Abstract:
A machine tool is provided where the support rigidity of the saddle is improved without increasing the height of the headstock. The machine tool includes a headstock situated on a fixed bed and a saddle having two different heights disposed on the fixed bed so as to be movable along a direction of an axis line of the headstock. A tool post is present on a column placed on the saddle so that the tool post is movable in a direction perpendicular to the axis line of the headstock. In this machine tool, the height of one portion of the saddle located toward the rear side of the tool is larger than the height of another portion of the saddle located toward the front side of the tool.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a machine tool in which a saddle is reciprocally movably disposed on a fixed bed. More particularly, the invention relates to the structure of the saddle. 
     2. Discussion of the Related Art 
     Among conventional machine tools there is, for example, a composite machining lathe in which one tool post is used for both lathe turning and rotating-tool machining. In this composite machining lathe, as shown in FIG. 4, on top of a fixed bed  200 , a saddle  201  is disposed so as to be movable in the Z-axis direction (the perpendicular direction with respect to the plane of the drawing) by two linear guides  202 . On top of the saddle  201 , a column  204  is disposed so as to be movable by two linear guides  203  in a direction which is perpendicular to the Z-axis and in which the height increases with decreasing distance to the front (the direction indicated by arrow “a”). 
     Further, on a front sloping surface  204   a  of the column  204 , a tool post  205  is disposed so as to be movable in the X-axis direction and rotationally indexable to a specified angle. In addition, a headstock  206  is fixed to the fixed bed  200 , and an automatic tool exchanger  207  is disposed on a sidewall of the column  204 . 
     The saddle  201  is formed into a rectangular shape, as seen in a side view, with a height dimension (plate thickness) t unchanged from the front to the rear so that a line B interconnecting the linear guides  202  for the saddle and an axis line C of the linear guides  203  for the column are parallel to each other. Also, since heavy articles such as the column  204 , the tool post  205  and the automatic tool exchanger  207  are mounted on the saddle  201 , it is common practice to set the plate thickness t as large as possible to increase support. 
     However, increasing the plate thickness t of the saddle  201  as in the conventional lathe causes the height position of the tool post  205  to increase as well. As a result, the height h of the axis of the headstock  206  would become higher, which may deteriorate workability and machining precision. 
     SUMMARY OF THE INVENTION 
     In view of the above problems in machining lathes, an object of the invention is to provide a machine tool capable of improving the support rigidity for the saddle without increasing the height of the axis of the headstock. 
     In order to achieve the above and other objects, the present invention provides a machine tool comprising a fixed bed, a headstock disposed on the fixed bed, a saddle movably disposed on top of the fixed bed, a column disposed on the saddle, and a tool post disposed on the column so that the tool post is movable relative to the headstock. The saddle includes a first portion disposed closer to the headstock and a second portion disposed further from the headstock than the first portion and they are dimensioned so that a height of the second portion is larger than a height of the first portion. 
     In a further embodiment, the machine tool as described above includes a tool magazine, where one or more tools are mounted, is fitted to the portion of the saddle located toward the rear side of the tool. 
     According to the machine tool of this invention, since the saddle dimensions are set so that its rear-side height dimension is larger than its front-side height dimension, the saddle has increased rigidity to support such heavy articles as the column and the tool post without increasing the height dimension of the whole saddle. Therefore, the height of the axis of the tool post and the height of the axis of the headstock do not have to be increased. Thus deterioration in workability and machining precision can be prevented. 
     Also, in proportion to the degree to which the height dimension of the rear side portion of the saddle is increased, the area of the rear side wall can be enlarged, making it possible to attach, for example, an automatic tool exchanger to the rear side wall of the saddle having high rigidity. In such a case, the weight load of the column supporting the tool post can be reduced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a right side view of a composite machining lathe according to a first embodiment of the present invention; 
     FIG. 2 is an enlarged right side view of the composite machining lathe; 
     FIG. 3 is a side view showing a modification of the saddle shown in the first embodiment; and 
     FIG. 4 is a schematic side view showing a conventional saddle structure. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of the present invention is described below with reference to the accompanying drawings. 
     FIGS. 1 and 2 are views for explaining a composite machining lathe according to an embodiment of the invention, both showing right side views of the composite machining lathe. 
     Referring to the figures, a composite machining lathe (machine tool)  1  is capable of performing both lathe turning and rotating-tool machining. Roughly referring to the construction of this composite machining lathe  1 , a saddle  4  is disposed on top of a fixed bed  2  so as to be movable in the Z-axis by two linear guides  15 . A column  5  is disposed on top of the saddle  4  so as to be movable in a horizontal direction perpendicular to the Z-axis by two linear guides  16 . Moreover, a tool post  6  is disposed on the column  5  so as to be movable in the X-axis direction. 
     A headstock  7  is disposed and fixed at a left-side end portion of the fixed bed  2 , as viewed from the front. A main spindle (not shown) equipped with a chuck  8  for gripping a workpiece is provided on the headstock  7 , and a spindle motor  13  rotationally drives this main spindle. In addition, a door  1   a , which opens and closes, is formed in a cover, not shown. 
     The tool post  6  includes a support base  9  disposed on a forwardly-declined sloping surface  5   a  of the column  5  so as to be movable in the X-axis direction, and a tool post body  11  is supported on the support base  9  so as to be turnable by means of a rotationally indexing device  10 . It is preferable that the angle of the forwardly declined sloping surface  5   a  be roughly  60  degrees. 
     The tool post body  11  comprises a tool spindle  14  in which a tool T 2  is removably fitted at its front portion, a tool spindle head  12  for rotatably supporting the tool spindle  14 , and a spindle motor  13  which is disposed within the tool spindle head  12  and which rotationally drives the tool spindle  14 . 
