JP5232210B2 - Screw drive device for electric injection molding machine - Google Patents

Description

  The present invention relates to a screw drive device that drives a screw in a rotational direction and an axial direction in an electric injection molding machine comprising a cylinder having a nozzle provided at a tip thereof and a screw provided in the cylinder. It is.

  An electric injection molding machine driven by a servo motor is excellent in control response and energy efficiency. In recent years, a high-power servo motor has been incorporated, and its importance is increasing. The electric injection molding machine is also provided with an injection device comprising a heating cylinder and a screw or the like that is driven in the rotation direction and the axial direction within the heating cylinder, as is well known. The screw driving device for driving the screw is provided with a first motor for driving the screw in the rotational direction and a second motor for driving in the axial direction. Therefore, the heating cylinder is heated by the heater, and the first motor is driven to rotate the screw to supply the material resin. If it does so, it will generate | occur | produce with the shearing effect | action by the heat | fever of a heater and rotation of a screw, resin will be fuse | melted and sent ahead, a screw will suck back in an axial direction, and molten resin will be measured. When the second motor is driven to drive the screw in the axial direction, the measured molten resin can be injected.

  For example, the screw can be driven independently in the rotational direction and the axial direction by a ball screw and a spline mechanism provided coaxially at the rear end of the screw. With respect to such a ball screw and spline mechanism, first and second motors are provided on the sides thereof so that the driving force of the motor can be transmitted through a predetermined pulley and belt or a large-diameter gear. Screw drive devices are also well known. However, such power transmission parts such as pulleys and gears have a large moment of inertia and become a load when accelerating. Then, the screw cannot be driven at high speed in the axial direction, and the injection speed cannot be increased. If the first and second motors are arranged in the axial direction of the screw and the screw is driven directly via a ball screw or a spline mechanism, there is no need to provide power transmission parts such as pulleys and gears that become acceleration loads. The injection speed can be increased. Such a screw drive device is proposed in Patent Documents 1, 2, and 3, for example.

Japanese Patent No. 4279838 JP 2009-45891 A JP-A-7-205223

  In the screw drive device described in Patent Document 1, a hollow transmission shaft is provided at the rear end of the screw, and a shaft portion of a ball screw is rotatably inserted into the hollow portion of the transmission shaft via a bearing mechanism. Has been. A ball nut is screwed into the ball screw, and the ball nut is fixed to the casing. The first motor is provided in the vicinity of the rear end of the screw coaxially with the screw. The rotor, ie, the rotor, has a cylindrical shape, is covered with the transmission shaft, and rotates through the spline groove and the key. Is transmitted to the transmission shaft. A stator, that is, a stator is provided so as to surround the rotor. Therefore, when the first motor is driven, the screw can be rotated via the transmission shaft. The second motor is provided behind the first motor, and the rotor is provided so as to extend the shaft portion of the ball screw so that the ball screw can be rotated. The stator surrounds the rotor. Accordingly, when the second motor is driven, the ball screw rotates and the ball screw can be driven in the axial direction with respect to the ball nut, and the screw can be driven in the axial direction.

  Patent Literature 2 and Patent Literature 3 also describe a screw driving device having a configuration similar to the screw driving device described in Patent Literature 1, that is, a screw driving device in which first and second motors are provided coaxially with the screw. Yes. In the screw drive device described in Patent Document 2, the first motor is provided in the vicinity of the rear end of the screw, and the ball nut is fixed to the rotor of the first motor together with the hollow transmission shaft. Therefore, the ball nut is rotated by the rotor together with the transmission shaft and the screw. The ball screw is restricted from moving in the axial direction, and its shaft portion is separated from the transmission shaft. The second motor is provided behind the first motor and rotates the ball screw. Accordingly, when the ball motor is rotated by driving the second motor, the ball nut can be driven in the axial direction, and thereby the screw can be driven in the axial direction via the transmission shaft. Further, when the first motor is driven, the screw can be rotated. At this time, if the ball nut rotates with respect to the ball screw, the screw is driven in the axial direction. Therefore, the second motor is also driven so that the ball screw and the ball nut are rotated at the same rotational speed.

