Patent Publication Number: US-2002001419-A1

Title: Linear bearing

Description:
FIELD OF THE INVENTION  
       [0001] The present invention relates to a linear bearing, particularly a linear bearing used for a high load and/or an offset load, for example, in a guide of a press or a guide of a die set.  
       BACKGROUND OF THE INVENTION  
       [0002] Linear bearings of various structures have been commercialized.  
       [0003]FIGS. 5 and 6 show a linear bearing with a conventional structure as a first example (A). FIG. 5 is a vertical sectional view, and FIG. 6 is an A-A sectional view of FIG. 5 with a partially expanded view.  
       [0004] The linear bearing shown in these drawings is composed of a guide shaft  1 , an outer cylinder  3  provided around the guide shaft  1  relatively movably in the axial direction, many rigid balls  4  provided between the guide shaft  1  and the outer cylinder  3 , and a cage  2  provided in the clearance between the guide shaft  1  and the outer cylinder  3  for holding the many rigid balls  4 . This linear bearing is called a linear ball bearing.  
       [0005]FIGS. 7 and 8 show a linear bearing with a conventional structure as a second example (B). FIG. 7 is a vertical sectional view, and FIG. 8 is an A-A sectional view of FIG. 7 with a partially expanded view.  
       [0006] The linear bearing shown in these drawings is composed of a guide shaft  5 , an outer cylinder  6  provided around the guide shaft  5  relatively movably in the axial direction, many rollers  7  provided between the guide shaft  5  and the outer cylinder  6 , and a cage  8  provided in the clearance between the guide shaft  5  and the outer cylinder  6  for holding the many rollers  7 . The outer surface of the guide shaft  5  and the inner surface of the outer cylinder  6  have flat faces  9  and  10  facing each other in parallel to each other as rolling faces along which the rollers  7  roll. The linear bearing is called a linear roller bearing.  
       [0007]FIGS. 9 and 10 show a linear bearing with a conventional structure as a third example (C). FIG. 9 is a vertical sectional view, and FIG. 10 is an A-A sectional view of FIG. 9 with a partial expanded view.  
       [0008] The linear bearing shown in these drawings is composed of a guide shaft  11 , an outer cylinder  12  provided around the guide shaft  11  relatively movably in the axial direction, many rollers  13  provided between the guide shaft  11  and the outer cylinder  12 , and a cage  14  provided in the clearance between the guide shaft  11  and the outer cylinder  12  for holding the many rollers  13 . In the linear bearing, the outer surface of the guide shaft  11  and the inner surface of the outer cylinder  12  have 90° V grooves  15  and  16  formed to face each other in the axial direction as rolling faces along which the rollers  13  roll, and the many rollers  13  are disposed in these V grooves  15  and  16  by the cage  14  in such a manner that the rolling axes of the rollers may be perpendicular to each other alternately. This linear bearing is called a linear cross roller bearing.  
       [0009] The actions of the linear bearings with these structures are not described here in detail, since they are well-known.  
       [0010] The conventional linear bearings (A), (B) and (C) described above have the following problems.  
       [0011] At first, in the linear bearing (A), since rigid balls are used as rolling bodies provided between the guide shaft and the outer cylinder, the rigid balls contact the rolling faces of the guide shaft and the outer cylinder at points. So, since large contact pressures act at the contact points, the load capacity is small.  
       [0012] On the contrary, in the linear bearings (B) and (C), since rollers are used instead of rigid balls as rolling bodies provided between the guide shaft and the outer cylinder, the rollers contact the rolling faces of the guide shaft and the outer cylinder at lines. So, the load capacity is larger. However, in the linear bearing (B), flat faces as rolling faces must be formed on the outer surface of the guide shaft and the inner surface of the outer cylinder, to increase the machining work, and since the parallelism of the flat faces is important, an advanced machining technique is necessary to inevitably raise the production cost. In the linear bearing (C), since the rolling faces are V grooves, the parallelism is as important as the flat faces, and in addition, to let the V grooves of the respective sides accurately face each other, the circumferential pitch of the V grooves is important to require a further higher machining technique.  
       [0013] Furthermore, in the linear bearings (B) and (C), the rotation of the outer cylinder around the guide shaft is inhibited. So, when the guide shaft and the outer cylinder are installed to the respective elements of the apparatus to be mounted with the linear bearing, it is necessary to accurately position the respective elements, making the adjustment work complicated and very troublesome.  
