JP2012092917A - Ball screw device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ball screw device in which dynamic friction torque hardly increases even when a nut is contracted by cooling.SOLUTION: This ball screw device includes a screw shaft 10, a nut 20 screwed to the screw shaft 10 through a plurality of rolling elements 30, and a cooling structure 40 to cool the nut 20, wherein the plurality of rolling elements 30 each provided with a pre-load in a two-point contact state by using a pre-load direction as a tensile direction are incorporated between a thread groove 10a of the screw shaft 10 and a thread groove 20a of the nut 20. Circulation paths 21c, 22c and a second through-hole 52 are formed in the nuts 21, 22 and a spacer 50, and a cooling medium is supplied to them to form a cooling structure. A sealing structure 70 is arranged between the circulation paths 21c, 22c and the second through-hole 52. The cooling through-holes 20b, 20c, a tube 4, a cooling liquid introduction pipe 5 and a cooling liquid discharge pipe 6 have shapes and areas of the respective passage cross-sectional surfaces identical to or nearly identical to one another, and they are connected in series to one another.

Description

  The present invention relates to a ball screw device, and more particularly to a ball screw device capable of cooling a nut.

Conventionally, in a screw device having a feed screw shaft and a feed nut screwed into the feed screw shaft to be relatively rotatable, point contact or surface contact occurs during rotation. The feed nut) may be provided with cooling means.
As such a screw device, a screw device in which a cooling pipe in which a refrigerant circulates is disposed in the feed nut is disclosed as the cooling means (heat exchanger) (for example, Patent Document 1).

JP 52-63557 A

However, in the screw device disclosed in Patent Document 1, heat shrinkage occurs in the feed nut cooled by the heat exchanger, and as a result, there is a problem that torque increases.
Specifically, the temperature rise value θ of the screw device is represented by the following formula (1). In the following formula (1), t is the elapsed time, CM is the heat capacity of the screw device, β is the unit time from the screw device, the amount of heat released per unit temperature difference, and Q is the amount of heat per unit time generated from the nut. is there.

Further, Q in the formula (1) is represented by the following formula (2). In the following formula (2), T is the dynamic friction torque, and n is the rotational speed of the shaft.
Q = Tx60nx2π / 1000 = 0.12πnT (2)
As shown in Patent Document 1, if the feed nut is simply cooled, β in equation (1) increases, but if the torque increases simultaneously as described above, Q is also larger than in equation (2). As a result, the temperature rise value obtained by Q / β increases. Therefore, there is a problem that the cooling efficiency as a whole is reduced by simply cooling the feed nut.

Here, FIG.10 and FIG.11 is the schematic diagram which showed the relationship between the preload direction for every preload form, and the heat contraction direction of a nut. FIG. 10 is a diagram showing a preload form in a two-point contact state in which the preload direction is the compression direction, and FIG.
As shown in FIGS. 10 and 11, the ball screw device 1 includes a screw shaft 10 and a nut 20 that is screwed onto the screw shaft 10 via a plurality of rolling elements 30. The rolling element 30 is preloaded between the screw groove 10 a of the screw shaft 10 and the screw groove 20 a of the nut 20.

  When the nut 20 is cooled and thermal contraction f toward the center occurs, in the preload state shown in FIGS. 10 and 11, the nut 20 contracts in the direction of increasing the preload Fa0, and the dynamic friction torque increases. End up. Accordingly, the present invention has been made paying attention to the above-mentioned problems, and an object of the present invention is to provide a ball screw device in which the dynamic friction torque hardly increases even when the nut contracts due to cooling.

