Patent Publication Number: US-2012042740-A1

Title: Linear motion mechanism and robot

Description:
This is a continuation of International Application PCT/JP2010/005178, with an international filing date of Aug. 23, 2010, which is hereby incorporated by reference herein its entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a linear motion mechanism and a robot. 
     BACKGROUND ART 
     As disclosed in Patent literatures 1 and 2, for example, linear motion mechanisms using magnetic joints have been known. In particular, in the linear motion mechanism disclosed in Patent literature 1, a pinion is provided on a rotation shaft from which a blind is suspended and supported. A vertically-disposed rack is engaged with the pinion. An inner-side magnet, which constitutes one part of the magnetic joint, is provided in the rack. An outer-side magnet, which constitutes the other part of the magnetic joint, is disposed so as to be opposed to the inner-side magnet. The outer-side magnet is vertically moved by a drive device. When the outer-side magnet is vertically moved by driving the drive device, the inner-side magnet is magnetically attracted and thereby vertically moved. In this way, the rack is vertically moved and the pinion is thereby rotated. As a result, the rotation shaft rotates and therefore the blind opens/closes. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent literature 1: Japanese Unexamined Patent Application Publication No. 7-91153 
         Patent literature 2: Japanese Patent No. 2635226 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     In the linear motion mechanism disclosed in Patent literature 1, if an excessive load is exerted on the inner-side magnet or on the outer-side magnet, their mutual joint relation is broken. When this happened, it is necessary to perform a readjustment process of the origin point or a similar process to restore the joint relation between the inner-side magnet and the outer-side magnet. Therefore, it requires a complicated process after the joint relation between the inner-side magnet and the outer-side magnet is broken. 
     The present invention has been made to solve such problems, and an object thereof is to provide a linear motion mechanism and a robot in which when the magnetic joint is disengaged, the joint relation of the magnetic joint can be easily restored. 
     Solution to Problem 
     A linear motion mechanism in accordance with the present invention includes: a movable part that receives a reaction force from a guild disposed in one axis direction, and moves along the guide; a sliding part that slides along the guides; a magnetic joint that magnetically joins the movable part to the sliding part; and a restoration member that restores a joint relation between the movable part and the sliding part. In this way, even if the magnetic joint is disengaged, the joint relation of the magnetic joint can be easily restored again by the restoration member. Therefore, in the linear motion mechanism, the joint relation of the magnetic joint can be easily restored. 
     A reaction force transmission part is preferably formed in the sliding part with a space in the one axis direction; the movable part is preferably disposed in the space portion of the reaction force transmission part; and the restoration member is preferably disposed between the reaction force transmission part and the movable part. 
     The linear motion mechanism preferably also includes a restraint mechanism that restrains a rotation of the sliding part around an axis of the guide. 
     As the magnetic joint, a magnet is preferably provided in one of the movable part and the sliding part, a member that is magnetically attracted by the magnet is preferably provided in the other of the movable part and the sliding part; and the magnet and the member that is magnetically attracted by the magnet are preferably disposed so as to be opposed to each other. 
     The magnetic joint is preferably disposed on both sides of the guide. In this way, it is possible to roughly cancel out the forces that would otherwise cause the movable part to move toward the sliding part side due to the joining force of the magnetic joint. 
     The linear motion mechanism preferably also includes an assist mechanism that assists the joint relation between the movable part and the sliding part. In this way, the burden on the magnetic joint can be reduced, and therefore the size of the magnetic joint can be reduced. 
     The linear motion mechanism preferably also includes: a measurement unit that measures a distance in the one axis direction between the movable part and the sliding part; and a control unit that receives a measurement value of the measurement unit, calculates a displacement of the sliding part with respect to the movable part, and when the calculated displacement is equal to or greater than a threshold, stops a movement of the movable part. In this way, the joint relation between the movable part and the sliding part will not be easily disengaged. 
     A robot in accordance with the present invention includes the above-described linear motion mechanism. In this way, even if the magnetic joint is disengaged, the joint relation of the magnetic joint can be easily restored again by the restoration member. Therefore, the joint relation of the magnetic joint can be easily restored. 
