Feed screw device

Abstract

To provide a feed screw device which can be used at a speed above a critical speed while suppressing resonance even when a ball screw has a long support interval in such a specification that a screw shaft extends in the vertical direction.SOLUTION: A feed screw device includes a ball screw including a vertically extending screw shaft, both ends of which are rotatably supported via a bearing on an upper base part and a lower base part, and a nut threaded to the screw shaft via a ball, a pair of intermediate supports each arranged around the screw shaft in a vertically movable manner, a pair of frame bodies mounted to the pair of intermediate supports, respectively, and connected to each other with a connection member, a linear guide part penetrating through a shaft, and having a pair of outer cylinders mounted to a pair of frame bodies, respectively, and a pair of shock absorbers. The nut has a state of being moved in the vertical direction together with the pair of intermediate supports and the pair of frame bodies in contact with the intermediate support or the frame body located on the upper side and a state of being in no contact with the intermediate support or the frame body located on the upper side.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] As the rotation speed of the ball screw increases, the vibration 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] A known countermeasure against this resonance is 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, making 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. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Utility Model Application Publication No. 02-004736 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when the feed screw device described in Patent Document 1 is applied to a ball screw whose screw shaft extends vertically, the slider cannot support the intermediate support from below, 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. [Means for solving the problem]

[0008] The above object of the present invention can be achieved by the following configuration. [1] A ball screw including a vertically extending screw shaft whose both ends are rotatably supported by an upper base portion and a lower base portion via bearings, and a nut that is screwed onto the screw shaft via a ball; A pair of intermediate supports are located on both sides of the nut in the vertical direction, are arranged to be movable up and down around the screw shaft, and are formed to be able to contact the screw shaft; a pair of frame bodies respectively attached to the pair of intermediate supports between the upper base portion and the lower base portion and connected by connecting members; a linear motion guide portion having a pair of outer cylinders that pass through a shaft attached to the upper base portion and the lower base portion and to which the pair of frames are attached, respectively; a pair of shock absorbers respectively provided between the upper base portion and the frame body located above, and between the lower base portion and the frame body located below; Equipped with The nut has a state in which it contacts the intermediate support or the frame body located above and moves in the up and down direction 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 or the frame body located above. Feed screw device. [Effects of the Invention]

[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. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is an overall view of a feed screw device showing the resonance prevention device in a first state. [Figure 2] FIG. 2 is an overall view of the feed screw device showing the resonance prevention device in the second state. [Figure 3] FIG. 3 is a central cross-sectional view showing the intermediate support. [Figure 4] FIG. 4 is a diagram showing a feed screw device according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

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

[0012] (First embodiment) As shown in Figures 1 and 2, the feed screw device 1 of the first embodiment comprises 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 comprises a screw shaft 11 extending vertically and having a spiral screw groove 11a on its outer peripheral surface, a nut 12 having a spiral screw groove (not shown) on its inner peripheral surface corresponding to the screw groove 11a of the screw shaft 11, a plurality of balls (not shown) rolling 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 sealing member (not shown) that seals the gap between the screw shaft 11 and the nut 12. A drive motor 60 that rotates and drives 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] A plurality of circulation parts (not shown) are provided on the outer circumferential surface of the nut 12. Each of the circulation parts has a scooping part that penetrates the nut 12 so that both ends advance into the load track and scoop up the balls. As a result, the balls scooped up at one end of the load track pass through the circulation parts and are returned to the other end of the load track, forming an infinite circulation path. A flange portion 13 is formed on one axial end of the nut 12. The flange portion 13 is fixed to a moving table 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 so as to be movable up and down around the screw shaft 11, a pair of frame bodies 30, 31 attached to the pair of intermediate supports 20, 20, respectively, a linear guide section 40 that guides the up and down movement of the intermediate support 20, and a pair of buffer devices 50, 51 provided on the upper base plate 2 and the lower base plate 3, respectively. The intermediate supports 20 are cylindrical members fitted onto the screw shaft 11 extending in the vertical direction, and a pair of intermediate supports 20 are provided on both the vertical sides of the nut 12 which moves along the screw shaft 11. As shown in Fig. 3, the intermediate supports 20 are attached to the frame bodies 30 and 31 which extend in the horizontal direction.

