JP2001021018A - Ball screw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ball screw which is capable of eliminating competitive contact of balls, preventing the rise of friction torque or early damage on the balls, and suppressing reduction in load capacity, and which is easy to assemble. SOLUTION: Spacers 6 are interposed between respective balls 3 provided between thread grooves 4, 5 of a screw shaft 1 and a nut 2. The outside diameter of each spacer 6 is smaller than that of a ball 3, and the difference in diameter between the ball 3 and the spacer 6 is deterimined to be larger than the amount of elastic deformation produced in the spacer 6 when an allowable load is applied. The contact surface of the spacer 6 and the ball 3 is formed into a spherical recessed surface 8 along the outside diametrical surface of the ball 3, or formed into a conical recessed surface or a pyramid-like recessed surface. The recessed surface 8 forms an oil basin part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ball screw for various uses, and more particularly, to a ball screw used in a high load application such as an electric injection molding machine and an electric press machine.

[0002]

2. Description of the Related Art A ball screw has a screw shaft and a nut provided with spiral screw grooves, and a number of balls are interposed between the screw shaft and the nut screw grooves. These balls are circulated infinitely by a circulation path provided in the nut. There are various types of circulation paths, for example, a return tube, a coma (deflector), an end cap, and the like. Because the ball screw circulates the ball and converts the rotational force into a linear force, adopting a structure that eliminates competition between balls, such as a retainer that is generally used for bearings, uses a spiral This is difficult because it must be matched to the thread groove. Therefore, a general ball screw does not have a retainer, and has a configuration in which only a ball is accommodated in a screw groove.

However, in a case where a ball screw without a retainer receives a high load or swings, the ball screw shown in FIG.
As shown in FIG. 7, the balls 53 rotating in contact with the screw shaft 51 and the nut 52 compete with each other, that is, the adjacent balls 53 rub against each other so as to move in opposite directions at the contact portions a of each other. Occurs. Therefore, the rotational torque increases, and sometimes the ball 53 is damaged early. Further, as shown in FIG. 3, the adjacent balls 53, 53 move in opposite directions at the contact portions a of each other, so that it is difficult for lubricant to enter the contact portions a of the balls 53, 53. At the time of rotation or at high speed, sufficient lubrication is not performed, and poor lubrication is likely to occur at the contact portion a between the balls 53.

A ball screw provided with a retainer has been proposed in which a retainer connecting between balls is formed as a flexible endless belt. But,
In an application that receives a high load, the ball may cause compression and tension to the retainer under a high load, and the retainer may be broken. Also, as described above, since the balls circulate between the screw grooves, in order to have a structure in which all the balls are connected, it is necessary to insert the balls into the spiral screw grooves and finally connect the retainer. This makes it difficult to assemble the ball screw. Further, since the use of the return tube method requires that a ball with a retainer be inserted into the return tube, connecting all the balls with the retainer requires a ball screw shaft as shown in FIG. 51 to one end 51
It is necessary that a has a shape in which a thread is cut through. As shown in FIG. 2B, both ends 51a, 5a of the screw shaft 51 are provided.
If 1b is a threaded cut-up, it is necessary to cut the retainer at least at one place.

[0005] In order to eliminate the competition between balls, besides the one using a retainer, the one in which a spacer ball (a ball smaller than the used ball diameter) is interposed between adjacent balls has been proposed. However, the spacer balls do not act on the load transmission between the screw shaft and the nut, and the number of balls for general load transmission is reduced by the amount of the spacer balls, so the load capacity of the ball screw is reduced. Would.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a ball screw which can eliminate the competing contact between balls, thereby preventing an increase in friction torque and early damage of the balls, a reduction in load capacity and a simple assembly. To provide. It is another object of the present invention to further reduce the load capacity. Still another object of the present invention is to improve lubricity with a simple configuration. Still another object of the present invention is to improve productivity.

