Abstract:
An electrical discharge machining apparatus includes: a surface plate that a workpiece is placed on; a machining tank that surrounds the surface plate, retains a machining liquid, and has at least a part that serves as a substantially box-shaped vertically moveable ascent/descent machining tank, the ascent/descent machining tank having an outlet in an ascent/descent inner wall of the ascent/descent machining tank, the outlet allowing the machining liquid to overflow to the ascent/descent machining tank; an ascent/descent device that raises and lowers the ascent/descent machining tank; a sub-tank that receives the machining liquid that leaks out from the machining tank; a slit that is provided in an end wall of the sub-tank for allowing a connection member to pass through, the connection member connecting the ascent/descent machining tank and the ascent/descent device; and a seal that is arranged in a gap between the ascent/descent machining tank and an inner wall of the sub-tank and prevents the machining liquid in the machining tank from leaking out into the sub-tank, the electrical discharge machining apparatus creating an electrical discharge in a small gap between the workpiece and an electrode to machine the workpiece, the workpiece being immersed in the machining liquid retained in the machining tank, wherein a slit-like receiving opening is provided at a bottom of the ascent/descent machining tank on the ascent/descent inner wall side, the slit-like receiving opening receiving the machining liquid that leaks through the seal and drips along the ascent/descent inner wall and recovering the machining liquid in the ascent/descent machining tank.

Description:
FIELD 
       [0001]    The present invention relates to an electrical discharge machining apparatus that machines a workpiece immersed in a machining liquid, such as a wire electrical discharge machining apparatus and a die sinking electrical discharge machining apparatus. 
       BACKGROUND 
       [0002]    Conventional electrical discharge machining apparatuses have been disclosed that create an electrical discharge in a small gap between a workpiece and an electrode to machine the workpiece, which is immersed in a machining liquid retained in a machining tank. Such conventional electrical discharge machining apparatuses include a surface plate on which the workpiece is placed, the machining tank that surrounds the surface plate, retains the machining liquid, and has at least a part that serves as a vertically moveable ascent/descent machining tank, the ascent/descent machining tank having an outlet in its ascent/descent inner wall, the outlet allowing the machining liquid to overflow, an ascent/descent device that raises and lowers the ascent/descent machining tank, a sub-tank that receives the machining liquid that overflows from the machining tank, and a seal arranged in a gap between the ascent/descent machining tank and the inner wall of the sub-tank to prevent the machining liquid in the machining tank from leaking out into the sub-tank (for example, see Patent Literatures 1 and 2). 
       CITATION LIST 
     Patent Literature 
       [0000]    
       
         Patent Literature 1: U.S. Pat. No. 5,173,737 
         Patent Literature 2: U.S. Pat. No. 5,264,293 
       
     
       SUMMARY 
     Technical Problem 
       [0005]    The seal of the conventional electrical discharge machining apparatuses disclosed in Patent Literatures 1 and 2 may wear out due to operation over a long period and cause the machining liquid to leak through the gap between the ascent/descent inner wall and the inner wall of the sub-tank. The sub-tank has a slit for allowing a connection member to pass through. The connection member connects the ascent/descent machining tank and the ascent/descent device, which is placed outside the sub-tank. This poses a problem that the machining liquid that has leaked out through the seal flows on a bottom face of the ascent/descent machining tank to approach the slit and splashes through the slit and onto the floor surface outside the sub-tank where the electrical discharge machining apparatus is installed to stain the floor surface. 
         [0006]    The present invention has been achieved in view of the above, and an object of the present invention is to provide an electrical discharge machining apparatus that prevents a machining liquid that has leaked through a seal from splashing through a slit in a sub-tank and onto a floor surface outside the sub-tank where the electrical discharge machining apparatus is installed. 
