Abstract:
A stacker crane includes a lower carriage including a lower drive wheel, a lower travel motor, and a support located apart from the lower drive wheel; an upper carriage including an upper drive wheel and an upper travel motor that drives the upper drive wheel; and a mast fixed to the lower carriage, standing upward from the lower carriage and connected to the upper carriage, and including a transfer device capable of moving up and down. A displacement mechanism that raises and lowers the support is provided on the lower carriage between a grounded position supported by a lower rail and a retracted position lifted off the lower rail. The support is lowered to the grounded position when the stacker crane is installed between the lower rail and the upper rail and when the stacker crane is stopped for maintenance, and the support is raised to the retracted position when the stacker crane is operated.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a stacker crane and a method for operating the same, and in particular relates to reducing stress between a mast and a lower frame. 
     2. Description of the Related Art 
     The applicant has proposed providing travel motors in upper and lower carriages of a stacker crane so as to cause the upper and lower carriages to travel in a synchronized manner (See, for example, JP 2002-106414A). If the upper and lower carriages run out of synchronization, a strong force is exerted on the connection between the mast and the carriages, and therefore, in JP 2002-106414A, the mast is attached pivotally to the lower carriage. 
     However, a pivotal mast is difficult to stand upright during installation of the stacker crane. Similarly, if the mast does not stand upright, it is difficult to perform maintenance on the stacker crane. Furthermore, if a mast with a large weight is to be pivoted, a large pivoting mechanism is needed. 
     SUMMARY OF THE INVENTION 
     Preferred embodiments of the present invention provide a stacker crane with a simple structure that significantly reduces stress exerted on a connection between a mast and a lower carriage during normal traveling, while the mast is stood upright during installation and maintenance of the stacker crane. 
     A stacker crane according to a preferred embodiment of the present invention includes a lower carriage including a lower drive wheel in contact with a lower rail, a lower travel motor that drives the lower drive wheel, and a support located apart from the lower drive wheel along a length direction of lower rail; an upper carriage including an upper drive wheel in contact with an upper rail, and an upper travel motor that drives the upper drive wheel; and a mast fixed to the lower carriage, standing upward from the lower carriage, connected to the upper carriage, and having a transfer device attached so as to be capable of being elevated, wherein the lower carriage is provided with a displacement mechanism that raises and lowers the support between a grounded position supported by the lower rail and a retracted position lifted upward off the lower rail. 
     In a method for operating a stacker crane according to another preferred embodiment of the present invention, the support is lowered to the grounded position and supported by the lower rail, when the stacker crane is installed between the lower rail and the upper rail and also when the stacker crane is stopped so as to perform maintenance, and the support is raised to the retracted position lifted upward off the lower rail when the stacker crane is operated. 
     A state is considered in which the upper carriage and the lower carriage run out of synchronized travel and the mast tilts from a perpendicular state. Here, if the support is in contact with the lower rail, a strong force is exerted on the connection between the mast and the lower carriage, and therefore high rigidity is required at the connection. By contrast, if the support is allowed to be raised and lowered between a grounded position and a retracted position and further, the support is retracted during operation of the stacker crane, or in other words, during normal operations excluding maintenance, testing, or the like, the strong force is not exerted on the connection if the mast tilts within an allowable range. As a result, the weight of the mast and the lower carriage is reduced, and the durability and reliability thereof are increased. Also, if the support is operated during installation of the stacker crane, during maintenance, and the like, the orientation of the lower carriage is stabilized, and the mast stands upright perpendicularly. Accordingly, the stacker crane is installed accurately and easily, and maintenance is also easier. Furthermore, since the mast may be fixed to the lower carriage, the structure of the stacker crane is simpler compared to the case where the mast is able to pivot with respect to the lower carriage. 
     Preferably, the lower carriage includes a main body including the lower drive wheel and the lower travel motor, and the support located either in front of or behind the main body, and the displacement mechanism includes at least an eccentric pin including a circular plate, a round bar including a base end that is integrated with the circular plate and is eccentric relative to the center of the circular plate, a screw portion provided at a leading end of the round bar, and a manipulation portion that rotates the circular plate, at least a receiving hole provided in the support for the circular plate or the round bar, and at least a receiving hole provided in the main body for the round bar or the circular plate. Thus, the support may be raised and lowered between the grounded position and the retracted position by rotating the eccentric pin with the manipulation portion. 
