JP6561586B2 - Ball screw - Google Patents

Description

  The present invention relates to a ball screw, and more particularly to a preload technique for a double nut type ball screw.

  As a double nut type ball screw, for example, a technique disclosed in Patent Document 1 is disclosed. The ball screw described in the document has a screw shaft and two nuts through which the screw shaft passes. A spacer is interposed between the two nuts, and a preload is applied by a fixed position preload.

JP 2009-204141 A

  However, in the ball screw described in Patent Document 1, a spacer is interposed between the opposing surfaces of two nuts, and a preload is applied by changing the thickness of the spacer, so the thickness of the spacer is changed. In the preload adjustment, there is a problem that a relatively large adjustment time and cost are required until a desired preload is obtained.

  Therefore, the present invention has been made paying attention to such a problem, and an object thereof is to provide a ball screw capable of adjusting a preload without using a spacer.

In order to solve the above-described problems, a ball screw according to an aspect of the present invention is provided on a screw shaft, two nuts through which the screw shaft passes and abuts each other, and a contact side between the two nuts. A fixed position preload applying mechanism, the fixed position preload applying mechanism including a convex portion provided on one of the two nuts and extending in the axial direction toward the other nut, and the other nut Provided on the outer peripheral surface of the convex portion, four pressing surfaces formed on the outer peripheral surface of the convex portion, and the pressing surface of the convex portion on the outer peripheral surface of the other nut. It has four female screws penetratingly formed at opposing positions, and four push screws screwed into the four female screws, respectively, and the convex part is formed from a plurality of projecting parts spaced apart in the circumferential direction The four pressing surfaces are the front Is formed from a surface facing the circumferential direction of the outer surface of the plurality of projecting portions, the four by tightening the set screw, the two nuts each other to press the pressing surface of the four places formed in the convex portion A preload is applied by a force that shifts the phase around the axis, and the position where the preload is applied is maintained.

According to the ball screw according to the aspect of the present invention, it is possible to apply preload by tightening four push screws on the four pressing surfaces and shifting the phases of the two nuts around each other. Preload can be applied without using a spacer.
Here, in the ball screw according to an aspect of the present invention, the four pressing surfaces are configured by four planes formed at point-symmetric positions on the convex portion with the screw shaft center as a symmetric point. The four push screws screwed into the four female screws are composed of two push screws arranged at point-symmetrical positions as a set of pre-loading push screws, and arranged at point-symmetrical positions. It is preferable that the two push screws are a set of pre-load releasing push screws.

  If it is such a structure, among the press screws corresponding to the four pressing surfaces, two pre-loading press screws arranged at point-symmetrical positions and two screws arranged at point-symmetrical positions Therefore, the two nuts provided at point-symmetrical positions do not twist each other, and the two nuts do not twist each other. It is suitable for maintaining the position where the preload is applied while applying.

The ball screw according to one aspect of the present invention preferably includes a preload application state monitoring mechanism that monitors a preload state applied by the fixed position preload application mechanism. Further, the preload application state monitoring mechanism includes a strain sensor capable of detecting an axial force acting between the surfaces where the two nuts face each other, and a detected value of the axial force detected by the strain sensor. Preferably, the controller monitors the preload loss state due to changes over time, and determines the preload loss state based on the acquired detected axial force value. Moreover, it is preferable that the said strain sensor is each accommodated in the recessed part formed in several places of the surface where the said two nuts oppose.
With such a configuration, the preload application state monitoring mechanism can monitor the preload state applied by the fixed position preload application mechanism. This is suitable for easily determining the maintenance time when re-preloading should be applied and the maintenance or replacement time of the ball screw based on the state.

