JPH0775859B2 - Plasticizing / injecting device of injection molding machine, drive mechanism used therefor, and control method thereof - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasticizing / injecting apparatus for an injection molding machine having a coaxial plunger, and particularly, an injection characterized in that a plasticizing cylinder and a plasticizing screw are formed in a conical shape. The present invention relates to a plasticizing / injecting device for a molding machine, and a novel electric drive mechanism and control method used for the device.

[0002]

[Prior art and its problems] Conventionally, plasticization of injection molding machines
The in-line screw method is a method that occupies a large proportion in various methods of the injection device.

According to this method, one straight rod-shaped plasticizing screw bears both the plasticizing mechanism and the injection mechanism, and a straight rod-shaped (cylindrical) plasticizing screw having a spiral groove is used. By rotating in a long cylindrical cylinder, the molding material (resin) is melted and plasticized and transported forward, and the plasticizing screw is retracted by the storage pressure in front of the molten material, and the required injection amount is measured. To do. Next, stop the rotation of the screw when a predetermined amount is stored,
This time, the plasticizing screw is advanced by the sliding drive mechanism and the molten material is injected from the nozzle into the cavity.

However, such a method has the following problems. The check valve attached to the tip of the plasticizing screw was prone to failure, making maintenance difficult. Since the plasticizing screw is a mechanism that allows not only rotational movement but also sliding movement (advancing and retreating movement), its driving force transmission mechanism is complicated and is prone to failure. The relative positional relationship with the heating zone fluctuated as the screw moved forward and backward, and the kneading and melting state was unstable. It was necessary to set the cylinder length longer in consideration of the screw retreat length. Further, since it is a system in which the plasticizing screw is originally used for the purpose of plasticization and repeatedly measured, the viscosity of the molten material tends to vary. Due to various problems such as the above, a defective product that cannot be ignored was formed in the molded product.

Further, as a solution to some of the above problems, there is also a plasticizing / injecting device having a mechanism in which an injection plunger is slidably incorporated in a plasticizing screw to share plasticization and injection. .

However, this also has the following problems, that is, since the plasticizing screw has a straight rod shape (cylindrical shape), for example, oil-containing resin, polyamide, polybutylene terephthalate, polyethylene terephthalate, etc. In the case of a resin having a low viscosity, there is a problem that the molten resin idles and cannot be transported forward.

By the way, in order to secure the transportation force by rotating the screw in the cylinder, (friction force between the molten material and the inner wall of the cylinder "cylinder friction force Tb")> (friction force between the molten material and the outer peripheral wall of the screw) "Screw friction force Ts"), the larger the cylinder friction force Tb, the better.
It can be said that the smaller the screw frictional force Ts, the greater the transporting force obtained.

However, in the straight rod-shaped or column-shaped plasticizing screw of the above-mentioned example, the vector direction of the transporting force (or propulsive force) generated from the rotation of the spiral groove is parallel to the rotation axis direction of the plasticizing screw, For this reason, this acting force (transporting force) is also parallel to the inner peripheral surface of the plasticizing cylinder, so no component force in the direction perpendicular to the inner peripheral surface is generated and it is difficult to generate a drag force on the inner peripheral surface. . Therefore, both frictional forces Tb are actually
, Ts are not different, and the molten material is in a state of idling at the same position. For example, since the nut screwed into the screw does not exert a force that suppresses the rotation, the nut rotates only at that position and is in the same state as the state where the nut does not move in the axial direction of the screw.

First, the present invention solves this problem. Next, the conventional drive mechanism of the above-mentioned method relies on an electric motor to drive the rotation of the plasticizing screw and an injection cylinder driven by pneumatic or hydraulic power to drive the forward / backward movement at the time of injection. There were problems of increased points, complicated and large size of mechanism, and complicated maintenance.

Further, as another mechanism, an AC servo motor is used to perform not only rotational driving but also pressure generating and holding operations such as injection pressure and holding pressure. However, such a mechanism has a drawback that the drive control device for the motor itself is expensive and various sensors and amplifiers such as a pressure sensor are required, which makes the mechanism expensive. Originally, the molten resin material, which is the driven body of the injection molding machine, has the physical properties of a non-Newtonian fluid / viscoelastic body.Therefore, the relationship between the amount of movement of the plunger and the amount of movement of the molten material and The relationship with the compressive force received by the material was not proportionally determined uniquely, and the followability was poor.

