Method for controlling the supply of raw materials to a molding machine, a raw material supply device, and a method for molding raw materials.

Abstract

The present invention provides a method for controlling the supply of raw materials to a molding machine, a raw material supply device, and a raw material molding method, which enable the molding machine to operate stably and continuously even if there are variations in the supply quantity and properties of the raw materials supplied to the molding machine. [Solution] A method for controlling the supply of raw materials to a molding machine comprising a receiving section for receiving raw materials, a faceplate having a nozzle from which the raw materials are extruded, and a pushing mechanism for pushing the raw materials from the receiving section to the faceplate, wherein when the load of the pushing mechanism is outside a predetermined range, the amount of raw materials supplied to the molding machine is fed back and controlled by sample PI control so that the load comes within the predetermined range.

Description

Technical Field

[0001] The present invention relates to a method for controlling the supply of raw materials to a molding machine, a raw material supply device, and a raw material molding method.

Background Art

[0002] A molding machine that processes raw materials such as waste plastics and urethane into molded products such as pellet-shaped RPF (Refuse Paper & Plastic Fuel) is widely used. As shown in FIG. 8, the molding machine 5 pushes the raw materials accommodated in the receiving portion 51 into the face plate 52 having a heated nozzle 52h by means of a screw conveyor 53 provided inside the receiving portion 51, and extrudes the raw materials from this nozzle 52h, thereby molding a molded product such as RPF.

[0003] In such a molding machine, due to variations in the supply amount and properties of the raw materials, the current value of the motor 54 of the screw conveyor 53 that pushes the raw materials fluctuates. Therefore, an overload state may occur in which the current value of the motor 54 of the screw conveyor 53 becomes excessive, and control is performed to prevent this.

[0004] Specifically, for example, as shown in FIG. 9, when the motor current value of the screw conveyor becomes equal to or greater than a set value (a value close to the trip value of the motor), the screw conveyor of the molding machine is temporarily stopped and reversed and rotated forward repeatedly. As a result of performing such control, if the motor current value of the screw conveyor becomes less than the set value, the continuous operation of the screw conveyor is restarted. Also, if the motor current value of the screw conveyor does not become less than the set value even after the temporary stop, reverse rotation, and forward rotation of the screw conveyor of the molding machine are repeated a certain number of times, it is determined that a serious failure has occurred in the molding machine, and the screw conveyor is completely stopped.

[0005] However, if the amount of raw material supplied is adjusted by controlling the ON / OFF state of the molding machine's screw conveyor in accordance with the load on the molding machine, areas with uneven density of raw material will be formed within the receiving section of the molding machine. Then, when the rotation of the screw conveyor is restarted, the raw material will not be mixed uniformly, making it impossible to stably produce molded products.

[0006] For example, Patent Document 1 discloses a technology for preventing overloading of raw materials in a molding machine by controlling the drive of a crushing device that crushes raw materials to be fed into the molding machine based on load information of the molding machine. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2006-070209 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] In the technology described in Patent Document 1, a reference value (for example, 70% to 80% of the motor's rated output) is set for the load on the molding machine, and when this reference value is exceeded, the motor speed of the crushing device is reduced, thereby decreasing the amount of raw material supplied to the molding machine. In other words, the control of whether or not to adjust the amount of raw material supplied to the molding machine is performed based on whether or not the load on the molding machine exceeds the above reference value, and is not performed continuously. For this reason, as also described in Patent Document 1, there was still a problem that the load on the molding machine could become excessive and lead to a shutdown, especially when the load fluctuations of the molding machine were sudden.

[0009] The present invention has been made to solve the above problems, and aims to provide a method for controlling the supply of raw materials to a molding machine, a raw material supply device, and a raw material molding method that can operate the molding machine stably and continuously even if there are variations in the amount and properties of the raw materials supplied to the molding machine. [Means for solving the problem]

[0010] The means to solve the above problems are as follows: [1] A method for controlling the supply of raw materials to a molding machine comprising a receiving section for receiving raw materials, a faceplate having a nozzle from which the raw materials are extruded, and a pushing mechanism for pushing the raw materials from the receiving section to the faceplate, wherein when the load of the pushing mechanism is outside a predetermined range, the amount of raw materials supplied to the molding machine is fed back and controlled by sample PI control so that the load comes within the predetermined range.