  In the screw drive device described in Patent Document 3, the second motor that drives the screw in the axial direction is provided near the rear end of the screw, and the first motor that rotates the screw is provided behind the second motor. A ball screw is fixed to the rear end portion of the screw, and the second motor rotates a ball nut screwed into the ball screw. This ball screw has a hollow cylindrical shape, and an axial spline groove is formed on the inner peripheral surface thereof. A drive pin having a key that engages with the spline groove is inserted into the ball screw, and the drive pin can be rotated by the first motor. Accordingly, when the second motor is driven to rotate the ball nut, the ball screw is driven in the axial direction, and the screw can be driven in the axial direction. When the first and second motors are rotated at the same rotational speed, the second motor rotates the ball nut, and the first motor rotates the ball screw via the drive pin. Then, the screw is driven in the rotational direction and not driven in the axial direction.

  In any of the screw driving devices described in Patent Documents 1 to 3, the first and second motors are provided coaxially with the screw, so there is no need to provide a power transmission mechanism such as a pulley or gear having a high moment of inertia. . Therefore, the screw can be driven at high speed, which is excellent in this respect. However, there are problems. Specifically, in these screw drive devices, since the first and second motors are arranged in series in the axial direction, the device becomes longer in the axial direction and the overall length of the machine becomes longer. This will require installation space. There are other problems. For example, in the screw drive devices described in Patent Document 1 and Patent Document 3, a spline groove or a key must be formed on a shaft for driving the screw. This makes machining and assembly difficult and increases costs. Moreover, in the screw drive device described in Patent Document 2, there are many parts such as a sleeve and a guide shaft, and it is difficult to process, assemble, and maintain.

  An object of the present invention is to provide a screw drive device that solves the above-described problems. Specifically, it is simple and can be easily machined, assembled and maintained, and can be provided at low cost. An object of the present invention is to provide a screw drive device that is sufficiently compact, has a short overall machine length, and can drive and inject a screw at high speed.

  In order to achieve the above object, according to the present invention, a screw drive device for driving a screw includes a ball screw having one end fixed to the rear end of the screw, and a ball nut screwed into the ball screw. And first and second motors. The first motor includes a first rotor formed hollow from a cylindrical portion and a bottom portion, and a first stator, and the other end of the ball screw is fixed to the bottom portion of the first rotor. To do. The second motor includes a cylindrical second rotor and a second stator, and a ball nut is fixed to the inner peripheral surface of the second rotor. And it arrange | positions so that this 2nd motor may become inside a 1st motor.

Thus, in order to achieve the above object, the invention according to claim 1 is a cylinder in which a nozzle is provided at a tip, and a screw provided in the cylinder so as to be driven in a rotational direction and an axial direction. A screw driving device for driving the screw in an electric injection molding machine comprising: a screw that is fixed to a rear end of the screw, and a screw that is screwed to the ball screw. And a first and second motors, and the first motor is composed of a first rotor and a first stator, and the first rotor is composed of a cylindrical portion and a bottom portion. The other end of the ball screw is fixed to the bottom and is capable of moving in the axial direction integrally with the ball screw. And the second stator, the second rotor is formed in a cylindrical shape, the ball nut is fixed inside, the movement in the axial direction is restricted, and the second motor is the first stator. It is comprised so that it may be arrange | positioned inside 1 motor.
According to a second aspect of the present invention, in the screw driving device according to the first aspect, the screw driving device includes a hollow motor housing, and the first and second stators are respectively an outer peripheral surface and an inner peripheral surface of the motor housing. And the first rotor is arranged outside the first stator, and the second rotor is arranged inside the second stator.
According to a third aspect of the present invention, in the screw driving device according to the first aspect, the screw driving device includes a hollow large-diameter motor housing and a small-diameter motor housing, and the first and second stators are each of the large-diameter motor housing. Provided on inner peripheral surfaces of the diameter motor housing and the small diameter motor housing, the first and second rotors are respectively arranged inside the first and second stators.
The invention according to claim 4 is the screw drive device according to any one of claims 1 to 3, wherein at least the first stator or the first rotor has an axial length of the screw. It is configured to be longer by the injection stroke length.

