GB2142098A

GB2142098A - Linear bearing

Info

Publication number: GB2142098A
Application number: GB08413249A
Authority: GB
Inventors: Hiroshi Teramachi
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-05-26
Filing date: 1984-05-23
Publication date: 1985-01-09
Also published as: FR2546587A1; GB2142098B; IT1174553B; JPS6148022B2; KR840008948A; KR860001682B1; IT8421117A1; JPS59219520A; IT8421117A0; DE3419434A1; DE3419434C2; FR2546587B1; GB8413249D0

Abstract

A linear bearing for use in, for example, a machining centre has a main body (1) constituted by a ceiling portion (2) and skirt portions (4,5) defining a central cavity (3) therebetween. Each skirt portion is provided in its inner surface with a race-receiving groove (6,7) having an abutment (8,9) projecting at its lower edge and with a non-loaded ball passage (10,11) bored therethrough. A pair of bearing races (12,13) each constituted by an arcuate member of semicircular cross-section having a part barrel-like outer peripheral surface is rockably mounted within a corresponding race-receiving groove, the arcuate member being provided in its inner surface centre with a loaded ball groove (14,15) having a curvature centre which is coincident with that of the race-receiving groove. A race-pressing member (29) is constituted by a wedge member adjustably screwed to the ceiling portion and presses the bearing races toward the abutments with its wedge surfaces. A track bar (16) is fitted in the central cavity of the main body and is provided on its right and left side surfaces with loaded ball grooves (19,20). A pair of front and rear end covers are secured to the ends of the main body, and are provided in their inner surfaces with ball turning grooves providing communication between loaded ball passages, which are defined by the loaded ball grooves on the bearing races and track bar, and non-loaded ball passages formed through the main body, as well as race retaining grooves for supporting one of the ends of the bearing races. Balls (B) are recirculated through the loaded ball passages and non-loaded ball passages. <IMAGE>

Description

SPECIFICATION Linear bearing The present invention relates to a linear bearing suitable for use in various sliding parts such as the table saddle of a machine tool, the slider of a machining centre, and the slider of a transportation robot for reciprocative transportation of a heavy object. More particularly, the present invention pertains to a linear bearing having an automatic aligning function.

In a typical convenmtional linear bearing, as shown in Figure 21 of the accompanying drawings, for example, a main body 110 of the bearing has longitudinal recesses 111, 112 respectively fitted with bearing races 113, 114 of rectangular crosssection similarly extending in the longitudinal direction of the main body 110. The bearing races 113, 114 are screwed in the recesses 111, to form respective loaded ball passages between loaded ball grooves 116, 117 on the bearing races 113, 114 and loaded ball grooves 119,120Onatrackbar118.

Further, the loaded ball grooves 116,117,119,120 and their corresponding non-loaded ball grooves communicate with each other to form respective endless tracks through which balls are recirculated, thereby allowing the main body 110 to effect a linear slide motion.

When a transportation robot, for example, is to be constructed employing a linear bearing having the above-described construction, plurality of track bars 118 are generally laid end to end so as to extend coaxially in the longitudinal direction under the necessity of enlarging the transportation operation range. In the case where the track bars 118 are laid over a long distance, however, mounting errors or other failures may prevent the longitudinal axes of the track bars 118 connected to each other from aligning with each other in a straight line, so that the track bars 118 may horizontally or vertically bend disadvantageously.In such case, since the upper surfaces 113a, 114a and rear surfaces 113b, 114b of the bearing races 113, 114 are respectively closely secured to the wall surfaces of the recesses 111, 112 of the main body 110 according to the conventional construction, the contact pressure of the balls locally increases when the main body 110 passes the bent portion of the aligned track bars 118, thus causing dents in the surfaces of the loaded ball grooves 116, 117, 119, 120. Also, when passing the bent portion of the lined track bars 118, the main body 110 encounters an increased resistance to its sliding motion, so that it is not possible to ensure a smooth linear slide motion of the main body 110.