In order to solve the above-mentioned problems, the present inventor has made extensive studies and, as a result of adopting a preload type in which the total preload is hardly increased, the dynamic friction torque is hardly increased even when the nut is contracted by cooling. I found out.
This invention is based on the said knowledge by this inventor, The ball screw apparatus which concerns on Claim 1 of this invention for solving the said subject is the said screw via one screw shaft and several rolling elements. A plurality of nuts screwed to the screw shaft; spacers arranged between the plurality of nuts arranged in the axial direction; and cooling means for cooling the nuts, wherein the rolling element pulls in a preload direction. A preload is applied in a two-point contact state as a direction, and the cooling means corresponds to the plurality of cooling through holes formed along at least one nut axial direction of the plurality of nuts and the cooling through holes. The through holes formed in the spacer, including adjacent through holes, have the same or substantially the same cross-sectional shape and cross-sectional area, and at the axial end of the nut, these cooling through holes are The shape and area of the channel cross section is the same or nearly the same A flow path forming member is connected in series to form a flow path, and a cooling medium introduction pipe and a cooling medium discharge pipe having the same or almost the same shape and area of the cross section of the flow path are connected in series to the inlet and outlet of the flow path. And a gap formed between one opening of the cooling through hole formed in at least one of the plurality of nuts and one opening of the through hole formed in the spacer. It is characterized in that a sealing means for sealing is provided.

  According to the ball screw device of the first aspect of the present invention, since the cooling means is provided in the nut and the preloading method of the nut is the two-point contact preload in the pulling direction, the shrinkage in the radial direction is a preload load. However, since the contraction in the axial direction acts to alleviate this, the total preload is hardly increased. Therefore, it is possible to provide a ball screw device in which the dynamic friction torque hardly increases even when the nut contracts due to cooling. Further, according to the ball screw device according to claim 1 of the present invention, the adjacent cooling through-holes are compared with those formed by connecting the flow path forming members having different cross-sectional areas to form the flow paths. Since the pressure loss of the cooling medium flowing in the flow path is small, the cooling efficiency is high. Furthermore, according to the ball screw device according to claim 1 of the present invention, a double nut preload is applied, and a plurality of circulation paths formed in the plurality of nuts and a plurality of through holes penetrating the spacer are connected. The nut can be cooled at the same time, and leakage of the cooling medium can be prevented by providing a close contact member between the opening of the through hole of the spacer and the opening of the circulation path of the nut. Therefore, it is possible to provide a ball screw device that can efficiently cool the double nut preload ball screw and prevent leakage of the cooling medium from the nut.

It is sectional drawing which follows the axial direction which shows the structure in 1st Embodiment of the ball screw apparatus which concerns on this invention. It is an A arrow directional view of the ball screw device of FIG. It is a figure which shows the relationship between the preload state of a two-point contact state which made the tension direction the preload direction, and shrinkage | contraction in 1st Embodiment of the ball screw apparatus which concerns on this invention. It is sectional drawing which follows the axial direction which shows the structure in 2nd Embodiment of the ball screw apparatus which concerns on this invention. It is sectional drawing which follows the axial direction which shows the structure of the sealing means in Example 2. FIG. It is sectional drawing which follows the axial direction which shows the structure of another sealing means in Example 2. FIG. It is a graph which shows the result of having measured the temperature rise value and torque of a nut at the time of driving the ball screw apparatus of Example 1 and cooling a nut. It is a graph which shows the result of having measured the temperature rise value and torque of a nut at the time of driving the ball screw apparatus of the comparative example 1, and cooling a nut. It is sectional drawing which follows the axial direction which shows the structure of the ball screw apparatus of the comparative example 1. It is a figure which shows the relationship between the preload state of a two-point contact state which made the preload direction the compression direction, and contraction. It is a figure which shows the relationship between an oversize ball | bowl preload state and shrinkage | contraction.

(First embodiment)
Hereinafter, a first embodiment of a ball screw device according to the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view along the axial direction showing the configuration of the ball screw device according to the first embodiment of the present invention.
As shown in FIG. 1, the ball screw device 1 of this embodiment includes a screw shaft 10 and a nut 20. The screw shaft 10 and the nut 20 are screwed together via a plurality of rolling elements 30. The nut 20 is formed in a cylindrical shape with an inner diameter larger than the outer diameter of the screw shaft 10. A screw groove 20 a is formed on the inner peripheral surface of the nut 20 so as to face the screw groove 10 a formed in a spiral shape on the outer peripheral surface of the screw shaft 10. The rolling element 30 can roll on the rolling path formed by the thread groove 10a and the thread groove 20a.

