Patent Publication Number: US-2016221184-A1

Title: Robot

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2015-015703, filed Jan. 29, 2015. The contents of this application are incorporated herein by reference in their entirety. 
     BACKGROUND 
     1. Field of the Invention 
     The embodiments disclosed herein relate to a robot. 
     2. Discussion of the Background 
     Japanese Unexamined Patent Application Publication No. 2003-200376 discloses an industrial robot that includes a base, a turnable portion, a lower arm, and an upper arm. The turnable portion turns about an S axis relative to the base. The lower arm swings about an L axis relative to the turnable portion. The upper arm swings about a U axis relative to the lower arm. The lower arm operates by a motor that is coaxial with the L axis, and the upper arm operates by a motor that is coaxial with the U axis. 
     SUMMARY 
     According to one aspect of the present disclosure, a robot includes a base, a first arm, a second arm, a first motor, and a second motor. The first arm is disposed on the base and swingable about a first axis parallel to an installation surface on which the base is installed. The second arm is disposed on the first arm and swingable about a second axis parallel to the first axis. The first motor is configured to move the first arm about the first axis relative to the base. The first motor includes a first body and a first protrusion. The first body has an axial dimension in a direction along an output shaft of the first motor and a perpendicular dimension in a direction approximately perpendicular to the output shaft of the first motor. The axial dimension is smaller than the perpendicular dimension. The first protrusion protrudes from a surface of the first body in a direction along the output shaft of the first motor and is disposed at a position displaced from the output shaft of the first motor. The second motor is configured to move the second arm about the second axis relative to the first arm. The second motor includes a second body and a second protrusion. The second body has an axial dimension in a direction along an output shaft of the second motor and a perpendicular dimension in a direction approximately perpendicular to the output shaft of the second motor. The axial dimension is smaller than the perpendicular dimension. The second protrusion protrudes from a surface of the second body in a direction along the output shaft of the second motor and is disposed at a position displaced from the output shaft of the second motor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the present disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1  is a perspective view of a robot according to an embodiment; 
         FIG. 2  is a side view of the robot illustrated in  FIG. 1 ; 
         FIG. 3  is a rear view of the robot illustrated in  FIG. 1 ; 
         FIG. 4  illustrates the robot illustrated in  FIG. 3  with some elements taken away; 
         FIG. 5  illustrates a positional relationship between a motor and a cable in relation to a movement of a first arm; 
         FIG. 6  illustrates a positional relationship between the motor and the cable in relation to a movement of the first arm; 
         FIG. 7  illustrates a positional relationship between the motor and the cable in relation to a movement of the first arm; 
         FIG. 8  illustrates a positional relationship between a motor and the cable in relation to a movement of a second arm; 
         FIG. 9  illustrates a positional relationship between the motor and the cable in relation to a movement of the second arm; 
         FIG. 10  illustrates a positional relationship between the motor and the cable in relation to a movement of the second arm; 
         FIG. 11  is a perspective view of the motor illustrating an external appearance of the motor; and 
         FIG. 12  is a cross-sectional view of the motor. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     The embodiments will now be described with reference to the accompanying drawings, wherein like reference numerals designate corresponding or identical elements throughout the various drawings. 
     Configuration of Robot 
       FIG. 1  is a perspective view of a robot according to this embodiment on which a motor is mountable.  FIG. 2  is a side view of the robot illustrated in  FIG. 1 .  FIG. 3  is a rear view of the robot illustrated in  FIG. 1 .  FIG. 4  illustrates the robot illustrated in  FIG. 3  with some elements taken away.  FIGS. 5 to 7  illustrate positional relationships between a motor and a cable in relation to movements of a first arm.  FIGS. 8 to 10  illustrate positional relationships between a motor and the cable in relation to movements of a second arm. The robot,  1 , illustrated in the drawings is an industrial robot that works on workpieces, not illustrated. 
     As illustrated in  FIGS. 1 to 4 , the robot  1  includes a base  3 , a turnable portion  5 , a first arm (first arm)  7 , a second arm (second arm)  9 , and an end base  11 . The base  3 , the turnable portion (base)  5 , the first arm  7 , the second arm  9 , and the end base  11  are coupled to each other in this order from the base end of the robot  1  to the distal end of the robot  1 . The robot  1  is supplied power and other sources of energy for the robot  1 &#39;s electrical components through a cable C. 
