Patent Publication Number: US-2023158691-A1

Title: Joint device for robot

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a by-pass continuation application of International Application No. PCT/KR2021/008360, filed on Jul. 1, 2021, which is based on and claims priority to Korean Patent Application No. 10-2020-0093748, filed on Jul. 28, 2020, and Korean Patent Application No. 10-2020-0122546, filed on Sep. 22, 2020, in the Korean Intellectual Property Office, the disclosures of which are incorporated by reference herein in their entireties. 
    
    
     BACKGROUND 
     1. Field 
     The disclosure relates to a joint device for a robot, and more particularly, to a joint device for a robot having two-directional degrees of freedom of rotation using friction wheels. 
     2. Description of Related Art 
     A joint structure used in a robot may be manufactured in such a manner that a plurality of rotation shafts are sequentially combined. Specifically, a joint for a robot has a series structure in which a motor is directly connected to each rotation shaft, a link structure in which a heavy motor is concentrated to a lower end of a mechanism using a wire or a link, or an interference drive structure in which a plurality of degrees of freedom are connected in parallel. 
     The interference drive structure is widely used as a joint structure for a robot because a weight can be efficiently distributed by disposing a drive source near an upper shaft, a structure is simple, and modularization can be made in units of shafts. 
     In the related art, interference drive structures mainly use bevel gears or wires. However, in a case where a bevel gear is used, there are problems in that the gear needs to be machined with high precision, the production cost is very high, and it is difficult to support a load in an axial direction. In addition, when a wire is used, there are problems in that a degree of difficulty is high in terms of assembly and maintenance, and the volume of the entire structure increases because the wire needs to have a radius of curvature having a specific value or more. 
     SUMMARY 
     Provided is a joint device for a robot having two-directional degrees of freedom of rotation using friction wheels. 
     According to an aspect of the disclosure, a joint device for a robot, includes: a first shaft; a second shaft disposed perpendicular to the first shaft; a first friction wheel rotatably supported by a first end of the first shaft; a second friction wheel rotatably supported by a second end of the first shaft; a driving device configured to rotate each of the first friction wheel and the second friction wheel; and a third friction wheel rotatably supported by a first end of the second shaft, and contacting the first friction wheel and the second friction wheels, wherein when the first friction wheel and the second friction wheel rotate in the same direction, the third friction wheel rotates in a pitch direction, and when the first friction wheel and the second friction wheel rotate in different directions, the third friction wheel rotates in a roll direction. 
     Each of the first friction wheel, the second friction wheel, and the third friction wheel may have a truncated cone shape, and 
     a side surface of the third friction wheel contacts a side surface of each of the first friction wheel and the second friction wheel. 
     The third friction wheel may contact the first friction wheel along a first line, the third friction wheel may contact the second friction wheel along a second line, and the first line and the second line may intersect at an intersection between a central axis of the first shaft and a central axis of the second shaft. 
     The joint device may further include: a first pressing member pressing the first friction wheel toward the third friction wheel; and a second pressing member pressing the second friction wheel toward the third friction wheel. 
     Each of the first pressing member and the second pressing member may include a disk spring fitted on the first shaft. 
     The joint device may further include: a first nut fitted at the first end of the first shaft to support an end of the first pressing member; and a second nut fitted at the second end of the first shaft to support an end of the second pressing member. 
     The joint device may further include: a first bearing interposed between the first shaft and the first friction wheel; and a second bearing interposed between the first shaft and the second friction wheel. 
     Each of the first bearing and the second bearing may be an angular ball bearing. 
     The joint device may further include: a first pressing member pressing the first friction wheel toward the third friction wheel; and a second pressing member pressing the second friction wheel toward the third friction wheel, the first bearing may include an inner ring that contacts the first pressing member, and an outer ring that contacts the first friction wheel, and the second bearing member includes an inner ring that contacts the second pressing member, and an outer ring that contacts the second friction wheel. 
     The first pressing member may have a convex shape toward the inner ring of the first bearing, and the second pressing member may have a convex shape toward the inner ring of the second bearing. 
     The driving device may include: a first motor configured to rotate the first friction wheel; and a second motor configured to rotate the second friction wheel. 
     The driving device may further include: a first pulley coupled to the first friction wheel; a second pulley coupled to the second friction wheel; a first timing belt configured to provide a driving force of the first motor to the first pulley; and a second timing belt configured to provide a driving force of the second motor to the second pulley. 
     The joint device may further include: a fourth friction wheel rotatably supported by a second end of the second shaft, the second shaft intersecting the first shaft, and the fourth friction wheel may contact each of the first friction wheel and the second friction wheel. 
