JPH028179B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention has a steel ball inserted between a screw shaft and a nut so that they can move relative to each other, and this nut is an angular contact ball bearing installed on the outer periphery of the nut. Concerning a limited sliding ball screw with contact ball bearings.

Conventionally, a steel ball is interposed between the screw shaft and the nut to allow it to roll freely, and instead of the conventional feeding operation using sliding friction, this ball screw allows for extremely light feeding operation due to rolling friction. is provided.

However, in the case of such a ball screw,
The structure was such that the steel ball rotated around the thread groove of the screw shaft and nut one and a half to three times, was picked up into the ball tube, and returned to its original position, which caused the problem of increased noise. Ta.

In addition, in conventional limited sliding ball screws, in order to obtain the maximum stroke of the nut or screw shaft while preventing a decrease in load capacity, a distance equivalent to approximately 2/3 of the total length of the nut (axial length It is common to set the number of turns of the ball to
I was using a nut with a length commensurate with the increase in stroke. However, since machining the thread grooves on the inner circumferential surface of the nut is a difficult task,
The longer the axial length of the nut, the longer the machining time and the higher the cost.
There was also a problem that the grinding accuracy was reduced and the smooth rolling of the balls was hindered. In addition, since the number of turns of the ball was set at a distance of about 2/3 of the total length of the nut, there was another problem in that the load capacity was reduced by about 30%. Furthermore, there was a problem in that dust easily entered the thread groove of the screw shaft from the end face of the nut, and the dust solidified with the lubricating oil, impeding the smooth rotation of the steel ball and making the relative movement of the screw shaft and nut heavier. .

Furthermore, in conventional ball screws, there is an axial clearance (backlash) between the steel balls fitted between the thread grooves of the screw shaft and the 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 were caused by backlash between the steel ball and the screw groove, but also the response of the screw shaft or nut was poor. To counter this, countermeasures have been proposed, such as inserting a spacer between the left and right nuts to apply preload, and forcibly shifting the nuts in the compression 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 press-fitting operation during assembly becomes inefficient.

In addition to the relative rotation and axial movement of the screw shaft and nut in the ball screw, in particular, the screw shaft and nut are rotatably supported with respect to a fixed member such as a frame or a housing that supports the nut. There are times when it is necessary to coerce. In such a case, a ball bearing with steel balls interposed between the inner ring and the outer ring is interposed between the fixing member and the nut. However, mounting such a ball bearing increases the outer diameter of the entire ball screw, which poses a problem that it is not suitable for applications such as transmission devices that require precision and miniaturization.

The present invention has been made in view of these conventional problems, and an object of the present invention is to pick up a steel ball that has rolled in a thread groove formed on a screw shaft and then screw it back into the screw shaft. By removing the ball tube that returns to the groove, the problem of noise when the steel ball returns is eliminated.

Furthermore, another purpose is to create a difference in the thread groove pitch of the nut fitted onto the screw shaft, so that preload is applied to the steel ball, thereby eliminating the need for preload applying members such as spacers. The purpose is to reduce the number of parts used and lower costs.

Still another object of the present invention is to increase the maximum stroke of the nut or the screw shaft without increasing the axial length of the nut by integrally providing the nut extension on the nut mounted on the screw shaft. The objective is to increase the load capacity and increase the load capacity. Yet another purpose is to prevent dust from entering the inside of the nut.

Furthermore, it is an object of the present invention to improve the outer diameter of the entire ball screw by substituting the nut for the inner ring that is a component of the ball bearing that rotatably supports the nut with respect to the fixed member. The goal is to make it smaller and more compact.

In the following, the invention will be explained in detail with reference to the illustrated embodiments. In Figure 1, 1 is a ball screw,
The screw shaft 2 constituting the ball screw 1 has a screw groove 3.
is provided. 4 also has a steel ball 5 on the screw shaft 2.
A cylindrical nut that is screwed together and is movable in the axial and rotational directions, and the inner circumference of this nut 4 is also provided with a spiral threaded groove 6 for rolling a steel ball 5. It corresponds to the thread groove 3 of the screw shaft 2.