     The base  3  is fixed to an installation surface and supports the entire robot  1 . 
     The turnable portion  5  is disposed on the base  3 . The turnable portion  5  is turnable about a turning axis, namely, a first axis Ax 1 , which extends in the vertical direction, relative to the base  3 . The turnable portion  5  is driven into turning operation about the first axis Ax 1  by a power source, namely, a first motor (not illustrated), which is accommodated in the turnable portion  5 . The first axis Ax 1  will be occasionally referred to as “S axis”. 
     The first arm  7  is swingable about a swing axis, namely, a second axis Ax 2  (corresponding to the first axis recited in the appended claims) relative to the turnable portion  5 . The second axis Ax 2  passes through a connection portion  6  (the end of the first arm  7  on the side of the turnable portion  5 ), at which the turnable portion  5  and the first arm  7  are coupled to each other. The first arm  7  includes a first arm member  7   a  and a second arm member  7   b . The first arm member  7   a  and the second arm member  7   b  extend and face each other at a predetermined distance in a direction along the second axis Ax 2 . The connection portion  6 , at which the turnable portion  5  and the first arm  7  are coupled to each other, is equipped with a second motor (corresponding to the first motor recited in the appended claims) M 2  ( 20 ). 
     The first arm  7  is driven by a power source, namely, the second motor M 2 , into swing operation about the second axis Ax 2 . Specifically, as illustrated in  FIG. 6 , the first arm  7  is swingable in a first direction D 1  (frontward) up to a first swing angle θ 1  relative to a first reference line LS 1 . The first reference line LS 1  is in a direction approximately perpendicular to the installation surface and passes through the second axis Ax 2 . As illustrated in  FIG. 7 , the first arm  7  is also swingable relative to the first reference line LS 1  in a second direction D 2  (rearward), which is opposite to the first direction D 1 , up to a second swing angle θ 2 . The second swing angle θ 2  is smaller than the first swing angle θ 1  (θ 1 &gt;θ 2 ). The second axis Ax 2  will be occasionally referred to as “L axis”. 
     The second arm  9  includes a base end  9   a  and a distal end  9   b . The base end  9   a  is on the side of the first arm  7 , and the distal end  9   b  is on the side of the end base  11 . The base end  9   a  is swingable about a swing axis, namely, a third axis Ax 3  (corresponding to the second axis recited in the appended claims) relative to the first arm  7 . The third axis Ax 3  passes through a connection portion  10  (the end of the first arm  7  on the side of the base end  9   a ), at which the first arm  7  and the second arm  9  are coupled to each other. This configuration makes the second arm  9  as a whole swingable about the third axis Ax 3  relative to the first arm  7 . The connection portion  10 , at which the first arm  7  and the second arm  9  are coupled to each other, is equipped with a third motor (the second motor recited in the appended claims) M 3  ( 20 ). 
     The second arm  9  (base end  9   a ) is driven by a power source, namely, the third motor M 3 , into swing operation about the third axis Ax 3 . As illustrated in  FIG. 9 , the second arm  9  is swingable in the first direction D 1  up to a first swing angle θ 3  relative to a second reference line LS 2 . The second reference line LS 2  is in the direction approximately perpendicular to the installation surface and passes through the third axis Ax 3 . As illustrated in  FIG. 10 , the second arm  9  is also swingable relative to the second reference line LS 2  in the second direction D 2 , which is opposite to the first direction D 1 , up to a second swing angle θ 4 . The second swing angle θ 4  is smaller than the first swing angle θ 3 . The third axis Ax 3  extends in parallel to the second axis Ax 2 . The third axis Ax 3  will be occasionally referred to as “U axis”. 
     The distal end  9   b  is turnable about a turning axis, namely, a fourth axis Ax 4 , relative to the base end  9   a . The fourth axis Ax 4  passes through the center of the second arm  9 . The distal end  9   b  is driven by a power source, namely, a fourth motor, into turning operation about the fourth axis Ax 4 . The fourth axis Ax 4  will be occasionally referred to as “R axis”. 
