quantity evaluation means ends the feedback control and ends heating by the heater when the gradient becomes zero. This makes it possible to perform appropriate temperature control.

[0014] (2) In the thermoforming device according to (1), the output measuring means is an ammeter that measures a current flowing through the heater, the output value is a current value obtained from the ammeter; is preferred.

[0015] (3) In the thermoforming device according to (1), the output measuring means is a thermometer that measures the surface temperature of the heater, the output value is a temperature obtained from the thermometer; is preferred.

[0016] According to the above aspect (2) or (3), by using the current value or heater temperature as the output measurement means, it becomes possible to investigate the change accurately.

[0017] In order to achieve the above object, a thermoforming method according to another aspect of the present invention has the following features.

[0018] (4) In a thermoforming method in which a resin sheet as a workpiece is heated by a heater, a temperature measuring unit that measures the surface temperature of the resin sheet; an output control unit that controls the output of the heater; an output measuring means for measuring the output of the heater, a first temperature control means provided in the output control unit controls heating by the heater so that the surface temperature becomes a target temperature; When the surface temperature reaches a target temperature under the control of the first temperature control means, a feedback control is started by a second temperature control means provided in the output control unit, which performs control according to a comparison result between the surface temperature and the target temperature, and the feedback control is continued until the internal temperature of the resin sheet reaches a temperature close to the target temperature; a heat quantity evaluation means that evaluates a change in the output value given by the heater to the resin sheet as a slope by linear approximation based on the output value of the output measurement means, and when the slope becomes zero, the feedback control by the second temperature control means is terminated; It is characterized by:

[0019] (5) In the thermoforming method according to (4), the output measuring means is an ammeter that measures a current flowing through the heater, the output value is a current value obtained from the ammeter; is preferred.

[0020] (6) In the thermoforming method according to (4), the output measuring means is a thermometer that measures the surface temperature of the heater, the output value is a temperature obtained from the thermometer; is preferred.

[0021] According to the aspects (4) to (6) above, similar to the thermoforming device described in (1), it is possible to optimally heat the resin sheet, thereby improving the productivity of the thermoforming device. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 2 is a schematic diagram of a thermoforming device according to the present embodiment. [Figure 2] FIG. 2 is a plan view of the heater unit of the present embodiment. [Figure 3] FIG. 2 is a plan view of the heater element of the present embodiment. [Figure 4] 3A and 3B are diagrams illustrating the principle of heater temperature control in the present embodiment. [Figure 5] FIG. 3 is a block diagram relating to control of a heating unit in the present embodiment. [Figure 6] 4 is a flowchart relating to temperature control in the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0023] First, the outline of the configuration of a thermoforming apparatus 100 according to an embodiment of the present invention will be described.

[0024] 1 shows a schematic diagram of a thermoforming apparatus 100 of this embodiment. The thermoforming apparatus 100 comprises a sheet supply section 20, a heating section 30, a forming section 40, and a formed product removal section 60, each of which is connected to and controlled by a control panel 50. The thermoforming apparatus 100 is capable of thermoforming a sheet S1, which is an object to be heated, to produce a formed product S2. A thick sheet S1 cut into a rectangle is prepared as the sheet S1.

[0025] The material of the resin sheet S1 is assumed to be a carbon fiber heating composite material made by adding carbon fiber to plastic, a so-called composite material made by adding glass or aramid fiber to plastic with a thickness of about 1 to 10 mm, or a thick single material cut into a rectangular sheet. However, a film-like material may also be used, or a method of unwinding a rolled material for use may be adopted. In other words, it is not prohibited to use a heated object other than those described in this embodiment. Furthermore, it is not prohibited to increase or decrease the thickness.

[0026] The sheet supply unit 20 is provided on the sheet input side with a sheet supply means 98 that adsorbs and conveys the sheet S1, and a sheet holding means 99 that receives and holds the sheet S1 conveyed by the sheet supply means 98. Depending on the surface condition of the sheet S1, other conveying means may be used, such as chucking the edge of the sheet S1 and conveying it, instead of adsorbing and conveying it.

[0027] The heating section 30 has the function of heating and softening the supplied sheet S1 using the heater unit 10. The heater unit 10 is composed of an upper heating means 11 that heats the sheet S1 from above, and a lower heating means 12 that heats the sheet S1 from below.

