Feed screw device

Abstract

The present invention comprises a ball screw provided with a threaded shaft and a nut, a pair of intermediate supports positioned so as to be vertically movable around the threaded shaft, a pair of frame bodies respectively attached to the pair of intermediate supports and connected by a connection member, a linear-motion guiding part having a pair of outer cylinders which pass through the shaft and to which the pair of frame bodies are respectively attached, and a pair of buffer devices. The nut has a state in which the nut comes into contact with the intermediate support or the frame body positioned above and moves in the vertical direction together with the pair of intermediate supports and the pair of frame bodies, and a state in which the nut is not in contact with the intermediate support or the frame body positioned above.

Description

Feed screw device

[0001] The present invention relates to a feed screw device.

[0002] As the rotation speed of the ball screw increases, the frequency of the screw shaft approaches the natural frequency, causing the screw shaft to resonate and vibrate violently. The rotation speed of the ball screw at this time is called the critical speed, and since this critical speed is inversely proportional to the square of the support interval of the screw shaft, it is usually preferable for the support interval of the screw shaft to be short.

[0003] As a countermeasure against this resonance, it is known to attach two intermediate supports with a small gap between them and the screw shaft between the nut and the bearings that support both ends of the screw shaft (see, for example, Patent Document 1). When the ball screw exceeds the critical speed and begins to vibrate, the screw shaft comes into contact with these intermediate supports, shortening the support interval, which makes it possible to raise the upper limit of the rotation speed within the specification conditions.

[0004] Patent Document 1 discloses the configuration of a feed screw support device in which a linear guide device is provided parallel to the screw shaft between bearings at both ends of the horizontally extending screw shaft, and a pair of intermediate supports are attached to the slider of the linear guide device, which receive the radial load of the screw shaft and engage with the nut to move in the screw axial direction.

[0005] Japan Utility Model Publication No. 02-004736

[0006] However, when the feed screw device described in Patent Document 1 is applied to a ball screw whose screw shaft extends vertically, the intermediate support cannot be supported from below by the slider, so the nut that moves upward from the axial center of the screw shaft lifts the intermediate support and slider, which increases the load.In addition, if the support interval of the ball screw becomes long, the intermediate support cannot be linked to the appropriate position, which may result in the resonance prevention effect not being fully realized.

[0007] The present invention has been made in view of the above-mentioned problems, and its object is to provide a feed screw device that can be used with a screw shaft extending vertically, by suppressing resonance and increasing the upper limit of the critical speed.

[0008] The above object of the present invention can be achieved by the following configuration. a ball screw including a screw shaft extending in the vertical direction, both ends of which are rotatably supported by an upper base portion and a lower base portion via bearings, and a nut screwed onto the screw shaft via balls; a pair of intermediate supports located on both sides of the nut in the vertical direction, each arranged to be movable up and down around the screw shaft, and formed to be able to come into contact with the screw shaft; a pair of frame bodies attached to the pair of intermediate supports between the upper base portion and the lower base portion and connected by a connecting member; a linear motion guide section having a pair of outer cylinders that pass through shafts attached to the upper base portion and the lower base portion and to which the pair of frame bodies are attached, respectively; and a pair of buffer devices provided between the upper base portion and the frame body located above, and between the lower base portion and the frame body located below,

[0009] According to the feed screw device of the present invention, in a specification in which the screw shaft extends vertically, even if the support interval of the ball screw is long, the upper limit of the critical speed can be increased and used without resonance.

[0010] Fig. 1 is an overall view of a feed screw device showing a resonance prevention device in a first state. Fig. 2 is an overall view of a feed screw device showing a resonance prevention device in a second state. Fig. 3 is a central cross-sectional view showing an intermediate support. Fig. 4 is a view showing a feed screw device of a second embodiment.

[0011] A feed screw device according to an embodiment of the present invention will be described in detail below with reference to the drawings. Fig. 1 is an overall view of the feed screw device showing a resonance prevention device in a first state. Fig. 2 is an overall view of the feed screw device showing a resonance prevention device in a second state. Fig. 3 is a central cross-sectional view showing an intermediate support.

[0012] (First embodiment) As shown in Figures 1 and 2, the feed screw device 1 of the first embodiment includes an upper base plate 2 (upper base portion), a lower base plate 3 (lower base portion), a ball screw 10 whose both ends are supported by the upper base plate 2 and the lower base plate 3, and a resonance prevention device 100 that suppresses resonance of the ball screw 10.