     The end base  11  includes a base end  11   a  and a distal end  11   b . The base end  11   a  is on the side of the second arm  9 , and the distal end  11   b  is on the side of the distal end of the robot  1 . The base end  11   a  is swingable about a swing axis, namely, a fifth axis Ax 5  relative to the distal end  9   b . The fifth axis Ax 5  passes through a connection portion at which the second arm  9  (distal end  9   b ) and the end base  11  (base end  11   a ) are coupled to each other. The base end  11   a  is driven by a power source, namely, a fifth motor, into swing movement about the fifth axis Ax 5 . The fifth axis Ax 5  will be occasionally referred to as “B axis”. 
     The distal end  11   b  is mounted on the base end  11   a  in a rotatable manner about a rotation axis, namely, a sixth axis Ax 6 , relative to the base end  11   a . The sixth axis Ax 6  passes through the center of the end base  11 . The distal end  11   b  is driven by a power source, namely, a sixth motor, into rotational movement about the sixth axis Ax 6 . The sixth axis Ax 6  will be occasionally referred to as “T axis”. An end effector is attachable to the end base  11 . A non-limiting example of the end effector is a welding torch. 
     Configurations of Motors 
     Next, the first to sixth motors provided in the robot  1  will be described in detail. The first to sixth motors have similar configurations and may hereinafter occasionally be referred to as “motor  20 ” collectively.  FIG. 11  is a perspective view of the motor illustrating an external appearance of the motor  20 .  FIG. 12  is a cross-sectional view of the motor  20 . As illustrated in  FIGS. 11 and 12 , the motor  20  (M 2 , M 3 ) includes a casing (body)  30 , a rotor  40 , a stator  50 , an encoder  60 , and a brake (protrusion)  70 . 
     The casing  30  holds elements such as the rotor  40 , the stator  50 , and the encoder  60 . In this embodiment, the casing  30  has a circular outer shape. The casing  30  includes a first surface  30   a , a second surface (a surface)  30   b , and a third surface  30   c . The first surface  30   a  and the second surface  30   b  are orthogonal to the output shaft, Ax, of the motor  20 . The third surface  30   c  has a circular shape extending along the output shaft Ax. The casing  30  has an axial dimension in a direction along the output shaft Ax of the motor  20  and a perpendicular dimension in direction approximately perpendicular to the output shaft Ax. The axial dimension is smaller than the perpendicular dimension. Specifically, the casing  30  has such a flat shape that dimension L 1 , which is between the first surface  30   a  and the second surface  30   b , is smaller than dimension L 2 , which is the diameter of the third surface  30   c  (L 1 &lt;L 2 ). In this embodiment, the dimension L 1  is equal to or less than half the dimension L 2 . 
     The rotor  40  includes a rotator  42  and a brake pad  44 . The rotator  42  is a member that can be driven into rotation about the output shaft Ax. The rotator  42  is rotatable by ring-shaped bearings  46   a  and  46   b , which are fixed to the casing  30 . The bearings  46   a  and  46   b  are aligned in a direction along the output shaft Ax with a predetermined distance between the bearings  46   a  and  46   b . On the outer surface of the rotor  40 , magnets  48  are aligned in the circumferential direction. The rotator  42  includes a shaft member  43 . The shaft member  43  protrudes from the first surface  30   a  of the casing  30 . 
     The brake pad  44  is a member that performs braking operation as controlled by the brake  70 . The brake pad  44  is disposed over the circumference of the rotator  42 . The brake pad  44  has a ring shape. The brake pad  44  is coaxial with the output shaft Ax. The outer edge of the brake pad  44  is further outward than the outer edge of the rotator  42 . That is, the outer diameter of the brake pad  44  is larger than the outer diameter of the rotator  42 . In this embodiment, the brake pad  44  is made of metal. 
     The stator  50  is a member that imparts rotational force to the rotor  40 . The stator  50  includes a core  52  and a coil  54 . In this embodiment, the core  52  has a ring shape. The core  52  faces the outer surface of the rotator  42 . The coil  54  is disposed on the core  52 . 
