JP4459545B2 - Ball screw device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention, for example, a ball screw device that is suitable for an application that requires excellent operability at low torque, such as a ball screw device incorporated in a feeding device for a measuring machine, that does not like torque fluctuation or ball clogging. About.
[0002]
[Prior art]
As a conventional ball screw device of this type, for example, the one shown in FIG. 7 is known. In this ball screw device 1, a nut 6 having a helical thread groove 4 corresponding to the screw groove 2 is screwed onto a screw shaft 3 having a helical thread groove 2 on the outer peripheral surface.
[0003]
The screw groove 4 of the nut 6 and the screw groove 2 of the screw shaft 3 are opposed to each other to form a spiral load raceway between which a plurality of balls 5 as rolling elements are rolled. It is loaded movably. The nut 6 (or the screw shaft 3) is moved in the axial direction through the rolling of the ball 5 by the rotation of the screw shaft 3 (or the nut 6).
[0004]
As shown in the figure, in the case of a ball circulation type ball screw device, for example, a part of the outer peripheral surface of the nut 6 is a flat surface and a set of two holes communicating with the screw grooves 2 and 4 on the flat surface. 7 is formed so as to straddle the screw shaft 3, and both ends of a substantially U-shaped circulation tube 8 as an example of a ball circulation member are fitted into the pair of holes 7. The ball 5 revolving along the load trajectory is picked up by the circulation tube 8 from the middle of the load trajectory and returned to the original load trajectory, whereby the ball 5 is infinitely circulated.
[0005]
By the way, in the conventional ball screw device 1, the groove shape of the screw groove 2 of the screw shaft 3 and the groove groove 4 of the nut 6 are both Gothic arc shapes (offset R) or balls that contact the ball 5 at two points. 5 has a circular arc shape (single R) that contacts at one point.
[0006]
FIG. 8 shows the most general example in which the groove shape of the screw groove 2 of the screw shaft 3 is a Gothic arc shape, and the groove shape of the screw groove 4 of the nut 6 is a Gothic arc shape. As shown in FIG. 10, the groove shape of the screw groove 2 of the screw shaft 3 is a Gothic arc shape and the groove shape of the screw groove 4 of the nut 6 is a circular arc shape, or as shown in FIG. The groove shape of the screw groove 2 is a circular arc shape, the groove shape of the screw groove 4 of the nut 6 is a Gothic arc shape, or the groove shape of the screw groove 2 of the screw shaft 3 is as shown in FIG. An example is a circular arc shape in which the groove shape of the thread groove 4 of the nut 6 is a circular arc shape.
[0007]
In any screw groove shape, if the ball diameter is Dw and the groove radius in the cross section perpendicular to the screw groove is R, the ratio R / Dw is approximately 0.50 <R / Dw ≦ 0.70. Generally it is set by the range.
R / Dw is set in such a range by making the contact surface of the screw grooves 2 and 4 with the ball 5 into a concave surface close to the outer shape of the ball 5, This is because the contact area (contact ellipse) is increased to lower the contact surface pressure and increase the rigidity and load capacity of the ball screw device.
[0008]
[Problems to be solved by the invention]
By the way, in a sliding bearing, the PV value, which is the product of the pressure P and the sliding speed V when friction is considered as one work, is a measure of the load capacity (durability). It is said that it promotes, and if it is low, it is difficult to wear.
Therefore, with respect to the ball screw device, the screw groove 2 of the screw shaft 3 and the screw groove 4 of the nut 6 are formed in a concave shape close to the outer shape of the ball 5 so that the screw grooves 2, 4 and the ball 5 are brought into close contact with each other. Although it has the effect of lowering the surface pressure P and increasing the rigidity and load capacity, if it is turned back, since the screw grooves 2, 4 and the ball 5 are not point contacts, there is also a micro slip V in the contact surface. It will be. In particular, in the case of a ball screw device, unlike a rolling bearing, there is twist due to a lead, so this sliding component V may inevitably become large. This is not a pure rolling friction, but is unique to a ball screw device. There is a limit to producing friction and obtaining excellent operability at low torque.
[0009]
Further, as the groove radius R of the screw grooves 2 and 4 becomes closer to the radius of the ball 5, the change in the contact angle of the ball 5 due to the processing error of the screw grooves 2 and 4 becomes more sensitive, and it is difficult to obtain a stable contact angle. It becomes. That is, the contact angle of the ball 5 varies due to processing errors of the thread grooves 2 and 4.
Furthermore, even if the groove shapes of the screw grooves 2 and 4 are both Gothic arc shapes and aiming at four-point contact, a stable ball 5 such that a two-point or three-point contact ball 5 exists due to processing errors. In particular, in the case of a specification (low torque, low preload) in which preload is not positively applied to the ball screw device, the influence of the machining error becomes strong.
