Abstract:
A low-friction linear motion apparatus includes a track bar having two parallel guide rails on two opposite sides thereof, and a sliding member forming a mating cavity on two opposite undersides thereof and provided with multiple bearing rods on the mating cavities, which rest against the guide rails when the sliding member is slidably fitted over the track bar. At least one side of the sliding member is installed with a clamping device/holder to adjust the interval between the bearing rods and guide rails for minimal friction. Each guide rail is partially set in a parallel slot on each side wall of the track bar and partially exposed for resting against the bearing rods. The sliding member can move along the longitudinal direction of the track bar with little friction due to line contacts or non-circulating point contacts.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates generally to a low-friction linear motion apparatus that has a guide structure to provide with a relative linear motion of two objects by means of line contact or surface contact, and a self-alignment mechanism to automatically adjust contact position between components.  
         [0003]     2. The Related Art  
         [0004]     Referring to  FIG. 1 , a conventional linear motion apparatus provides with a relative linear motion of a sliding member and a guide track, which has a guide structure with low resistance. In this structure, balls are assembled between the sliding member and the guide track in a circulating pattern to reduce friction between their contact surfaces due to point contacts.  
         [0005]     Although the point contacts can provide a significant reduction in friction between two contact surfaces, its components cannot bear with a larger impact, thereby being easily damaged. Further, when the balls circularly move, it is easy to generate vibration.  
         [0006]     Further, the conventional linear motion apparatus has not a self-alignment mechanism to correct any shifts and tilting problem that may result from machining errors or deformation. It will generate a shift of contact points. Accordingly, all loads are borne on diagonal balls and guide grooves, thereby reducing its service life.  
         [0007]     Another problem of the conventional linear motion apparatus is that the apparatus has not a pressure-adjusting mechanism to adjust the distance between the bearing rods. This may also affect the service life of the parts.  
         [0008]     Still another problem of the conventional linear motion apparatus is that the guide track and the guide rail are formed as one-piece, thereby making it difficult to handle in subsequent process. The guided track is easily deformed or warped during heat treatment and grinding processes. Therefore, the assembling requires certain skilled person in order to prevent the problems described above.  
         [0009]     Thus, it is desired to provide a low-friction linear motion apparatus that can substantially reduces or obviates the limitations and disadvantages of the prior art.  
       SUMMARY OF THE INVENTION  
       [0010]     A primary objective of the present invention is to provide a low-friction linear motion apparatus that makes use of line contacts or non-circulating point contacts of multiple guide rails and bearing rods, thereby enabling the linear motion apparatus to bear greater load and extend the service life.  
         [0011]     A second objective of the present invention is to provide a low-friction linear motion apparatus that provides micro-adjustment of the interval between the bearing rods and guide rails to correct factory alignment errors.  
         [0012]     A third objective of the present invention is to provide a low-friction linear motion apparatus that provides micro-adjustment of the distance between two rows of bearing rods to match the load requirement so that the resultant friction can be controlled at a minimal level.  
         [0013]     A fourth objective of the present invention is to provide a low-friction linear motion apparatus that incorporates a parallel slot on each side of the track bar to facilitate the mounting of the guide rail obviating the use of the heat treatment and polishing processes, thus enabling easy assembling at reduced costs.  
         [0014]     The low-friction linear motion apparatus includes a track bar with two guide rails on its two sides running through the full length of the track, and a sliding member which is supported by multiple bearing rods, which are arranged in two row format on two shoulder walls of the sliding member with a mating cavity, corresponding to the positions of the guide rails. Each guide rail is partially set in a parallel slot on the side wall of the track bar and partially exposed with outward curved surface to provide sliding contacts with the bearing rods also bulging out on the opposite surface when the sliding member is slidably assembled. The bearing rods rest against the bearing rails by line contact or non-circulating point contact with each other and slidably move in longitudinal direction, which will not generate welding phenomena.  
         [0015]     The low-friction linear motion apparatus according to the present invention can prevent the deformation of the bearings, and minimize thermal heat accumulation due to friction between two contact surfaces.  
