Abstract:
A multi-joint robot for loading/unloading a work into/from a cassette, which includes a hand part holding the work, an arm part rotatably holding the hand part, a link mechanism rotatably holding the base end side of the arm part and moving so that the moving route of the base end side of the arm part becomes linear in a direction roughly orthogonal to a direction for loading/unloading the work, and a driving device for moving the tip side of the arm part so as to linearly interpolate it in a direction for loading/unloading the work according to the movement of the link mechanism.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an articulated robot which is used to load/unload a work-piece to/from a cassette. Specifically, the present invention relates to an articulated robot which is capable of performing a stable operation with linear interpolation. 
     2. Description of Related Art 
     In order to load/unload a large work-piece such as a semiconductor wafer to/from a cassette, an articulated robot is used in which a plurality of arms is turnably connected with each other to perform extensible operation or the like by transmitting a rotating force of a rotating drive source. 
     For example, there is a SCARA (Selective Compliance Assembly Robot Arm) type robot as described in Japanese Patent Laid-Open No. 2003-170384. This robot realizes bending and stretching of an arm body (first arm and second arm) by turning the first arm and the second arm in a horizontal plane. Further, loading/unloading of a work-piece is performed by means of that a hand part turnably held at a tip end of the second arm is advanced and retreated to and from the cassette. 
     According to the SCARA type robot as described in Japanese Patent Laid-Open No. 2003-170384, there is a merit that an installation space for a running axis (rail or the like for running a base in a horizontal direction on which a plurality of arms is installed) is not required, which is different from a case that a cylindrical coordinate type robot is used. 
     However, in the conventional SCARA type robot, when the first arm and the second arm are controlled with linear interpolation (in other words, when one point on an arm is controlled to be linearly moved), an angular velocity of the second arm is rapidly changed due to overlapping of the two arms and thus carrying of a semiconductor wafer may be unstable. More specifically, it will be described below with reference to  FIG. 9 . 
       FIG. 9  is an explanatory view showing states in which the first arm  101  and the second arm  102  are controlled with linear interpolation in a conventional SCARA type robot  100 . In  FIG. 9(   a ), the conventional SCARA type robot  100  includes a first arm  101  whose base end part  104  is mounted on a base (not shown), a second arm  102  which is connected with a tip end part of the first arm  101 , and a hand part  103  which is connected with a tip end part of the second arm  102 . The hand part  103  supports a work-piece (object to be carried)  200 . 
     In order to move the work-piece  200  in an “a” direction (the “X”-axis direction in the X-Y coordinate system), it is assumed that the first arm  101  and the second arm  102  are controlled with linear interpolation (in other words, a case that a tip end part “X” of the second arm  102  is linearly moved in the “a” direction). When the second arm  102  is turned in a counterclockwise direction around the tip end part of the first arm  101  while the first arm  101  is turned in a clockwise direction around the base end portion  104 , the work-piece  200  is linearly moved in the “a” direction. 
     In this robot  100 , when an effective length of the first arm  101  is set to be “L 101 ” and an effective length of the second arm  102  is set to be “L 102 ” (see  FIG. 9(   a )), an attitude in which an angle formed by the first arm  101  and the second arm  102  becomes 0° becomes a singular point. When linear interpolation is performed to pass the vicinity of the singular point, in other words, when “L” shown in  FIG. 9(   a ) traces a trajectory of a value close to (“L 101 ”-“L 102 ”), the first arm  101  and the second arm  102  are turned as shown from  FIG. 9(   a ) to  FIG. 9(   b ). After that, as shown in  FIGS. 9(   b ) and  9 ( c ), the second arm  102  is turned with angular velocity in a clockwise direction around the tip end part of the first arm  101 . On the other hand, the first arm  101  is always turned in the clockwise direction around the base end part  104  in  FIG. 9(   a ) through  FIG. 9(   c ). 
     In  FIG. 9 , in order to carry the work-piece  200  stably, a carrying speed in the “a” direction of the work-piece  200  is set to be constant (a carrying distance in the “a” direction of the work-piece  200  (moving distance of the tip end part “X” of the second arm  102 ) from  FIG. 9(   a ) to  FIG. 9(   b ) is set to be substantially the same as that from  FIG. 9(   b ) to  FIG. 9(   c )). When paying attention to a turning angle of the first arm  101 , the turning angle from  FIG. 9(   a ) to  FIG. 9(   b ) is about 90°-θ 2  (θ 1  is regarded as about 0°) and the turning angle from  FIG. 9(   b ) to  FIG. 9(   c ) is θ 2 +θ 3 . In these turning angles, the angle of about 90°-θ 2  from  FIG. 9(   a ) to  FIG. 9(   b ) is obviously large. In other words, in order to set a carrying speed in the “a” direction of the work-piece  200  to be constant when the tip end part “X” of the second arm  102  is moved near the singular point, an angular velocity of the first arm  101  is required to be rapidly (at a high speed) changed with the base end part  104  of the first arm as the singular point. This may cause vibration to the first arm  101  and the second arm  102  and thus carrying of the work-piece  200  may be unstable. 
