ball screw

Abstract

To provide a ball screw capable of changing a preload on a real time basis, without being provided without providing an extra facility.SOLUTION: A plurality of rolling elements includes, at least, a plurality of first rolling elements having first dimensions, and a plurality of second rolling elements having second dimensions larger than the first dimensions. When a screw shaft and a nut are at first relative positions where an external load is applied to a ball screw, the plurality of second rolling elements is disposed over a whole length of a rolling path. When the screw shaft and the nut are at second relative positions where the external load is not applied to the ball screw, at least one of the plurality of first rolling elements is disposed in the rolling path.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a ball screw. [Background technology]

[0002] Ball screws are used in devices that require precise positioning, such as machine tools and robots. To achieve high-precision positioning in a ball screw, a preload is generally applied to the ball screw to eliminate axial clearance, reduce the amount of elastic displacement due to axial load, and increase rigidity. There are various methods for applying this preload, such as the spacer preload method.

[0003] In existing ball screw designs, the preload is set according to the expected external load. However, in devices where the external load is applied to the ball screw for a short period of time, the time when the external load is not applied (the preload does not work) is long, and therefore the time when wasted torque (friction loss) is generated is also long. In addition, in high-cycle devices, the heat generated by the ball screw due to the preload cannot be ignored.

[0004] Patent Documents 1 and 2 disclose methods for controlling preload.

[0005] Patent Document 1 discloses a ball screw device having a first nut and a second nut that are threaded onto a screw shaft, where relative rotation between the first nut and the second nut is prevented by a key means, and where a spacer is inserted between the nuts and preload is adjusted by variably controlling the axial thickness of the spacer. The spacer is configured so that piezoelectric sheets are attached alternately to the surface facing the first nut and the surface facing the second nut, causing elastic deformation in the spacer when the two nuts are tightly clamped together.

[0006] Patent Document 2 discloses a preload recovery device for a ball screw, which includes a screw shaft, a plurality of nuts that are threadedly engaged with the screw shaft via a plurality of rolling elements, and a preload applying mechanism disposed between adjacent nuts. The preload applying mechanism includes a spacer having a cylindrical portion with a cylindrical inner surface that is disposed at the joint between the adjacent nuts, and a spacer housing having a small-diameter cylindrical portion that houses the cylindrical portion of the spacer formed on at least one of the adjacent nuts. Threaded portions are formed on the contact surfaces of the spacer and the spacer housing, and when the preload between the adjacent nuts decreases, the preload between the adjacent nuts is restored by adjusting the screwing positions of the female and male threaded portions between the spacer and the spacer housing. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-009054 [Patent Document 2] Japanese Patent Application Publication No. 02-221747 Summary of the Invention [Problem to be solved by the invention]

[0008] The technology in Patent Document 1 uses a double-nut type ball screw and provides an adjustment mechanism in the space between them to adjust the preload. However, this method does not provide any auxiliary equipment for preload adjustment, so it is not possible to change the preload in real time during the cycle.

[0009] In the technology of Patent Document 2, the preload can be changed in real time during the cycle, but additional auxiliary equipment for preload adjustment is required, which increases the size and cost of the device.

[0010] The above-mentioned existing ball screws are cooled by auxiliary equipment such as a cooling device to counter heat generation in the ball screws due to preload, but this increases the size and cost of the device.

[0011] The present invention provides a ball screw that can change the preload in real time without providing any extra equipment. [Means for solving the problem]

[0012] The above object of the present invention can be achieved by the following configuration. (1) a plurality of rolling elements; a screw shaft having a spiral screw shaft groove on its outer circumferential surface; A nut disposed around the screw shaft and having a spiral nut groove on its inner circumferential surface; a rolling path formed by the opposing screw shaft groove and the opposing nut groove, in which the plurality of rolling elements are disposed; a circulation path in which the plurality of rolling elements are arranged and connected to the rolling path, and through which the plurality of rolling elements sent out from the rolling path move and return to the rolling path as the screw shaft and the nut move relative to each other; A ball screw comprising: the plurality of rolling elements include at least a plurality of first rolling elements having a first dimension and a plurality of second rolling elements having a second dimension larger than the first dimension; When an external load is applied to the ball screw and the screw shaft and the nut are in a first relative position, the plurality of second rolling elements are arranged over the entire length of the rolling path, When the screw shaft and the nut are in a second relative position where no external load is applied to the ball screw, at least one of the plurality of first rolling elements is disposed in the rolling path. Ball screw. (2) When the screw shaft and the nut are in the second relative position, the plurality of first rolling elements are arranged over the entire length of the rolling path. (1) The ball screw described in (1). (3) When the screw shaft and the nut are in the second relative position, the first rolling elements and the second rolling elements are alternately arranged in the rolling paths. (1) The ball screw described in (1). [Effects of the Invention]

[0013] According to the present invention, the preload can be changed in real time without providing any extra equipment. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a side view of a ball screw according to a first embodiment of the present invention, showing a state in which no external load is applied. [Figure 2] FIG. 2 is a side view of the ball screw according to the first embodiment, showing a state in which an external load is applied. [Figure 3] FIG. 3 is a side view of the ball screw according to the second embodiment. [Figure 4] FIG. 4 is a side view of a ball screw according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an embodiment of a ball screw according to the present invention will be described in detail with reference to the drawings. Figures 1 and 2 are side views of a ball screw 100 according to a first embodiment of the present invention, with Figure 1 showing a state in which no external load is applied and Figure 2 showing a state in which an external load is applied.