[0010]
Since the movement state (spinning / revolution) of the ball 5 in the nut 6 of the ball screw device is affected by the contact angle and contact state of the ball 5, the contact angle and contact state of the ball 5 change within one nut 6. Then, variations occur in the motion state of each individual ball 5 (the number of rotations of the ball, the revolution speed), and the ball 5 is clogged up or has a torque fluctuation, which adversely affects the operability of the ball screw device.
[0011]
Further, when the groove shape of the thread grooves 2 and 4 is a circular arc shape, the contact angle of the ball 5 greatly changes depending on the external load and the initial clearance, so that excellent operability can be stably achieved with low torque. It is not suitable as a groove shape to obtain.
The present invention has been made to eliminate such inconveniences, and provides a ball screw device that can stably obtain excellent operability at low torque without torque fluctuation or ball clogging. Objective.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 includes a screw shaft having a helical thread groove on an outer peripheral surface, and a thread groove corresponding to the screw groove of the screw shaft on the inner peripheral surface. A ball screw device comprising: a nut screwed to a screw shaft; and a plurality of balls loaded so as to be able to roll on a load track formed between the two screw grooves, wherein the diameter of the ball is Dw, the screw When the groove radius in the cross section perpendicular to the groove of the shaft and the screw groove of the nut is R, the groove shapes of both the screw grooves are both Gothic arc shapes, and at least one of the screw shaft and the nut The screw groove satisfies the relationship of 0.70 <R / Dw ≦ 1.0 .
[0013]
As a preferred form of the ball screw device according to the present invention, the groove shapes of both the screw grooves are both Gothic arc shapes, and at least one of the screw shaft and the nut is 0.80 ≦ R / Dw. Those satisfying the relation of ≦ 1.0 .
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory view showing a screw shaft of a ball screw device as an example of an embodiment of the present invention and a thread groove shape of a nut, and FIG. 2 is a screw shaft of a ball screw device according to another embodiment of the present invention. FIG. 3 is an explanatory view showing a screw groove shape of a nut, FIG. 3 is an explanatory view showing a screw shaft shape and a screw groove shape of a nut of a ball screw device according to another embodiment of the present invention, and FIGS. 4 to 6 are PV values and torques. FIG. 7 is a graph showing the relationship between R and D / Dw, and in each of the embodiments, the basic configuration of the ball screw device is explained using only the conventional ball screw device described in FIG. In addition, the same reference numerals are assigned to the overlapping portions, and the description thereof is omitted.
[0015]
As shown in FIG. 1, a ball screw device as an example of an embodiment of the present invention has a diameter of a ball 5 of Dw, a groove radius in a groove perpendicular section of a screw groove 2 of a screw shaft 3 and a screw groove 4 of a nut 6. When R is R, both the groove shapes of the screw grooves 2 and 4 are gothic arc shapes, and the screw groove 2 of the screw shaft 3 is a groove shape satisfying the relationship of R / Dw> 0.70. Yes.
[0016]
Thus, in this embodiment, the contact surface pressure P between the ball 5 and the screw groove 2 is increased by intentionally increasing R / Dw to bring the surface of the screw groove 2 of the screw shaft 3 closer to a flat surface. Since the slip component V is reduced, the PV value is lowered, and therefore, excellent operability can be stably obtained with low torque without torque fluctuation and clogging of the ball.
[0017]
In FIG. 1, for the sake of convenience, the groove shape of the thread groove 2 is a V groove. Ultimately, R / Dw = ∞ (the groove shape is a V-groove, which is also included in the gothic arc groove in the present invention) where the thread groove surface with which the ball 5 contacts is a flat surface. If /Dw>0.70, it was confirmed that the effect was sufficiently obtained.
[0018]
Further, as the groove radius R increases, it becomes less susceptible to the processing error of the screw groove 2, a stable contact angle and contact state of the ball 5 can be obtained, and variations in the motion state of the ball 5 are reduced. Furthermore, if the thread groove shape is a V groove, the contact angle of the ball 5 is constant.
Next, with reference to FIG.2 and FIG.3, the ball screw apparatus which is other embodiment of this invention is demonstrated. In addition, about an effect, since it is substantially the same as the said embodiment, description is abbreviate | omitted.
[0019]
In the embodiment shown in FIG. 2, when the diameter of the ball 5 is Dw, and the groove radius in the cross section perpendicular to the thread groove 2 of the screw shaft 3 and the thread groove 4 of the nut 6 is R, both the thread grooves 2, 4 are used. Both of the groove shapes are Gothic arc shapes, and the thread groove 4 of the nut 6 is R / Dw> 0.70 (in FIG. 2, for the sake of convenience, the thread groove is R / Dw = ∞ for the sake of convenience. 4 is a V-groove).
[0020]
In the embodiment shown in FIG. 3, when the diameter of the ball 5 is Dw, and the groove radius in the groove perpendicular section of the screw groove 2 of the screw shaft 3 and the screw groove 4 of the nut 6 is R, both the screw grooves 2, 4 are used. Both of the groove shapes are gothic arc shapes, and the screw groove 2 of the screw shaft 3 and the screw groove 4 of the nut 6 are both R / Dw> 0.70 (in FIG. 3, for the sake of convenience, for the sake of convenience) R / Dw = ∞, and the groove shape of the screw grooves 2 and 4 is a V groove).
