Patent Publication Number: US-2023160423-A1

Title: Ball spline having bypass track

Description:
TECHNICAL FIELD 
     The present invention relates to a ball spline, and more particularly, to a ball spline with detour tracks that is capable of allowing a nut part to rotatingly move at a given angle with respect to a spline shaft at a given section thereof. 
     BACKGROUND ART 
     The ball spline is a type of linear motion bearing transmitting a linear motion accurately in the industrial fields of automobiles and semiconductors. 
     As shown in  FIG.  1   , a conventional ball spline  10  includes load track grooves  2  for accommodating balls  1  therein in such a manner as to expose one side surface of each ball  1  to the outside, so that the balls  1 , which move along the load track grooves  2 , enter non-load circulating holes  5  along circulating grooves  4  of retainers  3 , and are thus circulated endlessly. The conventional ball spline  10  includes a nut  6  with the load track grooves  2  adapted to accommodate the balls  1  therein in such a manner as to each have an arch-shaped section with the radius of curvature greater than the radius of each ball  1 , but each load track groove  2  is machined to form the same two arches on the left and right sides of the circular center axis thereof. As a result, the balls  1  are accommodated in the load track grooves  2  in such a manner as to come into contact with each load track groove  2  at the two contact points formed on the left and right sides of the circular center axis of each load track groove  2 . If the balls  1  are accommodated in the load track grooves  2 , the two contact points with which the balls  1  come into close contact become large with respect to the angles being open from the centers of the balls  1 , thereby preventing the balls  1  from falling down into the load track grooves  2 , and so as to allow the balls  1  to be gently circulated while the balls  1  are moving from the load track grooves  2  to the non-load circulating holes  5  along the circulating grooves  4  of the retainers  3 , the load track grooves  2  have curved peripheries formed on the front end peripheries thereof. The balls  1  move along the curved end peripheries of the load track grooves  2 , while moving, so that no impacts occur to thus prevent noise or vibrations from occurring. 
     In the case where a spline shaft  8  is inserted into the nut  6 , the spline shaft  8  is configured to have a track groove  9  concavely extended in a longitudinal direction thereof in such a manner as to allow the balls  1  located protrudingly from the inner periphery of the nut  6  to be fitted thereto, and accordingly, the spline shaft  8  can perform forward and backward movements gently with respect to the nut  6  accurately by means of the balls  1 . Through the circulation of the balls  1 , the spline shaft  8  can perform the forward and backward movements, irrespective of its length. 
     The track groove  9  of the spline shaft  8  may have an arch-shaped section, but the track groove  9  is machined in the same manner as the load track grooves  2 , so that the balls  1  move with 4-point contacts. 
     A reference numeral  7  in  FIG.  1    represents a seal located between the nut  6  and each retainer  3 , and a reference numeral  4 a a circulating protrusion protruding inward from each retainer  3 . 
     As shown in  FIG.  1   , the conventional ball spline  10  is configured to allow the nut  6  to which the retainers  3  are fastened to reciprocate along the spline shaft  8  in the longitudinal direction of the spline shaft  8 , but in this case, the nut  6  cannot rotate with respect to the spline shaft  8 . 
       FIG.  2    is a schematic sectional view showing a moving means coupled to the conventional ball spline.  FIG.  2    is shown to explain the application of the conventional ball spline. 
     As shown in  FIG.  2   , a moving means V has a bracket D 3  as a hollow body with a circular section located on the outer periphery of the nut  6 , a rolling bearing B located on the outer periphery of the bracket IB, and a wheel W mounted on the bracket IB in such a manner as to rotate unitarily with the inner race of the rolling bearing B. Under the above-mentioned configuration, the moving means V can move forwards and backwards in a direction vertical to the surface as shown in  FIG.  2    by means of the rolling bearing B supported rotatably against the wheel W. As shown in  FIG.  2   , a pinion P is located on the outer end periphery of the spline shaft  8 , and the spline shaft  8  is pushed outward to allow the pinion P to engage with a rack R located in up and down directions (See a dash-dotted line of  FIG.  2   ). If the spline shaft  8  rotates, the moving means V moves along the rack R in the up and down directions. As shown in  FIG.  2   , the spline shaft  8  can move in forward and backward directions, and as the pinion P located on the end periphery of the spline shaft  8  engages with the rack R, further, the spline shaft  8  can move in up and down directions. 