[0017] 3, the intermediate support 20 is formed in a cylindrical shape with an inner diameter slightly larger than the outer diameter of the screw shaft 11. As a result, the intermediate support 20 moves up and down along the screw shaft 11 with a small gap formed between the inner peripheral surface of the intermediate support 20 and the outer peripheral surface of the screw shaft 11 inserted through the intermediate support 20. On the other hand, when the screw shaft 11 resonates above a predetermined level, the inner surface of the intermediate support 20 comes into contact with the outer surface of the screw shaft 11, thereby allowing the intermediate support 20 to suppress the vibration of the screw shaft 11. 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 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 frames 30, 31 are plate-like members that have a plane perpendicular to the screw shaft 11 and extend horizontally, through which the screw shaft 11 extending vertically and a shaft 41 (described later) are inserted. Similar to the intermediate support 20, the pair of frames 30, 31 are provided on both the upper and lower sides of the nut 12. Each frame body 30, 31 is fitted with an intermediate support 20 through which the screw shaft 11 is inserted and a linear guide portion 40 through which the shaft 41 is inserted, and these are mounted and fixed so that they are 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 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 portion 40 to be attached and supported, and are not limited to plate-like members.

[0020] The linear guide portions 40 are cylindrical members that are fitted onto the exterior of the shaft 41 and move up and down along the shaft 41, and similar to the intermediate supports 20, a pair of linear guide portions 40 are provided, one above the other. Each linear motion guide unit 40 has a pair of outer cylinders, which are cylindrical members that pass through a shaft 41 extending parallel to the screw shaft 11 and are attached to the pair of frames 30, 31, respectively, and a linear ball bearing (not shown) that holds a plurality of balls (not shown) aligned along the axial direction on the inner peripheral surface of each outer cylinder. This allows the linear motion guide unit 40 to move smoothly up and down along the shaft 41.

[0021] The shaft 41 has both ends supported by the upper base plate 2 and the lower base plate 3, and extends in the vertical direction parallel to the screw shaft 11, and is arranged side by side with the screw shaft 11 in the left-right direction. Like the screw shaft 11, the shaft 41 is inserted through a pair of upper and lower frame bodies 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.

[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 section 40 attached to a pair of frame bodies 30, 31 to move up and down along the shaft 41, the intermediate support 20, which is inserted with a gap from the outer peripheral 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 dropping downward more than a predetermined amount. 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 buffer devices 50, 51 can prevent the pair of frame bodies 30, 31, which are connected together via the connecting member 33 and move up and down together, from colliding forcefully with the upper base plate 2 or the lower base plate 3. The buffer devices 50, 51 may be any device capable of preventing the frame bodies 30, 31 from colliding forcefully with the upper and lower base plates 2, 3, and may be air cylinders, hydraulic cylinders, damper members equipped with elastic members, or buffer materials equipped with elastic members. In addition, the buffer devices 50, 51 may be used in combination with tension springs or constant force springs (not shown) that are provided to offset the weight of the frame bodies 30, 31, so that the positions of the frame bodies 30, 31 when the nut 12 is not acting are maintained at the axial center of the screw shaft 11.

[0024] (Action and effect) When the ball screw 10 is driven by the drive motor 60 and the screw shaft 11 rotates 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 therefore there is a risk of resonance even when the rotational speed of the screw shaft 11 is relatively low. In response to this, the resonance prevention device 100 of this embodiment provides a pair of intermediate supports 20, which are maintained spaced apart by a distance L1 between suppression fulcrums, on both the top and bottom sides of the nut 12. The intermediate supports 20 are configured so that, when the screw shaft 11 starts to resonate at a predetermined level or greater, their inner circumferential surfaces come into contact with the outer circumferential surface of the screw shaft 11, forming contact points (fulcrums). 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, which significantly increases the value of the critical speed u and makes it difficult for the screw shaft 11 to resonate. In other words, the feed screw device 1 equipped with the resonance prevention device 100 can be used at rotation speeds that exceed those that would not be tolerated with a standard specification ball screw 1.

