JP2010007851A - Ball screw - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve sealing performance of a ball screw by improving lubricating condition of a contact surface between a lip part of a seal and a screw shaft. <P>SOLUTION: A gap of a dimension smaller than a fastening margin of a seal 4 relative to a screw shaft 2 is provided between a raceway, which is formed by a spiral groove 11 of a nut 1 and a spiral groove 21 of the screw shaft 2, and a ball 3. With this structure, when the nut 1 reciprocates in the axial direction, direction of the force applying between the ball 3 and both the spiral grooves 11 and 21 and between the seal 4 and the screw shaft 2 is changed by direction of the movement, and a contact position of a lip part 42a of the seal 4 with the screw shaft 2 in the axial direction changes. With this change, a lubricant sealed inside the nut 1 is adhered to the lip part 42a at a different position, and lubricating condition of a contact surface between the lip part 42a of the seal 4 and the screw shaft 2 is thereby improved. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a ball screw.

A ball screw used in an electric injection molding machine or the like includes a nut having a spiral groove formed on the inner peripheral surface, a screw shaft having a spiral groove formed on the outer peripheral surface, a spiral groove of the nut, and a spiral groove of the screw shaft. And a ball disposed between the formed track grooves.
Since the ball of such a ball screw rolls in the groove along with the rotational movement of the screw shaft, if foreign matter such as dust or abrasion powder adhering to the screw shaft enters the nut, the foreign matter that has entered the nut Can hinder the rolling motion of the ball and cause damage such as seizure. In order to prevent foreign matter from entering the nut, ring-shaped seals are arranged at both axial ends of the nut.

  In Patent Document 1 below, as a ball screw seal, a main body (disc-shaped seal main body) having an edge fixed to a nut, and an outer peripheral surface of a screw shaft and a spiral groove are brought into contact with each other in an elastically deformed state. It has a lip portion (annular cylindrical portion of the seal piece), and the tip portion in contact with the screw shaft of the lip portion has a circular arc shape.

Japanese Patent No. 3616452

  Ball screws usually have preload applied to eliminate the axial clearance between the ball and the raceway groove, but the tightening force of the lip portion of the seal against the screw shaft (the outer surface of the screw shaft and the spiral groove) If the seal is large (the interference on the screw shaft of the seal is large), the lubrication state of the contact surface of the lip portion with the screw shaft is liable to be poor, and the lip portion is worn early and the seal performance deteriorates. is there.

  An object of the present invention is to improve the lubrication state of the contact surface of the lip portion of the seal with the screw shaft and improve the sealing performance of the ball screw.

  In order to solve the above problems, the present invention includes a nut having a spiral groove formed on the inner peripheral surface, a screw shaft having a spiral groove formed on the outer peripheral surface, a spiral groove of the nut, and a spiral groove of the screw shaft. A ball screw having a ball disposed between the raceway grooves and a ring-shaped seal disposed at both ends of the nut in the axial direction, the seal including a body having an edge fixed to the nut And a lip portion that contacts the outer peripheral surface of the screw shaft and the spiral groove in an elastically deformed state, and a gap having a size smaller than the interference with respect to the screw shaft of the seal is provided between the raceway groove and the ball. A ball screw is provided.

  In the ball screw of the present invention, by providing a clearance smaller than the interference with respect to the screw shaft of the seal between the raceway groove formed by the spiral groove of the nut and the spiral groove of the screw shaft and the ball, When the nut reciprocates in the axial direction (relative to the screw shaft), the contact position in the axial direction between the seal lip and the screw shaft changes. That is, when the nut reciprocates in the axial direction, the ball comes into contact with the spiral groove of the nut and the spiral groove of the screw shaft, and the axial direction is between the ball and the spiral grooves and between the seal and the screw groove. Although a force is applied, the direction of the force changes depending on the direction of the reciprocating motion, so that the contact position in the axial direction between the lip portion of the seal and the screw shaft changes. Along with this, the lubricant sealed inside the nut adheres to different positions of the lip portion.

As described above, according to the ball screw of the present invention, the lubricant is spread over the contact surface of the lip portion with the screw shaft by changing the contact position of the seal lip portion with the screw shaft. The lubrication state at the contact surface with the screw shaft is improved.
It is preferable that the lip portion has a durometer A50 to 90, the interference is 10% or less of the diameter of the ball, and the gap is 20% or less of the interference.

