Patent Publication Number: US-2010122596-A1

Title: Ball Screw

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a ball screw applied for linear transmission, and more particularly to a ball screw, which can effectively extend the service life of the rolling assembly. 
     2. Description of the Prior Art 
     As for precision machineries, in order to control the feed rate precisely and with low friction coefficient, ball screws are used for precision transmission. Such a ball screw is normally provided with a screw, a nut and plural balls between the screw and the nut. The balls roll circularly within the nut through return assemblies provided on the nut. Referring to  FIG. 9 , a nut  51  is moveably mounted on a screw  50  and provided with a return assembly  52  at each of two opposite ends thereof. The screw  50 , the nut  51  and the return assemblies  52  define a circulation path  54  for endless circulation of a rolling assembly  55 . In order to avoid undesired rotation of the rolling assembly  55 , the circulation path  54  is defined with guiding grooves  541 . The rolling assembly  55  is provided with two linking portions  551  at two opposite sides thereof for linking plural rolling elements  550  together. The linking portions  551  slide along the guiding grooves  541  of the circulation path  54 , and the guiding grooves  541  at the two sides of the respective return assemblies  52  are disposed along the arcs defined by the smallest radius and the biggest radius of a return portion  520 , so that when the rolling assembly  55  passes through the return portion  520 , the linking portions  551  at the two sides of the rolling assembly  55  will slide along the guiding grooves at the two sides of the return assembly  52  and bend therein, the direction in which the linking portions  551  bend is obviously vertical to the bendable direction of the linking portions  551 , thus causing serious damage to the linking portions  551 . 
     After entering one of the return assemblies  52 , the linking portions  551  will move along the guiding grooves  541  at the two sides of the one of the return assemblies  52  and pass through the right-angled return portion  520  of the one of the return assemblies  52  and then pass through the right-angled return portion  520  of the other of the return assemblies  52  and finally return between the screw  50  and the nut  51 . When passing the right-angled return portion  520 , the linking portions  551  at the two sides of the rolling assembly  50  are located within the arcs defined by the smallest radius and biggest radius of the return portion  520 , namely one of the linking portions  551  is located within the arc defined by the biggest radius of the return portion  520  and subject to an improper stretching force, and the other of the linking portions  551  is located within the arc defined by the smallest radius of the return portion  520  and subject to an improper extrusion force. Due to the design of the linking portions  551  of the rolling assembly  55 , the bendable direction of the rolling assembly  55  is located at a side where no linking portions  551  are disposed. The direction in which the guiding grooves  541  at the two sides of each of the return assemblies  52  guide the linking portions to bend is located on the linking portions at the two sides of the rolling assembly  55 , so that when passing the respective return portions  520 , one of the linking portions  551  will be improperly stretched, and meanwhile the other of the linking portions  551  will be extruded. As a result, the linking portions  551  of the rolling assembly  55  are more likely to rupture due to being improperly stretched or extruded. 
     When the linking portions  551  at the two sides of the rolling assembly  55  are improperly stretched and extruded synchronously within the return portion  520 , they slide at very high speed, and the rolling elements  550  which change the moving direction quickly when entering the return portion  520  are likely to collide with the inner surface of the return assembly  52  to cause vibration. Therefore, when passing the return portion  520 , the rolling assembly  55  will be affected by the vibration of the rolling elements  550  or the pulling force between the rolling elements  550 , in addition, the rolling assembly  50  is more likely to rupture immediately since the linking portions  551  at the two sides of the rolling assembly  55  are improperly or excessively stretched or extruded. Moreover, since the linking portions  551  at the two sides of the rolling assembly  55  are stretched or extruded synchronously, the rolling elements  550  will deviate from its original path, thus causing undesired friction which will make the circulation of the rolling assembly unsmooth. Additionally, the improper collision will cause noise. 
     The present invention has arisen to mitigate and/or obviate the afore-described disadvantages. 
     SUMMARY OF THE INVENTION 
     The technical problems to be solved: 
     When the rolling assembly which rolls within the conventional ball screw passes through the right-angled return portion of the return assembly, the linking portions of the rolling assembly will slide along the arc routes defined by the smallest radius and the biggest radius of the return portion, so that the rolling assembly is likely to rupture due to the excessive deformation of the linking portions within the return portion, and the improper deformation of the linking portions will greatly increase the friction between the rolling assembly and the return assemblies to cause the unsmooth circulation of the rolling assembly and noise. 