     The joint device may further include: a frame rotatably supporting the first end and the second end of the first shaft. 
     The first shaft and the second shaft may be integrally formed, when the first friction wheel and the second friction wheel rotate in the same direction, the first shaft, the second shaft, and the third friction wheel may rotate around the first shaft, and when the first friction wheel and the second friction wheel rotate in different directions, the third friction wheel may rotate around the second shaft. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a perspective view of a joint device for a robot according to an embodiment of the disclosure; 
         FIG.  2    is an exploded perspective view of the joint device for the robot of  FIG.  1   ; 
         FIG.  3    is an exploded perspective view of components fitted on a first shaft; 
         FIG.  4    is a cross-sectional view taken along line A-A of the joint device for the robot of  FIG.  1   ; 
         FIG.  5    is a view illustrating a state in which a third friction wheel rotates in a roll direction; and 
         FIG.  6    is a view illustrating a state in which the third friction wheel rotates in a pitch direction. 
     
    
    
     DETAILED DESCRIPTION 
     It should be understood that embodiments to be described below are exemplarily provided to help the understanding of the disclosure, and the disclosure may be modified in various ways, unlike the embodiments described herein. However, in the following description of the disclosure, if it is determined that a detail description of a related known function or component may unnecessarily obscure the gist of the disclosure, the detailed description and concrete illustration thereof will be omitted. Further, the accompanying drawings are not necessarily illustrated to scale but dimensions of some components may be exaggerated to help the understanding of the disclosure. 
     The terms used in the specification and the claims are general terms selected in consideration of functions in the disclosure. However, these terms may vary depending on intentions of those skilled in the art, legal or technical interpretation, emergence of new technologies, and the like. Also, some terms may be arbitrarily selected by the applicant. These terms may be construed as meanings defined in the specification, and may be construed based on the entire text of the specification and the common technical knowledge in the art unless specifically defined. 
     In the specification, the expressions “have”, “may have”, “include”, “may include”, and the like indicate the presence of stated features (e.g., numbers, functions, operations, or components such as parts), but do not preclude the presence or additional features. 
     In addition, in the specification, components required for describing each embodiment of the disclosure are described, and the components are not necessarily limited thereto. Therefore, some components may be changed or omitted and other components may be added. In addition, components may be arranged in different independent devices in a distributed manner. 
     Furthermore, embodiments of the disclosure will hereinafter be described in detail with reference to the accompanying drawings and contents described in the accompanying drawings, but the disclosure is not limited or restricted by the embodiments. 
     Hereinafter, the disclosure will be described in more detail with reference to the accompanying drawings. 
       FIG.  1    is a perspective view of a joint device for a robot according to an embodiment of the disclosure.  FIG.  2    is an exploded perspective view of the joint device for the robot of  FIG.  1   .  FIG.  3    is an exploded perspective view of components fitted on a first shaft.  FIG.  4    is a cross-sectional view taken along line A-A of the joint device for the robot of  FIG.  1   . 
     Referring to  FIGS.  1  to  4   , a joint device  1  for a robot according to an embodiment of the disclosure may include a first shaft  100 , a second shaft  200 , a first friction wheel  300 , a second friction wheel  400 , a third friction wheel  500 , and a driving device  600 . 
     The first shaft  100  may rotatably support the first friction wheel  300  and the second friction wheel  400  at opposite ends of the first shaft  100 , respectively. Accordingly, the first and second friction wheels  300  and  400  may rotate around the first shaft  100  with the same rotation axis. 
     The first shaft  100  may be disposed parallel to a Y axis. That is, the rotation axis of the first and second friction wheels  300  and  400  may be parallel to the Y axis. The first shaft  100  may have a cylindrical shape. 
     The second shaft  200  may rotatably support the third friction wheel  500  at one end of the second shaft  200 . Accordingly, the third friction wheel  500  may rotate around the second shaft  200 . 
     The second shaft  200  may be disposed perpendicular to the first shaft  100 . For example, the second shaft  200  may be disposed parallel to an X axis. That is, a rotation axis of the third friction wheel  500  may be parallel to the X axis. Like the first shaft  100 , the second shaft  200  may have a cylindrical shape. 
     The second shaft  200  may be integrally formed with the first shaft  100 . Specifically, the first and second shafts  100  and  200  may together form an integral shaft having a “T” or “X” shape to rotatably support the first, second, and third friction wheels  300 ,  400 , and  500 . However, the first and second shafts  100  and  200  may be formed separately, rather than integrally formed. 