     A mechanism may be used in which a bottom surface of the support is directly in contact with the lower rail, but preferably, the support includes a roller that comes into contact with an upper surface of the lower rail at the grounded position and is lifted off the lower rail at the retracted position. Thus, not only is the mast kept upright by the support at the grounded position, but the stacker crane is easily moved by a manual push or the like during installation and during maintenance. 
     Preferably, the support includes at least a guide roller that faces a guide surface on an underside of the lower rail, is at an opposite position to the roller and is attached to the support with a gap between the guide roller and the guide surface of the lower rail both at the grounded position and at the retracted position. Thus, if the mast tilts toward the support beyond the allowable range, the roller will come into contact with the lower rail to prevent further tilting. Also, if the mast tilts toward the side opposite to the support beyond the allowable range, the guide roller will come into contact with the guide surface of the lower rail to prevent further tilting. 
     Preferably, when the support is grounded at the grounded position, along the length direction of the lower rail, the center of gravity of the mast and the position of contact between the lower drive wheel and the lower rail are the same. If the support is lowered to the grounded position, the weight from the mast is exerted directly on the point of contact between the drive wheel and the lower rail, and the mast stands upright perpendicularly. If two or more drive wheels are provided and are in contact with two or more lower rails, the center of gravity of the mast is preferably positioned on a line connecting the points of contact between the drive wheels and the lower rails. 
     Preferably, the displacement mechanism makes the support up and down with respect to the main body between the retracted position and the grounded position. 
     More preferably, the displacement mechanism is configured to make the mast perpendicular to the main body when the stacker crane is installed between the lower rail and the upper rail and also when the stacker crane is stopped to perform maintenance. This configuration makes it easier to perform installation and maintenance of the stacker crane. Also, if the support is retracted, operation of the stacker crane may be started from a state in which the mast is perpendicular to the lower carriage. Since the mast is perpendicular to the lower carriage, a moment of force that causes the mast to tilt is less likely to act thereon. 
     In particular, it is preferable that at a position along the length direction of the lower rail, the mast is fixed directly above the lower drive wheel. Thus, the weight from the mast is exerted directly on the point of contact between the lower drive wheel and the travel rail, and a moment of force that causes the mast to tilt is less likely to act thereon. 
     Most preferably, the support includes at least a roller in contact with an upper surface of the lower rail at the grounded position and lifted off the lower rail at the retracted position, and a guide roller facing the guide surface on the underside of the lower rail at an opposite position to the roller, the guide roller is attached to the support with a gap between the guide roller and the guide surface of the lower rail both at the grounded position and at the retracted position, neither the roller nor the guide roller comes into contact with the lower rail when tilting of the mast to the lower carriage is within the allowable range, and if the tilting of the mast to the lower carriage exceeds the allowable range, the roller or the guide roller comes into contact with the lower rail. 
     Thus, at the retracted position, the stacker crane may be moved by a manual push or the like with the roller. During operation of the stacker crane, even if the mast tilts within the allowable range due to the upper and lower carriages running out of synchronization for some reason, a strong force is not exerted on the connection between the mast and the lower carriage. Accordingly, the durability and reliability of the connection are improved, and the weight of the connection is reduced. Also, if the mast tilts beyond the allowable range, the roller comes into contact with the lower rail to prevent further tilting. Also, if the mast tilts beyond the allowable range in the opposite direction, the guide roller comes into contact with the guide surface of the lower rail to prevent further tilting. 
     The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial cutout side view of a stacker crane and upper and lower travel rails according to a preferred embodiment of the present invention. 
         FIG. 2  is a cross-sectional view taken along line A-A in  FIG. 1 . 
         FIG. 3  is an enlarged cross-sectional view taken along line B-B in  FIG. 1 . 
         FIG. 4  is a diagram showing a structure for attaching an eccentric pin. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, preferred embodiments of the present invention will be described. The scope of the present invention should be construed based on the description of the claims and in accordance with the understanding of a person skilled in the art, with reference to the description of the specification and known techniques in the field. 
