JP2001239564A - Controller for injection molding machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize and enhance an accuracy of an overall pressure control by preventing a generation of a surge pressure or hunting. SOLUTION: A part or the entirety of a molding step is partitioned according to a magnitude of a pressure value and (or) a pressure change rate. A filter constant switching circuit 4 for setting a cut-off frequency of a noise filter 3 to a high value in the partition having a large pressure value and (or) pressure change rate and setting the frequency to a low value in the partition having a small pressure value and (or) pressure change rate is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an injection molding machine having a pressure control system for performing pressure feedback control.

[0002]

2. Description of the Related Art In general, a control device of an injection molding machine controls an injection pressure, a back pressure and the like based on a pressure detection value obtained from a detection signal detected from a pressure detector such as a load cell and a preset pressure command value. A pressure control system for performing feedback control on pressure is provided (Japanese Patent Publication No. 7-6772).
No. 0).

In the case of this type of control device, since a detection signal obtained from a pressure detector (load cell) is superimposed with noise generated from a driving servomotor or the like, the detection signal is subjected to a noise filter (in this specification, a noise filter). The noise is removed through a low-pass filter.

However, when a noise filter is used, a delay occurs between the input value and the output value of the noise filter based on the filter constant, so that the pressure value actually generated and the pressure value obtained from the noise filter are delayed. In particular, in a region where high responsiveness is required, such as in an injection process, there has been a problem that a surge pressure significantly exceeding a command value is generated or hunting occurs.

The present invention has been made to solve the problems existing in the prior art, and can prevent the occurrence of surge pressure and hunting, thereby stabilizing the entire pressure control and improving the accuracy. An object of the present invention is to provide a control device for an injection molding machine.

[0006]

According to the present invention, a detection signal So detected by a pressure detector 2 is passed through a noise filter 3 to obtain a pressure detection value Sd, and this pressure detection value Sd is set in advance. When configuring the control device 1 of the injection molding machine M having the pressure control system Cp for performing the pressure feedback control based on the pressure command value Sc, a part or all of the molding process is performed using the pressure value and / or the pressure change rate. The section is classified according to the size. In the section where the pressure value and / or the pressure change rate is large, the cutoff frequency of the noise filter 3 is set high, and in the section where the pressure value and / or the pressure change rate is small, the cutoff frequency is set. Is provided with a filter constant switching circuit 4 for setting a low value.

In this case, according to a preferred embodiment, a load cell 2s can be applied to the pressure detector 2. Further, a section having a large pressure value and / or a rate of change in pressure can be applied to the injection step, and a section having a small pressure value and / or a rate of change in pressure can be applied to the measuring step.

Accordingly, in a section where the pressure value and the pressure change rate are relatively large, such as in an injection step, the cutoff frequency of the noise filter 3 is set high by the filter constant switching circuit 4, so that the surge pressure is reduced. The generation and hunting are prevented, and the cutoff frequency of the noise filter 3 is set low by the filter constant switching circuit 4 in a section where the pressure value and the pressure change rate are relatively small, such as in a measuring step. The control is stabilized and the accuracy is improved.

[0009]

Next, preferred embodiments of the present invention will be described in detail with reference to the drawings.

First, the configuration of an injection molding machine M provided with a control device 1 according to the present embodiment will be described with reference to FIG.

An injection molding machine M shown in FIG. 1 shows only an injection device Mi without a mold clamping device. The injection device Mi includes an injection table 11 and a drive table 12 which are separated from each other. The front end of the injection table 11 supports the rear end of the heating cylinder 13. Heating cylinder 13
Has an injection nozzle 14 at the front end, a hopper 15 at the rear to supply the molding material into the heating cylinder 13, and a screw 16 inserted through the heating cylinder 13. On the other hand, four tie bars 17 are provided between the injection table 11 and the drive table 12, and a slide block 18 is slidably mounted on the tie bars 17. A rotary block 20 integrally having a driven pulley 19 is rotatably supported at the front end of the slide block 18, and the rear end of the screw 16 is coupled to the center of the rotary block 20. Further, a servomotor 21 for screw rotation is mounted on the side surface of the slide block 18, and an endless timing belt 23 is stretched between a driven pulley 22 fixed to a rotating shaft of the servomotor 21 and the driven pulley 19 to rotate the screw. Drive mechanism.