     When the spline shaft  8  in the ball spline  10  is pushed outward to thus cause the pinion P to move toward the rack R so as to perform the above-mentioned movements, however, the teeth of the pinion P are not located at the spaces between the teeth of the rack R, so that undesirably, the teeth of the pinion P collide against the teeth of the rack R and thus do not engage with the teeth of the rack R, thereby making the pinion P or the rack R broken. 
     DISCLOSURE 
     Technical Problem 
     Accordingly, the present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a ball spline with detour tracks that is configured to allow a nut to be rotatable in a given range with respect to a spline shaft through the detour tracks. 
     Technical Solution 
     To accomplish the above-mentioned objects, according to the present invention, there is provided a ball spline with detour tracks that is configured to have a bar-shaped spline shaft, a nut part movable along a longitudinal direction of the spline shaft in such a manner as to insert the spline shaft thereinto, and a plurality of balls circulatedly provided between the nut part and the spline shaft, wherein the nut part includes a nut as a cylindrical hollow body adapted to insert the spline shaft thereinto and retainers as hollow bodies located on both longitudinal sides of the nut in such a manner as to insert the spline shaft thereinto, the spline shaft includes one or more tracks concavely extended along the longitudinal direction thereof, the nut includes one or more load track grooves concavely formed in a longitudinal direction thereof on an inner peripheral surface as a hollow portion into which the spline shaft is inserted and one or more non-load circulating portions formed in the longitudinal direction thereof in parallel with the load track grooves, each retainer includes circulating grooves curvedly concaved on the inner peripheral surface thereof in such a manner as to allow one side to face the end periphery of the load track groove and to allow the other side to face the end periphery of the non-load circulating portion, the balls are changed in direction in the circulating grooves of both longitudinal side retainers, run between the tracks and the load track grooves, and circulatedly move along the non-load circulating portions, and each track includes a track groove formed in the longitudinal direction of the spline shaft and detour tracks whose both longitudinal sides are connected to the track groove. 
     According to the present invention, the detour tracks may include detour track grooves spaced apart from the track groove in parallel with the track groove and inclined track grooves inclinedly extended from both longitudinal sides of the detour track grooves in such a manner as to be connected to the track groove. 
     According to the present invention, the detour tracks are located on both circumferential sides of the spline shaft, while placing the track groove therebetween. 
     According to the present invention, the detour tracks are formed more deeply than the track groove, so that the balls have gaps between the detour tracks and the load track grooves. 
     According to the present invention, each retainer may include a cylindrical inner surface, and the circulating grooves are open to the inner surface. 
     According to the present invention, each load track groove faces the track groove and has expanded track portions on both longitudinal ends thereof. 
     According to the present invention, further, the ball spline may include a ball bush having one or more bush load track grooves concavely formed in the inner peripheral surface of the nut in the longitudinal direction of the nut, one or more bush non-load circulating portions formed on positions spaced apart from the bush load track grooves in the longitudinal direction of the nut, one or more bush circulating grooves curvedly concaved on the inner peripheral surface facing the nut in such a manner as to allow one side to face the bush load track grooves and to allow the other side to face the non-load circulating portions, and a plurality of balls changed in direction in the bush circulating grooves and circulatedly moving between the bush load track grooves and the outer peripheral surface of the spline shaft and along the bush non-load circulating portions. 
     Advantageous Effects 
     According to the present invention, the ball spline  100  with the detour tracks is configured to allow the nut  120  to be rotatable in a given range with respect to the spline shaft  110  through the detour tracks  111 - 1 , thereby allowing the nut  120  to have a gap in the rotation direction thereof, preventing the inclined track grooves  111   b - 1  of the detour tracks  111 - 1  from being damaged by the contacts with the balls  150 , and keeping the retainers  130  from being damaged by the interference with the spline shaft  110 , so that the ball spline  100  according to the present invention can a high bending resistance. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG.  1    is an exploded perspective view showing a conventional ball spline. 
         FIG.  2    is a partially front sectional view showing an application example of the conventional ball spline. 
         FIG.  3    is a perspective view showing a ball spline with detour tracks according to the present invention, in which some parts are omitted. 
         FIG.  4    is a sectional view showing a portion of a spline shaft of the ball spline with detour tracks according to the present invention. 
         FIG.  5    is a perspective view showing a nut of the ball spline with detour tracks according to the present invention. 
         FIG.  6    is a sectional view showing a longitudinal portion of the ball spline with detour tracks according to the present invention. 
         FIG.  7    is a perspective view showing a retainer of the ball spline with detour tracks according to the present invention. 
         FIG.  8    is a partially cutaway perspective view showing a variation of the ball spline with detour tracks according to the present invention. 