     Advantageous Effects of Invention 
     In accordance with the present invention, it is possible to provide a linear motion mechanism and a robot in which when a magnetic joint is disengaged, the joint relation of the magnetic joint can be easily restored. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a partial cross-section schematically showing a robot in accordance with a first exemplary embodiment according to the present invention; 
         FIG. 2  is a horizontal cross-section schematically showing a linear motion mechanism in accordance with a first exemplary embodiment according to the present invention; 
         FIG. 3  is a side view schematically showing a part of a linear motion mechanism in accordance with a first exemplary embodiment according to the present invention; 
         FIG. 4  shows a characteristic between a magnetic joint and a restoration member; 
         FIG. 5  is a figure for explaining a displacement of a sliding part with respect to a movable part; 
         FIG. 6  is a block diagram of a control system in a robot in accordance with a first exemplary embodiment according to the present invention; 
         FIG. 7  shows a configuration of a magnetic joint in a linear motion mechanism in accordance with a second exemplary embodiment according to the present invention; 
         FIG. 8  schematically shows a relation between a movable part and a sliding part in a linear motion mechanism in accordance with a third exemplary embodiment according to the present invention; 
         FIG. 9  schematically shows a position of a magnetic joint; 
         FIG. 10  is a front view schematically showing a robot in accordance with a fourth exemplary embodiment according to the present invention; 
         FIG. 11  is a front view schematically showing a robot in accordance with a fifth exemplary embodiment according to the present invention; and 
         FIG. 12  is a block diagram of a control system in a robot in accordance with a fifth exemplary embodiment according to the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Exemplary Embodiment 
     A first exemplary embodiment of a linear motion mechanism and a robot in accordance with the present invention is explained with reference to the drawings. As shown in  FIGS. 1 to 3 , a robot  1  includes a linear motion mechanism  100  and a robot arm  200 . The linear motion mechanism  100  includes a drive mechanism  110 , a sliding part  120 , a magnetic joint  130 , restoration members  140 , and a restraint mechanism  150 . 
     The drive mechanism  110  includes a pedestal  111 , a drive motor  112 , a gear train (not shown), a ball screw nut (guide)  113 , and a movable part  114 . Specifically, the drive motor  112  is mounted on the pedestal  111 . The gear train is housed within the pedestal  111 . The ball screw nut  113  is rotatably supported on the pedestal  111 . That is, the ball screw nut  113  is disposed in a vertical direction. The rotational driving force of the drive motor  112  is transmitted to the ball screw nut  113  through the gear train. 
     The movable part  114  has such a thickness that the movable part  114  is not shaken in the vertical direction when the sliding part  120  is moved by means of the magnetic joint  130 . As shown in  FIG. 1 , a through-hole is formed in the vertical direction in the movable part  114 . A female thread is formed in this through-hole, and serves as a female thread part  1141 . The female thread part  1141  engages with the ball screw nut  113  through a bearing. The movable part  114  includes a first magnetic member (magnet)  131  that constitutes a part of the magnetic joint  130 . 
     The sliding part  120  includes a base part  121  and reaction force transmission parts  122 . The base part  121  supports the robot arm  200 . The side portion on the movable part  114  side in the base part  121  includes the reaction force transmission parts  122 , which are spaced from each other in the vertical direction. The side portion on the movable part  114  side in the base part  121  also includes a second magnetic member (magnet)  132  that constitutes a part of the magnetic joint  130  between the upper and lower reaction force transmission parts  122 . Note that a position at which the second magnetic member  132  of the sliding part  120  is opposed to the first magnetic member  131  of the movable part  114  is defined as the origin point of the sliding part  120 . 
     The reaction force transmission parts  122  protrude from the base part  121  roughly horizontally in roughly the same directions. That is, as shown in  FIG. 2 , the reaction force transmission parts  122  of this exemplary embodiment are disposed in the same plane. One end of each reaction force transmission part  122  is joined to the base part  121 . In the other end, a cut-out portion  1221  is formed. The ball screw nut  113  is housed within this cut-out portion  1221 . The movable part  114  is disposed in the space portion between the vertically-arranged reaction force transmission parts  122 . 
