JPH054533B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) The present invention has a ball inserted between the screw shaft and the nut to enable relative rotational or linear movement, and an annular ball located approximately in the center of the outer periphery of the nut. This invention relates to a linear feed device using a ball screw unit provided with a flange.

(Problems to be solved by the prior art and the invention) Conventionally, feeding devices such as cutting tools and work tables have a series of balls interposed between the screw shaft and the thread groove of the nut. A ball screw unit has been provided which is capable of freely rolling and can perform a very light feeding operation using rolling friction, instead of the conventional one that uses sliding friction to perform feeding operation.

However, in conventional ball screw units, an annular flange for fixing a transmission member such as a gear is provided at one end of a cylindrical nut. If the inner periphery of the nut is carburized and quenched to release the
The heat treatment strain that occurs on the inner periphery of the nut on the side opposite to the flange forming side becomes relatively large. As shown in the figure, the problem was that the depth of the hardened layer was uneven. In addition, if the base metal of the nut is exposed to the outside, there is a drawback that the quality of the nut is deteriorated, such as impressions being formed on the thread groove surface when the balls roll. Therefore, as a countermeasure to the above problem, a method is generally adopted in which the hardened layer is made thicker to increase the grinding allowance, but it is said that making the hardened layer thicker requires more time for heat treatment and increases the cost of the product. This caused another drawback.

In addition, in conventional ball screw units, there is backlash (axial clearance) in the balls fitted between both thread grooves of the screw shaft and nut, so when either the screw shaft or the nut moves in the axial direction, However, there were problems in that not only uneven wear and noise occurred due to backlash between the ball and the thread groove, but also the compatibility of the screw or nut was poor. To counter this, countermeasures have been proposed, such as inserting a spacer to apply preload (preliminary compression) between the left and right pairs of nuts, and forcibly shifting the nuts in the compression direction or expansion direction to eliminate backlash. However, since unnecessary stress is applied to the nut, it becomes necessary to provide sufficient mechanical reinforcement, and the pressure work applied during assembly becomes inefficient. In order to eliminate such backlash, a technique has been known in which a preload is applied by providing a pitch difference between the thread grooves between the screw shafts of a single nut without using a spacer. With a pitch difference like this, the direction of contact between the nut and the thread groove and the ball is symmetrical with respect to the orthogonal plane where the left and right sides are perpendicular to the screw axis with the center of the nut as the border. It has a contact structure that is inclined to the left and right, and the left and right balls apply tension or pressure load to the screw shaft or nut in the thrust direction through the thread groove, and the reaction force is used to apply preload to the balls. It is.

However, when a combined load of a moment load and a thrust load is applied to the ball screw unit, the contact load on either the left or right ball increases due to the thrust load, and decreases on the opposite side. When a moment load is applied to the nut in this state, the ball on the side where the contact load is larger is loaded with a load greater than the predetermined preload, which prevents rattling, but the ball on the side where the contact load is smaller is loaded. There was a possibility that rattling would occur due to the moment load.

Furthermore, when constructing a linear feed device using such a ball screw unit, the screw shaft tends to run out due to a moment load, making it difficult to accurately feed the screw shaft linearly.

The present invention was made in order to solve the above drawbacks of the prior art, and its purpose is to provide an annular flange extending radially outward for fixing a transmission member at approximately the center of the outer periphery of the nut, and to heat-treat the nut. By suppressing the distortion that occurs on the inner periphery of the nut as much as possible, we aim to improve the quality of the nut and reduce the price of the nut.Furthermore, the row of balls interposed between the nut and the screw shaft is arranged to the left and right with the annular flange as the border. By distributing and applying preload to the left and right ball rows with a pitch difference, rattling can be effectively prevented even when a combined load of thrust load and moment load is applied, and the ball is fed by the screw shaft. It is an object of the present invention to provide a linear feeding device capable of accurately linearly feeding a movable member.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a screw shaft having a helical thread groove formed thereon, and a helical thread having a spiral thread corresponding to the thread groove on the inner periphery. A nut having grooves formed with pitch differences and an annular flange extending radially outward at approximately the center of the outer periphery; a transmission member attached to the annular flange; a ball guide that picks up a ball in a corresponding thread groove of a nut and returns it to the thread groove; a ball bearing that is attached to the outer periphery of the nut and the ball guide;
It consists of a housing that rotatably supports the nut via the ball bearing, and a plurality of ball rows that align and circulate between the screw shaft and the corresponding thread groove of the nut via the ball guide, and In a linear feed device that linearly moves the screw shaft by rotationally driving a nut, ball guides are installed on the left and right sides of the annular flange, and are connected between the screw shaft and the corresponding thread groove of the nut via the ball guide. Ball rows for aligning and circulating are also independently provided on the left and right sides of the annular flange, and a preload is applied to each ball row by providing a pitch difference between the screw shaft and the thread groove of the nut,
Furthermore, the ball bearings are also provided on the left and right sides of the annular flange, so that the nut is supported with respect to the housing on the left and right sides of the annular flange.