     
    
    
     MODE FOR INVENTION 
     Hereinafter, an explanation of a ball spline with detour tracks according to the present invention will now be described in detail with reference to the attached drawings. 
       FIG.  3    is a perspective view showing a ball spline with detour tracks according to the present invention, in which some parts are omitted,  FIG.  4    is a sectional view showing a portion of a spline shaft of the ball spline with detour tracks according to the present invention,  FIG.  5    is a perspective view showing a nut of the ball spline with detour tracks according to the present invention,  FIG.  6    is a sectional view showing a longitudinal portion of the ball spline with detour tracks according to the present invention,  FIG.  7    is a perspective view showing a retainer of the ball spline with detour tracks according to the present invention, and  FIG.  8    is a partially cutaway perspective view showing a variation of the ball spline with detour tracks according to the present invention. 
     As shown in  FIGS.  3  and  5   , a ball spline with detour tracks according to the present invention includes a bar-shaped spline shaft  110 , a nut part movable along a longitudinal direction of the spline shaft  110  in such a manner as to insert the spline shaft  110  thereinto, and a plurality of balls  150  circulatedly provided between the nut part and the spline shaft  110 . 
     The nut part includes a nut  120  as a cylindrical hollow body adapted to insert the spline shaft  110  thereinto and retainers  130  as hollow bodies located on both longitudinal sides of the nut  120  in such a manner as to insert the spline shaft  110  thereinto. The nut  120  is made of high carbon steel such as bearing steel. Each retainer  130  has a doughnut-like shape formed by removing the center of a disc-like shape. The retainers  130  are made of engineering plastic (Nylon 6, Nylon 66, or Nylon 6 and Nylon 66 containing glass fibers), but of course, they may be made of a metal such as bearing steel, like the nut  120 . Even though not shown, further, seals as hollow bodies may be located between the nut  120  and one side retainer  130  and between the nut  120  and the other side retainer  130 . As shown in  FIG.  1   , the retainers  130  are coupled to the nut  120  by means of bolts. 
     The spline shaft  110  has one or more tracks concavely extended along the longitudinal direction thereof. The spline shaft  110  with the bar-shaped circular section is made by concavely machining the tracks on the outer peripheral surface thereof. In this case, two tracks may be provided on positions opposite to each other, and otherwise, five tracks may be provided at intervals of 90°. The spline shaft  110  has a shaft mounting part  113  fitted to the end periphery thereof in such a manner as to become reduced in diameter. The shaft mounting part  113  has a key groove (not shown) formed thereon and a pinion disposed thereon. 
     The nut  120  includes one or more load track grooves  125  concavely formed in a longitudinal direction thereof on an inner peripheral surface  121  as a hollow portion into which the spline shaft  110  is inserted and one or more non-load circulating portions  127  formed in the longitudinal direction thereof in parallel with the load track grooves  125 . The number of load track grooves  125  and the number of non-load circulating portions  127  are the same as the number of tracks formed on the spline shaft  110 . The non-load circulating portions  127  are through holes formed on the nut  120  in the longitudinal direction of the nut  120 . The load track grooves  125  are formed on the positions facing the tracks. 
     Each retainer  130  has circulating grooves  133  curvedly concaved on the inner peripheral surface facing the nut  120 . One or more circulating grooves  133  are formed. The number of circulating grooves  133  is the same as the number of tracks. One side of each circulating groove  133  faces the end periphery of the load track groove  125  corresponding thereto and the other side faces the end periphery of the non-load circulating portion  127  corresponding thereto. 
     The balls  150  are changed in direction in the circulating grooves  133  of both longitudinal side retainers  130 , run between the tracks and the load track grooves  125 , and circulatedly move along the non-load circulating portions  127 . The technology for the circulation of the balls  150  is well known in the art, and for the brevity of the description, accordingly, an explanation of the circulation technology will be avoided. 
     Each track has a track groove  111  formed in the longitudinal direction of the spline shaft  110  and detour tracks  111 - 1  whose both longitudinal sides are connected to the track groove  111 . If an external force in a rotation direction is applied to the nut  120  or the spline shaft  110 , the balls  140  move along the spaces between the detour tracks  111 - 1  and the load track grooves  125 , thereby allowing the nut  120  to rotate to a given angle with respect to the spline shaft  110 . 