  As described above, according to the present invention, the preload can be adjusted without using a spacer.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view showing a first embodiment of a ball screw according to one aspect of the present invention, in which a part is broken away. It is ZZ sectional drawing of FIG. It is an end view of the nut in the YY section of FIG. It is explanatory drawing of one Embodiment of the 1st nut which comprises the ball screw which concerns on 1 aspect of this invention, The figure (a) is a top view, (b) is a right view of (a). It is explanatory drawing of one Embodiment of the 2nd nut which comprises the ball screw which concerns on 1 aspect of this invention, The figure (a) is a top view, (b) is XX sectional drawing in (a). . It is explanatory drawing of other embodiment of the 1st nut which comprises the ball screw which concerns on 1 aspect of this invention, The figure (a) is a top view, (b) is a right view of (a). It is a top view which shows 2nd embodiment of the ball screw which concerns on 1 aspect of this invention, In the same figure, one part was fractured | ruptured and shown. It is explanatory drawing of 3rd embodiment of the ball screw which concerns on 1 aspect of this invention, The figure (a) is a top view which fractures | ruptures a part, (b) is YY sectional drawing in (a) (C) is a typical perspective view of the distortion sensor which comprises the preload provision state monitoring mechanism.

  Embodiments of a ball screw according to an aspect of the present invention will be described below with reference to the drawings as appropriate. The drawings are schematic. For this reason, it should be noted that the relationship between the thickness and the planar dimension, the ratio, and the like are different from the actual ones, and the dimensional relationship and the ratio are different between the drawings. Further, the following embodiments exemplify apparatuses and methods for embodying the technical idea of the present invention, and the technical idea of the present invention is the material, shape, structure, and arrangement of components. Etc. are not specified in the following embodiments.

The ball screw of the first embodiment is a double nut type ball screw, and includes a screw shaft 10 and two nuts 20A and 20B through which the screw shaft 10 passes, as shown in FIG. The two nuts 20A and 20B have a cylindrical shape in which the first nut 20A has an annular flange 25 and the second nut 20B has no flange.
FIG. 2 shows a longitudinal section of the circulation circuit portion of the first nut 20A. Since the configuration of the circulation circuit is the same for the two nuts 20A and 20B, the illustration and description of the circulation circuit are omitted for the second nut 20B.

  As shown in the figure, a spiral thread groove 11 is formed on the outer peripheral surface of the screw shaft 10, and a spiral thread facing the thread groove 11 of the screw shaft 10 is formed on the inner peripheral surface of the first nut 20 </ b> A. A thread groove 21 is formed. Each thread groove 11, 21 is formed in a Gothic arch shape. A spiral rolling path 40 is provided by these thread grooves 11, 21, and a plurality of balls 30 are interposed in the rolling path 40 so as to freely roll. In the present embodiment, the first nut 20A has two rolling paths 40.

  Each rolling path 40 is provided with a return tube 50 having a ball circulation path. The return tube 50 is fixed to a flat portion formed on the outer peripheral surface of the nut with a fixing bracket 60. As a result, the plurality of rolling balls 30 move up to one end of the rolling path 40 and then are lifted up by the return tube 50 and moved to the opposite end through the ball circulation passage in the return tube 50. In addition, a circulation circuit is configured to return to the rolling path 40 from the other end.

Here, as shown in FIG. 3, the ball screw is provided with a fixed position preload applying mechanism 1 in a contact side portion between the two nuts 20 </ b> A and 20 </ b> B. In the present embodiment, as the fixed position preload applying mechanism 1, one first nut 20A is provided with a convex portion 2 extending in the axial direction, and the other second nut 20B is a concave portion capable of accommodating this convex portion 2. 5 is provided.
Specifically, as shown in FIG. 4, one first nut 20 </ b> A has the convex portion 2 formed in a cylindrical shape coaxial with the screw shaft 10, and is provided integrally with an end surface 20 t on the other nut side. . On the outer peripheral surface of the cylindrical convex portion 4, four planes are formed by notches spaced in the circumferential direction at point-symmetric positions on the outer peripheral surface of the convex portion 2, as shown in FIG. Each plane is provided as a pressing surface 3A, 3B, 4A, 4B. Each pressing surface 3A, 3B, 4A, 4B is parallel to the axis of the screw shaft 1, and is a plane orthogonal to the plane portion (the mounting surface of the return tube 50) formed on the outer peripheral surface 20g of the first nut 20A. It is said that.

