Machine tool

A machine tool includes a rotation table unit including a rotation table configured to rotate with respect to a first axis. The rotation table unit is configured to move along a second axis that is orthogonal to the first axis. The machine tool includes a spindle unit including a spindle configured to rotate with respect to a third axis that is orthogonal to the first axis and the second axis. The spindle unit is configured to move along the third axis. The machine tool includes a bed that supports the rotation table unit and the spindle unit. A front part of an upper surface of the bed includes a recess in which the rotation table unit is arranged. The spindle unit is located at a rear part of the upper surface of the bed.

TECHNICAL FIELD

The present disclosure relates to a machine tool used to machine a workpiece that is supported by a spindle unit.

BACKGROUND ART

Patent Literature 1 discloses a machine tool that includes a workpiece rotation apparatus and a tool holder. The workpiece rotation apparatus includes a circular table. The tool holder is spaced upward from the workpiece rotation apparatus. Patent Literature 1 does not disclose a detailed structure of the table of the workpiece rotation apparatus.

Patent Literature 2 discloses a machine tool that includes a column with a spindle that extends in a horizontal surface. The column is movably supported in the extending direction of the spindle. The column is moved by the rotation of a lead screw extending in the same direction as the spindle. The lead screw is located at a lower part of the column and on an upper surface of a bed.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Problems that the Invention is to Solve

In the machine tool of Patent Literature 1, the tool holder downwardly holds a tool. This unavoidably increases the height of the entire machine tool of Patent Literature 1 and enlarges the machine tool. The enlargement of the machine tool increases the weight of the machine tool. Thus, the machine tool is installed in a factory under limited conditions. In a case where the machine tool is increased in size and weight, the natural frequency of the machine decreases while the amplitude of natural vibration increases. This lowers the machining accuracy.

In the machine tool of Patent Literature 2, the lead screw that moves the column is located below the spindle. Thus, the lead screw is located below the center of gravity of the column, and a movement driving force produced by the lead screw acts on the column as a moment that inclines the spindle. Particularly, the occurrence of an accuracy error occurs in the pitch or the like of the lead screw may potentially lower a movement accuracy of the column and incline the column. As a result, the machining accuracy decreases.

It is an objective of the present disclosure to provide a machine tool in which the accuracy of machining is improved.

Solution to Problem

A machine tool according to an aspect of the present disclosure includes a rotation table unit including a rotation table configured to rotate with respect to a first axis. The rotation table unit is configured to move along a second axis that is orthogonal to the first axis. The machine tool includes a spindle unit including a spindle configured to rotate with respect to a third axis that is orthogonal to the first axis and the second axis. The spindle unit is configured to move along the third axis. The machine tool includes a bed that supports the rotation table unit and the spindle unit. A front part of an upper surface of the bed includes a recess in which the rotation table unit is arranged. The spindle unit is located at a rear part of the upper surface of the bed.

A machine tool according to another aspect of the present disclosure includes a spindle unit including a spindle configured to rotate with respect to a horizontal axis. The spindle unit is configured to move along the axis. The machine tool includes linear motors respectively arranged on opposite sides of the spindle unit. The linear motors are configured to move the spindle unit along the axis.

A machine tool according to a further aspect of the present disclosure includes a rotation table unit including a rotation table configured to rotate with respect to a first axis. The rotation table unit is configured to move along a second axis that is orthogonal to the first axis. The machine tool includes a spindle unit including a spindle configured to rotate with respect to a third axis that is orthogonal to the first axis and the second axis. The spindle unit is configured to move along the third axis. The machine tool includes linear motors respectively arranged on opposite sides of the spindle unit. The linear motors are configured to move the spindle unit along the third axis. A center of gravity of the spindle unit is located in a range of a thickness of each of the linear motors in an up-down direction of the linear motors.

DESCRIPTION OF EMBODIMENTS

Embodiment

A machine tool according to an embodiment will now be described. The machine tool of the present embodiment is a lathe.