On the other hand, at the rear of the slide block 18,
The nut portion 26 is coaxially and integrally provided, and
By screwing the front side of the ball screw portion 27 rotatably supported by the nut 2 to the nut portion 26, the ball screw mechanism 2
5 is constituted. On the other hand, a driven pulley 28 is mounted on the rear end of the ball screw portion 27 projecting rearward from the drive base 12, and a servo motor 29 for screw advance / retreat is mounted on a support plate 12s mounted on the drive base 12. An endless timing belt 31 is bridged between a driven pulley 30 fixed to a rotating shaft of the servomotor 29 and a driven pulley 28 to constitute a screw mechanism driving mechanism.

In FIG. 1, reference numeral 1 denotes a control device provided in the injection molding machine M, and particularly, a pressure control system Cp is extracted and shown. Reference numeral 2s denotes a load cell constituting the pressure detector 2, which detects the pressure applied to the screw 16 by being interposed between the rotary block 20 and the slide block 18. Reference numeral 4 denotes a filter constant switching circuit, which includes a changeover switch unit 35, a first filter unit 3a, and a second filter unit 3.
b is provided. The load cell 2s is connected to the common contact 35c of the changeover switch 35, the input of the first filter 3a is connected to the first contact 35a, and the input of the second filter 3b is connected to the second contact 35b. I do.

In this case, the first filter section 3a and the second filter section 3b each use a low-pass filter, and the filter constants of the first filter section 3a and the second filter section 3b are set as follows. First, the molding process is divided into two sections according to the magnitude of the pressure value and the pressure change rate. In the embodiment, the injection step (injection filling step) in which the pressure value and the pressure change rate are large and high responsiveness is required, and the measuring step (back pressure) in which the pressure value and the pressure change rate are small and high responsiveness is not so required Process). Then, the first filter unit 3a sets a filter constant having a low cutoff frequency suitable for the measuring step, and sets the second filter unit 3b
Sets a filter constant with a high cutoff frequency suitable for the injection process.

On the other hand, the output section of the first filter section 3a and the output section of the second filter section 3b are connected to the input side of the pressure control section 36, and the output side of the pressure control section 36 is connected to the servomotor 29. . Reference numeral 37 denotes a command unit. The command unit 37 applies a pressure command value Sc to the pressure control unit 36 and a switching control signal to the changeover switch unit 35.

Next, the operation (function) of the control device 1 according to the present embodiment will be described with reference to FIG. 1 and the flowchart of FIG.

First, in the weighing step, the changeover switch 35 is switched to the first contact 35a side by the command section 37 to perform weighing (steps S1 and S2). Therefore, in the measurement process, the first filter unit 3a in which a filter constant with a low cutoff frequency is set is used. In the weighing process, the screw 16 rotates to perform weighing by controlling the drive of the servomotor 21, and the back pressure control is performed by controlling the drive of the servomotor 29. The back pressure is detected by the load cell 2s, and the detection signal So detected by the load cell 2s is applied to the first filter unit 3a. From the first filter unit 3a, a pressure detection value Sd from which noise has been removed is obtained.
d is given to the input side of the pressure control unit 36. In the pressure control unit 36, the detected pressure value Sd and the pressure command value Sc given from the command unit 37 are compared and calculated, a deviation is obtained, and a control signal for canceling the deviation is generated. As a result, the drive of the servomotor 29 is controlled based on the control signal, and the feedback control for the back pressure is performed.