[0028] Fig. 2 shows a plan view of the heater unit. Fig. 3 shows a plan view of the heater element. The heater elements H3 are arranged in a tiled pattern on the heater unit 10 as shown in Fig. 2. The heater elements H3 include a main heater H1 and a secondary heater H2. The main heater H1 is disposed approximately in the center of the surface on the heating side, and the secondary heaters H2 are disposed to surround it.

[0029] A thermocouple thermometer 34 is attached to the main heater H1, and measures the temperature of the main heater H1 as a heater measurement temperature Dhm. A radiation thermometer 33 is disposed near the main heater H1 as a temperature measurement unit, and detects the surface temperature of the sheet S1 supplied to the heating unit 30 as a sheet surface temperature Dss. Multiple secondary heaters H2 are arranged in the x and y directions to surround the main heater H1.

[0030] The heater element H3 is a rapid-response, high-speed tracking heater, consisting of a zigzag heater element H32 arranged on one surface of an approximately octagonal insulating plate H31. Heat-transfer alloys such as nickel-chromium or iron-chromium can be used for the heater element H32. The amount of heat generated by each heater element H3 is controlled by the amount of power supplied. By controlling the amount of power supplied to each heater element H3, the amount of heat generated by each heater element H3 can be adjusted. By varying the combination of the amounts of power supplied to each heater element H3, the amount of heat generated by the entire heater unit 10 can be controlled.

[0031] For example, when adjusting the heat output of heater element H3, the firing ratio RL of the secondary heater H2 is set based on the value of the primary heater H1. Then, by setting the firing ratio RL of the secondary heater H2 higher than that of the primary heater H1, uniform heating can be achieved. Note that the arrangement of heater elements H3 shown in FIG. 2 is merely an example and may be changed as desired. For example, a method could be considered in which the primary heater H1 is positioned at the front of the sheet S1 in the conveying direction, and the firing ratio RL of the secondary heater H2 at the rear in the conveying direction is lowered to prevent overheating during conveyance.

[0032] The forming unit 40 has the function of forming the heated and softened sheet S1. The forming unit 40 is configured to perform vacuum forming or pressure forming, and has an upper mold 41 arranged above the supplied sheet S1 and a clamp 42 arranged below the sheet S1. The sheet S1 is held by the clamp 42 and moved toward or away from the upper mold 41 by an elevating table (not shown), and thermoforming is performed using a cavity formed in the upper mold 41. At this time, vacuum forming or pressure forming is performed by generating a pressure difference within the cavity of the upper mold 41.

[0033] The control panel 50 controls the heating section 30, the molding section 40, etc., and is equipped with a PLC (Programmable Logic Controller) 31, etc. The control panel 50 controls the drive device for controlling the temperature and moving the heater unit 10 (upper heating means 11 and lower heating means 12) provided in the heating section 30, and also operates the upper mold 41 and clamp 42 of the molding section 40 to move up and down, and a differential pressure generating circuit (not shown).

[0034] After the sheet S1 is formed in the forming section 40, the upper mold 41 and the clamp 42 are moved to the retracted position, and the formed product S2 is sent to the formed product removal section 60. The formed product removal section 60 is provided with a removal means 61 that removes the formed product S2 after forming. Similar to the sheet supply section 20, the formed product S2 is sucked and conveyed by the removal means 61 and removed. Of course, this does not prevent the use of a conveying means other than sucking and conveying for the removal means 61, and it does not prevent the use of a means for trimming the formed product S2 in this process.

[0035] Next, the molding procedure and control using the thermoforming device 100 will be described.

[0036] First, sheet S1 is fed into sheet supply section 20 of thermoforming apparatus 100. Sheet S1 is fed while stacked on a pallet SL, and sheet S1 is moved by sheet supply means 98. Then, sheet S1 is conveyed by sheet holding means 99 and moved to heating section 30. In heating section 30, the upper surface of sheet S1 is heated by upper heating means 11, and the lower surface of sheet S1 is heated by lower heating means 12. Heating control at this time will be described later.