         [0016]     The present invention is characterized in that the sliding contact portions of the guide rails and the bearing rods are made of different materials. The guide rails may be made of metal while the bearing rods may be made of ceramic material, so that the contact surfaces will not be welded under high operating temperature.  
         [0017]     The present invention is also characterized in that the distance between the two-row bearing rods shall always be less than the diameter of the corresponding guide rail to enable a tight fit between the two-row bearing rods.  
         [0018]     These along with other features of novelty, which characterize the present invention, are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, the operating advantages and the specific objectives attained by its uses, references should be made to the accompanying drawings and descriptive matter illustrated in preferred embodiments of the present invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]      FIG. 1  is a perspective view of a conventional sliding apparatus;  
         [0020]      FIG. 2  is an exploded view of a low-friction linear motion apparatus according to a first embodiment of the present invention;  
         [0021]      FIG. 3  is a sectional view of  FIG. 2 ;  
         [0022]      FIG. 4  is an exploded view of a low-friction linear motion apparatus according to a second embodiment of the present invention;  
         [0023]      FIG. 5  is an exploded view of a low-friction linear motion apparatus according to a third embodiment of the present invention;  
         [0024]      FIG. 6  is an exploded view of a low-friction linear motion apparatus according to a fourth embodiment of the present invention;  
         [0025]      FIG. 7  is an exploded view of a low-friction linear motion apparatus according to a fifth embodiment of the present invention;  
         [0026]      FIG. 8  is an exploded view of a low-friction linear motion apparatus according to a sixth embodiment of the present invention;  
         [0027]      FIG. 9  is an end view of a low-friction linear motion apparatus according to a seventh embodiment of the present invention;  
         [0028]      FIG. 10  is an end view of a low-friction linear motion apparatus according to an eighth embodiment of the present invention;  
         [0029]      FIG. 11  is an exploded view of a low-friction linear motion apparatus according to a ninth embodiment of the present invention;  
         [0030]      FIG. 12  is an end view of a the low-friction linear motion apparatus according to a tenth embodiment of the present invention; and  
         [0031]      FIG. 13  is an end view of a low-friction linear motion apparatus according to an eleventh embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0032]     Referring to  FIGS. 2 and 3 , a low-friction linear motion apparatus in accordance with a first embodiment of the present invention comprises a track bar  10  and a sliding member  20  mounted on the track bar  10 , which provide with a relative linear motion of two objects. The sliding member  20  moves along the track bar  20 , two contact surfaces of which have different materials with minimal friction.  
         [0033]     The track bar  10  has two parallel guide rails  11  on its two sides. Each guide rails  11  is partially set in a parallel slot on each side of the track bar  10  and partially exposed with outward curved surface.  
         [0034]     The sliding member  20  has a mating cavity on its underside, in which two rows of bearing rods  21  are attached on each shoulder wall of the mating cavity. When the linear motion apparatus is assembled, the two-row bearing rods  21  on each side is slidably fitted onto the guide rail  11  of the sliding member  20  on the same side, thereby providing line contacts for linear motion of the sliding member  20  along the track bar  10 .  
         [0035]     The guide rails  11  and bearing rods  21  are used on two sides to support the thrust load over the sliding member  20 , wherein the number of guide rails  11  for the linear motion apparatus may vary depending on the row number of bearing rods  21  used for supporting the sliding member  20 , and the choice of using guide rails on one side or two sides also depends on the design requirements.  
         [0036]     In the first embodiment, each guide rail  11  is fitted into a parallel slot  12  on each side of the track bar  10 , where each guide rail  11  is a tubular body running through the full length of the track bar  10 . The sliding member  20  has a mating cavity on an under side thereof, in which two rows of bearing rods  21  are mounted on an inner surface of each shoulder wall of the cavity, where each bearing rod  21  is also a tubular body limited by the length of the sliding member  20 .  
         [0037]     The distance between the two-row bearing rods  21  is always less than the diameter of the corresponding guide rail  11 ; thereby enabling the guide rail  11  to tightly fit between the two-row bearing rods  21 .  
         [0038]     The sliding contact portions between the guide rails  11  and the bearing rods  21  shall be made of different materials. For example, the guide rail  11  may be made of metal while the bearing rod  21  may be made of ceramic material, so that the contact surfaces will not be welded under high operating temperature.  
