JPH07317870A - Ball screw device - Google Patents

Abstract

PURPOSE:To facilitate use through rotation of a nut by reducing the generation of the inertia moment of a rotary part. CONSTITUTION:A ball screw device comprises a screw shaft 1 in the outer peripheral surface of which a ball screw groove 1a is formed; a ball nut 2 in the inner peripheral surface of which a ball screw groove 2a positioned facing the ball screw groove 1a of the screw shaft 1 is formed; a number of balls 3 fitted between the ball screw groove 1a of the screw shaft 1 and the ball screw groove 2a of the ball nut 2 and performing helical movement of the ball nut 2 based on the screw shaft 1; and a tube type circulation passage 12 through which the balls 3 are circulated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention linearly moves a table or the like of a machine tool, a woodworking machine, a laser processing machine, an electronic component mounting machine, a long stroke carrier machine or the like which requires a relatively long stroke. The present invention relates to a ball screw device for use in, especially to an improvement of a ball screw device for fixing a screw shaft and rotating a nut.

[0002]

2. Description of the Related Art In a ball screw device, a ball screw having a ball screw groove on its outer peripheral surface is provided with a ball nut having a ball screw groove on its inner peripheral surface through a large number of balls rolling in these screw grooves. They are screwed together, and are used to axially move a table or the like on which the ball nut is mounted by rotating either the screw shaft or the ball nut.

Generally, the ball screw device is disadvantageous in that it is used by rotating the shaft because the moment of inertia of the screw shaft increases as the screw shaft becomes longer, and it is advantageous to use it by rotating the nut. FIG. 7 shows an example of the usage of such a ball screw device, in which the ball nut is rotated. That is, the screw shaft 1 has shaft fixing blocks 101 and 10 each having both ends attached to the base 100.
It is fixed by 1 and is non-rotatably supported. The guide rails 10 are provided on both sides of the screw shaft 1 in parallel with the screw shaft 1 in parallel.
2, 102 are arranged and fixed to the base 100. Two sliders 103 are fitted to each guide rail 102 so as to be slidable in the axial direction of the guide rails 102. Table T on those sliders 103
Is placed and fixed. Below that table T,
The ball nut 2 is rotatably supported by the housing H, and the ball nut 2 is attached to the motor M inscribed in the housing H by a timing belt 26.

The ball nut 2 is rotated by rotating the motor M. Since the screw shaft 1 is non-rotatably fixed, the ball nut 2 itself moves along the screw shaft 1 while rotating. As a result, the table T moves smoothly in the axial direction while being guided by the slider 103.

[0005]

In the case of the ball screw device shown in FIG. 7 in which the screw shaft is fixed and the nut is rotated, the end cap type ball screw device shown in FIG. It is used. This has end caps 4 at both ends of a nut body 2A of a ball nut 2 that is screwed onto a screw shaft 1 via balls 3, and the end caps 4 have a U-shape as a ball circulation path. The curved path 5 is internally provided. The ball 3 that has moved to the end of the ball nut body 2A while rolling between the ball screw groove 1a on the outer periphery of the screw shaft 1 and the ball screw groove 2a on the inner periphery of the ball nut 2 has one end. It is guided to the curved path 5 of the cap 4 and makes a U-turn, enters an axial ball return path 6 provided in the ball nut body 2A, and rolls over it to move over the ball screw grooves 1a, 2a. Then, the circulation is repeated until it reaches the opposite end, is guided to the curved path 5 of the other end cap 4, makes a reverse U-turn, and returns to the original position.

The ball nut body 2A has an inner ring ball groove 7a of a support bearing 7 formed on the outer periphery thereof, and is rotatably supported via a bearing ball 9 on a bearing outer ring 8 having an outer ring ball groove 8a on the inner periphery. , The nut is rotated smoothly. However, since such an end cap type ball screw device is used for rotating the nut, it is difficult to reduce the outer diameter of the nut in terms of design. Therefore, the moment of inertia of the rotating portion of the nut cannot be set small. The load inertia on the drive motor is inevitably large, and as a result, the responsiveness of the nut rotation to the drive motor deteriorates, and the positioning accuracy of the table deteriorates.

Therefore, the present invention has been made in view of such conventional problems, and in a ball screw device used for nut rotation, the moment of inertia of the rotating portion is reduced to make the nut rotation relative to the drive motor. It is an object of the present invention to provide a ball screw device which has good responsiveness and can improve the positioning accuracy of the table and the feed rate of the table.

