JP2017089661A - Ball Screw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To extremely suppress the fatigue of a ball screw, and to elongate a life of the ball screw by solving a problem that, when a load distribution to balls is uneven, there arises the early-stage exfoliation of a screw shaft or a screw groove surface, thus causing the generation of vibration and noise.SOLUTION: In a ball screw having ball rows 4a, 4b, the ball rows 4a, 4b are constituted of one set of a ball groove which is composed of a large number of balls, and the balls are different in diameters at each row. Here, the unevenness of a load distribution in the ball screw is alleviated, a stress concentration is alleviated, breakage by the fatigue from a load which is repeatedly applied is thereby delayed, and a life of the ball screw can be elongated.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a ball screw used as a feed screw for moving a movable part by a linear actuator or the like.

  As a transmission mechanism that linearly moves a movable part in various machines such as a linear actuator, a ball screw that drives a movable part by changing a rotary motion of a motor or the like into a linear motion is known. This ball screw is a transmission mechanism using a screw in which a ball composed of a steel ball is inserted between a screw shaft and a male screw and a female screw of a nut. By inserting this ball between the screw shaft and the nut, the efficiency of converting rotational motion into linear motion is improved. Since the ball inserted between the male screw and the female screw moves while rolling along the screw groove, the ball train is provided with a set of balls that are wound around the screw shaft at least once to circulate. . A ball screw provided with a plurality of ball rows is also known (see, for example, Patent Document 1).

International Publication No. 2015/102109

  In the conventional ball screw, when the lead of the nut and the lead of the screw shaft are different, when receiving an axial load, a ball that receives a load, a ball that does not receive a load, or a ball that receives a load only slightly is generated. . Thus, when the load distribution on the ball is not uniform, there is a problem in that the surface of each thread groove of the screw shaft or nut is prematurely peeled, causing vibration and noise.

  In view of the above problems, an object of the present invention is to provide a ball screw that suppresses the uneven load distribution on the ball and extends the life.

  The ball screw of the first aspect of the present invention has two or more ball rows, and the ball row is composed of a set of ball groups made up of a large number of balls, and the balls have different diameters for each row.

  The ball screw of the second aspect of the present invention has two or more nuts arranged in series on the screw shaft, and the total number of rows is two or more. The nut connected in series is regarded as one nut, and the ball The row is composed of a set of balls composed of a large number of balls, and the balls have different diameters for each row.

  In the ball screw of the present invention, the uneven load distribution inside the ball screw is alleviated and the stress concentration is alleviated. Therefore, damage due to fatigue from repeatedly applied load can be delayed and the life of the ball screw can be extended. .

It is explanatory drawing of the ball screw of the 1st Embodiment of this invention. It is a figure which shows the relationship between the lead | read | reed of a nut, the lead | read | reed of a screw shaft, a contact angle, and a load. It is explanatory drawing of the ball screw of the 2nd Embodiment of this invention.

  FIG. 1 is an explanatory diagram of a ball screw according to the first embodiment. Reference numeral 1 denotes a screw shaft of a ball screw, and a nut 2 is screwed to the screw shaft 1 via a ball 3 made of a hard sphere. In this embodiment, the ball row formed by a set of balls circulating around the screw shaft is an example of a ball screw having two rows 4a and 4b. In the present embodiment, each of the ball rows 4a and 4b formed of a set of balls made up of a large number of balls 3 is wound around the screw shaft 1 by 3.5 turns and passed through the tubes 5a and 5b. The balls 3 are configured to return to their original positions, and are formed so as to circulate in the grooves of the male screw and female screw of the screw shaft 1 and the nut 2.

The configuration described above is the same as the configuration of the conventional ball screw having two rows of ball rows. However, the difference in the present invention is that each row is arranged so as to alleviate uneven load distribution inside the ball screw. The ball diameter is changed. In the embodiment shown in FIG. 1, the ball diameters of the plurality of ball rows are different from each other. The diameter of the balls 3 in the ball row 4a on the left side of the drawing is formed to be different from the diameter of the balls 3 in the ball row 4b on the right side of the drawing.

In an inexpensive and non-grinded rolled or cut nut, or a rolled screw shaft, it is difficult to produce the nut lead and screw shaft lead equally, which reduces the life of the ball screw. There is a risk.