     In order to solve the above technical problems, the present invention provides a ball screw. The ball screw in accordance with the present invention comprises a screw, a nut, two return assemblies and a rolling assembly. The screw is provided with a screw helical rolling groove and a screw thread, and the nut is provided with a nut helical rolling groove opposite the screw helical rolling groove and a nut thread opposite to the screw thread. The screw rolling groove cooperates with the nut rolling groove to define a loaded path, and a guiding space is defined between the screw thread and the nut thread. The nut is provided with a receiving groove in each of two opposite ends thereof for accommodation of the return assemblies. Each of the return assemblies is provided with a linking portion, a return portion and a connecting portion in order and further defined with a linking portion passage, a return portion passage and a connecting portion passage in the linking portion, the return portion and the connecting portion, respectively, wherein the linking portion passage is linked up with the loaded path, and both ends of the return portion passage are connected to the linking portion passage and the connecting portion passage, thus defining a return passage, the other end of the connecting portion passage is connected to the other return assembly through the rolling passage, each of the linking portion passage, the return portion passage and the connecting portion passage is defined with two guiding grooves in the return passage, one end of the two guiding grooves of the linking portion passage is linked up with the guiding space and has a first angular difference with respect to the other end of the two guiding grooves of the linking portion passage. The rolling assembly includes a chain having plural rolling elements. The chain includes two linking portions at two sides thereof. The linking portions of the chain slide within the guiding space between the screw and the nut and the guiding grooves of the return passage, when the rolling assembly moves from the guiding space to the return portion passage, the linking portions of the chain will be guided by the guiding grooves of the linking portion passage to move and twist an angle of the first angular difference of about 90 degrees. 
     There is a second angular difference between two ends of the guiding grooves of the connecting portion passage of each of the return assemblies, and the second angular difference is about half of the first angular difference. The direction where the guiding grooves of the connection portion passage twist is opposite to the direction where the guiding grooves of the linking portion passage. Due to the twisting of the connecting portions of the two return assemblies, before arriving at the return portion passage of the other return assembly, the linking portions of the rolling assembly has been guided to bend in the bendable direction to avoid the improper deformation. After passing the return portion passage, the linking portions of the rolling assembly will twist an angle of about 90 degrees within the sequent linking portion passage and then enter the guiding space smoothly. 
     As compared to the conventional technology, the present invention has the following advantages: 
     1. Avoiding improper bending failure: when the rolling assembly is rolling within the circulation path defined by the screw, the nut and the two return assemblies, the rolling assembly will twist the angle of the first angular difference within the linking portion passage of the return passage of one of the return assemblies through the guiding of the guiding grooves, and then the rolling assembly will bend in the bendable direction to smoothly pass through the return portion passage, thus avoiding the serious deformation to avoid improper bending failure. 
     2. Reducing interference and improper collision: since the guiding grooves of the return portion passage is provided to make the rolling assembly avoid passing the arc routes defined by the smallest and biggest radius of the return portion passage, the linking portions of the rolling assembly can bend in the bendable direction, therefore, the linking portions at the two sides of the rolling assembly will share the load evenly to be synchronously stretched and extruded, thus avoiding the improper deformation of the overall rolling assembly, and the rolling elements will be kept rolling along the optimal path, thus avoiding the improper collision and interference with the return passage and the return elements to reduce the integral damage and the noise to the lowest. 
     3. Continuous guiding to form a complete recirculation: besides the above guiding design, the rolling assembly further utilizes the first angular difference design and the second angular difference design to twist within the two return assemblies to make the linking portions to bend in the bendable direction to avoid bending excessively within the serious deformation zone, thus forming a complete recirculation path to reduce the interference to the lowest for making the rolling assembly roll within the return passage more smoothly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a ball screw in accordance with the present invention; 
         FIG. 2  is an exploded view of the ball screw in accordance with the present invention; 
         FIG. 3  is a front view illustrating how the screw cooperates with the return assemblies to allow for passage of the rolling assembly in accordance with the present invention; 
         FIG. 4  is a front view of the return assembly in accordance with the present invention; 
         FIG. 5  is a side view of the return assembly in accordance with the present invention; 
         FIG. 6  is an exploded view of the two return elements of the return assembly in accordance with the present invention; 
         FIG. 7  is a perspective view illustrating how the screw cooperates with the first return elements of the two return assemblies in accordance with the present invention; 
         FIG. 8  is a perspective view illustrating how the rolling assembly twists along the return passage in accordance with the present invention; and 
         FIG. 9  is a plane view of a circulation path of a conventional ball screw. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will be clearer from the following description when viewed together with the accompanying drawings, which show, for purpose of illustrations only, the preferred embodiment in accordance with the present invention. 