As shown in FIGS. 5 and 3, the other second nut 20 </ b> B is provided with a concave portion 5 capable of accommodating the convex portion 2 of the first nut 20 </ b> A on the end surface 20 f on the side in contact with the first nut 20 </ b> A. . The concave portion 5 is formed in a cylindrical shape coaxial with the screw shaft 10, and the outer peripheral surface of the convex portion 2 and the inner peripheral surface of the cylindrical concave portion 5 are loosely fitted.
Furthermore, on the outer peripheral surface 20h of the second nut 20B, as shown in FIG. 5 (b), the positions facing the respective pressing surfaces 3A, 3B, 4A, 4B of the convex portion 2 (that is, point-symmetric positions). Female screws 6A, 6B, 7A, 7B are provided at four locations. Then, as shown in FIG. 3, push screws 8A, 8B, 9A, and 9B that are screwed into these four female screws 6A, 6B, 7A, and 7B are mounted, respectively. In a state where no pressing force is applied to the pressing surfaces 3A, 3B, 4A, and 4B, the axes of the female screws 6A, 6B, 7A, and 7B are orthogonal to the opposing pressing surfaces 3A, 3B, 4A, and 4B. It is provided as follows.

  Here, in FIG. 3, of the four push screws 8A, 8B, 9A, 9B, two push screws 8A, 8B arranged at point-symmetrical positions form a set of push screws for applying preload. The other two push screws 9A and 9B arranged at symmetrical positions form a set of push screws for preload release. As a result, the four pressing screws 8A, 8B, 9A, 9B are appropriately tightened to press the pressing surfaces 3A, 3B, 4A, 4B formed on the convex portion 2, and the two nuts 20A, 20B are pivoted together. A fixed-position preload applying mechanism 1 that can apply preload by a force that shifts the phase around each other is configured.

Next, the effect of the ball screw of this embodiment is demonstrated.
When the ball screw of this embodiment is assembled, the two nuts 20A and 20B are brought into contact with the opposing surfaces 20t and 20f. At this time, the first nut 20A is positioned such that the four female screws 6A, 6B, 7A, 7B of the second nut 20B are positioned at positions facing the pressing surfaces 3A, 3B, 4A, 4B of the first nut 20A. The concave portion 5 of the second nut 20 </ b> B is fitted into the convex portion 2. The four push screws 8A, 8B, 9A, and 9B are screwed into the four female screws 6A, 6B, 7A, and 7B of the second nut 20B before or after the fitting.

Next, these push screws 8A, 8B, 9A, 9B are fastened to the four female screws 6A, 6B, 7A, 7B, and the pressing surfaces 3A, 3B, 4A, 4B formed on the convex portion 2 are pressed.
At this time, the direction of the leads of the two nuts 20A and 20B is set to a direction in which the rotation direction when the two push screws 8A and 8B are tightened is applied to the pre-load, so the two push screws 8A , 8B function as a preloading push screw, and the other two push screws 9A, 9B function as preload releasing push screws.

  As a result, by pre-tightening these four push screws 8A, 8B, 9A, 9B, the two nuts 20A, 20B are preloaded by a force that shifts their phases around the axis, and the preload is applied. Hold the position. Therefore, according to the ball screw of this embodiment, a preload can be given without using a spacer. Further, in the case of the ball screw according to the present embodiment, the entire length of the nut can be equal to or less than that of a normal double nut type ball screw having a spacer.