(Function) In the present invention, since the annular flange is provided at the center of the outer periphery of the nut, when heat-hardening the inner periphery of the nut, thermal distortion at the center of the nut is suppressed, and the openings at both ends and the center of the nut are The difference in thermal strain becomes smaller.
In addition, the balls rolling between the thread grooves of the nut and screw shaft are preloaded by the difference in the pitch of the thread grooves, eliminating backlash during relative movement between the screw shaft and the nut, and reducing the drive from the transmission member. Good responsiveness to. Since the ball rows are distributed to the left and right sides of the annular flange and a preload is applied to each ball row, the contact direction of each load ball is one set on the left and right with respect to the plane perpendicular to the screw axis. A symmetrical contact structure is constructed.

When a thrust load is applied to this ball screw unit, there are loaded balls compressed by the thrust load on both the left and right halves of the annular flange, and a moment load is generated that tries to rotate the nut across the annular flange. Even if the moment load is applied, this moment load is borne by the highly rigid load balls located on the left and right sides of the annular flange, thereby preventing rattling.

By installing ball bearings that support the nut on the left and right sides of the annular flange,
The nut can be rotated in a well-balanced and stable manner.

(Example) The present invention will be explained below based on the illustrated example. In FIGS. 1 to 4 showing a linear feed device according to an embodiment of the present invention, 1' indicates the entire ball screw unit used in this linear feed device, and this ball screw unit 1' generally has a threaded It consists of a ball screw 1 consisting of a shaft 2 and a nut 4, a housing 20 that rotatably supports the nut 4 via ball bearings 16 and 17, and a transmission member 13 that transmits rotational driving force to the nut 4. .

The ball screw 1 includes a screw shaft 2 having a spiral thread groove 3 formed at a predetermined pitch on the outer periphery of the shaft;
It consists of a cylindrical nut 4 which is screwed onto the screw shaft 2 through a ball row 5 made of steel balls and is movable in the axial direction or rotational direction.

A spiral thread groove 6 for rolling the ball row 5 is also provided on the inner circumference of the nut 4, and the spiral thread groove 6 is made to correspond to the thread groove 3 on the screw shaft side. There is.

Here, the thread groove 6 of the nut 4 is the thread groove 6 on the center side of the nut, as shown in FIG.
The pitches P ₁ and P ₂ between the thread grooves 6 and 6 (provided that the condition P ₁ = P ₂ exists) are the pitches P ₃ between the other thread grooves 6 and 6,
It is larger than P ₄ (assuming that there is a condition of P ₃ =P ₄ ), and has the relationship of P ₁ , P ₂ =P ₃ +α and P ₁ , P ₂ =P ₄ +α. Therefore, the load ball ₅₁ located on the left side of the center of the nut 4 is preloaded to the left, while the load ball ₅₂ located on the right side is preloaded to the right, in the direction of axially outward expansion of the nut 4. It turns out. In addition, on the contrary, Pitzchi P ₁ ,
Make P ₂ smaller than the pitches P ₃ and P ₄ on both sides, and P ₁ and P ₂
By establishing the relationship of = P ₃ - α and P ₁ , P ₂ = P ₄ - α, the load ball 5 ₁ on the left side and the load ball 5 ₂ on the right side are respectively placed inside the nut 4 in the axial direction. Preload can be applied in the compression direction.

7 is an annular flange provided approximately at the center of the outer circumference of the nut 4 so as to extend radially outward, and has an outer diameter larger than the outer diameter of the nut 4;
Further, a plurality of access holes 8 are provided at predetermined intervals in the circumferential direction. A mounting hole 8 is provided in the annular flange 7 in advance.
If this is provided, when fixing the nut 4 to the member to be fixed via the annular flange 7, there is no need to drill a mounting hole for the bolt insertion, and therefore the fixing operation of the nut 4 is relatively simplified. It will be easy.

Numerals 9 and 10 are ball guides such as return tubes that are arranged symmetrically on the left and right sides of the annular flange 7 on the outer periphery of the nut 4. Both ends of the ball guides 9 and 10, which have a substantially U-shaped cross section, They are inserted into radial communicating holes 4a, 4a, 4b, 4b that penetrate through and open into the inside of the nut. The communication holes 4a, 4a on one side of the respective communication holes 4a, 4a, 4b, 4b have a row of balls that roll spirally between the thread groove 3 of the screw shaft 2 and the thread groove 6 of the nut 4. The communication holes 4b, 4b on the other side are opened inside the nut at the rolling start end position of the ball row 5.
It opens inside the nut at the rolling end position.