As shown inFIGS.1and2, a lathe unit10with a lathe21includes an installment base11. The installment base11is installed on a mount surface (not shown), such as a floor surface in a factory. The installment base11includes installment members12at three positions on a lower surface of the installment base11. That is, two installment members12are located at the front side of the installment base11, and one installment member12is located at the rear side of the installment base11. The height of each installment member12can adjusted by the action of the corresponding inclined cam surface13. Thus, the height and inclination of the lathe unit10is adjusted by adjusting the height of each installment member12.

As shown inFIGS.1and2, the upper surface of the installment base11is provided with two front support legs15and one rear support leg16. The upper end of each of the support legs15,16is provided with a vibration absorber14, which includes an air damper. The front support legs15and the rear support leg16are located on a vertical axis (Y-axis) passing through the installment base11. The lathe21is supported on receiving plates17at the upper ends of the vibration absorbers14. Thus, the lathe21is supported by the three support legs15,16at three positions.

The structure of the lathe21will now be described.

As shown inFIGS.1and6, the lathe21includes a bed22. The front part of the bed22includes a table support23. The table support23includes a recess232that opens on the left and right sides. The rear part of the bed22includes a spindle support24with a flat top plate28. The entire bed22is formed as an integrated body through casting. As shown inFIG.6, an upper surface231of the table support23are located on the same plane as an upper surface241of the top plate28of the spindle support24. The left and right opening portions of the recess232and the table support23are closed by end plates27, respectively.

As shown inFIGS.1and4to6, the table support23includes a rotation table unit25, and the spindle support24includes a spindle unit26.

The rotation table unit25has the following structure.

As shown inFIGS.6and7, an upper step301is arranged on each of two surfaces opposing each other in a Z-axis direction on the inner side of the recess232of the table support23. Each upper step301is a guiding surface extending in an X-axis direction. The upper steps301support a table-side movable body32of the rotation table unit25such that the table-side movable body32is movable in the X-axis direction. That is, the rotation table unit25is movable along the X-axis (second axis).

As shown inFIGS.7,9, and10, the plate-shaped table-side movable body32is entirely quadrilateral. The side edges of the table-side movable body32extending in the X-axis direction define first oil hydrostatic bearings31. The first oil hydrostatic bearings31each define a guided surface to which oil is supplied. The first oil hydrostatic bearings31are arranged on the lower surfaces, side surfaces, and upper surfaces of the side edges of the table-side movable body32. The first oil hydrostatic bearings31on the lower surfaces are supported on the horizontal surfaces of the upper steps301by oil films. The first oil hydrostatic bearings31on the side surfaces are supported on the vertical surfaces of the upper steps301by oil films. Two guide members45extending in the X-axis direction are supported on the upper surface of the table support23. The first oil hydrostatic bearings31on the upper surfaces are supported on the lower surfaces of the guide members45by oil films. The first oil hydrostatic bearing31correspond to linear movement oil hydrostatic bearings. A spacer44is attached to the upper surface of the table-side movable body32. The spacer44is located between the table-side movable body32and a rotation table39, which will be described below.

A lower step302is defined on the lower side of each upper step301, and a linear motor33is located between each lower step302and the table-side movable body32. That is, a fixed member of each linear motor33is fixed to the corresponding lower step302, and a movable member of each linear motor33is coupled to the table-side movable body32. Driving forces produced by the two linear motors33move the table-side movable body32in the X-axis direction.

A support hole42extends through a central portion of the table-side movable body32. Second oil hydrostatic bearings35are arranged on the wall surface of the support hole42and on upper and lower peripheral portions of the support hole42. The second oil hydrostatic bearings35are annular guiding surfaces to which oil is supplied. The second oil hydrostatic bearings35support a rotation shaft36that includes a rotational axis extending vertically (extending along the Y-axis). The circumferential surface of the rotation shaft36includes an annular recess43. The inner upper surface of the annular recess43is supported on the upper surfaces of the second oil hydrostatic bearings35by oil films. The inner circumferential surface of the annular recess43is supported on the side surfaces of the second oil hydrostatic bearings35by oil films. The inner lower surface of the annular recess43is supported on the lower surfaces of the second oil hydrostatic bearings35by oil films. The second oil hydrostatic bearing35correspond to rotation oil hydrostatic bearings.

