JPH11344094A - Ball screw for revolving nut - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent inertia from increasing at the time of revolution and make revolving balance of a nut excellent by making thickness of a ball screw nut thin and reducing a surface working part for mounting a return tube. SOLUTION: A surface working part 5 is reduced as compared with conventional one and a return tube 4 is mounted on the upper part and an extending dimension R up to an outside side surface of the return tube 4 is larger than D/2. Thickness (t) of a ball screw nut 1 can be reduced by this extending part (R-1/2D). By reducing a nut outside diameter D and thickness (t) and reducing the surface working part 5 by milling machining as compared with conventional one, deflection of revolving balance can be reduced and inertia can be reduced. Because revolution inertia becomes smaller by reducing thickness (t) in this way, starting is quick at the time of starting to revolve a ball screw nut and the ball screw nut quickly reverses for an operation command.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ball screw for rotating a nut used for a mold clamping device of an injection molding machine.

[0002]

2. Description of the Related Art Conventionally, in an injection molding machine, a resin heated and melted in a heating cylinder is injected at a high pressure, filled in a cavity of a mold, cooled and solidified in the cavity, and the mold is cooled. Is opened to take out the molded product.

[0003] The injection molding machine has a mold clamping device and an injection device, and the mold clamping device has a fixed platen and a movable platen.
The mold clamping cylinder moves the movable platen forward and backward to move the mold toward and away from the mold. On the other hand, the injection device includes a heating cylinder for heating and melting the resin supplied from the hopper, and an injection nozzle for injecting the melted resin, and a screw is disposed in the heating cylinder so as to be able to move forward and backward. The resin can be injected by moving the screw forward, and can be measured by moving the screw backward. Incidentally, there has been provided an injection molding machine using a servomotor for moving a mold clamping device forward and backward.

FIG. 3 is a front view of a conventional mold clamping device, FIG. 4 is a side view of the mold clamping device, and FIG. 5 is a detailed view of a servo motor.
In addition, the upper side from the center line of FIG.
The portion below the center line indicates the mold open state of the mold clamping device.

In FIGS. 3 to 5, reference numeral 11 denotes a movable platen to which a movable mold (not shown) is attached, reference numeral 12 denotes a toggle support, and a tie bar 13 connects the toggle support 12 and a fixed platen (not shown). The movable platen 11 slides along the tie bar 13 to close, close, and open the mold. For this purpose, a toggle mechanism 14 is provided between the toggle support 12 and the movable platen 11, and the toggle mechanism 14 is operated by a driving device 15 to move the movable platen 11 forward and backward.

The toggle mechanism 14 is connected to the toggle lever 16 and the movable platen 11 which are swingably supported by the toggle support 12 and swings with respect to the toggle lever 16 and the movable platen 11. Arm 17 freely supported, crosshead 20 fixed to ball screw shaft 18 via nut 19, and toggle lever-2
1 and the crosshead 20 are connected to each other, and are constituted by a toggle lever 16 and a toggle lever 21 supported swingably with respect to the crosshead 20.

In the center of the toggle support 12,
The driving device 15 is disposed so as to project rearward. The driving device 15 is directly fixed to the toggle support 12 by a bolt 22. The driving device 15 includes a driving device case 23,
A servo motor 24 disposed in the drive case 23;
And rotatably supported with respect to the drive case 23,
It comprises a hollow rotary sleeve 25 as an output shaft for outputting the rotation of the servo motor 24.

The drive device case 23 is a toggle support 1
2, a side wall 26 disposed in contact with the side wall 2, a side wall 27 disposed opposite to the side wall 26, and a cylindrical cover 28 connecting the side walls 26, 27. The servo motor 24 comprises a stator core 29 fixed to the drive case 23 and a rotor core 30 rotatably disposed on the inner peripheral side of the stator core 29. Further, the rotary sleeve 25 has a large diameter portion 25a and a large diameter portion 25a.
The large diameter portion 25a is rotatably supported by the bearing 31 on the side wall 26, and the small diameter portion 25b is
1 rotatably supports the side wall 27.

A ball screw nut 32 is fixed to the inner periphery of the large diameter portion 25a by a bolt 33.
The rotor core 30 is fitted and fixed to the outer periphery of the small diameter portion 25b. The ball screw shaft 18 extends rearward from the crosshead 20, penetrates the toggle support 12, and is screwed to the ball screw nut 32. And servo motor 2
By driving the ball screw nut 18 to rotate the ball screw nut 32, the ball screw shaft 18 is advanced and retracted.
In the retreat limit position, the toggle mechanism 14 is positioned below the center line in FIG. 2 to form a mold-open state of the mold clamping device, and in the forward limit position of the ball screw shaft 18, the toggle mechanism 14 is The mold closed state of the mold clamping device can be formed in a state shown above the center line in FIG.