[0007]

In a ball screw according to the present invention, spiral screw grooves are provided on an outer diameter surface of a screw shaft and an inner diameter surface of a nut loosely fitted on the outer periphery of the screw shaft, respectively.
In a ball screw in which a plurality of balls are interposed between the screw shaft and the thread groove of the nut, a spacer is interposed between the balls. The outer diameter of the spacer is smaller than the outer diameter of the ball, and the diameter difference between the ball and the spacer is larger than the amount of elastic deformation generated by the ball when an allowable load is applied. As described above, since the spacer is interposed between the balls, the ball comes into sliding contact with the non-rotating spacer, so that the balls do not compete with each other, that is, the balls do not rub against each other due to the rotation. Therefore, it is possible to prevent the rotational torque of the ball screw from increasing and prevent the ball from being damaged early. Further, since the spacer is used, it can be adopted regardless of the shape of the screw shaft and the circulation method of the ball screw.
In addition, since each spacer is independent and not connected as an integral member, there is no problem of compression by a ball under a high load as occurs in the case of a retainer, and there is no problem of being cut by a tensile load, and the spacer is used. Since there is no need to connect them to each other, assembly is easy. Because the spacers are not connected to each other,
The material does not need to be flexible and can be changed according to the conditions of use of the ball screw. For example, in applications where a high load is applied, a material resistant to a compressive load may be used to prevent the spacer from being crushed. Further, the spacer has an outer diameter smaller than the outer diameter of the ball, and a diameter difference between the ball and the spacer as a diameter difference larger than an elastic deformation amount generated by the ball when an allowable load of the ball screw is applied. Therefore, even when the ball is elastically deformed by the load, no radial load is applied to the spacer. Therefore, even when a large load is applied, if the load is within the allowable load, the spacer does not come into strong contact with the thread groove or the like and does not generate frictional resistance, and the smooth operation of the ball screw is maintained.

[0008] In the present invention, the contact surface of the spacer with the ball may be a spherical concave surface along the outer diameter surface of the ball. In the present invention, the contact surface of the spacer with the ball may be a conical concave surface. in this way,
By forming the contact surface between the spacer and the ball as a concave surface, the thickness between the balls of the spacer can be reduced and the distance between the balls can be reduced without causing the problem of falling of the spacer. By reducing the distance between the balls in this way, a reduction in the load capacity of the ball screw is prevented as much as possible.

When the contact surface of the spacer with the ball is concave, an oil reservoir may be formed on the concave surface. The oil reservoir may be a gap between a spherical ball or a conical concave ball, or may be a deeper concave portion in the concave surface. By providing the oil reservoir in this manner, the lubricant can be held between the ball and the spacer, and the two can be easily lubricated, and poor lubrication does not easily occur.

[0010] In the present invention, the spacer may be one in which the contact surfaces with the balls on both sides communicate with each other.
When the both surfaces of the spacer are thus communicated with each other, the lubricant can pass through the communicating portion, and the lubrication performance can be further improved. In the case where the ball contact surfaces on both sides are in the form of a spacer that communicates with each other, for example, by penetrating the center portion of the spacer that needs to be thinnest, the distance between the balls is further reduced, and the load capacity is increased. be able to.

In the present invention, the spacer may be made of a sintered metal. In this case, the spacer may be made of a sintered metal mainly composed of stainless steel obtained by sintering a metal powder injection molded product. By injection molding and sintering the spacers in this manner, a large amount of spacers can be efficiently produced. In addition, by using a sintered metal mainly stainless steel,
Rust is unlikely to occur.

In the present invention, the spacer may be made of a synthetic resin having self-lubricating properties.
When made of synthetic resin, it is easy to manufacture and excellent in mass productivity.
Further, by using a self-lubricating synthetic resin, the lubricating performance is improved, and the friction torque can be further reduced.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIGS. This ball screw is provided with spiral screw grooves 4 and 5 on the outer diameter surface of a screw shaft 1 and the inner diameter surface of a nut 2, respectively, and a plurality of balls 3 are interposed between the screw grooves 4 and 5. In the screw, spacer 6 between each ball 3
Is interposed. The nut 2 is provided with a circulation path 7 for circulating the ball 3 interposed between the screw shaft 1 and the screw grooves 4 and 5 of the nut 2 from the screw grooves 4 and 5. The materials of the screw shaft 1, the nut 2, and the ball 3 are each made of a bearing steel or a tempered material such as case hardened steel.