       SUMMARY OF THE INVENTION  
       [0014] The object of the present invention is to solve the above mentioned problems of the prior art, by providing a linear bearing having a large load capacity, easy to manufacture, lower in production cost, and easy to adjust in the installation on an apparatus.  
       [0015] This object can be achieved by a linear bearing, which is composed of a guide shaft, an outer cylinder provided around the guide shaft relatively movably in the axial direction, many rollers provided between the guide shaft and the outer cylinder, and a cage provided in the clearance between the guide shaft and the outer cylinder for holding the many rollers, characterized in that the outer cylinder has a circular cylindrical surface as its inner wall, that each of the rollers has an outwardly bulging circular arc rotation face as its peripheral surface, that the radius of the circular arcs of the circular arc rotation faces of the rollers is smaller than the radius of the circular cylindrical surface formed as the inner wall of the outer cylinder, and that the guide shaft has grooves in the axial direction, each having a circular cylindrical surface with a radius larger than the radius of the circular arcs of the circular arc rotation faces of the rollers.  
       [0016] In this linear bearing, it is optimum that the radius of the circular cylindrical surface formed as the inner wall of the outer cylinder or the radius of the circular cylindrical surfaces of the grooves is set at 1.04 to 1.08 times the radius of the circular arcs of the circular arc rotation faces, and that the radius of the circular cylindrical surfaces of the grooves is equal to the radius of the circular cylindrical surface formed as the inner wall of the outer cylinder.  
       [0017] In this linear bearing, the rollers have their peripheral circular arc rotation faces kept in contact with the circular cylindrical surface formed as the inner wall of the outer cylinder and the circular cylindrical surfaces of the grooves in the guide shaft. So, the contacts are substantially linear, and the load capacity can be kept large. Furthermore, in order to form the rolling faces of the outer cylinder and the guide shaft, in contact with which the rollers roll, it is only required to machine the grooves each with a circular cylindrical surface, in the outer surface of the guide shaft. So, the accuracy in the pitch of the grooves around the guide shaft is not so important, to allow easier machining. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0018]FIG. 1 is a vertical sectional view showing a preferred embodiment of the linear bearing of the present invention.  
     [0019]FIG. 2 is an A-A sectional view of FIG. 1.  
     [0020]FIG. 3 is an illustration showing a partially expanded view of FIG. 2.  
     [0021]FIG. 4 is an illustration showing the view of FIG. 2, without any roller for better understanding.  
     [0022]FIG. 5 is a vertical sectional view showing the structure of a conventional linear bearing as a first example.  
     [0023]FIG. 6 is an A-A sectional view of FIG. 5 with a partially expanded view.  
     [0024]FIG. 7 is a vertical sectional view showing the structure of a conventional linear bearing as a second example.  
     [0025]FIG. 8 is an A-A sectional view of FIG. 7 with a partially expanded view.  
     [0026]FIG. 9 is a vertical sectional view showing the structure of a conventional linear bearing as a third example.  
     [0027]FIG. 10 is an A-A sectional view of FIG. 9 with a partially expanded view. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
     [0028] A preferred embodiment of the present invention is described below in detail in reference to attached drawings of FIGS.  1  to  4 .  
     [0029] In these drawings, symbol  20  generally indicates a linear bearing. The linear bearing  20  is composed of a guide shaft  21 , an outer cylinder  22  provided around the guide shaft  21  relatively movably in the axial direction, many rollers  23  provided between the guide shaft  21  and the outer cylinder  22 , and a cage  25  provided in the clearance between the guide shaft  21  and the outer cylinder  22  for holding the many rollers  23  by keeping the rollers  23  engaged with the holding holes  24  formed in the cage  25 . FIG. 1 shows only a part of the guide shaft  21 , and its length can be adequate. The basic constitution is the same as that described for the conventional linear bearing (B).  
     [0030] However, in the linear bearing  20  of the present invention, unlike the conventional linear bearing (B), the outer cylinder  22  has a circular cylindrical surface formed as the inner wall  26 , as shown in FIGS.  2  to  4 , and each of the rollers  23  is like a barrel having an outwardly bulging circular arc rotation face  27  as its peripheral surface. And the radius r of the circular arc of the circular arc rotation face  27  of the roller  23  is smaller than the radius R of the circular cylindrical surface formed as the inner wall  26  of the outer cylinder  22 , and the guide shaft  21  has grooves  28  formed in the axial direction, each having a circular cylindrical surface with a radius R′ larger than the radius r of the circular arc of the circular arc rotation face  27  of the roller  23 .  
