JPH0448340B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a holding force control method for an electric injection molding machine using a servo motor as a drive source.

[Conventional technology]

Injection molding machines of the type that use an electric motor as a drive source and convert the rotational force into thrust using mechanical means such as a screw shaft or a link mechanism to perform injection are already known. These injection molding machines use an electric motor with a constant rotation speed as the drive source, and control the speed and force by
It uses a mechanical gear mechanism.

[Problems to be Solved by the Invention] By the way, when injection molding of synthetic resin is carried out using a molding machine that uses an electric motor as a drive source, force control is required in addition to speed control, and it is difficult to control the speed and force. Control of both is essential. For example, regarding the operation of the injection mechanism, the injection plunger moves forward under speed control for injection filling, and when filling is almost completed, it is switched to pressure control for injection holding pressure, and the cooling contraction of the resin occurs. control is performed to compensate for any shortfalls.

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

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

The present invention has been developed in light of the above, and although it uses an electric motor as a drive source, its purpose is to use other means such as hydraulic pressure to control the holding pressure during injection holding pressure. It is an object of the present invention to provide a new method for controlling the holding force of an electric injection molding machine, which can be carried out without using the present invention.

[Means to solve the problem]

The features of the present invention for the above-mentioned purpose are that a servo motor is used as the drive source of the injection mechanism, and the rotational force of the servo motor is converted into the thrust of the injection plunger via a transmission mechanism, and when performing injection and holding pressure, it is possible to maintain The objective is to control the holding force in the pressure process by controlling the output torque of the servo motor.

[Example] The present invention will be described in detail below 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 tie bars 12, 12 have a required number of tie bars 12, 12 installed over the lengths 0, 11, and a movable platen 13 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 rotatably mounted on a fixed plate 10 as a fixed member using a ball bearing or the like, and is moved in the axial direction by rotation of the rotary disk 16. This ball screw has high transmission efficiency and low starting friction. Also, rotary disk 1
A gear 17 is attached to 6, and 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 which is equipped with an injection screw 20 that also serves as an injection plunger.
and a housing 22 on the machine stand 3 which 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, an extension shaft 26 whose tip is supported by the movable member 25 is integrally connected to the screw 20. Further, the rotating shaft 24 and the extension shaft 26 have 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.

Inside the lower part of the housing 22 is the rotation shaft 2.
4 and an extension shaft 26, a transmission shaft 31 is provided passing 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 a clutch mechanism 32.
We are in contact with each other freely through the .

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 extension 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 coupling ring 32c fixed to the inner end, and the excitation part is fixed to the housing side. A joint 33 for connecting the transmission shaft 30 is attached to the outer end of the clutch shaft 32b. This joint 33
The transmission shaft 30 and the transmission shaft 30 are connected by a means 34 that allows movement in the axial direction, such as a spline or a key, so that when the injection mechanism 2 moves forward or backward relative to the mold clamping mechanism 1, they are connected to each other. The connected transmission shafts 30 and 31 are arranged so as not to impede their movement.

A transmission gear 35 that meshes with the gear 17 of the rotary disc 16 is attached to the transmission shaft 30 close to the inside of the fixed plate 10, and the transmission gear 35 rotates the rotational force of the transmission shaft 30. The plunger 1 is transmitted to the disc 16 and is screwed into the rotary disc 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 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 and 39 are connected to the transmission gears 36 and 37.
The transmission gear 3 is provided with a coupling ring connected to the housing, and an excitation part fixed to the housing side, and by the action of the clutch plate and the excitation part inside, the transmission gear 3
6, 37 and the transmission shaft 31 can be 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 with a tachometer generator 41 fixed to the tachometer generator 41 .

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 retraction 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 switchers 53 and 54 of the 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 forward/reverse rotation of the servo motor 40 as well as the number of rotations (speed), maximum torque (current), etc. according to commands from the central control device 51, and controls the tachometer generator 41. The signal is fed back to perform closed-loop control of the rotational speed (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 6 are connected, 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 6 for detecting strong mold clamping
1 and a current setting device 62 for injection and filling detection are connected via a signal switch 63 operated by a command from a central control device 51.

Next, control of the mold clamping mechanism 1 will be explained.

