JP2992328B2 - Holding pressure control device of electric injection molding machine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a dwell control device for an electric injection molding machine.

(Prior art) Conventionally, a resin heated and fluidized in a heating cylinder is injected into a mold by high pressure, cooled and solidified or cured therein, and then the mold is opened to take out a molded product. In the injection molding machine, the resin is supplied into the heating cylinder while the screw is retracted in the measuring step. At this time, a back pressure is applied to the screw.

Also, when the resin is filled in the mold and the injection process is completed, subsequently, in order to replenish the shrinkage of the resin due to cooling,
The process enters a pressure holding step of maintaining the resin pressure at a set value.

FIG. 2 is a schematic view of a drive mechanism of a conventional electric injection molding machine.

In the figure, reference numeral 2 denotes an injection motor, and an output shaft 2A of the injection motor 2 is connected to a pulley 4. Pulley 4
Is connected to a pulley 6 via a timing belt 5. A ball screw 8 is integrally attached to the pulley 6, and a nut 10 meshes with the ball screw 8.

And the nut 10 is fixed to the plate 12,
The plate 12 is arranged movably in the direction of arrow A along the guide bar 14, and the screw position is detected by the screw position detector 15. The rotation speed of the injection motor 2 is detected by an injection motor speed detector 64.

Here, the plate 12 is integrated with the plate 18 via the load cell 16. A screw 20 is rotatably attached to the plate 18 so that it can move in the direction of arrow A along the guide bar 14 similarly to the plate 12.

The plate 18 has a screw rotation motor 22
The rotation generated by the screw rotation motor 22 is transmitted to the screw 20 via the pulley 24, the timing belt 26, and the pulley 28, and rotates the screw 20. The rotation speed of the screw rotation motor 22 is detected by a screw rotation motor speed detector 65.

Reference numeral 30 denotes a hopper, 32 denotes a resin (pellet), 34 denotes a heating cylinder, 36 denotes a molten resin immediately before the injection, and 38 denotes a nozzle portion from which the molten resin is injected.

 Next, the operation of this embodiment will be described.

During the weighing process, the screw 20 is rotated by the screw rotation motor 22 through the pulleys 24 and 28 and the timing belt 26 and retreats, whereby the resin (pellet) 32 supplied from the hopper 30 is melted and heated. Stored at 34 tips.

At this time, the pulley 4, the timing belt 5, the pulley 6, the ball screw 8,
A forward force, that is, back pressure, is applied via the nut 10, the plate 12, the load cell 16, and the plate 18. If the back pressure is an appropriate value, the screw 20 retreats and the molten resin 36 at the tip of the heating cylinder 34 increases sequentially.

The position of the screw 20 is detected by the screw position detector 15 detecting the position of the plate 12, and when the screw 20 retreats to a preset position, the screw rotation motor 22 and the injection motor 2 are stopped, The weighing process is completed.

Next, when the speed of the injection motor 2 is controlled according to the speed set value while the screw rotation motor 22 is controlled not to rotate, the screw 20 advances without rotating, and as a result, the molten resin 36 It is filled into a mold (not shown) from the nozzle portion 38.

Then, when the detected value of the load cell 16 disposed between the plates 12 and 18 exceeds the set value, filling is completed and the pressure holding process is started, so that the output of the load cell 16 becomes equal to the set value of the pressure holding. The injection motor 2 is controlled.

FIG. 3 is a control block diagram of a conventional pressure holding control device of an electric injection molding machine.

In the figure, reference numeral 2 denotes an injection motor, and reference numeral 16 denotes a load cell for detecting a pressure changed by displacement of the screw 20 after filling is completed. The detected pressure value detected by the load cell 16 is fed back to a subtractor 71, which compares the detected pressure value with a set pressure value, and supplies a deviation to a compensator 72.

The result of the compensation operation in the compensator 72 is given to the servo amplifier 62 as a speed command. The servo amplifier 62 drives the injection motor 2 so that the speed command is equal to the speed detection voltage value (controls the amount of armature current).
Then, the screw 20 is moved forward and backward.

