JPH046536B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for monitoring a controlled variable of a plastic molding machine, and more particularly to a method of monitoring the temperature of an injection molding machine.

[Conventional technology]

Conventionally, the temperature of an injection molding machine has been monitored using a temperature controller. In this temperature controller, as shown in Fig. 5, an upper limit temperature THH higher than the set target temperature TH and a lower limit temperature THL lower than it are set at the same time. It is monitored whether the temperature th detected by the injection molding machine is within the temperature monitoring width THW sandwiched between the temperatures THL. Here, target temperature TH, upper limit temperature
THH, lower limit temperature THL, and temperature monitoring width THW have a relationship expressed by the following equation.

1/2THW=｜TH-THH｜=｜TH-THL｜...(1) Then, the temperature controller detects that the detected temperature th is the upper limit temperature.
Higher than THH (th＞THH) or lower limit temperature
An alarm (abnormal temperature signal) is generated when the temperature is lower than THL (th<THL). Note that in the temperature controller, when the target temperature TH is changed, the upper limit temperature THH and lower limit temperature THL also change accordingly.

[Problem that the invention seeks to solve]

However, with the conventional temperature monitoring method for injection molding machines using such a temperature controller, as will be explained in detail later, when starting the temperature or changing the target temperature setting, even though there is no temperature abnormality, However, the disadvantage is that an alarm is generated. The reason why the setting of the target temperature is changed in the injection molding machine is as follows, for example. In other words, if you interrupt molding for a short period of time (about 1 to 4 hours), the temperature control may have been turned off.
It takes time to start up the molding machine next time. Therefore, in such a case, the target temperature is set lower than the temperature during normal operation to maintain heat during the interruption of molding.

Next, the above-mentioned drawbacks of the conventional technology will be explained in more detail with reference to the drawings.

Referring to FIG. 6, when time t is 0, the target temperature
Assume that the temperature of the injection molding machine (for example, cylinder temperature, mold temperature, etc.) is started with TH set to “TH ₁ ”. At this time, the upper limit temperature THH and the lower limit temperature THL are also set to "THH ₁ " and "THL ₁ " simultaneously at time t=0. For that reason,
An alarm occurs while the detected temperature th is lower than the lower limit temperature THL ₁ . On the other hand, assume that the target temperature TH is changed from "TH ₁ " to "TH ₂ " at time t ₁ due to, for example, interruption of molding and heat retention after completion of temperature rise.
At this time, the upper limit temperature THH and lower limit temperature THL are also
At time t= _t1 , "THH ₂ " and "THL ₂ " simultaneously
The setting is changed to . Therefore, as in this example, the upper limit temperature THH ₂ after the setting is changed is lower than the target temperature TH ₁ before the setting is changed (THH ₂ < TH ₁ ).
If the detected temperature th is the upper limit temperature after setting change THH ₂
As the temperature rises temporarily, an alarm will be issued during this time. This kind of thing also occurs when the target temperature TH is changed from " _TH2 " to " _TH1 " at time _t2 in order to start molding again.

On the other hand, in order to prevent such false alarms from occurring, the target temperature TH should not be set or changed all at once, but should be set so that the detected temperature TH always falls within the temperature monitoring width THW, as shown in Figure 6. Another method is for the operator to gradually change the target temperature TH to the final target temperature. However, in such a method, the operator monitors the detected temperature TH and changes the target temperature TH every time the setting of the target temperature TH is changed.
The disadvantage was that the settings had to be changed gradually.

An object of the present invention is to provide a control amount monitoring method for a plastic molding machine that does not generate false alarms even if the target value is changed all at once when starting up the plastic molding machine or changing the target value. It's about doing.

[Means for solving problems]

The present invention monitors whether a controlled variable detected by a plastic molding machine is within a controlled variable monitoring range sandwiched between an upper limit higher than a target value and a lower limit lower than the target value, and A control amount monitoring method for a plastic molding machine that generates an alarm when the control amount is higher than the lower limit value or lower than the lower limit value, and when changing the target value to increase the control amount, the upper limit value is However, regarding the lower limit value,
The lower limit value before the target value change is maintained as long as the first predetermined condition is not met, and the lower limit value is changed when the first condition is met, and conversely, the target value is set so as to lower the control amount. When changing the target value, the lower limit value is changed when changing the target value, but the upper limit value is changed when changing the target value.
The upper limit value before the target value change is maintained as long as the first predetermined condition is not met, and the upper limit value is changed when the second condition is met, and the controlled variable monitoring width is changed even in the area where the target value is constant. It is characterized by being made variable.