The invention aims as its primary object at overcoming the above-described problems of the prior art, and according to the invention, a linear bearing comprises a main body being an integral member constituted by a ceiling portion and opposed skirt portions defining a central cavity therebetween, each skirt portion being provided in its inner surface with a race-receiving groove open to the central cavity, the race-receiving groove having an abutment projecting at its edge remote from the ceiling portion, and each skirt portion further having a non-loaded ball passage formed therethrough; a pair of bearing races each constituted by an arcuate member of substantially semicircular cross-section and having a part barrel-like outer peripheral surface rockably mounted within a respective of the racereceiving grooves, the arcuate member being provided along its inner surface with a loaded ball groove having a curvature centre which is coincident with that of the respective race-receiving groove; a race-pressing member constituted by a wedge member adjustably screwed to the inner surface of the ceiling portion of the main body and arranged to press the bearing races towards the abutments with its wedge surfaces which simultaneously abut on the side surfaces of the bearing races; a track bar fitted in the central cavity of the main body and provided on its opposed side surfaces with loaded ball grooves each having a curvature centre which is coincident with that of the corresponding loaded ball groove on a respective one of the bearing races; a pair of end covers constituted by cover members secured to end surfaces of the main body, each cover member being provided in its inner surfaces with ball turning grooves providing communication between loaded ball passages, which are defined by the loaded ball grooves on the bearing races and track bar, and the non-loaded ball passages formed through the main body, as well as race retaining grooves for supporting one of the ends of the bearing races; and balls adapted to be recirculated through the loaded ball passages and respective non-loaded ball passages.

With this construction an automatic aligning function is provided by the bearing races which have a part barrel-like appearance as they are rockable within the corresponding race-receiving grooves of the main body of the bearing so that the bearing races can change their directions to properly follow any vertical or horizontal bend of the track bar The invention will now be described in more detail by reference to the accompanying drawings, in which Figure 1 is a front elevation of a preferred example of linear bearing in accordance with the invention; Figure 2 is a plan of the linear bearing; Figure 3 is a front elevation of the linear bearing with one of the end covers thereof removed; Figure 4 is an obliquely cut sectional side elevational view taken on the line IV-IV in Figure 1; Figure 5 is a section taken on the line V-V in Figure 3;; Figure 6 is a front elevation of a main body of the bearing; Figure 7 is a plan of the main body; Figure 8 is a bottom view of the main body; Figure 9 is a side elevation of the main body; Figure 10 is a front elevation of bearing races; Figure 11 is a side elevation of one of the the bearing races shown in Figure 10; Figure 12 is a vertical sectional view of a track bar taken through an intermediate portion thereof in the longitudinal direction; Figure 13 is a side elevation of the track bar; Figure 14 is a front elevation of an end cover, showing the outer surface thereof; Figure 15 is a rear view of the end cover, showing the inner surface thereof; Figure 16 is a bottom view of the end cover; Figure 17 is a section taken on the line XVII-XVII in Figure 15;; Figure 18 is an obliquely cut sectional end view taken on the line XVIII-XVIII in Figure 15; Figure 19 is a vertical sectional view of a racepressing member, taken through an intermediate portion thereof in the longitudinal direction; Figure 20 is a plan view of the race-pressing member; and, Figure 21 is a front elevation of a conventional linear bearing, by way of comparison.

A linear slide bearing in accordance with the invention has a main body which is an integral member of channel-like cross-section constituted by a ceiling portion 2 and left and right skirt portions 4, 5 defining therebetween a central cavity 3 having a substantially rectangular cross-section.

Left and right race-receiving grooves 6,7 of semicircular cross-section are formed in the oppos ing inner surfaces of the skirt portions 4,5 in symmetry with each other with respect to the longitudinal axis of the main body 1 such as to open to the central cavity 3. Abutments 8,9 project at the respective bottom edges of the arcuate race receiving grooves 6,7, that is, the lower edges of the arcuate grooves remote from the ceiling portion 2.It is to be noted that the symbol Oi denotes the curvature centre of each of the race-receiving grooves 6,7 which is set on an imaginary line YI-Y1 intersecting the longitudinal axis X1-X1 of the main body 1 at an angle of about 55 . Non-loaded ball passages 10, 11 of circular cross-section are bored through the solid portions of the skirt portions 4,5.

