JP2539017B2 - Screw rotation control device of injection molding machine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an apparatus for controlling a screw rotation of an injection molding machine in accordance with resin characteristics.

(Prior Art) An inverter is used when the screw is rotationally driven by using an induction motor, and an example of the rotational speed control will be described with reference to FIGS. 2 and 3.

The screw rotation in the plasticizing step of the injection molding machine operates as follows.

The hopper 6 stores granular resin pellets 8. The screw 1 is rotationally driven by an induction motor 4 via a speed reducer having an appropriate speed reduction ratio. The rotation speed command at this time is given from the control device 10 to the inverter 11, and the rotation speed of the induction motor 4 is proportional to the rotation speed command.
It is controlled by the frequency control. The resin pellet 8 is heated by shearing due to the rotation of the screw 1 and by the band heater 5 wound around the screw cylinder 2,
The molten resin is transferred to the front while being melted, and an amount of molten resin required for one injection is stored in the screw front portion A. The molten resin is injected into a mold (not shown) from the nozzle 3 at the tip of the screw cylinder 2 by advancing the screw 1 by a hydraulic cylinder (not shown) or the like, where it is cooled and solidified to form a molded product.

Incidentally, in controlling an induction motor by an inverter, generally, as shown in FIG. 3, a "constant torque region" in which a generated torque is constant regardless of a frequency and a torque x frequency = constant "is constant. Constant horsepower area ". The frequency at this boundary is called the base frequency.
Conventionally, the maximum frequency of operation was held internally as a fixed constant, and it was not possible for the user to easily change it.

(Problems to be Solved by the Invention) In general, most of injection molding machines are general-purpose machines, and accordingly, the resins used are also diversified, and light-load resins (for example, PS resins) to heavy-load resins (for example, , PC resin), and the same molding machine is used, and the rotation speed is wide ranging from high speed to low speed.

Now, in consideration of the above characteristics of the induction motor by the frequency control of the inverter, if various resins having different load characteristics are handled by using the same injection molding machine, the following problems will occur.

That is, considering that the maximum frequency of operation is the base frequency, that is, when the operation is designed to be performed in the constant torque region, considering that the light load resin generally drives the screw rotation at high speed. On the other hand, if a large reduction ratio is used and a torque capable of operating with a heavy load resin is to be secured, it is inevitable that the electric motor and the inverter must be increased in size, and space and economy are reduced. Be at a disadvantage.

In addition, to avoid this, when designing by expanding the maximum operating frequency to the constant horsepower range that enables high-speed rotation, the torque will be reduced for light load resin, but when you design heavy load resin, Makes the overcurrent protection of the inverter easy to work, which makes it extremely difficult for the operator to handle.

SUMMARY OF THE INVENTION The present invention eliminates these points, and aims to provide a control device capable of controlling the screw rotation speed and torque adapted to different molding conditions by manual switch switching.

(Means for Solving the Problems) Therefore, the present invention is a screw rotation control device for driving the screw rotation of an injection molding machine by an induction motor controlled through an inverter, and the operating frequency of the induction motor is a base frequency. Input a selection switch that can be arbitrarily selected within the above constant horsepower range and a constant torque range below the base frequency, and a selection signal of the selection switch, and output a frequency command signal according to the resin characteristics based on the same signal. A control device,
A screw rotation control device for an injection molding machine, comprising an inverter that receives a frequency command signal from the control device and outputs a frequency corresponding to the signal,
This is to solve the above-mentioned problem.

(Operation) The selection switch is operated according to the load characteristics of the resin used for actual molding to specify a constant horsepower region above the base frequency or a constant torque region below it, and select an operating frequency within each region.

When the selection switch is operated, the area information and the operating frequency information are sent to the control device. The control device calculates the frequency command voltage value based on each of the above information and outputs it to the inverter. The inverter controls the rotation of the induction motor at an operating frequency based on the voltage value.

That is, in the present invention, by simply operating the selection switch, the screw rotation is automatically controlled, for example, at a proper rotation speed within a constant torque region where the heavy load resin has a high torque, but the speed slows down to some extent. Although the torque is small for the load resin, the screw rotation is controlled at an appropriate rotation speed within the constant horsepower range where high-speed operation is possible.

(Example) Hereinafter, the Example of this invention is described based on drawing.