  When the hardness of the lip portion of the seal is Durometer A50 to 90, if the interference with the screw shaft of the seal exceeds 10% of the ball diameter, the amount of heat generated when using the ball screw may become a problem. If the lip hardness is Durometer A50-90 and the interference with the screw shaft of the seal is 10% or less of the ball diameter, the clearance between the raceway groove and the ball will be 20% or less of this interference. By making this dimension, the lubricant enclosed in the nut is particularly difficult to leak.

It is preferable that the cross-section of the tip portion contacting the screw shaft of the lip portion is an arc shape.
The present invention also includes a nut having a spiral groove formed on the inner peripheral surface, a screw shaft having a spiral groove formed on the outer peripheral surface, and a raceway groove formed by the spiral groove of the nut and the spiral groove of the screw shaft. And a ball screw having ring-shaped seals disposed at both ends of the nut in the axial direction, the seal including a main body having an edge fixed to the nut, and an outer periphery of the screw shaft. A lip portion that contacts the surface and the spiral groove in an elastically deformed state, and the cross-sectional shape of the spiral groove of the screw shaft is a shape in which two arcs having the same radius and different centers are connected (gothic arc shape) The radius of the two arcs is smaller than the diameter of the ball, and both the arcs are smoothly connected.

In this ball screw, the spiral groove of the screw shaft has a cross-sectional shape of a Gothic arc, the radius of the two arcs is smaller than the diameter of the ball, and both arcs are smoothly connected. The contact state between the lip portion of the seal and the screw shaft is improved as compared with the above.
In this ball screw, the cross-section of the tip portion contacting the screw shaft of the lip portion is an arc shape having a radius r, and both arcs forming the cross-sectional shape of the spiral groove of the screw shaft are arcs having a radius R larger than the radius r. If they are connected smoothly, no gap is generated between the lip portion of the seal and the spiral groove of the screw shaft, so that the contact state between the lip portion of the seal and the screw shaft is further improved.

  The present invention also includes a nut having a spiral groove formed on an inner peripheral surface, a screw shaft having a spiral groove formed on the outer peripheral surface, and a raceway groove formed by the spiral groove of the nut and the spiral groove of the screw shaft. A ball screw having a ball disposed and ring-shaped seals disposed at both ends of the nut in the axial direction, the seal including a body having an edge fixed to the nut, and an outer peripheral surface of the screw shaft And a lip portion that comes into contact with the spiral groove in an elastically deformed state, and the edge portion has a bent portion in which an outer peripheral portion of the disc-shaped body is bent perpendicularly to the plate surface. A ball screw characterized in that a seal is fixed to the nut by bringing a stopper member fixed to the nut into contact with the portion.

  In this ball screw, the seal is fixed to the nut by bringing a stop member fixed to the nut into contact with a bent portion of the main body of the seal. Therefore, the fixing position of the seal with respect to the nut can be adjusted in the circumferential direction of the seal and the nut. Therefore, by fixing the seal to the nut while finely adjusting the position in the circumferential direction, it is possible to obtain an optimal positional relationship, so that high sealing performance can be obtained.

  According to the ball screw of the present invention, since the lubrication state of the contact surface of the lip portion of the seal with the screw shaft is improved, the lip portion is less likely to be worn, so that the sealing performance is improved.

It is a figure which shows the external shape of the ball screw equivalent to embodiment of this invention. FIG. 2 is a partially broken view of an outward flange in the ball screw of FIG. 1. It is a front view of the seal | sticker of the ball screw of FIG. It is a figure explaining the contact state with the screw axis of the seal in an ideal state. It is a figure explaining the contact state with the screw axis of the seal in the state where the nut is moving to the right relative to the screw axis. It is a figure explaining the contact state with the screw axis of a seal in the state where the nut has moved to the left relative to the screw axis. The cross-sectional shape of the spiral groove of the screw shaft is a Gothic arc shape, and two arcs are smoothly connected by an arc having a radius R, and the relationship between the radius R and the radius r of the arc at the tip of the seal is r <R. It is a figure which shows an example (a) and the example (b) connected in the state where it was Gothic arc shape and two circular arcs were pointed. The cross-sectional shape of the spiral groove of the screw shaft is an example of a Gothic arc shape, and two arcs are smoothly connected by an arc having a radius R, and the radius R and the radius r of the arc at the tip of the seal are It is a figure which shows (a) when a relationship is r> R, and (b) when r <R. It is a figure which shows the external shape of the ball screw different from FIG. 1 which can apply this invention. FIG. 3 is a view showing an example of a method for fixing a seal to a flange side of a nut, which is different from FIG. 2. FIG. 3 is a view illustrating an example of a method for fixing a seal to a side opposite to a flange of a nut, which is different from FIG. 2.