     Further, in order to rapidly change (at a high speed) the angular velocity of the first arm  101 , a remarkably large driving force (torque) is required. However, in order to realize this requirement, an expensive motor is required and, as a result, manufacturing cost may be increased. 
     With respect to this point, according to the articulated robot disclosed in Japanese Patent Laid-Open No. Hei 11-138474, it can be structured that the singular point is not generated during carrying of the work-piece. In other words, in this articulated robot, a first turning shaft is formed at an eccentric position to the center of rotation of a rotary table to structure the rotary table as a first arm part and an arm which is turnably held around the first turning shaft is structured as a second arm part, a third arm part is turnably held at a tip end of the second arm part, and a hand part is turnably held at a tip end of the third arm part. In addition, the first arm part, the second arm part, the third arm part and the hand part are respectively turned and controlled so as not to generate the singular point. However, this “turning and controlling respectively” becomes a complicated control due to a lot of control parameters, and a great deal of labor is required to prepare the control program. 
     In view of the problems described above, an object of the present invention is directed to provide an articulated robot which is capable of stably carrying a work-piece with simple control without using an expensive motor generating a large driving force. 
     SUMMARY OF THE INVENTION 
     In order to solve the problems as described above, the present invention provides the following: 
     (1) An articulated robot for loading/unloading a work-piece in/from a cassette comprising a hand part for holding the work-piece, an arm part which turnably holds the hand part, a link mechanism which turnably holds a base end side of the arm part and which operates to cause a moving trajectory of the base end side of the arm part to form a straight line in a direction substantially perpendicular to a loading/unloading direction, and a drive means for moving the arm part so as to perform linear interpolation in the loading/unloading direction while matching with movement of the link mechanism. 
     According to the present invention, an articulated robot includes a hand part for holding a work-piece, an arm part which turnably holds the hand part, a link mechanism which turnably holds a base end side of the arm part and which operates to cause a moving trajectory of the base end side of the arm part to form a straight line in a direction substantially perpendicular to a loading/unloading direction, and a drive means (for example, a motor) for moving the arm part (or a tip end side of the arm part) so as to perform linear interpolation in the loading/unloading direction while matching with movement of the link mechanism. Therefore, a work-piece such as a semiconductor wafer can be carried stably. In other words, even when the arm part is moved so as to perform linear interpolation, since the base end side of the arm part is controlled to move to optimal positions, rapid speed variation of the arm part and the link mechanism is not required (singular point is not generated). Therefore, occurrence of vibration in the arm part and the link mechanism can be prevented and thus the work-piece can be carried stably. 
     Further, since rapid speed variation of the arm part and the link mechanism is not required, the work-piece can be carried stably without using an expensive motor generating a large driving force. In addition, in the articulated robot disclosed in Japanese Patent Laid-Open No. Hei 11-138474, the first arm part, the second arm part, the third arm part and the hand part are required to be respectively turnably controlled. However, according to the present invention, it is sufficient that the link mechanism, the arm part and the hand part are turnably controlled. Therefore, the number of control parameters can be reduced (as a result, labor for preparing the control program can be reduced) and thus the work-piece can be carried stably with a simple control. 
     In the conventional SCARA type robot  100  (see  FIG. 9 ), in order to carry the work-piece  200  at a constant carrying speed, a rapid speed variation of the first arm  101  is required (see  FIG. 9(   b )→ FIG. 9(   c )). However, when the first arm  101  is turned at a speed more than a predetermined angular velocity, there is a possibility that the SCARA type robot  100  itself results in failure and thus processing for preventing the speed of the first arm  101  from exceeding is adopted. However, according to the articulated robot in accordance with the present invention, since the special processing described above is not required, manufacturing cost can be greatly reduced. 
     (2) The articulated robot according to the above-mentioned (1), wherein the link mechanism includes a base side link part which is disposed on an base end side of the articulated robot and an arm side link part which is disposed on a side of the arm part and which is connected with the base side link part, and lengths of the base side link part and the arm side link part are substantially the same, and a turning angle ratio between the base side link part and the arm side link part is 1:2. 
     According to the present invention, the link mechanism described above includes a base side link part which is disposed on an base end side of the articulated robot and an arm side link part which is disposed on a side of the arm part and which is connected with the base side link part, and both lengths are substantially the same (substantially equal to each other), and a turning angle ratio of the both parts is set to be 1:2. Therefore, the base end side of the arm part is always adequately controlled on a predetermined straight line and rapid speed variations of the arm part and the link mechanism are not required and thus the work-piece can be carried stably. 
     With regard to this point, when a running axis for running the base in a horizontal direction is provided in the conventional cylindrical coordinate system robot, it is possible to move the connection point linearly. However, when the running axis is provided, its installation space is required and, in addition, components which may be dust generation parts such as a rail are required and thus it is not suitable to be used in a clean room. On the other hand, according to the articulated robot in accordance with the present invention, components which may be dust generation parts such as a rail are not required, the articulated robot in accordance with the present invention can be used in a clean room adequately. 