As the circulation path 7, as will be described later, various types can be adopted. In this example, an end cap type ball screw is used. That is, nut 2
A pair of end caps 2b, two ends of which are connected to a nut main body 2a with connecting members (not shown) such as bolts at both ends thereof.
2c. The circulation path 7 includes a lubricating through hole 7a penetrating the nut body 2a in the axial direction, and guide grooves 7b, provided in the end caps 2b, 2c, and extending from the screw groove 4 of the screw shaft 1 to the circulation through hole 7a. 7c. Each ball 3 of the screw groove 4 of the screw shaft 1 is scooped up by one of the guide grooves 7b and 7c in accordance with the rotation direction of the screw shaft 2 according to the rotation direction of the screw shaft 2, and passes through the circulation through hole 7a. Are returned to the screw groove 4 of the screw shaft 1 from the guide grooves 7b and 7c.

The spacer 6 will be described. The spacer 6 is shaped to be in contact with the ball 3 at at least one point or surface. In this example, the spacer 6 has concave surfaces 8, 8 on both surfaces that are to be in contact with the ball 3, and an outer diameter surface is spherical. The concave surface 8 has a spherical shape along the outer diameter surface of the ball 3. The concave surface 8 has a gothic arch shape. The shape of the concave surface 8 of the spacer 6 may be substantially the same as the outer diameter of the ball or a spherical shape having a slightly larger radius of curvature as shown in FIG. 4 instead of the above shape. This concave surface 8 is, as shown in FIG.
It may be a pyramidal surface or a conical surface as shown in FIG. In any of the above examples, the gap between the concave surface 8 and the ball 3 becomes an oil reservoir 8a. In addition, an oil sump (not shown) further depressed from the concave surface 8
May be provided. The concave surfaces 8 on both sides of the spacer 6 are shown in FIG.
As shown in (1), a communication hole 10 may be provided to communicate with each other. The communication hole 10 is provided at the center of the spacer 6. The communication hole 10 may be provided in the spacer 6 shown in FIGS. 1, 4 and 5.

In the spacer 6 of each of these examples, the boundary 8b between the concave surface 8 and the outer diameter surface is formed into a smooth surface or a chamfered shape so that the ball 3 comes into contact with the boundary 8b. Even when a load is applied, the spacer 6 and the ball 3 are not damaged.

The outer diameter D of the spacer 6 is smaller than the outer diameter of the ball 3, and the difference in diameter between the ball 3 and the spacer 6 is the maximum elasticity generated by the ball 3 within the allowable load of the ball screw. The diameter difference is larger than the deformation amount. However, if the outer diameter dimension D of the spacer 6 is too small, the ball 3 will rotate or fall between the balls 3. Therefore, it is desirable that the outer diameter dimension D be equal to or larger than the outer diameter dimension that does not cause the rotation or the fall. The thickness t of the spacer 6 in the direction between the balls is made as thin as possible within a range necessary for strength or the like. The thickness t of the spacer 6 can be adjusted within a range of a value obtained by dividing the outer diameter D of the ball 3 by the total number n of the balls 3 inserted into one circulation system, that is, a range of D / n. desirable. The above-mentioned one circulation system is one endless path formed by the thread grooves 4 and 5 between the screw shaft 1 and the nut 3 and the circulation path 7, and in the example of FIG. In the case of one piece type, a circulatory system corresponding to the number of pieces is configured.

As the material of the spacer 6, various materials can be selected according to the performance requirements of the ball screw. For example, spacer 6
May be made of a sintered alloy. In this case, a sintered alloy obtained by sintering a metal powder injection-molded product may be used, and the sintered alloy may be mainly composed of stainless steel. An example of a production method by injection molding will be described. First, a metal powder and a binder made of plastic and wax are kneaded by a kneader, and the kneaded product is granulated into pellets. The pellets are supplied to a hopper of an injection molding machine, and are molded by being pressed into a mold in a heated and molten state. The spacer 6 is obtained by sintering the molded product. The spacer 6 may be formed of a self-lubricating synthetic resin in addition to the above-described materials. Examples of the synthetic resin include polyimide (PI) containing a reinforcing material and polyamide (PA).
Etc. can be used.