     Referring to  FIGS. 1-3 , a ball screw in accordance with the present invention comprises a screw  10 , a nut  20 , two return assemblies  30  and a rolling assembly  40 . 
     The screw  10  is provided with a screw helical rolling groove  11  in an outer circumferential surface thereof and a screw thread  12  defined by the screw helical groove  11 . 
     The nut  20  is provided with an insertion hole  21  for insertion of the screw  10 , and the insertion hole  21  is provided with a nut helical rolling groove  22  in its inner circumferential surface opposite the screw helical rolling groove  11 , and a nut thread  23  defined by the nut helical rolling groove  22 . The screw rolling groove  11  and the nut rolling groove  22  cooperate with each to define a loaded path A, and a guiding space B is defined between the screw thread  12  and the nut thread  23 . The nut  20  is provided with a receiving groove  24  in each of two opposite ends thereof and a rolling passage  25  between the two receiving grooves  24 . The receiving grooves  24  are connected to the loaded path A, respectively. 
     The two return assemblies  30  are disposed in the receiving grooves  24 , respectively. As shown in  FIGS. 3-4 , each of the return assemblies  30  is provided with a linking portion  31 , a return portion  32  and a connecting portion  33  in order. Each of the return assemblies  30  is further defined with a linking portion passage  34 , a return portion passage  35  and a connecting portion passage  36  in the linking portion  31 , the return portion  32  and the connecting portion  33 , respectively. One end of the linking portion passage  34  is linked up with the loaded path A, and both ends of the return portion passage  35  are connected to the other end of the linking portion passage  34  and one end of the connecting portion passage  36 , thus defining a return passage C. The other end of the connecting portion passage  36  is connected to the rolling passage  25 . Each of the linking portion passage  34 , the return portion passage  35  and the connecting portion passage  36  is defined with two guiding grooves  340 ,  350 ,  360  in the return passage C. One end of the two guiding grooves  340  of the linking portion passage  34  is linked up with the guiding space B, and then the two guiding grooves  340  will twist an angle, and finally, the other end of the two guiding grooves  340  of the linking portion passage  34  will be linked up to one end of the guiding grooves  350  of the return portion passage  35 . The other end of the guiding grooves  350  of the return portion passage  35  is linked up with the guiding grooves  360  of the connecting portion passage  36 . The guiding grooves  360  of the connecting portion passage  36  will twist an angle relative to the guiding grooves  350  of the return portion passage  35 . The return passage C is linked up with the loaded path A to form a complete circulation path D. 
     The rolling assembly  40  includes a chain  41  and plural rolling elements  42 . As shown in  FIG. 3 , the chain  41  includes plural spacers  410  and two linking portions  411  that are linked together. Each pair of neighboring spacers  410  defines an accommodation space  412  for a rolling element  42 . The linking portions  411  are slidably disposed in the guiding space B and the guiding grooves  340 ,  350  and  360 . 
     Referring to  FIGS. 3-5 , the end of the guiding grooves  340  of the linking portion passage  34  of the return passage C, which is connected with the guiding space B, is denoted by the first point E 1 , and the end, which is connected with the return portion passage  35 , is denoted by the second point E 2 . There is a first angular difference between the first point E 1  and the second point E 2  with respect to the center point of the linking portion passage  34 , and the first angular difference ranges from 80 to 100 degrees, preferably 90 degrees. 
     In the guiding grooves  360  of the connecting portion passage  36  of the return passage C, the end of the guiding grooves  360 , which is connected with the return portion passage  35 , is denoted by the first point F 1 , and the other end of the guiding grooves  360 , which is linked up with the other return assembly  30 , is denoted by the second point F 2 . When the two points are projected on the cross section of the connecting portion passage  36 , there is a second angular difference between the first point F 1  and the second point F 2  with respect to the center of the connecting portion passage  36 , and the angular difference F ranges from 30 to 60 degrees, preferably 45 degrees. 