[0013] The ball screw 10 is rotatably supported at both ends via bearings 15 and includes a screw shaft 11 that extends vertically and has a helical screw groove 11a on its outer circumferential surface, a nut 12 that has a helical screw groove (not shown) on its inner circumferential surface that corresponds to the screw groove 11a of the screw shaft 11, a plurality of balls (not shown) that roll on a load track formed by the screw groove 11a of the screw shaft 11 and the screw groove of the nut 12, and a seal member (not shown) that seals a gap between the screw shaft 11 and the nut 12. A drive motor 60 that rotates the screw shaft 11 is provided at one end (the lower end in the illustrated example) of the screw shaft 11 via a coupling 16.

[0014] The outer peripheral surface of the nut 12 is provided with multiple circulation components (not shown), each having a scooping portion that penetrates the nut 12 so that both ends extend into the load track and scoop up balls. As a result, balls scooped up at one end of the load track pass through the circulation component and are returned to the other end of the load track, forming an infinite circulation path. The nut 12 has a flange portion 13 formed on one axial end. The flange portion 13 is fixed to a moving platform or the like of a mechanical device (not shown) with a mounting bolt or the like.

[0015] As described above, the ball screw 10 can move the nut 12 (and a movable table, etc., attached to the nut 12) up and down along the screw shaft 11 by rotating the screw shaft 11 axially using the drive motor 60.

[0016] (Resonance prevention device) The resonance prevention device 100 includes a pair of intermediate supports 20, 20 located on both vertical sides of the nut 12 and arranged to be vertically movable around the screw shaft 11, a pair of frame bodies 30, 31 attached to the pair of intermediate supports 20, 20, respectively, a linear motion guide unit 40 that guides the vertical movement of the intermediate supports 20, and a pair of buffer devices 50, 51 attached to the upper base plate 2 and the lower base plate 3, respectively. The intermediate supports 20 are cylindrical members that are fitted onto the screw shaft 11 extending in the vertical direction, and a pair of intermediate supports 20 are provided on both vertical sides of the nut 12 that moves along the screw shaft 11. As shown in Figure 3, the intermediate supports 20 are attached to the frame bodies 30, 31 extending in the horizontal direction.

[0017] As shown in FIG. 3 , the intermediate support 20 is cylindrical, with an inner diameter slightly larger than the outer diameter of the screw shaft 11. This allows the intermediate support 20 to move up and down along the screw shaft 11, with a small gap formed between the inner circumferential surface of the intermediate support 20 and the outer circumferential surface of the screw shaft 11 inserted through the intermediate support 20. On the other hand, when the screw shaft 11 resonates at a predetermined frequency or higher, the inner circumferential surface of the intermediate support 20 comes into contact with the outer circumferential surface of the screw shaft 11, thereby suppressing the vibration of the screw shaft 11 with the intermediate support 20. The intermediate support 20 is a guide bush that can come into contact with the outer circumferential surface of the resonating screw shaft 11 and is made of an oil-resistant synthetic resin. The guide bush that constitutes the intermediate support 20 is not limited to synthetic resin, and may be made of a low-friction material such as a self-lubricating metal or an oil-impregnated metal.

[0018] The pair of frame bodies 30, 31 are plate-like members that have a plane perpendicular to the screw shaft 11 and extend horizontally, and through which the screw shaft 11 extending vertically and a shaft 41 (described later) are inserted. The pair of frame bodies 30, 31 are provided in pairs on both sides of the nut 12 in the vertical direction, similar to the intermediate support 20. The intermediate support 20, through which the screw shaft 11 is inserted, and the linear guide portion 40, through which the shaft 41 is inserted, are fitted and fixed to each frame body 30, 31, and thereby arranged side by side in the horizontal direction.

[0019] The pair of upper and lower frame bodies 30, 31 are connected by a connecting member 33 extending in the vertical direction. As a result, the vertical distance between the pair of upper and lower intermediate supports 20, 20 attached to the pair of upper and lower frame bodies 30, 31 (also referred to as the distance L1 between the restraining fulcrums) is always kept constant. This configuration can be seen in Figures 1 to 3. Furthermore, the pair of frame bodies 30, 31 need only have a shape that allows the intermediate support 20 and the linear guide unit 40 to be attached and supported, and is not limited to plate-like members.