     The first friction wheel  300  and the second friction wheel  400  may rotate in a state where they are fitted on the first shaft  100 . The first and second friction wheels  300  and  400  may have a truncated cone shape. 
     The first and second friction wheels  300  and  400  may be arranged to be symmetric with respect to the second shaft  200 . Specifically, the first and second friction wheels  300  and  400  may be disposed to have a cross section that becomes smaller as being closer to the second shaft  200 . 
     The third friction wheel  500  may rotate in a state where they are fitted on the second shaft  200 . The third friction wheel  500  may have a truncated cone shape. Specifically, the third friction wheel  500  may be disposed to have a cross section that becomes smaller as being closer to the first shaft  100 . 
     The third friction wheel  500  may contact the first and second friction wheels  300  and  400  simultaneously at different positions. Accordingly, the third friction wheel  500  may be passively rotated by a rotational force transferred from the first and second friction wheels  300  and  400  due to a frictional force generated in portions contacting the first and second friction wheels  300  and  400 . 
     The first, second, and third friction wheels  300 ,  400 , and  500  may be formed of aluminum, but their material is not limited thereto. Accordingly, it is possible to reduce the weight of the joint device  1  for the robot and lower the overall specifications of the joint device  1  for the robot. 
     In addition, the first, second, and third friction wheels  300 ,  400 , and  500  may smoothly rotate without noise because they continuously contact each other without teeth formed on their surfaces, which does not cause backlash. In addition, the first, second, and third friction wheels  300 ,  400 , and  500  may be produced at a lower cost than gears, and may require fewer parts than wires, thereby reducing maintenance costs. 
     Specifically, a side surface of the third friction wheel  500  may simultaneously contact respective side surfaces of the first and second friction wheels  300  and  400 . Specifically, the third friction wheel  500  may contact the first friction wheel  300  along a first line L 1 , and contact the second friction wheel  400  along a second line L 2 . Also, the first and second lines L 1  and L 2  may intersect at an intersection between central axes C 1  and C 2  of the first and second shafts  100  and  200 . 
     When the first and second friction wheels  300  and  400  rotate in the same direction, the third friction wheel  500  may rotate in a pitch direction because the third friction wheel  500  receives a frictional force from the first and second friction wheels  300  and  400  in the same direction. The pitch direction may be a direction of rotation with respect to a rotation axis parallel to the Y axis. 
     When the first and second friction wheels  300  and  400  rotate in opposite directions, the third friction wheel  500  may rotate in a roll direction because the third friction wheel  500  receives a frictional force from the first and second friction wheels  300  and  400  in different directions. The roll direction may be a direction of rotation with respect to a rotation axis parallel to the X axis. 
     That is, the third friction wheel  500  may be passively rotated by a rotational force transferred from the first and second friction wheels  300  and  400 , and may have two degrees of freedom of rotation depending on the rotation directions of the first and second friction wheels  300  and  400 . A process in which the third friction wheel  500  rotates based on the two degrees of freedom of rotation will be described in detail with reference to  FIGS.  5  and  6   . 
     A connection plate  510  may be disposed on a front surface of the third friction wheel  500 . The connection plate  510  may have a disk shape and may be coupled to the third friction wheel  500  to rotate integrally with the third friction wheel  500 . 
     Any one of various robot structures may be coupled to the connection plate  510 . For example, any one of various parts of the robot, such as an arm, a hand, a foot, a leg, and a head, may be coupled to the connection plate  510  to rotate together with the third friction wheel  500 . 
     Bearings  501  and  502  may be disposed between the third friction wheel  500  and the second shaft  200 . Although the two bearings  501  and  502  are illustrated, the number of bearings is not limited thereto. 
     The bearings  501  and  502  may be angular ball bearings, but the bearing type is not limited thereto. The bearings  501  and  502  enables the third friction wheel  500  to easily rotate relative to the second shaft  200 , which is stationary. 
     The driving device  600  may rotate each of the first and second friction wheels  300  and  400 . For example, the driving device  600  may include a first motor  610  and a second motor  620 . The first motor  610  may rotate the first friction wheel  300 , and the second motor  620  may rotate the second friction wheel  400 . 
     The first and second motors  610  and  620  may be supported by a frame  700 , and may be positioned behind the first, second, and third friction wheels  300 ,  400 , and  500 . 
     For example, the driving device  600  may further include a first pulley  630 , a second pulley  640 , a first timing belt  650 , and a second timing belt  660 . 
     The first and second pulleys  630  and  640  may be fitted on the first shaft  100  to rotate around the first shaft  100 . The first pulley  630  may be disposed on a rear surface of the first friction wheel  300 , and the second pulley  640  may be disposed at a rear surface of the second friction wheel  400 . 
