JPH0428530B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a low-pressure mold clamping method for an electric injection molding machine using a servo motor as a drive source.

[Prior Art] Mechanically driven molding machines that use an electric motor as a drive source and directly transmit and drive the rotational force of the motor using gears, link mechanisms, etc. are already known.

This conventional molding machine uses an electric motor with a constant rotational speed as a driving source, and changes in speed and force are performed using mechanical means such as a variable speed gear mechanism.

[Problems to be Solved by the Invention] By the way, when an electric motor is used as a drive source for a resin molding machine, it is necessary to control force in addition to speed control. For example, regarding the operation of a mold clamping device, the movable plate moves forward at high speed to close the mold.
Next, after shifting to low-speed forward movement, low-pressure mold clamping is applied to protect the mold, and after checking for foreign matter between the molds, the process shifts to strong mold clamping.

Therefore, a molding cycle has a speed control region and a force control region, and unless some means of force control, which has not been done in the past, is taken, the electric motor cannot be used to drive the molding machine. It could not be used as a source.

For this reason, even though it is called an electric injection molding machine, in practice it uses hydraulic pressure as an auxiliary to control force, and strictly speaking it uses both electric power and hydraulic pressure. It was meant to be used.

This invention was conceived in view of the above circumstances, and its purpose is to use a servo motor as an electric motor, and perform low-pressure mold clamping in the final section of the mold closing slowdown process using other means such as hydraulic pressure. It is an object of the present invention to provide a low-pressure mold clamping method for an electric injection molding machine that can be performed reliably without using the above methods in combination, and can prevent damage to the mold due to the presence of foreign matter.

[Means for Solving the Problems] The feature of the present invention according to the above object is that the drive source of the mold clamping mechanism is a servo motor, the rotational force of the servo motor is converted to the thrust of the movable platen through a transmission mechanism, and the When performing low-pressure mold clamping after closing the mold by moving the movable platen, the torque setting value in the final section of the mold closing slowdown process by speed control is required as the speed setting value for mold closing slowdown. The upper limit of the output torque is regulated by setting it lower than the torque, and due to the relationship between the speed setting value and the torque setting value, the final section of the mold closing slowdown process is shifted from the speed control area to the force control area and the pressure is lowered. The purpose is to perform mold clamping.

When controlling the speed of a servo motor, the torque must be set to a high enough value to maintain the speed, and conversely, when clamping the mold, the torque must be set to a high enough value to quickly reach the set pressure value. It is considered difficult to control speed and torque simultaneously because a high speed setting value is required.

Therefore, when performing low-pressure mold clamping by controlling the output torque of the servo motor, even if you try to protect the mold by reducing the speed, if a foreign object gets between the molds, the set speed may not be maintained. As a result, the servo motor has to generate the maximum output to obtain a predetermined speed, and as a result, the mold is damaged as a result of clamping the mold with the maximum torque.

Conversely, even if you attempt to clamp the mold at low pressure, the predetermined pressure will not be reached when the mold is closed and there is only slight resistance due to frictional force, so the servo motor will generate maximum output. As a result of clamping the mold at maximum speed, the mold is damaged.

However, by setting the torque setting value in the final section of mold closing slowdown lower than the torque required for the speed setting value of mold closing slowdown,
In the case of the present invention in which the upper limit of the output torque is regulated, the servo motor does not generate a torque exceeding the torque setting value, and mold clamping does not proceed, thereby preventing damage to the mold due to foreign matter.

[Example] Hereinafter, the present invention will be described in detail using the illustrated injection molding machine as an example.

FIG. 1 schematically shows the main structure of an injection molding machine in which a servo motor is used as a common driving source for a mold clamping mechanism 1 and an injection mechanism 2.

The mold clamping mechanism 1 includes a pair of fixed plates 10 and 11 provided facing each other on a machine stand 3, and the fixed plate 1.
The present invention has a required number of tie bars 12, 12 which are constructed over the lengths 0 and 11, and a movable platen 13 which is movably attached to the tie bars 12, 12.

Molds 14, 14 are provided on the opposing surfaces of the fixed plate 11 and the movable plate 13, respectively, and a large diameter plunger with a ball screw groove on the outer circumferential surface is provided on the opposite surface of the movable plate 13. 15 are connected.

The plunger 15 is screwed into a screw receiver of a rotary disk 16 which is rotatably attached to a fixed platen 10, which is a fixed member, using a ball bearing or the like, and is moved in the axial direction by rotation of the rotary disk 16. The plunger 15 using such a ball screw has high transmission efficiency and low starting friction.