Each non-loaded ball passage is substantially equal in curvature to balls and has a diameter larger than the ball diameter. The non-loaded ball passages 10, 11 are axially provided over the entire length of the main body 1. Thus, as shown in Figure 3 and 6, the non-loaded bail passages 10,11 intersectthecorres ponding imaginary lines Y1-Y1 intersecting the longitudinal axis X1-X1 of the main body 1 at an angle of about 55 . Tapped holes 2a are bored through the ceiling portion 2 of the main body 1 at predeter mined spacings along the centre of the ceiling portion 2 in the longitudinal direction.

The main body 1, having the above-described construction, is formed from a light-weight material such as a synthetic resin. The light-weight main body 1 effectively decreases the interia and therefore can be suitably used for the linear bearing which is required to move at high speed with repetitional start and stop.

A pair of left and right bearing races 12, 13, each being an arcuate member having a semicircular cross-section, are received in the race-receiving grooves 6 and 7 formed in the main body 1. As specifically shown in Figures 3,10 and 11, loaded ball grooves 14, 15, each having a semicircular cross-section, are formed in the inner peripheral surfaces of the bearing races 12, 13 such as to extend in the axial direction of the main body 1 correspond inglytothe non-loaded ball passages 10,11 bored through the main body 1. The curvature centre 2 of each loaded ball groove is coincident with the curvature centre Oi of the corresponding racereceiving groove.Thus, the loaded ball grooves 14, 15 have their respective curvature centres 2 set on the corresponding imaginary lines Y2-Y2 each intersecting, at an angle of about 55 , the symmetry axis X2-X2 which is coincident with the longitudinal axisX1-X1 of the main body 1.In addition, balls B1 under load contact the surfaces of the corresponding loaded ball grooves 14, 15 at a contact angle B which is selected to be 45". Consequently, the area of contact between the surface of each loaded ball B1 and the surface of the associated loaded ball groove 14 or 15, afforded by elastic deformation of the ball and the groove, is increased to reduce the level of the load born by the unit area of the contact region thereby to increase the load bearing capacity of the linear bearing as a whole.

Further, each of the loaded ball grooves 14,15 is constituted by a groove having an arcuate crosssection with a radius of curvature which is about a half of that of the ball. The formation of the loaded ball grooves 14, 15 by such arcuate grooves permits each loaded ball B1 to make contact at two points in the direction of contact even when a preload (precompression) is applied to the bearing or a load is applied thereto in any direction. Therefore, the loaded balls B1 perform an excellent relative motion without causing any differential slip. Moreover, since the arcuate grooves permit the loaded balls B1 to make two-point contact, even when a heavy load is applied, the balls are elastically deformed to make it possible to obtain a wide width of contact, resulting in an increase in rigidity.Furthermore, both the ideal arrangement, in which the two arcuate grooves are provided with a proper angle of contact, and the structure, which permits each pall to make two-point contact, provide a space for elastic deformation of the ball. Therefore, even if the mounting surface has any error, it is absorbed inside the bearing, so that it is possible to obtain a natural, smooth motion of the bearing.

Moreover, each of the bearing races 12, 13 has an outer peripheral surface with a barrel-like appearance as shown in Figures 4,5 and 10. Consequently, longitudinal clearances 01, 01 and lateral clearances 02, 02 are formed between the race-receiving grooves 6,7 each constituted by a flat surface and the end portions of the barrel-shaped bearing races 12, 13, so that the bearing races 12, 13 are able to swing vertically and horizontally with their central portions as the fulcrums with respect to the race receiving grooves 6, 7 of the main body 1. Accord ingly, even in the case where a track bar 16, described later, is bent, when the main body 1 passes the bent portion of the track bar 16, the bearing races 12, 13 swing to change their directions in proportion to the degree of bend so as to properly follow the bend of the track bar 16. When the main body 1 reaches a normal, straight portion of the track bar 16, the bearing races 12, 13 swing again to return to their normal, straight portion of the track bar 16, the bearing races 12, 13 swing again to return to their normal state, thereby allowing their symmetry axis X2-X2 to coincide with the longitudinal axis X3-X3 of the track bar 16. Thus, the linear bearing provides a self aligning operation.