     The encoder  60  is a rotation detector that detects the rotation of the rotor  40 . A non-limiting example of the encoder  60  is a rotary encoder capable of detecting amounts by which the motor  20  is driven, such as the number of rotations of the rotor  40 , the rotational angle of the rotor  40 , and/or the rotational speed of the rotor  40 . The encoder  60  is partially disposed in a depression  42   a  of the rotator  42 . 
     The brake  70  is a braking device that causes the rotating rotor  40  to brake. The brake  70  protrudes outward from the second surface  30   b  of the casing  30  along the output shaft Ax. The brake  70  is decentered from the output shaft Ax. The brake  7  includes a case  72 , a friction material  74 , a holding member  76 , a biasing member  78 , and a coil  79 . 
     The case  72  accommodates the holding member  76 , the biasing member  78 , and the coil  79 . In this embodiment, the case  72  is fixed to the casing  30  with a screw. In the embodiment illustrated in  FIG. 11 , the case  72  has a solid cylindrical outer shape. The case  72  may be designed into any convenient shape. 
     The friction material  74  comes into sliding contact with the brake pad  44  of the rotor  40  to impart frictional force to the brake pad  44 . The friction material  74  is disposed on the holding member  76 . Examples of the material of the friction material  74  include, but are not limited to, resin mold, semi-metallic material, and sintered alloy (of iron and/or copper). 
     The holding member  76  holds the friction material  74 . In this embodiment, the holding member  76  is made of metal. The holding member  76  has an approximately T shape. The holding member  76  includes a body  76   a  and a holder  76   b.    
     In this embodiment, the body  76   a  has a solid cylindrical shape. The body  76   a  extends in the direction along the output shaft Ax. In this embodiment, the holder  76   b  has a disc shape. The holder  76   b  is disposed on one end (the end closer to the brake pad  44 ) of the body  76   a . The outer diameter of the holder  76   b  is larger than the outer diameter of the body  76   a . The holder  76   b  faces the brake pad  44  of the rotor  40 . That is, the friction material  74  faces the brake pad  44 . 
     The holding member  76  is movable (sliding-movable) in the direction along the output shaft Ax. Specifically, the holding member  76  is movable between a first position (initial position) and a second position. At the first position, the holder  76   b  contacts the coil  79 . At the second position, the friction material  74  sliding-contacts the brake pad  44 . 
     The biasing member  78  biases the holding member  76 . In this embodiment, the biasing member  78  is a coil spring. The biasing member  78  is disposed on the other end of the body  76   a  of the holding member  76 . When the holding member  76  is at the first position, the biasing member  78  biases the holding member  76  toward the rotor  40 . 
     The coil  79  regulates the movement of the holding member  76 . The coil  79  surrounds the body  76   a  of the holding member  76 . When current is supplied through the coil  79 , the coil  79  effects electromagnetic force against the biasing force of the biasing member  78  to pull the holder  76   b  and holds the holding member  76  at the first position. When no current is supplied through the coil  79 , the coil  79  releases the holding member  76 . 
     When supply of current through the coil  79  is discontinued, the brake  70  with the above-described configuration causes the coil  79  to release the holding member  76 , and allows the biasing force of the biasing member  78  to move the holding member  76  toward the rotor  40 . That is, the brake  70  positions the holding member  76  at the second position. Then, the brake  70  causes the friction material  74  to sliding-contact the brake pad  44  to impart frictional force to the brake pad  44 . This configuration causes the rotating rotor  40  to decelerate or stop and prevents the stationary rotor  40  from rotating. 
     When current is supplied through the coil  79 , the brake  70  causes the coil  79  to pull the holding member  76  to separate the friction material  74  and the brake pad  44  from each other. That is, the brake  70  positions the holding member  76  at the first position. This configuration makes the rotor  40  rotatable. 
     Motor Arrangement 
     Next, arrangement of the motor  20  (second motor M 2 , third motor M 3 ) with the above-described configuration will be described. The second motor M 2  is disposed at the connection portion  6 , at which the turnable portion  5  and the first arm  7  are coupled to each other. The second motor M 2  is disposed on the second arm member  7   b  of the first arm  7  and is fixed to the turnable portion  5 . Specifically, the second motor M 2  is fixed to the turnable portion  5  with the output shaft Ax coaxial with the second axis Ax 2 . 