     The first timing belt  650  may partially surround a circumference of the first pulley  630  to provide a driving force of the first motor  610  to the first pulley  630 . In addition, the first pulley  630  may be coupled to the first friction wheel  300  to rotate integrally with the first friction wheel  300 . 
     Similarly, the second timing belt  660  may partially surround a circumference of the second pulley  640  to provide a driving force of the second motor  620  to the second pulley  640 , and the second pulley  640  may be coupled to the second friction wheel  400  to rotate integrally with the second friction wheel  400 . 
     However, the above-described structure of the driving device  600  is an example, and the structure of the driving device  600  is not limited thereto. The driving device  600  may be implemented in any structure as long as it is capable of rotating the first and second friction wheels  300  and  400 . 
     The joint device  1  for the robot may further include a first pressing member  310  and a second pressing member  410 . The first pressing member  310  may press the first friction wheel  300  toward the third friction wheel  500 . The second pressing member  410  may press the second friction wheel  400  toward the third friction wheel  500 . 
     As a result, the first and second pressing members  310  and  410  provide a pre-load to the first and second friction wheels  300  and  400 , thereby providing a sufficient frictional force to the third friction wheel  500 . Accordingly, a rotational force of the first and second friction wheels  300  and  400  may be easily transferred to the third friction wheel  500 . 
     For example, the first and second pressing members  310  and  410  may be disk springs fitted on the first shaft  100 . The disc springs are capable of pressurize the first and second friction wheels  300  and  400 , respectively, with a large elastic force even with a small displacement. Accordingly, the rotational force of the first and second friction wheels  300  and  400  can be more effectively transferred to the third friction wheel  500 , so that the joint device  1  for the robot can be manufactured in a small size. 
     The joint device  1  for the robot may further include a first nut  320  and a second nut  420 . The first nut  320  may be fitted at one end of the first shaft  100  to support one end of the first pressing member  310 . The second nut  420  may be fitted at the other end of the first shaft  100  to support one end of the second pressing member  410 . 
     For example, the first and second nuts  320  and  420  may be fixed by screw threads formed on side surfaces of the first shaft  100 . The pre-load of the first and second pressing members  310  and  410  may be adjusted depending on how much the first and second nuts  320  and  420  are tightened on the first shaft  100 . 
     The joint device  1  for the robot may further include a first bearing  330  and a second bearing  430 . The first bearing  330  may be disposed between the first shaft  100  and the first friction wheel  300 . The second bearing  430  may be disposed between the first shaft  100  and the second friction wheel  400 . 
     The first and second bearings  330  and  430  enable the first and second friction wheels  300  and  400  to easily rotate relative to the first shaft  100 , which is stationary. 
     The first and second bearings  330  and  430  may be angular ball bearings, each being capable of transferring an axial-directional load in an easier way. The angular ball bearing is capable of transferring a load in an axial direction as well as in a radial direction in an easy way because a straight line connecting contact points between a ball and inner and outer rings forms a predetermined angle with respect to the radial direction. 
     Accordingly, the first bearing  330  makes it possible to more easily transfer an elastic force transferred from the first pressing member  310  to the first friction wheel  300 . Similarly, the second bearing  430  makes it possible to more easily transfer an elastic force from the second pressing member  410  to the second friction wheel  400 . 
     Specifically, the inner ring  331  and the outer ring  333  of the first bearing  330  may contact the first pressing member  310  and the first friction wheel  300 , respectively. Accordingly, an elastic force of the first pressing member  310  may be transferred sequentially through the inner ring  331 , the ball  332 , and the outer ring  333  of the first bearing  330 , and finally transferred to the first friction wheel  300 . 
     Similarly, the inner ring  431  and the outer ring  433  of the second bearing  430  may contact the second pressing member  410  and the second friction wheel  400 , respectively. Accordingly, an elastic force of the second pressing member  410  may be transferred sequentially through the inner ring  431 , the ball  432 , and the outer ring  433  of the second bearing  430 , and finally transferred to the second friction wheel  400 . 
     That is, the first and second pressing members  310  and  410  may press the inner rings  331  and  431  of the first and second bearings  330  and  430 , which are stationary together with the first shaft  100 . Accordingly, since the objects pressed by the first and second pressing members  310  and  410  are stationary, it is possible to minimize wear resulting from friction. 
     In addition, the first and second pressing members  310  and  410  may have a convex shape toward the inner rings  331  and  431  of the first and second bearings  330  and  430 . For example, the first and second pressing members  310  and  410  may be cone-shaped disk springs each having an opening in a central portion. 