  As shown in FIG. 1, the ball screw of this embodiment includes a semicircular arc tube (flow path forming member) 4, a coolant introduction pipe (cooling medium introduction pipe) 5, and a coolant discharge pipe (cooling medium discharge). Piping) 6 and connectors 71 to 74 are provided. In FIG. 1, the ball circulation member and the seal are omitted.

  In the nut 20, two cooling through holes 20 b and 20 c penetrating in the axial direction are formed at positions facing each other in the diameter direction of the nut 20. These through holes 20b and 20c for cooling are connected by a semicircular arc-shaped tube 4 at the end of the nut 20 on the flange 20d side. One end of the tube 4 and the cooling through hole 20 b are connected by a connector 71. The other end of the tube 4 and the cooling through hole 20 c are connected by a connector 72. Thereby, the flow path which consists of the through-holes 20b and 20c for cooling and the tube 4 is formed.

  The end of the cooling through hole 20 b where the tube 4 is not connected is connected to the coolant introduction pipe 5 via the connector 73. The end portion of the cooling through hole 20 c to which the tube 4 is not connected is connected to the coolant discharge pipe 6 via the connector 74. That is, the inlet and outlet of this flow path are provided at the ends of the cooling through holes 20b and 20c that are not connected by the tube 4. FIG. 2 shows a view of the ball screw device 1 of FIG.

As a result, the coolant is supplied from the coolant introduction pipe 5 → the connector 73 → the cooling through hole 20 b of the nut 20 → the connector 71 → the tube 4 → the connector 72 → the cooling through hole 20 c of the nut 1 → the connector 74 → the cooling liquid discharge pipe. It flows in order of 6. In the flow of the cooling liquid, the nut 20 is cooled directly by the flow of the cooling water in the cooling through holes 20b and 20c.
According to the ball screw of this embodiment, all of the cooling fluid introduction piping 5 and the cooling fluid discharge piping 6 connected to the flow path composed of the cooling through holes 20b and 20c of the nut 20 and the tube 4, and the inlet / outlet of this flow path. , The flow path cross-section (the cross-sectional shape and cross-sectional area of the flow path) is the same, so the pressure loss of the coolant is reduced. Therefore, the cooling efficiency is increased and the burden on the coolant supply pump is reduced.

  In addition, since the two cooling through holes 20b and 20c are connected in series to the coolant introduction pipe 5, the flow rate is kept constant, so the two cooling through holes 20b and 20c are provided with the coolant. The cooling effect is enhanced as compared with the case where the flow passage cross section becomes larger at the branch point and the flow velocity is reduced as in the case where the inlet pipe 5 is connected in parallel.

Between the screw groove 10a of the screw shaft 10 and the screw groove 20a of the nut 20, a plurality of rolling elements 30 which are offset lead preloaded (two-point contact preload) with a preload load Fa0 with the preload direction set as the tension direction are incorporated. It is.
FIG. 3 is a diagram showing the relationship between the preload state and the contraction in the two-point contact state where the tension direction is the preload direction.

As shown in FIG. 3, when a two-point contact preload in the tensile direction is applied to the nut 20, the thermal contraction f1 in the radial direction acts in a direction to increase the preload load Fa0, but the thermal contraction f2 in the axial direction is Since this acts to reduce this, the total preload is hardly increased.
For this reason, in the ball screw device 1 according to the present invention, the two-point contact preload in the tensile direction is applied to the nut 20, so that the preload torque does not increase even if the nut 20 is cooled, and the ball screw device 1 is efficiently Can be cooled.

(Second Embodiment)
FIG. 4 is a view showing a second embodiment of the ball screw device according to the present invention. As shown in FIG. 4, this embodiment employs a double nut preload system, whereas the first embodiment employs an offset lead preload as the preload system.