In order to improve the life of the ball screw, the number of balls and the number of balls are generally increased to reduce the load applied to one ball. However, this not only increases the size of the ball screw, but if the lead of the nut does not match the lead of the screw shaft (lead error), even if the number of balls is increased, the number of balls subjected to the load is constant depending on the degree. There is a problem that the load does not increase and the load is not distributed. In this regard, according to the present embodiment, the life of the ball screw can be improved without changing the size of the ball screw.

In the present embodiment, as shown in FIG. 2, there are a ball 3 a that contacts the groove 6 due to an axial load Fa received by the nut and a ball 3 b that does not contact the groove 6. In this case, the lead of the nut La, the lead Lb of the screw shaft, the contact angle α of the ball 3, and how many turns of the adjacent ball row (ball circulation path) (not shown) are separated (here, c turns) ) To determine the difference in ball diameter between adjacent balls 3a and 3b. When La-Lb> 0, the ball diameter of the circuit on the front side in the direction of the axial load Fa received by the nut among adjacent ball rows is relatively reduced by c × (La−Lb) / sin α. To do. In the case of La−Lb <0, the ball diameter of the circuit on the front side in the axial load direction received by the nut among adjacent ball rows is relatively increased by c × (La−Lb) / sin α. To form. By changing the ball diameter for each ball row in this way, the load distribution due to lead errors is suppressed, and the ball screw has high durability even when high accuracy cannot be obtained at low cost. Can be obtained.

In addition, the ball screw of this embodiment cannot be applied to a ball screw that receives an equivalent axial load from both directions. This is because a large load distribution is biased when an axial load is received from the opposite direction.

In the ball screw of this embodiment, it is not necessary to change the diameters of the balls 3 in all the ball rows 4a. For example, in the case of a ball screw having four rows, the diameter of the ball 3 can be changed every two rows. At this time, if a relatively small ball is placed in a ball train that receives a large load due to a lead error, and a relatively large ball is placed in a ball train that does not receive a load due to a read error or receives a slight load Good.

Moreover, the ball screw of this embodiment is applicable to both uses of shaft rotation nut movement and nut rotation shaft movement.

Moreover, the ball screw of this embodiment is applicable when the axial load in the reverse direction is always lighter than the axial load in a constant direction.

The ball screw connects either the screw shaft 1 or the nut 2 to a drive source such as a motor, connects the other to a driven body, and changes the rotational motion to a linear motion to linearly move the driven body. is there. For example, the screw shaft 1 is connected to a driving source such as a motor, the nut 2 is coupled to the driven body, and the screw shaft 1 is rotated to linearly move the nut 2 to linearly move the driven body. Or conversely, a driving source such as a motor is connected to the nut 2, the driven body is connected to the screw shaft 1, and the screw shaft 1 and the driven body are linearly moved by rotating the nut 2. Thus, it is used as a transmission mechanism that converts rotational motion into linear motion. It is also used as a mechanism for converting linear motion into rotational motion.

As described above, the force is transmitted by converting the rotational motion into a linear motion. Therefore, in the conventional ball screw, the load distribution in the ball screw is non-uniform, and part of the screw shaft 1 and the nut 2 is partially generated. This means that concentrated stress is applied to the region. Therefore, if the ball screw is used for a long time, the screw shaft 1 and the nut 2 are damaged due to fatigue due to repeated load in the relative movement section region (relative movement stroke range) of the screw shaft 1 and the nut 2, and the ball screw There is a problem of shortening the lifespan.

Therefore, in this embodiment, the non-uniform load distribution is reduced by changing the diameter of the balls 3 of the ball row connected in series. In the first embodiment, by changing the diameters of the balls 3 of the ball rows 4a and 4b of the nut 2, the concentrated stress on the screw shaft 1 and the nut 2 is reduced, and the internal stress of the screw shaft 1 and the nut 2 is reduced. The non-uniformity was eased and eliminated. By reducing the uneven load distribution inside the ball screw and preventing concentrated stress from occurring, damage from fatigue due to repeated stress of the screw shaft 1 and nut 2 caused by long-term use of the ball screw is minimized. Can prevent and extend the life of the ball screw.

The first embodiment shown in FIG. 1 is an example of a ball screw having two rows of balls, but the present invention can be applied to a ball screw having a larger number of rows. That is, even in a ball screw having three or more ball rows, the ball diameter of each row is changed so as to alleviate uneven load distribution inside the ball screw. Also in this case, by varying the diameters of the balls 3 in the ball train arranged in series, the unevenness of the load distribution inside the ball screw can be alleviated and the life of the ball screw can be extended.