A rotation motor37is arranged at the lower end of the rotation shaft36. The rotation shaft36is rotated by the rotation motor37with respect to the axis of the rotation shaft36.

The first oil hydrostatic bearings31are located on the same height as the second oil hydrostatic bearings35. The rotation motor37is located below the first oil hydrostatic bearings31and the second oil hydrostatic bearings35.

The rotation table39is attached to the upper end of the rotation shaft36. A tool such as a tool bit201is supported on the rotation table39. In the present embodiment, the tip of the tool bit201is located on the rotational axis (first axis) of the rotation table39extending along the Y-axis.

As shown inFIGS.1,4, and7, the front surface of the table support23is provided with a deformation adjuster41at the same heights as the first oil hydrostatic bearings31and the second oil hydrostatic bearings35. The middle portion of the deformation adjuster41is recessed in a gently curved manner. An end member46is arranged at each of opposite ends of the deformation adjuster41. The end members46protrude frontward from the deformation adjuster41. The two end members46respectively include threaded holes that extend in reverse spiral directions. External screws at opposite ends of an adjustment rod47, which has a hexagonal cross-section, are respectively fastened to the threaded holes of the two end members46. Thus, the adjustment rod47functions as a turnbuckle. By rotating the adjustment rod47, the action of reverse threads finely adjusts the distance between the two end members46so that the curvedness of the table support23is finely adjusted. As a result, fine adjustment is made for the distance between the vertical surfaces of the two upper steps301and for the position in a movement path of the table-side movable body32. Nuts48,49that resist loosening are fastened to the external screws at the opposite ends of the adjustment rod47, which respectively protrude from the end members46.

The spindle unit26has the following structure.

As shown inFIGS.1,3, and10, a unit base51is mounted on and fixed to the upper surface of the spindle support24, and receiving members52are integrally arranged on opposite sides of the unit base51. As shown inFIGS.6and8, sliders55on opposite sides of a spindle-side movable body54are respectively supported on the two receiving members52by third oil hydrostatic bearings53such that the sliders55are movable in the Z-axis direction. That is, the lower surface and the side surface (vertical surface) of each slider55defines the third oil hydrostatic bearing53, to which oil is supplied. The upward surface and the side surface (vertical surface) of each receiving member52support the corresponding third oil hydrostatic bearing53by an oil film and guide movement of the spindle-side movable body54in the Z-axis direction.

The spindle-side movable body54is made of a metal ceramic composite material. For reduction in weight and toughness, the metal ceramic composite material is obtained by, for example, dispersing powders in an iron cast. The spindle-side movable body54supports a spindle bearing56.

The spindle-side movable body54is moved in the Z-axis direction by linear motors61on opposite sides of the spindle-side movable body54. The linear motors61extend along the Z-axis. The linear motors61each include a fixed member612, which includes a permanent magnet (not shown), and a movable member611, which includes a flat coil (not shown). The fixed members612are joined to the unit base51, and the movable members611are joined to the spindle-side movable body54. That is, the fixed member612is indirectly fixed to the bed22, and the movable member611is fixed to the spindle unit. The movable member611is located in a slit613of the fixed member612. A configuration may be employed in which the fixed member612includes a flat coil and the movable member611includes a permanent magnet. Alternatively, the two members612,611may each include a flat coil.

As shown inFIGS.6and7, the spindle bearing56supports a spindle58that is rotated by a rotation motor57. The spindle58includes a rotational axis (third axis) extending along the Z-axis. The tip of the spindle58includes an air chuck59. A workpiece202is secured to the tip of the air chuck59.

As shown inFIG.8, the center of gravity a of the spindle unit26is located in a direction corresponding to the Y-axis (vertical direction) in a range of the vertical width of the slit613of each linear motor61. In the present embodiment, the center of gravity a is located at the middle in the range of the thickness of the movable member611of the slit613. That is, the center of gravity a is located at the same height as the slit613or the movable member611.

The bed22, the unit base51, and the components related to the bed22and the unit base51will now be described in detail.