     (3) The articulated robot according to the above-mentioned (1), wherein the link mechanism includes a base side link part which is disposed on an base end side of the articulated robot and an arm side link part which is disposed on a side of the arm part and which is connected with the base side link part, and a length of the base side link part is formed longer than a length of the arm side link part, and a base of the link mechanism is disposed in a state that a center position of the base of the link mechanism is shifted from the moving trajectory of the base end side of the arm part. 
     According to the present invention, the link mechanism described above includes a base side link part which is disposed on an base end side of the articulated robot and an arm side link part whose length is longer than a length of the arm side link part and which is disposed on the base end side and connected with the base side link part, and a base of the link mechanism is disposed in a state that a center position of the base of the link mechanism is shifted from the moving trajectory of the base end side of the arm part. Therefore, a work-piece can be carried stably. 
     In other words, even when the arm part is moved to perform linear interpolation, since the base end side of the arm part is controlled to move to optimal positions, rapid speed variation of the arm part and the link mechanism is not required (singular point is not generated). Therefore, occurrence of vibration in the arm part and the link mechanism can be prevented and thus the work-piece can be carried stably. 
     Further, the present invention is provided with an excellent merit because improvement of efficiency and downsizing can be realized simultaneously. More specifically described, in recent years, there is a case that a plurality of cassettes is disposed in a direction perpendicular to a loading/unloading direction of a work-piece to/from a cassette in order to enhance efficiency of carrying the work-piece. In this case, it is possible to cope with the case by making lengths of respective portions such as the base side link part and the arm side link part simply longer. However, when the lengths of the respective portions are simply made longer, turning ranges of the respective portions become larger. Therefore, a useless space occurs and demand of downsizing in recent years cannot be satisfied. Especially, the articulated robot is often installed in a clean room at a generally high cost and thus it is required to shorten an occupation distance in the loading/unloading direction of a work-piece to/from a cassette as short as possible. Accordingly, in the articulated robot in accordance with the present invention, since the length of the base side link part is set to be longer than the length of the arm side link part, it is possible to cope with a plurality of cassettes which are respectively disposed adjacent to each other to realize improvement of efficiency. In addition, the base of the link mechanism is disposed in a state that its center position is shifted from the moving trajectory of the base end side of the arm part. Therefore, an occupation distance in the loading/unloading direction of a work-piece to/from a cassette is shortened to realize downsizing. 
     Further, the length of the base side link part is set to be longer than the length of the arm side link part. Therefore, it is possible to move faster to a cassette on both ends of a plurality of cassettes which is, for example, respectively disposed adjacent to each other. Moreover, in an articulated robot, there is a request that weight is decreased along with closer to the tip end in order to carry a work-piece stably. With regard to this point, in the articulated robot in accordance with the present invention, since the length of the arm side link part is shorter than the length of the base side link part, stable carrying of a work-piece can be attained. 
     Further, since rapid speed variation of the arm part and the link mechanism is not required, the work-piece can be carried stably without using an expensive motor generating a large driving force. In addition, in the articulated robot disclosed in Japanese Patent Laid-Open No. Hei 11-138474, the first arm part, the second arm part, the third arm part and the hand part are required to be respectively turnably controlled. However, according to the present invention, it is sufficient that the link mechanism, the arm part and the hand part are turnably controlled respectively. Therefore, the number of axes can be reduced and it is manufactured at a low cost. Further, since the number of control parameters is reduced, labor for preparing the control program can be reduced and thus the work-piece can be carried stably with a simple control. 
     Further, in the conventional SCARA type robot  100  (see  FIG. 9 ), when the work-piece  200  is to be carried at a constant carrying speed, a rapid speed variation of the first arm  101  is required (see  FIG. 9(   b )→ FIG. 9(   c )). However, when the first arm  101  is turned at a speed more than a predetermined angular velocity, there is a possibility that the SCARA type robot  100  itself results in failure and thus processing for preventing the speed of the first arm  101  from exceeding is adopted. However, according to the articulated robot in accordance with the present invention, the special processing described above is not required and thus manufacturing cost can be greatly reduced. 
     (4) The articulated robot according to the above-mentioned (3), wherein the base of the link mechanism is disposed in a state that the center position of the base of the link mechanism is shifted on a side to the cassette or on a side to a target position where the work-piece is carried in or carried out from the moving trajectory of the base end side of the arm part. 
     According to the present invention, the base of the link mechanism described above is disposed in a state that the center position of the base of the link mechanism is shifted on a side to the cassette or on a side to a target position where the work-piece is carried in or carried out from the moving trajectory of the base end side of the arm part. Therefore, the work-piece can be stably carried while shortening an occupation distance in the loading/unloading direction to/from a cassette or on a side to a target position where the work-piece is carried in or carried out. Further, the base end side of the arm part can be always adequately controlled on a predetermined straight line and rapid speed variations of the arm part and the link mechanism are not required and thus the work-piece can be carried stably. 