[Effect]

When starting up the plastic molding machine or changing the target value to a higher value, the lower limit of the set temperature remains at the previous value until the first condition is met, so no false alarms occur. . Similarly, when changing the target value to a lower value, the upper limit value remains at the previous value until the second condition is satisfied, so that false alarms can be prevented from occurring.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

In the following embodiments, a case will be described in which the plastic molding machine is an injection molding machine and the controlled variable is temperature.

Referring to FIG. 4, a temperature control system for an injection molding machine to which an embodiment of the present invention is applied includes thermocouples, etc. provided in a control system 1 for the cylinder, mold, hydraulic oil, etc. of the injection molding machine. It has a temperature sensor 2. The temperature th detected by the temperature sensor 2 is transferred to the A/D converter 3.
is converted into a digital value by temperature controller 4.
Enter.

The temperature controller 4 includes a direct digital control (DDC) calculation processing section 41 and an upper/lower limit audit processing section 4.
2, and a memory 43 such as RAM. The DDC calculation processing unit 41 receives the detected temperature th input via the A/D converter 3 and the set target temperature TH,
The heater 6 is driven and controlled via the fixed relay (SSR) or the electromagnetic contactor 5 so that these differences are reduced. The upper/lower limit monitoring processing unit 41 implements the temperature monitoring method according to the present invention, and is
When the detected temperature th input via the D converter 3 is higher than the upper limit temperature THH or lower than the lower limit temperature THL, a temperature abnormality signal is sent to the alarm device 7,
Generate an alarm.

The memory 43 stores “TH ₁ ” as the target temperature TH,
“TH ₂ ”, upper limit temperature THH, “THH ₁ ”,
“THH ₂ ”, “THL ₁ ” as the lower limit temperature THL,
“THL ₂ ” is stored, as well as a deviation “ΔTH”, an initial temperature “TH ₀ ”, a heating constant “x ₁ ”, and a cooling constant “x ₂ ”.

Note that 8 is a setting input device such as a keyboard or digital switch for setting the target temperature TH, etc., and 9 is a display device such as a cathode ray tube (CRT), liquid crystal display (LCD), or light emitting diode (LED).

An example of the temperature monitoring method of this embodiment executed by the upper/lower limit monitoring processing section 42 will be described below.

Referring to FIG. 1, at time t=0, the target temperature
Suppose that TH is set to “TH ₁ ” and the temperature after injection molding is raised. At this time, the upper/lower limit monitoring processing unit 4
2 sets “THH ₁ ” as the upper limit temperature THH and initial temperature “TH ₀ ” as the lower limit temperature THL, and monitors the detected temperature th. As a result, the detected temperature th is
The target temperature TH ₁ is controlled by the DDC processing unit 41.
The lower limit temperature is the initial temperature TH ₀ , which is lower than the detection temperature TH.
No alarm is generated by the alarm device 7. When the deviation between the detected temperature th and the target temperature TH ₁ becomes ΔTH, the upper/lower limit monitoring processing unit 42 determines that the temperature increase is complete, and sets the lower limit temperature THL from "TH ₀ " to "THL ₁ ". At this time, the upper limit temperature THH remains “THH ₁ ”. Therefore, from now on, until the target temperature TH is changed, the upper/lower limit monitoring processing unit 42 will keep the upper limit temperature "THH ₁ " and the lower limit temperature "THL ₁ ".
Temperature monitoring is performed as follows.

Next, assume that the target temperature TH is changed from “TH ₁ ” to “TH ₂ ” at time t=t ₁ in order to interrupt the molding and maintain the temperature after the completion of temperature rise. At this time, the upper
The lower limit monitoring processing unit 42 maintains "THH ₁ " as the upper limit temperature THH, and sets the lower limit temperature THL to "THL ₁ ".
Change the setting from “THL ₂ ” to “THL 2” and monitor the detected temperature th. As a result, the detected temperature th gradually decreases toward the target temperature TH ₂ under the control of the DDC calculation processing unit 41, but the upper limit temperature is "THH ₁ ".
Since this is higher than the detected temperature th, the alarm device 7 will not issue an alarm. When the deviation between the detected temperature th and the target temperature TH ₂ becomes ΔTH, the upper/lower limit monitoring processing unit 42 changes the upper limit temperature THH from “THH ₁ ” to “THH ₂ ”. At this time, the lower limit temperature THL
remains “THL ₂ ”. Therefore, from now on,
Until the target temperature TH is changed, the upper/lower limit monitoring processing unit 42 monitors the detected temperature th as the upper limit temperature THH ₂ and the lower limit temperature THL ₂ .