Here, as shown in FIG. 2, the thread grooves 6 of the nut 4 are
The pitch P ₁ between them is the pitch P ₂ between the other thread grooves 6, 6,
It is larger than P ₃ and has the relationship of P ₁ = P ₂ + α and P ₁ = P ₃ + α. Therefore, _{the load} steel balls _{X 1} ... It will receive preload in the expansion direction toward X and Y. Conversely, by making the pitch P ₁ smaller than the pitches P ₂ and P ₃ on both sides and establishing the relationships P ₁ = P ₂ - α and P ₁ = P ₃ - α, the left side Load steel ball X ₁ …X ₅
A preload can be applied to the load steel balls Y ₁ to _{Y 6} on the right side of the nut 4 in the axially inward compression direction of the nut 4, respectively.

Reference numeral 7 denotes a cylindrical nut extension part which integrally locks the base end 8 on both end surfaces of the nut 4 and has the bent tip 9 on the opposite side fitted into the thread groove 3 all around. The distance is set longer than about 1/2 of the axial length of 4. Since the nut 4 is provided with the nut extension 7, the number of turns of the steel ball 5 can be set to be greater than the axial length of the nut 4. Note that the relative movement distance of the screw shaft 2 or the nut 4 is the range up to the point where the bent end 9 of the nut extension 7 and the end of the retainer 10 (described later) come into contact, that is, in the illustrated embodiment, The distance is limited to the number of turns (see Figure 1). Here, the length of the nut extension part 7 is set to be larger than at least about 1/2 of the axial length of the nut 4, and the screw shaft 2 or the nut 4 is set within a distance corresponding to 5 turns of the steel ball. The purpose of relatively moving is to obtain the maximum stroke of the screw shaft 2 or nut 4 while applying preload to the steel ball 5 in the direction of expansion or compression, as shown in FIGS. 2A and 2B. As shown in FIG. 2, the width diameter _h1 between the inner circumferential surface of the nut extension part 7 and the thread of the screw shaft 2, and the width diameter between the groove bottom of the nut side thread groove 6 and the thread of the screw shaft 2. h ₂ has the same dimension, that is, the groove bottom of the nut side thread groove 6 is in contact with the inner circumferential surface of the nut extension 7 and is on an extension of the tangent line H parallel to the screw shaft 2, so that the inside of the thread groove 3 of the screw shaft 2 is The rolling steel ball transitions from a loaded region where it fits into the thread groove 6 on the nut side and receives a load, to a no-load region where it only contacts the inner circumferential surface of the nut extension 7 and receives no load. ,
Alternatively, the rolling transition in the opposite direction can be smoothly performed. In this case, as shown in FIG. 3, the no-load ball in the no-load area is connected to both sides of the thread groove 3 on the screw shaft side and the inner peripheral surface of the nut extension 7 at three points 5a, 5b, and 5c. Since the balls are in contact and supported at the three points, the alignment and circulation movement of the balls is not impaired. Further, since the bent tip 9 is tightly fitted into the thread groove 3 by a single spiral ridge formed on its inner circumference, the nut extension 7
The interior space is completely isolated from the outside.

Reference numeral 10 denotes a cylindrical retainer that is inserted between the screw shaft 2 and the nut 4, and this retainer 10 rotates between the screw groove 3 of the screw shaft 2 and the screw groove 6 on the nut side corresponding to the screw groove 3. A large number of moving steel balls are held within the ball hole 11, and the steel balls are configured to freely rotate within the ball hole 11. The relative motion among the retainer 10, screw shaft 2, and nut 4 is in the following relationship. i.e. Natsu 4
When the screw shaft 2 is rotated with the retainer 10 fixed in the rotational and axial directions, the retainer 10 moves in the axial direction together with the screw shaft 2. On the other hand, when the screw shaft 2 is rotated with the screw shaft 2 fixed in the axial direction and the nut 4 fixed in the rotation direction at the same time, the retainer 11 locks the nut 4.
It will move along with the axial direction. In short, the retainer 10 performs linear motion together with either the screw shaft 2 or the nut 4, which is a member that moves in the axial direction.

