As shown in FIGS. 3A and 3B, the controller 4 proceeds from the start to step S1 to determine whether the injection material pressure is greater than a value that is obtained by adding the first threshold to the secondary pressure. When the injection material pressure is less than the value that is obtained by adding the first threshold to the secondary pressure, the controller 4 proceeds to step S2. In step S2, the controller 4 determines whether the injection material pressure is less than a value that is obtained by subtracting the second threshold from the secondary pressure. When the injection material pressure is greater than the value that is obtained by subtracting the second threshold from the secondary pressure, the controller 4 determines that the injection material pressure is normal. That is, with the secondary pressure as a criterion, a normal pressure range of the injection material pressure is defined as a range greater than the lower second threshold and less than the upper first threshold. When the injection material pressure is within the normal pressure range, the controller 4 determines that the injection material pressure is normal and returns to the start.

When it is determined in step S1 that the injection material pressure is greater than the secondary pressure and a difference between the injection material pressure and the secondary pressure is equal to or greater than the first threshold, the controller 4 proceeds to step S3. In step S3, the controller 4 checks whether the injection material pressure is greater than the secondary pressure and whether the difference between the injection material pressure and the secondary pressure is less than the third threshold. When the difference is equal to or greater than the third threshold, there is a high possibility that a vent-up occurs. At this time, the controller 4 executes stop processing SS.

In the stop processing SS, as shown in FIG. 5, the controller 4 confirms in step S31 whether the on-off means, that is, the on-off valve 39 can be controlled. When the on-off valve 39 is present, the controller 4 executes step S32 to close the on-off valve 39 and stop the gas supply. Next, regardless of the presence or absence of the on-off valve 39, the controller 4 executes step S33, waits for completion of a molding cycle currently being executed, and stops the molding cycle. The stop processing SS may be executed immediately or after a delay of a certain period of time or a certain cycle, depending on a cause, urgency classification of manned and unmanned operations, and the like. The controller 4 may execute alarm processing SB to be described later simultaneously with or prior to the stop processing SS in order to inform an operator of an abnormality.

When it is determined that the difference between the injection material pressure and the secondary pressure is less than the third threshold in step S3 of the flow chart in FIG. 33A, the controller 4 executes alarm processing SA. In the alarm processing SA, the controller 4 outputs an alarm indicating that there is a risk of a vent-up at the gas inlet 26. The alarm may be displayed as a message on a monitor attached to the controller 4, or may be output as an alarm sound from a speaker. Alternatively, the controller 4 may notify an administrator of the alarm by means of e-mail or the like.

When the alarm processing SA is executed, the controller 4 proceeds to step S4. In step S4, the controller 4 checks whether the feeder 44 is present and whether the feeder 44 is operable, that is, whether feeder control means is present. When no feeder control means is present, the controller 4 executes the stop processing SS. That is, the controller 4 operates and closes the on-off valve 39, stops the gas supply, waits for the completion of the molding cycle currently being executed, and then stops the molding cycle. When the feeder control means is present, the controller 4 proceeds to step S5.

In step S5, the controller 4 performs the supply amount reduction control. The supply amount reduction control is control for reducing an amount of the injection material supplied to the heating cylinder 17 by decreasing a driving speed of the feeder 44. By reducing the supply amount, the injection material pressure in the starvation section 22 is decreased. In this way, the injection material pressure is within the normal pressure range.

When the supply amount reduction control is performed, the controller 4 observes a progress in step S6. That is, the controller 4 monitors the injection material pressure to check whether the injection material pressure returns to the normal pressure range within the first stabilization time. When the injection material pressure returns to the normal pressure range within the first stabilization time, the controller 4 determines that the injection material pressure is normal. That is, the controller 4 returns the processing to the start. However, when the injection material pressure does not return to the normal pressure range within the first stabilization time, the controller 4 executes the stop processing SS already described.

Regarding step S2, only the processing when the injection material pressure is determined to be within the normal pressure range has been described. A case where the injection material pressure is out of the normal pressure range will be described. When it is detected in step S2 that the injection material pressure is equal to or less than the value that is obtained by subtracting the second threshold from the secondary pressure, the controller 4 determines that the injection material pressure falls below the normal pressure range, and proceeds to step S7.

In step S7, the controller 4 checks whether the injection material pressure is greater than a value that is obtained by subtracting the fourth threshold from the secondary pressure. When the injection material pressure is equal to or less than the value that is obtained by subtracting the fourth threshold from the secondary pressure, the stop processing SS already described is executed. When the injection material pressure is greater than the value that is obtained by subtracting the fourth threshold from the secondary pressure, the controller 4 executes the alarm processing SB. In the alarm processing SB, the controller 4 outputs an alarm indicating that there is a risk of a gas leakage or a decrease in a gas cylinder pressure due to a decrease in the injection material pressure. The alarm may be displayed as a message on a monitor attached to the controller 4, or may be output as an alarm sound from a speaker. Alternatively, the controller 4 may notify an administrator of the alarm by means of e-mail or the like.

When the alarm processing SB is executed, the controller 4 proceeds to step S8, In step SS, the controller 4 checks whether the feeder 44 is present and whether the feeder 44 is operable, that is, whether a feeder control means is present. When no feeder control means is present, the controller 4 executes the stop processing SS already described. When the feeder control means is present, the controller 4 proceeds to step S9.