     The second motor M 2  is coupled to a reducer (first reducer)  15 . The reducer  15  is disposed on the first arm member  7   a  of the first arm  7 . The input shaft of the reducer  15  is coaxial with the output shaft Ax of the second motor M 2 . That is, the output shaft Ax of the second motor M 2  and the input shaft of the reducer  15  are coaxial with the second axis Ax 2 . 
     With the second motor M 2  fixed to the turnable portion  5 , the brake  70  of the second motor M 2  is at a particular position. Specifically, as illustrated in  FIG. 3 , the brake  70  of the second motor M 2  protrudes outward in the direction along the second axis Ax 2 . As illustrated in  FIGS. 5 to 7 , in a view from the direction along the second axis Ax 2 , the brake  70  of the second motor M 2  is disposed at a position that is lower than the second axis Ax 2  in the direction toward the installation surface and that is further in the second direction D 2  than the first reference line LS 1 . 
     In a view from the direction along the second axis Ax 2 , the cable C overlaps the casing  30  of the second motor M 2  with the second surface  30   b  of the casing  30  in contact with or abutting on the cable C. Thus, as illustrated in  FIG. 3 , the second motor M 2  is disposed between the reducer  15  and the cable C in the direction along the second axis Ax 2 . The cable C is fixed to the turnable portion  5  with a fixture F 1  and fixed to the first arm  7  with a fixture F 2 . The fixture F 1  and the fixture F 2  are disposed across the second motor M 2 . Specifically, the fixture F 1  is at a position lower than the second motor M 2  in the direction toward the base end of the robot  1 . The fixture F 2  is at a position higher than the second motor M 2  in the direction toward the distal end of the robot  1 . The fixture F 1  keeps the cable C fixed to the turnable portion  5 , and the fixture F 2  keeps the cable C fixed to the first arm  7 . 
     The third motor M 3  is disposed at the connection portion  10 , at which the first arm  7  and the second arm  9  are coupled to each other. The third motor M 3  is fixed to the second arm  9 . Specifically, the output shaft Ax of the third motor M 3  is coaxial with the third axis Ax 3 . 
     The third motor M 3  is coupled to a reducer (second reducer)  17 . The reducer  17  is disposed on the side of the first arm member  7   a  of the first arm  7 . The input shaft of the reducer  17  is coaxial with the output shaft Ax of the third motor M 3 . Specifically, the output shaft Ax of the third motor M 3  and the input shaft of the reducer  17  are coaxial with the third axis Ax 3 . 
     With the third motor M 3  fixed to the second arm  9 , the brake  70  of the third motor M 3  is at a particular position. Specifically, as illustrated in  FIG. 3 , the brake  70  of the third motor M 3  protrudes outward in the direction along the third axis Ax 3 . While the second arm  9  is not swinging relative to the second reference line LS 2  (that is, when the second arm  9  is in the state illustrated in  FIG. 4 ), the brake  70  of the third motor M 3  is at a position that is further away from the second axis Ax 2  than the third axis Ax 3  is from the second axis Ax 2  in a view from the direction along the third axis Ax 3 . 
     In a view from the direction along the third axis Ax 3 , the cable C overlaps the casing  30  of the third motor M 3  with the second surface  30   b  of the casing  30  in contact with or abutting on the cable C. Thus, as illustrated in  FIG. 3 , the third motor M 3  is disposed between the reducer  17  and the cable C in the direction along the third axis Ax 3 . The cable C is fixed to the first arm  75  with a fixture F 3  and fixed to the second arm  9  with a fixture F 4 . The fixture F 3  and the fixture F 4  are disposed across the third motor M 3 . Specifically, the fixture F 3  is at a position lower than the third motor M 3  in the direction toward the base end of the robot  1 . The fixture F 4  is at a position higher than the third motor M 3  in the direction toward the distal end of the robot  1 . The fixture F 3  keeps the cable C fixed to the first arm  7 , and the fixture F 4  keeps the cable C fixed to the second arm  9 . 