[0016] The ball screw 100 is used in devices that require precise positioning, such as machine tools and robots. The ball screw 100 is installed on a stand or the like (not shown). The ball screw 100 includes a screw shaft 10, a nut 20 arranged around the screw shaft 10, and a plurality of rolling elements 30. The screw shaft 10 is connected to a power source such as a motor and rotates, and the nut 20, which is threaded onto the screw shaft 10 via the plurality of rolling elements 30, reciprocates along a straight line. In other words, the ball screw 10 converts rotational motion into linear motion. A device including components such as a slider and a table is connected to the nut 20.

[0017] The rolling elements 30 are spherical bodies such as steel balls, and are arranged in a rolling path 40 and a circulation path 50 connected to the rolling path 40. The rolling path 40 is formed by a spiral screw shaft groove 42 formed on the outer circumferential surface of the screw shaft 10 and a spiral nut groove 41 formed on the inner circumferential surface of the nut 20, which face each other. The circulation path 50 is a tubular path that cooperates with the rolling path 40 to form a loop-shaped path along which the rolling elements 30 can move. The rolling path 40 and the circulation path 50 are connected by a connecting path 21 provided in the nut 20. The rolling elements 30 sent out from the rolling path 40 travel through the circulation path 50 and return to the rolling path 40 via the connecting path 21.

[0018] As the ball screw 100 is driven, the screw shaft 10 and the nut 20 move relative to each other. As a result of this movement, the rolling elements 30 move through the rolling path 40 and the circulation path 50. Specifically, a plurality of rolling elements 30 are sent out from the rolling path 40, move through the circulation path 50, and then return to the rolling path 40. The rolling of the rolling elements 30 in the rolling path 40 reduces the contact resistance between the screw shaft 10 and the nut 20. Note that although the circulation components that make up the circulation path 50 are not shown, they may include a return tube, a return plate, a top, an end cap, an end deflector, etc., depending on the application. In addition, in FIG. 1, for convenience, one end and the other end of the circulable part are shown in the same phase.

[0019] In the ball screw 100, an external load (axial load) is generated in the axial direction during operation. For this reason, in designing the ball screw, a preload is set according to the external load expected from factors such as the weight of the transported object and the maximum speed.

[0020] The external load on the ball screw 100 is generated and fluctuates at a predetermined timing, more precisely, when the screw shaft 10 and the nut 20 are in a predetermined first relative position (predetermined stroke) in the axial direction, as shown in FIG. 2. For example, when the screw shaft 10 and the nut 20 are in a second relative position as shown in FIG. 1, no external load is generated on the ball screw 100. In conventional methods, a detection device that detects such fluctuations in the external load is separately provided on the ball screw, and the ball screw fluctuates the preload in response to the detected external load. For example, no preload is applied in the case of FIG. 1, but preload is applied in the case of FIG. 2. However, such an external device increases the size of the entire device, including the ball screw, and also increases costs.

[0021] Such a special detection device is not provided in the ball screw 100 of this embodiment. Instead, the ball screw 100 of this embodiment is devised with a plurality of rolling elements 30.

[0022] That is, in this embodiment, the plurality of rolling elements 30 includes at least a plurality of first rolling elements 31 having a first dimension and a plurality of second rolling elements 32 having a second dimension larger than the first dimension. When the rolling elements 30 are spherical, the dimension is determined by the diameter of the rolling elements 30. Furthermore, the arrangement of the first rolling elements 31 and the second rolling elements 32 is determined by the presence or absence of an external load.

[0023] 1 shows a state in which no external load is applied to the ball screw 100 and the screw shaft 10 and the nut 20 are in a second relative position. In this state, at least one of the multiple first rolling elements 31 is disposed in the rolling path 40.

[0024] 1, it is more preferable that the first rolling elements 31 are arranged over the entire length of the rolling path 40. In this case, all of the second rolling elements 32 are arranged in the circulation path 50.

[0025] 2 shows a state in which an external load is applied to the ball screw 100 and the screw shaft 10 and the nut 20 are in a first relative position. In this state, as shown in FIG. 2, the second rolling elements 32 are arranged over the entire length of the rolling path 40, and all of the first rolling elements 31 are arranged in the circulation path 50.