On the other hand, upon completion of the measuring process, the changeover switch unit 35 is switched to the second contact 35b by the command unit 37 (steps S3 and S4), and thereafter, the process proceeds to the injection process (step S5). In the injection step, the second filter unit 3 in which a filter constant with a high cutoff frequency is set
b is used. In the injection step, the drive of the servomotor 29 is controlled, and the screw 16 moves forward by the motion conversion by the ball screw mechanism 25. Thus, injection filling and holding pressure are performed. The injection pressure (including the holding pressure) is detected by the load cell 2s, and the detection signal So detected by the load cell 2s is applied to the second filter unit 3b.
The pressure detection value Sd from which noise has been removed is obtained from the second filter unit 3b, and the pressure detection value Sd is provided to the input side of the pressure control unit 36. In the pressure control unit 36,
The detected pressure value Sd and the pressure command value Sc given from the command unit 37 are compared and calculated, and a deviation is obtained, and a control signal for canceling the deviation is generated. As a result, the servo motor 29 is driven and controlled based on the control signal, and feedback control on the injection pressure is performed.

When the injection process is completed, the changeover switch unit 35 is again switched to the first contact 35a by the command unit 37 (steps S6 and S1). Thereafter, the process shifts to a weighing process, and thereafter, the same operation is repeated.

Therefore, according to the control device 1 of the present embodiment, in the injection step in which the pressure value and the pressure change rate are relatively large and high responsiveness is required, the second filter having a high cutoff frequency is set. Since the portion 3b is used, generation of surge pressure and hunting are prevented, and the pressure value and the rate of change of pressure are relatively small, and the cut-off frequency is set low in the weighing step where high response is not required. Since the first filter unit 3a is used, the pressure control is stabilized and the accuracy is improved.

The embodiment has been described in detail above.
The present invention is not limited to such an embodiment,
The detailed configuration, shape, method, and the like can be arbitrarily changed, added, or deleted without departing from the gist of the present invention. For example, although the embodiment shows the case where the injection step and the measurement step are divided, the injection step may be further divided into the injection filling step and the pressure holding step. In this case, the pressure change rate is large. It will be classified focusing on the degree. As described above, the classification may be performed based on either the pressure value or the pressure change rate. Further, although the embodiment shows the case where the cutoff frequency of the noise filter 3 is set to two high and low, three or more filter units 3a are provided by setting three or more cutoff frequencies. Good. Further, the noise filter 3 may be a digital filter or an analog filter, or may use a bandpass filter or the like. Note that the pressure detector 2 does not exclude use other than the load cell 2s.

[0022]

As described above, the control device of the injection molding machine according to the present invention classifies part or all of the molding process according to the pressure value and / or the magnitude of the pressure change rate, and In the section where the pressure change rate is large, the cutoff frequency of the noise filter is set high, and in the section where the pressure value and / or the pressure change rate is small, a filter constant switching circuit that sets the cutoff frequency low is provided. This has a remarkable effect that generation of surge pressure and hunting can be prevented, and that the entire pressure control can be stabilized and highly accurate.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a main part of a control device according to a preferred embodiment of the present invention;

FIG. 2 is a flowchart for explaining the operation (function) of the control device;

[Explanation of symbols]

 Reference Signs List 1 control device 2 pressure detector 2s load cell 3 noise filter M injection molding machine Cp pressure control system So detection signal Sd pressure detection value Sc pressure command value

Claims (4)

[Claims] 1. A pressure control system for obtaining a pressure detection value by passing a detection signal detected by a pressure detector through a noise filter, and performing pressure feedback control based on the pressure detection value and a preset pressure command value. In the control device of the injection molding machine, a part or the whole of the molding process is divided by the pressure value and / or the magnitude of the pressure change rate, and the section having the large pressure value and / or the pressure change rate is a section of the noise filter. A control apparatus for an injection molding machine, comprising: a filter constant switching circuit that sets a high cutoff frequency and sets a low cutoff frequency in a section where a pressure value and / or a pressure change rate is small. 2. A control device for an injection molding machine according to claim 1, wherein said pressure detector is a load cell. 3. The control device for an injection molding machine according to claim 1, wherein a section having a large pressure value and / or a pressure change rate is an injection step. 4. The control device for an injection molding machine according to claim 1, wherein the section having a small pressure value and / or a pressure change rate is a measuring step.