Further, a gear 17 is attached to the rotary disk 16,
This gear 17 and a transmission gear to be described later mesh with each other.

The injection mechanism 2 includes an injection heating cylinder 21 containing an injection screw 20 therein, and a housing 22 on the machine base 3 that also serves to hold the injection heating cylinder 21. Inside the housing 22, a rotating shaft 24 having a threaded shaft 23 is horizontally mounted, and a movable member 25 is screwed onto the threaded shaft 23.

Further, at the rear end of the screw 20, the movable member 2
An extension shaft 26 with a tip end bearing on the screw 20
It is connected to the same body. Further, the rotating shaft 24 and the extension shaft 26 are provided with a gear 27 for advancing the screw and a gear 28 for rotating the screw at positions that do not interfere with each other. A back pressure control device 29 using a brake that includes a hysteresis brake fixed to 22a is attached.

A transmission shaft 31 parallel to the rotation shaft 24 and the extension shaft 26 is provided in the lower part of the housing 22 and extends through the housing 22 . Further, a power transmission shaft 30 parallel to the plunger 15 is provided below the mold clamping mechanism 1, passing through the pair of fixed plates 10 and 11.

These two transmission shafts 30 and 31 on the mold clamping mechanism side and the injection mechanism side are connected to each other via a clutch mechanism 32 so as to be able to freely approach and separate.

The clutch mechanism 32 includes a clutch member 32a fixed to the shaft end of the transmission shaft 31, a clutch shaft 32b disposed on the extended axis of the transmission shaft 31 and penetrating through the housing wall, and a clutch member 32b fixed to the shaft end of the transmission shaft 31. It consists of a cup ring 32c fixed to the inner end, and the excitation part is fixed to the housing side. Further, a joint 33 for connecting the transmission shaft 30 is attached to the outer end of the clutch shaft 32b.

This joint 33 is connected to a means 34 that allows movement in the axial direction, such as a spline or a key.
When the injection mechanism 2 moves forward or backward relative to the mold clamping mechanism 1, the transmission shafts 30 and 31 connected to each other are arranged so as not to obstruct the movement.

A transmission gear 35 is attached to the transmission shaft 30 close to the inside of the fixed plate 10 and meshed with the gear 17 of the rotary plate 16.
The rotational force of the transmission shaft 30 is transmitted to the rotating disk 16, and the plastic gear 1 screwed together with the rotating disk 16
5 is pushed out in the axial direction by the rotation of the rotary plate 16, and moves the movable plate 13 in the mold closing direction or the mold opening direction using the tie bars 12, 12 as guide members.

The transmission shaft 31 also includes the gears 27 and 28.
Transmission gears 37 and 36 meshing with the clutch members 38 and 39 are provided through clutch members 38 and 39, respectively. The clutch members 38, 39 are provided with couplings communicating with the transmission shafts 36, 37 and an excitation section fixed to the housing side, and by the action of the clutch plate and the excitation section inside, the transmission gear 36 ，
37 and the transmission shaft 31 are coupled or released.

Furthermore, the shaft portion of the transmission shaft 31 that protrudes outward from the housing wall portion 22a is connected to the housing wall portion 22a.
It is connected to an electric servo motor 40 having a tachometer generator 41 fixed thereto.

The clutch mechanism 32 is also provided with a device 42 for maintaining mold clamping force. This force retaining device 42 is composed of an electromagnetically actuated brake member 42a fixed to the housing wall 22a and a coupling 42b attached to the clutch shaft side.

43 is a mold opening stop position detector, 44 is a mold opening deceleration position detector, 45 is a mold closing deceleration position detector, 46 is a low pressure mold clamping position detector, 47 is a strong mold clamping position detector,
48 is a metering stop position detector, 49 is a secondary pressure switching position detector, 50 is a retreat position detector, etc., which are comprised of a proximity switch, a limit switch, a phototube, etc.

FIG. 2 shows an example of a control device, in which speed setters V ₀ to V ₇ and torque Signal switching devices 53 and 54 of setting devices F ₀ to _{F 7} are provided in parallel with a forward/reverse rotation command circuit 55 of the servo motor 40 .

The servo motor control amplifier 52 has a function of controlling the forward rotation/reverse rotation of the servo motor 40 and the maximum values of the rotational speed (speed), torque (current), etc. according to commands from the central control device 51, and controls the tachometer generator. 41 is fed back to perform closed loop control of the rotational speed.