On the other hand, numeral 12 is an angular contact ball bearing attached to the top surface of the nut 4 on the screw shaft 2 side.
It constitutes a front-to-back combination or a back-to-back combination in a rolling bearing. As clearly shown in FIG. 4, this ball bearing 12 is formed by inserting two balls between the outer ring and the nut, and this ball bearing 12 is an angular bearing with a contact angle of approximately 45 degrees. It consists of Yuracontact ball bearings and has a face-to-face structure. The outer ring 13 has a fixing flange 1 on the top surface.
4, and at the same time, a branch jetty 16 with ball grooves 15, 15 formed on both sides for ball storage.
It has at the center of the bottom surface. On the other hand, the inner ring is formed by a combination of a nut 4 screwed onto the screw shaft 2 and a nut auxiliary member 17 provided on the side of the nut 4.
Ball grooves 18, 18 corresponding to the ball grooves 15, 15 of the outer ring are provided at the corners of the step formed on the upper surface of the nut auxiliary member 17, and the nut 4,
At least two ball tracks are formed between the outer ring 17 and the outer ring 13. Reference numeral 19 denotes a pressing member, such as a double nut, which applies preload to the balls rolling on the two ball orbits, and is attached to the side of the nut auxiliary member 17. By biasing the nut auxiliary member 17 in one direction using the pressing member 19, a preload can be applied to the ball inserted between the outer ring and the nut. Therefore, in this embodiment, the preload can be easily adjusted by simply operating the pressing member.

5 and 6 show other embodiments of applying preload to the balls of a bearing that also constitutes an angular contact ball bearing, and in the back-to-back structure shown in FIG. At the center of the upper surface of the nut 4a, which serves as an inner ring screwed onto the screw shaft 2, there are ball grooves 18a, 18a on both sides.
While the branch protrusion 16a is provided with a split type, the outer ring is of a split type.
Ball grooves 15a, 15a corresponding to the ball grooves 18a, 18a on the nut side are formed on the bottom surface of each pair of outer rings 13a, 13a. By fitting a spacer _S1 between the pair of outer rings 13a, 13a, the balls placed between the ball grooves 15a, 18a on each outer ring side and the nut side are pulled in the tensile direction (the balls separate from each other). A preload can be applied in the direction of compression (direction in which the balls approach each other) or in the compression direction (direction in which the balls approach each other). In the front-to-face combination structure shown in FIG. 6, a recess is formed in the upper surface of the nut 4b screwed onto the screw shaft 2, and ball grooves 18b, 18b are formed at both corners of the recess. is provided. On the other hand, ball grooves 15b, 15b corresponding to the ball grooves 18b, 18b on the nut side are formed on the inner surface of each pair of outer rings 13b, 13b. Therefore, the corresponding ball grooves 15b, 1 on the outer ring side and the nut side
After putting the ball between 8b, each outer ring 13b, 13
By fitting the spacer S ₂ between b, it is possible to similarly apply a preload to the ball. Note that R ₁ ,
_R2 is an annular ring that rotatably holds the ball within the ball hole. In this embodiment, a spacer is provided between the pair of annularly arranged outer rings to apply preload, so there is an advantage that the preload can be finely adjusted.

Note that the outer ring 1 of the angular contact ball bearings 12, 12a, 12b shown in FIGS. 4 to 6
3, 13a, and 13b are fixed to the frame or housing of the machine tool. That is, this outer ring is fixed in both the axial direction and the rotational direction.

In the above configuration, when the screw shaft 2 is driven to rotate with the nuts 4, 4a, 4b fixed in the rotational direction, the screw shaft 2 moves in the axial direction with respect to the fixed nuts 4, 4a, 4b. On the contrary, when the nuts 4, 4a, 4b are rotated at fixed positions, the screw shaft 2 can be moved in the axial direction by the screw feeding action of the nuts. In this case, nuts 4,4
a and 4b are rotatably supported on ball bearings 12.

By the way, when the screw shaft is linearly moved in the axial direction by rotationally driving the nut, if a preload is applied to the two balls of the ball bearing, the gap between the nut and the fixed member such as the outer ring or housing will be reduced. Since it can completely eliminate bumps, it can be used in a wide range of applications, such as feeding machine tool press tables and other workpiece feeding machines in industrial machinery.

The present invention has the above-described structure and operation, and as a ball screw, it is possible to apply preload by simply making a difference in the pitch of the nut side thread groove 6 as shown in FIG. There is no need to use a preload applying member. Furthermore, the ball tube that picks up the steel balls that have rolled in the thread groove formed on the screw shaft and then returns them to the thread groove can be removed, thereby eliminating the noise that occurs when the steel balls return, unlike in the prior art.