Hereinafter, embodiments of the present invention will be described.
FIG. 1 is a view showing the outer shape of the ball screw of this embodiment.
This ball screw includes a nut 1, a screw shaft 2, a ball 3, a seal 4, and a return tube 5. A spiral groove 11 is formed on the inner peripheral surface of the nut 1. A spiral groove 21 is formed on the outer peripheral surface of the screw shaft 2. The ball 3 is disposed between the raceway groove formed by the spiral groove 11 of the nut 1 and the spiral groove 21 of the screw shaft 2. The seal 4 has a ring shape and is disposed at both axial ends inside the nut 1. The return tube 5 is used for returning the ball 3 from the end point of the raceway groove to the start point via the outside. In this example, three return tubes 5 are provided because the number of circuits is three. Although not shown, the nut 1 has one greasing hole in each circuit, and discharge holes are formed at both ends in the axial direction.

  An outward flange 6 is formed at one axial end of the nut 1. FIG. 2 is a partially cutaway view of the outward flange 6. As shown in this figure, the outward flange 6 is formed with a plurality of radially extending screw holes 61 in the circumferential direction, and the seal 4 is attached to the shaft of the nut 1 by the screws 17 screwed into the screw holes 61. It is fixed at one end of the direction. A similar screw hole is formed at the other axial end of the nut 1, and the seal 4 is fixed to the other axial end of the nut 6 by a screw screwed into the screw hole.

  FIG. 3 is a front view of the seal 4. The seal 4 includes a main body 41 and a rubber molded body 42. The main body 41 of the seal 4 includes an edge portion 41 a fixed to the inner peripheral surface 13 of the nut 6 (on the one end side in the axial direction, the inner peripheral surface 62 of the outward flange 6). The edge portion 41a in this example has a shape in which the outer peripheral portion of the disc-shaped main body 41 is bent perpendicularly to the plate surface. The rubber molded body 42 has a lip portion 42a that contacts the outer peripheral surface 22 of the screw shaft 2 and the spiral groove 21 in an elastically deformed state. The tip of the lip portion 42a has a circular cross section.

FIG. 4 is a diagram for explaining a contact state of the seal 4 with the screw shaft 2 in an ideal state.
As shown in FIG. 4A, the ideal state is the center of a circle that forms a raceway groove formed by the spiral groove 11 of the nut 1 and the spiral groove 21 of the screw shaft 2, and is arranged in this raceway groove. The state where the centers of the balls 3 are coincident is indicated.
In this embodiment, the cross section of the spiral groove 11 of the nut 1 and the spiral groove 21 of the screw shaft 2 is formed in an arc shape, and “interference” with respect to the screw shaft 2 of the seal 4 between the raceway groove and the ball 3. A gap having a smaller dimension (for example, a dimension of 20% or less of the interference) is provided. In other words, the ball 3 having a diameter A2 smaller than the diameter A1 of the circle forming the raceway groove by the “dimension smaller than the interference” is incorporated. Further, the hardness of the rubber molded body 42 including the lip portion 42 a is durometer A50 to 90, and the “interference” with respect to the screw shaft 2 of the seal 4 is 10% or less of the diameter A2 of the ball 3.

In this ideal state, the contact state between the lip portion 42a of the seal 4 and the spiral groove 21 and the outer peripheral surface 22 of the screw shaft 2 at each position of the same cross-sectional circle of the screw shaft 2 is shown in FIGS. ). A broken line shows the design shape of the lip part 42a.
FIG. 5 shows a state in which the nut 1 moves to the right relative to the screw shaft 2. In this case, the ball 3 comes into contact with the spiral groove 11 of the nut 1 and the spiral groove 21 of the screw shaft 2, and an axial force is applied between the ball 3 and both the spiral grooves 11 and 21. The direction of this force is on the right side, and accordingly, the lip portion 42a that is inclined to the right side from the design shape in FIG. 4A and arranged on the right side from the center C of the spiral groove 21 is shown in FIG. As a result, the design shape is tilted to the left and the tip almost coincides with the center line C. That is, the contact position in the axial direction between the lip portion 42a of the seal 4 and the screw shaft 2 changes. Similarly, the contact state between the lip portion 42a of the seal 4 and the spiral groove 21 and the outer peripheral surface 22 of the screw shaft 2 at each position on the same cross-sectional circle of the screw shaft 2 shown in FIGS. 4 (b) to 4 (d). Changes as shown in FIGS.