As described above, when the ball motor 24 is driven to rotate the ball screw nut 32, the ball screw nut 32 and the ball screw shaft 18 convert the rotary motion into a linear motion. , The toggle mechanism 14 is operated to close, close and open the mold.

FIG. 6 shows a known ball screw for moving such a toggle mechanism back and forth. The ball screw is a screw in which balls 36 for rolling bearings are arranged in a row in a coiled space formed by opposing a thread groove 34 of a male screw and a thread groove 35 of a female screw. The screw passes through a hole or tube 37 in the nut body as shown in FIG. 6 and is returned to the thread groove at the other end of the nut. Ball screw is
The feature is that the coefficient of friction is extremely small as compared with general sliding contact screws.

As is apparent from FIG. 6, the ball 36 circulates along a helical passage provided in the ball screw nut 19. Since the passage of the ball 36 is provided in the nut as described above, the thickness t of the nut must be increased. When the wall thickness t becomes large, rotation inertia of the nut becomes a problem.

[0013]

SUMMARY OF THE INVENTION The present invention improves such a ball screw for rotating a nut and rotates the ball screw nut to move the ball screw forward and backward. In order to prevent the shear from becoming large and to improve the rotation balance of the nut, make the outer diameter of the nut as small as possible so that the surface processing part of the return tube mounting part is as small as possible. It is an object of the present invention to provide a low-inertia type ball screw having the above characteristics.

[0014]

SUMMARY OF THE INVENTION In a ball screw for rotating a nut, the thickness of the ball screw nut is reduced, and a surface processing portion for mounting a return tube is reduced. That extends beyond the outside diameter of the ball screw nut
The tube was attached. The ball screw for rotating the nut is preferably used for an ejector device or a mold clamping device of an injection molding machine.

[0015]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 (a) is a sectional view of a nut rotating ball screw according to the present invention and a servomotor for rotating the nut. The servo motor 41 has a dish-shaped first flange 43 for attaching to the toggle support 42, a dish-shaped second flange 44 arranged at a predetermined distance from the first flange 43, and A motor case comprising a cylindrical frame 45 disposed between the first flange 43 and the second flange 44 is provided, and a hollow output shaft 3 is provided for the motor case. It is rotatably supported.

For this purpose, the rear end (left end in FIG. 1) of the output shaft 3 is supported by a thrust bearing 46 and the front end (right end in FIG. 1) is rotatably supported in a thrust direction and a radial direction by a thrust bearing 47. In order to rotate the output shaft 3, the frame 45 is provided with a stator 48, and the output shaft 3 is provided with a rotor 4
9 are respectively fixed. A coil 50 is provided on the stator 48. A bolt 51 is provided between the first flange 43 and the second flange 44. By tightening the bolt 51, the status of the stator 48 is reduced.
Can be sandwiched between the first flange 43 and the second flange 44.

A fixing nut 4 is screwed to a rear end of the output shaft 3, and a ball screw nut 1 is fixed to a front end of the output shaft 3 by a bolt 5. Therefore, by tightening the fixing nut 4, the thrust bearings 46, 47 can be sandwiched and fixed while applying a preload. A ball screw shaft 2 is disposed so as to be screwed with the ball screw nut 1 and penetrate the output shaft 3, and a cross head (not shown) is fixed to the tip of the ball screw shaft 2. You.

Accordingly, when a current is supplied to the coil 50, the rotor 49 is rotated, and the rotation is transmitted to the ball screw nut 1 via the output shaft 3. As a result, due to the screwing of the ball screw nut 1 and the ball screw shaft 2, the rotational movement of the ball screw nut 1 in the direction of arrow A becomes the linear movement of the ball screw shaft 2 in the direction of arrow B. Converted,
The ball screw shaft 2 and the crosshead are advanced and retracted by the stroke Sb. That is, when the crosshead is advanced, the toggle mechanism is extended and the movable platen is advanced, the mold is closed and the mold is clamped, and when the crosshead is retracted, the toggle mechanism is bent and the movable platen is retracted. The mold is opened.

The ball screw A has a structure as shown in the conventional type shown in FIG. 6, that is, the ball is prevented from being entirely contained within the thickness t of the ball screw nut 19, and FIG. As shown in FIG. 2A, a return tube 4 for circulating the ball is formed so as to protrude outside the outer diameter of the ball screw nut 1.