     Advantageous Effects 
     As has been described hereinbefore, in the robot  1  according to this embodiment, the casing  30  of the motor  20  has a smaller axial dimension, which is in the direction along the output shaft Ax, than the perpendicular dimension of the casing  30  in the direction approximately perpendicular to the output shaft Ax. That is, the casing  30  has a flat shape. Thus, the casing  30  is flat and the motor  20  is disposed with its output shaft Ax parallel to the swing axis. This configuration decreases the dimension of the motor  20  in the width direction (L 1 ). 
     Here, motors used in conventional robots have larger dimensions in the axial direction because the motor section and the brake section are coaxial with each other. If such motor is used in a robot, it is necessary to circumvent the motor in the work of wiring the cable along the arm to the motor and other elements. That is, the cable is wired along the side of the arm opposite to the side on which the motor is disposed. This configuration involves addition of the width dimension of the motor and the width dimension of cable to the width dimension of the arm. As a result, the width dimension of the arm as a whole increases. 
     The brake  70  of the motor  20  according to this embodiment protrudes from the second surface  30   b  of the casing  30  in the direction along the output shaft Ax, and is disposed at a position displaced from the output shaft Ax. With this configuration, a space as minimal as possible and necessary to install the motor  20  has a space for the brake  70  and a space without the brake  70 . The space without the brake  70  can be utilized as a space for wiring the cable C. The space for wiring the cable C enables the cable C to be wired on the side of the arm on which the motor  20  is disposed. This configuration minimizes the width dimensions of the first arm  7  and the second arm  9 . 
     In this embodiment, the cable C overlaps the casing  30  of the second motor M 2  in a view from the direction along the second axis Ax 2 , and overlaps the casing  30  of the third motor M 3  in a view from the direction along the third axis Ax 3 . Here, the second surface  30   b  of the casing  30  is in contact with or abuts on the cable C. This configuration ensures that as illustrated in  FIG. 4 , the cable C passes through spaces in the motors M 2  and M 3  where the brakes  70  are not disposed. 
     In this embodiment, the robot  1  includes the reducer  15  and the reducer  17 . The reducer  15  is coupled to the second motor M 2  and has an input shaft coaxial with the output shaft Ax. The reducer  17  is coupled to the third motor M 3  and has an input shaft coaxial with the output shaft Ax. The second motor M 2  is disposed between the reducer  15  and the cable C in the direction along the second axis Ax 2 . The third motor M 3  is disposed between the reducer  17  and the cable C in the direction along the third axis Ax 3 . Thus, the motors M 2  and M 3  are disposed between the cable C and the respective reducers  15  and  17  in the respective axial directions. This configuration decreases the width dimensions of the first arm  7  and the second arm  9  even though the reducers  15  and  17  are coaxial with the motor  20 . 
     In this embodiment, the second motor M 2  is fixed to the turnable portion  5 . Since the second motor M 2  is fixed to the turnable portion  5 , the second motor M 2  itself does not turn relative to the turnable portion  5 . Specifically, the second motor M 2  is fixed with the brake  70  positioned to prevent the first arm  7  from taking an abnormal posture (such as involving forcible stretch of the cable C) when the first arm  7  swings and the cable C contacts the brake  70 . This configuration eliminates or minimizes excessive contact between the cable C and the brake  70 , and eliminates or minimizes resulting degradation, damage, and other similar occurrences to the cable C. The third motor M 3  is fixed to the second arm  9 . Since the third motor M 3  is fixed to the second arm  9 , the third motor M 3  turns together with the second arm  9 . Specifically, the third motor M 3  is fixed with the brake  70  positioned to prevent the second arm  9  from taking an abnormal posture when the second arm  9  swings and the cable C contacts the brake  70 . 