Thus, during the transition from the state of FIGS. 4 (a) to 4 (d) to the state of FIGS. 5 (a) to 5 (d), the tip of the lip portion 42a is connected to the spiral groove 21 of the screw shaft 2 in the axial direction. The outer peripheral surface 22 is slid. Along with this, the lubricant sealed inside the nut 1 adheres to different positions of the lip portion 42a.
FIG. 6 shows a state in which the nut 1 is moved to the left relative to the screw shaft 2. In this case, the ball 3 comes into contact with the spiral groove 11 of the nut 1 and the spiral groove 21 of the screw shaft 2, and an axial force is applied between the ball 3 and both the spiral grooves 11 and 21. The direction of this force is on the left side.Accordingly, the lip portion 42a that is inclined to the right side from the design shape in FIG. 4 (a) and whose tip is disposed on the right side by a distance L4 from the center C of the spiral groove 21 is In FIG. 6A, the tip is disposed on the right side from the center C of the spiral groove 21 by a distance L6 (<L4). That is, in FIG. 4A and FIG. 6A, the contact position in the axial direction between the lip portion 42 of the seal 4 and the screw shaft 2 changes.

Similarly, the contact state between the lip portion 42a of the seal 4 and the spiral groove 21 and the outer peripheral surface 22 of the screw shaft 2 at each position on the same cross-sectional circle of the screw shaft 2 shown in FIGS. 4 (b) to 4 (d). Changes as shown in FIGS.
As described above, during the transition from the state of FIGS. 4A to 4D to the state of FIGS. 6A to 6D, the tip of the lip portion 42a has the spiral groove 21 of the screw shaft 2 in the axial direction. The outer peripheral surface 22 is slid. Along with this, the lubricant sealed inside the nut 1 adheres to different positions of the lip portion 42a.

  Therefore, when the nut reciprocates in the axial direction, the contact position in the axial direction between the lip portion of the seal and the screw shaft changes between the state of FIG. 5 and the state of FIG. 6 across the state of FIG. Therefore, the lubricant enclosed in the nut adheres to the contact position of the lip portion in this range. Thereby, since the lubricant spreads to the tip of the lip portion, the lubrication state on the contact surface of the lip portion of the seal with the screw shaft is improved. As a result, since the lip portion is less likely to be worn, the sealing performance of the ball screw is improved.

FIG. 7A shows a cross-sectional shape of the spiral groove 21A of the screw shaft 2 in a shape (gothic arc shape) in which two arcs having the same radius (larger than the ball radius and smaller in diameter) and different centers are connected. In this example, two arcs are smoothly connected by an arc having a radius R. Further, the cross section of the tip portion of the lip portion 42a is formed in an arc shape having a radius r (<R).
As described above, when the relationship between the radius R and the radius r is r <R, no gap is generated between the seal lip portion 42a and the spiral groove 21A of the screw shaft. Therefore, as shown in FIG. 7B, the cross-sectional shape of the spiral groove 21B of the screw shaft 2 is Gothic arc shape, and compared with the case where both arcs are connected in a pointed state, The contact state between the lip portion and the screw shaft is improved.

FIG. 8A shows a case where the groove bottom is formed in an arc shape by forming a gothic arc-shaped spiral groove 21C with a grindstone or a grindstone dresser. In this case, the radius R and the radius r The relationship is r> R, and a gap is created between the tip of the lip 42a of the seal and the spiral groove 21A of the screw shaft 2.
FIG. 8B shows an example in which the cross-sectional shape of the lip portion 42a of the seal is different from that in FIG. 7A, but also in this example, the cross-sectional shape of the spiral groove 21D of the screw shaft 2 is Gothic arc shape. The two arcs are smoothly connected by an arc having a radius R. Further, the cross section of the tip portion of the lip portion 42a is formed in an arc shape having a radius r (> R). Also in this example, since no gap is generated between the seal lip 42a and the screw groove spiral groove 21D, the contact state between the seal lip and the screw shaft is improved.

  Even if the cross-sectional shape of the spiral groove is the shape shown in FIGS. 7B and 8A, the gap between the raceway groove and the ball is set smaller than the interference with respect to the screw shaft of the seal. Since the tip of the elastic member is elastically deformed, the contact state between the lip portion of the seal and the screw shaft can be maintained. On the other hand, in the case of the shapes shown in FIGS. 7A and 8B, the lip portion of the seal can be obtained without setting the clearance between the raceway groove and the ball smaller than the interference with respect to the screw shaft of the seal. And the screw shaft can be kept in contact with each other.