[0011] Here, sample PI control refers to a control method in which PI control is performed for a portion of the sample cycle, and the control value is maintained for the remainder of the sample cycle, and this process is repeated. [2] The raw material supply control method according to [1], wherein the amount of raw material supplied is controlled by feedforward control based on the physical properties of the raw material supplied to the receiving unit, in addition to the feedback control. [3] A raw material supply device for supplying raw materials to a molding machine comprising a receiving section for receiving the raw materials, a faceplate having a nozzle from which the raw materials are extruded, and a pushing mechanism for pushing the raw materials from the receiving section to the faceplate, the raw material supply device having a control unit that, when the load of the pushing mechanism is outside a predetermined range, provides feedback control of the amount of raw materials supplied to the molding machine by sample PI control so that the load comes within the predetermined range. [4] The raw material supply device according to [3], wherein the control unit controls the amount of raw material supplied to the receiving unit by feedforward control based on the physical characteristics of the raw material, in addition to the feedback control. [5] A method for molding raw materials, comprising a molding machine that includes a receiving section for receiving raw materials, a faceplate having a nozzle from which the raw materials are extruded, and a pushing mechanism for pushing the raw materials from the receiving section to the faceplate, wherein when the load of the pushing mechanism is outside a predetermined range, the amount of raw materials supplied to the receiving section is feedback controlled by sample PI control so that the load comes within the predetermined range. [6] The raw material molding method according to [5], wherein the amount of raw material supplied is controlled by feedforward control based on the physical properties of the raw material supplied to the receiving part, in addition to the feedback control. [Effects of the Invention]

[0012] According to the raw material supply control method and raw material supply device for a molding machine, as well as the raw material molding method of the present invention, the molding machine can be operated stably and continuously even if there are variations in the amount and properties of the raw materials supplied to the molding machine.

[0013] Specifically, in raw material supply control in a molding machine, there is a long delay between the control of the raw material supply amount and the resulting change in the load of the molding machine's pressing mechanism. Therefore, in this invention, when the load of the molding machine's pressing mechanism is outside a predetermined range, the amount of raw material supplied to the raw material molding device is fed back and controlled by sample PI control so that the load comes within the predetermined range. As a result, the control of the raw material supply amount to the raw material molding device can be performed more simply and reliably than when using general methods such as PID control, and the molding machine can be operated stably and continuously. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is a schematic diagram showing a raw material supply control method and raw material supply device to a molding machine, as well as a raw material molding method, according to the first embodiment of the present invention. [Figure 2]FIG. 2 is a block diagram showing an example of the processing flow of the raw material supply control method for a molding machine according to the first embodiment of the present invention. [Figure 3] FIG. 3 is a block diagram showing another example of the processing flow of the raw material supply control method for a molding machine according to the first embodiment of the present invention. [Figure 4] FIG. 4 is a schematic diagram showing a raw material supply control method and a raw material supply device for a molding machine, as well as a raw material molding method, according to the second embodiment of the present invention. [Figure 5] FIG. 5 is a schematic diagram showing a raw material supply control method and a raw material supply device for a molding machine, as well as a raw material molding method, according to the third embodiment of the present invention. [Figure 6] FIG. 6 is a graph showing an example of the operating status of a molding machine by a raw material supply control method for a conventional molding machine. [Figure 7] FIG. 7 is a graph showing an example of the operating status of a molding machine by the raw material supply control method for the molding machine of the present invention. [Figure 8] FIG. 8 is a schematic diagram showing the structure of a molding machine. [Figure 9] FIG. 9 is a flowchart showing an example of overload prevention control in a conventional molding machine.

Embodiments for Carrying Out the Invention

[0015] Hereinafter, embodiments of the raw material supply control method, the raw material supply device, and the raw material molding method for a molding machine of the present invention will be specifically described with reference to the drawings. (First Embodiment) FIG. 1 schematically shows a raw material supply control method and a raw material supply device for a molding machine, as well as a raw material molding method, according to the first embodiment of the present invention. Also, FIGS. 2 and 3 show the processing flow of the raw material supply control method for the molding machine of the first embodiment.