[0025] Specifically, a pair of intermediate supports 20 are integrally connected via frame bodies 30, 31 and connecting members 33, and each intermediate support 20 is connected via frame bodies 30, 31 to a linear guide section 40 that moves along a shaft 41 parallel to the screw axis 11. As a result, when the screw shaft 11 is not resonating, the intermediate support 20 moves up and down along the screw shaft 11 in a non-contact state where a gap is formed between the inner surface of the intermediate support 20 and the outer 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 peripheral surface of the intermediate support 20 comes into contact with the outer peripheral surface of the screw shaft 11, and the intermediate support 20 becomes a fulcrum that presses the screw shaft 11. As a result, the distance between the fulcrums automatically shortens from between the upper and lower base plates 2 and 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 FIGS. 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 frame bodies 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] 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 buffer device 51 (until they are switched to the second state), so the position of the support point where the intermediate support 20 supports the screw shaft 11 can be automatically optimized. As shown in Figure 2, when the second state is reached and the lower intermediate support 20 and frame body 31 are supported from below by the lower buffer device 51, no load is applied to the nut 12, allowing the nut 12 to move more smoothly.

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

[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 provided with a float or the like (not shown) that floats on the sea.

[0032] According to this configuration, the feed screw device 1 can be applied to wave power generation. Specifically, the feed screw device 1 of this embodiment is installed on the sea, and can rotate the screw shaft 11 around its axis by moving the nut 12 on the sea up and down along the screw shaft 11 due to the up and down movement of the waves, and this rotational movement of the screw shaft 11 can be input into 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 waves cause the nut 12 to move up and down unsteadily. However, according to this embodiment, the vertical positions of the frames 30, 31 that support the intermediate support 20 can be automatically optimized to match the wave movement. Furthermore, even if the waves change suddenly, the shock absorbers 50, 51 can 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: (1) A ball screw including a vertically extending screw shaft, both ends of which are rotatably supported by an upper base portion and a lower base portion via bearings, and a nut that is screwed onto the screw shaft via balls; A pair of intermediate supports are located on both sides of the nut in the vertical direction, are arranged to be movable up and down around the screw shaft, and are formed to be able to contact the screw shaft; a pair of frame bodies respectively attached to the pair of intermediate supports between the upper base portion and the lower base portion and connected by connecting members; a linear motion guide portion having a pair of outer cylinders that pass through a shaft attached to the upper base portion and the lower base portion and to which the pair of frames are attached, respectively; a pair of shock absorbers respectively provided between the upper base portion and the frame body located above, and between the lower base portion and the frame body located below; Equipped with The nut has a state in which it contacts the intermediate support or the frame body located above and moves in the up and down direction 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 or the frame body located above. Feed screw device. 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 pair of intermediate supports are guide bushes that can come into contact with the outer circumferential surface of the screw shaft. The feed screw device according to (1). According to this configuration, the intermediate support can smoothly and reliably press the outer peripheral surface of the resonating screw shaft, and serve as a fulcrum for the screw shaft.

[0036] (3) The linear guide portion has a pair of linear ball bearings each having the pair of outer cylinders. The feed screw device according to (1) or (2). According to this configuration, the outer cylinder is 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) A drive motor is attached to the end of the screw shaft via a coupling and rotates the screw shaft. The feed screw device according to any one of (1) to (3). 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) A generator is attached to the end of the screw shaft, which is rotated by the vertical movement of the nut, and is connected via a coupling. The feed screw device according to any one of (1) to (3). 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. [Explanation of symbols]

[0039] 1. Feed screw device 2 Upper base plate (upper base part) 3 Lower base plate (lower base part) 11 Screw shaft 11a screw groove 12 nuts 13 Flange 15 Bearings 16 Coupling 20 Intermediate Support 30 Frame 31 Frame 33 Connecting member 40 Linear guide section 41 Shaft 50 Shock absorber 51 Shock absorber 60 Drive motor 70 Generator 100 Resonance prevention device

Claims

1. a ball screw including a screw shaft extending in a vertical direction, both ends of which are rotatably supported by an upper base portion and a lower base portion via bearings, and a nut that is screwed onto the screw shaft via balls; A pair of intermediate supports are located on both sides of the nut in the vertical direction, are arranged to be movable up and down around the screw shaft, and are formed to be able to contact the screw shaft; a pair of frame bodies respectively attached to the pair of intermediate supports between the upper base portion and the lower base portion and connected by connecting members; a linear motion guide portion having a pair of outer cylinders that pass through a shaft attached to the upper base portion and the lower base portion and to which the pair of frames are attached, respectively; a pair of shock absorbers respectively provided between the upper base portion and the frame body located above, and between the lower base portion and the frame body located below; Equipped with The nut has a state in which it contacts the intermediate support or the frame body located above and moves in the up and down direction 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 or the frame body located above. Feed screw device.

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

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

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

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

Images