     With regard to this point, when a running axis for running the base in a horizontal direction is provided in the conventional cylindrical coordinate system robot, it is possible to move the connection point linearly. However, when the running axis is provided, its installation space is required and, in addition, components which may be dust generation parts such as a rail are required and thus it is not suitable to be used in a clean room. On the other hand, according to the articulated robot in accordance with the present invention, components which may be dust generation parts such as a rail are not required, the articulated robot can be used in a clean room adequately. 
     As described above, according to the present invention, occurrence of vibration in the arm part and the link mechanism can be prevented and thus the work-piece can be carried stably. Further, the work-piece can be carried stably without using an expensive motor generating a large driving force. In addition, special processing for preventing the speed of the arm part or the link mechanism from exceeding is not required and thus it is remarkably effective to reduce manufacturing cost. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a longitudinal sectional view showing an articulated robot in accordance with an embodiment of the present invention. 
         FIG. 2  is a transverse cross-sectional view showing the articulated robot shown in  FIG. 1 . 
         FIG. 3  is an explanatory view for explaining a mechanical operation of an articulated robot in accordance with an embodiment of the present invention. 
         FIG. 4  is an explanatory view for explaining another mechanical operation of an articulated robot in accordance with an embodiment of the present invention. 
         FIG. 5  is an explanatory view for explaining another mechanical operation of an articulated robot in accordance with an embodiment of the present invention. 
         FIG. 6  is a sectional view showing an articulated robot in accordance with another embodiment of the present invention. 
         FIG. 7  is an explanatory view for explaining a mechanical operation of an articulated robot in accordance with another embodiment of the present invention. 
         FIG. 8  is an explanatory view for explaining linearity of a connection point in an articulated robot in accordance with another embodiment of the present invention. 
         FIG. 9  is an explanatory view for explaining a manner in which a first arm and a second arm are controlled with linear interpolation in a conventional SCARA type robot. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Referring now to the drawings, the present invention will be described in detail on the basis of a first embodiment. 
       FIG. 1  is a longitudinal sectional view showing an articulated robot  1  in accordance with an embodiment of the present invention. Further,  FIG. 2  is a transverse cross-sectional view showing the articulated robot  1  shown in  FIG. 1 . Especially,  FIG. 2(   a ) is a cross-sectional view along the “A-A” line in  FIG. 1  and  FIG. 2(   b ) is a cross-sectional view along the “B-B”&#39; line in  FIG. 1 . 
     In  FIG. 1  and  FIG. 2 , an articulated robot  1  includes a base  2 , a link mechanism  3 , an arm part  6  and a hand part  7 . The link mechanism  3  is provided with a base side link part  4  and an arm side link part  5  which are turnably connected with each other and have the same length. 
     The base  2  includes an elevating/lowering motor  20 , a guide shaft  21  which is rotated by the elevating/lowering motor  20  and in which a vertical direction is set to be its longitudinal direction, and an elevating/lowering cylinder  8  which is guided by the guide shaft  21  to move up and down in the vertical direction. 
     The base side link part  4  is connected with the elevating/lowering cylinder  8  through a connecting shaft  8   b  and held so as to be capable of turning by a link mechanism motor  8   a  which is built in the elevating/lowering cylinder  8 . Further, the base side link part  4  is moved up and down with respect to the base  2  along with the elevating/lowering cylinder  8  which moves up and down. 
     A base side pulley  4   a , an arm side pulley  4   b  and a belt  4   c  are built in the base side link part  4 . Also, a ratio of diameters of the base side pulley  4   a  and the arm side pulley  4   b  is set to be 2:1. Further, the arm side pulley  4   b  and the arm side link part  5  are connected with each other by the connecting shaft  4   d . Therefore, a turning angle ratio between the base side pulley  4   a  and the arm side pulley  4   b , in other words, a turning angle ratio between the base side link part  4  and the arm side link part  5  is 1:2. As a result, in the link mechanism  3 , a center point (fixed point “Y”) of the base side pulley  4   a  in the base side link part  4  and a center point (connection point “Z”) of the connecting shaft  5   a  which turnably connects the arm side link part  5  with the arm part  6  are always controlled on a predetermined straight line. 
     The arm part  6  is connected with the tip end of the arm side link part  5  through the connecting shaft  5   a  and held so as to be capable of turning by an arm part motor  51  which is built in the arm side link part  5 . In  FIG. 1 , for convenience of description, the arm part motor  51  is built in the arm side link part  5  but the present invention is not limited to this structure. For example, the arm part motor  51  may be built in the arm part  6  or it may be disposed anywhere. The hand part  7  is structured of an upper support frame  7   a  and a lower support frame  7   b  which are disposed in parallel to each other. The upper support frame  7   a  and the lower support frame  7   b  are connected with the tip end of the arm part  6  through a connecting shaft  6   c  and a connecting shaft  6   d  respectively and they are held so that they can be turned by a lower support frame motor  6   a  and an upper support frame motor  6   b  which are respectively built in the arm part  6 . 
