JP2013180491A - Heating device, injection molding machine and method of controlling heater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the following performance of a temperature of an injection material to a target temperature.SOLUTION: A heating device includes a heater provided at an outer periphery of an injection cylinder and heating an injection material in the injection cylinder through a wall of the injection cylinder, a temperature sensor for detecting a temperature of the injection material in the injection cylinder, and a control means for controlling the driving of the heater. The control means uses a temperature obtained by adding an adjustment value in accordance with a difference between a target temperature of the injection material and the temperature detected by the temperature sensor to the target temperature of the injection material as a target temperature of the heater, and controls the driving of the heater.

Description

  The present invention relates to a temperature control technique for an injection material in an injection molding machine.

  In injection molding, the quality of a molded product depends greatly on the molten state (fluidity) of the injection material. For this reason, temperature control of the injection material existing in the injection cylinder is important. The injection material is heated by a heater provided on the outer periphery of the injection cylinder. The temperature control of the injection material is performed by driving control of the heater (for example, Patent Document 1).

Japanese Patent No. 2618588

  Since the heater is provided on the outer periphery of the injection cylinder, the heat generated by the heater is conducted to the injection material through the wall of the injection cylinder. For this reason, there is a time lag until the temperature of the heater matches the temperature of the injection material. As a result, the temperature of the injection material may fluctuate with respect to the target temperature, or it may take too much time to reach the target temperature.

  An object of the present invention is to improve the followability of the temperature of an injection material with respect to a target temperature.

  According to the present invention, a heater provided on the outer periphery of the injection cylinder for heating the injection material in the injection cylinder through the wall of the injection cylinder, and a temperature sensor for detecting the temperature of the injection material in the injection cylinder And a control means for controlling the driving of the heater, the control means adds an adjustment value according to the difference between the target temperature and the temperature detected by the temperature sensor to the target temperature of the injection material A heating device that controls the driving of the heater is provided by using the measured temperature as the target temperature of the heater.

  According to the present invention, the followability of the temperature of the injection material with respect to the target temperature can be improved.

Explanatory drawing of the heating apparatus which concerns on one Embodiment of this invention. (A) And (B) is a figure which shows the example of arrangement | positioning of a temperature sensor. (A) And (B) is explanatory drawing of the control content of a heater, and the temperature change of an injection material. (A) And (B) is a figure which shows the example of arrangement | positioning of the temperature sensor in a reference example. (A) And (B) is explanatory drawing of the control content of the heater in a reference example, and the temperature change of an injection material. (A) And (B) is explanatory drawing of the control content of the heater in a reference example, and the temperature change of an injection material.

<Device configuration>
FIG. 1 is an explanatory diagram of a heating apparatus A according to an embodiment of the present invention. The heating device A is a heating device for an injection molding machine including the injection cylinder 1 and is a device for heating the injection material 20 in the injection cylinder. The injection material 20 is, for example, a resin material, is introduced into the injection cylinder 1 in the form of a pellet-like solid, and is melted by the heating device A.

  The injection cylinder 1 is a cylindrical member having an internal space 1a for storing the injection material 20 and a wall 1b that defines the internal space 1a. A nozzle 2 for injecting an injection material 20 into a mold is provided at the tip of the injection cylinder 1. The screw 3 conveys the injection material 20 supplied from a hopper (not shown) to the internal space 1a.

  The heater 4 is a heating element that generates heat when energized, and is provided on the outer periphery of the injection cylinder 1. The heat generated by the heater 4 heats the injection material 20 accommodated in the internal space 1a through the wall 1b of the injection cylinder 1. The injection material 20 conveyed by the screw 3 is stored at the tip of the screw 3 while being melted by the heat from the heater 4 and the shearing heat at the time of conveyance.

  The temperature sensors 5 and 6 are temperature sensors such as thermocouples. The temperature sensor 5 is a temperature sensor for detecting the temperature of the heater 4, and the temperature sensor 6 is for detecting the temperature of the injection material 20, particularly for detecting the temperature of the injection material 20 stored in a molten state at the tip of the screw 3. It is a temperature sensor. Therefore, it is preferable that the temperature sensor 5 is disposed close to the heater 4 and the temperature sensor 6 is disposed close to the injection material 20. In the case of the present embodiment, the temperature sensors 5 and 6 are disposed in the wall portion 1b of any injection cylinder 1, but may be external. For example, the temperature sensor 5 may be attached to the heater 4. The temperature sensor 6 may be disposed in the internal space 1a.