  As described above, the present invention provides a screw in an electric injection molding machine comprising a cylinder provided with a nozzle at the tip, and a screw provided in the cylinder so as to be driven in the rotational direction and the axial direction. The screw driving device is configured to be driven, and the screw driving device includes a ball screw having one end fixed to a rear end portion of the screw, a ball nut screwed to the ball screw, a first, 2 motors. That is, since the number of parts is small and a spline mechanism or the like that is difficult to machine, assemble, or maintain is not required, the apparatus can be provided at low cost. The first motor includes a first rotor and a first stator. The first rotor is formed hollow from the cylindrical portion and the bottom portion, and the other end of the ball screw is fixed to the bottom portion. Axial movement is possible integrally with the ball screw, the second motor is composed of a second rotor and a second stator, and the second rotor is formed in a cylindrical shape with a ball nut inside. And axial movement is restricted. Therefore, when the second motor is driven, the ball nut can be rotated. Since the ball nut is restricted from moving in the axial direction by the second rotor, the ball screw is driven in the axial direction and the screw is driven in the axial direction. can do. Further, when the first and second motors are driven at the same rotational speed, the screw can be rotated. The first and second motors rotate the ball screw and ball nut directly without using gears, pulleys, belts, etc., so the number of parts can be reduced and the overall inertia can be reduced. It can also be driven at high speed. According to the present invention, since the second motor is disposed inside the first motor, the axial length can be short. That is, the screw drive device is compact, and an effect peculiar to the present invention that the overall machine length can be shortened can be obtained. Since the second motor is arranged on the inner side, the second rotor has a small diameter and a small moment of inertia. Then, the screw can be driven in the axial direction at high speed, and there is no problem even when the screw is injected at high speed.

  According to another invention, the screw drive device includes a hollow motor housing, the first and second stators are provided on the outer peripheral surface and the inner peripheral surface of the motor housing, respectively, and the first rotor is the first stator. On the outside, the second rotor is arranged inside the second stator, respectively. That is, since the first and second stators are provided in the motor housing, which is a common member, the number of parts is small and the overall weight can be reduced. According to still another invention, the screw drive device includes a hollow large-diameter motor housing and a small-diameter motor housing, and the first and second stators are provided on inner peripheral surfaces of the large-diameter motor housing and the small-diameter motor housing, respectively. Since the first and second rotors are respectively disposed inside the first and second stators, the first rotor is housed inside the large-diameter motor housing, so that the rotating portion is not exposed. According to another invention, at least the first stator or the first rotor is longer in the axial direction by the length of the screw injection stroke. The first rotor moves in the axial direction integrally with the screw and ball screw during injection, but at least the first stator or the first rotor is longer by the injection stroke length. Even in this case, it is guaranteed that the first stator and the first rotor overlap, and the driving force of the motor does not change.

It is side surface sectional drawing which shows the screw drive device which concerns on embodiment of this invention. It is side surface sectional drawing which shows the screw drive device which concerns on other embodiment of this invention.

  Embodiments of the present invention will be described below. The electric injection molding machine according to the present embodiment is also composed of an injection device, a mold clamping device, and the like, and each device is driven by a plurality of servo motors. As shown in part of the injection device 1 in FIG. 1, the injection device 1 includes a cylinder 2 in which an injection nozzle is provided at the tip and a heater is wound around an outer peripheral surface, and in the cylinder 2. The screw 3 is configured to be drivable in the axial direction and the rotational direction. In FIG. 1, the injection nozzle and the heater are not shown. A screw driving device 5 according to the present embodiment for driving the screw 3 is provided at the rear portion of the injection device 1.

  The screw drive device 5 according to the present embodiment is composed of a ball screw 6, a ball nut 7, and first and second motors 9 and 10 for driving these, and parts are compared with those of a conventional screw drive device. It is configured with little and simple. One end 6 a of the ball screw 6 is fixed to the rear end of the screw 3, and rotates integrally with the screw 3. A ball nut 7 is screwed onto the ball screw 6. Therefore, when the ball nut 7 is rotated, the ball screw 6 is driven in the axial direction and the screw 3 is driven. Although simply shown in FIG. 1, a sucking back coupling mechanism is provided at the connecting portion between the rear end of the screw 3 and one end 6a of the ball screw 6 according to the specifications of the apparatus. It can also be inserted.