[0020] The linear guide units 40 are cylindrical members that are fitted to the exterior of the shaft 41 and move up and down along the shaft 41, and are provided in pairs, one above the other, similar to the intermediate supports 20. Each linear guide unit 40 has an outer cylinder that is a pair of cylindrical members that penetrates the shaft 41 that extends parallel to the screw shaft 11 and is attached to each of the pair of frames 30, 31, and a linear ball bearing (not shown) that holds a plurality of balls (not shown) aligned along the axial direction on the inner surface of each outer cylinder. This allows the linear guide units 40 to move smoothly up and down along the shaft 41.

[0021] The shaft 41 extends in the vertical direction parallel to the screw shaft 11 and is arranged side by side in the left-right direction with the screw shaft 11, with both ends supported by the upper base plate 2 and the lower base plate 3. The shaft 41, like the screw shaft 11, is inserted through a pair of upper and lower frames 30, 31. Both ends of the shaft 41 are fixed to the upper base plate 2 and the lower base plate 3, and unlike the screw shaft 11, it does not rotate axially.

[0022] As a result, the pair of upper and lower linear guide units 40 move smoothly up and down along the shaft 41 arranged parallel to the screw shaft 11. At this time, the upper linear guide unit 40 is connected to the upper intermediate support 20 via the upper frame body 30, and the lower linear guide unit 40 is connected to the lower intermediate support 20 via the lower frame body 31. In other words, by guiding each linear guide unit 40 attached to the pair of frame bodies 30, 31 to move up and down along the shaft 41, the intermediate support 20 inserted with a gap from the outer circumferential surface of the screw shaft 11 can be guided to move up and down along the screw shaft 11 while maintaining that state.

[0023] One of the pair of shock absorbers 50, 51 is provided between the upper base plate 2 and the upper frame body 30, and the other shock absorber 51 is provided between the lower base plate 3 and the lower frame body 31. In particular, the lower shock absorber 51 elastically supports the lower surface of the frame body 31, which moves up and down along the shaft 41 (screw shaft 11), thereby preventing the pair of intermediate supports 20, 20 from falling downward more than a predetermined distance. The lower shock absorber 51 may be configured to support the lower intermediate support 20 or the lower linear guide unit 40. As a result, the shock absorbers 50, 51 can prevent the pair of frame bodies 30, 31, which move up and down integrally because they are integrally connected via the connecting member 33, from colliding forcefully with the upper base plate 2 or the lower base plate 3. The shock absorbers 50, 51 may be any device capable of preventing the frames 30, 31 from colliding forcefully with the upper and lower base plates 2, 3, and may be an air cylinder, a hydraulic cylinder, a damper member equipped with an elastic member, or a shock absorber equipped with an elastic member. The shock absorbers 50, 51 may also be used in combination with a tension spring or a constant force spring (not shown) that is provided to offset the weight of the frames 30, 31, so that the positions of the frames 30, 31 when the nut 12 is not acting are maintained at the center in the axial direction of the screw shaft 11.

[0024] (Operation and Effect) When the ball screw 10 is driven by the drive motor 60 to rotate the screw shaft 11 in a predetermined direction, the nut 12 moves upward or downward along the screw shaft 11. At this time, if the fulcrum distance of the screw shaft 11 is long, the value of the critical speed u, which is inversely proportional to the square of the fulcrum distance, becomes small, and resonance may occur even at a relatively low rotational speed of the screw shaft 11. In response to this, the resonance prevention device 100 of this embodiment provides a pair of intermediate supports 20 on both the upper and lower sides of the nut 12, which are maintained spaced apart by a suppression fulcrum distance L1. The intermediate supports 20 are configured so that their inner circumferential surfaces contact the outer circumferential surface of the screw shaft 11, forming contact points (fulcrums), when the screw shaft 11 begins to resonate at a predetermined level or greater. As a result, when resonance occurs in the screw shaft 11, the fulcrum distance is shortened from the normal fulcrum distance L to the suppression fulcrum distance L1, significantly increasing the value of the critical speed u and making it more difficult for the screw shaft 11 to resonate. That is, the feed screw device 1 provided with the resonance prevention device 100 can be used at a rotation speed exceeding that which would not be permissible with a ball screw 1 of normal specifications.