As shown inFIGS.3and7, the front end of the unit base51is located above the table support23.

As shown inFIGS.5,6, and8, a vertically-extending side plate71is arranged integrally with each of the left and right ends of the bed22. A front lower plate72extends between the lower ends of the two side plates71below the table support23. The front lower plate72is arranged integrally with the two side plates71. A rear lower plate78(corresponding to a bulged portion) extends between the lower ends of the two side plates71below the spindle support24. The rear lower plate78is arranged integrally with the two side plates71.

As shown inFIGS.2and6, a front leg coupling portion73(corresponding to a first load receiving portion) is arranged at each of the left and right ends on the lower surface of the front lower plate72. That is, the front leg coupling portions73are respectively arranged at the opposite ends on the lower surface of the front lower plate72in a movement direction of the rotation table39corresponding to the X-axis. The front leg coupling portions73are respectively mounted on the receiving plates17, which are located at the upper ends of the support legs15, and coupled to the receiving plates17by bolts (not shown). The rear end of the rear lower plate78includes a through portion76. The through portion76opposes a rear leg coupling portion77(corresponding to a second load receiving portion) on the lower surface of the top plate28of the spindle support24. The rear leg coupling portion77is located below the spindle58; specifically, below the rotational axis of the spindle58. More specifically, the rear leg coupling portion77is located in a region where the spindle bearing56moves and at a position corresponding to a middle position between the left and right third oil hydrostatic bearings53. The rear leg coupling portion77is mounted on the receiving plates17, which are located at the upper end of the rear support leg16, and coupled to the receiving plate17by a bolt (not shown). The rear leg coupling portion77is located above the front leg coupling portions73.

Accordingly, the lathe21is supported by the front support legs15at two positions located at the same height in the X-axis direction and supported by the rear support leg16at one position extending through the middle of the two front support legs15in the Z-axis direction. The lathe21is supported in the front-rear direction (Z-axis direction) with a height difference such that the lathe21is supported at a higher position on the rear side than on the front side. In other words, the point at which the rear support leg16supports the lathe21is higher than the points at which the front support legs15support the lathe21.

As shown inFIGS.6to8, the rear lower plate78is located between the front leg coupling portion73and the rear leg coupling portion77. The rear lower plate78has a curved or spherical shape that bulges in a substantially arcuate manner in the front-rear direction and the left-right direction.

As shown inFIGS.6and8, the bed22includes a cavity95surrounded by the top plate28, the side plates71, and the rear lower plate78. The bed22includes reinforcement walls81,82,83. The reinforcement walls81,82,83include two reinforcement vertical walls81, two reinforcement inclined walls82, and multiple reinforcement horizontal walls83. The reinforcement vertical walls81extend between the top plate28and the rear lower plate78. The reinforcement inclined walls82extend between the top plate28and lower end regions of the two reinforcement vertical walls81. The reinforcement horizontal walls83extend, for example, between the top plate28and the reinforcement inclined walls82, between the reinforcement inclined walls82and the rear lower plate78, and between the reinforcement vertical walls81and the side plates71. The lower surface of the unit base51includes a reinforcement defined by two inclined walls85and a bridge86that extends between the lower ends of the two inclined walls85. The bridge86is in contact with the upper surface of the top plate28. The unit base51includes horizontal walls90. The lower portions of the unit base51on opposite sides each include a plate91that extends sideward. Reinforcement ribs92are arranged between the plates91and the side wall of the unit base51. The reinforcement ribs92are arranged integrally with the unit base51.

As shown inFIGS.1,6, and8, through-holes88are arranged for weight reduction. The shapes of through-holes88are, for example, circular or triangular.

The operation of the lathe21will now be described.

