JPH04312824A - Method of controlling mold clamping device of injection molder and method of setting origin therefor - Google Patents

Abstract

PURPOSE:To improve positioning characteristics, realize high speed movement by high hydraulic pressure and obtain highly accurate and favorable mold clamping characteristics by a method wherein the detection of position to total stroke is executed with a positional scale and the relative positional detection between a movable base and a movable platen is executed with the encoder annexed to an AC servo motor. CONSTITUTION:The position of a movable platen base 12 is detected with a scale 30, while the relative position of a main movable platen 13 to the movable platen base 12 is detected with the encoder signal of an AC servo motor 26. in the scale 30, the origin of a mold clamping ram before driving is taken as the scale value of zero and the scale value is taken to the right as the positional detected value to the total stroke. Further, on the coordinate of the main movable platen 13, the output of the encoder under the condition that the movable platen base 12 and the main movable platen 13 are brought into tight contact close limit with each other is taken as an origin or zero.

Description

[Detailed description of the invention]

0001

OBJECTS OF THE INVENTION The present invention relates to a method of controlling a mold clamping device of an injection molding machine and a method of setting the origin of a position scale therefor.

0002

2. Description of the Related Art Mold clamping in an injection molding machine is generally performed by a clamping ram mechanism, which is a hydraulic piston mechanism. Such ram mechanisms often have a structure that includes a main ram and a boost ram to increase the moving speed of the main ram. Although such a hydraulic type is characterized by being capable of high-pressure (high-horsepower) and high-speed mold clamping operations, it also has the drawback of not being able to provide fine position control characteristics. In particular, the accuracy of the speed switching position is not sufficient.
There is a problem that a large impact is likely to occur at the moment when the mating surfaces of the mold are closed, and in extreme cases, the mold may be damaged. For this reason, the mold clamping operation in the mold clamping device is controlled by highly accurate AC.
It is being considered that a servo motor may be used.

0003

[Problems to be Solved by the Invention] However, when closing the mold of a large injection molding machine by driving only an AC servo motor, the servo motor has a speed of 40 to 50 m/min for opening and closing the mold. Various characteristics are required, such as (1) sufficient mold clamping force, and (2) rapid start-up of mold opening/closing operations. In order to satisfy these required characteristics, a servo motor with extremely high ratings and excellent performance is required. Since such a servo motor is expensive, there is a problem in that the price of the injection molding machine increases. In particular, there has been no suitable means when it is necessary to temporarily stop the motor during high-speed operation. In addition, for accurate mold clamping control, it is necessary to accurately recognize the position of the parts that move for mold clamping and to set the origin accurately, but many molds are used in the same injection molding machine. There is also the problem that it is not always easy to set the origin of the scale, as it is common for the molds to have different thicknesses.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for controlling a mold clamping device that has the necessary mold clamping characteristics, is highly accurate, and is low in cost.

Another object of the present invention is to provide an origin setting method that can easily and accurately set the origin of a scale position for mold clamping control.

[0006]

[Means for Solving the Problems] According to the present invention, there is provided a hydraulic drive unit that presses and drives a movable base, and a mold that is fixed to the movable base and is used for injection molding through a moving mechanism and a movable platen due to its rotation. a servo motor that moves the movable base to close it, and a position scale that detects the position of the movable base. A control method for a mold clamping device of an injection molding machine, wherein the position detection for the entire stroke is performed using the position scale, and the relative position between the movable base and the movable platen is detected using an encoder attached to the servo motor. The closing limit of the movable platen is set as the origin of the encoder, the movable platen and the movable base are separated by a predetermined distance, and the servo motor is used to reduce the deviation of the movable platen from the set position. It is characterized by controlling to correct the position of the movable platen.

Further, according to the present invention, there is provided a hydraulic drive unit that presses and drives a movable base, and a hydraulic drive unit that is fixed to the movable base and moves to close a mold used for injection molding via a moving mechanism and a movable platen due to its rotation. a servo motor for detecting the position of the movable base, and a position scale for detecting the position of the movable base, the high-speed movement is performed by the hydraulic drive unit, and the low-speed movement immediately before mold clamping and the pressure increase at the time of mold clamping are performed by the servo motor. A method for setting the origin of a position scale for controlling a mold clamping device of an injection molding machine, wherein the movable base is moved in a state where the movable platen and the movable base are in close contact with each other until the value of the position scale does not change. a step of advancing the hydraulic drive unit in a state where the value of the position scale does not change, a step of driving the servo motor to advance the movable platen to increase pressure, and a step of setting the mold clamping pressure. The process of determining the encoder value of the servo motor when the value is reached, and the difference between the final value of the position scale and the encoder value of the servo motor when the mold clamping pressure reaches the set value is used as the origin of the position scale. The method is characterized by comprising a setting process.

