JPS646931B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for measuring a molding material when molding a synthetic resin using an injection molding machine equipped with an injection screw.

[Prior Art] When measuring molding material by rotating and retracting an injection screw, even when a screw rotation end signal is given, due to the characteristics of metering control, the injection screw does not stop immediately, but after a delay time. It has the property of stopping. Furthermore, the delay time becomes longer as the screw rotation speed increases due to the influence of inertia, and therefore the measurement variation also increases. In the conventional weighing method to reduce measurement variations, the screw position is detected and the set value of the screw rotation speed is changed to a low value (set by a low speed setting device) just before the end of the weighing process. After this becomes low, a screw rotation stop signal is given to stop the screw rotation.

In the measuring process, it is necessary to improve the reproducibility of the screw stop position in order to improve the quality of the molded product, but the ultimate goal is to keep the plasticized state of the material the same for each molding cycle, so that the material is stored in the heating cylinder. The goal is to keep the amount of molding material constant, that is, to keep the state of the molding material constant.

[Problems to be Solved by the Invention] With the above-mentioned conventional means, when the set value of the screw rotation speed is drastically changed, unless the set value of the low speed setting device is reset, the metering position (screw stop position) will be lost. may shift, or the measurement position variation between molding cycles will increase.

In addition, in order to obtain conditions with little variation in measurement, the set value of the low speed setting device or its switching position must be determined by trial and error, resulting in poor workability. On the other hand, if the setting value of the low speed setting device is set to a lower value in order to improve the reproducibility of the metering position, a sudden change in the rotational speed of the screw will occur when changing the speed, and a sudden change will also occur in the plasticization state of the material. This causes a state where there is almost no correlation between the screw rotation speed and the screw retraction speed, and if the screw rotation speed has a long low speed section (low speed setting value), the screw retraction speed may become unstable. Even if the length increases, the instability of the plasticized state of the material increases, and the metering position (screw stop position) appears to be stable, the state of the molding material actually stored in the heating cylinder may be different. There were times when I got used to it.

[Means for Solving the Problem] This invention was devised to solve the above-mentioned conventional problem, and its purpose is to minimize the slowdown section to the necessary minimum to maintain the plasticized state. We have developed a new weighing method that can shorten the unstable section as much as possible, automatically stabilize the weighing position even when changing the screw rotation speed setting, and improve the accuracy of the weighing position. It is about providing.

The features of the present invention for the above-mentioned purpose include, based on an arbitrarily set measurement setting position, a plurality of screw rotation speed switching positions set in front of the reference position, and a plurality of screw rotation speed switching positions that are provided corresponding to the switching positions. A plurality of screw rotational speed setting values are provided, which are set to decrease as the screw approaches the set position, and each time the screw position reaches the screw rotational speed switching position, the screw rotational speed corresponds to the screw rotational speed switching position. A slowdown program that controls the screw rotation drive device by switching the speed command value so that the screw rotation speed set value is similar to the one previously set, and decelerates the screw rotation speed. Screw rotation speed slowdown program control is performed before the end of metering using a slowdown start point selection program that selects and determines the screw rotation speed switching position corresponding to the speed setting value immediately below the setting value of the rotation speed setting device. It is in.

Further, the present invention will be explained in detail with reference to illustrated embodiments.

[Embodiment] Reference numeral 1 in the figure is an injection device, in which a hopper 4 is provided at the rear of a heating cylinder 3 in which an injection screw 2 is housed. Further, an injection ram 6 of an injection cylinder 5 is connected to the rear end of the injection screw 2, and an electric servo motor 7 equipped with a tachometer generator 8 on the injection cylinder side is connected within the rear end of the injection ram 6. Drive shaft 7a
is spline fitted in the axial direction.

In such an injection device 1, the molding material 9 of the hopper 4 can be fed into the heating cylinder 3 by rotating the injection screw 2 by the electric servo motor 7, and the material pressure generated by feeding can be The injection screw 2 is moved backward to measure the material to be pumped into the tip of the heating cylinder.