FIG. 3 is a diagram showing the control relationship between rotational speed and torque in the servo motor 40, and setting values A and B indicate the main operating side of forward and reverse rotation. In addition, the speed setting value and torque setting value are shown with the maximum speed and maximum torque of the servo motor 40 as 100, respectively, and the setting value is
The operating ranges V ₀ -V ₇ and F ₀ -F ₇ are designated 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 and F ₀ , and based on the commands from the central control device 51 within the range of one molding cycle time set by the time setting device T0. 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 as the output torque upper limit value of the servo motor 40 by each torque setting device F ₁ to F ₄ . be done.

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 reaches the set value A of _V1 .
Rotates at high speed until. At this time, a large starting current is generated in the servo motor 40 to accelerate it, but no large load is applied to it other than during startup, so even if the torque setting device _F1 is activated, the torque will be as shown in the actual value _B1 . The movable platen 13 moves forward in the mold clamping direction at high speed.

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 set speed of the speed setting device _V2 . As a result, the area between c and d becomes a deceleration region, where regenerative braking occurs in the motor, resulting in slowdown, and the area between d and e becomes a low speed. In other words, reverse rotational torque is applied during deceleration.

3 Low Pressure Mold Clamping When the movable platen 13 reaches the operating position of the position detector 46, the signal switch 54 is activated by the signal and switches to the torque setting device _F2 . Since this torque setting value is set lower than the torque required for the above-mentioned speed setting value, the rotational speed necessary to maintain the speed of V ₂ cannot be obtained, so the torque setting value is set by the tachometer generator 41. As the speed increases, feedback is applied and the output of the servo motor 40 attempts to increase, but since the upper limit of the output torque is regulated by the torque setting value of _F2 , no torque greater than _F2 is generated, and the movable platen 13 is torque _F2
The mold is moved with low force, and low-pressure mold clamping is performed there.

Therefore, although the range between e and g is within the operating range of the speed setter _V2 , it automatically switches to force control depending on the relationship with the torque setting value, and changes from the speed control area to the force control area. Change. 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 servo motor 4 is
Since the input to 0 is interrupted, 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 _V3 and the torque setting device _F3 .
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 come into contact with each other, and it seems unnecessary to set a high speed like in _V3 , but this is because the strong mold clamping is to start up in a short time. be.

When the molds are completely in contact with each other and the movable platen 13 is prevented from moving forward, the speed execution value A ₁ becomes 0, so the servo motor 40 increases its output, but a large load is applied to the movable platen. 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 . When this strong mold clamping is completed, the detection value of the current detector 60 of the servo motor 40 is determined by the current setting device 61.
The comparator 59 detects that the set value has been reached. Note that the time setting device _T2 may be used for confirmation instead of the comparator.

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 1 side. Therefore, the torque execution value _B1 of the servo motor at the end of the mold clamping stroke takes a zero 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 stroke is completed, the clutch mechanism 32 is closed, the force holding device 42 is released, and then the speed setting device _V4 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 stroke, 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 then decreases. As a result, the movable plate 13 moves to j-
Open the mold by moving backwards at high speed.

6 Low speed mold opening When the movable platen 13 reaches the position of the position detector 44, the speed setting device _V5 is activated by the signal, and the k-
The vehicle is decelerated between 1 and 1, and moves backward at low speed between 1 and 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 the movable platen 13 reaches the position of the position detector 43.

Next, control of the injection device 2 will be explained.

FIG. 4 shows a servo motor 40 in the injection device 2.
FIG. 3 is a diagram showing the control relationship between the rotational speed and torque of
Setting values, etc. are shown in the same way as in the figure. Also, the rotation is reverse rotation.

1 Injection Stroke The servo motor 40 is accelerated to a set value A by the speed setting device _V6 , as shown in the execution value _A1 , and becomes a high-speed rotation. Normally, even if the torque setting device _F5 operates, the injection screw 2
Unless there is a large load on 0, the actual value B ₁ will be as shown. Then, when the resin filling is completed at point r, the torque suddenly increases. When the torque reaches the set value α of the current setting device 62 for injection filling detection, the time setting device _T3 is activated. At point s, the torque execution value _B1 reaches the set value B due to the increase in load, and on the contrary, the speed decreases as shown by the execution value _A1 , and the injection screw 20 performs resin filling.