Furthermore, in the ball screw of the present invention, the number of turns of the steel ball can be set over a distance equal to or longer than the axial length of the nut by integrally providing the nut extension part on the nut fitted onto the screw shaft. Therefore, the stroke of the nut or screw shaft can be increased by about 20 to 30% compared to conventional limited sliding ball screws without increasing the axial length of the nut. In addition, since a series of steel balls are wound around the entire length of the nut, it is possible to support thrust loads over the entire length of the nut, increasing the load carrying capacity for thrust loads by approximately 30% compared to conventional models. can be done. Furthermore, since the stroke of the nut or screw shaft can be increased without changing the axial length of the nut, it is equivalent to shortening the axial length of the nut by the length corresponding to the increased stroke, and therefore Grinding accuracy can be improved when forming thread grooves. In addition, by providing a nut extension, dust is completely prevented from entering the inside of the nut.
Precise relative movement between the screw shaft and nut can be guaranteed over a long period of time.

Furthermore, as mentioned above, the ball screw according to the present invention has a preload structure, and the axial backlash of the ball screw is zero, so there is no play between the screw shaft and the nut, and therefore there is no play during axial movement. The responsiveness of the ball screw movement is excellent. Furthermore, there is no play when changing the feed direction when moving in the axial direction, so followability is good.
Further, since the preloaded ball screw has high rigidity, accurate positioning is possible and there is no wear, making it durable for long-term use.

Furthermore, in the present invention, the angular contact ball bearing, which rotatably supports the nut with respect to a fixed member such as a housing, is configured so that the inner ring, which is a component thereof, is substituted for the nut. The diameter can be kept small, and the effect can be obtained that it can be applied to devices with limited installation space and occupied space, which is extremely beneficial in practical use. Furthermore, since a preload is applied to the angular contact ball bearing, the nut can be firmly supported on the fixing member without buckling, thereby further improving the operation and responsiveness of the ball screw.

[Brief explanation of drawings]

The drawings show one embodiment of the present invention, and FIG. 1 is a half-cut vertical cross-sectional view of the ball screw of the present invention, FIG.
C is an explanatory diagram showing the relative movement of the nut or screw shaft;
Figure 3 is an enlarged sectional view of the main parts, Figures 4 and 5.
FIG. 6 is a half-cut vertical sectional view showing each embodiment of the angular contact ball bearing. DESCRIPTION OF SYMBOLS 1... Ball screw, 2... Screw shaft, 3, 6... Thread groove, 4... Nut (inner ring), 5... Steel ball, 7... Nut extension part, 10... Cage, 12... Angular contact ball bearing, 13... Outer ring.

Claims (1)

[Scope of Claims] 1. A screw shaft having a spiral thread groove formed therein, a nut having a spiral thread groove corresponding to the thread groove formed on the inner periphery, and a nut interposed between both of the thread grooves. a plurality of steel balls rolling between the screw shaft and the nut;
a pair of nut extensions provided at both ends of the nut, the pitch between the thread grooves on the central side of the nut is different from the pitch between other thread grooves of the nut, and In a limited sliding ball screw in which the left and right steel balls are preloaded in the direction of expansion or compression, an outer ring is provided on the outer circumferential surface of the nut via the balls, thereby creating an angular contact in which the nut also serves as the inner ring. A ball bearing is configured, and at least two ball orbits are formed between the nut and the outer ring, and the ball bearing is provided with a pressing member that applies preload to the balls rolling on the ball orbit. A limited sliding ball screw with angular contact ball bearings. 2. A screw shaft having a spiral thread groove formed thereon, a nut having a spiral thread groove corresponding to the thread groove formed on the inner periphery, and a thread between the screw shaft and the nut interposed between both of these thread grooves. Multiple steel balls rolling between the
In a limited sliding ball screw comprising a retainer interposed between the screw shaft and the nut and rotatably holding the steel balls, the pitch between the thread grooves on the center side of the nut is adjusted to the other screws of the nut. By making the pitch between the grooves different, by applying preload in the expansion direction or compression direction to the left and right steel balls with the center of the nut as a border, and by providing an outer ring with balls interposed on the outer peripheral surface of the nut. , an angular contact ball bearing is formed in which the nut also serves as an inner ring, and a preload is applied to the angular contact ball bearing, and furthermore, nut extensions that are longer than at least half the axial length of the nut are provided at both ends of the nut. The width diameter between the inner peripheral surface of the nut extension part and the thread of the screw shaft and the width diameter between the groove bottom of the nut side thread groove and the thread of the screw shaft are set to be the same dimension. Limited sliding ball screw with Yuracontact ball bearing.