[0037] Next, the heated sheet S1 is transported to the forming section 40. In the forming section 40, the sheet S1 is formed using an upper mold 41 and a clamp 42. Then, the formed product S2 is moved to the formed product removal section 60, where the formed product S2 is removed using a removal means 61.

[0038] Next, the control of heating in the heating unit 30 will be described. FIG. 4 is a diagram illustrating the principle of heater temperature control. The vertical axis represents temperature (°C) and the horizontal axis represents elapsed time (t). Heater temperature information T1 is information based on data obtained from a thermocouple thermometer 34, surface temperature information T2 is information based on data obtained from a radiation thermometer 33, and internal temperature information T3 is temperature information obtained from a thermocouple embedded in the sheet S1 (not shown). However, since it is not possible to embed a thermocouple in the sheet S1 when manufacturing a product, this thermocouple is only used for testing purposes to confirm temperature changes.

[0039] Furthermore, surface temperature information T2 is obtained by averaging information obtained from multiple locations on sheet S1 using multiple radiation thermometers 33, and internal temperature information T3 is obtained by averaging multiple pieces of internal temperature information. The range of heating control, which will be described later, is indicated as a heating control period P1, and the range of temperature maintenance control is indicated as a temperature maintenance control period P2. The target temperature Td and first temperature setting information Ihd1 (the temperature information set at the beginning of heating by heater unit 10 among the heater temperature setting information Ihd) are indicated by dashed dotted lines.

[0040] A block diagram relating to the control of the heater unit is shown in Figure 5. The control panel 50 of the heating section 30 is provided with a touch panel 32 used as a user interface. Operations such as selecting identification information related to the sheet S1 can be performed from the touch panel 32. Temperature information from the radiation thermometer 33 and thermocouple thermometer 34 is transmitted to the PLC 31.

[0041] The controller 35 has the function of controlling the amount of power supplied to the heater unit 10 based on the ignition ratio RL output from the PLC 31. The controller 35 is disposed between the AC power supply and the heater elements H3, and although not shown, is connected to each of the heater elements H3 that make up the heater unit 10. An ammeter 37 for measuring the amount of power is also provided in the wiring to the heater elements H3. An A / D converter 36 is disposed midway through each circuit.

[0042] In the heating control, the amount of power supplied to the heater unit 10 is controlled by the operating device 35 to heat the sheet S1 to a certain temperature (target temperature Td). The first temperature control means 312 performs heating control on the heater unit 10. The target sheet temperature information Its is information that indicates the target surface temperature of the sheet S1 and is used as a condition for the PLC 31 to change the heater temperature setting information Ihd in the heating control. The heater temperature setting information Ihd is information that the PLC 31 uses to set the heater temperature in the heating control.

[0043] In the heating control, the first temperature control means 312 retrieves the heater temperature setting information Ihd stored in the storage device 311 in accordance with the comparison result between the seat surface temperature Dss and the target seat temperature information Its, determines the amount of power to be supplied while referring to the seat surface temperature Dss, and transmits the amount of power to the operation device 35, thereby controlling the amount of power. Then, the heating instruction by the heater unit 10 is continued until the seat surface temperature Dss reaches the target temperature Td. Note that the heating control at this time may be performed, for example, by lowering the set temperature while constantly updating the heater temperature setting information Ihd based on the first temperature setting information Ihd1, and determining the ignition ratio RL so as to gradually lower the target seat temperature information Its accordingly.

[0044] The switching means 314 compares the seat surface temperature Dss with the target temperature Td, and when the seat surface temperature Dss reaches the target temperature Td, switches the temperature control of the heater unit 10 performed by the PLC 31 from heating control to temperature maintenance control. That is, it switches from the first temperature control means 312 that performs heating control to the second temperature control means 313 that performs temperature maintenance control.

[0045] The second temperature control means 313 performs temperature maintenance control on the heater unit 10. In the temperature maintenance control, the temperature of the heater unit 10 is controlled based on the sheet surface temperature Dss so that the temperature of the sheet S1 approaches the target temperature Td. The second temperature control means 313 controls the temperature of the sheet S1 by feedback control such as PID control or PI control.