  Specifically, as shown in FIG. 4, the ball screw device 1 of the present embodiment includes a first nut 21 and a second nut that are screwed onto a common screw shaft 10 via a plurality of rolling elements 30. 22 and a spacer 50. The spacer 50 has an annular shape having substantially the same inner diameter as the inner diameters of the first nut 21 and the second nut 22, and prevents relative rotation between the first nut 21 and the second nut 22. Further, by providing the spacer 50, a plurality of rolling elements 30 incorporated between the thread grooves 21 a and 22 a of the first nut 21 and the second nut 22 and the thread groove 10 a of the ball screw 10. A preload in a two-point contact state is given by a preload load Fa0. Note that the preload direction is the tensile direction as in the first embodiment.

  Next, the sealing means in 2nd Embodiment is demonstrated below with reference to FIG. A sealing means 70 is provided between the first nut 21 and the second nut 22 and the spacer 50. Specifically, one of the circulation paths 21c and 22c (on the contact surfaces 21b and 22b side) is provided on the contact surfaces 21b and 22b of the first nut 21 and the second nut 22 with the spacer 50, respectively. First accommodating portions (concave portions) 21d and 22d are formed so as to surround. And the annular | circular shaped elastic member 71 surrounding the circulation paths 21c and 22c is installed in the 1st accommodating parts 21d and 22d. The elastic member 71 is, for example, an O-ring. The sealing means 70 includes first accommodating portions 21 d and 22 d and an elastic member 71. Thus, the sealing means 70 is provided between the first nut 21 and the second nut 22 and the spacer 50, so that the cooling medium does not leak from this portion. The sealing means 70 ensures a sealed state, and if the sealing state with the spacer 50 is sufficient, the sealing means 70 is either the first nut 21 or the second nut 22. There may be, and it does not necessarily need to be provided in both the 1st accommodating parts 21d and 22d.

Further, another sealing means in the second embodiment will be described with reference to FIG. The ball screw device according to the present embodiment is different from the above-described embodiment of the sealing means only in the configuration of the sealing means, and thus the description of the same configuration given the same reference numeral is omitted.
As shown in FIG. 6, the present embodiment is characterized in that a sealing means 70 installed between the spacer 50 and the nuts 21 and 22 is formed on the spacer 50 side. Specifically, the second through hole 52 is formed on one surface 50a of the spacer 50 facing the first nut 21 and the other surface 50b of the spacer 50 facing the second nut 22 respectively. A second accommodating portion (concave portion) 51 is formed so as to surround one opening portion, and an elastic member (for example, an O-ring or the like) 71 is installed in the second accommodating portion 51. The sealing means 70 includes a second accommodating portion 51 and an elastic member 71. The sealing means 70 ensures a sealed state, and if the sealing state with the spacer 50 is sufficient, the sealing means 70 is either the first nut 21 or the second nut 22. The second storage portions 51 and 51 may not necessarily be provided on both surfaces of the both surfaces 50a and 50b.

As described above, since the sealing means 70 is formed on the spacer 50 side, for example, the second accommodating portion 51 may be formed on the spacer 50 side. Can be reduced.
As mentioned above, although embodiment of this invention has been described, this invention is not limited to this, A various change and improvement can be performed. For example, the accommodating portion that accommodates the elastic member is formed on a nut (first nut or second nut) on one surface side of the spacer, and is formed on the spacer on the other surface side of the spacer. May be. The elastic member is more preferably provided on the nut side. This is advantageous in that the troublesomeness of attaching and detaching the elastic member every time the preload is adjusted (spacer processing) can be eliminated by installing an elastic member on the spacer side in order to adjust the amount of preload by the thickness of the spacer. Because.

Examples of the ball screw device according to the present invention will be described below.
FIG. 7 shows the temperature rise value and torque of the nut when the ball screw device of the first embodiment (see FIG. 1) is driven as the ball screw device of Example 1 and the nut is cooled during the drive. It is a graph which shows the result measured simultaneously.
FIG. 8 is a graph showing the results of simultaneously measuring the temperature rise value and torque of the nut when the ball screw device of Comparative Example 1 was driven and the nut was cooled during the driving.