Therefore, in order to eliminate variations in the speed and pressure repeatedly applied to the plunger, it is meaningless to improve various response accuracy by advanced feedback control.

Therefore, the present invention solves the above-mentioned problems, and an object of the present invention is to form a conical plasticizing screw in which an injection plunger is coaxially incorporated and to plasticize the plasticizing screw. The mechanism and the injection mechanism are shared by different mechanisms to perform electric drive and control, so that the plasticization / injection of a completely new type injection molding machine that is compact and highly reliable and has high plasticization / injection accuracy An apparatus, a drive mechanism thereof, and a control method thereof are provided.

[0013]

In order to achieve the above-mentioned object, the present invention is constructed as follows. First, a plasticizing / injecting device has a plasticizing cylinder (12) whose inner surface is formed in a right circular cone shape having a constant taper angle, and a plasticizing cylinder (12) is coaxial with a tip portion (12t) of the plasticizing cylinder (12). And an injection cylinder (24) provided with a nozzle (26) at its tip, and rotatably held in the plasticizing cylinder (12) with the tip side being plasticized cylinder (1).
A conical outer contour shape corresponding to the inner surface shape of 2) is formed,
A plasticizing screw (14) in which a spiral groove (20) is engraved at least over the entire side surface of the conical body.
And arranged on the rotation axis of the plasticizing screw (14),
An injection plunger (16) that slides in the axial direction and moves back and forth into the injection cylinder (24), the inner surface of the tip portion (12t) of the plasticizing cylinder (12), and the tip of the plasticizing screw (14). And a flow path (22) which is formed with an appropriate gap between the spiral groove (20) and the portion (14t) and communicates with the inside of the injection cylinder (24) from the spiral groove (20). There is.

Next, the drive mechanism of such a device applies the rotational drive force from the drive source (30) to the electromagnetic clutch A (36).
Via a plasticizing screw rotation mechanism that is transmitted to the plasticizing screw (14) via the
A ball screw (48) transmitted through the electromagnetic clutch B (46), a rotation speed detecting means (56) for detecting the rotation speed of the ball screw (48), and the ball screw (48) is screwed at one end. An injection ram (49) which is joined to the other end of the injection ram (16) so as to be rotatable, and a frame (29) which holds the injection ram (49) slidably.
And a cylinder portion (30a) fixed to the injection plunger sliding mechanism.

The drive source of the plasticizing screw rotating mechanism and the drive source of the injection plunger sliding mechanism may be shared by a single drive source (30). In addition, the drive source can sufficiently cope with the inverter-controlled electric motor (30) and can be configured at low cost.

The above method of controlling the mechanism is such that, when the injection cylinder (24) is filled with a predetermined amount of the molten material, the electromagnetic clutch A (36) is disengaged to temporarily stop the plasticizing screw rotation mechanism. The electromagnetic clutch B (46) is actuated to transmit the rotational force to the ball screw (48) to actuate the injection plunger sliding mechanism. It is characterized in that the rotational pressure equal to or higher than the rotational torque set on the basis of is set to the slip state to maintain the pressure holding state.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, one example of a concrete embodiment of the present invention constructed as described above will be described in detail with reference to the drawings. FIG. 1 is a vertical sectional view showing the whole of this embodiment.

As shown in FIG. 1, a plasticizing / injecting apparatus 10 of an injection molding machine according to an embodiment of the present invention mainly comprises a plasticizing cylinder 12 and a plasticizing screw 1 internally arranged therein.
4, an injection plunger 16 arranged coaxially with the plasticizing screw 14, and a drive mechanism for these.

The plasticizing cylinder 12 has a cylindrical shape, and the inner surface shape thereof is a right circular cone shape whose diameter is gradually reduced from the middle toward the tip (left side in the drawing) (hereinafter referred to as "conical inner surface"). Be formed). A funnel-shaped hopper 18 is attached through a penetrating opening to the body portion 12b of the plasticizing cylinder 12 where the conical inner surface thereof starts. Further, a cylindrical injection cylinder 24 having an inner diameter that matches the diameter of the injection plunger 16 described later is integrally attached to the tip portion 12t of the plasticizing cylinder 12. further,
At the tip portion (left end in the drawing) of the injection cylinder 24,
The nozzle 26 is formed by reducing the diameter.