[0046] The heat quantity evaluation means 315 acquires the current value Dac obtained from the ammeter 37 or the heater measurement temperature Dhm obtained from the thermocouple thermometer 34, and has the function of evaluating its change over time to determine the end of temperature maintenance control. The amount of power supplied to the heater unit 10 is controlled by the controller 35, which acquires the current value Dac or the heater measurement temperature Dhm as its output. The heat quantity evaluation means 315 then linearly approximates the curve drawn from the change over time using a method such as the least squares method, and makes a judgment based on the slope I. The timing for moving the sheet S1 to the forming section 40 is then determined.

[0047] A flowchart related to temperature control is shown in Figure 6. In step S11 of Figure 6, heater temperature setting information Ihd and target seat temperature information Its are set. The first temperature control means 312 sets the heater temperature setting information Ihd and target seat temperature information Its and starts heating control. By this process, the PLC 31 outputs an ignition ratio RL corresponding to the heater temperature setting information Ihd to the operation device 35.

[0048] In step S12, a keep-warm setting is performed for the heater unit 10. The first temperature control means 312 sets the temperature of the heater unit (main heater H1) 10 to the temperature set by the heater temperature setting information Ihd. For example, the first temperature control means 312 compares the heater measurement temperature Dhm with the current heater temperature setting information Ihd, changes the ignition ratio RL according to the comparison result, and passes the information to the operation device 35.

[0049] At this time, the output value of the heater unit 10 is recorded in the storage device 311. Specifically, the current value Dac obtained from the ammeter 37 is recorded in the storage device 311. For example, if it is the first time, it is recorded as first current value information Dac1. Alternatively, the heater measured temperature Dhm is recorded in the storage device 311. For example, if it is the first time, it is recorded as first temperature information Dhm1.

[0050] In step S13, the seat surface temperature Dss is acquired. The first temperature control means 312 acquires the seat surface temperature Dss. The seat surface temperature Dss is the surface temperature of the seat S1 acquired by the radiation thermometer 33 arranged near the main heater H1.

[0051] In step S14, it is determined whether the seat surface temperature Dss has reached the target temperature. The first temperature control means 312 compares the seat surface temperature Dss obtained in step S13 with the target temperature Td. If the seat surface temperature Dss is lower than the target temperature Td (step S14: No), the process returns to step S12. If the seat surface temperature Dss has reached the target temperature Td (step S14: Yes), the process proceeds to step S15. From step S15, the control is switched by the switching means 314 from heating control by the first temperature control means 312 to temperature maintenance control by the second temperature control means 313.

[0052] In step S15, the seat surface temperature Dss and the current value Dac are acquired. The heater measured temperature Dhm is also acquired. The second temperature control means 313 records the output value of the heater unit 10 in the memory device 311, as in step S13. Specifically, the current value Dac obtained from the ammeter 37 or the heater measured temperature Dhm is recorded in the memory device 311. If this is the first time, it is recorded as second current value information Dac2 or second temperature information Dhm2.

[0053] In step S16, a comparison amount is calculated. The second temperature control means 313 calculates a comparison amount between the seat surface temperature Dss acquired in step S15 and the target temperature Td. The comparison amount is calculated, for example, based on the difference between the seat surface temperature Dss and the target temperature Td.

[0054] In step S17, the ignition ratio RL is corrected in accordance with the comparison amount. The second temperature control means 313 corrects the ignition ratio RL to be output to the operation unit 35 in accordance with the comparison amount calculated in step S16. The operation unit 35 controls the amount of power supplied to the heater unit 10 in accordance with the corrected ignition ratio RL, thereby performing feedback control to bring the seat surface temperature Dss closer to the target temperature Td.

[0055] In step S18, it is determined whether the seat surface temperature has reached the target temperature. The second temperature control means 313 determines whether the seat surface temperature Dss has reached the target temperature Td. If the seat surface temperature Dss has reached the target temperature Td (step S18: Yes), the process proceeds to step S19; if not (step S18: No), the process returns to step S15.

[0056] In step S19, it is determined whether the slope I is zero. The heat quantity evaluation means 315 linearly approximates the change in heater temperature based on the current value Dac or the heater measurement temperature Dhm to determine the slope I. If the slope I is not zero (step S19: No), the process returns to step S15. For example, a temperature change curve is determined using the heater measurement temperature Dhm, such as the first temperature information Dhm1 and the second temperature information Dhm2, and the slope I is linearly approximated to check the slope I. If it is determined to be zero (step S19: Yes), the process ends. Then, the sheet S1 is transported to the forming unit 40. For example, the slope I of the first approximated line L1 shown in FIG. 4 is not zero, so the process returns to step S15. However, the slope I of the second approximated line L2 is zero, so the process ends.