     As shown in  FIG. 1 , the magnetic joint  130  includes the first magnetic member  131  and the second magnetic member  132 . The first magnetic member  131  is disposed in the side portion of the movable part  114  located on the base part  121  side of the sliding part  120 . The second magnetic member  132  is disposed in the side portion of the sliding part  120  located on the movable part  114  side. In this way, when the sliding part  120  is positioned at the origin point, the first magnetic member  131  and the second magnetic member  132  are opposed to each other. The first magnetic member  131  and the second magnetic member  132  exert a magnetic attractive force so that the magnetic joint relation between the sliding part  120  and the movable part  114  is not broken when the robot arm  200  is vertically moved and/or when a load is exerted on the sliding part  120 . 
     Each of the restoration members  140  is an elastic member such as a spring and a rubber. Each of the restoration members  140  is disposed between the movable part  114  and a respective one of the reaction force transmission parts  122  of the sliding part  120 . For example, springs are used as the restoration members  140 , each spring is placed over the ball screw nut  113  between the movable part  114  and a respective one the reaction force transmission parts  122  of the sliding part  120 . The restoration members  140  exert a restoration force that acts to move and return the sliding part  120  to the origin point when the joint relation between the movable part  114  and the sliding part  120  by the magnetic joint  130  is disengaged. 
     As shown in  FIGS. 2 and 3 , the restraint mechanism  150  includes support columns  151  and linear rails  152 . The support columns  151  are disposed on both sides of the ball screw nut  113  as viewed from the top. The height of the support columns  151  is roughly equal to that of the ball screw nut  113 . 
     Each of the linear rails  152  includes a rail  1521  and a slider  1522 . The rail  1521  is disposed on the side of the support column  151  located on the base part  121  side of the sliding part  120 . The slider  1522  is disposed on the side of the base part  121  of the sliding part  120  located on the support column  151  side. The slider  1522  is coupled to the rail  1521  in such a manner that the slider  1522  can move in the axis direction along the rail  1521  and that any displacement in the directions other than the axis direction can be restrained. In this way, it is possible to restrain the rotation of the sliding part  120  around the axis of the ball screw nut  113 . As a result, since the second magnetic member  132  of the sliding part  120  and the first magnetic member  131  of the movable part  114  are magnetically joined to each other, it is also possible to restrain the rotation of the movable part  114  around the axis of the ball screw nut  113 . 
     In the linear motion mechanism  100  having the configuration like this, when the drive motor  112  is driven based on a control signal from a control unit  400  ( FIG. 6 ), the rotational driving force of the drive motor  112  is transmitted to the ball screw nut  113  through the gear train. As a result, the ball screw nut  113  rotates and the movable part  114  moves upward or downward. Then, since the movable part  114  and the sliding part  120  are magnetically joined to each other, the sliding part  120  also moves upward or downward as the movable part  114  moves upward or downward. As a result, the robot arm  200  can be moved to a desired height. In this state, if the magnetic joint  130  is disengaged due to an upward or downward load exerted on the sliding part  120  and the sliding part  120  thereby moves in the direction in which the load is exerted, one of the restoration members  140  disposed above or below the movable part  114  contracts. The contracted restoration member  140  exerts a restoration force that acts to push up or push down the sliding part  120  and thereby restores the magnetic joint relation between the movable part  114  and the sliding part  120 . As a result, the sliding part  120  returns to the origin point. As described above, even when the magnetic joint is disengaged, the linear motion mechanism  100  can restore the joint relation of the magnetic joint  130  again by the restoration member  140 . Therefore, in the linear motion mechanism  100 , the joint relation of the magnetic joint  130  can be easily restored. 
     Note that the magnetic joint  130  and the restoration member  140  are preferably adjusted so that the characteristic shown in  FIG. 4  is satisfied. Specifically, as shown in  FIG. 5 , the displacement of the sliding part  120  with respect to the movable part  114  is represented by “X” and the load exerted on the sliding part  120  is represented by “F”. 
     When the robot arm  200  is moved upward or downward, even if a load larger than the load that is supposed to be exerted on the sliding part  120  is exerted on the sliding part  120 , the joint relation of the magnetic joint  130  is maintained. Then, when the load exerted on the sliding part  120  reaches a certain magnitude, the sliding part  120  is gradually pulled away from the movable part  114  and the joint relation of the magnetic joint  130  is weakened. At this point, as the sliding part  120  is pulled away from the movable part  114 , the load exerted on the sliding part  120  becomes smaller. However, the joint relation of the magnetic joint  130  also becomes smaller. Eventually, as the joint relation becomes almost zero, the restoration force exerted by the restoration member  140  becomes stronger in proportion to the displacement as a substitute for the magnetic joint. 