     In this embodiment, control signals for driving the elevating/lowering motor  20 , the link mechanism motor  8   a , the arm part motor  51 , the lower support frame motor  6   a  and the upper support frame motor  6   b  are appropriately transmitted from a computer (not shown) on the basis of programs having been inputted by an operator. 
       FIG. 3  is an explanatory view for explaining a mechanical operation of the articulated robot  1  in accordance with an embodiment of the present invention. In  FIG. 3 , an operation will be described in which a work-piece (for example, a circular semiconductor wafer)  30  is taken out from a lower cassette in the drawing to put in an upper cassette in the drawing. 
     In  FIG. 3(   a ), the work-piece  30  is placed on the tip end of the upper support frame  7   a  of the hand part  7 . The lower support frame  7   b  of the hand part  7  is not used in this operation and thus it is set in a bent state as shown in the drawing. 
     The upper support frame  7   a  of the hand part  7  is linearly moved in a positive direction of the “y”-axis while keeping its orientation in order to take out the work-piece  30  from the lower cassette in the drawing. More specifically, the arm part  6  is turned in a clockwise direction around the connection point “Z” by the arm part motor  51  and the upper support frame  7   a  of the hand part  7  is turned in a counterclockwise direction around the connecting shaft  6   c  by the upper support frame motor  6   b . In this case, a moving trajectory of the connection point “Z” becomes a straight line in a direction perpendicular to an unloading direction of the work-piece  30  (the “x”-axis direction). 
     After that, when the upper support frame  7   a  of the hand part  7  has been moved upward by a predetermined distance in the drawing, taking out of the work-piece  30  is completed ( FIG. 3(   b )). Next, the arm part  6  is turned in the clockwise direction around the connection point “Z” by a predetermined angle together with the upper support frame  7   a  of the hand part  7 . As a result, the orientation of the upper support frame  7   a  of the hand part  7  is reversed by 180° from a downward orientation to an upward orientation ( FIG. 3(   c )). In this embodiment, in  FIG. 3(   b ) and  FIG. 3(   c ), the lower support frame  7   b  is overlapped with the upper support frame  7   a  and performs the same operation as the upper support frame  7   a.    
     Lastly, the arm part  6  is turned in the clockwise direction around the connection point “Z” by the arm part motor  51  and the upper support frame  7   a  of the hand part  7  is turned in the counterclockwise direction around the connecting shaft  6   c  by the upper support frame motor  6   b . As a result, the work-piece  30  is placed in the upper cassette in the drawing ( FIG. 3(   d )). In this embodiment, in  FIG. 3(   d ), similarly to  FIG. 3(   a ), the lower support frame  7   b  of the hand part  7  is set to be a bent state as shown in the drawing. 
       FIG. 4  and  FIG. 5  are explanatory views for explaining another mechanical operation of the articulated robot  1  in accordance with an embodiment of the present invention. In  FIG. 4  and  FIG. 5 , operations will be described in which work-pieces (a circular semiconductor wafer)  30  are respectively taken out from left and right side lower cassettes in the drawing by the articulated robot  1  and are respectively placed in left and right side upper cassettes in the drawing. 
     In  FIG. 4(   a ), in the articulated robot  1 , the work-piece  30  is placed on the tip end of the upper support frame  7   a  of the hand part  7 . Next, similar to the case described with reference to  FIG. 3(   b ) through  FIG. 3(   d ), the arm part  6  is turned in a clockwise direction around the connection point “Z” by the aim part motor  51 , and the upper support frame  7   a  of the hand part  7  is turned in a counterclockwise direction around the connecting shaft  6   c  by the upper support frame motor  6   b . As a result, taking out of the work-piece  30  is completed ( FIG. 4(   b )). After that, the arm part  6  is turned in the counterclockwise direction around the connection point “Z” by a predetermined angle together with the upper support frame  7   a  of the hand part  7  in an integral manner and the orientation of the upper support frame  7   a  of the hand part  7  is reversed by 180° from a downward orientation to an upward orientation ( FIG. 4(   c )). Lastly, the arm part  6  is turned in a clockwise direction around the connection point “Z” by the arm part motor  51  and the upper support frame  7   a  of the hand part  7  is turned in a counterclockwise direction around the connecting shaft  6   c  by the upper support frame motor  6   b . As a result, the work-piece  30  is placed in a left side upper cassette in the drawing ( FIG. 4(   d )). 