In addition, the ball screw type to which the present invention can be applied includes not only the return tube method shown in FIG. 1 but also a type in which the circulating member is not exposed outside the nut as shown in FIG. The present invention can be applied to various types of ball screws.
Furthermore, in order to make the clearance between the raceway groove and the ball smaller than the interference with respect to the screw shaft of the seal, it is advantageous to make the cross-sectional shape of the spiral groove into a gothic arc shape.

10 and 11 show an example in which the method for fixing the seal 4 to the nut 1 is different from that in FIG.
FIG. 10 shows a method of fixing the seal 4 to the flange 6 side of the nut 1. FIG. 10A is a view of the nut 1 as viewed from the flange 6 side. FIG. 10B is a partially cutaway sectional view showing a state in which the seal 4 is fixed to the flange 6 side of the nut 1. In FIG. 10A, a circle forming the inner peripheral surface 62 of the flange 6 and a circle forming the inner peripheral surface 12 between the spiral grooves 11 of the nut 1 are visible.

  Four substantially circular circles at equal intervals in the circumferential direction at positions that are radially outward from the inner circumferential surface 62 of the flange 6 to which the edge portion 41a of the seal 4 is fitted, and on the end side in the axial direction. The recess 63 is formed. Each of the circles forming the recesses 63 is partially missing from the arc on the inner peripheral surface 62 side of the flange 6. In each recess 63, a female screw 64 is formed concentrically with the circle forming each recess 63. Since the bolt 8 is screwed to each female screw 64 via a washer (stop member) 7, the depth of each recess 63 is slightly larger than the total dimension of the head 81 of the bolt 8 and the thickness of the washer 7. Has been. Further, the outer diameter of the washer 7 is slightly smaller than the diameter of the circle forming the recess 63, and the washer 7 disposed in the recess 63 protrudes from the inner peripheral surface 62 of the flange 6 toward the radial center of the nut 1. Is formed.

  When attaching the seal 4 to the flange 6 side of the nut 1, first, the edge portion 41 a of the main body 41 of the seal 4 is fitted into the inner peripheral surface 62 of the flange 6. Next, the bolt 8 through which the shaft portion 82 is inserted into the hole of the washer 7 is inserted into each recess 63, and the shaft portion 82 is screwed into the female screw 64. Along with this, the distal end 71 of the washer 7 on the radial center side of the nut 1 hits the bent portion 41 b of the seal 4 and is deformed. FIG. 10B shows this state, and the state before the tip 71 is deformed is indicated by a two-dot chain line. That is, in this example, the seal 4 is fixed to the flange 6 side of the nut 1 by bringing the washer (stopping member) 7 fixed to the flange 6 side of the nut 1 into contact with the bent portion 41 b of the seal 4. Yes.

  The washer 7 has a lower rigidity than the main body 41 of the seal 4. Specifically, a material having a higher Young's modulus than the material of the washer 7 is used as the material of the main body 41 of the seal 4, or the thickness is changed in the case of the same material. For example, when the washer 7 and the main body 41 of the seal 4 are formed of the same stainless steel, the main body 41 of the seal 4 is formed by drawing and the plate thickness is about 1.5 to 2 times the thickness of the washer 7. And Thereby, when the bolt 8 is tightened, only the washer 7 is substantially elastically deformed or plastically deformed, and the deformation amount of the main body 41 of the seal 4 can be suppressed to a negligible level.

  Therefore, in this example, the fixing position of the seal 4 with respect to the flange 6 side of the nut 1 can be adjusted in the circumferential direction of the seal 4 and the nut 1. Therefore, by fixing the seal 4 to the nut 1 while finely adjusting the position in the circumferential direction, it is possible to obtain an optimal positional relationship, so that high sealing performance can be obtained. Further, as compared with the fixing method of FIG. 2, it is not necessary to provide a deep screw hole 61 in the thickness direction of the flange 6.

FIG. 11 shows a method of fixing the seal 4 to the axial end of the nut 1 opposite to the flange 6.
In this example, female screws 14 penetrating the position of the inner peripheral surface 13 serving as the attachment portion of the seal 4 at the axial end of the nut 1 are formed at four locations in the circumferential direction, and set screws that are screwed into the female screws 14. A (stopping member) 9 is used to fix the seal 4 to the nut 1. The set screw 9 includes a shaft portion 91 screwed into the female screw 14 and a conical portion 92 at the tip.