         [0039]     When assembled, each outward curved guide rail  11  is fitted in the gap between two-row bearing rods  21  on the same side of the sliding member  20 . The bearing rods  21  and the guide rails  11  rest against each other to support linear motion of the sliding member  20  carrying a load along the track bar  10 .  
         [0040]     Referring to  FIG. 4 , the track bar  10  in accordance with a second embodiment of the present invention includes a cover strip  13  mounted thereon by multiple screws inserted through holes on a top of the cover strip  13 , so as to form a parallel slot  12  on each side of the track bar  10 . The parallel slot  12  is to receive a guide rail  11  running through the full length of the track bar  10 . These two guide rails  11  on two sides of the track bar  10  are fixed in the parallel slots  13 . The overall structure and the rest of components of the linear motion apparatus are identical to those in the first embodiment.  
         [0041]     Referring to  FIG. 5 , the track bar  10  in accordance with a third embodiment of the present invention is an integral unit, whereas the track bar  10  in the second embodiment is formed of a one-piece bar with screws. The two parallel slots  12  each have a deep groove  12   a  at the innermost depth running in parallel with the slot  12  and through the full length of the track bar  10 . Therefore, these two deep grooves  12   a  create an overhang portion  13  at a top of the track bar  10 .  
         [0042]     To assemble the track bar  10 , the guide rail  11  is first placed into the slots  12  on each side of the track bar  10 , and then multiple screws are inserted through top holes of the track bar  10  to clamp down the guide rails  11  by pressing the overhang portion  13  against the tubular guide rails  11  partially held in the parallel slots  12 . As such, the guide rails  11  running through the track bar  10  can be micro-adjusted by loosening or tightening of the screws to control the interval and line contacts between the guide rails  11  and the bearing rods  21 . Only the unique features of this embodiment are illustrated herein, while the overall structure and the rest of components are identical to those in previous embodiments.  
         [0043]     Referring to  FIG. 6 , the sliding member  20  in accordance with a fourth embodiment of the present invention includes multiple clamping devices  26  and screws  22  to position the bearing rods  21  with high precision. The clamping devices  26  are lined up against a dugout portion  23  in the mating cavity of the sliding member  20 , and then screws  22  are inserted through corresponding holes on a side wall of the sliding member  20  to fix the clamping devices  26  in place. Each U-shaped clamping device  26  has grooves on an inner surface to receive the bearing rods  21 . As such, the positions of the bearing rods  21  relative to the guide rails  11  can be micro-adjusted by loosening or tightening of the screws  22  in order to reduce the friction between contact surfaces.  
         [0044]     The sliding contact surfaces on the mating cavity of the sliding member  20  can be lubricated by oily substance, so that friction between the guide rails  11  and the bearing rods  21  can be further reduced for better performance.  
         [0045]     The clamping devices  26  can be installed either on one side or two sides of the sliding member  20 , depending on the design requirement of the linear motion apparatus. Only the unique features of this embodiment are illustrated herein, while the overall structure and the rest of components are identical to those in previous embodiments.  
         [0046]     Referring to  FIG. 7 , the sliding member  20  in accordance with a fifth embodiment of the present invention includes two holders  25  and multiple screws  22  to position the bearing rods  21  with high precision. The holder  25  is a long narrow strip disposed parallel to the bearing rods  21 , which are lined up on the dugout portion  23  in the mating cavity of the sliding member  20 , and then multiple screws  22  are inserted through corresponding holes on a side wall of the sliding member  20  to fix the holders  25  in place. The surface of each holder  25  has multiple grooves that are either caved inward or slanted for securing the bearing rods  21 .  
         [0047]     As such, the positions of the bearing rods  21  relative to the guide rails  11  can be micro-adjusted for minimal friction in the linear motion of the sliding member  20 , and the distance between the two rows of bearing rods  21  can be set accurately. The choice to use the holder  25  either on one side or two sides of the sliding member  10  depends on the design requirements. Only the unique features of this embodiment are illustrated herein, while the overall structure and the rest of components are identical to those in previous embodiments.  