Next, in order to start molding again, time t=t ₂
Assume that the target temperature TH is changed from "TH ₂ " to "TH ₁ ". At this time, the upper/lower limit monitoring processing unit 42 maintains "THL ₂ " as the lower limit temperature THL, and changes the upper limit temperature THH from "THH ₂ " to "THH ₁ ".
Change the settings to and monitor the detected temperature th. As a result, the detected temperature th gradually increases toward the target temperature TH ₁ under the control of the DDC calculation processing unit 41, but since the lower limit temperature THL is “THL ₂ ” and is lower than the detected temperature th, the alarm device 7 No further alarms will be generated. Detected temperature th and target temperature
When the deviation from TH ₁ becomes ΔTH, the upper/lower limit monitoring processing unit 42 changes the lower limit temperature THL from “THL ₂ ” to “THL ₁ ”. At this time, the upper limit temperature THH
remains “THH ₁ ”. Therefore, from now on,
Until the target temperature TH is changed, the upper/lower limit monitoring processing unit 42 monitors the detected temperature th with the upper limit temperature and lower limit temperature set as " _THH1 " and " _THL1 ", respectively.

In the above embodiment, the condition for changing the lower limit temperature or upper limit temperature is that the deviation between the detected temperature and the target temperature is less than or equal to a predetermined deviation. However, as described below, heating time or It is also possible to take advantage of the fact that the cooling time has elapsed.

Referring to FIG. 2, at time t=0, the target temperature
Assume that TH is set to “TH ₁ ” and the temperature of the injection molding machine is started. At this time, the upper/lower limit monitoring processing unit 4
2 sets “THH ₁ ” and initial temperature “TH ₀ ” as upper limit temperature THH and lower limit temperature THL, respectively, and monitors detected temperature th. As a result, the detected temperature th gradually increases toward the target temperature TH ₁ under the control of the DDC calculation processing section 41, but since the lower limit temperature THL is the initial temperature TH ₀ and is lower than the detected temperature th, the alarm device 7 No further alarms will be generated. When the initial heating time “T ₀ ” expressed by the following equation has elapsed from time t=0, the upper/lower limit monitoring processing unit 42 determines that the temperature rise has been completed and changes the lower limit temperature THL from “TH ₀ ” to “THL ₁ ”. Set.

T ₀ = x ₁ · | TH ₁ −TH ₀ | ...(2) Here, the heating constant x ₁ [sec/°C] is a count determined from the heating characteristics of temperature. At this time, the upper limit temperature THH remains “THH ₁ ”. Therefore, from now on, until the target temperature TH is changed, the upper/lower limit monitoring processing section 42 will maintain the upper limit temperature THH and the lower limit temperature.
The detected temperature th is monitored by setting THL as “THH ₁ ” and “THL ₁ ” respectively.

Next, assume that the target temperature TH is changed from "TH ₁ " to "TH ₂ " at time t=t ₁ in order to interrupt molding and perform heat retention after completion of temperature rise. At this time,
The upper/lower limit monitoring processing unit 42 maintains "THH ₁ " as the upper limit temperature THH, changes the setting of the lower limit temperature THL from "THL ₁ " to "THL ₂ ", and monitors the detected temperature th. As a result, the detected temperature th is
The target temperature TH ₂ is controlled by the DDC processing unit 41.
However, since the upper limit temperature is “THH ₁ ” which is higher than the detected temperature th, the alarm device 7 does not issue an alarm. Time t
= t ₁ , when the cooling time “T ₁ ” expressed by the following equation has elapsed, the upper/lower limit monitoring processing unit 42 detects the upper limit temperature.
Change THH from “THH ₁ ” to “THH ₂ ”.

T ₁ = x ₂ · | TH ₁ −TH ₂ | ...(3) Here, the cooling constant x ₂ [sec/°C] is a coefficient determined from the temperature cooling characteristic. At this time, the lower limit temperature THL remains “THL ₂ ”. Therefore, from now on until the target temperature TH is changed, the upper/lower limit monitoring processing unit 42 monitors the detected temperature th with the upper limit temperature THH and lower limit temperature THL as "THH ₂ " and "THL ₂ ", respectively. .

Next, in order to start molding again, time t=t ₂
Assume that the target temperature TH is changed from "TH ₂ " to "TH ₁ ". At this time, the upper/lower limit monitoring processing unit 42 maintains "THL ₂ " as the lower limit temperature THL, and changes the upper limit temperature THH from "THH ₂ " to "THH ₁ ".
Change the settings to and monitor the detected temperature th. As a result, the detected temperature th gradually increases toward the target temperature TH ₁ under the control of the DDC calculation processing unit 41, but since the lower limit temperature THL is “THL ₂ ” and is lower than the detected temperature th, the alarm device 7 No further alarms will be generated. When the heating time “T ₂ ” expressed by the following equation has elapsed from time t=t ₂ , the upper/lower monitoring processing unit 42 changes the lower limit temperature THL from “THL ₂ ” to “THL ₁ ”.