If, for example, the spacer 6 does not have sufficient elasticity in accordance with the kind of material of the spacer 6, etc., as a means for preventing a gap between the ball 3 and the spacer 6, As shown in the conceptual diagram of FIG. 3, an elastic body 9 may be interposed between the adjacent spacers 6,6. At least one elastic body 9 is provided for each circulation system. The elastic body 9 may be various kinds of spring members such as a coil spring, a leaf spring or a wire spring, or may be a rubber-like elastic body such as rubber or plastic.

According to the ball screw having this configuration, the ball 3
Since the spacer 6 is interposed therebetween, the ball 3 comes into sliding contact with the non-rotating spacer 6, as shown in the conceptual diagram of FIG.
The competition in which the balls 6 rub against each other in the opposite direction due to the rotation is eliminated. For this reason, it is possible to prevent an increase in the rotational torque of the ball screw and early damage of the ball 3. Also,
Since the spacer 6 is used, it can be adopted regardless of the shape of the screw shaft 2 and the circulation method of the ball screw. Further, since the spacers 6 are independent of each other and are not connected as one body, there is no problem of the ball being compressed by a ball under a high load, which occurs in the case of a retainer, or being cut off by a tensile load. Are not required to be connected to each other, so that assembly is easy. Since the spacers 6 are not connected to each other, the spacers 6 do not need to be made of a flexible material, and can be changed according to the use conditions of the ball screw. For example, in applications where a high load is applied, a material resistant to a compressive load may be used to prevent the spacer from being crushed. Further, the spacer 6 has an outer diameter smaller than the outer diameter of the ball, and the difference in diameter between the ball 3 and the spacer 6 is determined by an elastic deformation generated by the ball 3 when a maximum load is applied under an allowable load of the ball screw. Since the diameter difference is larger than the amount, even when the ball is elastically deformed by a load, a radial load is not applied to the spacer 6. Therefore, even when a large load is applied, if the load is within the allowable load, the spacer 6 does not strongly contact the thread grooves 4, 5 and the like, so that frictional resistance does not occur, and the smooth operation of the ball screw is maintained. Since the thickness t of the spacer 6 in the inter-ball direction is not so large, the number of balls capable of receiving the load becomes larger than that of the conventional spacer ball, and the load capacity of the ball screw is reduced. Can be bigger.

As for lubrication, the provision of the spacers 6 allows the ball 3 to rotate only on one side as shown in FIG.
Since the oil reservoir 8a is formed on the concave surface 8 of the spacer 6 to hold the lubricant, lubrication between the ball 3 and the spacer 6 is easily performed, and poor lubrication is less likely to occur.

The function of assembling the ball screw will be described. Although the spacer 6 depends on the type of material, if the spacer 6 does not have elasticity, a gap is generated between the ball 3 and the spacer 6. In addition, even with elasticity, there is a possibility that a gap larger than the elasticity is generated. However, such a gap can be filled by inserting the elastic body 9 as described above with reference to FIG. As described above, when a certain gap or more occurs, the spacer 6 may fall down. However, the thickness t of the spacer 6 (FIG. 1) is determined by (the outer diameter of the ball 3) ÷ (1 the ball 3 inserted into the circulation system).
By adjusting the thickness of the spacer 6 within (the total number of), all the spacers 6 can be prevented from falling down.

FIGS. 7 to 9 show a ball screw according to another embodiment of the present invention. In the example of FIG. 7, a top ball screw is used.
A is composed of a circulating component 12 called a piece. The circulation component 12 is a component that communicates substantially one round of the thread groove 5 of the nut 2, and a plurality of the circulation components 12 are provided for one nut 2. FIG.
Is a return tube type ball screw, and the circulation path 7B is constituted by the return tube 13. The return tube 13 is provided between both ends of the thread groove 5 of the nut 2. The example of FIG. 9 is a guide plate type ball screw, and the circulation path 7 </ b> C is formed by a guide groove of the guide plate 14 provided in the nut 2. At the entrance of the circulation path 7C composed of guide grooves,
Deflector 15 for scooping ball 3 between screw grooves 4 and 5
Is provided. In each of the examples of FIGS.
Any of the spacers 6 described in the above embodiments is
It is used between each ball 3. In each of the examples of FIGS. 7 to 9, the other configurations described above are the same as those of the embodiment of FIG. 1.