[0016] The raw material supply control method, raw material supply device, and raw material forming method of the first embodiment are applicable to a molding machine that processes raw materials such as waste plastic and urethane into molded products, specifically pellet-shaped RPF (Refuse Paper & Plastic Fuel). As shown in FIG. 1, the molding machine 5 includes a receiving portion 51 for receiving raw materials, a face plate 52 having a nozzle 52h through which the raw materials are extruded, and a pushing mechanism 53 for pushing the raw materials from the receiving portion 51 into the face plate 52. The pushing mechanism 53 is provided inside the receiving portion 51. In this embodiment, the pushing mechanism 53 is composed of a screw conveyor, but it is not limited to this as long as it has the function of pushing the raw materials from the receiving portion 51 into the face plate 52. The molding machine 5 pushes the raw materials accommodated in the receiving portion 51 into the face plate 52 having the heated nozzle 52h by the pushing mechanism 53, and extrudes the raw materials from this nozzle 52h to form RPF.

[0017] The raw material supply device 1A of the first embodiment is a device that supplies raw materials to the above-described molding machine 5, and includes a supply conveyor 13, a motor 14, an inverter 15, and a raw material supply control device 2. The supply conveyor 13 conveys the raw materials supplied to the receiving portion 51 of the molding machine 5 and is driven by the motor 14. The rotational speed of the motor 14, that is, the speed of the supply conveyor 13, is controlled by the inverter 15.

[0018] The raw material supply control device 2 has a control unit 21 that feedback-controls the supply amount of the raw materials to the molding machine 5 by sample PI control so that the load of the pushing mechanism 53 is within a predetermined range when the load of the pushing mechanism 53 is outside the predetermined range. Sample PI control is a control method in which PI control is executed only for a part of the sample period, for example, about 1 / 5 to 1 / 20 of the sample period, and the control value is maintained for the remaining time of the sample period, and intermittent control is repeated.

[0019] In raw material supply control in a molding machine, there is a long delay between changing the raw material supply amount (the control value) and the resulting change in the load of the molding machine's indentation mechanism (the measured value). Therefore, in this embodiment, sample PI control is employed to control the raw material supply amount to the molding machine 5, and the sample cycle is set to exceed the aforementioned delay time. This makes it possible to control the load of the molding machine's indentation mechanism more easily and reliably compared to using general methods such as PID control.

[0020] Specifically, as shown in Figure 2, the current value of the motor 54 of the pushing mechanism (screw conveyor) 53 of the molding machine 5 is taken as the measured value (PV), and the speed of the supply conveyor 13, i.e., the rotational speed of the motor 14, is taken as the control value (MV). The rotational speed of the motor 14, which is the control value, is then controlled so that the measured value, the current value of the motor 54, stabilizes at the set value (SV).

[0021] The setting value is preferably set to a value of 80-100% of the rated current of the motor 54. This prevents the molding machine 5 from becoming overloaded, even if there are variations in the amount and properties of the raw materials supplied to the molding machine 5, and allows it to operate stably and continuously.

[0022] Furthermore, it is preferable to control the rotational speed of the motor 14, which is the control value, within a predetermined range above and below a preset reference value, for example, within a range of 80 to 120% of the reference value. This prevents sudden changes in the speed of the supply conveyor 13.

[0023] When the raw material is waste plastic, it is preferable that the sample period for sample PI control be 4.0 to 6.0 seconds, the gain of the measured value be 4.0 to 6.0, and the integration time (I) be 80.0 to 120.0 seconds. When the raw material is urethane, it is preferable that the sample period for sample PI control be 16.0 to 24.0 seconds, the gain of the measured value (PV) be 2.4 to 3.6, and the integration time (I) be 40.0 to 60.0 seconds.

