Abstract:
In an elevating device for raising and lowering a heavy member by rotating a rotation axis extending in a direction crossing a vertical direction, the rotation axis has one end portion to which the heavy member is connected. The rotation axis includes a bendable portion adapted to transmit a rotational force. A leading end portion of the free end portion is vertically suspended from the bendable portion of the rotation axis regardless of a stop position of the rotation axis. A rotation applied by the heavy member to the rotation axis is suppressed by the suspended leading end portion. With such an elevating device, unexpected rotation of the rotation axis is positively suppressed in a cost-effective manner.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to an elevating device for raising and lowering a heavy member by rotating a rotation axis; and, more particularly, to an elevating device having a mechanism for preventing unexpected rotation due to gravity of the heavy member while the rotation axis stops. 
       BACKGROUND OF THE INVENTION 
       [0002]    Conventionally, a ball screw mechanism has been widely used for raising and lowering a heavy member. For example, a plasma etching apparatus has a radio frequency power supply unit for plasma generation as a heavy equipment weighing about 70 kg to about 80 kg, and the ball screw mechanism is used for raising and lowering the radio frequency power supply unit which needs to be raised and lowered for maintenance. Specifically, when a rotation axis is rotated by using a handle, the rotation of the rotation axis is transferred to a shaft of a ball screw through a gear train, thus raising and lowering the radio frequency power supply unit. 
         [0003]    In that case, however, while the rotation of the rotation axis stops, the raised heavy equipment may move down by reversely rotating the rotation axis by its gravity. 
         [0004]    This may theoretically be prevented by making a lead angle of the ball screw smaller than a static friction angle so that a self-locking action is obtained. In this case, however, since the static friction angle of the ball screw is small, the lead angle of the ball screw becomes extremely reduced. As a result, a pitch of the screw is reduced, which is not practical. 
         [0005]    In order to prevent the aforementioned problem, there have been proposed a ratchet mechanism disclosed in Japanese Patent Laid-open Publication No. H11-125318 and a friction break. 
         [0006]    However, the ratchet mechanism acts in only one direction, and may be released. If it is released, it cannot function to prevent a reverse rotation. Further, a ratchet claw or the like may be broken, so that the ratchet mechanism has a poor reliability in general. Meanwhile, when the friction brake is used, a brake pad needs to be replaced when it is worn out, increasing the cost of consumables. Besides, the brake needs to be adjusted regularly, so that the maintenance cost increases. 
         [0007]    In a case where a worm wheel and a worm gear are provided in the gear train between the rotation axis and the ball screw shaft, a reverse rotation can be prevented by making a lead angle of the worm gear smaller than a static friction angle so that a self-locking mechanism is obtained. However, if an initial speed is applied thereto, no brake does work other than the friction between the gears. As a result, the heavy equipment may move down due to the rotation of the gears. 
       SUMMARY OF THE INVENTION 
       [0008]    It is, therefore, an object of the present invention to provide an elevating device capable of positively preventing unexpected rotation of a rotation axis due to gravity of a heavy member in a cost-effective manner. 
         [0009]    The present inventors have noticed that an initial speed of a rotation axis is slow at first but gradually accelerates, like a speed increase on a slope. That is, the present inventors have found that a reverse rotation of the rotation axis can be easily prevented by suppressing the rotation of the rotation axis while no initial speed is applied thereto. 
         [0010]    In accordance with the present invention, there is provided an elevating device for raising and lowering a heavy member by rotating a rotation axis extending in a direction crossing a vertical direction, the rotation axis having one end portion to which the heavy member is connected and the other free end portion, wherein the rotation axis comprises a bendable portion adapted to transmit a rotational force and to be bent regardless of a rotation stop position of the rotation axis; and a leading end portion of the free end portion adapted to be vertically suspended from the bendable portion of the rotation axis, a rotation applied by the heavy member to the rotation axis being suppressed by the suspended leading end portion. 