  FIG. 2A is a cross-sectional view of the injection cylinder 1 showing an arrangement example of the temperature sensors 5 and 6. As shown in the figure, the temperature sensor 5 is preferably disposed on the heater 4 side from a position L that is half the wall thickness d of the wall 1b, and more preferably viewed from the outer peripheral surface of the wall 1b. It is preferable to be disposed on the heater 4 side from a position that is 1/4 of the wall thickness of the wall portion 1b. Conversely, the temperature sensor 6 is preferably disposed on the inner space 1a side from a position L that is half the thickness d of the wall portion 1b, and more preferably the wall portion as viewed from the inner peripheral surface of the wall portion 1b. It is preferable to be disposed on the inner space 1a side from a position of 1/4 of the thickness of 1b, and it may be in contact with the injection material 20. As shown in FIG. 2B, the temperature sensors 5 and 6 may be located on opposite sides of the internal space 1a. Usually, since the injection material 20 has a temperature distribution in the axial direction of the injection cylinder 1, the temperature sensors 5 and 6 are preferably arranged on a common cross section of the injection cylinder 1.

  The signal processing circuits 7 and 8 are circuits that process the output signals of the temperature sensors 5 and 6, respectively, and include, for example, an A / D conversion circuit and an amplifier circuit. The heater driver 11 is a drive circuit that turns on / off the energization of the heater 4. The controller 10 is a processing circuit that controls the driving of the heater 4 via the heater driver 11, and is a CPU, for example. The storage unit 9 is, for example, a ROM or a RAM, and stores a control program executed by the controller 10 and various setting values. The display unit 12 is a liquid crystal display device, for example, and notifies the temperature detection result of the injection material 20 by the temperature sensor 5, the occurrence of an error, and the like.

<Control of heater>
The controller 10 controls the driving of the heater 4 so that the temperature of the injection material 20 follows the target temperature. In the case of this embodiment, control based on the temperature detection result of the injection material 20 by the temperature sensor 6 is mainly performed. The heat generated by the heater 4 is conducted to the injection material 20 through the wall portion 1 b of the injection cylinder 1. For this reason, there is a time lag until the temperature of the heater 4 and the temperature of the injection material 20 coincide. This becomes a factor that deteriorates the followability of the temperature of the injection material 20 with respect to the target temperature. This point will be described with reference to two comparative examples.

  4A and 4B show the arrangement of the temperature sensor TS in the comparative example. Each of the two comparative examples has one temperature sensor TS, and in the arrangement example shown in FIG. 4A (hereinafter referred to as comparative example 1), the temperature sensor TS is arranged at a position close to the heater 4. 4B shows an example in which the temperature sensor TS is arranged at a position close to the injection material 20 (internal space 1a).

  In Comparative Example 1 shown in FIG. 4A, the detection result of the temperature sensor TS is closer to the temperature of the heater 4 than the temperature of the injection material 20. In the first comparative example, the drive control of the heater 4 assumes a case where the target temperature of the injection material 20 is set as the target temperature of the heater 4.

  FIG. 5A shows the rise of the detected temperature of the temperature sensor TS and the estimated temperature of the injection material 20 from when the power is turned on to the start of molding in this case. The temperature detected by the temperature sensor TS can be regarded as the temperature of the heater 4.

  Although the temperature of the heater 4 and the injection material 20 starts to rise from the time when the power is turned on (room temperature), the temperature of the heater 4 is reduced by the influence of the thermal responsiveness determined by the material of the injection cylinder 1 and the thickness of the wall portion 1b. Even if the target temperature has been reached, the temperature of the injection material 20 does not immediately reach the target temperature, but arrives with a delay.

  The temperature of the heater 4 can be notified to the operator by displaying the temperature detected by the temperature sensor TS on the display unit 12, for example. However, in Comparative Example 1, since the temperature of the injection material 20 itself is not detected, it cannot be notified to the operator. The operator needs to empirically determine that the injection material 20 has reached the target temperature. If the injection material 20 does not reach the target temperature and molding is started, an injection failure may occur.