[0024] Furthermore, as shown in Figure 3, in addition to the feedback control described above, the control unit 21 may also control the amount of raw material supplied to the receiving section 51 of the molding machine 5 by feedforward control based on the physical characteristics of the raw material. Here, the physical characteristics of the raw material refer to properties such as weight, bulk density, and color. When performing feedforward control based on the physical characteristics of the raw material, a sensor or camera (not shown) for acquiring properties such as weight, bulk density, and color of the raw material is appropriately installed on the supply conveyor 13 of the raw material supply device 1A. The data acquired by this sensor or camera is then input to the control unit 21 of the raw material supply control device 2 and used for feedforward control. Specifically, for example, feedforward control is performed so that the rotation speed of the motor 14 is reduced when the weight or bulk density of the raw material is large, and the rotation speed of the motor 14 is increased when the weight or bulk density of the raw material is small. Alternatively, feedforward control is performed to change the rotation speed of the motor 14 by determining the weight or bulk density of the raw material from its color.

[0025] In this embodiment, the raw material supply control device 2 is composed of a general-purpose computer such as a PLC (Programmable Logic Controller). The control unit 21 of the raw material supply control device 2 is realized by setting a program on the PLC that can execute the control described above. The calculation time for the control value by the PLC, i.e., the rotational speed of the motor 14, is, for example, about 10 to 20 milliseconds.

[0026] In the raw material supply control method, raw material supply device, and raw material molding method of this embodiment, the amount of raw material supplied can be controlled simply and reliably with relatively little computation. Therefore, there is no need to use a large computer such as a DCS (Distributed Control System), and the amount of raw material supplied can be controlled using a general-purpose computer such as a PLC (Programmable Logic Controller).

[0027] As described above, the raw material supply control method to the molding machine in this embodiment is achieved by controlling the amount of raw material supplied to the molding machine 5 so that the load on the pressing mechanism 53 of the molding machine 5, when it is outside a predetermined range, comes within a predetermined range.

[0028] Furthermore, the raw material molding method of this embodiment is realized by applying the raw material supply control method described above to the molding of raw materials by the molding machine 5. (Second Embodiment) Figure 4 schematically shows a raw material supply control method and raw material supply device to a molding machine, as well as a raw material molding method, according to a second embodiment of the present invention.

[0029] The raw material supply device 1B of the second embodiment is configured similarly to the raw material supply device 1A of the first embodiment, but lacks the supply conveyor 13, motor 14, and inverter 15. Instead, it is provided with a raw material storage hopper 11 and a supply damper 12. Raw materials are then directly supplied from the raw material storage hopper 11 to the receiving section 51 of the molding machine 5. In other respects, the raw material supply device 1B of the second embodiment is configured similarly to the raw material supply device 1A of the first embodiment.

[0030] The raw material storage hopper 11 stores the raw materials that are supplied to the receiving section 51 of the molding machine 5. The supply of raw materials from the raw material storage hopper 11 to the receiving section 51 of the molding machine 5 is controlled by the opening and closing operation of the supply damper 12 located at the bottom of the raw material storage hopper 11.

[0031] In the second embodiment, the amount of raw material supplied to the molding machine 5 is controlled in the same manner as in the first embodiment. That is, as shown in Figures 2 and 3, the current value of the motor 54 of the pushing mechanism (screw conveyor) 53 of the molding machine 5 is used as the measured value (PV), and the opening degree of the supply damper 12 is used as the control value (MV). Then, the opening degree of the supply damper 12 and the raw material storage level in the raw material storage hopper 11 are controlled so that the measured value, the current value of the motor 54, stabilizes at the set value (SV). (Third embodiment) Figure 5 schematically shows a raw material supply control method and raw material supply device to a molding machine, as well as a raw material molding method, according to a third embodiment of the present invention.

[0032] The raw material supply device 1C of the third embodiment is configured similarly to the raw material supply device 1A of the first embodiment, but in addition to the supply conveyor 13, motor 14, and inverter 15, it is also equipped with a raw material storage hopper 11 and a supply damper 12. Raw materials are supplied from the raw material storage hopper 11 to the receiving section 51 of the molding machine 5 via the supply conveyor 13. In other respects, the raw material supply device 1C of the third embodiment is configured similarly to the raw material supply device 1A of the first embodiment.