         [0011]    For example, the rotation applied by the heavy member to the rotation axis can be suppressed by making a braking torque applied to the rotation axis due to a weight of the suspended leading end portion greater than a rotational torque applied by the heavy member to the rotation axis. 
         [0012]    Furthermore, when the suspended free end portion is rotated by the rotational force applied by the heavy member to the rotation axis, the rotation of the rotation axis is suppressed by the contact between the leading end portion and a wall surface or the like adjacent thereto. In this case, the weight of the leading end portion becomes no problem. Even when an initial speed is applied to the rotation axis, the rotation of the rotation axis can be prevented after the leading end portion contacts with the wall surface or the like. 
         [0013]    The bendable portion has one or more links as a part of the rotation axis, and each of the links has both end portions rotatably coupled to another link or the rotation axis wherein respective coupling shafts provided at both ends of the link are extended in different directions. Accordingly, even when the rotation axis stops at any rotation angle, the leading end portion can be vertically suspended. In case the number of the links is one and the coupling shafts provided at both sides of the link are extended perpendicular to each other, the leading end portion can be vertically suspended more readily. 
         [0014]    The rotation axis and the heavy member may be connected to each other through a ball screw for raising and lowering the heavy member and a gear train for connecting the ball screw and the rotation axis. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0015]    The above and other objects and features of the present invention will become apparent from the following description of preferred embodiments given in conjunction with the accompanying drawings, in which: 
           [0016]      FIG. 1  is a perspective view of an etching apparatus using an elevating device in accordance with an embodiment of the present invention; 
           [0017]      FIGS. 2A and 2B  show a schematic cross sectional view of principal parts taken along line A-A of  FIG. 1  and a view thereof seen in the direction of arrow B of  FIG. 1 , respectively; 
           [0018]      FIGS. 3A and 3B  illustrate a configuration of the elevating device, wherein  FIG. 3A  is a front view thereof seen in the direction of arrow B of  FIG. 1 , and  FIG. 3B  provides a bottom view thereof; 
           [0019]      FIG. 4  offers a perspective view depicting a state where a handle  40  is attached to a rotation axis  30 ; 
           [0020]      FIG. 5  presents a perspective view showing a state where the handle  40  is separated from the rotation axis  30 ; 
           [0021]      FIGS. 6A and 6B  represent a state where a leading end portion is suspended regardless of a rotation angle of the rotation axis; and 
           [0022]      FIG. 7  describes another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0023]    Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. 
         [0024]    Here, there will be described a case where the present invention is applied to a plasma etching apparatus as an example.  FIG. 1  is a perspective view of an etching apparatus using an elevating device in accordance with an embodiment of the present invention; and  FIGS. 2A and 2B  show a schematic cross sectional view of principal parts taken along line A-A of  FIG. 1  and a view thereof seen in the direction of arrow B of  FIG. 1 , respectively. 
         [0025]    A plasma etching apparatus  10  includes an airtight chamber (processing chamber)  11  having a wall made of, e.g., aluminum. In the chamber  11 , there are provided a susceptor (not shown) for horizontally supporting a semiconductor wafer (hereinafter, simply referred to as “wafer”) as a target substrate, the susceptor serving as a lower electrode, and an upper electrode  12  disposed above the susceptor to face it. The plasma etching apparatus  10  is constructed as a lower side dual frequency application type in which a first radio frequency power of a higher radio frequency (e.g., 100 MHz) for plasma generation and a second radio frequency power of a lower radio frequency (e.g., 3.2 MHz) for ion attraction are applied to the susceptor as the lower electrode. 
         [0026]    A radio frequency power supply unit  13  is provided under the chamber  11 . The radio frequency power supply unit  13  includes: a first matcher  14  disposed directly under the chamber  11 , for the first radio frequency power; a second matcher  15  disposed under the first matcher  14 , for the second radio frequency power; a first radio frequency power supply  16  provided under the second matcher  15 , for supplying a first radio frequency power; and a second radio frequency power supply (not shown) provided at a side of the first radio frequency power, for supplying a second radio frequency power. 