The track bar 16 is fitted in the central cavity 3 of the main body 1 and mounted to a movable or fixed part of a machine tool or the like by the use of bolts or other fixing means. As shown in Figure 3, 12 and 13, the track bar 16 has on its left and right inclined -surfaces 17, 18 loaded ball grooves 19,20 of semicircular cross-section axially extending corres pondinglyto the loaded ball grooves 14,15 on the bearing races 12, 13. The curvature centre 03 of each of the loaded ball grooves 19,20 is set on an imaginary line Y3-Y3 intersecting, at an angle of about 55", the longitudinal axis X3-X3 of the track bar 16 which coincides with the longitudinal axis X1-X1 of the main body 1.In addition, the curvature centre 03 iS coincident with both the curvature centre O, of each of the race-receiving grooves 6,7 and the curvature centre 02 Of the loaded ball grooves 14,15 formed in the bearing races 12, 13. Thus, two loaded passages are defined by these loaded ball grooves 14,15 and 19,20. Further, similarly to the loaded ball grooves 14, 15 on the bearing races 12,13, each of the loaded ball grooves 19,20 on the track bar 16 is constituted by a groove having an arcuate cross section with a radius of curvature which is about a half of that of the ball.Moreover, similarly to the loaded ball grooves 14, 15 on the bearing races 12, 13, the loaded ball grooves 19,20 on the track bar 16 have a contact angle B1' of 45" with respect to the loaded balls B1 to increase the load bearing capacity of the bearing.

Balls B, adapted to be interposed between the bearing races 12, 13 and the track bar 16so as to recirculate, include loaded balls B1, which are bear ing a load while rolling along the passages respec tively defined between the loaded ball grooves 14, 15 on the bearing races 12, 13 and the loaded ball grooves 19,20 on the track bar 16, and non-loaded balls B2, which roll through the non-loaded ball passages 10, 11 formed through the main body 1. It is to be noted that the same ball B is referred to as the loaded ball B1 when it is in the loaded region and as the non-loaded ball B2 when it rolls along the non-loaded region.

End covers 21,22 are attached to the longitudinal end surfaces of the main body 1 by the use of bolts or other fixing means. The end covers 21,22 are made of a synthetic resin material by injection moulding or a die casting alloy by die casting. The construction of the end covers 21,22 will be described hereinunderthrough one end cover 21 with reference to Figures 14to 18. The end cover 21 is constituted by a cover member of channel-like cross-section which has in its centre a substantially rectangular central cavity 23 and is provided with left and right skirt portions 24, 25 interposing the central cavity 23 therebetween. Thus, the end cover 21 has an inner peripheral configuration similar to that of the main body 1.The end cover 21 further has ball turning grooves 26a, 26b formed such as to curve toward the corresponding outer surfaces of the cover member. The disposition of the ball turning grooves 26a, 26b will be explained hereinunder in more detail. As shown in Figure 15, each of the ball turning grooves 26a, 26b is disposed on an imaginary line Y4-Y4 intersecting, at an angle of about 55", the longitudinal axis X4-X4 of the end cover 21 which coincides with the longitudinal axis X1-X1 of the main body 1, and extends by a predetermined length along the intersection line Y4-Y4.Thus, the starting ends of the ball turning grooves 26a, 26b correspond to one of the ends of the loaded ball passages respectively defined by the loaded ball grooves 14, 15 on the bearing races 12, 13 and the loaded ball grooves 19,20 on the track bar 16, while the terminating ends of the ball turning grooves 26a, 26b correspond to one of the ends of the non-loaded ball passages 10, 11 formed through the main body 1.

To sum up, the ball turning grooves 26a, 26b have the starting ends thereof communicating with the loaded passages defined by the loaded ball grooves 14, 15 and 19,20, and the terminating ends thereof communicating with the non-loaded ball passages 10, 11.Accordingly, the end cover 21 with the ball turning grooves 26a, 26b provides a communication between the front sides of the loaded ball passages respectively defined by the loaded ball grooves 14, 15 and 19, 20, and the front sides of the non-loaded ball passages 10, 11. On the other hand, the other sides of the loaded ball passages defined by the loaded ball grooves 14, 15 and 19,20 and the other sides of the non-loaded ball passages 10, 11 com municate with each other through the other end cover 22 having the same construction as that of the end cover 21. Thus, a ball recirculating passage is completed by cooperation of a loaded ball passage defined by the loaded ball grooves 14,19 and the non-loaded ball passage 10, for example (see Figure 3).