     The robot arm  200  includes a multi-joint arm part  210  and a hand part  220 . The arm part  210  of this exemplary embodiment includes a first arm  211 , a second arm  212 , and a third arm  213 . One end of the first arm  211  is connected on the top surface of the base part  121  of the sliding part  120 . At the other end of the first arm  211 , one end of the second arm  212  is rotatably connected. At the other end of the second arm  212 , one end of the third arm  213  is rotatably connected. At the other end of the third arm  213 , the hand part  220  is rotatably connected. As shown in  FIG. 6 , these arms include respective drive motors  310 ,  320  and  330  at their connection portions (joint portions). Similarly to typical robot hands, the hand part  220  also includes a drive motor (not shown). In this way, they function as a robot arm  200 . That is, the control unit  400  shown in  FIG. 6  generates a control signal based on a program stored on a storage unit  500  or based on an operation signal from an operation unit  600 , and controls the drive motors  310 ,  320  and  330 , the drive motor of the hand part  220 , and the drive motor  112  and the like of the linear motion mechanism  100  based on the control signal. 
     Second Exemplary Embodiment 
     Although the magnetic joint  130  is composed of the first magnetic member  131  and the second magnetic member  132  in the first exemplary embodiment, the present invention is not limited to this configuration. That is, as shown as a magnetic joint  1300  in  FIG. 7 , the magnetic joint may be composed of a magnetic member  1310  and a member  1320  made of iron or the like that is magnetically attracted by the magnetic member  1310 . In this way, inexpensive iron or the like can be used as a substrate for the magnetic member, thus contributing to the reduction in cost. Note that although the magnetic member  1310  is disposed in the movable part  114  and the member  1320  made of iron or the like is disposed in the sliding part  120  in the magnetic joint  1300  shown in  FIG. 7 , the reversed configuration may be also employed. 
     Third Exemplary Embodiment 
     Although the movable part  114  and the sliding part  120  are magnetically joined to each other by using only one magnetic joint in the first and second exemplary embodiments, the present invention is not limited to this configuration. That is, as shown in  FIGS. 8 and 9 , magnetic joints  2300  are preferably arranged on both sides of the ball screw nut  113 . Similarly to the second exemplary embodiment, each of the magnetic joints  2300  includes a magnetic member  2310  and a member  2320  made of iron or the like. The magnetic members  2310  are arranged in the outer circumferential portion of the movable part  114  so as to sandwich the ball screw nut  113  therebetween. That is, magnetic members  2310  are disposed in a point-symmetrical arrangement with respect to the center of the ball screw nut  113 . The sliding part  120  includes side-wall parts  123  that cover the ball screw nut  113  from the sides. The side-wall parts  123  protrude from the side of the base part  121  located on the movable part  114  side. The members  2320  made of iron or the like are disposed roughly at the center in the vertical direction of the side-wall parts  123 . With the configuration like this, the movable part  114  supports the sliding part  120  from the portions located on both sides of the ball screw nut  113 . Therefore, it is possible to roughly cancel out the forces that would otherwise cause the movable part  114  to move toward the sliding part  120  side due to the joining force of the magnetic joint, and thereby to reduce the frictional wear of the ball screw nut  113 . 
     Fourth Exemplary Embodiment 
     Although the sliding part  120  is supported by the magnetic joint alone in the first to third exemplary embodiments, the present invention is not limited to this configuration. That is, as shown in  FIG. 10 , the sliding part  120  is preferably supported by an assist mechanism  700  such as a gas spring, a gas balancer, and an air cylinder from the bottom of the sliding part  120 . With the configuration like this, the burden on the magnetic joint can be reduced, and therefore the size of the magnetic joint can be reduced. 