     On the other hand, in  FIG. 5(   a ), in the articulated robot  1 , a work-piece  30  is placed on the tip end of the upper support frame  7   a  of the hand part  7 . Next, similar to the case described with reference to  FIG. 3(   b ) through  FIG. 3(   d ), the arm part  6  is turned in a counterclockwise direction around the connection point “Z” by the arm part motor  51 , and the upper support frame  7   a  of the hand part  7  is turned in a clockwise direction around the connecting shaft  6   c  by the upper support frame motor  6   b . As a result, the work-piece  30  is taken out ( FIG. 5(   b )). After that, the arm part  6  is turned in the clockwise direction around the connection point “Z” by a predetermined angle together with the upper support frame  7   a  of the hand part  7  in an integral manner and the orientation of the upper support frame  7   a  of the hand part  7  is reversed by 180° from a downward orientation to an upward orientation ( FIG. 5(   c )). Lastly, the arm part  6  is turned in the counterclockwise direction around the connection point “Z” by the arm part motor  51 , and the upper support frame  7   a  of the hand part  7  is turned in the clockwise direction around the connecting shaft  6   c  by the upper support frame motor  6   b . As a result, the work-piece  30  is placed in a right side upper cassette in the drawing ( FIG. 5(   d )). 
     As described above, another mechanical operation of the articulated robot  1  has been described with reference to  FIG. 4  and  FIG. 5 . However, a work-piece  30  can be carried, for example, from a left side lower cassette in the drawing to a right side upper cassette in the drawing by moving the connection point “Z” on and along the “x”-axis. More specifically, when the articulated robot  1  is in the state shown in  FIG. 4(   b ), the connection point “Z” is linearly moved in a positive direction of the x-axis and the arm part  6  is turned around the connection point “Z” and the hand part  7  is turned around the connecting shaft  6   c . As a result, the articulated robot  1  in the state shown in  FIG. 4(   b ) is changed to the state shown in  FIG. 5(   c ). As described above, when a state of the articulated robot  1  is changed in a flow of  FIG. 4(   a )→ FIG. 4(   b )→ FIG. 5(   c )→ FIG. 5(   d ), the work-piece  30  can be carried from the left side lower cassette in the drawing to the right side upper cassette in the drawing. 
     As described above, according to  FIG. 3  through  FIG. 5 , it is understood that, even when the arm part  6  and the link mechanism  3  (the base side link part  4  and the arm side link part  5 ) are controlled with linear interpolation, the connection point “Z” of the arm part  6  is moved at optimal positions and thus rapid speed variation of the arm part  6  and the link mechanism  3  is not required (a singular point is not generated). In other words, in the linear interpolation of  FIG. 4(   a )→ FIG. 4(   b ), in the linear interpolation of  FIG. 4(   c )→ FIG. 4(   d ), in the linear interpolation of  FIG. 5(   a )→ FIG. 5(   b ), in the linear interpolation of  FIG. 5(   c )→ FIG. 5(   d ), in the linear interpolation of  FIG. 3(   a )→ FIG. 3(   b ) and, in the linear interpolation of  FIG. 3(   c )→ FIG. 3(   d ), a singular point that is provided in the conventional articulated robot is not generated. Therefore, occurrence of vibration in the arm part  6  and the link mechanism  3  can be prevented and thus the work-piece  30  can be carried stably. 
     Further, according to  FIG. 3  through  FIG. 5 , a work-piece can be stably carried with simple control by turnably controlling the base side link part  4 , the arm part  6  and the hand part  7  respectively (in other words, especially, by not turnably controlling the arm side link part  5  of the link mechanism  3 ). 
     Another embodiment of the present invention will be described below with reference to the accompanying drawings. In this second embodiment, the same notational symbols are used in the same structure as the embodiment described above. 
       FIG. 6  is a sectional view showing an articulated robot  71  in accordance with another embodiment of the present invention. Specifically,  FIG. 6(   a ) is a planar sectional view showing the articulated robot  71  and  FIG. 6(   b ) is a longitudinal sectional view showing the articulated robot  71 . 
     In  FIG. 6(   a ) and  FIG. 6(   b ), the articulated robot  71  includes a base  2 , a link mechanism  73 , an arm part  6  and a hand part  7 . The link mechanism  73  is provided with a base side link part  74  and an arm side link part  75  which are turnably connected with each other. 
     The base  2  includes an elevating/lowering cylinder  8  moving up and down in a vertical direction by rotation of an elevating/lowering motor (not shown). In this embodiment, the elevating/lowering cylinder  8  is guided by a guide shaft (not shown) to move up and down where a vertical direction in the drawing is a longitudinal direction. 
     The base side link part  74  is connected with the elevating/lowering cylinder  8  through a connecting shaft  8   b  and held so as to be capable of turning by a link mechanism motor  8   a  which is built in the elevating/lowering cylinder  8 . Further, the base side link part  74  is moved up and down to the base  2  along with moving up and down of the elevating/lowering cylinder  8 . 
     A base side pulley  74   a , an arm side pulley  74   b  and a belt  74   c  are built in the base side link part  74 . Further, the arm side pulley  74   b  and the arm side link part  75  are connected with each other by the connecting shaft  74   d . Therefore, when a turning angle ratio between the base side pulley  74   a  and the arm side pulley  74   b , in other words, a turning angle ratio between the base side link part  74  and the arm side link part  75  is appropriately adjusted, in the link mechanism  73 , a moving trajectory of a center point (connection point “Z”) of the connecting shaft  75   a  which turnably connects the arm side link part  75  with the arm part  6  is controlled on a predetermined straight line. 