As a result, the screw 20 compresses the resin in the heating cylinder 34, and the reaction force is detected by the load cell 16 as a pressure detection value. Then, control is performed so that the detected pressure value is equal to the set pressure value.

(Problems to be Solved by the Invention) However, in the conventional pressure holding control device for an electric injection molding machine, when a pressure set value is changed, an overshoot occurs or a large normal deviation remains. Not preferred.

FIG. 4 is a diagram showing a set value waveform and a detected value waveform in the pressure holding step.

During the injection process, a pressure waveform determined by the injection temperature and the load pressure is shown. However, when the pressure-holding process is started, the pressure control is started as described above. Deviations remain.

Therefore, if the gain is increased in order to reduce the steady-state deviation and increase the response, the system becomes unstable in a transient state due to the influence of the nonlinearity of the system and the like, causing vibration and overshoot.

On the other hand, if the gain is reduced to avoid overshoot, the response will be slow and the steady-state error will increase.

The present invention solves the above-described problems of the pressure holding control device of the conventional electric injection molding machine, and can suppress occurrence of overshoot at a change point of the pressure set value in the pressure holding step, and can reduce the steady-state deviation. It is an object of the present invention to provide a pressure holding control device of an electric injection molding machine capable of reducing the pressure.

(Means for Solving the Problems) For this purpose, in the pressure holding control device for an electric injection molding machine according to the present invention, a load cell for detecting a resin pressure and a pressure setting having a step-like waveform by inputting a set value are provided. A setting input device for generating a value, a pattern generator for receiving the pressure setting value sent from the setting input device, deforming the step-like waveform and generating a pressure command value having a first-order lag waveform, and the load cell A compensator for generating a speed command based on a deviation between a pressure detection value of the resin pressure detected by the above-described method and a pressure command value having a first-order lag waveform generated by the pattern generator; And an injection motor driven in accordance with a given speed command.

(Action) According to the present invention, as described above, in the pressure holding control device of the electric injection molding machine, the load cell for detecting the resin pressure and the pressure set value having the step-like waveform by inputting the set value are input. A setting input device to generate, a pattern generator for receiving the pressure set value sent from the setting input device, changing the step-like waveform, and generating a pressure command value having a first-order lag waveform, and detecting by the load cell A compensator that generates a speed command based on a deviation between the detected pressure of the resin pressure and a pressure command value having a first-order lag waveform generated by the pattern generator.
An injection motor driven according to a speed command sent from the compensator.

In this case, in the transient state when the pressure set value rises in steps and falls, the pressure command value and the pressure detection value become substantially equal, and the influence of nonlinearity can be ignored.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of a pressure holding control device of the electric injection molding machine of the present invention, and FIG. 5 is a circuit diagram of a pressure holding control device of the electric injection molding machine of the present invention.

In FIG. 5, 2 is an injection motor, 14 is a screw position detector, 16 is a load cell for detecting resin pressure,
50 is a CPU, 52 is a setting input device for inputting set values such as screw position and pressure, 54 is a ROM, 56 is a RAM, 58 is a screw position input interface, 60 is a D / A converter, and 62 is an injection A servo amplifier for driving the motor 2, 64 is a speed detector for detecting the speed of the injection motor 2, and 66 is an A / D converter.

In FIG. 1, reference numeral 2 denotes an injection motor, and reference numeral 16 denotes a load cell for detecting a pressure changed by displacement of the screw 20 (see FIG. 2) after filling is completed.
The detected pressure value detected by the load cell 16 is fed back to a subtractor 71, which compares the detected pressure value with the pressure command value sent from the pattern generator 74.
Supplied to 72.

The result of the compensation operation in the compensator 72 is given to the servo amplifier 62 as a speed command. The servo amplifier 62 drives the injection motor 2 so that the speed command is equal to the speed detection voltage value (controls the amount of armature current).
Then, the screw 20 is moved forward and backward.