[0025] Specifically, the pair of intermediate supports 20 are integrally connected via frame bodies 30, 31 and a connecting member 33, and each intermediate support 20 is connected via the frame bodies 30, 31 to a linear guide unit 40 that moves along a shaft 41 parallel to the screw shaft 11. As a result, when the screw shaft 11 is not resonating, the intermediate supports 20 move up and down along the screw shaft 11 in a non-contact state where a gap is formed between the inner circumferential surface of the intermediate support 20 and the outer circumferential surface of the screw shaft 11. On the other hand, when the rotation speed of the screw shaft 11 increases and resonates with an amplitude equal to or greater than a predetermined value, the inner circumferential surface of the intermediate support 20 comes into contact with the outer circumferential surface of the screw shaft 11, and the intermediate support 20 serves as a fulcrum that presses the screw shaft 11. As a result, the distance between the fulcrums is automatically shortened from between the upper and lower base plates 2, 3 to between the pair of intermediate supports 20. According to this configuration, the pair of intermediate supports 20, 20 contact the outer surface of the screw shaft 11 only when the screw shaft 11 resonates, and therefore when the screw shaft 11 is not resonating, they are out of contact with the screw shaft 11 and do not hinder the movement of the nut 12.

[0026] The configuration in which the intermediate support 20 moves will be described with reference to Figures 1 and 2. As shown in Figure 1, the resonance prevention device 100 has a first state in which the nut 12, which moves up and down along the screw shaft 11, comes into contact with the upper intermediate support 20 and moves up and down together with the pair of intermediate supports 20, 20 and the pair of frames 30, 31, and a second state in which the nut 12 does not come into contact with the upper intermediate support 20, as shown in Figure 2.

[0027] In the first state shown in Fig. 1, the nut 12 moves up and down along the screw shaft 11 while supporting the upper intermediate support 20. As a result, the intermediate support 20 and the frame bodies 30, 31 move in synchronization with the nut 12 until they approach the lower surface and are supported by the lower shock absorber 51 (until the state is switched to the second state), so the position of the support point that supports the screw shaft 11 by the intermediate support 20 can be automatically optimized. As shown in Fig. 2, when the second state is reached and the lower intermediate support 20 and the frame body 31 are supported by the lower shock absorber 51, no load is applied to the nut 12, allowing the nut 12 to move more smoothly.

[0028] Furthermore, the intermediate support 20 can reliably prevent the intermediate support 20 and the frame bodies 30 and 31 supporting the intermediate support 20 from colliding forcefully with the upper base plate 2 and the lower base plate 3 by means of a pair of shock absorbers 50 and 51 .

[0029] In this embodiment, since the screw shaft 11 extends vertically, no member is required to support the deflection of the screw shaft 11, and therefore the buffer devices 50, 51 that support the screw shaft 11 and the intermediate support 20 can be constructed simply and inexpensively.

[0030] Second Embodiment Next, a feed screw device 1 according to a second embodiment will be described with reference to Fig. 4. Fig. 4 is a diagram showing the feed screw device according to the second embodiment.

[0031] A generator 70 is provided in place of the drive motor 60 at the end (the lower end in the illustrated example) of the screw shaft 11 via a coupling 16. The nut 12 is also provided with a float or the like (not shown) that floats on the sea.

[0032] This configuration allows the feed screw device 1 to be applied to wave power generation. Specifically, the feed screw device 1 of this embodiment is installed on the sea. The up-and-down movement of waves causes the nut 12 on the sea to move up and down along the screw shaft 11, thereby rotating the screw shaft 11. This rotational movement of the screw shaft 11 can then be input to the generator 70 to generate electricity. Due to the characteristics of waves, the ball screw 10 requires a long stroke and high-speed rotation, and the up-and-down movement of the nut 12 is unsteady due to the waves. However, this embodiment allows the vertical position of the frame bodies 30, 31 supporting the intermediate support 20 to be automatically optimized in accordance with the wave movement. Furthermore, even when the wave conditions suddenly change, the shock absorbers 50, 51 prevent the intermediate support 20 from contacting the upper and lower base plates 2, 3.

[0033] The present invention is not limited to the above-described embodiments, and modifications and improvements are possible as appropriate.