The central control device 51 also includes the position detector 4.
3 to 50, time setters _T0 to _T7 , the force holding device 42, clutch mechanisms 32, 38, 39, and setter 5.
A control amplifier 57 and an operation switch 58 of the screw back pressure control device 29, which is activated by the command No. 6, are connected to it, and a current detector 60 of the servo motor 40 is connected to a comparator 59 connected to the central control device 51. Current setting device 61 for detecting strong mold clamping
and a current setting device 62 for injection and filling detection are connected via a signal switch 63 operated by a command from the central control device 51.

Next, control of the mold clamping mechanism will be explained.

FIG. 3 is a diagram showing the control relationship between rotational speed and torque in the servo motor 40, in which setting values A and B indicate the main operating side of forward and reverse rotation, and the speed setting value and torque setting value indicate the maximum speed and torque of the servo motor 40. Maximum torque is shown as 100 respectively, and the setting device V ₀ above
The operating range of ~V ₇ is indicated with the same reference numerals. Note that current and torque are in a proportional relationship.

Furthermore, the actual values A ₁ and B ₁ are shown in a simplified manner,
The state of increase/decrease depends on the characteristics of the servo motor 40 and the servo motor control amplifier 52, and changes depending on the state of the mechanism and load.

In the above control device, the maximum speed and maximum torque are set by the common setting devices V ₀ to F ₀ , and the maximum speed and the maximum torque are set by the common setting devices V 0 to F 0 , and the commands from the central control device 51 are set within the range of one molding cycle time set by the time setting device T ₀ . Based on this, as shown in the figure, the speed setting value A is set by each speed setting device V ₁ to V ₅ and the torque setting value B is set to the output torque upper limit value of the servo motor 40 by each torque setting device F ₁ to F ₄ . is set as .

(1) High-speed mold closing In response to the input, the servo motor 40 is accelerated between a and b as shown in the execution value _A1 , and the set value A of _V1 is reached.
Rotates at high speed until. At this time, a large starting current is generated in the servo motor 40 to accelerate it, but a large load is not applied to it other than during starting.
Even if the torque setting device F ₁ is activated, the torque remains at the actual value.
As shown in _B1 , the movable platen 13 moves forward in the mold closing direction at a high speed as the movable platen 13 moves at a high speed between b and c.

(2) Mold Closing Slowdown When the movable platen 13 reaches the operating position of the position detector 45, the signal switch 53 is activated by a signal, and the speed is switched to the setting speed of the speed setting device _V2 . As a result, the area between c and d becomes a deceleration region, and regenerative braking occurs in the servo motor 40 to slow down the area between c and d.
The speed is low between d. That is, a reverse rotation torque is applied during deceleration.

(3) Low-pressure mold clamping When the movable platen 13 reaches the operating position of the position detection detector 46 at low speed in the final section of the mold closing slowdown process, the signal switch 54 is activated by a signal and the torque setting device F ₂ is activated. Switch to . Since the torque setting value is set lower than the torque required for the speed setting value, the rotational speed necessary to maintain the speed of V ₂ cannot be obtained, and the tachometer generator 41
When _the speed reaches _the set speed due to This does not occur, and the movable platen 13 moves with a low force due to the torque _F2 , and low-pressure mold clamping is performed there.

That is, while the final section e-g is within the operating range of the speed setter _V2 , the speed of the servo motor 40 required to maintain the speed set value is
Since the torque setting value is set to a value smaller than the output torque value of This is a transition to a region where force is controlled according to output torque.

When a foreign object is present between the molds and the forward movement of the movable platen 13 is restricted, an abnormal signal is generated due to the time-up of the time setting device _T7 , and the input to the servo motor 40 is interrupted. Therefore, damage to the mold is prevented.

(4) Strong mold clamping The molds 14, 14 are almost closed, the movable platen 13 reaches the position of the position detector 47, and the signal switches between the speed setting device V ₃ and the torque setting device F ₃ . The speed setting value at this position is set higher than the slowdown speed setting value. At this time, the molds 14 and 14 are already in contact with each other, or are just about to contact each other, so it seems unnecessary to set a high speed like in V ₃ , but this allows strong mold clamping to start up in a short time. It's for a reason.

When the molds 14, 14 are completely in contact and the movable platen 13 is prevented from moving forward, the speed execution value _A1 becomes the O value, so the servo motor 40 increases its output, but a large load is applied to it. The movable plate 13 does not move forward,
The torque execution value _B1 increases to the torque setting value _F3 between g and h, and the molds 14, 14 are strongly clamped by the force of the torque _F3 .

Completion of this strong mold clamping can be confirmed by using a comparator 59 to detect that the detected value of the current detector 60 of the servo motor 40 has reached the set value of the current setting device 61. It can also be confirmed by T ₂ .