[0008]

[Operation] The mold clamping device according to the present invention is provided with both a mold clamping ram, which is a hydraulic drive unit, and an AC servo motor, and the AC servo motor performs low-speed speed control and pressure control. Position detection for the entire stroke is performed by a position scale attached to the movable base, and the relative position between the movable base and the movable platen is detected by an encoder signal of an AC servo motor with the closing limit as the origin. The movable platen and the movable base are separated in advance by a predetermined distance, that is, set to a negative value, and the position of the movable platen is controlled using the encoder signal of the AC servo motor so as to reduce the deviation from the command value. This allows highly accurate position control over any short distance.

[0009] Also, the position scale value when the movable plate and movable base are closed and brought into close contact with the mold, and the encoder of the servo motor when the movable plate is driven and the pressure value rises to the set value. By setting the difference with the value as the origin of the position scale, it becomes possible to easily set the origin of the position scale.

0010

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a partial sectional view showing a mold clamping mechanism of an injection molding machine to which the present invention is applied. This mold clamping mechanism is a tie bar 11
It has a sliding shaft called . A movable platen base 12 and a main movable platen 13 are engaged with the sliding shaft through through holes 12a and 13a provided therein, and are slidable with respect to the tie bar 11. The movable platen base 12 is connected to the mold clamping ram 14 by a connecting member 15. The speed control of this mold clamping ram is performed by a control device (not shown).

A substantially cylindrical rotating member 17 having a bearing 16 and a flange portion that engages with the bearing is disposed at the center of the movable plate base 12, and these are attached to the movable plate base 12 by bolts 20. The rotating member 17 is held so as to be freely rotatable by the fixed lid 19 and the bearing holder 18 provided in contact with the inner surface thereof. A recess is formed in the surface of the lid 19 that contacts the bearing holder 18, and a pressure sensor 21 such as a load cell is attached thereto, and its output is sent to a control device (not shown) as feedback information for pressure control. It is given. A thread is cut inside the through hole provided in the center of the rotating member 17, and a first gear 22 is connected to the bolt 2 on the end surface of the rotating member 17 on the mold clamping ram side.
It is fixed at 3.

On the other hand, an AC servo motor 26 is fixed to the lower surface of the movable platen base.
A pinion 25 is attached to the rotating shaft of the motor 6, and a second gear 24 is provided between the pinion 25 and the first gear 22 to engage with both. These gears 22,2
4, 25 so that their central axes are on the same straight line,
It is rotatably attached to an arm (not shown). Note that the AC servo motor used here is 1/6 to 1/2 times faster than when everything is driven by an AC servo motor.
A rating of 2 is sufficient. This AC servo motor has a built-in encoder that detects rotation, and its output is given to a control device (not shown), thereby controlling speed and torque. Main movable plate 1
A shaft body 27 whose surface is threaded is fixed to the center of the rotary member 3, and this screw together with the screw provided in the through hole of the rotating member 17 forms a ball screw. Further, the movable platen base 12 is provided with a scale 30 for detecting its position.

By adopting such a structure, A
When the C servo motor 26 is driven, the pinion 25 and the second
The gear 24 and the first gear 22 rotate in this order, and the rotating member 1
7 will rotate around the shaft body 27. As a result,
The main movable platen 13 is moved relative to the movable platen base 12. The main movable plate 13 is connected to a part of the mold (not shown), and when the main movable plate 13 moves,
When the mold is opened and closed and force is applied to the main movable platen 13, pressure is applied to the mold.