       Solution to Problem 
       [0007]    To solve the above described problem and achieve the object an electrical discharge machining apparatus according to the present invention includes: a surface plate that a workpiece is placed on; a machining tank that surrounds the surface plate, retains a machining liquid, and has at least a part that serves as a box-shaped vertically moveable ascent/descent machining tank, the ascent/descent machining tank having an outlet in an ascent/descent inner wall of the ascent/descent machining tank, the outlet allowing the machining liquid to overflow; an ascent/descent device that raises and lowers the ascent/descent machining tank; a sub-tank that receives the machining liquid that overflows from the machining tank; a slit that is provided in an end wall of the sub-tank for allowing a connection member to pass through, the connection member connecting the ascent/descent machining tank and the ascent/descent device; and a seal that is arranged in a gap between the ascent/descent machining tank and an inner wall of the sub-tank and prevents the machining liquid in the machining tank from leaking out into the sub-tank. The electrical discharge machining apparatus creating an electrical discharge in a small gap between the workpiece and an electrode to machine the workpiece, the workpiece being immersed in the machining liquid retained in the machining tank. A slit-like receiving opening is provided at a bottom of the ascent/descent machining tank on the ascent/descent inner wall side, the slit-like receiving opening receiving the machining liquid that leaks through the seal and drips along the ascent/descent inner wall and recovering the machining liquid in the ascent/descent machining tank. 
       Advantageous Effects of Invention 
       [0008]    An electrical discharge machining apparatus according to the present invention produces an effect of preventing a machining liquid that has leaked through a seal from splashing through a slit in a sub-tank and onto the floor surface outside the sub-tank where the electrical discharge machining apparatus is installed. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0009]      FIG. 1  is a longitudinal sectional view schematically illustrating an embodiment of a wire electrical discharge machining apparatus according to the present invention. 
           [0010]      FIG. 2  is a perspective view schematically illustrating the shapes of a machining tank and an ascent/descent machining tank of the wire electrical discharge machining apparatus according to the embodiment. 
           [0011]      FIG. 3  is a longitudinal sectional view schematically illustrating the shapes of the machining tank, the ascent/descent machining tank, and a sub-tank of the wire electrical discharge machining apparatus according to the embodiment. 
           [0012]      FIG. 4  is a perspective view illustrating the shapes of a machining tank, an ascent/descent machining tank, and a sub-tank of a wire electrical discharge machining apparatus that includes an ascent/descent device of a different form. 
           [0013]      FIG. 5  is a rear perspective view of the wire electrical discharge machining apparatus illustrated in  FIG. 4 . 
           [0014]      FIG. 6  is a longitudinal sectional view illustrating the ascent/descent machining tank and the sub-tank according to a first embodiment. 
           [0015]      FIG. 7  is a longitudinal sectional view along the line A-A in  FIG. 6 . 
           [0016]      FIG. 8  is a longitudinal sectional view, like  FIG. 7 , illustrating an ascent/descent machining tank and a sub-tank according to a second embodiment. 
           [0017]      FIG. 9  is a longitudinal sectional view, like  FIG. 7 , illustrating an ascent/descent machining tank and a sub-tank according to a third embodiment. 
           [0018]      FIG. 10  is a longitudinal sectional view, like  FIG. 6 , illustrating an ascent/descent machining tank according to a fourth embodiment. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0019]    Exemplary embodiments of a wire electrical discharge machining apparatus, which is presented as an electrical discharge machining apparatus according to the present invention, will be described in detail below with reference to the drawings. The present invention is not limited to the embodiments. 
       First Embodiment 
       [0020]      FIG. 1  is a longitudinal sectional view schematically illustrating an embodiment of a wire electrical discharge machining apparatus according to the present invention;  FIG. 2  is a perspective view schematically illustrating the shapes of a machining tank and an ascent/descent machining tank of the wire electrical discharge machining apparatus according to the embodiment;  FIG. 3  is a longitudinal sectional view schematically illustrating the shapes of the machining tank, the ascent/descent machining tank, and a sub-tank of the wire electrical discharge machining apparatus according to the embodiment. In  FIG. 2 , a workpiece, a surface plate, and a machining liquid are omitted. Additionally, a sub-tank  26 , which wraps around the outer periphery of the wire electrical discharge machining apparatus, is partially cut away to clarify the arrangement of an ascent/descent device  50 . 
         [0021]    As illustrated in  FIGS. 1 to 3 , a wire electrical discharge machining apparatus  1  includes a wire supply bobbin  2  retained thereon. A wire electrode  3  is unwound from the wire supply bobbin  2 . An upper wire guide  5  and a lower wire guide  6  each include a feeding unit and a wire guide unit internally and hold the wire electrode  3  above and below a workpiece  7 . A Z-axis main spindle  10  has an extremity that the upper wire guide  5  is fixed to. A Z-axis guide  11  slidably supports, in an up-and-down direction, the main spindle  10  along the guide  11 . A motor  12  is directly connected to a feed screw  13  having a nut that is coupled to the main spindle  10  such that the rotation of the motor  12  allows the nut to drive the main spindle  10  in the up-and-down direction. 