     The arm part  6  is connected with the tip end of the arm side link part  75  through the connecting shaft  75   a  and held so as to be capable of turning by an arm part motor  751  which is built in the arm side link part  75 . In  FIG. 6 , for convenience of description, the arm part motor  751  is built in the arm side link part  75  but the present invention is not limited to this structure. For example, the arm part motor  751  may be built in the arm part  6  or it may be disposed anywhere. 
     The hand part  7  is structured of an upper support frame  7   a  and a lower support frame  7   b  which are disposed in parallel to each other. The upper support frame  7   a  and the lower support frame  7   b  are connected with the tip end of the arm part  6  through a connecting shaft  6   c  and a connecting shaft  6   d  respectively and they are held so that they can be turned by a lower support frame motor  6   a  and an upper support frame motor  6   b  which are respectively built in the arm part  6 . 
     In this embodiment, control signals for driving the elevating/lowering motor (not shown), the link mechanism motor  8   a , the arm part motor  751 , the lower support frame motor  6   a  and the upper support frame motor  6   b  are appropriately transmitted from a computer (not shown) on the basis of programs which are inputted by an operator. 
       FIG. 7  is an explanatory view for explaining a mechanical operation of the articulated robot  71  in accordance with another embodiment of the present invention. In  FIG. 7 , an operation will be described in which a work-piece (for example, a circular semiconductor wafer)  30  is taken out from a cassette  40   a  to put in a cassette  40   d  which is apart from the cassette  40   a  by “3p” in a rightward direction in the drawing.  FIG. 7  shows a state where the work-piece  30  is taken out from the cassette  40   a  (the articulated robot  71  on a left side in the drawing) and a state before the work-piece  30  is placed in the cassette  40   d  (the articulated robot  71 ′ on a right side in the drawing). In this embodiment, the cassettes  40   a  through  40   d  are target positions where the work-piece  30  is carried out or carried in and, when the position of carrying into and carrying out is defined, a processing apparatus may be adopted instead of the cassette. 
     In  FIG. 7 , a length of the base side link part  74  is set to be “L 1 ”, a length of the arm side link part  75  is set to be “L 2 ”, a length of the arm part  6  is set to be “L 3 ”, and intervals of four cassettes  40   a  through  40   d  are respectively set to be “P”. Further, a radius on the arm side (see  FIG. 6 ) of the base side link part  74  is set to be “R 1 ”. In addition, a practical area in which the articulated robot  71  is capable of loading and unloading in and from the cassettes  40   a  through  40   d  is set to be about 2×(L 1 +L 2 ) at the maximum. 
     In  FIG. 7 , the work-piece  30  is placed on the tip end of the upper support frame  7   a  of the articulated robot  71  on a left side in the drawing. In this embodiment, the lower support frame  7   b  of the hand part  7  is not used in this operation and thus it is set in a bent state as shown in the drawing. 
     The upper support frame  7   a  of the hand part  7  is linearly moved in a positive direction of the “y”-axis while keeping its orientation in order to take out the work-piece  30  from the cassette  40   a . More specifically, the arm part  6  is turned in a clockwise direction around the connection point “Z” by the arm part motor  51  and the upper support frame  7   a  of the hand part  7  is turned in a counterclockwise direction around the connecting shaft  6   c  by the upper support frame motor  6   b . In this case, a moving trajectory of the connection point “Z” becomes a straight line in a direction perpendicular to the unloading direction of the work-piece  30  (positive direction of the “x”-axis). When the upper support frame  7   a  of the hand part  7  has been moved in the positive direction of the “y”-axis by a predetermined distance, taking out of the work-piece  30  from the cassette  40   a  is completed. 
     Next, it will be described that this work-piece  30  is loaded into the cassette  40   d.    
     First, the connection point “Z” is linearly moved in a positive direction of the “x”-axis. In this case, the connection point “Z” is linearly moved while the arm part  6  is turned around the connection point “Z” and the hand part  7  is turned around the connecting shaft  6   c . As a result, the upper support frame  7   a  can be moved to a position just before the cassette  40   d  (see the articulated robot  71 ′ on a right side in the drawing). In this embodiment, in the articulated robot  71 ′ on the right side in the drawing, the lower support frame  7   b  is overlapped with the upper support frame  7   a.    
     After that, the arm part  6  is turned in a clockwise direction around the connection point “Z” by the arm part motor  751  and the upper support frame  7   a  of the hand part  7  is turned in a counterclockwise direction around the connecting shaft  6   c  by the upper support frame motor  6   b . As a result, the upper support frame  7   a  of the hand part  7  is entered into the cassette  40   d . In this case, a moving trajectory of the connection point “Z” becomes a straight line in a direction perpendicular to the loading direction of the work-piece  30  (negative direction of the “x”-axis). After the upper support frame  7   a  of the hand part  7  has moved by a predetermined distance in the negative direction of the “y”-axis, the work-piece  30  is placed in the cassette  40   d.    