  In the present embodiment, the arrangement of the first and second motors 9 and 10 is characterized. A common casing to which these motors 9 and 10 are attached, that is, the motor housing 13 is as follows. . The motor housing 13 has a substantially cylindrical shape with a predetermined thickness. The screw 3 side, that is, the front portion is enlarged in diameter to form a first step portion 16, and the rear portion is contracted by a predetermined length. A second stepped portion 17 is formed in diameter. The annular component 13a including the second step portion 17 constitutes the motor housing 13, but can be separated from the motor housing 13 as needed during maintenance. Since the annular part 13a is provided with the stator of the first motor 9 as will be described next, the part 13a can also be called a motor housing of the first motor 9. The motor housing 13 is provided with a first motor 9 on the outer side and a second motor 10 on the inner side, as will be described below. Thus, the motor housing 13 is fixed to the injection device 1. That is, a disc-shaped plate 19 with a hollow center is fixed to the rear end portion of the cylinder 2. The motor housing 13 is fixed to the plate 19 with bolts or the like at its end face. The state of being fixed in this way is shown in FIG.

  The first motor 9 includes a first rotor 21 that is formed in a hollow shape, and a first stator 22 that is provided inside the first rotor 21. The first stator 22 includes a stator core 22a and a stator coil 22b, and is provided on the second step portion 17 on the outer peripheral surface of the motor housing 13, that is, the annular component 13a. The first rotor 21 includes a cylindrical portion 21 a and a disk-shaped bottom portion 21 b that closes one end of the cylindrical portion 21 a, and the inner peripheral surface of the cylindrical portion 21 a is connected to the first stator 22. Opposing each other with a predetermined gap. The other end 6b of the ball screw 6 is fixed to the center of the bottom 21b of the first rotor 21. Therefore, the first rotor 21 and the ball screw 6 rotate integrally and can move in the axial direction. In the present embodiment, the cylindrical portion 21a of the first rotor 21 is formed so that its axial length is equal to or longer than the injection stroke length of the screw 2. Therefore, even if the screw 2 is driven in the axial direction, the first stator 22 does not protrude from the cylindrical portion 21a, and the first stator 22 and the first rotor 21 always face each other with a predetermined gap. Become.

  The second motor 10 includes a second rotor 24 that is formed in a cylindrical shape, and a second stator 25 that is provided outside the second rotor 24. The second stator 25 also includes a stator iron core 25 a and a stator coil 25 b, and the second stator 25 is provided on the inner peripheral surface 13 c of the motor housing 13. The second rotor 24 is attached to the inner side of the motor housing 13 via predetermined ball bearing mechanisms 26, 27, and 28 so as to be rotatable and in a state in which movement in the axial direction is restricted. A predetermined gap is provided between the outer peripheral surface and the second stator 25. The ball nut 7 is fixed inside the second rotor 24, that is, inside the cylinder. Therefore, the ball nut 7 can be rotated by the second rotor 24 but cannot move in the axial direction. The second motor 10 housed in the motor housing 13 in this way is covered by a disk-shaped motor cover 30 having a hole.

  In the screw drive device 5 according to the present embodiment, since the second motor 10 is arranged inside the first motor 9 in this way, the axial machine length is short and compact.

  The operation of the injection device 1 provided with the screw drive device 5 according to the present embodiment will be described. When measuring in the injection device 1, it is necessary to rotate the screw 3 in order to melt and knead the resin. Further, when the molten resin is sent to the front of the screw 3, it is necessary to retract the screw 3 little by little while applying a predetermined back pressure. The first and second motors 9 and 10 are driven so as to have the same rotational speed. Then, since the ball screw 6 rotates, the screw 3 rotates. Since the ball screw 6 and the ball nut 7 rotate at the same rotation speed, the axial position of the screw 3 is maintained constant. Resin is supplied into the cylinder 2 from a hopper not shown in FIG. The resin is melted by the heat of the heater and the shearing action of the screw 3 and sent to the front of the screw 3. When the rotational speed of the second motor 10 is slightly changed with respect to the first motor 9, the ball screw 6 rotates relative to the ball nut 7, the ball screw 6 is driven in the axial direction, and the screw 3 rotates. Retreat little by little. When the current supplied to the first and second motors 9 and 10 is adjusted to control the difference in rotational speed, the screw 3 can be moved backward while applying a predetermined back pressure. When the screw 3 moves backward by a predetermined stroke length, the rotation of the first and second motors 9 and 10 is stopped. Weighing is complete. In FIG. 1, the first rotor 21 and the ball screw 6 in a state where the weighing is completed are indicated by a one-dot chain line.