       FIGS. 1 to 4  show a stacker crane  2  according to a preferred embodiment of the present invention. In the drawings, reference numeral  4  indicates a lower carriage including a main body  5  and a support  28 , reference numeral  6  indicates an upper carriage, and a mast  8  fixed to the lower carriage  4  connects the upper and lower carriages  4  and  6 . The mast  8  may be fixed to the upper carriage  6  or be attached pivotally to the upper carriage  6 . The mast  8  may be a perpendicular tube that raises and lowers a transfer device  10  such as a SCARA arm, and instead of directly raising and lowering the transfer device  10 , the mast  8  may raise and lower an elevating platform on which a transfer device is mounted. Reference numeral  11  indicates a transfer motor that drives the transfer device  10 . 
     The stacker crane  2  travels inside of an automated warehouse (not shown) or the like, the lower carriage  4  travels along a lower rail  12 , and the upper carriage  6  travels along an upper rail  14 . The upper surface of the lower rail  12  is a tread  16 , the underside surface thereof is a guide surface  18 , and reference numeral  20  indicates a side surface thereof. One drive wheel  22  and a travel motor  24  therefor are provided in the main body  5  of the lower carriage  4 , for example. The support  28  is attached to the bridge  26  of the main body  5  and may be raised and lowered between a grounded position and a retracted position. In the grounded state, the support  28  is supported in contact with the tread  16  of the lower rail  12 . In the retracted position, the support  28  is lifted and is not in contact with the tread  16  of the lower rail  12 . 
     The support  28  includes one driven roller  30 , for example. The main body  5  and the support  28  respectively include guide rollers  32  and  33  that face the guide surface  18 , and guide rollers  34  and  35  that are guided by the side surface  20 . The guide rollers  32  to  35  are provided in pairs on both the left and right of the lower rail  12 , and the guide rollers  33  are separated from the guide surface  18  by a gap, when the support is at the grounded position and also when it is at the retracted position. When the mast  8  tilts forward beyond an allowable range, the guide rollers  33  come into contact with the guide surface  18  to restrict forward tilting. In the present specification, the left and right direction is the direction orthogonal or substantially orthogonal to the lower rail  12  or the upper rail  14  in a horizontal plane, and regarding front and rear, the main body  5  is in the front and the support  28  is in the rear. 
     As shown in  FIG. 3 , the guide rollers  33  are attached to the support  28  by bearings  37 , and the guide rollers  35  are attached to the support  28  by bearings  36 . The guide rollers  32 ,  34 , and  35  may always be in contact with the lower rail  12 , or may be configured to come into contact with the lower rail  12  when the mast  8  tilts left or right beyond the allowable range. 
     Returning to  FIG. 1 , a pair of left and right drive wheels  40  are provided on the upper carriage  6 , for example, are driven by an upper travel motor  41  to travel, and are in contact with the side surface of the upper rail  14 . Also, for example, a pair of left and right guide rollers  42  are provided on the upper carriage  6  to guide the upper carriage  6  so that it does not shake left and right with respect to the upper rail  14 . Further, sprockets, gears, or the like are provided inside of the upper carriage  6  in addition to the drive motor  41  for the chain or belt to raise and lower the transfer device  10 . The upper carriage  6  may have any configuration. 
       FIG. 2  shows the structure of the lower carriage  4 . An elevation motor  44  that raises and lowers the transfer device  10  is arranged to face the travel motor  24 . Also, the center of gravity of the mast  8  is located directly above the drive wheel  22 , and if the mast  8  is stood upright perpendicularly by the support  28 , the center of gravity of the mast  8  will be the same to the position of contact between the drive wheel  22  and the lower rail  12 , or in other words, the support will be directly above the center of the drive wheel  22  in the length direction. The main body  5  includes a pair of left and right bridges  26  and  26 , and between the bridges  26  and  26  the transfer motor  11  and the transfer device  10  are accommodated when the transfer device  10  is lowered. 