[0021]
【Example】
When R / Dw changes, the sum of the maximum PV values (ΣPVmax) at each contact part of four-point contact (screw shaft screw groove: two-point contact, nut screw groove: two-point contact) and friction torque The calculation results are shown in FIGS.
[0022]
FIG. 4 shows that the screw groove 4 of the nut 6 has a Gothic arc shape and R / Dw = 0.54, the screw groove 2 of the screw shaft 3 has a Gothic arc shape, and R / Dw is 0.54 to 1.5. When changed (corresponding to FIG. 1), FIG. 5 shows that the screw groove 2 of the screw shaft 3 has a Gothic arc shape and R / Dw = 0.54, and the screw groove 4 of the nut 6 has a Gothic arc shape. When Dw is changed from 0.54 to 1.5 (corresponding to FIG. 2), FIG. 6 shows that the screw groove 2 of the screw shaft 3 and the screw groove 4 of the nut 6 have a Gothic arc shape, and both R / Dw is 0. This is a case of changing from .54 to 1.5 (corresponding to FIG. 3). Each figure shows R / Dw on the horizontal axis, ΣPVmax on the left vertical axis, and friction torque on the right vertical axis. Moreover, the ball screw device of the same specification was used except for the shape of the thread groove. The specifications of the ball screw device are as follows.
[0023]
(Specifications of ball screw device)
Shaft diameter 25 mm x lead 6-2.5 turns per row, ball diameter Dw = 3.968 mm
Total ball preload load Fa0 = 500N, preload system = 4-point contact oversize ball preload external load = none, lubricant = mechanical oil VG68, shaft rotation-nut movement,
Rotation speed = 100min-1
As is clear from FIGS. 4 to 6, in any case, the R / Dw increases, so that both the PV value and the friction torque can be reduced even when the preload is constant, and the rate of the decrease is also high. It turns out that it becomes loose when R / Dw> 0.70. Further, it can be seen that when R / Dw ≧ 0.8, the decrease of both the PV value and the friction torque is almost saturated, and when R / Dw ≧ 1.0, the decrease is further saturated.
[0024]
The ball screw device of the present invention is not limited to the above-described embodiments, and can be appropriately changed without departing from the gist of the present invention.
For example, in the above-described embodiment, the case where the present invention is applied to a circulation tube type ball screw device is taken as an example. Instead, the present invention is applied to an end cap type or top type ball screw device. In addition, the present invention may be applied to a non-circulating ball screw device.
[0025]
【The invention's effect】
As is apparent from the above description, according to the present invention, slippage is increased even if the contact surface pressure between the ball and the screw groove increases by intentionally increasing R / Dw to bring the screw groove surface closer to a flat surface. Since the PV value is lowered by reducing the components, there is no torque fluctuation or clogging of the ball, and excellent operability can be stably obtained with low torque.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is an explanatory diagram showing a thread groove shape of a screw shaft and a nut of a ball screw device as an example of an embodiment of the present invention.
FIG. 2 is an explanatory view showing screw groove shapes of a screw shaft and a nut of a ball screw device according to another embodiment of the present invention.
FIG. 3 is an explanatory view showing a thread groove shape of a screw shaft and a nut of a ball screw device according to another embodiment of the present invention.
FIG. 4 is a graph showing the relationship between PV value and torque and R / Dw.
FIG. 5 is a graph showing the relationship between PV value and torque and R / Dw.
FIG. 6 is a graph showing the relationship between PV value and torque and R / Dw.
FIG. 7 is a cross-sectional view showing an example of a ball screw device.
FIG. 8 is an explanatory diagram showing a conventional screw shaft and a thread groove shape of a nut.
FIG. 9 is an explanatory view showing a conventional screw shaft and a thread groove shape of a nut.
FIG. 10 is an explanatory diagram showing a conventional screw shaft and a thread groove shape of a nut.
FIG. 11 is an explanatory view showing a conventional screw shaft and a thread groove shape of a nut.
[Explanation of symbols]
2 ... Thread groove (screw shaft side)
3 ... Screw shaft 4 ... Thread groove (Nut side)
5 ... Ball 6 ... Nut

Claims (1)

A screw shaft having a helical thread groove on the outer peripheral surface, a nut having a thread groove corresponding to the screw groove of the screw shaft on the inner peripheral surface and screwed to the screw shaft, and the two screw grooves A ball screw device comprising a number of balls rotatably mounted on a formed load track,
When the diameter of the ball is Dw, and the groove radius in the cross section perpendicular to the groove of the screw shaft and the screw groove of the nut is R, the groove shapes of both the screw grooves are both Gothic arc shapes, and the screw A ball screw device, wherein a thread groove of at least one of the shaft and the nut satisfies a relationship of 0.70 <R / Dw ≦ 1.0 .

Images