  FIG. 5B shows a change in the detected temperature of the temperature sensor TS during continuous molding and the estimated temperature of the injection material 20 in Comparative Example 1. Since a new injection material 20 is introduced for each shot, the temperature in the injection cylinder 1 decreases, but the temperature sensor TS is delayed in detecting the temperature decrease in the injection cylinder 1 due to the arrangement. In the meantime, the temperature drop of the injection material 20 proceeds, so that the temperature fluctuation of the injection material 20 becomes large and it takes time to return to the target temperature.

  Next, in Comparative Example 2 shown in FIG. 4B, the detection result of the temperature sensor TS is closer to the temperature of the injection material 20 than the temperature of the heater 4. In Comparative Example 2, similarly to Comparative Example 1, the drive control of the heater 4 assumes a case where the target temperature of the injection material 20 is set as the target temperature of the heater 4.

  FIG. 6A shows the rising temperature of the detected temperature of the temperature sensor TS and the estimated temperature of the heater 4 from when the power is turned on until the start of molding in this case. The temperature detected by the temperature sensor TS can be regarded as the temperature of the injection material 20.

  Although the temperature of the heater 4 and the injection material 20 starts to rise from the time when the power is turned on (room temperature), the injection material 20 has reached the target temperature due to the influence of the thermal responsiveness determined by the material of the injection cylinder 1 and the thickness of the wall 1b. In this case, the heater 4 has a higher temperature than the target temperature. Even if the heater 4 is controlled to be OFF at this time, the temperature of the injection material 20 continues to rise due to a delay in thermal response and overshoots the target temperature. Excessive overshoot may cause product defects such as resin burning.

  FIG. 6B shows how the detected temperature of the temperature sensor TS and the estimated temperature of the heater 4 change during continuous molding in Comparative Example 2. As described in Comparative Example 1, since a new injection material 20 is introduced for each shot, the temperature in the injection cylinder 1 decreases. In the case of the comparative example 2, the temperature sensor TS can detect the temperature drop in the injection cylinder 1 without delay, and the temperature fluctuation as in the comparative example 1 does not occur. However, there may be an overshoot due to a delay in thermal response, such as the behavior at startup.

Next, the control content of this embodiment is demonstrated. In Comparative Examples 1 and 2, the target temperature of the heater 4 is set as the target temperature of the injection material 20, but in this embodiment, the target temperature of the heater 4 is set as the temperature detection result of the injection material 20 (temperature detection result of the temperature sensor 6). Change according to. More specifically, as shown in the following equation, an adjustment value (f) corresponding to the difference (Tm−TM) between the target temperature Tm of the injection material 20 and the detected temperature TM detected by the temperature sensor 6. The temperature obtained by adding (Tm−TM)) is set as the target temperature Th of the heater 4.
Th = f (Tm−TM) + Tm
The adjustment value has a positive and negative value. If the detected temperature TM exceeds the target temperature Tm, the adjustment value becomes a negative value, and if not, the adjustment value becomes a positive value.

  The function f with the difference (Tm−TM) as a variable for determining the adjustment value is determined in advance according to the thermal responsiveness of the wall 1b of the injection cylinder 1, for example, the temperature difference (responsiveness) between the inside and outside of the wall 1b. ) Can be obtained in advance through experiments. Since the relationship between the target temperature Th of the heater 4 and the temperature of the injection material 20 depends only on the thermal responsiveness of the injection cylinder 1, the target temperature Tm is different depending on the type of the injection material 20 in the same injection cylinder 1. Even if it changes, the function f is the same. Most simply, f (Tm−TM) = Tm−TM can be set.

  In order to make the heater 4 follow the target temperature Th, there are a method not using the detection result of the temperature sensor 5 (referred to as method 1) and a method using it (referred to as method 2).

  In the case of the method 1, for example, the relationship between the ON / OFF duty ratio of the heater 4 and the heat generation temperature of the heater 4 is examined in advance, and this relationship is stored in the storage unit 9. And the duty ratio according to target temperature Th may be read from the memory | storage part 9, and the drive control of the heater 4 should just be performed. When this method 1 is adopted, the temperature sensor 5 is not necessary for the drive control of the heater 4. Therefore, the temperature sensor 5 can be omitted, but the temperature sensor 5 may be provided for the purpose of monitoring the temperature of the heater 4 (abnormality detection or the like). In the case of the method 2, there is a control in which the control amount of the heater 4 (for example, ON-OFF duty ratio) is determined from the difference between the target temperature Th and the temperature detection result of the temperature sensor 5 to control the driving of the heater 4.