     Each of the return assemblies  30  includes a first return element  300  and a second return element  301  that are oppositely combined together, as shown in  FIG. 6 . 
     Referring to  FIGS. 7-8 , when the rolling assembly  40  moves within the linking portion passage  34 , the linking portions  411  will be guided to move by the guiding grooves  340  from the first point E 1  to the second point E 2  of the linking portion passage  34 , thus twisting an angle of about 90 degrees that is the first angular difference. After passing through the return portion passage  35  to the connecting portion passage  36 , the rolling assembly  40  will move from the first point F 1  to the second point F 2  of the guiding grooves  360  of the connecting portion passage  36  and thus twist an angle of about 45 degrees that is the second angular difference. By such arrangements, a smooth recirculation is provided. 
     When the screw  10  rotates, the rolling assembly  40  will be synchronously driven to roll within the circulation path D, thus driving the nut  20  to linearly move on the screw  10 . Further, when the rolling assembly  40  rolls to the distal end of the loaded path A, namely entering one of the return assemblies  30 , the rolling assembly  40  will enter one end of the return passage C of the one of the return assemblies  30  and then roll out of the other of the return assemblies  30  to return to the start end of the loaded path A to complete the circulation within the circulation path D. The rolling assembly  40  is moved along the loaded path A, the linking portions will move along the guiding space B to cooperate with the rotation of the screw  10 . When rolling at the one of the return assemblies  30 , the rolling assembly  40  will enter the guiding grooves  340 ,  350 ,  360 , and twist the angle of the first angular difference E within the linking portion passage  34  to the optimal bending direction, and then the rolling assembly  40  will smoothly pass through the return portion passage  35  to the connecting portion passage  36 . After that, the rolling assembly  40  will twist the angle of the second angular difference F within the connecting portion passage  36  and then enter the other of the return assemblies  30 . Subsequently, the rolling assembly  40  will also twist the angle of the second angular difference F within the connecting portion passage  36  of the other of the return assemblies  30  and then pass through the return portion passage  35  to the linking portion passage  34 , and finally the rolling assembly  40  will also twist the angle of the first angular difference E within the linking portion passage  34  and then return to the loaded path, thus completing a circulation. 
     Based on a further analysis of the structure of the preferred embodiment of the present invention, it can be found that the present invention has the following advantages: 
     1. Avoiding improper bending failure: when the rolling assembly  40  is rolling within the circulation path defined by the screw  10 , the nut  20  and the two return assemblies  30 , the rolling assembly  40  will twist the angle of the first angular difference E within the linking portion passage  34  of the return passage C of one of the return assemblies  30  through the guiding of the guiding grooves  340 , and then the rolling assembly  40  will bend in the bendable direction to smoothly pass through the return portion passage  35 , thus avoiding the serious deformation to avoid improper bending failure. 
     2. Reducing interference and improper collision: since the guiding grooves  350  of the return portion passage  35  is provided to make the rolling assembly  40  avoid passing the arc routes defined by the smallest and biggest radius of the return portion passage  35 , the linking portions  411  of the rolling assembly  40  can bend in the bendable direction, therefore, the linking portions  411  at the two sides of the rolling assembly  40  will share the load evenly to be synchronously stretched and extruded, thus avoiding the improper deformation of the overall rolling assembly  40 , and the rolling elements  42  will be kept rolling along the optimal path, thus avoiding the improper collision and interference with the return passage C and the return elements to reduce the integral damage and the noise to the lowest. 
     3. Continuous guiding to form a complete recirculation: besides the above guiding design, the rolling assembly  40  further utilizes the first angular difference E design and the second angular difference F design to twist within the two return assemblies  30  to make the linking portions  411  to bend in the bendable direction to avoid bending excessively within the serious deformation zone, thus forming a complete recirculation path to reduce the interference to the lowest for making the rolling assembly  40  roll within the return passage C more smoothly. 
     While we have shown and described various embodiments in accordance with the present invention, it is clear to those skilled in the art that further embodiments may be made without departing from the scope of the present invention.