[0057] The thermoforming apparatus 100 of the first embodiment has the above-described configuration, and therefore provides the following functions and effects.

[0058] First, an advantage of the thermoforming device 100 is that it is possible to satisfy the optimum heating conditions for the sheet S1 by the heater unit 10 when thermoforming the sheet S1. This is because the thermoforming device 100 has the following configuration. First, the thermoforming device 100 has a heater (heater unit 10) that heats the resin sheet (sheet S1), which is the object to be heated, and is equipped with a temperature measurement unit (radiation thermometer 33) that measures the surface temperature of the sheet S1 (sheet surface temperature Dss), an output control unit (PLC 31) that controls the output of the heater unit 10, and output measurement means (ammeter 37 or thermocouple thermometer 34) that measures the output of the heater unit 10.

[0059] This is because the PLC 31 is characterized by having a first temperature control means 312 that controls the output of the heater unit 10 so that the seat surface temperature Dss measured by the radiation thermometer 33 gradually decreases from the initial temperature, a second temperature control means 313 that starts feedback control to perform control according to the comparison result between the seat surface temperature Dss and the target temperature Td after the seat surface temperature Dss has reached the target temperature Td under control of the first temperature control means 312, and a heat quantity evaluation means 315 that linearly approximates the change in the output value that the heater unit 10 gives to the seat S1 based on the output value of the output measurement means (ammeter 37 or thermocouple thermometer 34) and evaluates it as a slope I.

[0060] Of these, it is preferable that the output measurement means is an ammeter 37 that measures the current flowing through the heater unit 10, and the output value is the current value Dac obtained from the ammeter 37, or that the output measurement means is a thermocouple thermometer 34 that measures the surface temperature of the heater unit 10, and the output value is the heater measurement temperature Dhm obtained from the thermocouple thermometer 34.

[0061] The applicant has evaluated the output value of the heater unit 10 using the heat quantity evaluation means 315 as the current value Dac or the heater measurement temperature Dhm, and confirmed that the sheet surface temperature Dss and the internal temperature of the sheet S1 become the same when the linearly approximated slope I reaches zero. This behavior will be explained using Figure 4. Since it is difficult to actually embed a thermocouple to measure the internal temperature in the sheet S1 used to make the molded product S2, this behavior only occurs when one is embedded.

[0062] First, as shown in Figure 4, the approximate line L2 where the slope I is zero is identified and used as the end point of the temperature maintenance control period P2. At this point, the surface temperature information T2 and the internal temperature information T3 are nearly identical, and the target temperature Td has been reached. The applicant's experiments have confirmed that this tendency is not affected by the external temperature environment, etc.

[0063] When heating control is initiated by the first temperature control means 312, the temperature of the heater unit 10 indicated by heater temperature information T1 rises rapidly to the first temperature setting information Ihd1 (heater temperature setting information Ihd), and heating of the sheet S1 begins. Accordingly, the surface temperature of the sheet S1 indicated by surface temperature information T2 rises, followed by a delay in the rise of internal temperature information T3. Then, as heat retention control is performed by the second temperature control means 313, the internal temperature information T3 approaches the surface temperature information T2. ​​At this time, the output of the heater unit 10 is reduced, so the change in the heater temperature information T1 becomes gradual. The reason for evaluating the slope I using linear approximation is that the heater temperature information T1 fluctuates minutely, and therefore the temperature will continue to fluctuate up and down even after stabilizing. This is why the evaluation is handled using an approximated line.

[0064] When the gradient I reaches zero, it is assumed that both the surface temperature and internal temperature of the sheet S1 have reached the target temperature Td, and the temperature maintenance control by the second temperature control unit 313 is terminated. The heated sheet S1 is then moved to the next molding unit 40 for molding. This process enables the thermoforming device 100 to properly heat the sheet S1, contributing to improved yields of the molded product S2. As mentioned in the "Problems" section, setting the trigger to terminate the temperature maintenance control by time requires a longer time, which can result in drawdown of the sheet S1 or a worsening cycle time. However, adopting the control described in this embodiment allows for the appropriate determination of the end time of the temperature maintenance control, leading to reduced product defects and improved cycle time.