In order to control the mold clamping device having the above structure, the position of the movable platen base 12 is detected by the scale 30, and the relative position of the main movable platen 13 with respect to the movable platen base 12 is detected by the encoder signal of the AC servo motor 26. Detected by The scale 30 has a scale value 0 as the origin before the driving of the mold clamping ram, and a scale value Sc as a position detection value for the entire stroke to the right in FIG. In addition, the coordinates of the main movable platen 13 are set such that the encoder output is the origin 0 when the movable platen base 12 and the main movable platen 13 are brought into close contact with each other, and the coordinates of the main movable platen 13 are negative in the direction in which the movable platen base 12 opens from the main movable platen 13. The scale value Sx is taken as follows. That is, this scale value Sx represents the relative position between the main movable platen 13 and the movable platen base 12.

Control operations in such a configuration will be explained with reference to FIG. 2. When starting mold clamping, open the movable platen base 12 and main movable platen 13 by about 5 mm in advance (
Step S101). Therefore, Sx=-5mm. In this state, the mold clamping ram is driven so that the movable platen base 12 matches the set value Su (step S102). At this time, the value S obtained on the scale 30 for the set value
When c has a deviation of δ (step S103
), the AC servo motor 26 is driven to reduce this deviation (step S104). That is,
Sx is controlled so that Su=Sc+Sx. By doing this, position control is performed by highly accurate local position control using an AC servo motor. Such position control is particularly effective when stopping during high-speed operation.

Next, the control relationship between the mold clamping ram and the AC servo motor in this mold clamping device will be explained. First, during mold clamping, as shown in Fig. 3, the movable platen base 1
2 and the main movable platen 13 to the LS2A position. This position is a little before the forward limit during mold clamping.

In this position, the movable platen base 12 is fixed,
The AC servo motor 26 is immediately driven to rotate. As a result, the gear mechanisms 22, 24, 25 and the ball screw mechanism 17
, 22, the main movable platen 13 is moved to the forward limit LS2 position while its speed is controlled. Further, after the main movable platen 13 passes the position of LS2A, the position change detected by the encoder of the AC servo motor is smaller than a predetermined value, that is, it is not moving forward, and the load cell When the pressure detected by 21 increases and reaches the predetermined switching pressure value, after confirming that the main movable platen 13 has reached the forward limit position LS2, a switching signal to switch to pressure control is generated and the pressure increases. I do. This pressure control is performed by feeding back the detection output of the load cell 21.

On the other hand, when opening the mold, the pressure is lowered by feedback control of the AC servo motor 26 using the detection output of the load cell 21 so as to reversely trace the pressure curve in FIG. After confirming that the speed has decreased sufficiently, the speed is controlled by the AC servo motor 26. As a result, after the main movable platen 13 reaches the high-speed mold opening start position LS3A, which is a position sufficiently far from the forward limit, the mold clamping ram 14 and the boost are speed-controlled by hydraulic pressure to open at high speed. By performing such control, high-speed, high-pressure movement using hydraulic pressure and high-precision mold clamping using an AC servo motor are possible.

In the above control, the movable platen base 12
The origin is set to 0 when the main movable platen 13 is brought into close contact with the main movable platen 13, and this position is also the forward limit position of the mold, so setting the origin is extremely important. Even if many molds are used in the same injection molding machine, they usually have different thicknesses, and it is not always easy to set the origin of the scale.

For this reason, the following origin setting is performed. This origin setting is performed according to the flow shown in FIG. 6 stored in the memory within the control device. According to FIG. 6, when the preset switch is first pressed in the mold installation mode (step S201), the main movable platen and the movable platen base are brought into close contact by driving the AC servo motor, which is the main mold clamping device. and close (step S202)
, confirm that the closing limit has been reached. Next, the movable platen base is advanced relative to the mold at low speed and low pressure by the mold clamping ram, which is the main mold clamping device (step S203). Read the position scale value Sc at this time (step S204),
Check if there is a change in this reading (step S
205), if there is a change, it is not in contact with the mold yet, so return to step S203 and continue moving the movable platen base, and when there is no change in the reading value, it is assumed that the complete closing limit has been reached and the main mold is clamped. The device is locked (step S206). Next, the AC servo motor is driven to move the main movable plate forward to perform a boost operation (step S2
07). The increased pressure is obtained by reading the pressure sensor (step S208), and the increase in pressure at this time is represented by ΔP. The read pressure value is compared to see if it is equal to the set value (step S209), and if the set value has not been reached, the process returns to step S207 to further increase the pressure, and when the set value is reached, the encoder on the AC servo motor side Read the position Sx (step S210
). From Sc and Sx obtained in this way, (Sc-
Sx) as the origin of the scale (step S
211) This completes the origin presetting. By going through such a procedure, the local origin can be easily set, and the relative position with respect to the movable platen base can be constantly recognized.