         [0022]    A position detection unit  15  measures the Z-axis position of the main spindle  10  and controls the rotation of the motor  12 . A machining tank  20  is placed on an undepicted XY cross table and includes a table  21  internally. The workpiece  7  is placed on a surface plate  22  provided on the table  21  and is immersed in a machining liquid  23 . 
         [0023]    The machining tank  20  includes: an immobile machining tank  20 A, which is fixed to the top face of a bed  4  (see  FIG. 3 ); an ascent/descent machining tank  20 B, which is provided on the immobile machining tank  20 A on the upper side in such a manner that the ascent/descent machining tank  20 B is vertically movable; a rear-side tank wall  20 C, which is attached to the immobile machining tank  20 A and arranged on the rear side of the machining tank  20 ; and a bottom plate  20 D. The ascent/descent machining tank  20 B includes: an ascent/descent inner wall  20 Bc; an ascent/descent outer wall  20 Bb; and a bottom plate  20 Bg. A seal  30  seals a gap between an inner wall  26   b  of the sub-tank  26  and the ascent/descent inner wall  20 Bc of the ascent/descent machining tank  20 B to prevent the machining liquid retained in the machining tank  20  from leaking out. 
         [0024]    The ascent/descent machining tank  20 B is made up of flattened hollow box-like members (each made up of the ascent/descent inner wall  20 Bc, the ascent/descent outer wall  20 Bb, and the bottom plate  20 Bg). These hollow box-like members are connected such that they are in communication with each other and that they are formed into a substantially ⊃ shape as observed from above. The ascent/descent machining tank  20 B has a channel formed inside, into which the machining liquid  23  is released. The ascent/descent machining tank  20 B is arranged such that the ascent/descent machining tank  20 B faces the rear-side tank wall  20 C and is integrated into one piece with the rear-side tank wall  20 C with appropriate sealing therebetween in a manner that allows the ascent/descent machining tank  20 B to ascend and descend. The outside of the ascent/descent machining tank  20 B is wrapped with an outer wall  26   a  of the sub-tank  26 . 
         [0025]    The ascent/descent machining tank  20 B has a plurality of cutouts (drain ports)  20 Ba in an upper portion of its inner face in such a manner that the cutouts  20 Ba are disposed in the horizontal direction at predetermined intervals. The machining liquid  23  in the machining tank  20  is drained through the cutouts  20 Ba (the arrow A in  FIG. 1 ). Moving the ascent/descent machining tank  20 B in its vertical direction (the Z axis direction) can adjust the level of a machining liquid to a given height and maintain it thereto and thus substantially performs liquid level control. 
         [0026]    The reason that the plurality of cutouts  20 Ba are provided in the upper portion of the ascent/descent inner wall  20 Bc of the ascent/descent machining tank  20 B is, as described above, to allow the machining tank  20  to be lowered sufficiently during tooling change without lowering the machining liquid to an extremely low level. Note that the drain ports for a machining liquid formed in the upper portion of the ascent/descent inner wall  20 Bc of the ascent/descent machining tank  20 B are not limited to the cutouts  20 Ba and may be in any shape; for example, they may be slit-shaped holes extending in the horizontal direction. 
         [0027]    The ascent/descent machining tank  20 B, which is substantially ⊃ shaped as observed from above, has an end portion to which a connection member  20 Bd is attached, and a rack  51  is provided on the connection member  20 Bd in the vertical direction. A pinion  52  is arranged so as to mesh with the rack  51 . The pinion  52  is coupled to a motor  54  via a shaft coupling  53 . The rack  51 , the pinion  52 , the shaft coupling  53 , and the motor  54  constitute the ascent/descent device  50 , which raises and lowers the ascent/descent machining tank  20 B. 
         [0028]    A lower portion of the ascent/descent machining tank  20 B is accommodated in the sub-tank  26 , while the ascent/descent device  50  is disposed outside the sub-tank  26 . The sub-tank  26  has an end wall  26   c  (see  FIG. 3 ) at an end of the substantially ⊃ shape, as observed from above, of the sub-tank  26 , and a slit  26   d  is provided in the end wall  26   c . The connection member  20 Bd, which connects the ascent/descent machining tank  20 B and the ascent/descent device  50  placed outside the sub-tank  26 , passes through the slit  26   d.    