FIG. 1 shows a control block diagram which is a typical embodiment of the present invention. The general description of the screw rotation driving method by the inverter of the injection molding machine is the same as the conventional one, so that the description is omitted here.

By the way, the present invention has a drawback of the prior art as described above, "Injection molding machines use a wide variety of resins,
If the screw rotation is to be applied to a wide range of resins that have different characteristics within the constant torque range below the base frequency, the motor and inverter must be made larger, and if this is avoided, overcurrent protection will work. It becomes easier and the molding cycle time becomes longer. It is to eliminate the point.

Therefore, according to the present invention, the frequency range of high speed / medium torque or medium speed / high torque corresponding to the load characteristics is selected by operating the select switch within a range in which the overcurrent protection circuit of the inverter does not work, and the rotation speed of the screw is selected. And, the torque is adapted to various resins and controlled to rationalize the molding cycle.

That is, the manual switch 12 is switched according to the load condition depending on the type of resin, and the "high speed / medium torque" selects the constant horsepower region higher than the base frequency in FIG. Is to select a constant torque region lower than the base frequency in FIG.

When the manual switch 12 is operated, the frequency command value e _≠ the frequency command value e _≠ the control device 10 according to the selection of the switch is set in the inverter 11 by the controller 10.
It is input according to (an integer from 0 to 99). The operating frequency f _≠ is given to the induction motor 4 from the inverter 11 in proportion to the frequency command voltage e _≠ , and the electric motor 4 rotates at a rotation speed proportional to the operating frequency f _≠ .

In other words, the operating frequency f _≠ and the frequency command voltage e _≠ have a relationship of f _≠ = 10 · e _≠ If the maximum value (f ₀ ) of the operating frequency f _≠ 100 Hz, the maximum value e of the frequency command voltage e _{≠ 0} becomes _{e 0 = f 0/10 =} 100/10 = 10 [V].

Further, the frequency command value P set by the setter 13 and the frequency command voltage e _≠ have a relationship of e _≠ = f _x · P / 990.

f _x is the frequency selected by the manual switch 12, the maximum operating frequency is 100 Hz in “High speed / medium torque”, and the base frequency that is the maximum operating frequency in this area in “Medium speed / high torque” It becomes 60 Hz which is f _b .

Note that the constant 990 of e _≠ = f _× P / 990 has two digits in the setter 13, and the maximum display is related to 99.

Therefore, now the manual switch 12
Select the middle torque ", setting the setting device 13 to the maximum (99%), the frequency command voltage _{e 1 = 100 × 99/990} = 10 [V]
The operating frequency is 100Hz.

If you select the manual switch 12, that is, "medium speed / high torque", and set the setter 13 to the maximum (99)%,
The frequency command voltage is e ₂ = 60 × 99/990 = 6 [V], and the operating frequency is 60 Hz which is the base frequency.

In this way, when "high speed / medium torque" of the manual switch 12 is selected, operation up to 100 Hz is possible, and when "medium speed / high torque" of the switch 12 is selected, the maximum base frequency is Operation up to 60Hz is possible.

(Effects of the Invention) As described above in detail, according to the present invention, the optimum maximum operating frequency of the inverter according to the load characteristics of the resin is automatically determined only by manually operating the selection switch. It becomes an easy-to-use machine without overcurrent protection.

Further, according to the present invention, "medium load / high speed" and "heavy load / medium speed" can be roughly classified, and each can be designed with a different idea, so that the motor and the inverter can be downsized.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a screw rotation drive unit according to a typical embodiment of the present invention, FIG. 2 is a configuration diagram showing a conventional screw rotation drive unit, and FIG. 3 is a frequency and torque in inverter control of an induction motor. It is a characteristic diagram which shows the relationship of. Description of the main parts of the figure 1 …… Screw 4 …… Induction motor 10 …… Control device 11 …… Inverter 12 …… Manual switch 13 …… Setting device

Claims (1)

(57) [Claims] 1. A screw rotation control device for driving a screw rotation of an injection molding machine by an induction motor controlled through an inverter, wherein an operating frequency of the induction motor is within a constant horsepower region above a base frequency and below a base frequency. Of the selection switch that can be arbitrarily selected within the constant torque range of, the control device that inputs the selection signal of the selection switch, and outputs the frequency command signal according to the resin characteristics used based on the signal, and the frequency from the control device. A screw rotation control device for an injection molding machine, comprising: an inverter that receives a command signal and outputs a frequency corresponding to the command signal.