[0033] In the third embodiment, the amount of raw material supplied to the molding machine 5 is controlled in the same manner as in the first and second embodiments. That is, as shown in Figures 2 and 3, the current value of the motor 54 of the pushing mechanism (screw conveyor) 53 of the molding machine 5 is taken as the measured value (PV), and the rotational speed of the motor 14 of the supply conveyor 13 and the opening degree of the supply damper 12 are taken as the control values ​​(MV). The rotational speed of the motor 14 and the opening degree of the supply damper 12, which are the control values, are controlled so that the measured value, the current value of the motor 54, stabilizes at the set value (SV). [Examples]

[0034] The effectiveness of the present invention was verified by applying the raw material supply control method to a molding machine of the present invention to an actual molding machine and conducting a raw material supply control test. In this test, as shown in Figure 1, the raw material supply device 1A was assumed to have a supply conveyor 13, a motor 14, an inverter 15, and a raw material supply control device 2. As shown in Figure 2, the current value of the motor 54 of the pushing mechanism (screw conveyor) 53 of the molding machine 5 was used as the measured value (PV), and the speed of the supply conveyor 13, i.e., the rotational speed of the motor 14, was used as the control value (MV). The results of this test will be explained in comparison with the results obtained using a conventional raw material supply control method for a molding machine.

[0035] Figure 6 shows the operation of a molding machine using a conventional raw material supply control method. Figure 7 shows the operation of a molding machine using the raw material supply control method of the present invention. The test results shown in Figures 6 and 7 were obtained using a raw material supply device 1A, a raw material supply control device 2, and a molding machine 5 having the same configuration as the first embodiment described above. In this test, urethane was used as the raw material supplied to the molding machine 5.

[0036] In Figures 6 and 7, the lines that vibrate up and down in small increments represent the current values ​​of the pushing mechanism (screw conveyor) 53, and the stepped lines or smooth curves represent the measured rotational speeds of the motor 14.

[0037] As shown in Figure 6, in an example where a conventional raw material supply control method to a molding machine was applied, feedback control of the amount of raw material supplied to the molding machine was performed using step-like control. Specifically, when the measured value, the current value of the motor 54 of the pushing mechanism (screw conveyor) 53, exceeded the set value (SV) 260A + 5A for 45.0 seconds or more, the rotational speed of the motor 14, which is the control value, was reduced by 1.5 Hz. Also, when the current value of the motor 54 of the pushing mechanism (screw conveyor) 53 fell below the set value (SV) 260A - 5A for 45.0 seconds or more, the rotational speed of the motor 14 was increased by 1.5 Hz. Furthermore, considering the case where the deceleration control of the motor 14 could not keep up, rapid deceleration control of the motor 54 was also implemented. That is, when the current value of the motor 54 of the pushing mechanism (screw conveyor) 53 exceeded the set value 260A + 5A for 120 seconds or more, the rotational speed of the motor 14 was reduced by 20 Hz.

[0038] Furthermore, as shown in Figure 7, in an example where the raw material supply control method to a molding machine of the present invention was applied, feedback control of the amount of raw material supplied to the molding machine was performed by sample PI control. The sample period for sample PI control was 20 seconds, the gain of the measured value (PV) was 3.0, and the integration time (I) was 50.0 seconds.

[0039] As shown in Figure 6, in the conventional method of controlling the supply of raw materials to the molding machine, there were instances where the control of the amount of raw materials supplied to the molding machine 5 could not keep up, and the current value of the pushing mechanism (screw conveyor) 53 could not be stably controlled. Specifically, as shown in Figure 6, at an elapsed time of 16 minutes, the rotational speed of the motor 14 reached its upper limit of 60 Hz, and at an elapsed time of 20 minutes, the rotational speed of the motor 14 was reduced to 30 Hz by manual intervention. After that, the rotational speed of the motor 14 continued to increase until an elapsed time of 36 minutes, and at an elapsed time of 39 minutes, the rotational speed of the motor 14 was reduced by manual intervention. Then, at an elapsed time of 41 minutes, 120 seconds after this manual intervention, the aforementioned rapid deceleration control was activated, and the rotational speed of the motor 14 was reduced to 20 Hz and then to 30 Hz. Thus, with step control, the speed increase control of the motor 14 could be followed, but it could not cope with the length of the delay time between the control of the amount of raw material supplied and the reflection of the current value of the motor 54 of the pushing mechanism (screw conveyor) 53. As a result, the rotational speed of motor 14 tended to be increased too much, and the deceleration control of motor 14 could not keep up when the current value of motor 54 of the pushing mechanism (screw conveyor) 53 exceeded the set value, resulting in frequent manual intervention.

