Machine tool

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.

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 204a 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.

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 1a, 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 5a 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 5a be
 roughly 60 degrees.
 The tool post body 11 comprises a tool spindle 14 in which a tool T2 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 T1 to a delivery position P1. 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 T1, which has been indexed to the delivery
 position P1, to a tool exchanging position P2. 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 T2 fitted to the tool
 spindle 14 for the next-process tool T1 placed in the tool exchanging
 position P2.
 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 4a 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 2b are formed and are parallel to the sloping surface 5a of
 the column 5. Linear guide support seats 2c are inwardly layered down
 between the two support seats 2b, and a recessed portion 2d is recessed
 between the two support seats 2c. A ball screw 30 for feeding is disposed
 within the recessed portion 2d.
 Further, a front-side linear guide support seat 2e and a rear-side linear
 guide support seat 2f that is positioned at a place lower than the support
 seat 2e 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 2e and 2f.
 Rails 15a of the linear guides 15 are fixed at the linear guide support
 seats 2e, 2f, respectively, where a block 15b internally containing
 rollers is fitted to each of the rails 15a 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 4b formed horizontally opposite to a
 lower face 5b of the column 5, and lower-face front-and-rear bed support
 seats 4c, 4d formed opposite to the front-side and rear-side linear guide
 support seats 2e, 2f of the fixed bed 2, respectively. The blocks 15b of
 the linear guides 15 are fixed to the bed support seats 4c, 4d,
 respectively. Also, blocks 16b containing internal rollers of the linear
 guides 16 are fixed to the column support seat 4b, and a rail 16a fixed to
 the lower face 5b of the column 5 is movably fitted to the blocks 16b.
 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 4b of the saddle 4 and a line B that interconnects the front-and-rear
 linear guides 15 disposed on the bed support seats 4c, 4d 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 4a. 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.