[0008]

DISCLOSURE OF THE INVENTION A ball screw device of the present invention is a ball screw device used for nut rotation, comprising a screw shaft having a ball screw groove on its outer peripheral surface and a ball screw groove of the screw shaft. A large number of ball nuts that have opposing ball screw grooves on their inner peripheral surfaces and are fitted between the ball screw groove of the screw shaft and the ball screw groove of the ball nut to enable spiral movement of the ball nut with respect to the screw shaft. Ball and
It is characterized by having a tube type circulation path for circulating those balls.

[0009]

Since the ball nut using the tube type circulation path has a structure in which the ball return path is provided outside the ball nut body by using the tube, the wall thickness of the body portion of the ball nut body can be considerably reduced. Further, the inner ring ball groove of the bearing portion that rotatably supports the ball nut is formed to be axially outward while avoiding interference with the circulation tube. As a result, the ball nut body becomes longer in the axial direction, but the moment of inertia J of the rotating part has a relationship of JαD ⁴ · L (D is the outer diameter, L is the length) ──── (1) Since the decrease in the inertia moment due to the decrease in the outer diameter of the body portion of the ball nut is considerably larger than the increase in the inertia moment due to the increase in the axial direction, the inertia moment of the entire ball nut is significantly reduced.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a plan view of an embodiment of the present invention in which half of the outer ring of the support bearing is cut away. 2 is a sectional view taken along line II-II of FIG. 1, and FIG. 3 is a partial sectional view of FIG. It should be noted that the same or corresponding parts as in the conventional case are designated by the same reference numerals, and detailed description thereof will be omitted.

The ball nut 2 screwed onto the screw shaft 1 has a central portion having an outer diameter smaller than that of both ends, and a part of the side surface of the cylindrical body is chamfered to form a flat surface. A circulation tube 12, which is a tube-type circulation path, is fixed to the flat surface 11a by a screw 14 via a presser foot 13, which is a so-called tube pop-out type ball nut. In this embodiment, the number of threads of the thread groove 1a of the screw shaft and the thread groove 2a of the ball nut is one, so that there is also one circulation tube 12. A chamfered flat surface 11b is also formed on the body portion on the opposite side of the flat surface 11a to balance the rotation.

Both ends of the ball nut 2 have a diameter larger than that of the central portion, and an inner ring groove 15 of the bearing is formed on the outer peripheral surface thereof. Then, a large number of bearing balls 16 are inserted into the inner ring groove 15, and a bearing outer ring 18 having an outer ring groove 17 which is an outer ring raceway of the bearing balls 16 on the inner peripheral surface is mounted on the outer side of the bearing balls 16 to support the bearing 20. It is configured. This support bearing 20 has a mounting flange 21 on its outer surface, and is fixed to a housing (not shown) by passing a bolt through a screw hole 22 provided in the flange 21 to rotatably support the ball nut 2.

When the ball screw device constructed as described above is used, both ends of the screw shaft 1 are fixed by the shaft fixing blocks 101, 101 so as to be non-rotatably supported, as shown in FIG. On the other hand, the ball nut 2 is attached to the table T of the machine via the housing H by the attachment flange 21 of the support bearing 20 thereof. In this way, the timing pulley 25 is attached to one end (the left end in FIG. 1) of the ball nut 2 rotatably supported by the support bearing 20, and is fixed by the bolt B. Then, the timing belt 26 is stretched between the timing pulley 25 and the pulley attached to the motor M mounted on the housing H or the table T.

Thus, the table T can be fed in the axial direction of the screw shaft 1 by driving the motor M and rotating the ball nut 2. When the ball nut 2 is rotated, the outer diameter of the ball nut 2 is smaller than that of the conventional one in most parts except for both ends, and therefore is proportional to the fourth power of the outer diameter as shown in the above formula (1). As a result, the moment of inertia is reduced, and in the case of this embodiment, the result of 12 to 16% reduction in the conventional case was obtained.

Further, since the tube type circulation path is used, it is not necessary to provide a ball return path inside the nut in the end cap type circulation path, and the length of the circulation tube is reduced even when the screw lead corresponds to a special screw. Since it can be changed, the influence on the moment of inertia can be reduced. As a result, the degree of freedom in selecting the shaft diameter of the screw shaft 1 and the screw lead is increased, and it is possible to easily meet the requirements for the special shaft diameter and the screw lead.