Although not shown, heating means such as a band heater is wound around the outer periphery of the plasticizing cylinder 12 as in the conventional case. The plasticizing screw 14 has a shape whose outer contour conforms to the inner hollow shape including the conical inner surface of the plasticizing cylinder 12, and is rotatably held. That is, its trunk is cylindrical and is attached to the inner wall of the plasticizing cylinder 12 via a bearing 15. From the middle, the tip 14t is a right circular cone (to be exact, a "cut-off head" is truncated). It is formed into a right circular cone "), and its trunk portion 14m is connected to a drive mechanism described later.

The trunk portion 14m of the plasticizing screw 14 and the outer peripheral surface of the cone (hereinafter referred to as "cone side surface") are
A spiral groove 20 spirally wound is formed from a position corresponding to the hopper 18 of the plasticizing cylinder 12 (substantially immediately below the hopper 18) toward the tip portion 14t.

Further, the trunk portion 14 of the plasticizing screw 14
The diameter of m is much larger than that of the conventional straight rod (about 10 times in the present embodiment), and conversely, the axial length thereof is considerably shorter than that of the conventional one (the present embodiment). In about 1/7). However, the groove extension of the spiral groove 20 is longer than that of the conventional example.

Between the conical inner surface of the plasticizing cylinder tip portion 12t and the plasticizing screw tip portion 14t, a flow path 22 for communicating the spiral groove 20 with the inner space of the injection cylinder 24 is formed.
Are formed with a constant gap.

The injection plunger 16 has a cylindrical shape and is slidably fitted on the rotary shaft (on the central axis) of the plasticizing screw 14, and can be advanced and retracted in the axial direction by a drive mechanism described later. It is built in freely. In the normal state, the injection plunger 16 is moved to a position where its tip end surface is aligned with the tip end portion of the plasticizing screw 14, and when actuated, advances from the tip end portion of the plasticizing screw 14 to inject the injection cylinder 2
It is designed to be inserted into the inside of the unit 4. The injection plunger 16 and the inner space of the injection cylinder 24 are formed so as to be slidable and airtight.

In the present embodiment, the above-mentioned spiral groove 20 is formed on the cylindrical portion directly below the hopper-18 and on the side surface of the conical body. However, immediately below the hopper-18, the side surface of the conical body begins, The spiral groove 20 may be formed from that portion.

[Operation of Embodiment] Next, by configuring the plasticizing / injecting apparatus of this embodiment as described above, it operates as follows.

First, the solid molding material (resin material) stored in the hopper 18 is supplied to the spiral groove 20 of the plasticizing screw 14 from the drop opening of the hopper 18. The plasticizing screw 14 is rotating around its axis, and the molding material supplied to the spiral groove 20 is melted (plasticized) by frictional heat between molecules and between the molecule and the plasticized cylinder surface, and further heating from the outside. )
To be made. Further, the molten material (or plastic material) is flowed by the vortex motion in the spiral groove 20 and uniformly mixed (kneading). Then, by the rotation of the spiral groove 20, the spiral groove 20 is sequentially fed to the tip portion 14t, passes through the flow path 22,
The inside space of the injection cylinder 24 is sequentially filled.

At this time, since the normal line of the conical inner surface of the plasticizing cylinder 12 and the side surface of the conical body of the plasticizing screw 14 are inclined by the taper angle Θ with respect to the rotation axis L,
The component force of the acting force F in the direction parallel to the rotation axis L direction generated by the rotation of the plasticizing screw 14 acts as a vertical reaction force N on the inner surface of the conical shape. This drag force N increases the cylinder friction force Tb.

This is described above (the frictional force between the molten material and the inner wall of the cylinder "cylinder frictional force Tb")> (the frictional force between the molten material and the outer peripheral wall of the screw "screw frictional force Ts").
In this relationship, the larger the cylinder friction force Tb, the better,
It is possible to obtain a larger transport capacity, in accordance with the theory of.

Next, the amount of the melted material filled is measured by storing a predetermined amount in the inner space of the injection cylinder 24. That is, it is performed by sensing the pressure (back pressure) generated on the tip end surface of the injection plunger 16 filled with the molten material. Examples of such a mechanism include a configuration in which a compression coil spring and a limit switch are provided behind the injection plunger 16 and the limit switch detects the backward movement of the injection plunger 16 due to back pressure.