         [0029]    The motor  54  is provided with an encoder  55 , which detects the number of rotations. Signals of the encoder  55  are input to a control device  100  such that the control device  100  controls the ascent/descent device  50 . Note that the ascent/descent device  50  is provided on each of the two ends of the substantially ⊃ shaped ascent/descent machining tank  20 B, however only one of them is illustrated in  FIG. 2 . 
         [0030]    The ascent/descent device  50  operates on the basis of drive signals from the control device  100 . The sub-tank  26  has a front face on which an ascent/descent switch  57  is provided. By operating the ascent/descent switch  57 , the ascent/descent machining tank  20 B can be moved up and down. 
         [0031]    A machining liquid supply device  40  is constituted by a polluted liquid tank  40   a  and a clean liquid tank  40   b . A filter pump  41  is placed above the polluted liquid tank  40   a  and is connected to a filter  43 . A supply pump  45  is placed above the clean liquid tank  40   b  and is coupled to upper and lower nozzles  47  and  48  to supply and eject the machining liquid to the wire electrode  3  and the workpiece  7 . The machining liquid that has overflown into the ascent/descent machining tank  20 B flows from a drain port  29  through an elastic communication member  24  to be drained into the machining liquid supply device  40 . 
         [0032]    When the machining liquid is supplied, the ascent/descent machining tank  20 B controls the level of the machining liquid  23  with an overflow liquid level control method. Specifically, the ascent/descent machining tank  20 B moves to an appropriate height for the machining liquid in which the workpiece  7  is to be immersed. Then, the supply pump  45  is operated to supply the machining liquid  23  to the machining tank  20 . The machining tank  20  is filled with the machining liquid  23  and the machining liquid  23  starts overflowing at the height of the cutouts  20 Ba. This maintains the liquid level at a constant height. 
         [0033]    To machine the workpiece  7 , the motor  12  is driven to move the upper nozzle  47 , which is fixed to the extremity of the Z-axis main spindle  10 , to a vicinity of the workpiece  7 . After the machining tank  20  is filled with the machining liquid, the machining liquid is ejected from the upper and lower nozzles  47  and  48 , and the wire electrode  3  is supplied by a wire moving unit. By allowing the workpiece  7  to achieve a given movement relative to the wire electrode  3  while electrical discharge power is supplied to the wire electrode  3  by a power supply, a desired shape is machined. 
         [0034]      FIG. 4  is a perspective view illustrating the shapes of a machining tank, an ascent/descent machining tank, and a sub-tank of a wire electrical discharge machining apparatus that includes an ascent/descent device of a different form;  FIG. 5  is a rear perspective view of the wire electrical discharge machining apparatus illustrated in  FIG. 4 . A wire electrical discharge machining apparatus  1   a  illustrated in  FIGS. 4 and 5  includes an ascent/descent device  50   a , which has a different form from the ascent/descent device  50  illustrated in  FIGS. 1 and 2 . 
         [0035]    An ascent/descent machining tank  20 B, which is substantially shaped as observed from above, has an end portion to which a connection member  20 Bd is attached. A belt (or a chain)  51   a  is placed over a pulley that is attached to an upper portion of a rear-side tank wall  20 C and a pulley that is of a motor  54   a  and is attached to a lower portion of the rear-side tank wall  20 C. The belt (or the chain)  51   a  is coupled to the connection member  20 Bd. The rotation of the motor  54   a  enables the belt  51   a  to run up and down and thereby raise and lower the ascent/descent machining tank  20 B. The belt (or the chain)  51   a , the pulleys, and the motor  54   a  constitute the ascent/descent device  50   a . Except for the ascent/descent device  50   a , the wire electrical discharge machining apparatus  1   a  is similar to the wire electrical discharge machining apparatus  1  illustrated in  FIGS. 1 to 3  and thus is designated with identical symbols, and the description is omitted. 
         [0036]    The wire electrical discharge machining apparatus according to the present embodiment may be applied to the wire electrical discharge machining apparatus  1 , which includes the pinion &amp; rack type ascent/descent device  50 , and to the wire electrical discharge machining apparatus  1   a , which includes the belt (or chain) type ascent/descent device  50   a.    