FIG. 3 is an explanatory diagram of a ball screw according to the second embodiment. In the second embodiment, an example is shown in which two nuts 2 a and 2 b are connected to each other and a ball screw that finally functions as one nut 2 is configured. Two nuts 2 a and 2 b are connected to form one nut 2, and are screwed onto the screw shaft 1. Each nut 2a, 2b is provided with two rows of ball rows 4a, 4b. In the second embodiment, each ball row 4a, 4b is wound around the screw shaft 1 by 3.5 turns and returned to the original position by the tubes 5a, 5b as in the first embodiment. The ball 3 is composed of a set of balls.

Also in this embodiment, the ball diameter of each row is changed so as to alleviate uneven load distribution inside the ball screw. For this purpose, the balls 3 of the ball rows arranged in series are formed so that the diameters thereof are different from each other. That is, a relatively small ball should be placed in a ball train that receives a large load due to a lead error, and a relatively large ball should be placed in a ball train that does not receive a load due to a read error or receives a slight load. . As a result, similar to the first embodiment, the nonuniformity of the internal stress generated in the screw shaft 1 and the nut 2 is alleviated, and the load distribution is made uniform. Therefore, also in the second embodiment, the internal stress is made uniform so that the axial force is uniform in the entire region where the screw shaft 1 and the nut 2 are screwed together, and the non-uniform load distribution is alleviated. By doing so, damage to the ball screw due to fatigue was prevented as much as possible, and the life of the ball screw was extended.

In the second embodiment, the two nuts 2a and 2b are connected to act as one nut 2. However, the number of nuts to be connected may be increased. Even in such a case, the diameter of the balls 3 of the ball rows arranged in series may be formed to be different for each row.

In addition, a nut having a single row of balls is provided, and the nuts of the single row of rows are arranged at both ends of the nuts. If the balls are formed so as to be different from the diameters of the balls in the row, the load distribution inside the ball screw shaft is easily non-uniform in the ball screw when a plurality of nuts are connected to act as one nut. Can be relaxed.

In each of the embodiments described above, by changing the ball diameter of the ball row, the load distribution inside the ball screw is relaxed and the life of the ball screw is extended. The load distribution inside the ball screw can be made uniform by selecting the shape and matching the axial rigidity of the screw shaft and the nut. The nut has a larger outer shape and higher rigidity than the screw shaft. As a result, the internal stress of the ball screw becomes non-uniform.

Therefore, by selecting the material and shape of the screw shaft and nut, if the axial rigidity of the screw shaft and nut is matched, the other is linearly moved by rotating either the screw shaft or the nut. When a force is applied to the screw shaft, the screw shaft and the nut bend in the same way. As a result, in the entire area where the screw shaft and the nut are screwed together via the ball, the load is uniformly applied and the internal stress is also uniformed and the load distribution Becomes uniform. As a result, since no concentrated stress is generated, the occurrence of breakage due to fatigue is delayed, and the life of the ball screw can be extended.

A force is applied so that a predetermined load per pitch is applied to the screw shaft in the axial direction, and a displacement amount per pitch at that time and a force are applied so that a predetermined load per pitch is applied to the nut in the axial direction. In addition, the amount of displacement per pitch at that time is obtained, and the material and shape of the screw shaft and nut are selected and designed so that the amount of amount of displacement roughly matches.

In addition, the screw shaft and the nut are formed of the same material, and the screw shaft and the nut are designed so that the areas of the cross sections of the screw shaft and the nut when they are cut in a direction perpendicular to the axis of the screw shaft are the same. If the cross-sectional areas match, the axial force applied to the screw shaft and nut will be deflected evenly, and a uniform stress will be generated over the entire area where the screw shaft and nut are screwed together via the ball. The load distribution of the screw becomes uniform, and the life of the ball screw can be extended.

1 Screw shaft 2 Nut 2a, 2b Nut 3 Ball 4a, 4b Ball row 5a, 5b Tube 6 Groove α Contact angle

Claims (2)

In a ball screw having two or more ball rows,
The ball row is composed of a set of balls composed of a large number of balls,
The ball screw has a different diameter for each row. In a ball screw in which two or more nuts are arranged in series on the screw shaft and the total number of rows is two or more, the nuts connected in series are regarded as one nut,
The ball row is composed of a set of balls composed of a large number of balls,
The ball screw has a different diameter for each row.

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