When the completion of strong mold clamping is detected, the force holding device 4
2 operates to maintain the force holding state, and then the clutch mechanism 32 is opened to release the servo motor 40 from the mold clamping mechanism side.

Therefore, the torque execution B ₁ of the servo motor 40 at the completion of the mold clamping process has an O value as shown in the figure. Therefore, the area between e and h becomes a force control region.

(5) High-speed mold opening After the injection process is completed, the clutch mechanism 32 is closed and the force holding device 42 is released, and then the speed setting device V ₄ and the torque setting device are opened by the mold opening signal.
_F4 works. In this case, the servo motor 40
The rotational direction is opposite to the rotational direction during the mold clamping step, and the rotational speed increases to the set value A by accelerating between ij.

Moreover, the torque only increases due to the starting load and decreases. As a result, the movable platen 13 moves backward at high speed between j and k to open the mold.

(6) Low speed mold opening When the movable platen 13 reaches the position of the position detector 44, the deceleration setting device _V5 is activated by the signal, and the k-
The vehicle is decelerated between 1 and 1 and then retreats at low speed between 1 and 1 m.

This low-speed mold opening is performed to prevent ejection of the molded product or shock when stopped. If you want to limit the ejection force by mechanical knock, you can also control the force by switching to a low torque setting. can. The low-speed mold opening of the movable platen 13 is performed until it reaches the position of the position detector 43.

The electric injection molding machine in the above embodiment has a configuration in which a single servo motor 40 performs all drives for opening and closing the mold, clamping the mold, injection, and metering, but the low-pressure mold clamping method of the present invention The present invention is not limited to electric injection molding machines having such a configuration.

[Effects of the Invention] As described above, this invention uses a servo motor as the drive source of the mold clamping mechanism, converts the rotational force of the servo motor into the thrust of the movable platen through the transmission mechanism, and by the movement of the movable platen. When performing mold clamping following mold closing, the torque setting value in the final section of the mold closing slowdown process by speed control is set lower than the torque required for the mold closing slowdown speed setting value. The upper limit of the output torque is regulated, and the final section of the mold closing slowdown process is shifted from the speed control area to the force control area to perform low pressure mold clamping based on the relationship between the speed setting value and torque setting value.
It has the following effects.

Even if the drive source is a servo motor, low-pressure mold clamping in the final section of the mold closing slowdown process is performed smoothly by controlling the output torque, and the force can be reliably controlled without using hydraulic pressure etc. can.

When controlling force using hydraulic pressure, it is affected by the oil temperature and the characteristics of the regulating valve in the hydraulic circuit, but when controlling the output torque of a servo motor,
There is no such problem, and the actual values for speed and force almost match the set values, so
Low-pressure mold clamping can be performed with appropriate mold clamping force.

When there is a foreign object between the molds and the mold clamping is obstructed, the servo motor tries to increase the output in order to obtain the specified speed, but since the upper limit of output torque is limited, the servo motor Since the motor does not generate a torque exceeding the torque setting value and mold clamping does not proceed, damage to the mold due to foreign matter is prevented.

[Brief explanation of drawings]

The drawings show an embodiment of the low-pressure mold clamping method for an electric injection molding machine according to the present invention, and FIG. 1 is a schematic vertical sectional view of the electric injection molding machine, and FIG. 2 is a block diagram of the control device. , FIG. 3 is a diagram showing the control relationship between the speed and torque of the servo motor during mold closing and mold clamping. 1... mold clamping mechanism, 15... plunger, 40...
... Servo motor, 41 ... Tachometer generator, 51 ... Centralized control device, 52 ... Servo motor control amplifier, 53, 54 ... Signal switch, 55
...Forward/reverse rotation command circuit, 56... Setting device, 57
... Control amplifier, 58 ... Operation switch, 59
... Comparator, 60 ... Current detector, 61,
62...Current setting device.

Claims (1)

[Claims] 1 The drive source of the mold clamping mechanism is a servo motor, and the rotational force of the servo motor is converted into the thrust force of a movable platen through a transmission mechanism, and the movement of the movable platen closes the mold and subsequently clamps the mold. To do this, the torque setting value in the final section of the mold closing slowdown process by speed control is set lower than the torque required for the mold closing slowdown speed setting, and the upper limit of the output torque is regulated. A low-pressure mold of an electric injection molding machine characterized by performing low-pressure mold clamping by shifting the final section of the mold closing slowdown process from a speed control region to a force control region according to the relationship between set values and torque set values. Tightening method.