FIG. 2 shows a comparison between the ball screw nut of the present invention (FIG. 2A) and a conventional ball screw nut (also FIG. 2B).
In the conventional structure shown in FIG. 2B, a surface processed portion 5 is formed on a part of the ball screw nut and cut off (generally by milling), and a return tube 4 is attached to this portion. - Nchu - Bed 4 Bo - are Osame' than the outer diameter D ₁ to the inside of the ball screw nut 19. Therefore, all the balls are within the thickness (D ₁ -d) / 2 of the ball screw nut.

On the other hand, in the ball screw nut according to the present invention, as shown in FIG. 2A, the number of the surface processing portions 5 is smaller than that of the conventional one, and the return tube 4 is mounted on the upper portion.
The overhang dimension R of the return tube 4 up to the outer end face is larger than D / 2 (R> D / 2). This overhang (R
−1 / 2D), the thickness t of the ball screw nut 1 can be reduced.

In the case of a ball screw nut, if the wall thickness t is large, the mass is naturally large. Therefore, the balance and inertia at the time of rotation become problems. In the present invention, the nut outer diameter D and the wall thickness t are reduced, and the surface processing portion 5 by the milling machine processing is made smaller than in the prior art, so that the fluctuation of the rotational balance can be reduced and the inertia can be reduced. Since the rotation inertia is reduced by reducing the wall thickness t in this manner, the ball screw nut starts up quickly at the start of rotation, and is quickly reversed in response to an operation command.

When the thickness of the mold is changed, the movable mold may collide with the fixed mold due to a setting error. However, due to the reduction of the inertia, damage such as breakage is reduced. it can. If the inertia is large, there is a danger that the mold will be damaged or parts such as the toggle and the motor mechanism will be damaged. However, this can be avoided by the present invention.

Incidentally, Table 1 shows the nut dimensions of a conventional general ball screw, and Table 2 shows the nut dimensions of the ball screw of the present invention.

[0025]

[Table 1]

[0026]

[Table 2]

As is apparent from the above table, in the present invention (Table 1), the nut outer diameter D can be reduced even if the shaft diameter, the screw lead and the ball diameter are the same as those of the prior art. It can be seen that the ratio of the inner diameter to the outer diameter of the nut can be increased.

[0028]

(1) According to the first aspect, the inertia of the rotary nut of the ball screw can be reduced, so that the start-up at the start of the machine operation can be accelerated. (2) Since the dimensions of the nut can be reduced and the inertia can be reduced, when the mold is changed, even if there is a mistake in setting, the movable mold can be prevented from colliding with the fixed mold to damage the mold and the like. it can.

[Brief description of the drawings]

FIG. 1A is a cross-sectional view showing a nut rotation ball screw according to the present invention and a driving unit thereof. (b) is a front view of a ball screw shaft and a ball screw nut to be screwed thereto, (c) is a view as viewed from an arrow X in (a), and (d) is a view as viewed from an arrow Y in (a).

FIG. 2 is a comparison diagram of a known ball screw nut with the present invention.

FIG. 3 is a front view of a conventional mold clamping device.

FIG. 4 is a side view of FIG. 3;

FIG. 5 is a detailed view of the servomotor of FIG. 3;

6A and 6B show details of a known ball screw; FIG. 6A is a longitudinal sectional view, and FIG.

[Explanation of symbols]

1 ball screw nut 4 return
5 Surface processing part 11 Movable platen 12 Toggle support 13 Tie bar 14 Toggle mechanism 15 Drive 16 Toggle lever 17 Arm 18 Ball screw shaft 19 Nut 20 Crosshead 21 Toggle lever 22 Bolt 23 Drive case 24 Servo motor 25 Rotating sleeve 26 Side wall 25a Large diameter section 25b Small diameter section 27 Side wall 28 Cylindrical cover 29 Stator core 30 Rotor core 31 Bearing 32 Ball screw nut 33 Bolt 34 (Male screw) Thread groove 35 (Female thread) Thread groove 36 Ball

Claims (2)

[Claims] 1. A ball screw for rotating a nut, comprising:
The thickness of the screw thread nut is reduced, the number of surface processing portions for mounting the return tube is reduced, and the return tube projecting from the outer diameter of the ball screw nut to the surface processing portion is reduced. A ball screw for rotating a nut, wherein a ball screw for mounting the nut is provided. 2. The ball screw for rotating a nut according to claim 1, wherein the ball screw is used for an ejector device or a mold clamping device of an injection molding machine.