  In particular, in the present embodiment, among the four push screws 8A, 8B, 9A, 9B, the two preload-applying push screws 8A, 8B arranged at point-symmetric positions are point-symmetrical positions. Since the other two preloading push screws 9A and 9B are arranged, the nut is twisted by the two push screws 8A and 8B and the push screws 9A and 9B provided at point-symmetric positions. Instead, the preload can be applied by the force that shifts the phases of the two nuts 20A and 20B around the axis.

It should be noted that the ball screw according to the present invention is not limited to the above embodiment, and it is needless to say that various modifications can be made without departing from the spirit of the present invention.
For example, in the said embodiment, the convex part 2 of the 1st nut 20A is formed in the cylindrical shape coaxial with the screw shaft 1, and the four pressing surfaces 3A, 3B, 4A, 4B are the cylindrical convex parts 2. Although the example formed from the surface by the notch formed in the outer peripheral surface of this was demonstrated, it is not limited to this.

For example, as shown in another embodiment of the first nut 20A in FIG. 6, a plurality of convex portions 2A and 2B are formed from a plurality of projecting portions spaced apart in the circumferential direction, and the four pressing surfaces have a plurality of convex portions. Of the outer surfaces of the portions (overhanging portions) 2A and 2B, they can be formed from the planes 3A and 4A and the planes 3B and 4B facing the circumferential direction, respectively.
Further, for example, in the ball screw of the first embodiment, the convex portion 2 is provided in the first nut 20A having the flange 25 out of the two nuts 20A and 20B, and the convex portion 2 is accommodated in the other second nut 20B. Although the example which provided the possible recessed part 5 was demonstrated, not only this but the 2nd nut which does not have a flange among two nuts 20A and 20B so that the ball screw of 2nd embodiment may be shown, for example in FIG. 20B is provided with the convex portion 2 having the pressing surfaces 3 and 4, and the other first nut 20A having the flange 25 is a female screw into which the pair of the concave portion 5 and the push screws 8 and 9 that can accommodate the convex portion 2 are screwed. 6 and 7 may be provided.

  Further, for example, as in the third embodiment shown in FIG. 8, in addition to the above-described fixed position preload application mechanism 1, a preload application state monitoring mechanism 70 that monitors the preload state applied by the fixed position preload application mechanism 1 is also provided. Can be provided. The ball screw according to the third embodiment is different from the ball screw according to the first embodiment only in that a preload application state monitoring mechanism 70 is further provided.

  As shown in the figure, the preload application state monitoring mechanism 70 includes a strain sensor 80 capable of detecting an axial force acting between the surfaces 20t and 20f facing the two nuts 20A and 20B. In this example, as shown in FIG. 5B, the strain sensors 80 are arranged at equal intervals at four locations in the circumferential direction on the end face 20t of the first nut 20A. Each strain sensor 80 is connected to the controller 90 via a signal line. In this example, the example in which the strain sensors 80 are equally distributed at four locations in the circumferential direction is shown, but the present invention is not limited thereto, and the preload application state monitoring mechanism 70 may be configured by one or a plurality of strain sensors 80. . Moreover, you may arrange | position not only to the end surface 20t of 20 A of 1st nuts but to the end surface 20f of the 2nd nut 20B.

  In the present embodiment, bottomed cylindrical recesses 71 are formed at four intervals in the circumferential direction on the end surface 20t of the first nut 20A at equal intervals, and female threads 73 are formed along the axial direction on the bottom surface of each recess 71. ing. A strain sensor 80 is accommodated in each recess 71. Each strain sensor 80 has a cylindrical shape that can be fitted into the recess 71, and a stepped mounting hole 82 into which a fastening screw 72 for fixing to the female screw 73 can be inserted is provided at the center. As the strain sensor 80, a load cell using a strain gauge, a crystal piezoelectric element, or the like can be used.