     The detour tracks  111 - 1  include detour track grooves  111   b  spaced apart from the track groove  111  in parallel with the track groove  111  and inclined track grooves  111   b - 1  inclinedly extended from both longitudinal sides of the detour track grooves  111   b  in such a manner as to be connected to the track groove  111 . If the balls  150  run between the track grooves  111  and the load track grooves  125  and then move between the load track grooves  125  and the detour tracks  111 - 1 , they move along one side inclined track grooves  111   b - 1 , the detour track grooves  111   b,  the other side inclined track grooves  111   b - 1 , and the track grooves  111 . 
     Each ball  150  has 2-point contacts with the track groove  111  and 2-point contacts with the load track groove  125 , so that it moves with 4-point contacts. The track groove  111  and the load track groove  125  have the shape of an arch with the radius of curvature greater than the radius of each ball  150 , and accordingly, each of them can have 2-point contacts with each ball  150 . This is the known technology in the conventional practices, and for the brevity of the description, therefore, an explanation of the balls  150  will be avoided. 
     As shown in  FIG.  4   , the detour tracks  111 - 1  are located on both circumferential sides of the spline shaft  110 , while placing the track groove  111  therebetween. The detour tracks  111 - 1  are formed more deeply than the track groove  111 , so that the balls  150  have gaps between the detour tracks  111 - 1  and the load track grooves  125 . As the balls  150  have gaps between the detour tracks  111 - 1  and the load track grooves  125 , the nut  120  can have a gap in the rotation direction with respect to the spline shaft  110 , so that in the process of the rack and pinion engagement as shown in  FIG.  2   , the engagement can be gently performed. 
     A reference numeral  111   a    
     in  FIGS.  2  and  3    represents the track groove  111  parallel with the detour track grooves  111   b.    
     As shown in  FIGS.  5  and  6   , each load track groove  125  faces the track groove  111  and has expanded track portions  125   a  on both longitudinal ends thereof. If the balls  150  move to thus reach the expanded track portions  125   a,  gaps of the balls  150  between the expanded track portions  125   a  and the detour tracks  111 - 1  become large, and accordingly, the damages of the inclined track grooves  111   b - 1  caused by the balls  150  can be suppressed or prevented. 
     As shown in  FIG.  7   , each retainer  130  has a cylindrical inner surface  131 , and the circulating grooves  133  are open to the inner surface  131 , so that the circulating grooves  133  have inner peripheral openings  135  formed on the inner peripheries thereof in such a manner as to be open to the inner surface  131 . Accordingly, the retainer  130  does not have any protruding components inwardly from the inner surface  131  thereof in the radius direction thereof, and the retainer  130  does not have any interference with the inclined track grooves  111   b - 1 , while moving, so that the retainer  130  can be prevented from being broken by the occurrence of the interference with the inclined track grooves  111   b - 1 . 
     As shown in  FIG.  8   , further, the ball spline with the detour tracks according to the present invention may include a ball bush. The tracks are formed on the spline shaft  110  at the positions facing each other, and the ball bush is located on the space between the tracks. As the ball bush is provided, the stiffness for the radius direction load applied to the nut  120  can be improved. The tracks are spaced apart from each other at an angle of 180°, and the ball bush is located on the space between both tracks. 
     The ball bush includes one or more bush load track grooves  125 - 1  concavely formed in the inner peripheral surface of the nut  120  in the longitudinal direction of the nut  120 , one or more bush non-load circulating portions  127 - 1  formed on positions spaced apart from the bush load track grooves  125 - 1  in the longitudinal direction of the nut  120 , one or more bush circulating grooves  133 - 1  curvedly concaved on the inner peripheral surface facing the nut  120  in such a manner as to allow one side to face the bush load track grooves  125 - 1  and allow the other side to face the non-load circulating portions  127 - 1 , and a plurality of balls  150 - 1  changed in direction in the bush circulating grooves  133 - 1  and circulatedly moving between the bush load track grooves  125 - 1  and the outer peripheral surface of the spline shaft  110  and along the bush non-load circulating portions  127 - 1 . The bush non-load circulating portions  127 - 1  are through holes formed in the longitudinal direction of the nut  120 . The bush load track grooves  125 - 1  face the outer peripheral surface of the spline shaft  110  which has an arch-shaped section. The balls  150 - 1  move between the bush load track grooves  125 - 1  and the outer peripheral surface of the spline shaft  110  (having the arch-shaped section), are changed in direction in the bush circulating grooves  133 - 1 , and are then guided to move along the bush non-load circulating portions  127 - 1 , so that the balls  150 - 1  are endlessly circulated. 
     INDUSTRIAL APPLICABILITY 
     The ball spline  100  with the detour tracks according to the present invention can be applied to various applications.