     Fifth Exemplary Embodiment 
     Although the first to fourth exemplary embodiments do not adopt such a configuration that the operation of the drive motor  112  is controlled when the displacement of the sliding part  120  with respect to the movable part  114  becomes larger, the present invention is not limited to such configurations. That is, as shown in  FIGS. 11 and 12 , it is preferable to adopt such a configuration that the drive motor  112  is controlled based on the vertical distance L between the movable part  114  and the sliding part  120 . Specifically, in addition to the above-described components, the linear motion mechanism  100  may include a measurement unit  800  such as a range sensor. The measurement unit  800  measures a vertical distance L between the movable part  114  and the sliding part  120 . For example, the measurement unit  800  is disposed on the top surface of the lower reaction force transmission part  122  in the sliding part  120 . The measurement unit  800  measures a distance between the bottom surface of the movable part  114  and the upper surface of the lower reaction force transmission part  122  in the sliding part  120 . The measurement unit  800  outputs the measured measurement value to the control unit  400 . The control unit  400  subtracts the input measurement value from a predefined distance between the bottom surface of the movable part  114  and the upper surface of the lower reaction force transmission part  122  in the sliding part  120  to calculate the displacement of the sliding part  120  with respect to the movable part  114 . Then, when the calculated displacement is equal to or greater than a predetermined threshold, the control unit  400  stops the operation of the drive motor  112 . In short, the load exerted on the sliding part  120  can be associated with the distance L between the movable part  114  and the sliding part  120 . Therefore, it is possible to determine that when the displacement is large, a large load is exerted on the sliding part  120 . Therefore, in this exemplary embodiment, when a large load is exerted on the sliding part  120 , the operation of the drive motor  112  is suspended so that the joint relation with the movable part  114  is not disengaged due to the large load. With the configuration like this, the joint relation between the movable part  114  and the sliding part  120  will not be easily disengaged. 
     Note that the present invention is not limited to the above-described exemplary embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, although the ball screw nut  113  is engaged with the female thread part  1141  of the movable part  114  through a bearing so that the drive mechanism  110  can transmit the rotational driving force in the above-described exemplary embodiments, the present invention is not limited to this configuration. That is, a rack may be used as a substitute for the ball screw nut  113 . By engaging the rack with a pinion gear provided on the rotation shaft of the drive motor mounted on the movable part  114 , the movable part  114  can be vertically moved. In short, any configurations in which the movable part  114  can be moved in one axis direction can be employed. 
     Although the movable part  114  of the linear motion mechanism  100  is disposed so as to move in the vertically direction in the above-described exemplary embodiments, the movable part  114  may be disposed so as to move in the horizontal direction. 
     Although the robot arm  200  is attached to the linear motion mechanism  100  in the above-described exemplary embodiments, the use of the linear motion mechanism  100  is not limited to any particular uses. 
     Although the linear rails are used as the restraint mechanism  150  in the above-described exemplary embodiments, in short, any configurations in which the rotation of the sliding part  120  around the axis of the ball screw nut  113  can be restrained can be employed. 
     INDUSTRIAL APPLICABILITY 
     A linear motion mechanism and a robot in accordance with the present invention can be used as a linear motion mechanism and a robot in which when a magnetic joint is disengaged, the joint relation of the magnetic joint can be easily restored. 
     REFERENCE SIGNS LIST 
     
         
           100  LINEAR MOTION MECHANISM 
           110  DRIVE MECHANISM 
           111  PEDESTAL 
           112  DRIVE MOTOR 
           113  BALL SCREW NUT 
           114  MOVABLE PART 
           1141  FEMALE THREAD PART 
           120  SLIDING PART 
           121  BASE PART 
           122  REACTION FORCE TRANSMISSION PART 
           1221  CUT-OUT PORTION 
           123  SIDE-WALL PART 
           130  MAGNETIC JOINT 
           131  FIRST MAGNETIC MEMBER 
           132  SECOND MAGNETIC MEMBER 
           140  RESTORATION MEMBER 
           150  RESTRAINT MECHANISM 
           151  SUPPORT COLUMN 
           152  LINEAR RAIL 
           1521  RAIL 
           1522  SLIDER 
           200  ROBOT ARM 
           210  ARM PART 
           211  FIRST ARM 
           212  SECOND ARM 
           213  THIRD ARM 
           220  HAND PART 
           310  DRIVE MOTOR 
           400  CONTROL UNIT 
           500  STORAGE UNIT 
           600  OPERATION UNIT 
           700  ASSIST MECHANISM 
           800  MEASUREMENT UNIT 
           1300  MAGNETIC JOINT 
           1310  MAGNETIC MEMBER 
           1320  MEMBER MADE OF IRON OR THE LIKE 
           2300  MAGNETIC JOINT 
           2320  MEMBER MADE OF IRON OR THE LIKE