The configuration of the ball screw device of Example 1 and Comparative Example 1 is shown in Table 1, the driving conditions of Example 1 and Comparative Example 1 are shown in Table 2, and the cooling conditions of Example 1 and Comparative Example 1 are shown in Table 3. .
Here, as shown in FIG. 9, the configuration of the ball screw device of Comparative Example 1 includes a plurality of oversized ball preloads (four-point contact preload) with a preload load Fa0 between the screw grooves 10a and 20a. This embodiment differs from the first embodiment in that the rolling element 30 is incorporated.
In FIGS. 7 and 8, the time when the temperature of the nut suddenly decreases is the start of cooling.

  As shown in FIGS. 7 and 8, it can be seen that both the first embodiment and the first comparative example decrease the temperature of the nut when the cooling is started, but the ball screw device of the first embodiment decreases the temperature of the shaft. Can be seen to be large. In the feed system driven by the ball screw device, the temperature change of the shaft that directly affects the table accuracy becomes important.

  When attention is paid to the change in torque, in Comparative Example 1, the torque increases up to about twice that before cooling. This is because the nut undergoes heat shrinkage due to cooling, the direction of the heat shrinkage coincides with the preload direction, and the preload load is high. This heat generation diminishes the heat dissipation effect by cooling, and as a result, the cooling effect as a whole is reduced. Moreover, an excessive preload is caused, and as a result, the lifetime of the ball screw device is reduced.

  On the other hand, the torque of the ball screw device of Example 1 hardly changes before and after cooling. This is because the radial direction increases the preload load in the direction of heat shrinkage of the nut due to cooling, but the axial direction acts in the direction of decreasing the preload load, and these interact with each other. As a result, in the ball screw device of the first embodiment, a high cooling effect is obtained without being affected by the mature shrinkage of the nut.

  As mentioned above, although embodiment of this invention has been described, this invention is not limited to this, A various change and improvement can be performed.

DESCRIPTION OF SYMBOLS 1 Ball screw apparatus 10 Screw shaft 20 Nut 21 1st nut 22 2nd nut 30 Rolling body 50 Spacer 51 Second accommodating part 70 Sealing means 71 Elastic member

Claims (3)

One screw shaft, a plurality of nuts screwed to the screw shaft via a plurality of rolling elements, a spacer disposed between the plurality of nuts arranged in the axial direction, and cooling for cooling the nut Means and
The rolling element is preloaded in a two-point contact state with the preload direction as the tension direction,
The cooling means includes a plurality of cooling through holes formed along at least one nut axial direction of the plurality of nuts, and a through hole formed in the spacer corresponding to the cooling through hole,
Adjacent cooling through-holes have the same or almost the same cross-sectional shape and cross-sectional area. At the axial end of the nut, these cooling through-holes have the same or almost the same cross-sectional shape and area. A flow path forming member is connected in series to form a flow path, and a cooling medium introduction pipe and a cooling medium discharge pipe having the same or almost the same shape and area of the cross section of the flow path are provided at the inlet and the outlet of the flow path. Connected in series,
Sealing that seals a gap formed between one opening of the cooling through hole formed in at least one nut of the plurality of nuts and one opening of the through hole formed in the spacer. A ball screw device, characterized in that means are provided.   The sealing means includes a first accommodating portion formed so as to surround one opening of the through hole in a contact surface of at least one nut of the plurality of nuts with the spacer, and the first accommodating portion. The ball screw device according to claim 1, further comprising an annular elastic member accommodated in the portion.   The sealing means includes a second accommodating portion formed so as to surround one opening of the through hole in a contact surface of the spacer with the at least one nut of the plurality of nuts; The ball screw device according to claim 1, further comprising an annular elastic member accommodated in the accommodating portion.

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