The end cover 21 is further provided in its inner surface with race-retaining grooves 27,28 of semicir cularshape in plan. Each of the race-retaining grooves 27,28 has its centre disposed on the imaginary line Y4-Y4 intersecting the longitudinal axis X4-X4 of the side cover 22 at an angle of about 55 . The race-retaining grooves 27, 28 have a radius larger than that of the bearing race end portion in order to allow the bearing races 12, 13 to swing vertically and horizontally.

The reference numeral 29 denotes a race-pressing member adjustably screwed to the ceiling portion 2 of the main body 1 through fixing means, such as bolts 30. The race-pressing member 29 is constituted by a wedge member formed from a plate of trapezoidal cross-section. The race-pressing member 29 is supported by the bolts 30 screwed into the respective tapped holes 2a formed in the ceiling portion 2. Wedge surfaces 29a, 29b of the racepressing member 29 are made to abut on longitudinal upper inner side surfaces 12a, 13a of the bearing races 12, 13 mounted within the race-receiving grooves 6, 7 formed in the main body 1. Then, the race-pressing member 29 under this state is upwardly pulled by means of a screwing operation. Consequently, through its wedge action, the race-pressing member 29 forcedly enters both gaps defined between the ceiling portion 2 and the longitudinal upper inner side surfaces 12a, 13a of the bearing races 12, 13 opposing each other, to fit with the bearing races 12,13. As a result, the bearing races 12, 13 are pressed in their respective rotational directions by the race-pressing member 29 through the longitudinal upper inner side surfaces 12a, 13a.

Accordingly, in Figure 3, one bearing race 12 is pressed so as to rotate counterclockwise, while the other bearing race 13 is pressed so as to rotate clockwise, and longitudinal lower inner side surfaces 12b, 13b, opposite to the inner side surfaces 12a, 13a, abut on the abutments 8, 10, respectively.In this case, since the curvature centre Oi of each of the race-receiving grooves 6,7 is completely coincident with the curvature centre 02 of each of the loaded ball grooves 14, 15formed in the bearing races 12, 13, respectively, there is no possibility of any undesirable displacement of the curvature centre 02 of each of the loaded ball grooves 14,15 formed in the bearing races 12, 13, even if there is any error in operation for mounting the bearing races 12, 13 by means of the race-pressing member 29. Thus, the left and right bearing races 12, 13 can be simuitaneously fixed with high accuracy simply by manipulating a single race-pressing member 29.

The following is the description of the operation of the linear bearing in accordance with the invention, having the above-described construction.

The main body unit of a linear bearing unit in accordance with the invention is mounted on the track bar 16 of a machining centre (not shown), for example, and a necessary instrument or tool is set on the main body 1. Then, the unit is moved back and forth, so that the loaded balls B1, which are held within the loaded ball passages defined by the loaded ball grooves 14, 15 on the bearing races 12, 13 and the loaded ball grooves 19,20 on the track bar 16 are made to run in one direction while being guided by the loaded ball passages.In due course, the loaded balls B1 are turned to change the running direction from the linear direction to the circular direction by the ball turning grooves 26a, 26b formed in the end cover 22, and are sent into the non-loaded ball passages 10, 11 formed through the main body 1 to run as the non-loaded balls 82.

Thereafter, the non-loaded balls B2 running out of the non-loaded ball passages 10, 11 are then turned to change the direction from the linear direction to the circular direction by the ball turning grooves 26a, 26b formed in the other end cover 21, and are returned to the loaded ball passages defined by the loaded ball grooves 14,15 on the bearing races 12, 13 and the loaded ball grooves 19,20 on the track bar 16to roll along these passages as the loaded balls B1 again. Thereafter, the balls B repeat recirculation through the same movements.