  3A and 3B illustrate a case where the drive control of the heater 4 is performed with f (Tm−TM) = Tm−TM. FIG. 3 (A)))) shows the rise of the detected temperature of the temperature sensors 5 and 6 and the change of the target temperature Th from when the power is turned on until the start of molding. The temperature detected by the temperature sensor 5 can be regarded as the temperature TH of the heater 4, and the temperature detected by the temperature sensor 6 can be regarded as the temperature TM of the resin material 20.

  When the absolute value of the difference between the temperature TM of the resin material 20 and the target temperature Tm is relatively large, the absolute value of the adjustment value is also large. When the absolute value of the difference is relatively small, the absolute value of the adjustment value is also large. Relatively small. For this reason, for example, as shown in FIG. 3A, when the temperature TM of the resin material 20 is lower than the target temperature Tm, the target temperature Th of the heater 4 increases according to the degree of separation. As the temperature difference between the temperature TM of the resin material 20 and the target temperature Tm decreases, the target temperature Th also converges to the target temperature Tm. For this reason, it is possible to prevent overshooting when the temperature reaches the target temperature Tm while speeding up the rise of the temperature TM of the resin material 20.

  FIG. 3B shows the rise of the detected temperature of the temperature sensors 5 and 6 and the change in the target temperature Th during continuous molding. The target temperature Th is calculated according to the decrease, and the temperature of the heater 4 changes synchronously. Therefore, temperature fluctuations of the resin material 20 can also be suppressed.

  As described above, in this embodiment, the temperature of the resin material 20 can be constantly maintained at the target temperature Tm relatively easily, and the followability of the temperature of the injection material 20 with respect to the target temperature Tm can be improved.

  In addition, control of the heater 4 of this embodiment can be performed for every heater 4. FIG. For example, it is assumed that regions R1 to R3 are virtually divided in the longitudinal direction of the injection cylinder 1 as shown in FIG. In the example of the figure, the heater 4 is provided for each region, but the temperature sensor 6 is also provided for each region R1 to R3. And target temperature Tm is set for every area | region R1-R3, and the drive of the heater 4 is controlled for every area | region R1-R3. By doing so, the temperature of the injection material 20 can be controlled in accordance with the position in the injection cylinder 1, and melting can proceed as the injection material 20 moves to the nozzle 2 side. It becomes possible.

Claims (7)

A heater that is provided on the outer periphery of the injection cylinder and that heats the injection material in the injection cylinder through the wall of the injection cylinder;
A temperature sensor for detecting the temperature of the injection material in the injection cylinder;
Control means for controlling the drive of the heater,
The control means includes
A heating device that controls driving of the heater by setting a temperature obtained by adding an adjustment value according to a difference between the target temperature and the temperature detected by the temperature sensor to the target temperature of the injection material as a target temperature of the heater.   The heating device according to claim 1, wherein the absolute value of the adjustment value is relatively large when the absolute value of the difference is relatively large, and is relatively small when the absolute value of the difference is relatively small. .   The heating apparatus according to claim 1, wherein the adjustment value is the difference. The adjustment value is
The heating apparatus according to claim 1, wherein the heating apparatus is a function that is determined in advance according to a thermal responsiveness of the wall portion of the injection cylinder and that uses the difference as a variable. The heater and the temperature sensor are provided for each region divided in the longitudinal direction of the injection cylinder,
The target temperature of the injection material is set for each region,
The control means includes
The heating apparatus according to claim 1, wherein driving of the heater is controlled for each region.   The injection molding machine provided with the heating apparatus of any one of Claims 1 thru | or 4. A method for controlling a heater provided on an outer periphery of an injection cylinder and heating an injection material in the injection cylinder via a wall portion of the injection cylinder,
A detection step of detecting the temperature of the injection material in the injection cylinder;
A control step for controlling the driving of the heater by setting a temperature obtained by adding an adjustment value corresponding to a difference between the target temperature and the temperature detected in the detection step to the target temperature of the injection material;
A heater control method including:

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