     [0031] In this embodiment, eight grooves  28  are formed in the axial direction at equal intervals around the guide shaft  21 . The cage  25  has eight rows of holding holes  24  corresponding to the eight grooves  28 , and each of the rows has seven holding holes  24 .  
     [0032] Therefore in this embodiment, fifty six rollers  23  are held by the cage  25  in the clearance between the guide shaft  21  and the outer cylinder  22 .  
     [0033] In this preferred embodiment, the radius R of the circular cylindrical surface formed as the inner wall  26  of the outer cylinder  22  or the radius R′ of the circular cylindrical surfaces of the grooves  28  is set at 1.04 to 1.08 times the radius r of the circular arcs of the circular arc rotation faces  27 . Furthermore, in this preferred embodiment, the radius R′ of the circular cylindrical surfaces of the grooves  28  is equal (or almost equal) to the radius R of the circular cylindrical surface formed as the inner wall  26  of the outer cylinder  22 .  
     [0034] This can be expressed by the following formula:  
     [0035] (Radius R of the circular cylindrical surface formed as the inner wall  26  of the outer cylinder  22 )=(Radius R′ of the circular cylindrical surfaces of the grooves  28 )=(or ≈) (Radius r of the circular arcs of the circular arc rotation faces  27 )×1.04˜1.08  
     [0036] The linear bearing  20  of the present invention constituted as described above acts as described below.  
     [0037] First of all, in the linear bearing  20 , the peripheral circular arc rotation faces  27  of the rollers  23  contact the circular cylindrical surface formed as the inner wall  26  of the outer cylinder  22  and the circular cylindrical surfaces of the grooves  28  of the guide shaft  21 , and since the radius R of the circular cylindrical surface formed as the inner wall  26  of the outer cylinder  22  and the radius R′ of the circular cylindrical surfaces of the grooves  28  is set, for example, at about 1.04 to 1.08 times the radius r of the circular arcs of the circular arc rotation faces  27 , their contacts are substantially linear, and the load capacity can be kept large.  
     [0038] Furthermore, in this linear bearing  20 , in order to form the rotation faces of the outer cylinder  22  and the guide shaft  21 , in contact with which the rollers  23  roll, it is only required to machine the grooves  28  each with a circular cylindrical surface, in the outer surface of the guide shaft  21 . That is, while the rollers  23  are required to be engaged with the circular cylindrical surfaces of the predetermined grooves in the guide shaft  21 , they can be engaged at any positions with the circular cylindrical surface formed as the inner wall  26  of the outer cylinder  22 . So, the accuracy in the pitch of the grooves  28  around the guide shaft  22  is not so important, to allow easier machining.  
     [0039] Moreover, because of the above constitution, the guide shaft  21  and the outer cylinder  22  can rotate relatively. So, when the guide shaft  21  and the outer cylinder  22  are installed to the respective elements of the apparatus to be mounted with the linear bearing, the adjustment in the rotating direction is possible, and therefore, the adjustment at the time of installation is easy, to save trouble.  
     Industrial Applicability  
     [0040] The present invention as described above provides the following advantages as a linear bearing for a high load and/or an offset load, for example, in a guide of a press or a guide of a die set.  
     [0041] a. In this linear bearing, since the rollers have their peripheral circular arc rotation faces kept in contact with the circular cylindrical surface formed as the inner wall of the outer cylinder and with the circular cylindrical faces of the grooves of the guide shaft, the contacts are substantially linear, and the load capacity can be kept large.  
     [0042] b. In order to form the rolling faces of the outer cylinder and the guide shaft, in contact with which the rollers roll, it is only required to machine the grooves each with a circular cylindrical surface in the outer surface of the guide shaft, and since the accuracy in the pitch of the grooves around the guide shaft is not so important, machining is very easy and the production cost can be kept low.  
     [0043] c. The guide shaft and the outer cylinder can rotate relatively. So, when the guide shaft and the outer cylinder are installed to the respective elements of the apparatus to be mounted with the linear bearing, the adjustment in the rotating direction is possible, and therefore, the adjustment at the time of installation is easy, to save trouble.