As a result, each ball 50 forming the two ball rows ₅ that spirally rolls between the thread grooves 3 and 6 of the screw shaft 2 and the nut 4 moves toward the ball guides 9 and 10 at its rolling end position. After being picked up from inside the screw grooves 3 and 6 by the ball guides 9 and 1,
0 and returns to the thread groove 3 at the rolling start position.
6 and repeats the alignment cycle. Each ball guide 9, 10 has a guide presser 11,
12, it is integrally attached to the outer periphery of the nut 4.

13 is connected to the annular flange 7 by bolts 10.
A transmission member such as a worm gear is fixed to the outer periphery of the worm 15 and is meshed with the worm 15 on the power side. Ball bearings 16 and 17 are angular contact bearings mounted on both ends of the outer periphery of the nut 4, and are constructed with balls interposed between an outer ring and an inner ring. 18 and 19 are Natsu 4
A spacer press-fitted between the annular flange 7 at the center of the outer periphery and both ball bearings 16 and 17 applies preload in the expansion direction to the balls on the ball bearings 16 and 17 side.

20 is a housing for fixedly supporting the ball screw unit 1', and 21 is a housing for pressing the ball screw unit 1' from the opening side of the housing toward the rear end side when fixing the ball screw unit 1' to the housing 20. This is a fixing nut for The fixing nut 21 also acts as a member for taking up a reaction force when applying preload to the ball bearing 17 on one side using the spacer 19.

In the ball screw unit configured as described above, when the worm 15 is rotated by a drive motor (not shown), the nut 4 is rotated via the transmission member 13, and the screw shaft 2 is rotated to either the left or the right in the figure. Move in direction. When the nut rotates four times, the two rows of balls 5, 5 provided on the left and right through the central flange 7 circulate between the screw shaft 2 and the thread grooves 3, 6 of the nut 4 and through the ball guides 9, 10. do. A preload is applied to the ball 5 interposed between the nut 4 and the thread grooves 3 and 6 of the screw shaft 2.
Since the backlash (axial clearance) between the screw shaft 2 and the nut 4 is zero, the screw shaft 2 is
Accurately follows the rotation of 5. Also, when changing the axial feed direction, there is no play and the followability is good.

In addition, since a preload is applied to each ball 5, the rigidity is high, and even if a shock load is applied, such as when a movable member such as a work table suddenly starts, the ball 5... deforms and the screw shaft 2 There is no wobbling when moving, and responsiveness is dramatically improved.

Furthermore, in this embodiment, the ball bearing 16,
Preload is also applied to 17 by the spacer 19, but since the nut 4 on the ball screw 1 side has a single structure, the ball bearings 16, 17
The preload applied to the ball screw 1 side is not interfered with by the preload applied to the ball screw 1 side, and therefore the preload on the ball screw 1 side can be adjusted accurately.

6a to 6d schematically show the contact directions of the loaded balls of the present invention and the conventional example. That is, as shown in FIGS. 6c and d, the contact direction of each conventional load ball is a pair of contact structures (B _L and B _r ).

When such a nut 12 is subjected to a thrust load T directed to the right in the figure and a moment load M clockwise, the preload applied to the ball B _r in the left half of the nut 12 due to the thrust load T tends to become smaller. (See Figure 6c). Therefore, when the moment load M acts in this state, the ball example in the right half as a whole, especially the ball B _r1 located at the right end
is crushed and deformed by the direction of the moment load, and the smooth circulation of the balls is obstructed (see Figure 6d).

On the other hand, in the present invention, as shown in FIGS. 6a and 6b, the contact direction of the ball due to the application of preload is determined by a pair of contact arrangements that are symmetrically inclined in the left and right halves of the nut 4. Structure (B _L0
and B _L1 and B _r0 and B _r1 ).

When a combined load of a thrust load T and a moment load M is applied to such a nut 4, the nut 4
Since a contact structure is adopted that applies preload to each row _of balls distributed in the left and right halves of the ball, each row of balls is loaded with high rigidity and preload is applied regardless of the direction of the thrust load T.
B _r0 exists. Therefore, even if a moment load M acts in this state, the moment load M is shared and supported by each highly rigid load ball B _L0 and B _r0 , and the increase in the load on the ball B _r1 is reduced. This ensures smooth circulation of the ball.

Furthermore, the moment load M acting on the nut 4 acts through the annular flange 7,
Since this annular flange 7 is provided at the center, the load applied to the balls B _L0 and B _r1 located at both ends of the nut 4 is equally distributed to the left and right, and the moment load M can be supported in a well-balanced manner. , it is possible to further increase the load capacity against the moment load M.