[0040] In contrast, as shown in Figure 7, the raw material supply control method for the molding machine of the present invention allows for continuous and appropriate control of the raw material supply amount to the molding machine 5, and it was confirmed that the current value of the pushing mechanism (screw conveyor) 53 can be stably controlled. Specifically, from 20 to 35 minutes of elapsed time, while the current value of the motor 54 of the pushing mechanism (screw conveyor) 53 was increasing, the rotational speed of the motor 14 was reduced to around 25 Hz. Then, the rotational speed of the motor 14 was maintained at around 25 Hz until the current value of the motor 54 of the pushing mechanism (screw conveyor) 53 decreased. As a result, the rotational speed of the motor 14 stabilized at around 30 Hz. Thus, the sample PI control was able to address the length of the delay time between the control of the raw material supply amount and its reflection in the current value of the motor 54 of the pushing mechanism (screw conveyor) 53. Furthermore, the tendency to increase the rotational speed of the motor 14 too much, as seen in step control, was also improved.

[0041] The reason why the rotational speed of motor 14 in the test results shown in Figure 7 is lower than that of motor 14 in the test results shown in Figure 6 is due to the difference in the materials used in the raw materials in the two tests. If the same raw materials as those used in the test example shown in Figure 6 were used in the test example shown in Figure 7, the rotational speed of motor 14 in the test results shown in Figure 7 would be around 45 Hz, the same level as the rotational speed of motor 14 in the test results shown in Figure 6. [Explanation of Symbols]

[0042] 1A~1C Raw material supply device 11. Raw material storage hopper 12 Supply damper 13. Supply conveyor 14 motors 15 Inverter 2. Raw material supply control device 21 Control Unit 5 Molding machine 51 Receptor part 52 face plate 52h nozzle 53. Screw conveyor (pushing mechanism) 54 Motor

Claims

1. A receiving section for receiving raw materials, A faceplate having a nozzle from which the raw material is extruded, A pushing mechanism for pushing the raw material from the receiving portion to the faceplate, A method for controlling the supply of raw materials to a molding machine equipped with the following: A raw material supply control method that, when the load of the pressing mechanism is outside a predetermined range, provides feedback control of the amount of raw material supplied to the molding machine by sample PI control so that the load is within the predetermined range.

2. The raw material supply control method according to claim 1, further comprising controlling the amount of raw material supplied to the receiving unit by feedforward control based on the physical characteristics of the raw material, in addition to the feedback control described above.

3. A receiving section for receiving the aforementioned raw materials, A faceplate having a nozzle from which the raw material is extruded, A pushing mechanism for pushing the raw material from the receiving portion to the faceplate, A raw material supply device that supplies raw materials to a molding machine equipped with the following: A raw material supply device having a control unit that, when the load of the pressing mechanism is outside a predetermined range, feedback controls the amount of raw material supplied to the molding machine by sample PI control so that the load is within the predetermined range.

4. The raw material supply device according to claim 3, wherein the control unit controls the amount of raw material supplied to the receiving unit by feedforward control based on the physical characteristics of the raw material, in addition to the feedback control.

5. A receiving section for receiving raw materials, A faceplate having a nozzle from which the raw material is extruded, A pushing mechanism for pushing the raw material from the receiving portion to the faceplate, A method for molding raw materials, comprising molding the raw materials using a molding machine equipped with the following: A raw material molding method comprising, when the load of the pressing mechanism is outside a predetermined range, feedback control of the amount of raw material supplied to the receiving part by sample PI control so that the load is within the predetermined range.

6. The raw material molding method according to claim 5, further comprising controlling the amount of raw material supplied by feedforward control based on the physical properties of the raw material supplied to the receiving unit, in addition to the feedback control described above.

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