As a result, the screw 20 compresses the resin in the heating cylinder 34, and the reaction force is detected by the load cell 16 as a pressure detection value. Then, control is performed so that the detected pressure value is equal to the set pressure value.

The pressure command value supplied to the subtractor 71 is generated by a pattern generator 74,
The pressure set value is input to the.

The pattern generator 74 constitutes a kind of filter, and transforms a waveform of a pressure set value set in a step-like manner by a pressure program such as a dwell pressure setting program or a back pressure setting program into a first-order lag waveform.

FIG. 6 is a diagram showing a pressure set value and a pressure command value set by the holding pressure control device of the electric injection molding machine according to the present invention.

The pressure set value is set in steps by the pressure program, whereas the waveform of the pressure command value output from the pattern generator 74 (FIG. 1) is a first-order lag waveform.

In the step input waveform in the conventional pressure holding control device of the electric injection molding machine, since the system cannot follow the set value, a large deviation occurs transiently, which causes the influence of the nonlinearity of the system. Vibration.

In the pressure holding control device of the electric injection molding machine of the present invention,
If the parameters are set appropriately and the rise speed is within the range that can be physically followed, the finger cooling value and the detected value will be almost equal even in the transient state, and the effect of nonlinearity will be reduced. Can be ignored.

Therefore, it is possible to increase the gain,
A good response waveform can be obtained without leaving a steady deviation.

It should be noted that the present invention is not limited to the above embodiment, and various modifications are possible based on the gist of the present invention.
They are not excluded from the scope of the present invention.

(Effects of the Invention) As described in detail above, according to the present invention, in a pressure-holding control device for an electric injection molding machine, a load cell for detecting a resin pressure and a step-like waveform are inputted by inputting a set value. A setting input device for generating a pressure set value having: a pattern generator for receiving the pressure set value sent from the setting input device, deforming the step-like waveform, and generating a pressure command value having a first-order lag waveform A compensator that generates a speed command based on a deviation between a pressure detection value of the resin pressure detected by the load cell and a pressure command value having a first-order lag waveform generated by the pattern generator. An injection motor driven in accordance with the speed command sent from the compensator.

In this case, since the speed command is generated based on the pressure command value having the first-order lag waveform, even if the pressure set value generated by the setting input device rises or falls in a step shape, the speed command is generated. The effect of the added nonlinearity can be neglected. Therefore, it is possible to suppress the occurrence of overshoot at the pressure set value change point in the pressure holding step, and to reduce the steady-state deviation, thereby improving the quality of the molded product.

[Brief description of the drawings]

FIG. 1 is a block diagram of a pressure-holding control device of an electric injection molding machine according to the present invention, FIG. 2 is a schematic diagram of a driving mechanism of a conventional electric injection molding machine, and FIG. FIG. 4 is a diagram showing a set value waveform and a detected value waveform in a pressure holding process, FIG. 5 is a circuit diagram of a pressure holding control device of the electric injection molding machine of the present invention, and FIG. It is a figure which shows the pressure set value and the pressure command value set by the pressure holding control device of the electric injection molding machine of the present invention. 2. Injection motor, 16 Load cell, 62 Servo amplifier, 71 Subtractor, 72 Compensator, 73 Speed detector, 74 Pattern generator

Continued on the front page (58) Fields surveyed (Int.Cl. ⁶ , DB name) B29C 45/57 B29C 45/76-45/77 B29C 45/46-45/50 G05B 13/00-13/02

Claims (1)

(57) [Claims] (A) a load cell for detecting a resin pressure; (b) a setting input device for generating a pressure setting value having a step-like waveform by inputting a setting value; and (c) the setting input device. A pattern generator for receiving the pressure set value sent from the above and deforming the step-like waveform to generate a pressure command value having a first-order lag waveform; and (d) a pressure detection value of the resin pressure detected by the load cell. A compensator for generating a speed command based on a deviation from a pressure command value having a first-order lag waveform generated by the pattern generator; and (e) driven in accordance with the speed command sent from the compensator. A pressure holding control device for an electric injection molding machine, comprising: an injection motor.