[0065] Furthermore, by employing this process in the heating unit 30, if the rise in the internal temperature of the sheet S1 becomes slower than the surface temperature Dss due to the influence of the external temperature environment, the amount of power required from the heater unit 10 increases. As a result, even if the temperature maintenance control period P2 becomes longer, the slope I becomes zero at the timing when the surface temperature information T2 and the internal temperature information T3 in FIG. 4 overlap. It has been confirmed that similar results can be obtained even if the material of the sheet S1 changes. In other words, it becomes possible to respond to changes in the material of the sheet S1 and changes in the external temperature environment.

[0066] The process of determining the temperature maintenance control period P2 is determined by the PLC 31 provided on the control panel 50, which contributes to reducing the workload of on-site workers as mentioned in the problem section. This contributes to shortening the work time required to determine parameters, etc., and ultimately to reducing the production cost of the molded product S2.

[0067] The thermoforming apparatus 100 according to the present invention has been described above, but it is not limited thereto and various modifications are possible without departing from the spirit of the invention. For example, it is possible to change the conveying means for the sheet S1 or the removal means for the molded product S2. Furthermore, while the sheet S1 is described as a composite material, it is not possible to apply the present invention to sheet materials or film materials made of a single material. However, it is preferable to apply the present invention to relatively thick resin materials or composite materials with different temperature conditions. This is because thick materials, such as those made of a material heated by the heater unit 10, are more likely to experience a discrepancy between the surface temperature Dss and the internal temperature. [Explanation of symbols]

[0068] I Tilt S1 Seat Td target temperature Dss sheet surface temperature 10 Heater unit 31 PLC 33 Radiation thermometer 34 Thermocouple Thermometer 37 Ammeter 100 Thermoforming equipment 312 first temperature control means 313 Second temperature control means 315 Heat Evaluation Method

Claims

1. In a thermoforming device having a heater for heating a resin sheet as an object to be heated, a temperature measuring unit that measures the surface temperature of the resin sheet; an output control unit that controls the output of the heater; an output measuring means for measuring the output of the heater, The output control unit a first temperature control means for controlling an output of the heater based on the surface temperature measured by the temperature measurement unit; a second temperature control means that starts a feedback control according to a comparison result between the surface temperature and the target temperature after the surface temperature reaches the target temperature under the control of the first temperature control means; a heat quantity evaluation means for evaluating a change in the output value applied by the heater to the resin sheet as a slope by linear approximation based on the output value of the output measurement means; A thermoforming device characterized by:

2. 2. The thermoforming apparatus of claim 1, the output measuring means is an ammeter that measures a current flowing through the heater, the output value is a current value obtained from the ammeter; A thermoforming device characterized by:

3. 2. The thermoforming apparatus of claim 1, the output measuring means is a thermometer that measures the surface temperature of the heater, the output value is a temperature obtained from the thermometer; A thermoforming device characterized by:

4. In a thermoforming method in which a resin sheet as a workpiece is heated by a heater, a temperature measuring unit that measures the surface temperature of the resin sheet; an output control unit that controls the output of the heater; an output measuring means for measuring the output of the heater, a first temperature control means provided in the output control unit controls heating by the heater so that the surface temperature becomes a target temperature; When the surface temperature reaches a target temperature under the control of the first temperature control means, a feedback control is started by a second temperature control means provided in the output control unit, which performs control according to a comparison result between the surface temperature and the target temperature, and the feedback control is continued until the internal temperature of the resin sheet reaches a temperature close to the target temperature; a heat quantity evaluation means for evaluating a change in the output value given by the heater to the resin sheet as a slope by linear approximation based on the output value of the output measurement means, and terminating the feedback control by the second temperature control means when the slope becomes zero; A thermoforming method characterized by:

5. The thermoforming method according to claim 4, the output measuring means is an ammeter that measures a current flowing through the heater, the output value is a current value obtained from the ammeter; A thermoforming method characterized by:

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