T ₂ = x ₁ · | TH ₂ − TH ₁ | ...(4) At this time, the upper limit temperature THH remains "THH ₁ ". Therefore, from now on, until the target temperature TH is changed, the upper/lower limit monitoring processing unit 42 monitors the detected temperature th with the upper limit temperature THH and lower limit temperature THL as "THH ₁ " and "THL ₁ ", respectively. conduct.

Note that, of course, the above two embodiments may be combined. In the above explanation, the case where the injection molding machine is normal has been described, but next, a monitoring method that combines the above two embodiments will be explained in the case where an abnormal temperature occurs.

Referring to FIG. 3, abnormality (1) indicates an overshoot abnormality. In the example, the upper limit temperature THH and lower limit temperature THL can be set independently, so the upper limit temperature
THH ₁ can be set to the decomposition temperature of the resin due to overshoot. Abnormality (2) indicates an undershoot abnormality. Abnormality (3) occurs when the heating time “T ₂ ” starts from the point when the target temperature TH is changed from “TH _{2 ” to “TH 1 ”} .
Indicates a lower limit abnormality that occurred when the lower limit temperature THL was changed from "THL ₂ " to "THL ₁ " after the elapsed time. Such a temperature abnormality occurs, for example, when there is a problem with temperature rise due to heater breakage or the like. Also, abnormality (4) occurs when the upper limit temperature THH is changed from "THH ₁ " to "THH ₂ " after the cooling time "T ₁ " has elapsed since the time when the target temperature TH was changed from "TH ₁ " to "TH ₂ ". Indicates an upper limit abnormality that occurs at times. Such a temperature abnormality occurs, for example, when there is a problem with the cooling function of the cylinder or the temperature sensor 2.

In addition, in the above-mentioned embodiment, the case where the control amount is temperature has been explained, but the control amount is not limited to this, and may be injection speed, screw rotation speed, pressure, etc. Further, the plastic molding machine is not limited to an injection molding machine, and other plastic molding machines such as an extrusion molding machine may be used.

[Effects of the Invention] As is clear from the above description, according to the present invention, false alarms can be prevented from occurring. Furthermore, since the upper limit value and lower limit value can be set independently, fluctuations in the control amount can be sensitively monitored. Furthermore, the operator only has to change the target value once and the rest is done automatically.
Operability can be improved.

[Brief explanation of drawings]

FIG. 1 is a time chart showing one embodiment of the present invention, FIG. 2 is a time chart showing another embodiment of the present invention, and FIG. 3 is a time chart for explaining the abnormality detection operation according to the present invention. , FIG. 4 is a block diagram showing a temperature control system for an injection molding machine to which the present invention is applied, FIG. 5 is a diagram for explaining a temperature monitoring method using a conventional temperature controller, and FIG. This is a time chart for explaining the drawbacks of the temperature monitoring method using a temperature controller shown in FIG. 1...Control system, 2...Temperature sensor, 3...A/
D converter, 4... Temperature controller, 41...
DDC calculation processing section, 42... Upper/lower limit monitoring processing section,
43...Memory, 5...SSR or electromagnetic contactor,
6... Heater, 7... Alarm device, 8... Setting input device, 9... Display device.

Claims (1)

[Claims] 1. Monitoring whether the temperature value detected by the plastic molding machine is within a temperature monitoring range between an upper limit value higher than the target value and a lower limit value lower than the target value; In a temperature monitoring method for a plastic molding machine that generates an alarm when the temperature value is higher than the upper limit value or lower than the lower limit value, when the target value is changed to increase the temperature value, the upper limit value is The lower limit value is changed when changing the target value, but the lower limit value before the target value change is maintained until the first predetermined condition is satisfied, and the lower limit value before the target value is changed.
If the lower limit value is changed when the following conditions are met, and conversely, the target value is changed to lower the temperature value, the lower limit value is changed when changing the target value, but
Regarding the upper limit value, the upper limit value before the target value change is maintained until the predetermined second condition is not met;
A temperature monitoring method for a plastic molding machine, characterized in that the upper limit value is changed when the second condition is satisfied, and the temperature monitoring width is made variable even in an area where the target value is constant. 2. A temperature monitoring method for a plastic molding machine according to claim 1, wherein the plastic molding machine is an injection molding machine. 3. The temperature monitoring method for a plastic molding machine according to claim 1, wherein the first and second conditions are such that the deviation between the temperature value and the changed target value is less than or equal to a predetermined deviation. 4. The first and second conditions are that, if the plastic molding machine is normal, a time period has elapsed from when the temperature value was changed to the target value after the change. A method for monitoring the temperature of a plastic molding machine according to item 1. 5. A temperature monitoring method for a plastic molding machine according to claim 1, wherein the first and second conditions are that a heating time and a cooling time, respectively, when the plastic molding machine is normal have elapsed.