     In this embodiment, the output shaft Ax of the second motor M 2  and the second axis Ax 2  are coaxial with each other. The first arm  7  is swingable in the first direction D 1  up to the first swing angle θ 1  relative to the first reference line LS 1 , which is in the direction approximately perpendicular to the installation surface and which passes through the second axis Ax 2 . The first arm  7  is also swingable relative to the first reference line LS 1  in the second direction D 2 , which is opposite to the first direction D 1 , up to the second swing angle θ 2 , which is smaller than the first swing angle θ 1 . In a view from the direction along the second axis Ax 2 , the brake  70  of the second motor M 2  is disposed at a position that is lower than the second axis Ax 2  in the direction toward the installation surface and that is further in the second direction D 2  than the first reference line LS 1 . 
     This configuration ensures that as illustrated in  FIG. 5 , the cable C passes through the center of the casing  30  of the second motor M 2  while the first arm  7  is not swinging. This eliminates the need for bending the cable C, and eliminates or minimizes load on the cable C. As illustrated in  FIG. 6 , when the first arm  7  swings by the first swing angle θ 1  in the first direction D 1 , the cable C is bent without contacting the brake  70 . As illustrated in  FIG. 7 , when the first arm  7  swings by the second swing angle θ 2  in the second direction D 2 , the cable C is curved on the brake  70  without taking an abnormal posture. This configuration eliminates or minimizes excessive load on the cable C, and eliminates or minimizes resulting degradation, damage, and other similar occurrences to the cable C. 
     In this embodiment, the output shaft Ax of the third motor M 3  and the third axis Ax 3  are coaxial with each other. The second arm  9  is swingable in the first direction D 1  up to the first swing angle θ 3  relative to the second reference line LS 2 , which is in the direction approximately perpendicular to the installation surface and which passes through the third axis Ax 3 . The second arm  9  is also swingable relative to the second reference line LS 2  in the second direction D 2 , which is opposite to the first direction D 1 , up to the second swing angle θ 4 , which is smaller than the first swing angle θ 3 . While the second arm  9  is not swinging relative to the second reference line LS 2 , the brake  70  of the third motor M 3  is at a position that is further away from the second axis Ax 2  than the third axis Ax 3  is from the second axis Ax 2  in a view from the direction along the third axis Ax 3 . 
     This configuration ensures that as illustrated in  FIG. 4 , the cable C is not bent on the brake  70  while the second arm  9  is not swinging. This configuration eliminates or minimizes load on the cable C. As illustrated in  FIG. 8 , when the second arm  9  swings in the second direction D 2 , facing upward, the cable C is stretched out, with no or minimal bending. As illustrated in  FIG. 9 , when the second arm  9  swings by the first swing angle θ 3  in the first direction D 1 , the cable C is bent without contacting the brake  70 . As illustrated in  FIG. 10 , when the second arm  9  swings by the second swing angle θ 4  in the second direction D 2 , the cable C is curved on the brake  70  without an abnormal posture. This configuration eliminates or minimizes excessive load on the cable C, and eliminates or minimizes resulting degradation, damage, and other similar occurrences to the cable C. 
     In this embodiment, the cable C is fixed with the fixtures F 1  to F 4 . The fixtures F 1  and F 2  are disposed across the second motor M 2 , and the fixtures F 3  and F 4  are disposed across the third motor M 3 . Arranging the fixtures F 1  to F 4  in this manner prevents the cable C from coming loose due to the swing of the first arm  7  and the second arm  9 . Preventing the cable C from coming loose eliminates or minimizes contact between the cable C and workpieces. It is noted that this arrangement of the fixtures F 1  to F 4  is not essential. Another possible embodiment is to omit the fixtures F 2  and F 3  and arrange the fixture F 1  and the fixture F 4  across the second motor M 2  and the third motor M 3 . It is also noted that the fixtures may not necessarily fix the cable C completely, but may be turnable metal fittings, turnable cable guides, or any other turnable fixtures. 
     The above-described embodiment should not be construed in a limiting sense. For example, while the above-described embodiment has been described as including the first arm  7  and the second arm  9 , an additional arm may be coupled to the second arm  9 . 
     While in the above-described embodiment the motor  20  has been described as having the configuration illustrated in  FIG. 12 , this configuration of the motor  20  should not be construed in a limiting sense. 
     Obviously, numerous modifications and variations of the present disclosure are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the present disclosure may be practiced otherwise than as specifically described herein.