[0026] That is, when an external load is applied to the ball screw 100, the second rolling elements 32 are always disposed in the rolling path 40. By disposing the large second rolling elements 32 in the rolling path 40, it is possible to apply a preload effectively in accordance with the external load applied to the rolling path 40. In particular, since a plurality of second rolling elements 32 are disposed over the entire length of the rolling path 40, it is possible to apply a preload more reliably.

[0027] Furthermore, the first rolling elements 31 are always disposed in the rolling paths 40 when no external load is applied to the ball screw 100. By disposing the small-sized first rolling elements 31 in the rolling paths 40, it is possible to suppress the application of preload to the rolling paths 40 when no external load is applied. This suppresses the generation of torque and heat due to friction loss and improves the efficiency of the device. In particular, when multiple first rolling elements 31 are disposed over the entire length of the rolling paths 40, it is possible to more effectively suppress the application of preload.

[0028] 3 is a side view of a ball screw 100 according to a second embodiment. In this embodiment, when no external load is applied to the ball screw 100 and the screw shaft 10 and the nut 20 are in a second relative position, the first rolling elements 31 and the second rolling elements 32 are alternately arranged and aligned in the rolling path 40. This arrangement of the first rolling elements 31 and the second rolling elements 32 also makes it possible to suppress the application of preload and to suppress the generation of torque and heat due to friction loss.

[0029] In summary, the ball screw 100 of the embodiment allows the preload to be changed in real time while the device is operating, without the need for special equipment for preload adjustment. This is achieved by appropriately arranging the first rolling elements 31 and the second rolling elements 32, which are different in size, in the rolling path 40 and the circulation path 50 through which they circulate. That is, at a first relative position between the screw shaft 10 and the nut 20 in which an external load is applied to the ball screw 100, the first rolling elements 31 and the second rolling elements 32 are arranged in predetermined positions in the rolling path 40 and the circulation path 50 so that a preload is applied to the ball screw 100. At a second relative position between the screw shaft 10 and the nut 20 in which no external load is applied to the ball screw 100, the first rolling elements 31 and the second rolling elements 32 are arranged in predetermined positions in the rolling path 40 and the circulation path 50 so that the preload is reduced or eliminated.

[0030] This ensures an appropriate preload according to the stroke position, while suppressing the application of preload and preventing torque and heat generation due to friction loss. The arrangement of the first rolling elements 31 and the second rolling elements 32 can be designed appropriately depending on factors such as the stroke length of the ball screw 100, the lengths of the rolling path 40 and the circulation path 50, and operating conditions. For example, if an external load occurs only at one specific point in the stroke position, the number of second rolling elements 32 may be reduced, or the length of the circulation path 50 may be increased.

[0031] 4 is a side view of a ball screw 100 according to a third embodiment. In this embodiment, an adapter 60 is attached to an end of a nut 20. Like the nut 20, the adapter 60 is movable relative to the screw shaft 10 and includes an extension path 61 that can extend the circulation path 50.

[0032] The present invention is not limited to the above-described embodiments, and can be appropriately modified, improved, etc. In addition, the material, shape, dimensions, numerical values, form, number, location, etc. of each component in the above-described embodiments are arbitrary and not limited as long as they can achieve the present invention. [Explanation of symbols]

[0033] 10 Screw shaft 20 nuts 21 Connecting Road 30 rolling elements 31 First rolling element 32 Second rolling element 40 Rolling Path 41 Nut Gutter 42 Screw shaft groove 50 Circulation path 60 adapter 61 Extension road 100 ball screw

Claims

1. A plurality of rolling elements; a screw shaft having a spiral screw shaft groove on its outer circumferential surface; A nut disposed around the screw shaft and having a spiral nut groove on its inner circumferential surface; a rolling path formed by the opposing screw shaft groove and the opposing nut groove, in which the plurality of rolling elements are disposed; a circulation path in which the plurality of rolling elements are arranged and connected to the rolling path, and through which the plurality of rolling elements sent out from the rolling path move and return to the rolling path as the screw shaft and the nut move relative to each other; A ball screw comprising: the plurality of rolling elements include at least a plurality of first rolling elements having a first dimension and a plurality of second rolling elements having a second dimension larger than the first dimension; When an external load is applied to the ball screw and the screw shaft and the nut are in a first relative position, the plurality of second rolling elements are arranged over the entire length of the rolling path, When the screw shaft and the nut are in a second relative position where no external load is applied to the ball screw, at least one of the plurality of first rolling elements is disposed in the rolling path. Ball screw.

2. When the screw shaft and the nut are in the second relative position, the plurality of first rolling elements are arranged over the entire length of the rolling path.

2. The ball screw according to claim 1.

3. When the screw shaft and the nut are in the second relative position, the first rolling elements and the second rolling elements are alternately arranged in the rolling path.

2. The ball screw according to claim 1.

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