In this way, when the injection cylinder 24 is filled with a predetermined amount, the rotation of the plasticizing screw 14 is stopped, and the injection plunger 16 is operated by the drive mechanism described later. At this time, the injection plunger 16
At the time of being inserted into the injection cylinder 24, the outer peripheral surface thereof closes the flow path 22.

When it further advances and is inserted into the injection cylinder 24, the molten material having no escape is injected and filled from the nozzle 26 into the cavity 28 with a predetermined injection pressure.

As described above, the outer peripheral surface of the injection plunger 16 closes the flow path 22, so that the backward flow of the molten material at the time of injection is prevented. In other words, the injection plunger 16
Also functions as a check valve. [Driving Mechanism] Next, a driving mechanism that is another invention of the present application will be described.

The driving mechanism of the present application is characterized in that the driving force from the driving source is transmitted through the two electromagnetic clutches (A) 36 and the electric clutch (B) 46, and these electromagnetic clutches (A) (B) are transmitted. The rotational motion (plasticizing process) and the sliding motion (injection filling process) are switched by intermittently switching the electromagnetic clutch (B) 46, and the slip state is maintained at a torque equal to or higher than the preset rotational torque of the electromagnetic clutch (B) 46. It is designed to hold pressure at.

The drive mechanism of the present application comprises a plasticizing screw rotation drive mechanism for rotating the plasticizing screw 14 and an injection plunger sliding mechanism for sliding the injection plunger (advancing and retracting movement).

First, the plasticizing screw rotation drive mechanism is constructed as follows. The electric motor 30, which is the drive source of the present device, has its rotation shaft (motor shaft) on the coaxial line L with the rotation shaft of the plasticizing screw 14, and one end of the frame 29 that is the base of the present device. It is located in. A gear 32 is attached to the motor shaft of the electric motor 30.
Is attached, and the gear 34 that meshes with this is the frame 2
9 is pivotally supported. The rotation shaft of the gear 34 is arranged with a rotation axis M parallel to the rotation axis L of the plasticizing screw 14 via an electromagnetic clutch (A) 36.
Are linked to.

Further, a gear 42 is attached to an end portion (left side in the drawing) of the shaft 38, and the gear 42 includes a gear 44 attached to a rear end portion (right side in the drawing) of the plasticizing screw 14. It is meshed.

With such a configuration, the rotational driving force of the electric motor 30 is once transmitted to the shaft 38 arranged as a bypass, via the gear 32, the gear 34, and the electromagnetic clutch (A) 36. , The gear 42, and the gear 44 to be transmitted to the plasticizing screw 14.

The above electric motor 30 uses an inverter-controlled induction motor instead of servo control, and this is sufficient. Next, the injection plunger sliding mechanism will be described.

The driving force (sliding force) of the injection plunger 16 is transmitted by the rotation axis L of the electric motor 30 and the plasticizing screw 1.
It is performed by a mechanism in which the rotation axis of 4 is matched. That is, a ball screw 48 is coaxially attached to the rotation shaft of the gear 32 attached to the motor shaft via a variable torque type electromagnetic clutch (B) 46, and the ball screw 48 extends along the central axis of the injection ram 49. Are screwed together. The injection ram 49 is held in the cylinder portion 30a, which is vertically fixed in the middle of the frame 29 and has both ends open, so that the injection ram 49 can freely slide (or move back and forth) in the axial direction.

The injection ram 49 has a cylinder portion 30.
Since it is slidably held in a and axial rotation is prevented, its shape does not have to be cylindrical and may be prismatic.

Further, the injection ram 49 is rotatably connected to the end portion (right end in the drawing) of the injection plunger 16 at the end surface portion on the plasticizing cylinder 14 side (left side in the drawing).

In order to rotate the injection plunger 16 integrally while the plasticizing cylinder 14 is rotating, as shown in this embodiment, the injection plunger 16 is connected through a spline 50 which can slide only. Preferably.

As described above, the gear 32, the electromagnetic clutch (B) 46, the ball screw 48, the injection ram 49, and the injection plunger 16 are arranged so that their respective central axes coincide with the rotation axis L.