         [0027]    The radio frequency power supply unit  13  can be raised and lowered by a ball screw mechanism having a ball screw  21 . The ball screw mechanism has the linear shafts  22  disposed as elevation guides at both sides of the ball screw  21 . The ball screw  21  and the linear shafts  22  provided at both sides thereof are arranged at opposite sides of the etching apparatus  10  with the radio frequency power supply unit  13  interposed therebetween. 
         [0028]      FIGS. 3A and 3B  illustrate a configuration of the elevating device, wherein  FIG. 3A  is a front view thereof seen in the direction of arrow B of  FIG. 1 , and  FIG. 3B  is a bottom view thereof. A worm wheel  23  is attached to a bottom portion of each ball screw  21 , and worm gears  24  are engaged with the respective worm wheels  23 . The shafts of the worm gears  24  are connected to each other by a single cross shaft  26  via respective couplings  25 . A bevel gear  27  is fixed between the coupling  25  and the worm gear  24  at one side. Further, the bevel gear  27  is engaged with another bevel gear  28  which is fixed to a base end portion  31  of the rotation axis  30 . 
         [0029]    The rotation axis  30  has the base end portion  31 , a bendable portion  32  and a leading end portion  33 . The base end portion  31  is held by a bracket  29  fixed to a frame of the etching apparatus  10 . Although the rotation axis  30  is disposed horizontally in the illustrated embodiment, it is not limited thereto. The rotation axis  30  may be disposed at any angle by means of the gear train provided between itself and the ball screw as long as it crosses a vertical direction. 
         [0030]    A square pillar-shaped connecting member  34  is provided at an end surface of the leading end portion  33  of the rotation axis  30 , and a handle  40  is detachably connected thereto. The handle  40  has a handle shaft  41 , a handle bar  42  and a grip  43 . A connection recess  44  into which the connecting member  34  is fitted is formed in a leading end of the handle shaft  41 . The handle shaft  41  may has a larger diameter portion  45  for easy grip. 
         [0031]    The bendable portion  32  transfers rotation, but not bending. The configuration of the bendable portion  32  will now be described in detail. The bendable portion  32  has a link  32   a  having at both end portions thereof coupling shafts  32   b  and  32   c  to be coupled with the rotation axis. The coupling shafts  32   b  and  32   c  are extended in different directions. Although they can be positioned at any angle, they are preferably positioned at a right angle. In other words, it is preferable that one coupling shaft  32   b  is extended vertically and the other coupling shaft  32   c  is extended horizontally, as shown in the illustrated embodiment. 
         [0032]      FIG. 4  offers a perspective view depicting a state where the handle  40  is attached to the rotation axis  30 . When the connecting member  34  of the leading end portion  33  is fitted into the connection recess  44  of the handle shaft  41  (see,  FIG. 3A ), the handle  40  is coupled to the rotation axis  30  as shown in  FIG. 4 . Moreover, when an operator rotates the grip  43  by one hand while holding the larger diameter portion  45  with the other hand, the rotation of the handle  40  is transmitted to the rotation axis  30 , and the bevel gear  28  is then rotated. The rotation of the bevel gear  28  is transferred to the bevel gear  27  oriented at a right angle with the bevel gear  28 , thereby rotating the cross shaft  26 . The cross shaft  26  equally rotates the worm gears  24  provided at both sides thereof. Further, the worm gears  24  rotate the respective worm wheels  23 , and the worm wheels  23  rotate the respective ball screws  21  provided at opposite sides. Due to the rotation of the ball screws  21 , the radio frequency power supply unit  13  is raised or lowered. 
         [0033]    When the radio frequency power supply unit  13  reaches a required height, the elevation operation is completed. Next, the handle shaft  41  is separated from the connecting member  34 . 