  When attaching the seal 4 to the inner peripheral surface 13 of the nut 1, first, the edge portion 41 a of the main body of the seal 4 is fitted into the inner peripheral surface 13 of the nut 1. Next, the shaft portion 91 of the set screw 9 is screwed into each female screw 14. Along with this, the conical portion 92 of the set screw 9 hits the bent portion 41 b of the seal 4. That is, in this example, the seal 4 is fixed to the nut 1 by bringing the set screw (stop member) 9 fixed to the nut 1 into contact with the bent portion 41 b of the seal 4.

  Therefore, in this example, the fixing position of the seal 4 with respect to the nut 1 can be adjusted in the circumferential direction of the seal 4 and the nut 1. Therefore, by fixing the seal 4 to the nut 1 while finely adjusting the position in the circumferential direction, it is possible to obtain an optimal positional relationship, so that high sealing performance can be obtained.

DESCRIPTION OF SYMBOLS 1 Nut 11 Spiral groove | channel of nut 12 Inner peripheral surface between spiral grooves of nut 13 Inner peripheral surface used as seal attachment part of nut 14 Female screw 17 Screw 2 Screw shaft 21 Spiral groove of screw shaft 21A-21D Spiral groove of screw shaft 3 Ball 4 Seal 41 Body 41a Edge 42 Rubber molded body 42a Lip part 5 Return tube 6 Outward flange 61 Screw hole 62 Inner peripheral surface of outward flange 63 Recess 64 Female screw 7 Washer (stopping member)
8 Bolt 81 Bolt head 82 Bolt shaft 9 Set screw (locking member)
91 Shaft portion of set screw 92 Conical portion of tip of set screw A1 Diameter of circle forming raceway groove A2 Diameter of ball C Center of spiral groove of screw shaft

Claims (6)

A nut having a spiral groove formed on the inner peripheral surface, a screw shaft having a spiral groove formed on the outer peripheral surface, and a ball disposed between the spiral groove of the nut and the raceway groove formed by the spiral groove of the screw shaft; A ball screw provided with ring-shaped seals arranged at both axial ends of the nut,
The seal includes a main body having an edge portion fixed to the nut, and a lip portion that contacts the outer peripheral surface of the screw shaft and the spiral groove in an elastically deformed state,
A ball screw characterized in that a clearance smaller than an interference with respect to the screw shaft of the seal is provided between the raceway groove and the ball.   2. The hardness of the lip portion is Durometer A50 to 90, the interference is 10% or less of the diameter of the ball, and the gap is 20% or less of the interference. Ball screw.   The ball screw according to claim 1, wherein a cross-section of a tip portion contacting the screw shaft of the lip portion is an arc shape. A nut having a spiral groove formed on the inner peripheral surface, a screw shaft having a spiral groove formed on the outer peripheral surface, and a ball disposed between the spiral groove of the nut and the raceway groove formed by the spiral groove of the screw shaft; A ball screw provided with ring-shaped seals arranged at both axial ends of the nut,
The seal includes a main body having an edge portion fixed to the nut, and a lip portion that contacts the outer peripheral surface of the screw shaft and the spiral groove in an elastically deformed state,
The spiral groove of the screw shaft has a cross-sectional shape in which two circular arcs having the same radius and different centers are connected (gothic arc shape), and the radius of the two circular arcs is smaller than the diameter of the ball. A ball screw characterized by being smoothly connected.   The tip of the lip portion contacting the screw shaft has an arcuate cross section with a radius r, and both arcs forming the cross-sectional shape of the spiral groove of the screw shaft are smoothly connected with an arc of radius R larger than the radius r. The ball screw according to claim 4, wherein the ball screw is provided. A nut having a spiral groove formed on the inner peripheral surface, a screw shaft having a spiral groove formed on the outer peripheral surface, and a ball disposed between the spiral groove of the nut and the raceway groove formed by the spiral groove of the screw shaft; A ball screw provided with ring-shaped seals arranged at both axial ends of the nut,
The seal includes a main body having an edge portion fixed to the nut, and a lip portion that contacts the outer peripheral surface of the screw shaft and the spiral groove in an elastically deformed state,
The edge portion has a bent portion in which the outer peripheral portion of the disc-shaped main body is bent perpendicularly to the plate surface, and a sealing member fixed to the nut is brought into contact with the bent portion to A ball screw characterized in that is fixed to a nut.

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