     As described above, according to  FIG. 7 , even when the arm part  6  and the link mechanism  73  (the base side link part  74  and the arm side link part  75 ) are controlled with linear interpolation, the connection point “Z” of the arm part  6  is controlled to move at optimal positions and thus rapid speed variation of the arm part  6  and the link mechanism  73  is not required (singular point is not generated). In the linear interpolation when the work-piece  30  is taken out from the cassette  40   a  and in the linear interpolation when the work-piece  30  is placed in the cassette  40   d , a singular point generated in the conventional articulated robot is not generated. Therefore, occurrence of vibration in the arm part  6  and the link mechanism  73  can be prevented and thus the work-piece  30  can be carried stably. 
     Further, as shown in  FIG. 7 , the length “L” of the base side link part  74  is set to be longer than the length “L 2 ” of the arm side link part  75 . In addition, the base  2  of the link mechanism  73  is disposed in a state that the center position of the base  2  is shifted by “A” on a side of the work-piece  30  (placed in the cassettes  40   a  through  40   d ) from the moving trajectory of the base end side (the connection point “Z”) of the arm part, in other words, that the center position of the base  2  is shifted by “A” on a side of a target position where a work-piece  30  in the cassettes  40   a  through  40   d , a processing apparatus or the like is carried out or carried in. Therefore, for example, in this embodiment, the articulated robot  71  is corresponded to four series cassettes in which four cassettes are adjacently disposed to enhance efficiency, and occupancy distance in a direction where the work-piece  30  is loaded/unloaded in/from the cassettes  40   a  through  40   d  (direction of the “y”-axis) is shortened and thus required space can be reduced. The distance “A” by which the center position of the base  2  of the link mechanism  73  is shifted to the side of the target position where the work-piece  30  in the cassette, the processing apparatus or the like is carried in or carried out can be set at a position for optimizing a space according to a process where the articulated robot  71  is disposed. For example, in  FIG. 7 , when processing apparatuses or other cassettes are arranged and disposed on an upper side in the drawing so as to face the cassettes  40   a  through  40   d , the “A” may be shifted in a direction shown by the arrow “Y”. In other words, when the work-piece  30  is carried between the cassettes  40   a  through  40   d  and the processing apparatus and another cassette on the upper side, a similar space saving effect can be obtained even when the center position of the base  72  of the link mechanism  73  is shifted either of the upper and lower directions in the drawing. Further, the “A” may be set to be zero if necessary. 
     In addition, since it is set that “L 1 ”&gt;“L 2 ”, movement can be performed from the cassette  40   a  to the cassette  40   d  quickly and thus time efficiency can be improved. Further, a weight of the arm side link part  75  is lighter than that of the base side link part  74  and thus the work-piece can be stably carried while vibration is prevented. 
     Further, according to  FIG. 7 , a work-piece can be stably carried with a simple control by turnably controlling the base side link part  74 , the arm part  6  and the hand part  7  respectively (in other words, by especially not turnably controlling the arm side link part  75  of the link mechanism  73 ). In this embodiment, four series cassettes in which four cassettes are adjacently disposed are shown but the present invention is not limited to this embodiment. Four or more cassettes may be used or three or less cassettes may be used. 
     EXAMPLES 
       FIG. 8  is an explanatory view for explaining linearity of the connection point “Z” in the articulated robot  71  in accordance with another embodiment of the present invention. Especially,  FIG. 8(   a ) is a plan view showing the articulated robot  71  and  FIG. 8(   b ) shows an error in the “y”-axis direction when the connection point “Z” is moved in a positive direction of the “x”-axis. 
     In  FIG. 8(   a ), the practical area “2×(L 1 +L 2 )” described above is about ±670 mm. 
     Therefore, when the error in this practical area is small to some extent, the articulated robot  71  is recognized to be practical. 
     In  FIG. 8(   b ), when the “X” coordinate is at positions of 100 mm or less, there is almost no error but, when the “X” coordinate becomes larger than 100 mm, there is a little error. However, in the practical area of about from −670 mm to 670 mm, the error is about 3 mm at the maximum, which may be negligible from a practical viewpoint. Therefore, the articulated robot  71  is provided with usefulness. The area of about from −670 mm to 670 mm is one example, and it may be changed according to arrangement of practically used cassettes or a space in a direction loading/unloading a work-piece in/from a cassette. 
     The articulated robot in accordance with the present invention is useful as a robot which is capable of carrying a work-piece such as a semiconductor wafer stably with a simple control and without using an expensive motor generating a large driving force. In addition, the articulated robot in accordance with the present invention is useful as a robot which is capable of stably carrying a work-piece such as a semiconductor wafer and reducing installation space. 
     While this invention has been described in conjunction with the specific embodiments outlined above, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. Accordingly, the preferred embodiments of the invention as set forth above are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the inventions as defined in the following claims.