The material is measured by detecting the retracted position of the injection screw 2 by a position detector 10 which is an absolute type rotary encoder provided between the tip of the injection ram 6 and the fixed part side of the injection device 1. The detected position is output as an electrical digital signal and input to a central control unit 11 connected to the position detector 10.

This central control device 11 is equipped with a microprocessor and a memory, and is connected to a servo motor control amplifier 12 through three circuits: a speed command circuit A, a torque command circuit B, and a rotation command circuit C. Furthermore, the central control device 11 includes a rotational speed setting device V for the injection screw 2, a torque setting device T for setting the output torque upper limit value of the electric servo motor 7, a metering setting device L, a distance setting device L ₁ to _{L 10} , Slowdown speed setters V ₁ to _{V 10} are connected. .

The servo motor control amplifier 12 is connected to the electric servo motor 7 and the tachometer generator 8, and according to instructions from the central controller 11,
Rotation, rotation speed (number of rotations) of electric servo motor 7,
It has a function of controlling the upper limit value of the output torque, etc., and a function of feeding back the signal of the tachometer generator 8 to perform constant speed control of the rotation speed.

Next, an example of a measuring method will be explained with reference to FIG.

First, during the weighing process, the microprocessor selects the distance setting device L ₁₀ to _{L 1} from the setting value l of the measurement setting device L.
The values l-l ₁₀ , l-l 9 , . . . obtained by subtracting the set values l ₁₀ to _{l 1} (l ₁₀ > l ₉ > l ₈ ... l _{3 >} l ₂ > l ₁ ), respectively.
Set l-l ₁ as the deceleration screw rotation speed switching position, compare the value l-l ₁₀ with the output of the screw position detection device 10, and when the screw position matches the position of value l-l ₁₀ , the slowdown speed V ₁₀ of the setting device Change the screw rotational speed command value to the setting value ν ₁₀ of the setting device, and in the same way, when the screw position reaches the value l-l ₉ , the screw rotational speed set by the V ₉ setting device When the command value is ν ₉ and the screw rotation speed command value is at the position of l-l ₁ , the screw rotation speed command value is ν ₁ (ν ₁₀ > ν ₉ > ν ₈ > ν ₇ >
ν ₆ > ν ₅ > ν ₄ > ν ₃ > ν ₂ > ν ₁ ), and the starting point of the slow-down program is determined by setting the setting value ν of the screw rotation speed setting device V to ν.
When ＞ν ₁₀ , it is l-l ₁₀ value, when ν ₁₀ ≧ν＞ν ₉ , it is l-l ₉
value, l-l ₈ value when ν ₉ ≧ν>ν ₈ , l-l ₇ value when ν ₈ ≧ν>ν ₇ , and similarly l-l ₁ value when ν ₂ ≧ν>ν ₁ . A screw rotation speed slowdown program including a slowdown start point selection program for selecting a screw rotation speed is set.

Needless to say, when the screw rotation speed setting value ν is set to the maximum molding function force, ν>
ν ₁₀ , and the rotation command, rotation speed command ν value, and torque command value (torque upper limit setting value) are
1 to the servo motor control amplifier 12, the electric servo motor 7 is activated and the metering process begins.

The signal from the tachometer generator 8 is fed back to the servo motor control amplifier 12 to control the drive of the electric servo motor 7, and constant speed control is performed so that the screw rotation speed S becomes the set value ν, and after a certain period of time, S = ν, and the screw rotation continues. In that way, the molding material 9
is plasticized and the screw 2 moves backward.

When the screw position reaches the l-l ₁₀ value, the screw rotation speed setting value is switched to the setting value ν ₁₀ of the slowdown speed setting device V ₁₀ , and the electric servo motor 7 is controlled by the rotation speed command value of ν ₁₀ , causing the screw to rotate. The speed S is reduced to a v ₁₀ value. Screw position is l
When the _-l9 value is reached, the screw rotational speed command value becomes the _v9 value corresponding to that position. Similarly, the screw rotation speed command value changes ν ₈ →ν ₇ →ν ₆ →ν ₅ →→ every time the screw rotation speed switching position for deceleration is reached.
The rotational speed of the screw is reduced as follows: ν ₄ →ν ₃ →ν ₂ →ν ₁ , and the screw rotational speed slowdown program control in the metering process is performed.