         [0037]    With reference to  FIGS. 6 and 7 , the characteristic configuration of the wire electrical discharge machining apparatuses  1  and  1   a  according to the first embodiment will now be described.  FIG. 6  is  FIG. 6  is a longitudinal sectional view illustrating the ascent/descent machining tank and the sub-tank according to the first embodiment;  FIG. 7  is a longitudinal sectional view along the line A-A in  FIG. 6 . 
         [0038]    As illustrated in  FIGS. 6 and 7 , a slit-like receiving opening  20 Bf is provided at the bottom of one of the ends of the ascent/descent machining tank  20 B on the ascent/descent inner wall  20 Bc side for receiving the machining liquid  23  that leaks through the seal  30  and drips along the ascent/descent inner wall  20 Bc and for recovering the machining liquid  23  in the ascent/descent machining tank  20 B. The receiving opening  20 Bf can be formed by cutting open a lower portion  20 Be of the ascent/descent inner wall  20 Bc. Providing the receiving opening  20 Bf only at each of the ends of the ascent/descent machining tank  20 B is sufficient. 
         [0039]    The slit-like receiving opening  20 Bf is provided to receive the machining liquid  23  that leaks through the seal  30  and drips along the ascent/descent inner wall  20 Bc and to collect the machining liquid  23  in the ascent/descent machining tank  20 B. Thus, there is no risk of the dripped machining liquid  23  flowing on the underside of the bottom plate  20 Bg of the ascent/descent machining tank  20 B and scattering toward the slit  26   d  to splash through the slit  26   d  and onto the floor surface outside the sub-tank  26  where the electrical discharge machining apparatus  1  or  1   a  is installed. 
       Second Embodiment 
       [0040]      FIG. 8  is a longitudinal sectional view, like  FIG. 7 , illustrating an ascent/descent machining tank and a sub-tank according to a second embodiment. As illustrated in  FIG. 8 , a ridge  20 Bh pointed downward is attached to the bottom of an ascent/descent machining tank  20 B on the slit  26   d  side in such a manner that the ridge  20 Bh is parallel with an end wall  20 Bi of the ascent/descent machining tank  20 B. 
         [0041]    By attaching the downward-pointed ridge  20 Bh to the bottom of the ascent/descent machining tank  20 B on the slit  26   d  side in such a manner that the ridge  20 Bh is parallel with the end wall  20 Bi of the ascent/descent machining tank  20 B, a machining liquid  23  that leaks through a seal  30  and drips along an ascent/descent inner wall  20 Bc to flow on the underside of a bottom plate  20 Bg and approach the slit  26   d  drips from the pointed edge of the ridge  20 Bh into a sub-tank  26 . Thus, there is no risk of the machining liquid  23  scattering toward the slit  26   d  and splashing through the slit  26   d  and onto the floor surface outside the sub-tank  26  where an electrical discharge machining apparatus  1  or  1   a  is installed. 
       Third Embodiment 
       [0042]      FIG. 9  is a longitudinal sectional view, like  FIG. 7 , illustrating an ascent/descent machining tank and a sub-tank according to a third embodiment. As illustrated in  FIG. 9 , the bottom of an ascent/descent machining tank  20 B on the slit  26   d  side has an upgrade toward the slit  26   d  (that is a downgrade toward the side opposite from the slit  26   d ). 
         [0043]    By providing the upgrade toward the slit  26   d  at the bottom of the ascent/descent machining tank  20 B on the slit  26   d  side (that is the downgrade toward the side opposite from the slit  26   d ), a machining liquid  23  that leaks through a seal  30  and drips along an ascent/descent inner wall  20 Bc to flow on the underside of a bottom plate  20 Bg flows toward the side opposite from the slit  26   d  and drips at the end of the down grade into a sub-tank  26 . Thus, there is no risk of the machining liquid  23  scattering toward the slit  26   d  and splashing through the slit  26   d  and onto the floor surface outside the sub-tank  26  where an electrical discharge machining apparatus  1  or  1   a  is installed. 