Furthermore, in the conventional end cap type,
In contrast to the structure in which the pulley is bolted to the ball nut via the resin end cap, in the case of this embodiment, the pulley 25 can be directly fixed to the metal ball nut 2 with the bolt B. The effect of improving the reliability of was also obtained. FIG. 5 shows a second embodiment.

In this embodiment, the screw shaft 1 and the ball nut 2 are double-threaded screws. Therefore, the number of the circulation tubes 12 is also two, each of which is chamfered on one flat surface 11a and on the other side which is not shown in the drawing. This is different from the first embodiment in that it is arranged on the plane at a phase of 180 °. Other configurations, operations, and effects are similar to those of the first embodiment.

In the above embodiment, the ball nut 2 and the timing belt 2 are used as the drive system of the ball screw device.
Although the one connected to the motor M via 6 is shown, the present invention is not limited to this, and a hollow motor having a hollow hole in the shaft core may be used instead. In that case, the hollow motor is mounted on the table T via a bracket, the screw shaft 1 is inserted into the hollow hole of the hollow motor, and the output portion of the hollow motor and the ball nut 2 are connected via a mounting jig.

Further, the ball circulation tube 12 may be a general general one formed by bending a circular pipe material into a substantially U shape. Alternatively, for example, the ball circulation tube is symmetrical in the pipe axis direction. It is also possible to use a split type ball circulation tube in which two U-shaped members having a semi-circular cross section which are split by an axis are assembled into a tube.

Further, in the first embodiment, the chamfered flat surface 11b is also formed on the body portion opposite to the flat surface 11a to balance the rotation, but the flat surface 11b is not provided in FIG.
As shown in FIG. 4, the holes 30 may be used to balance the rotation.

[0021]

As described above, in the nut rotation type ball screw device according to the present invention, the screw shaft is fitted between the ball screw groove of the screw shaft and the ball screw groove of the ball nut. The circulation path that circulates a large number of balls that enable the spiral movement of the ball nut with respect to is a tube type circulation path that protrudes outside the ball nut,
Since the outer circumference of the ball nut is rotatably supported by the support bearing, it is not necessary to provide the ball circulation path inside the ball nut, and the outer diameter of the ball nut can be made as small as possible. The inertia moment proportional to the fourth power of the diameter is significantly reduced, the responsiveness of the nut rotation to the drive motor is improved, and the positioning accuracy of the table is improved.

Further, since the tube type circulation path is provided, the degree of freedom in selecting the inner diameter of the ball nut, and thus the screw shaft shaft diameter and the screw lead is increased. The effect of being able to easily cope with is obtained. According to the invention of the embodiment of the present invention, in addition to the above respective effects, by directly bolting the pulley in the case of the belt drive system to the ball nut,
There is also an effect that the reliability is improved as compared with the conventional one in which the pulley is fastened via the end cap.

[Brief description of drawings]

FIG. 1 is a plan view showing a part of a first embodiment of the present invention by cutting away.

FIG. 2 is a sectional view taken along line II-II in FIG.

FIG. 3 is a partial vertical cross-sectional view of FIG.

FIG. 4 is a schematic diagram illustrating an example of a usage mode of the ball screw device of the present invention.

FIG. 5 is a plan view showing a part of the second embodiment of the present invention by cutting away.

FIG. 6A is a sectional view of another embodiment of the present invention, which corresponds to FIG. 2, and FIG. 6B is a view taken in the direction of arrow B in FIG.

FIG. 7 is a plan view showing an example of use of the ball screw device.

FIG. 8 is a plan view showing a part of a conventional end cap type ball screw device in section.

[Explanation of symbols]

 1 screw shaft 1a screw groove 2 ball nut 2a screw groove 3 ball 12 tube type circulation path (circulation tube) 20 support bearing

Claims (1)

[Claims] 1. A ball screw device used for nut rotation, comprising a screw shaft having a ball screw groove on the outer peripheral surface, and a ball screw groove on the inner peripheral surface facing the ball screw groove of the screw shaft. A nut, a number of balls fitted between the ball screw groove of the screw shaft and the ball screw groove of the ball nut to enable the spiral movement of the ball nut with respect to the screw shaft, and a tube type circulation that circulates these balls. A ball screw device, characterized in that the ball nut is rotatably supported by a support bearing on the outer periphery of the ball nut.