Patent Publication Number: US-2005115351-A1

Title: Seal structure for transfer robot

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
      The present application claims priority to Japanese patent application No. 2003-399441 filed Nov. 28, 2003 is hereby incorporated into the present application by this reference.  
     BACKGROUND OF THE INVENTION  
      (1) Field of the Invention  
      The present invention relates to a seal structure for a transfer robot for executing a transfer operation of a substrate such as a semiconductor wafer, a flat panel glass substrate and the like in a vacuum work chamber.  
      (2) Description of the Prior Art  
      The transfer robot for the vacuum work employs a seal structure for preventing the vacuum work chamber from being polluted, and there has been known as a conventional seal structure, a seal structure in which a sealing property is secured by a bellows with respect to a movement of an arm in a vertical direction (an elevating motion of the arm), and a sealing property is secured by a magnetic fluid seal with respect to a rotation of the arm (refer to, for example, Japanese Unexamined Patent Publication Nos. 2001-24045 and 2001-269890).  
     SUMMARY OF THE INVENTION  
      However, an amount of stroke of the arm in the vertical direction is increased in recent years. In accordance with the increase of the stroke amount, the bellows is made large in size, and a high rigidity is required in the bellows. Further, a cost of the magnetic fluid seal is extremely high.  
      The present invention is made by paying attention to the problems in the conventional seal structure as mentioned above, and an object of the present invention is to provide a seal structure of a transfer robot which does not cause a large size of the seal structure even in the case that an amount of stroke of an arm is increased in a vertical direction, does not require a high rigidity, and can sufficiently secure a sealing property without using an expensive magnetic fluid seal.  
      In accordance with the present invention, there is provided a seal structure for a transfer robot which is provided with an arm protruding upward from a main body housing and makes the arm to execute an elevating motion, a rotating motion and a bending and stretching motion, wherein between an upper end portion of the main body housing and an outer peripheral surface of an arm driving shaft, there are provided an annular mechanical seal which is pressure contacted with the outer peripheral surface of the arm driving shaft, an annular seal holding member which holds the annular mechanical seal, and a floating action holding means which is provided between the upper end portion of the main body housing and the annular seal holding member, holds the annular seal holding member so as to freely float and adjusts an attitude of the annular mechanical seal in accordance with a tilting motion of the arm driving shaft.  
      In the seal structure for the transfer robot in accordance with the present invention, in a state in which the arm moves downward to a portion near the lowest end position and a heavy substrate is held by the leading end of the extended arm, the arm driving shaft is tilted by a weight of the substrate. When the arm driving shaft is tilted, the attitude of the inexpensive annular mechanical seal such as a lip seal or the like is adjusted in accordance with the tilting motion of the arm driving shaft on the basis of an operation of the floating action holding means. On the basis of the adjustment of the attitude of the annular mechanical seal, a pressure distribution which the annular mechanical seal is applied from the arm driving shaft becomes approximately uniform, and it is possible to secure a sealing property and a long service life of the annular mechanical seal. In this case, in the case that no floating action holding means is provided, the pressure distribution which the annular mechanical seal is applied from the arm driving shaft becomes uneven due to the tilting motion of the arm driving shaft, so that it is hard to secure the sealing property, and the annular mechanical seal tends to be deteriorated.  
      In accordance with the provision of the bellows for sealing between the annular seal holding member and the floating action holding means, it is possible to shut off a communication state between the vacuum work chamber and the main body housing inner portion caused by a gap between the annular seal holding member and the floating action holding means and generated by floating the annular seal holding member, by means of the bellows, so that it is possible to prevent the vacuum work chamber from being polluted. Further, since the bellows is arranged between the annular seal holding member and the floating action holding means, and is not expanded and contracted in accordance with the elevating motion of the arm, it is not necessary to make the bellows large in size even in the case that the stroke amount of the arm in the vertical direction is increased, and it is not necessary to increase the rigidity of the bellows.  
      Said arm driving shaft is an arm first driving shaft for rotating the arm. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       FIG. 1  is a schematic view of a main portion of a transfer robot in accordance with an embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      In  FIG. 1 , a transfer robot is structured by a main body portion  1  and an arm  2 , and the arm  2  protrudes upward from a housing of the main body portion  1 , that is, a main body housing  11 , executes an elevating motion (a movement along an axis Z), a rotating motion (a rotation around an axis θ) and a bending and stretching motion (a movement along an axis A) within a vacuum work chamber  100  by an elevating mechanism  12 , an arm first driving shaft  13  and an arm second driving shaft  14  arranged within the main body housing  11 , and holds a substrate (not shown) such as a semiconductor wafer, a flat panel glass substrate in a leading end portion (not shown) so as to execute a transfer work.  