A tachometer 56 is mounted between the ball screw 48 and the electromagnetic clutch (B) 46 via gears 52 and 54. As a result, the number of rotations and the rotation status of the ball screw 48 are detected.

The gear 32 and the gear 34, the gear 42 and the gear 44, and the gear 52 and the gear 5 described in the above configuration are described.
The transmission means for 4 and 4 may be a mechanism in which pulleys and belts are combined in addition to the meshing of gears.

With such a structure, the power transmission to the injection plunger 16 is transmitted to the ball screw 48 via the electromagnetic clutch (B) 46 by the rotational force of the electric motor 30. Since the rotation of the injection ram 49 screwed into the ball screw 48 is blocked, the injection ram 49 is converted into an advancing / retreating motion along the rotation axis L and moves, so that the injection plunger 1 is connected.
6 also follows this, and moves back and forth in the plasticizing screw 14. The moving speed of this injection plunger 16 is
It is determined by the number of rotations of the ball screw 48, and this number of rotations is set by the frequency value under the inverter control of the electric motor 30.

[Operation of Driving Mechanism of this Embodiment and Control Method Thereof] By configuring each mechanism as described above, the plasticizing / injecting apparatus drives and is controlled as follows.

First, the electromagnetic clutch (A) 36 is connected and the plasticizing screw 16 is rotated to plasticize the plasticizing material supplied from the hopper 18, and the molten material is filled in the injection cylinder 24. At this time, the electromagnetic clutch 46 is disengaged and the ball screw 48 stops rotating, so that the injection plunger 16 rotates together with the plasticizing screw 14.

When the injection cylinder is filled with a predetermined amount of the molten material, the electromagnetic clutch (A) 36 is disconnected, the rotation of the plasticizing screw 14 is temporarily stopped, and the electromagnetic clutch (B) 46 is operated (connected). ) And let the ball screw 48
To rotate.

The rotation of the ball screw 48 causes the injection ram 49 screwed with the ball screw 48 to slide (advance). As a result, the coupled injection plunger 16 is exposed and advanced from the plasticizing screw 14, is inserted into the injection cylinder 24, and the melted material filled in the cavity has a predetermined pressure (set by the rotation speed of the ball screw). Injection filling into 28.

Then, the injection filling is completed, and the injection plunger 16 advances to the nozzle 26 and maintains the contact state, and shifts to the pressure holding step. The holding pressure in this pressure holding step is set by holding the electromagnetic clutch (B) 46 in the slip state. That is, the electric motor 30
While driving, the electric current of the electromagnetic clutch (B) 46 is controlled to set the rotational torque, and when the rotational torque is equal to or higher than the set rotational torque, the slip state is set.
The pressure acting on the injection plunger 16 is controlled.

By the way, conventionally, the pressure setting in the pressure-holding step has generally been changed stepwise because the resin pressure changes with time. The control of the drive mechanism of the present application is characterized in that the pressure setting with time is made to correspond to each current value setting of the electromagnetic clutch (B) 46.

Then, time-dependent current setting (pressure setting)
Is programmed in advance, and the program is set to be started by a signal from a tachometer 56 which is a rotation detecting means of the ball screw 48.

At the time when the injection filling process and the pressure holding process are completed, the ball screw 48 is rotated in the reverse direction, and the injection ram 4 is rotated.
9 causing the injection plunger 16 to retract into the plasticizing screw 14. In this case, the inner space of the injection cylinder 24 is almost kept in a vacuum state because the nozzle 26 is closed.

At this time, the electromagnetic clutch (B) 46 is disconnected, the electromagnetic clutch (A) 36 is connected, the plasticizing screw rotating mechanism is operated, and the plasticizing screw 14 is restarted.
Is rotated to start the plasticizing step described above.

As described above, by alternately operating the plasticizing screw rotating mechanism and the injection plunger sliding mechanism, the plasticizing step, the injection filling step, and the pressure holding step are successively repeated.

[0058]

As described above, in the plasticizing / injecting apparatus of the injection molding machine according to the present invention, the plasticizing mechanism and the injection mechanism are shared, and the plasticizing cylinder and the plasticizing screw incorporated therein. Since it has a conical shape, it is possible to secure a stable kneading state and to eliminate idle rotation of the molten material in the plasticizing cylinder to secure a stable transport force.