In the embodiments described above, the main movable platen is moved and the pressure is applied by the gear mechanism and the ball screw, but the main movable platen is not limited to this and can be moved by driving the servo motor. Any mode may be used as long as pressure is applied.

[0022]Also, in the embodiment, the switching from speed control by the servo motor to pressure control during mold clamping is performed when both position and pressure conditions are satisfied.
The switching may be performed based on only one of the conditions.

[0023]

[Effects of the Invention] As described above, according to the present invention, the position for the entire stroke is detected using a position scale, and the relative position between the movable base and the movable platen is detected using the encoder attached to the AC servo motor. Therefore, positioning characteristics are improved, and it becomes possible to obtain high-speed, high-pressure movement using hydraulic pressure and high-precision and good mold clamping characteristics using a servo motor.

Furthermore, according to the present invention, the origin of the position scale can be reliably set by a simple procedure, so that the positioning characteristics are further improved.

[Brief explanation of drawings]

FIG. 1 is a partial sectional view showing the configuration of a mold clamping device of an injection molding machine used in the present invention.

FIG. 2 is a flowchart showing a control method according to the present invention.

FIG. 3 is a graph showing the state of control in the vicinity of the switching point between speed control and pressure control to which the method according to the present invention is applied.

FIG. 4 is a graph showing speed control during mold opening using the method according to the present invention.

FIG. 5 is a graph showing how to switch to pressure control when the detected pressure value reaches a predetermined pressure value.

FIG. 6 is a flowchart showing a supplementary method for setting the origin of a position scale according to the present invention.

[Explanation of symbols]

11 Tie bar 12 Movable plate base 13 Main movable plate 14 Mold clamping ram 16 Bearing 17 Rotating member 21 Pressure sensor 22 First gear 24 Second gear 25 Pinion 26 AC servo motor 27 Shaft body 30 scale

Claims (2)

[Claims] 1. A hydraulic drive unit that presses and drives a movable base; a servomotor that is fixed to the movable base and that rotates to move a mold used for injection molding via a moving mechanism and a movable platen to close a mold used for injection molding; A mold clamping machine for an injection molding machine, comprising a position scale for detecting the position of a movable base body, and high-speed movement is performed by the hydraulic drive unit, and low-speed movement immediately before mold clamping and pressure increase during mold clamping are performed by the servo motor. The control method for the device includes detecting the position for the entire stroke using the position scale, detecting the relative position of the movable base and the movable platen using an encoder attached to the servo motor, and determining the closing limit of the movable platen using the encoder attached to the servo motor. The movable platen is set as the origin of the encoder, and the movable platen and the movable base body are separated by a predetermined distance in advance, and the position of the movable platen is controlled to be corrected by the servo motor so as to reduce the deviation from the set position of the movable platen. A method for controlling a mold clamping device of an injection molding machine, characterized in that: 2. A hydraulic drive unit that presses and drives a movable base; a servomotor that is fixed to the movable base and that rotates to move a mold used for injection molding via a moving mechanism and a movable platen to close the mold; A mold clamping machine for an injection molding machine, comprising a position scale for detecting the position of a movable base body, and high-speed movement is performed by the hydraulic drive unit, and low-speed movement immediately before mold clamping and pressure increase during mold clamping are performed by the servo motor. A method for setting the origin of a position scale for controlling a device, the method comprising:
a step of advancing the movable base with the movable platen and the movable base in close contact with each other until the value of the position scale no longer changes; and a process of moving the hydraulic drive unit with the movable base in a state where the value of the position scale no longer changes. fixed, and driving the servo motor to advance the movable plate to increase the pressure;
The process of determining the encoder value of the servo motor when the mold clamping pressure reaches the set value, and the difference between the final value of the position scale and the encoder value of the servo motor when the mold clamping pressure reaches the set value. A method for setting the origin of a position scale, comprising: setting the origin as the origin of the position scale.