         [0034]      FIG. 5  presents a perspective view showing a state where the handle  40  is separated from the rotation axis  30 . When the handle  40  is separated, the leading end portion  33  of the rotation axis  30  is suspended vertically downward from the bendable portion  32 . Although the handle  40  is made detachable from the leading end portion  33  in this embodiment, the handle  40  may be integrated with the leading end portion  33  as one unit. In that case, the handle  40  included in the leading end portion  33  is also suspended downward. 
         [0035]      FIGS. 6A and 6B  represent a state where the leading end portion  33  of the rotation axis  30  is suspended downward regardless of the position of the rotation axis  30 . In  FIG. 6A , the base end portion  31  is positioned such that the coupling shaft  32   b  is horizontally extended and the link  32   a  rotates about the coupling shaft  32   b  to be extended vertically with the leading end portion  33  suspended downward therefrom. In  FIG. 6B , the coupling shaft  32   b  is vertically extended. In this case, the leading end portion  33  rotates about the other coupling shaft  32   c  to be vertically suspended. Even when the base end portion  31  of the rotation axis  30  is positioned at an angle between those shown in  FIGS. 6A and 6B , the leading end portion  33  is suspended downward. 
         [0036]    When the rotation of the rotation axis  30  stops and the leading end portion  33  is vertically suspended, a rotational torque is applied to the rotation axis  30  by the gravity of the radio frequency power supply unit  13 . However, in the present invention, a braking torque applied to the rotation axis  30  by the weight of the leading end portion  33  is set to be larger than the rotational torque due to the gravity of the radio frequency power supply unit  13 , so that it is possible to prevent the rotation axis  30  from rotating in the direction that the heavy equipment descends. 
         [0037]      FIG. 7  shows another embodiment of the present invention. In this embodiment, the rotation axis  30  is arranged so that a frame  10   a  of the etching apparatus or the like is spaced apart from the center of the rotation axis  30  by a distance of L 1 . The rotation of the rotation axis  30  may not stop if the rotational torque due to the gravity of the heavy equipment cannot be suppressed because of a light weight of the leading end portion  33  of the rotation axis  30  or if the heavy equipment receives an acceleration even when the weight of the leading end portion  33  is sufficient to suppress the initial speed. In that case, the rotation axis  30  rotates in, e.g., a counterclockwise direction, from the state of  FIG. 6A , and then reaches a position of  FIG. 7 . At this time, the rotation of the rotation axis  30  can be suppressed by force by setting a distance L between the leading end of the leading end portion  33  and the center of the rotation axis  30  to be larger than the distance L 1 . 
         [0038]    As set forth above, in the elevating device of the present invention, the leading end portion  33  of the rotation axis  30  is connected to the bendable portion  32  and, also, the leading end portion  33  is suspended downward regardless of the stop position of the rotation axis  30 . Therefore, it is possible to prevent the heavy equipment or heavy member from descending due to rotation of the rotation axis caused by the gravity of the heavy member. In addition, the unintended descent prevention mechanism of the present invention is reliable because it is almost free from damages or abrasion. 
         [0039]    The present invention can be variously modified without being limited to the above embodiments. For example, although the bendable portion  32  in the above embodiments includes the link  32   a  and the coupling shafts  32   b  and  32   c , it is only an example. The bendable portion  32  may have a different configuration as long as it transmits rotation but not bending. For example, the link  32   a  may be formed as a spherical body or as strong meshes of steel. Moreover, although one link  32   a  is provided in the above embodiments of the present invention, two or more links  32   a  may be connected through coupling shafts. 
         [0040]    Although the elevating device using the ball screw is exemplified in the above embodiment, it is also possible for the elevating device to use, e.g., a conventional screw, other than the ball screw. 
         [0041]    The present invention can be applied to an elevation of a general heavy member as well as the elevation of the radio frequency power supply unit of the plasma etching apparatus. The aforementioned effects can be achieved in both cases. 
         [0042]    While the invention has been shown and described with respect to the preferred embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.