     Accordingly, the above-described shape of the first and second pressing members  310  and  410  makes it possible to press only the inner rings  331  and  431 , which are stationary, not the outer rings  333  and  433 , which are rotating, respectively. 
     The frame  700  may be disposed on a rear side of the joint device  1  for the robot to support the first shaft  100  and the driving device  600 . However, this is an example, and the shape and the arrangement of the frame  700  are not limited thereto. 
     In addition, the joint device  1  for the robot may further include a fourth friction wheel  800 . The fourth friction wheel  800  may be rotatably supported at the other end of the second shaft  200  intersecting the first shaft  100 . 
     The fourth friction wheel  800  may contact each of the first and second friction wheels  300  and  400 . For example, the fourth friction wheel  800  may have a truncated cone shape, and a side surface of the fourth friction wheel  800  may contact the side surfaces of the first and second friction wheels  300  and  400  simultaneously at different positions. 
     The fourth friction wheel  800  may have a shape to be symmetric to the third friction wheel  500  with respect to the first shaft  100 . Specifically, the fourth friction wheel  800  may have a truncated cone shape with a cross section gradually decreasing toward the first shaft  100 . 
     The fourth friction wheel  800  may face the third friction wheel  500 , and may rotate in the opposite direction to the third friction wheel  500 . 
     In addition, the fourth friction wheel  800  may support an area of each of the first and second pressing members  310  and  410  on the rear side thereof. Accordingly, the fourth friction wheel  800  may prevent the first and second friction wheels  300  and  400  from being deformed or the rotational axis of the first and second friction wheels  300  and  400  from being misaligned due to the elastic force of the first and second pressing members  310  and  410 . 
       FIG.  5    is a view illustrating a state in which the third friction wheel rotates in the roll direction. Referring to  FIG.  5   , the first and second friction wheels  300  and  400  may rotate in different directions. 
     For example, when the first friction wheel  300  rotates in an R 1  direction and the second friction wheel  400  rotates in an R 2  direction, the third friction wheel  500  rotates around the second shaft  200  in an R 4  direction. At this time, the fourth friction wheel  800  may rotate around the second shaft  200  in an R 3  direction as opposed to the third friction wheel  500 . 
     Conversely, when the first friction wheel  300  rotates in the R 2  direction and the second friction wheel  400  rotates in the R 1  direction, the third friction wheel  500  may rotate around the second shaft  200  in the R 3  direction. At this time, the fourth friction wheel  800  may rotate around the second shaft  200  in the R 4  direction as opposed to the third friction wheel  500 . 
     That is, when the first and second friction wheels  300  and  400  rotate in different directions, the third friction wheel  500  may rotate around the second shaft  200  in the roll direction. 
       FIG.  6    is a view illustrating a state in which the third friction wheel rotates in a pitch direction. Referring to  FIG.  6   , the first and second friction wheels  300  and  400  may rotate in the same direction. 
     For example, when both the first and second friction wheels  300  and  400  rotate in the R 1  direction, the third friction wheel  500  may rotate around the first shaft  100  in the R 1  direction. At this time, the fourth friction wheel  800  may rotate around the first shaft  100  in the R 2  direction as opposed to the third friction wheel  500 . 
     Conversely, when both the first and second friction wheels  300  and  400  rotate in the R 2  direction, the third friction wheel  500  may also rotate around the first shaft  100  in the R 2  direction. At this time, the fourth friction wheel  800  may rotate around the first shaft  100  in the R 1  direction as opposed to the third friction wheel  500 . 
     Specifically, the frame  700  may rotatably support both ends of the first shaft  100 , and the first and second shafts  100  and  200  may be integrally formed. In this case, when the first and second friction wheels  300  and  400  rotate in the same direction, the first shaft  100 , the second shaft  200 , and the third friction wheel  500  may rotate around the first shaft  100  in the R 1  or R 2  direction. 
     That is, when the first and second friction wheels  300  and  400  rotate in the same direction, the third friction wheel  500  may rotate around the first shaft  100  in the pitch direction. 
     Accordingly, the third friction wheel  500  may be passively rotated with two degrees of freedom of rotation depending on the rotation directions of the first and second friction wheels  300  and  400 . 
     Although embodiments of the disclosure have been illustrated and described, the disclosure is not limited to the specific embodiments as described above, and may be variously modified by those skilled in the art to which the disclosure pertains without departing from the gist of the disclosure as claimed in the appended claims. Such modifications fall within the scope of the claims.