      The arm first driving shaft  13  is a driving shaft which connects between an actuator (not shown) and a case  21  of the arm  2 , and rotates the arm  2 , and the arm second driving shaft  14  is a driving shaft which connects between another actuator (not shown) and a pulley (not shown) within the case  21  of the arm  2 , and bends and stretches the arm  2 . The arm first driving shaft  13  and the arm second driving shaft  14  are arranged on the same axis, and are rotatable without interfering with each other.  
      The elevating mechanism  12  is provided with a plurality of members  12   b  which are mounted to an outer peripheral portion of a table  12   a  mounting the arm first driving shaft  13  and the arm second driving shaft  14  thereon, and a guide member  12   c  which is provided in an inner peripheral surface of the main body housing  11  and allows a linear movement in a vertical direction of each of the elevating members  12   b  while engaging with each of the elevating members  12   b . The arm first driving shaft  13  and the arm second driving shaft  14  are moved upward and downward by elevating the elevating member  12   b  by the actuator (not shown), whereby the arm  2  is moved upward and downward.  
      The transfer robot is provided with a seal structure  3  for sealing between a vacuum work chamber  100  and a main body housing inner portion  200  in an atmospheric air side.  
      The seal structure  3  is provided in a side of an upper end portion  11   a  of the main body housing  11 . The seal structure  3  is constituted by a first seal structure  4  for sealing between an inner peripheral surface of the arm first driving shaft  13  and an outer peripheral surface of the arm second driving shaft  14 , and a second seal structure  5  for sealing between an outer peripheral surface of the arm first driving shaft  13  and the main body housing  11 .  
      The first seal structure  4  is constituted by an annular mechanical seal  41  which is formed by an annular lip seal or the like which is pressure contacted with an outer peripheral surface of the arm second driving shaft  14 , a grease  42  which is filled in the annular mechanical seal  41 , an annular dust seal  43  which is arranged in an outer side of the annular mechanical seal  41  as occasion demands, and an annular seal holding member  44  which holds the annular mechanical seal  41  and the annular dust seal  43  in an inner recess portion in a press fitting manner.  
      The second seal structure  5  is constituted by an annular mechanical seal  51  which is formed by an annular lip seal or the like which is pressure contacted with an outer peripheral surface of the arm first driving shaft  13 , a grease  52  which is filled in the annular mechanical seal  51 , an annular dust seal  53  which is arranged in an outer side of the annular mechanical seal  51  as occasion demands, an annular seal holding member  54  which holds the annular mechanical seal  51  and the annular dust seal  53  in an inner recess portion in a press fitting manner, and a floating action holding means  55  which is provided between the main body housing upper end portion  11   a  and the annular seal holding member  54  and holds the annular seal holding member  54  so as to freely float.  
      The floating action holding means  55  is constituted by a hollow disc portion  55   a  which is fixed to an inner side of a top plate of the main body housing  11 , a holding portion  55   b  which is fixed to the hollow disc portion  55   a  so as to extend annularly to a lower side, a direct acting bearing portion  55   c  which is arranged in a lower end of the holding portion  55   b , a hollow disc portion  55   d  in which the outer side engages the direct acting bearing portion  55   c  and the inner side is fixed to a lower end of the annular seal holding member  54 , and a bellows  55   e  which is arranged between the upper hollow disc portion  55   a  and the lower hollow disc portion  55   d.    
      In the transfer robot structured in the manner mentioned above, in the case that the heavy substrate is held by the leading end of the extended arm  2  in a state in which the arm  2  moves downward to a state illustrated in  FIG. 1 , that is, to a position near the lowest end position, the arm first driving shaft  13  is tilted due to the weight of the substrate. When the arm first driving shaft  13  is tilted, the attitude of the annular mechanical seal  51  is adjusted in accordance with the tilting motion of the arm first driving shaft  13  on the basis of the operation of the floating action holding means  55 . In other words, when the arm first driving shaft  13  is tilted, the hollow disc portion  55   d  is moved in a radial direction by the direct acting bearing portion  55   c , so that the attitude of the annular mechanical seal  51  is adjusted. In accordance with the attitude adjustment of the annular mechanical seal  51 , a pressure distribution which the annular mechanical seal  51  is applied from the arm first driving shaft  13  is approximately even, so that it is possible to secure a sealing property and achieve a long service life of the annular mechanical seal  51 .  
      Further, since the bellows  55   e  shuts off a communication state between the vacuum work chamber  100  and the main body housing inner portion  200  caused by a gap between the annular seal holding member  54  and the floating action holding means  55  and generated by floating the annular seal holding member  54 , it is possible to prevent the vacuum work chamber  100  from being polluted. Further, since the bellows  55   e  is arranged between the annular seal holding member  54  and the floating action holding means  55 , and is not expanded and contracted in accordance with the elevating motion of the arm  2 , the bellows  55   e  is not made large in size even in the case that the stroke amount of the arm  2  in the vertical direction is increased, and it is not necessary to increase the rigidity of the bellows  55   e.