     As shown in  FIGS. 3 and 4 , the driven roller  30  is arranged in the center in the left-right direction of the support  28 , and is supported by a pair of bearings  46  and  46 . For example, an attachment plate  48  on the support  28  is fixed by bolts  56  to an attachment plate  49  on the bridge  26 , and is configured such that its height can be adjusted with eccentric pins  50 . The eccentric pins  50  each include a circular plate  51  and a round bar  58  on the support  28 , the center line C-C of the round bar  58  is eccentric from the center line D-D of the circular plate  51 , and the center of an manipulation portion  52  such as a hexagonal hole is the same to the center line C-C. Further, the manipulation portion may be of any shape such as a nut shape instead of the hexagonal hole, and it is sufficient that the manipulation portion rotates the eccentric pin  50  according to a manual operation. A screw portion  60  is provided on the leading end of the round bar  58 , the circular plate  51  is accommodated in a hole  53  of the attachment plate  48 , the round bar  58  is accommodated in a round hole  59  of the attachment plate  49  and the screw portion  48  is fixed by the nut  62 , such that the eccentric pin  50  is prevented from rotating. As shown in  FIG. 3 , the hole  53  has a shape slightly different from a circle so that the circular plate  51  may rotate around the manipulation portion  52 . In the present preferred embodiment, the manipulation portion  52  preferably is provided on the support  28 , but the eccentric pin  50  may be arranged such that the manipulation portion  52  is located on the bridge  26 . Also, the eccentric pin  50  is a member that includes an axis on the attachment plate  48  and an axis on the attachment plate  49  and is able to be rotated by operating the manipulation portion  52 . 
     The manipulation portion  52  is rotated with a hexagonal wrench or the like, and for example, the eccentric pin  50  is rotated about the axis C-C, and the support  28  is raised and lowered by about several millimeters with respect to the main body  5 , for example. The example of  FIG. 3  shows a grounded state (grounded position) in which the driven roller  30  is in contact with the lower rail  12 . If the manipulation portion  52  is rotated from this state, a retracted state (retracted position) will be entered in which the driven roller  30  is lifted off the lower rail  12 . The gap between the driven roller  30  and the lower rail  12  in the retracted state determines the allowable range with respect to rearward tilting of the mast  8 . In the retracted state, the support  28  rises and the driven roller  30  is lifted from the lower rail  12 . In the grounded state, the support  28  lowers and the driven roller  30  comes into contact with the lower rail  12 . Also, the bolts  56  are inserted into a long holes  54  to adjust the height of the support  28  with the eccentric pin  50 , and by fastening the bolts  56  at that position, the height of the support  28  may be fixed. 
     An operation of the present preferred embodiment will be described next. When the stacker crane  2  is installed between the lower rail  12  and the upper rail  14  in an automated warehouse, it is brought into the grounded state by lowering the support  28 . At this time, the height of the support  28  is adjusted so that the mast  8  is perpendicular. Upon doing so, the stacker crane  2  may be installed, keeping the mast  8  in the perpendicular state, and since the orientation of the lower carriage  4  is stable, installation is easier. Also, at a time of performing maintenance, if the orientation of the lower carriage  4  is stabilized so that the mast  8  is kept in the perpendicular state, the task is easier. Furthermore, the stacker crane  2  may be moved by pushing manually or the like when installing and when performing maintenance. It is difficult to move the stacker crane  2  by pushing manually, when the support is in the retracted state, because the orientation of the lower carriage  4  is unstable and the mast  8  does not stand on its own. 
     During normal operation of the stacker crane  2 , the support  28  is raised so that the driven roller  30  is lifted off the lower rail  12 . Even if the upper and lower carriages  4  and  6  come out of synchronization and the mast  8  tilts rearward within the allowable range, a strong force is not exerted on the connection between the mast  8  and the lower carriage  4 . Accordingly, the durability and reliability of the connection are improved, and the weight of the connection portion is reduced. 
     If the mast  8  tilts rearward beyond the allowable range, the driven roller  30  comes into contact with the lower rail  12  and further rearward tilting is prevented. Also, if the mast  8  tilts forward beyond the allowable range, the guide roller  33  comes into contact with the guide surface  18  of the lower rail  12  and further forward tilting is prevented. 
     The center of gravity of the mast  8  in the grounded state is located directly above the center of the drive wheel  22 . Therefore, the weight from the mast  8  is exerted directly on the point of contact between the drive wheel  22  and the lower rail  12 , and there is no moment of force that causes the mast  8  to tilt. 
     While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.