Even in the case where the track bar 16 is bent horizontally or vertically, the pair of left and right bearing races 12, 13 integrated with each other by means of the race-pressing member 29 swing to change their directions so as to properly follow the bend of the track bar 16 by the clearances Oi and 02 formed between the bearing races 12, 13 and the race-receiving grooves 6,7. After the main body 1 has passed a vertically or horizontally bent portion of the track bar 16, the bearing races 12,13 swing again to change their directions along a normal, straight portion of the track bar 16 and return to their normal state, thereby allowing the symmetry axis X2-X2 of the bearing races 12, to coincide with the longitudinal axis X3-X3 of the track bar 16 and thus completing the aligning operation.It is to be noted that in the case where the track bar 16 is bent vertically, the change in direction of the bearing races 12,13 is attained by the vertical swing of the pair of left and right bearing races 12, 13 with their central portions as the fulcrums with respect to the race-pressing member 29 secured to the main body 1. On the other hand, in the case where the track bar 16 is horizontally bent, the bearing races 12, 13 change their directions through the integral horizontal swing of the race-pressing member 29 and the bearing races 12,13 integrated thereby on the connection of the race-pressing member 29 with the main body 1,that is, the position of the tapped hole 2a as the fulcrum.

The linear bearing of the invention, having the above-described construction and operation, offers the following various advantages: First of all, since the bearing races having a barrel-like appearance are swingably retained within the corresponding race-receiving grooves on the main body of the bearing, the bearing races are allowed to change their directions so as to properly follow the vertically or horizontally bent portion of the track bar. It is, therefore, possible not only to prevent the local increase in contact pressure of the balls which otherwise occurs when the main body passes the bent portion of the track bar but also to reduce the resistance encountered by the main body when it slides. Thus, it is advantageously possible to ensure the safety of the loaded ball passages and a smooth sliding motion of the main body of the bearing.Further, since each bearing race is constituted by an arcuate member of semicircular crosssection having a large torsional resistance, the bearing race is not twisted when a load is applied thereto. As a result, the contact pressure of the balls rolling along the bearing race can be maintained to be uniform,; hence, it is possible to ensure a smooth recirculation of the balls.

Moreover, since the pair of right and left bearing races retained by the fixing surfaces of the end covers can be simultaneously fixed simply by adjusting a single race-pressing member, the operation of mounting the bearing races is extremely simplified, thereby allowing a reduction in the production cost of the bearing as a whole. Furthermore, even when there is any error produced in the degree of clamping effected by the race-pressing member, since the curvature centre of each race-receiving groove and that of the loaded ball groove formed in the bearing race provided in the race-receiving groove are made coincident with each other, there is no possibility of any undesirable displacement of the curvature centre of the loaded ball groove. Accordingly, even when there is any mounting error produced,the contact pressure of the balls will advantageously never be nonuniform.

Claims

1. A linear bearing comprising a main body being an integral member constituted buy a ceiling portion and opposed skirt portions defining a central cavity therebetween, each skirt portion being provided in its inner surface with a race-receiving groove open to the central cavity, the race-receiving groove having an abutment projecting at its edge remote from the ceiling portion, and each skirt portion further having a non-loaded ball passage formed therethrough; a pair of bearing races each constituted by an arcuate member of substantially semicircular cross-section and having a part barrellike outer peripheral surface rockably mounted within a respective one of the race-receiving grooves, the arcuate member being provided along its inner surface with a loaded ball groove having a curvature centre which is coincident with that of the respective race-receiving groove; a race-pressing member constituted by a wedge member adjustably screwed to the inner surface of the ceiling portion of the main body and arranged to press the bearing races towards the abutments with its wedge surfaces which simultaneously abut on the side surfaces of the bearing races; a track bar fitted in the central cavity of the main body and provided on its opposed side surfaces with loaded ball grooves each having a curvature centre which is coincident with that of the corresponding loaded ball groove on a respective one of the bearing races; a pair of end covers constituted by cover members secured to end surfaces of the main body, each cover member being provided in its inner surfaces will ball turning grooves providing communication between loaded ball passages, which are defined by the loaded ball grooves on the bearing races and track bar, and the non-loaded ball passages formed through the main body, as well as race retaining grooves for supporting one of the ends of the bearing races; and balls adapted to be recirculated through the loaded ball passages and respective non-loaded ball passages.

2. A linear bearing according to claim 1, wherein the main body is formed of a light-weight synthetic resin.

3. A linear bearing according to claim 1 or claim 2, wherein the angle of contact between each ball and the corresponding loaded ball groove is substantially 45 .

4. A linear bearing according to any one of the preceding claims, wherein each of the loaded ball grooves, defining each loaded ball passage, is constituted by a groove having an arcuate crosssection.

5. A linear bearing, substantially as described with reference to Figures 1 to 20 of the accompanying drawings.