[0034] As described above, the present specification discloses the following: a ball screw including a vertically extending screw shaft rotatably supported at both ends by an upper base portion and a lower base portion via bearings, and a nut screwed onto the screw shaft via balls; a pair of intermediate supports located on both sides of the nut in the vertical direction, arranged to be movable up and down around the screw shaft, and formed to be able to come into contact with the screw shaft; a pair of frame bodies attached to the pair of intermediate supports between the upper base portion and the lower base portion and connected by a connecting member; a linear guide section having a pair of outer cylinders that pass through shafts attached to the upper base portion and the lower base portion and to which the pair of frame bodies are attached, respectively; and a pair of buffer devices provided between the upper base portion and the frame body located above, and between the lower base portion and the frame body located below, respectively; wherein the nut has a state in which it contacts the intermediate support located above or the frame body and moves up and down together with the pair of intermediate supports and the pair of frame bodies, and a state in which it does not contact the intermediate support located above or the frame body. According to this configuration, even when the ball screw is supported at a long interval in a specification in which the screw shaft extends vertically, resonance can be suppressed and the ball screw can be used at speeds above the critical speed.

[0035] (2) The feed screw device according to (1), wherein the pair of intermediate supports are guide bushes that can come into contact with the outer circumferential surface of the screw shaft. With this configuration, the intermediate supports can smoothly and reliably press the outer circumferential surface of the resonating screw shaft, thereby serving as a fulcrum for the screw shaft.

[0036] (3) The feed screw device according to (1) or (2), wherein the linear guide portion includes a pair of linear ball bearings each having the pair of outer cylinders. With this configuration, the outer cylinders are smoothly guided along the shaft, and therefore the movement of the intermediate support that moves up and down along the screw axis is also stable.

[0037] (4) The feed screw device according to any one of (1) to (3), wherein a drive motor is attached to an end of the screw shaft via a coupling and drives the screw shaft to rotate. According to this configuration, the position of the nut moving along the screw shaft can be controlled by controlling the movement of the drive motor.

[0038] (5) The feed screw device according to any one of (1) to (3), wherein a generator is attached to the end of the screw shaft, which is rotationally driven by the up and down movement of the nut, via a coupling. According to this configuration, the movement of the nut, which moves up and down due to waves, is converted into rotational motion of the screw shaft, and the rotational motion of the screw shaft is input to the generator, thereby making it possible to apply the feed screw device to wave power generation.

[0039] Although various embodiments have been described above with reference to the drawings, it goes without saying that the present invention is not limited to such examples. It is clear that a person skilled in the art can conceive of various modifications or alterations within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present invention. Furthermore, the components of the above-described embodiments may be combined in any manner without departing from the spirit of the invention.

[0040] This application is based on a Japanese patent application (Patent Application No. 2024-14894) filed on February 2, 2024, the contents of which are incorporated herein by reference.

[0041] REFERENCE SIGNS LIST 1 feed screw device 2 upper base plate (upper base portion) 3 lower base plate (lower base portion) 11 screw shaft 11a screw groove 12 nut 13 flange portion 15 bearing 16 coupling 20 intermediate support 30 frame body 31 frame body 33 connecting member 40 linear guide portion 41 shaft 50 shock absorber 51 shock absorber 60 drive motor 70 generator 100 resonance prevention device

Claims

1. A feed screw device comprising: a ball screw having a vertically extending screw shaft rotatably supported at both ends by an upper base portion and a lower base portion via bearings, and a nut screwed onto the screw shaft via balls; a pair of intermediate supports located on both vertical sides of the nut, each arranged to be able to move up and down around the screw shaft and formed to be able to come into contact with the screw shaft; a pair of frame bodies attached to the pair of intermediate supports between the upper base portion and the lower base portion and connected by a connecting member; a linear guide section having a pair of outer cylinders that pass through shafts attached to the upper base portion and the lower base portion and to which the pair of frame bodies are attached, respectively; and a pair of buffer devices provided between the upper base portion and the frame body located above, and between the lower base portion and the frame body located below, wherein the nut has a state in which it contacts the intermediate support located above or the frame body and moves up and down together with the pair of intermediate supports and the pair of frame bodies, and a state in which it is not in contact with the intermediate support located above or the frame body.

2. The feed screw device according to claim 1, wherein the pair of intermediate supports are guide bushes that are in contact with the outer circumferential surface of the screw shaft.

3. The feed screw device according to claim 1, wherein the linear guide portion has a pair of linear ball bearings each having the pair of outer cylinders.

4. A feed screw device according to any one of claims 1 to 3, wherein a drive motor is attached to the end of the screw shaft via a coupling, and the drive motor rotates the screw shaft.

5. A feed screw device according to any one of claims 1 to 3, wherein a generator is attached to the end of the screw shaft, which is rotated by the up and down movement of the nut, and is connected via a coupling.

Images