     The rotationally indexing device  10 , for positioning and fixing the tool post body  11  in a specified indexing angular position, performs lathe turning and milling of diagonal holes or similar functions in a clamped state in the angular position. 
     The composite machining lathe  1  has an automatic tool exchanger  20 . This automatic tool exchanger  20 , to which tools T are removably fitted, comprises a longitudinally-longer elliptical tool magazine  22  for indexing and positioning a next-process tool T 1  to a delivery position P 1 . The automatic tool exchanger  20  further comprises a transfer mechanism  25  having a transfer arm  23  and a drive cylinder  24 . The transfer arm  23  transfers the next-process tool T 1 , which has been indexed to the delivery position P 1 , to a tool exchanging position P 2 . A drive cylinder  24  drives the transfer arm  23  into a horizontal swing within a plane perpendicular to the headstock  7 . In addition, the tool exchanger  20  comprises a tool exchange mechanism (not shown) having an exchange arm and an exchange shaft for exchanging a process-completed tool T 2  fitted to the tool spindle  14  for the next-process tool T 1  placed in the tool exchanging position P 2 . 
     The tool magazine  22  is rotatably supported on a magazine support  26 , and the magazine support  26  is fixedly bolted to a rear side wall  4   a  of the saddle  4 . As this saddle  4  moves in the Z-axis direction, the tool magazine  22  also moves. This enables tool exchange irrespective of where the saddle  4  is positioned in the Z-axis direction. 
     The fixed bed  2  is formed into a generally triangular shape, as seen in the side view. In the front sloping portion of the fixed bed  2 , headstock support seats  2   b  are formed and are parallel to the sloping surface  5   a  of the column  5 . Linear guide support seats  2   c  are inwardly layered down between the two support seats  2   b , and a recessed portion  2   d  is recessed between the two support seats  2   c . A ball screw  30  for feeding is disposed within the recessed portion  2   d.    
     Further, a front-side linear guide support seat  2   e  and a rear-side linear guide support seat  2   f  that is positioned at a place lower than the support seat  2   e  are formed on the rear sloping portion of the fixed bed  2  in a layer-down state. A ball screw  31  for feeding is disposed between these support seats  2   e  and  2   f.    
     Rails  15   a  of the linear guides  15  are fixed at the linear guide support seats  2   e ,  2   f , respectively, where a block  15   b  internally containing rollers is fitted to each of the rails  15   a  so as to be slidable in the Z-axis direction. 
     The saddle  4  generally has a hook shape, as viewed in the side view, having an upper-face column support seat  4   b  formed horizontally opposite to a lower face  5   b  of the column  5 , and lower-face front-and-rear bed support seats  4   c ,  4   d  formed opposite to the front-side and rear-side linear guide support seats  2   e ,  2   f  of the fixed bed  2 , respectively. The blocks  15   b  of the linear guides  15  are fixed to the bed support seats  4   c ,  4   d , respectively. Also, blocks  16   b  containing internal rollers of the linear guides  16  are fixed to the column support seat  4   b , and a rail  16   a  fixed to the lower face  5   b  of the column  5  is movably fitted to the blocks  16   b.    
     The saddle  4  is formed so that the plate thickness (height dimension) t2 of a rear side portion in the back-and-forth direction, as viewed from the front becomes larger than the plate thickness (height dimension) t1 of a front-side portion. In a more preferred embodiment, the rear-side plate thickness t2 is approximately double the front-side plate thickness t1. Thus, an axis line C of the linear guides  16  set on the column support seat  4   b  of the saddle  4  and a line B that interconnects the front-and-rear linear guides  15  disposed on the bed support seats  4   c ,  4   d  are nonparallel to each other so as to intersect in front of the saddle  4 . 
     The operation and effects of the invention are described below. 
     According to this embodiment, since the rear-side plate thickness t2 of the saddle  4  is larger than the front-side plate thickness t1 of the saddle  4 , the rigidity of the saddle  4  as a whole to support the heavy articles of the column  5  and the tool post  6  can be enhanced. In addition the machining precision can be improved, while the height of the axis of the tool post  6 , as well as the height h of the axis of the headstock  7 , remain generally the same as in conventional lathes. 
     Also, since the rear-side plate thickness t2 of the saddle  4  is larger than its front-side counterpart, the rigidity of the rear-side portion can be particularly enhanced so that the tool magazine  22  with a multiplicity of tools mounted thereon can be fitted to the rear side wall  4   a . As a result, the column  5  is loaded only with enough weight to support the tool post  6 , thus decreasing the rigidity necessary for the column  5 . 
     In the above embodiment, the saddle  4  has a hook shape such that the rear-side plate thickness t2 is larger than the front-side plate thickness t1. However, the saddle of the present invention is not limited to this structure. For example, it is also possible to set an intermediate plate thickness t3 between the front-side plate thickness t1 and the rear-side plate thickness t2 so that t1&lt;t3&lt;t2 as shown in FIG.  3 . Further, the bottom surface of the saddle may be inclined so as to be parallel to the line B that interconnects the front-and-rear linear guides  15 . In such a case, the rigidity of the center portion of the saddle  4  can be enhanced, so that the support of the saddle as a whole can be further enhanced. 
     It is to be understood that although the present invention has been described with regard to preferred embodiments thereof, various other embodiments and variants may occur to those skilled in the art, which are within the scope and spirit of the invention, and such other embodiments and variants are intended to be covered by the following claims. 
     The text of Japanese priority application no. 11-120077 filed Apr. 27, 1999 is hereby incorporated by reference.