When the torque reaches the current set value α, the control enters the force control region from the speed control region. This switching is automatically performed based on the correlation between the speed setting value and the torque setting value, and filling and packing is completed under the control of the torque of _F5 . Time setter T ₃
At point t, when the time has expired, the time setting value _T4 is activated and the torque setting device _F6 is switched. Since the output torque of the servo motor 40 is limited, the torque setting value is set to _F6 , and secondary pressure (holding pressure) is applied by the advancement of the injection screw 20 according to the torque setting value, and the pressure holding state is controlled. The injection stroke ends when timer _T4 times up.
This compensates for the shortage caused by cooling shrinkage of the resin.

Note that the injection time may be controlled by setting a timer that is activated at the start of injection.

Further, the switching to the secondary pressure may be performed by detecting the position of the injection screw 20 using the detector 49.
Also, the time setting device _T3 switches to the secondary pressure after a certain period of time, but this time is extremely short, so
It may be switched immediately at the α point. Furthermore, if an excessive starting torque is required at the start of injection, such as in a mold for a pinpoint gate, a setting value of a setting device other than the injection filling torque may be used during that time.

2 Charging process When the time setting device T ₄ times up, the time setting device T ₅ is activated to cool the mold. After the time setting device T ₆ is activated due to time-up, the speed setting device V ₇ and torque setting device F ₇ are activated.
The servo motor 40 rotates forward and starts charging. At this time, the back pressure control brake 29 is activated to apply back pressure to the injection screw 20. The injection screw 20 moves backward under the pressure of the resin, and metering is completed by the action of the metering stop position detector 48. Furthermore, when the screw is moved back in the axial direction to prevent drooling, it stops at the operating position of the backward position detector 50.

In the above embodiments, the servo motor is used for all driving purposes such as mold clamping, injection, and metering, but it may be provided independently for each driving section.

Furthermore, although the in-line screw type was described in the embodiments, the present invention is not particularly limited to the in-line screw type, as the plunger type and the screw pre-placing type can be implemented in the same manner. .

[Effects of the Invention] As described above, in the present invention, the holding force can be controlled (torque control) by controlling the output torque of the servo motor, and the control range of speed and force can be switched. Since the control is performed electrically based on set values, centralized control is easy and operation is simple.Since the drive source by the servo motor is directly controlled, even when controlling multiple movable parts, it is possible to control multiple movable parts without using the conventional hydraulic system. There is no need to provide a pressure control valve, a flow rate control valve, etc. for each actuator to control them, and the following effects are also achieved.

(1) Since the speed is controlled in a closed loop, it has excellent reproducibility and stability, allowing precision and stable molding.

(2) Movement of movable members such as the injection plunger is performed by a rotating means and a screw shaft, and slips due to axial inertia do not occur, and the movement is smooth and accurate position control is achieved by braking the drive source. is obtained.

(3) It is not affected by oil temperature or regulating valve characteristics in a fluid-driven type, and the actual values for speed and force almost match the set values, so accurate molding conditions can be obtained. .

(4) By attaching the speed detector to the drive source, it can be handled easily and at low cost. (5) In addition, by attaching the encoder to the drive source, there is no need to install a position detector on the moving part, resulting in a simpler structure. It can also be done.

[Brief explanation of the drawing]

The drawings illustrate a method of controlling an electric injection molding machine according to the present invention, and FIG. 1 is a schematic longitudinal sectional view of the electric injection molding machine, FIG. 2 is a block diagram of the control device, and FIG. 3 is a schematic longitudinal sectional view of the electric injection molding machine. FIG. 4 is a diagram showing the control relationship between the speed and torque of the drive source in the mold clamping device. FIG. 4 is a diagram showing the control relationship between the speed and torque of the drive source in the injection device. 1...Mold clamping mechanism, 2...Injection mechanism, 15...Plunger, 20...Screw, 40...Servo motor.

Claims (1)

[Claims] 1. A servo motor is used as the drive source of the injection mechanism, and the rotational force of the servo motor is converted to the thrust of the injection plunger via a transmission mechanism, and when performing injection and pressure holding, the holding force in the pressure holding process is controlled. , a holding force control method for an electric injection molding machine, characterized in that the holding force is controlled by controlling the output torque of a servo motor.