When the screw position reaches the l value set by the meter setting device L, the central control device 11 turns off the rotation command and rotation speed command value and starts timing. When the rotation command to the servo motor control amplifier 12 is turned off, the electric servo motor 7 is stopped under braking control, and the screw stop position is slightly behind the metering setting value.

When the previously set braking time (the set value of the braking time is stored in the memory within the central control device 11) has elapsed, the central control device 11:
Turn off the torque command signal and complete the measurement process.
When the set value of the screw rotation speed setting device V is equal to or larger than ν ₁₀ , the screw position reaches the l-l ₉ value, and when it is larger than ν ₆ and smaller than ν ₇ , the screw position reaches the l-l ₅ value. Each screw rotation speed slowdown program control is started.

In addition, if the mold is changed and the measurement setting value is changed, the newly set l will be used as the standard.
_l1 ...l- _l10 is automatically set.

In the above embodiment, the electric servo motor 7 is used as the screw rotation drive device, but in a molding machine using an oil motor, a hydraulic servo valve may be used as the control valve of the oil motor, or a proportional electromagnetic A type flow control valve may also be used.

Alternatively, open-loop control using a proportional electromagnetic flow control valve may be used instead of detecting screw rotation and performing feedback control.

In addition, when setting the deceleration screw rotational speed switching position, it is best to know the response characteristics of the metering device through experiments, and set each slowdown control section (screw movement distance) to be approximately the same as the response distance during speed change.
Further, the lowest speed ν ₁ is preferably set to the minimum value of the screw rotation speed that allows stable plasticization.

In addition, in this example, the screw rotation speed switching position and the screw rotation speed setting value corresponding to each switching position were performed by calculating the distance setting with the setting device and setting the speed on the setting device, but this is not the same as the measurement setting. value,
The ratio may be automatically determined and set by calculating the maximum speed setting value.

[Effects of the Invention] This invention having the above-described configuration has the following effects.

Slowdown program control that slows down the screw rotation speed in multiple stages based on the screw position before the metering stops allows for highly accurate metering with good repeatability.

By controlling the screw rotation speed immediately before the end of metering to match regardless of the screw rotation speed setting, the metering stop position can be made to match regardless of the screw rotation speed setting, making it easier to set molding conditions in molding operations. do.

The stability of the plasticized state can be improved without causing a sudden change in the screw rotation speed.

[Brief explanation of drawings]

The drawings illustrate the material measuring method in injection molding according to the present invention, and FIG. 1 is a block diagram showing a part of the apparatus in longitudinal section, and FIG. 2 shows screw rotation command values, screw rotation speeds, and screw positions. FIG. 1... Injection device, 2... Injection screw, 3...
Heating tube, 4...hopper, 6...injection ram, 7...
...Electric servo motor, 8...Tachometer generator, 9...Molding material, 10...Position detector, 1
1... Central control device, 12... Servo motor control amplifier.

Claims (1)

[Claims] 1 In a method in which a hopper is provided at the rear of a heating cylinder containing an injection screw, and the molding material in the hopper is measured by rotation and backward movement of the injection screw, the reference value is determined based on an arbitrarily set measurement setting position. A plurality of screw rotation speed switching positions are set in front of the screw rotation speed position, and a plurality of screw rotation speed setting values are provided corresponding to the switching positions and are set to become smaller as the metering setting position is approached. Every time the screw rotation speed reaches the above screw rotation speed switching position, the speed command value is changed so that the screw rotation speed becomes the screw rotation speed setting value that was previously set in accordance with the screw rotation speed switching position. A slow-down program that controls the rotary drive device and decelerates the screw rotation speed, and a screw rotation speed switching position corresponding to the speed setting value immediately below the setting value of the screw rotation speed setting device is selected as the starting point of the slow-down program. A measuring method for injection molding, characterized in that a screw rotation speed slowdown program control is performed just before the end of measuring using a slowdown start point selection program determined by a slowdown start point selection program.