  The detected value of the axial force acting between the surfaces 20t and 20f facing the two nuts 20A and 20B, acquired by the strain sensor 80, is input to the controller 90 via a signal line. The controller 90 executes a preload application state monitoring program set in advance to monitor the preload loss state due to changes over time, and can determine the preload loss state based on the acquired axial force detection value. It is configured. Note that the preload state can be determined by comparison with a preload value set in advance.

If, for example, the ball 30 or the rolling path 40 is worn due to a change with time due to the operation of the ball screw, the two nuts 20A and 20B face each other when the preload initially applied by the fixed position preload applying mechanism 1 is released. The axial force acting between the surfaces 20t and 20f changes.
On the other hand, according to the ball screw of the third embodiment, each strain sensor 80 of the preload application state monitoring mechanism 70 has an axial direction in which the two nuts 20A and 20B act between the opposing surfaces 20t and 20f. Force can be detected. Then, the controller 90 can monitor the preload loss state due to the change with time, and can determine the preload loss state based on the acquired detected value of the axial force.
Therefore, according to the ball screw of the third embodiment provided with the preload application state monitoring mechanism 70, the preload loss state due to the change with time is monitored at any time, and the maintenance to which the repreload is applied based on the monitored preload loss state. It is possible to easily determine the timing and the maintenance or replacement timing of the ball screw.

DESCRIPTION OF SYMBOLS 1 Fixed position preload provision mechanism 2 Convex part 3A, 3B Press surface (For preload provision)
4A, 4B Press surface (for pre-load release)
5 Recess 6A, 6B Female thread (for preload application)
7A, 7B Female thread (for preload release)
8A, 8B set screw (for preloading)
9A, 9B Press screw (for preload release)
DESCRIPTION OF SYMBOLS 10 Thread shaft 11 Thread groove 20A (1st nut) 20A 1st nut 20B 2nd nut 21 Thread groove 25 (flank) 25 Flange 30 Ball 40 Rolling path 50 Return tube 60 Fixing bracket 70 Preload application state monitoring mechanism 80 Strain sensor 90 controller

Claims (5)

A screw shaft, two nuts through which the screw shaft penetrates and abutting each other, and a fixed position preload applying mechanism provided on a contact side between the two nuts,
The fixed position preload applying mechanism includes a convex portion provided on one of the two nuts and extending in the axial direction toward the other nut, and a convex portion of the one nut provided on the other nut. A recess that can accommodate a portion, four pressing surfaces formed on the outer peripheral surface of the convex portion, and 4 formed through the outer peripheral surface of the other nut at positions facing the pressing surface of the convex portion. Having four female screws and four push screws screwed into the four female screws,
The convex portion is formed from a plurality of projecting portions spaced apart in the circumferential direction, and the four pressing surfaces are formed from a surface facing the circumferential direction among the outer surfaces of the plurality of projecting portions,
The four push screws are tightened to press the four pressing surfaces formed on the convex portion to give a preload by a force that shifts the phases of the two nuts around each other, and to apply the preload. A ball screw characterized by maintaining a fixed position. The four pressing surfaces are composed of four planes formed at point-symmetrical positions on the convex portion with the screw shaft center as a symmetric point,
The four push screws screwed into the four female screws are composed of two push screws arranged in a point-symmetrical position as a set of preload-giving push screws, and the other push screws arranged in a point-symmetrical position. The ball screw according to claim 1, wherein the two push screws are a set of push screws for preload release. Ball screw according to claim 1 or 2 having a preloading state monitoring mechanism that monitors the preload imparted by the fixed position preload applying mechanism. The preload application state monitoring mechanism obtains a strain sensor capable of detecting an axial force acting between the opposing surfaces of the two nuts, and a detected value of the axial force detected by the strain sensor. And a controller to
The ball screw according to claim 3 , wherein the controller monitors a preload loss state due to a change with time, and determines the preload loss state based on the acquired detected value of the axial force. The ball screw according to claim 4 , wherein the strain sensors are respectively housed in recesses formed at a plurality of locations on a surface where the two nuts face each other.

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