In step S9, the controller 4 performs the supply amount increase control. The supply amount increase control is control for increasing the amount of the injection material supplied to the heating cylinder 17 by increasing the driving speed of the feeder 44. By increasing the supply amount of the injection material, the injection material pressure in the starvation section 22 is increased. In this way, the injection material pressure is within the normal pressure range.

When the supply amount increase control is performed, the controller 4 observes a progress in step S10. That is, the controller 4 monitors the injection material pressure to check whether the injection material pressure returns to the normal pressure range within the second stabilization time. When the injection material pressure returns to the normal pressure range within the second stabilization time, the controller 4 determines that the injection material pressure is normal. That is, the controller 4 returns the processing to the start. However, when the injection material pressure does not return to the normal pressure range within the second stabilization time and the injection material pressure is equal to or less than the value that is obtained by subtracting the second threshold from the secondary pressure, the controller 4 executes the stop processing SS already described.

In the injection molding machine 1 according to the present embodiment, it is also checked whether the supply of the injection material is normal. That is, the controller 4 executes step S21 as shown in FIG. 4. The controller 4 checks whether the injection material falls into the heating cylinder 17 at a predetermined interval by using the injection material detection sensor 46 which is injection material detection means. When the supply of the injection material is not normal, the controller 4 executes the stop processing SS already described.

The above is the method for controlling the injection molding machine according to the present embodiment, and it has been described that the first and second thresholds and the like are used for the secondary pressure to determine the normality or the abnormality of the injection material pressure or the like. It is desirable that the first and second thresholds are set in a range of 0.1 MPa to 1.5 MPa. and more preferably a range of 02 MPa to 1.0 MPa. The third and fourth thresholds may be set to numerical values slightly greater than the first and second thresholds, respectively.

For the first and second thresholds and the like, ratios may be used instead of using specific pressure values. For example, the normal range of the injection material pressure may be 95% to 110% of the secondary pressure, Determination using the ratios in this way is substantially the same as the determination using the first and second thresholds. That is, setting the first and second thresholds within the above numerical range is the same as setting the first threshold to 10% of the secondary pressure and the second threshold to 5% of the secondary pressure.

It is also possible to use upper and lower limits of the normal range. For example, when the secondary pressure is set to 10 MPa, the normal range may be from 10.5 MPa to 9.5 MPa. In this case, the same result can also be obtained as in a case of the determination using the first and second thresholds or the ratios.

The method for controlling the injection molding machine according to the present embodiment can be applied to a case of having a plurality of secondary pressure set values and performing control to change a pressure stepwise. In this case, the first and second thresholds and the like may be set so as to include maximum and minimum values of the plurality of secondary pressure set values, or set values corresponding to the first and second thresholds may be set for each secondary pressure set value.

As described above, in the present embodiment, the secondary pressure to be compared with the injection material pressure may use the secondary pressure set value set in the control means, or the measurement value of the secondary pressure detected by the secondary pressure gauge 42. This is because there is almost no difference between the secondary pressure set value and the measurement value of the secondary pressure when the starvation section 22 to which the gas is supplied is in a stable state.

In S7 in the present embodiment, the first, second, and fourth thresholds are used as a determination criterion for the alarm processing SB, that is, the alarm indicating the risk of the gas leakage or the decrease in the gas cylinder pressure. However, it is also possible to more directly use a difference between the secondary pressure and the primary pressure as the determination criterion for the risk of the decrease in the gas cylinder pressure. In this case, a fifth threshold may be used as the determination criterion for the difference between the primary pressure and the secondary pressure, and when the difference between the primary pressure and the secondary pressure is less than the fifth threshold, the alarm indicating the risk of the decrease in the gas cylinder pressure may be issued. The fifth threshold may be appropriately determined according to an amount of the gas used, and for example, 1 MPa may be used as one criterion. At this time, when the controller 4 has a gas supply source switching function, that is, a function to switch the gas cylinder 30 currently being used to another gas cylinder 30 by operating the gas cylinder on-off valves 31 and 31 in the present embodiment, gas supply source switching control may be performed to automatically switch the gas supply sources.

Although the invention made by the present inventor has been specifically described above based on the embodiment, it is needless to say that the present invention is not limited to the embodiment described above, and various modifications can be made without departing from the scope of the invention, hi addition, the measures may be changed between a case of the manned operation and a case of the unmanned operation. For example, in the case of the manned operation, a guideline for changing molding conditions may be displayed in a guidance manner instead of the supply amount increase control or the supply amount reduction control for the feeder 44, or in a case where the urgency is low; the processing may be stopped at the alarm processing to wait for measures of the operator, instead of executing the stop processing SS. A plurality of examples described above may be implemented in combination as appropriate.

Here, features of the embodiment of the injection molding machine for foam molding and the method for controlling the injection molding machine according to the present invention described above are briefly summarized in [1] to [17] below, respectively.

[1]

An injection molding machine (1) including;

- a heating cylinder (17) having a gas inlet (26);
- a screw (18) drivable in the heating cylinder (17);
- a gas supply device (28) con figured to supply a gas to the gas inlet (26);
- injection material pressure detection means (40) provided in a vicinity of the gas inlet (26) of the heating cylinder (