         [0048]     Referring to  FIG. 8 , the track bar  10  in accordance with a sixth embodiment of the present invention uses first screws  14  and second screws  15  to align the track bar  10  on a substructure  30 . The first screws  14  are directly locked onto the substructure  30 , while the second screws  15  are mounted vertically through the track bar  10 , with the tip touching a surface of the substructure  30 . As such, when a second screw  15  is driven deep into the track bar  10 , the tip of the second screw  15  is acted against the surface of the substructure  30  to create a counter-action force to pull the track bar  10  away from the substructure  30 .  
         [0049]     Through this mechanism, the height of the track bar  10  can be micro-adjusted to correct slightly its deformation. Only the unique features of this embodiment are illustrated herein, while the structures and the rest of components identical to those in previous embodiments will not be reiterated.  
         [0050]     Referring to  FIG. 9 , the sliding member  20  in accordance with a seventh embodiment of the present invention includes two troughs  23   a  and spurs  23   b  in the dugout portion  23  of the mating cavity for placing the bearing rods  21  with extra flexibility. These troughs  23   a  and spurs  23   b  are formed on upper and lower ends to correct any disalignment between the guide rails  11  and the bearing rods  21 , so that the positions of the bearing rods  21  and the guide rails  11  can be controlled to exact point contacts. Only the unique features of this embodiment are illustrated herein, while the overall structure and the rest of components are identical to those in previous embodiments.  
         [0051]     Referring to  FIG. 10 , the sliding member  20  in accordance with an eighth embodiment of the present invention includes two resilient clips  23   c  in the dugout portion  23  of the mating cavity for placing the bearing rods  21  with extra flexibility. A pair of resilient clips  23   c  is installed on upper and lower ends of the mating cavity, which replaces with the troughs  23   a  and spurs  23   b  in previous cases. Through this mechanism, the positions of the bearing rods  21  relative to the guide rails  11  can be micro-adjusted to exact point contacts. Only the unique features of this embodiment are illustrated herein, while the overall structure and the rest of components are identical to those used in previous embodiments.  
         [0052]     Referring to  FIG. 11 , the sliding member  20  of the linear motion apparatus in accordance with a ninth embodiment of the present invention includes two rows of ball bearings  24  lining the inner walls on the two sides. These ball bearings  24  are to replace the bearing rods  21  as used in all previous embodiments, which are non-circulating ball bearings that rotate in the same direction as the linear motion of the sliding member  20 . Only the unique features of this embodiment are illustrated herein, while the structures and the rest of components are identical to those in previous embodiments.  
         [0053]     Referring to  FIG. 12 , the guide rails  11  and the track bar  10  in accordance with a tenth embodiment of the present invention are formed as an integral unit. There are two parallel tracks  16  on each side of the guide rail  11 . The parallel tracks  16  rest against the bearing rods  21  when the sliding member  20  is slidably fitted onto the track bar  10 . Only the unique features of this embodiment are illustrated herein, while the structures and the rest of components are identical to those in previous embodiments.  
         [0054]     Referring to  FIG. 13 , the track bar  10  in accordance with an eleventh embodiment of the present invention is a cylindrical shaft, and the sliding member  20  is a cylindrical shell fitted around the track bar  10  to form a concentric cylindrical configuration. Multiple guide rails  11  mounted on a circumference of the cylindrical track bar  10  can be arranged to form a ring shape, triangular, quadrangular, or other polygonal shape, depending on the design requirements.  
         [0055]     The sliding member  20  has multiple catch grooves  21   a  on an inner surface thereof for placing corresponding bearing rods  21 , and the track bar  10  has multiple parallel slots on a circumference thereof for holding the guide rails  11 . When the cylindrical sliding member  20  is slid over the track bar  10 , the bearing rods  21  rest against the guide rails  11  to form sliding contacts for linear motion of the sliding member  20 .  
         [0056]     Although the present invention has been described with reference to the preferred embodiments thereof, it is apparent to those skilled in the art that a variety of modifications and changes may be made without departing from the scope of the present invention which is intended to be defined by the appended claims.