(Effects of the Invention) As described above, the ball screw unit of the present invention is provided with an annular flange extending radially outward at approximately the center of the outer periphery of the nut, so even if the thread groove on the inner periphery of the nut is carburized and quenched, the nut remains intact. Since the degree of heat treatment distortion that occurs on the inner periphery of both ends is reduced, not only can the depth of the effect layer be almost uniform when thread grooves are ground, but the base metal of the nut will not be exposed to the outside. . In this way, in the present invention,
Even after finishing the grinding, a hardened layer of uniform depth can be formed on the ball rolling surface of the thread groove of the nut, so even if the balls are circulated within the thread groove of the screw shaft and nut after the ball screw is assembled, , the conventional inconvenience of creating impressions on the shallow part of the hardened layer or on the externally exposed parts of the base metal is completely eliminated, thereby ensuring smooth alignment and circulation of the balls over a long period of time. This has the effect of greatly improving the quality of ball screws. Also, even after finishing the grinding,
Since the depth of the hardened layer can be made almost uniform, it is no longer necessary to thicken the hardened layer before finishing by grinding as in the past, and the heat treatment process of nuts can be completed in a short time, reducing costs. Helps reduce

In addition, the nut is driven at the center and supported at both ends, and preload is applied by creating a pitch difference between the rows of balls distributed between the left and right halves of the nut. There are also high-rigidity load balls in the ball row that are compressed by the thrust load, and even if a moment load is applied in this state, it can be taken care of by the high-rigidity load balls on the left and right, and the thrust It can effectively support the combined load of load and moment load.

In particular, when assembling the nut to the housing to configure a linear feed device, by providing ball bearings that support the nut on the left and right sides across the annular flange, the nut can be rotated in a well-balanced and stable manner. This does not cause the nut to twist, and in combination with the ball preload structure between the nut and the screw shaft, it is possible to accurately linearly feed a movable member such as a work table that moves integrally with the screw shaft.

[Brief explanation of the drawing]

1 is a longitudinal sectional view showing a ball screw unit according to the present invention, FIG. 2 is a plan view showing the ball screw of the ball screw unit of FIG. 1, and FIG. Figure 4 is a vertical cross-sectional view of the main part showing a state in which a pitch difference is provided in the thread groove of the ball screw side nut, Figure 5 is a vertical cross-sectional view of the main part showing a conventional ball screw with an end flange, and Figure 6 is a main part longitudinal cross-sectional view of the ball screw with a conventional end flange. This is a comparison of the contact structure of the loaded ball in the invention and the conventional example. Figures (a) and (b) are schematic cross-sectional views showing the ball contact structure of the present invention, and figures (c and d) are the conventional ball contact structure. FIG. Explanation of symbols, 1... Ball screw, 1'... Ball screw unit, 2... Screw shaft, 3... Thread groove (screw shaft), 4... Nut, 4a, 4b... Communication hole, 5... Ball example, 5 ₀ , 5 ₁ , 5 ₂ ... ball,
6... Thread groove (nut), 7... Flange, 8...
...Mounting hole, 9,10...Ball guide, 11,1
2... Guide presser, 13... Transmission member, 14...
Bolt, 15... Worm, 16, 17... Ball bearing, 18, 19... Spacer, 20... Housing, 21... Fixing nut.

Claims (1)

[Scope of Claims] 1. A screw shaft with a spiral thread groove formed thereon, and a spiral thread groove corresponding to the thread groove formed on the inner periphery with a pitch difference, and approximately in the center of the outer periphery in the radial direction. A nut provided with an extending annular flange, a transmission member attached to the annular flange, and a transmission member attached to the outer periphery of the nut to pick up the ball in the corresponding thread groove of the screw shaft and the nut and return it to the thread groove again. A ball guide, a ball bearing attached to the outer periphery of the nut and the ball guide, a housing that rotatably supports the nut via the ball bearing, and a connection between the screw shaft and the threaded groove of the nut via the ball guide. In the linear feeding device, which comprises a plurality of aligned and circulating ball rows, and which linearly moves the screw shaft by rotationally driving a nut through the transmission member, the ball guides are installed on the left and right sides of the annular flange, respectively. In addition, rows of balls that align and circulate between the corresponding thread grooves of the screw shaft and the nut via the ball guides are also provided independently on the left and right sides of the annular flange, and each ball row is connected to the thread grooves of the screw shaft and the nut. A straight line characterized in that a preload is applied by providing a pitch difference therebetween, and the ball bearings are also provided on the left and right sides of the annular flange, so that the nut is supported with respect to the housing on the left and right sides of the annular flange. Feeding device.