  With the first motor 9 stopped, only the second motor 10 is driven at high speed. Then, the ball nut 7 rotates at a high speed, and the ball screw 6 is driven in the axial direction. That is, the screw 3 is driven in the axial direction and molten resin is injected. In the present embodiment, since the second motor 10 is disposed inside the first motor 9, the second rotor 24 for rotating the ball nut 7 has a small diameter. Since it has such a small diameter, the moment of inertia of the rotating body composed of the second rotor 24 and the ball nut 7 is small, can be rotated with a large acceleration, and the screw 3 is driven in the axial direction at high speed. Can do.

  FIG. 2 shows a screw drive device 5 ′ according to the second embodiment. The same members as those of the screw drive device 5 according to the previous embodiment are denoted by the same reference numerals and will not be described in detail. In the screw drive device 5 ′ according to the second embodiment, the motor housing includes a large-diameter motor housing 31 and a small-diameter motor housing 32. The large-diameter motor housing 31 and the small-diameter motor housing 32 are joined at a portion closer to the front, and an annular space into which the first rotor 21 is inserted is formed between them. In the second motor 10, the second stator 25 is provided on the inner peripheral surface 32a of the small-diameter motor housing 32, and the second rotor 24 is provided on the inner side thereof, as in the previous embodiment. The first motor 9 is different from the previous embodiment, and the arrangement of the first rotor 21 and the first stator 22 is opposite. That is, the second stator 22 is provided on the inner peripheral surface 31a of the large-diameter motor housing 31, and the first rotor 21 is provided on the inner side. Therefore, most of the first rotor 21 is accommodated in the large-diameter motor housing 31 so that it is hardly exposed to the outside. In the present embodiment, a cylindrical sliding member 34 is provided on the outer peripheral surface of the small-diameter motor housing 32 so that the first rotor 21 can rotate smoothly. Also in this embodiment, the screw 3 can be driven in the same manner as the screw driving device 5 according to the previous embodiment.

  The embodiment of the present invention can be variously modified. For example, the first rotor 21 has been described such that the axial length of the cylindrical portion 21a is equal to or longer than the stroke length of the screw, but the axial direction of the first stator 22 has been described. May be formed to be equal to or longer than the stroke length of the screw. In this way, the length of the cylindrical portion 21a of the first rotor 21 can be shortened, so that the moment of inertia of the first rotor 21 can be reduced. Moreover, although the 1st rotor 21 demonstrated that the bottom part 21b was exhibiting the disk shape, the bottom part 21b may be formed from the several bar material like a spoke.

DESCRIPTION OF SYMBOLS 1 Injection apparatus 2 Cylinder 3 Screw 5 Screw drive apparatus 6 Ball screw 6a One end part 6b The other end part 7 Ball nut 9 1st motor 10 2nd motor 13 Motor housing 13c Inner peripheral surface 21 1st rotor 21a Cylinder Part 21b Bottom part 22 First stator 24 Second rotor 25 Second stator 31 Large-diameter motor housing 32 Small-diameter motor housing 34 Sliding member

Claims (4)

A screw driving device for driving the screw in an electric injection molding machine comprising a cylinder provided with a nozzle at a tip end and a screw provided in the cylinder so as to be driven in a rotational direction and an axial direction. ,
The screw driving device is composed of a ball screw having one end fixed to a rear end of the screw, a ball nut screwed to the ball screw, and first and second motors,
The first motor is composed of a first rotor and a first stator, the first rotor is formed hollow from a cylindrical portion and a bottom portion, and the other end of the ball screw is fixed to the bottom portion. And is capable of axial movement integrally with the ball screw,
The second motor includes a second rotor and a second stator, the second rotor is formed in a cylindrical shape, the ball nut is fixed inside, and the movement in the axial direction is restricted. And
The screw drive device characterized in that the second motor is disposed inside the first motor.   2. The screw drive device according to claim 1, wherein the screw drive device includes a hollow motor housing, and the first and second stators are provided on an outer peripheral surface and an inner peripheral surface of the motor housing, respectively. The screw drive device is characterized in that the rotor is disposed outside the first stator and the second rotor is disposed inside the second stator.   2. The screw drive device according to claim 1, wherein the screw drive device includes a hollow large-diameter motor housing and a small-diameter motor housing, and the first and second stators are respectively formed of the large-diameter motor housing and the small-diameter motor housing. A screw drive device provided on an inner peripheral surface, wherein the first and second rotors are respectively disposed inside the first and second stators.   The screw drive device according to any one of claims 1 to 3, wherein at least the first stator or the first rotor has an axial length that is longer by an injection stroke length of the screw. Screw drive device.

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