[0024]

According to the ball screw of the present invention, a spacer is interposed between the balls, the outer diameter of the spacer is smaller than the outer diameter of the ball, and the diameter difference between the ball and the spacer is equal to the allowable load. At the time of operation, since the diameter difference is larger than the amount of elastic deformation generated by the ball, competitive contact between the balls is eliminated,
An increase in friction torque and early damage of the ball can be prevented, a reduction in load capacity is suppressed, and assembly is simplified. If the contact surface of the spacer with the ball is a spherical concave surface along the outer diameter surface of the ball or a conical concave surface, the spacing between the balls can be reduced without causing the problem of falling of the spacer. It is possible to reduce the load capacity as much as possible. Also, when the ball contact surface of the spacer is concave as described above, when an oil reservoir is formed on the concave surface, the lubricant is retained to improve the lubrication performance, and the lubrication between the spacer and the ball is improved. Failure can be prevented. When the ball contact surfaces on both sides of the spacer are communicated with each other, the lubricity is improved, and the distance between the balls is further narrowed, so that a reduction in load capacity can be prevented as much as possible. When the spacer is made of a sintered metal mainly composed of stainless steel obtained by sintering an injection-molded product of a metal powder, mass productivity is excellent, rust hardly occurs, and strength is also excellent.
If the spacer is formed of a self-lubricating synthetic resin, it is excellent in mass productivity and excellent in lubrication performance,
Can be low torque.

[Brief description of the drawings]

1A is a sectional view of a ball screw according to an embodiment of the present invention, FIG. 1B is an enlarged sectional view of a spacer thereof, and FIG.
3 is a front view of the same seat. FIG.

FIG. 2 is an operation explanatory view showing a relationship between a spacer and a ball in the ball screw.

FIG. 3 is a conceptual diagram of a configuration in which an elastic body is provided between spacers.

FIG. 4 is a cross-sectional view of a modification of the spacer in the ball screw.

5A is a cross-sectional view of another modification of the spacer, and FIG. 5B is a front view thereof.

FIG. 6 is a sectional view of still another modification of the spacer.

FIG. 7 is a perspective view of a ball screw according to another embodiment of the present invention.

FIG. 8 is a perspective view of a ball screw according to still another embodiment of the present invention.

FIG. 9 is a sectional view of a ball screw according to still another embodiment of the present invention.

FIG. 10 is an operation explanatory view of a conventional ball screw.

FIG. 11 is an explanatory view of a screw shaft shape required for a conventional ball screw.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Screw shaft 2 ... Nut 3 ... Ball 4, 5 ... Screw groove 6 ... Spacer 7 ... Circulation path 8 ... Concave surface

Claims (7)

[Claims] A spiral screw groove is provided on each of an outer diameter surface of a screw shaft and an inner diameter surface of a nut loosely fitted on an outer periphery of the screw shaft, and a plurality of spiral screw grooves are provided between the screw shaft and the screw groove of the nut. In the ball screw with the balls interposed, a spacer is interposed between each ball, the outer diameter of this spacer is smaller than the outer diameter of the ball, and the diameter difference between the ball and the spacer is affected by the allowable load. A ball screw, wherein the diameter difference is larger than the amount of elastic deformation generated by the ball. 2. The ball screw according to claim 1, wherein the contact surface of the spacer with the ball is a spherical concave surface along the outer diameter surface of the ball. 3. The ball screw according to claim 1, wherein the contact surface of the spacer with the ball is a conical concave surface. 4. The ball screw according to claim 2, wherein an oil reservoir is formed on the concave surface of the spacer. 5. The ball screw according to claim 2, wherein contact surfaces of the spacer with the balls on both sides thereof communicate with each other. 6. The spacer is made of a sintered metal mainly composed of stainless steel obtained by sintering an injection-molded product of metal powder.
Or the ball screw according to claim 5. 7. The ball screw according to claim 4, wherein the spacer is formed of a self-lubricating synthetic resin.