Further, since the plasticizing screw has a conical shape, the length of the spiral groove can be secured more than that of the conventional example, and
Since the overall length (axial length) can be shortened, the injection molding machine can be downsized.

Since the drive mechanism is configured as an electromagnetic clutch and an electric motor controlled by an inverter, the plasticizing process, the injection filling process, and the pressure holding process are sequentially performed by utilizing the switching of the electric clutch and the slip of the electric clutch. It can be performed continuously.

That is, complicated feedback control is not required as in the case of using an expensive servo motor (compared to the invertor control motor) as in the conventional example, and the number of parts and maintenance management can be simplified. At the same time, there is an effect that the entire apparatus can be configured easily and inexpensively.

Further, since the holding pressure setting uses the slip of the electric clutch of the current control, there is also an effect that the control can be easily performed.

[Brief description of drawings]

FIG. 1 is a schematic view of a plasticizing / injecting apparatus of an injection molding machine according to the present invention.

[Explanation of symbols]

10 ・ ・ ・ Plasticization / injection device of injection molding machine 12 ・ ・ ・ Plasticizing cylinder 14 ・ ・ ・ Plasticizing screw 15 ・ ・ ・ Bearing 16 ・ ・ ・ Injection plunger 18 ・ ・ ・ Hopper 20 ・ ・ ・ Plasticizing screw Groove 22 ・ ・ ・ Plasticizing screw tip flow path 24 ・ ・ ・ Injection cylinder (plasticizing cylinder front part, nozzle) 28 ・ ・ ・ Mold 30 ・ ・ ・ Electric motor 36, 46 ・ ・ ・ Electromagnetic clutch 48 ・..Ball screw 50 ... Spline 56 ... Tachometer

Claims (5)

[Claims] 1. A plasticizing cylinder (12) whose inner surface is formed into a right circular cone shape having a constant taper angle, and is provided coaxially with a tip end (12t) of the plasticizing cylinder (12), An injection cylinder (24) having a nozzle (26) formed at its tip, and an injection cylinder (24) rotatably held in the plasticization cylinder (12),
Further, the tip end side has a conical outer contour shape corresponding to the inner surface shape of the plasticizing cylinder (12), and a plastic spiral groove (20) is engraved at least over the entire side surface of the conical shape body. A plasticizing screw (14), an injection plunger (16) arranged on the rotary shaft of the plasticizing screw (14) and slidingly moving axially into and out of the injection cylinder (24), It is formed by providing an appropriate gap between the inner surface of the tip portion (12t) of the cylinder (12) and the tip portion (14t) of the plasticizing screw (14), and is formed from the spiral groove (20) to the injection cylinder (20). 24) The flow path (2
2) and plasticizing the injection molding machine characterized by
Injection device. 2. A plasticizing screw (14) for rotating driving force from a driving source (30) through an electromagnetic clutch A (36).
The rotation driving force from the drive source (30) and the plasticizing screw rotation mechanism transmitted to the electromagnetic clutch B are transmitted to the electromagnetic clutch B.
A ball screw (48) transmitted via (46), a rotation speed detecting means (56) for detecting the rotation speed of the ball screw (48), and the ball screw (48) is screwed to one end portion of the other. An injection ram (49) to which an injection plunger (16) is rotatably connected at the end, and a cylinder part (30a) which slidably holds the injection ram (49) and is fixed to a frame (29). The drive mechanism used in the plasticizing / injecting apparatus of the injection molding machine according to claim 1, further comprising: 3. A single drive source (3) for the drive source of the plasticizing screw rotation mechanism and the drive source of the injection plunger sliding mechanism.
3. The drive mechanism according to claim 2, wherein the drive mechanism is shared by 0). 4. The drive mechanism according to claim 2, wherein the drive source is an inverter-controlled electric motor (30). 5. An injection cylinder (24) with a predetermined amount of molten material.
After the electromagnetic clutch A (36) is disconnected and the plasticizing screw rotation mechanism is temporarily stopped at the time of filling, the electromagnetic clutch B (46) is operated to transmit the rotational force to the ball screw (48). After the injection plunger sliding mechanism is operated and injection filling into the cavity (28) is completed, the electromagnetic clutch B (46) is kept in a slip state at a rotational torque equal to or higher than the rotational torque set based on the current. 3. A pressure state is maintained, 3.
3. The method for controlling the drive mechanism according to 3 or 4.