       Fourth Embodiment 
       [0044]      FIG. 10  is a longitudinal sectional view, like  FIG. 6 , illustrating an ascent/descent machining tank according to a fourth embodiment. As illustrated in  FIG. 10 , a slit-like receiving opening  20 Bf is provided at the bottom of an ascent/descent machining tank  20 B on the ascent/descent inner wall  20 Bc side for receiving a machining liquid  23  that leaks through a seal  30  and drips along the ascent/descent inner wall  20 Bc and for recovering the machining liquid  23  in an ascent/descent machining tank  20 . Additionally, a seal member  32  is attached to the edge of a bottom plate  20 Bg of the ascent/descent machining tank  20 B at which the ascent/descent machining tank  20 B is cut open to form the receiving opening  20 Bf. The seal member  32  is attached in such a manner that its edge is in contact with a plate member  4   b  arranged along a side face  4   a  of a bed  4  that supports a machining tank  20 . The receiving opening  20 Bf and the seal member  32  are provided along the entire length of the ascent/descent machining tank  20 B. 
         [0045]    The slit-like receiving opening  20 Bf is provided to receive the machining liquid  23  that leaks through the seal  30  and drips along the ascent/descent inner wall  20 Bc and to recover the machining liquid  23  in the ascent/descent machining tank  20 . Thus, there is no risk of the dripped machining liquid  23  flowing on the underside of the bottom plate  20 Bg of the ascent/descent machining tank  20 B and scattering toward the slit  26   d  to splash through the slit  26   d  and onto the floor surface outside a sub-tank  26  where an electrical discharge machining apparatus  1  or  1   a  is installed. Additionally, because of the seal member  32  attached to the edge of the bottom plate  20 Bg of the ascent/descent machining tank  20 B at which the ascent/descent machining tank  20 B is cut open to form the receiving opening  20 Bf, in such a manner that the edge of the seal member  32  is in contact with the plate member  4   b  arranged along the side face  4   a  of the bed  4  that supports the machining tank  20 , the ascent/descent machining tank  20 B according to the fourth embodiment is capable of recovering all the machining liquid  23  that has leaked from the seal  30  and thereby eliminates the need to provide the sub-tank  26 . 
         [0046]    While the ascent/descent machining tank  20 B according to the present embodiment is substantially P shaped such that the ascent/descent machining tank  20 B constitutes three faces of the machining tank  20 , the ascent/descent machining tank  20 B may be an ascent/descent machining tank that constitutes only one face of the machining tank  20 . Furthermore, while the machining tank  20  according to the present embodiment is fixed to the bed  4  and the main spindle moves along the X and Y axes, the present embodiment may be applied to a type of wire electrical discharge machining apparatus in which the machining tank  20  is provided on an XY cross table. The present embodiment may also be applied to a type of wire electrical discharge machining apparatus in which the main spindle travels along one of the X and Y axes and the machining tank  20  travels along the other of the X and Y axes. Furthermore, the ascent/descent machining tank  20 B according to the present embodiment may be applied to a die sinking electrical discharge machining apparatus. 
       REFERENCE SIGNS LIST 
       [0000]    
       
         
           
               1  and  1   a  wire electrical discharge machining apparatus,  2  wire supply bobbin,  3  wire electrode,  4  bed,  4   a  side face,  4   b  plate member,  5  upper wire guide,  6  lower wire guide,  7  workpiece,  10  main spindle,  11  guide, motor,  13  feed screw,  15  position detection unit,  20  machining tank,  20 A immobile machining tank,  20 B ascent/descent machining tank,  20 Ba cutout (drain port),  20 Bb ascent/descent outer wall,  20 Bc ascent/descent inner wall,  20 Bd connection member,  20 Be lower portion,  20 Bf receiving opening,  20 Bg bottom plate,  20 Bh ridge,  20 Bi end wall,  20 C rear-side tank wall,  20 D bottom plate,  21  table,  22  surface plate,  23  machining liquid,  24  communication member,  26  sub-tank,  26   a  outer wall,  26   b  inner wall,  26   c  end wall,  26   d  slit,  29  drain port,  30  seal,  32  seal member,  40  machining liquid supply device,  40   a  polluted liquid tank,  40   b  clean liquid tank,  41  filter pump,  43  filter,  45  supply pump,  47  upper nozzle, lower nozzle,  50  and  50   a  ascent/descent device,  51  rack,  51   a  belt (chain),  52  pinion,  53  shaft coupling,  54  and  54   a  motor,  55  encoder,  57  ascent/descent switch,  100  control device.