JP2589276B2 - Three degrees of freedom rolling bearing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a three-degree-of-freedom rolling bearing used for a joint of a robot arm, a manipulator, and the like.

[0002]

2. Description of the Related Art A conventional three-degree-of-freedom rolling bearing is shown in FIG.
The following are known. The prior art described above has a mechanism in which a rolling bearing having one degree of freedom is combined in three stages in the X, Y, and Z directions to form a gimbal structure.

[0003]

In the above-mentioned prior art, six or more bearings are required, and the bearing mechanism is arranged on the outer periphery, which makes it difficult to reduce the size and complicates the structure. In addition, since the accuracy of the center of rotation and the like are related to the accuracy of rotation of the six bearings, the accuracy of the mounting position, the rigidity of the gimbal support member, and the like, there has been a problem in improving the accuracy and managing the entire bearing mechanism.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, and an outer ring having a spherical internal space at least partially open to the outside, and a predetermined gap in the spherical internal space. And a plurality of spherical rolling elements disposed between the outer ring and the inner ring, wherein the inner ring is rotatable in three axial directions with respect to the outer ring. It is characterized by being arranged in.

[0005]

[Function] The rolling element rotates and revolves without contacting the inner and outer rings without slipping at both contact points, performs relative motion with three degrees of freedom, and supports forces (loads) acting in all directions on the movable shaft. Therefore, the rolling elements are arranged on both sides of the great circle. The movable shaft inclination angle can be about 30 °.

[0006]

Next, an embodiment of the present invention shown in FIGS. 1 and 2 will be described in detail. Reference numeral 1 denotes a spherical outer ring, in which a spherical inner ring 2 and an opening 4 for inserting a movable shaft 3 fixed toward the center of the inner ring 2 are formed. Between the inner ring 2 and the outer ring 1, a plurality of spherical rolling elements 5 having the same diameter are appropriately arranged. The diameter of the rolling element 5 is equal to the difference between the radii of the inner ring 2 and the outer ring 1, and the inner ring 2 and the outer ring 1 are positioned by the rolling elements 5 so that their centers coincide. Next, the operation will be described. The rolling element 5 can rotate and revolve without contact with the inner ring 2 and the outer ring 1 without slipping at both contact points, and can perform relative movement with three degrees of freedom. In order to support the forces (loads) acting on the movable shaft 3 in all directions, it is necessary to arrange the rolling elements 5 on both sides of all the great circles of the inner ring 2. In FIG. 1, the outer ring 1 is a fixed wheel and the inner ring 2 is a movable shaft, but the reverse is also possible. Although the opening is provided only in the upper part in FIG. 1, a structure in which the movable shaft 3 penetrates the outer ring 1 by opening also in the lower part may be employed. Further, in order to improve the rotation accuracy, the diameter of the rolling element 5 is made slightly larger than the difference between the radius of the inner ring 2 and the radius of the outer ring 1, and the pre-loaded state is assembled by, for example, a method such as cold fitting. Is also possible. Under ideal conditions, each rolling element 5
Since the relative positional relationship between them is maintained constant regardless of the movement of the movable shaft 3, it is also possible to configure without using a retainer. Next, the movement of the rolling elements is shown in FIG.
This will be described in detail. The speed of the contact point between the rolling element (center: C) and the inner ring in the ι direction is

(Equation 1) It is. Therefore, since the rolling element is rotating with the speed at the point of contact with the outer ring being 0, the revolving speed at the center of the rolling element is expressed by the following equation (2).

(Equation 2) Becomes When the revolution speed of the center of the rolling element (C) is expressed by using the revolution angular velocity vector ωc of the center of the rolling element,

(Equation 3) It is. From Expression (2) and Expression (3), Expression 4

(Equation 4) Becomes Considering a spherical surface concentric with the inner and outer rings and having a radius of (Ri + Rb), all the rolling elements Considering the rotating pitch plane, the center of the rolling element changes its position on the rotating pitch plane. The size is reduced at a ratio (1/2 or less) determined by the pitch radius and the rolling element radius. In other words, regardless of the position of the movable shaft, all rolling elements do not change their relative position regardless of their position, and always pitch in the same direction as the inner ring at the angular velocity reduced by the angular velocity of the inner ring. It turns out that it revolves on the surface. Therefore, similarly to a normal one-degree-of-freedom rolling bearing, even if the relative position of the rolling element is specified using the cage, no excessive force acts between the cage and the rolling element, and the rolling element and the inner and outer races are not affected. , It is possible to always maintain a pure rolling contact state. In the ideal case where the centrifugal force and the finite contact area are not considered, the relative position of the rolling elements can be kept constant even without the cage,
In the case of low-speed rotation, it is considered that the present bearing can be constructed without using a cage. The movable shaft inclination angle of the three-degree-of-freedom bearing can be calculated to be about 30 °. In the above embodiment, the outer shape of the outer ring 1 is spherical as shown in FIGS. 1 and 2; however, other shapes may be adopted according to the conditions of implementation.

[0007]

According to the present invention, an outer ring having a spherical internal space at least partially open to the outside, a spherical inner ring arranged with a predetermined gap in the spherical internal space, It has a plurality of spherical rolling elements disposed between the outer ring and the inner ring, and the inner ring is disposed so as to be rotatable in three axial directions with respect to the outer ring. .・ Relative motion with three degrees of freedom is possible between the inner ring and the outer ring with only the rolling motion between the inner ring, the outer ring and the rolling elements. -It can support forces (loads) in all directions acting on the movable shaft. -The structure is extremely simple and small compared to the gimbal structure. -Since the bearing mechanism is installed near the center of rotation, there is no hindrance when the actuator mechanism is provided outside.・ Rotation accuracy is determined by the accuracy of the inner ring, outer ring and rolling elements, so the concept and management method are clear.

[Brief description of the drawings]

FIG. 1 is an external perspective view of one embodiment of the present invention.

FIG. 2 is a front sectional view for explaining the operation of FIG. 1;

FIG. 3 is an external perspective view of a three-degree-of-freedom rolling bearing having a conventional gimbal structure.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Outer ring 2 Inner ring 3 Movable shaft 4 Opening 5 Rolling element

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tsutomu Yuine 3-5-8, Minamisenba, Chuo-ku, Osaka City Examiner Hitoshi Akizuki, Koyo Seiko Co., Ltd. (56) References U)

Claims (2)

(57) [Claims] 1. An outer ring having a spherical inner space at least partially open to the outside, a spherical inner ring arranged with a predetermined gap in the spherical inner space, the outer ring and the inner ring And a plurality of spherical rolling elements disposed between the inner ring and the inner ring, and the inner ring is disposed so as to be rotatable in three axial directions with respect to the outer ring. 2. The three-degree-of-freedom rolling bearing according to claim 1, wherein the diameter of the rolling element is equal to the difference between the radii of the inner ring and the outer ring, and the inner ring and the outer ring are positioned by the rolling element so that their centers coincide.