For example, machining the front surface of the workpiece202into a projected curved surface or a recessed curved surface rotates the spindle58and the air chuck59, which is used to secure the workpiece202. Further, the linear motors61work so as to move the spindle unit26in the Z-axis direction. Simultaneously, the rotation table39is turned with respect to the Y-axis while the rotation table unit25is moved back and forth in the X-axis direction. Accordingly, while the tip of the tool bit201is rotated with respect to the Y-axis, the tool bit201is moved back and forth in the X-axis direction and the workpiece202is moved back and forth in the Z-axis direction. In this manner, the workpiece202is cut into a projected curved surface or a recessed curved surface. Thus, the workpiece202is machined into various shapes by setting the speed, timing, stroke, and the like of the movement of the spindle unit26in the Z-axis direction and the movement of the rotation table unit25in the X-axis direction and by setting the rotation speed, the rotation range, and the like of the rotation table39.

The above-described embodiment provides the following advantages.

(1) The table support23at the front part of the bed22includes the recess232. The recess232accommodates the rotation table unit25. This lowers the position of the rotation table39. The rotation table unit25includes the plate-shaped movable body32. The outer portion of the movable body32defines the first oil hydrostatic bearings31. Further, the movable body32includes the second oil hydrostatic bearings35defined by the wall surface of the support hole42and the peripheral portions of the support hole42. The first oil hydrostatic bearings31is located at the same height as the second oil hydrostatic bearings35. This reduces the vertical dimension of the rotation table unit25. As a result, the height of the rotation table39is further reduced. This lowers the position of the tool bit201on the rotation table39and thus lowers the position of the spindle58supporting the workpiece202. Accordingly, the entire lathe21is reduced in thickness, size, and weight. This increases the natural frequency of the lathe21and reduces the amplitude of the vibration, thereby improving the machining accuracy. In addition, since the lathe21is reduced in size and weight, the lathe21is installed in a factory with fewer conditions and thus easily handled.

(2) The spindle unit26includes the spindle58that is rotated with respect to the horizontal Z-axis. Further, the spindle unit26is moved in the direction of the Z-axis by the third oil hydrostatic bearings53. The linear motors61are arranged on opposite sides of the spindle unit26, respectively. The linear motors61work so as to move the spindle unit26along the Z-axis. This produces a driving force on each of the opposite sides of the spindle unit26and thus reduces the offset load on the spindle unit26. Accordingly, the spindle unit26is moved in the Z-axis smoothly and accurately without being inclined by pitching or rolling. As a result, the machining accuracy is improved.

(3) The center of gravity a of the spindle unit26is set to be in the range of the thickness of the movable member611of each linear motor61in the up-down direction. Thus, when the spindle unit26is moved in the Z-axis direction, offset load hardly acts on the spindle unit26. Accordingly, the spindle unit26is moved in the Z-axis smoothly and accurately with almost no inclination of the spindle unit26. As a result, the machining accuracy is improved.

(4) The third oil hydrostatic bearings53of the spindle unit26are located below the linear motors61. Thus, the weight of the spindle unit26is received at the lower parts of the linear motors61. This limits the action of offset load on the linear motors61.

(5) The spindle-side movable body54is made of a metal ceramic composite material and thus reduced in size. This reduces the driving force needed to move the spindle unit26and allows for the use of a small linear motor61with a small power consumption. Further, the reduction in the weight of the entire spindle unit26lowers the inertial load that is produced when the spindle unit26is started and stopped. This limits the inclination of the spindle unit26that occurs when the spindle unit26is started and stopped. As a result, the machining accuracy is improved. Furthermore, the reduction in the weight of the spindle unit26lowers the amplitude of the spindle unit26that occurs when the spindle unit26vibrates. This also improves the machining accuracy.

(6) The linear motors61that move the spindle unit26are located at opposite sides of the spindle unit26. Thus, as compared with a configuration in which linear motors and a lead screw are located below a spindle unit, the total height of the spindle unit26is reduced. Accordingly, the entire lathe is reduced in size.

(7) Since the total height of the spindle unit26is reduced, the spindle unit26can be easily located on the upper side of the rotation table39without increasing the total height of the machine tool so much. Thus, the front end of the unit base51is extended frontward to form an overhang. As a result, the forward end of the spindle unit26approaches the rotation table39. This reduces the machining area of the machine tool and improves the degree of freedom in various types of machining, thereby increasing the versatility of the lathe.

(8) The lathe21is supported at three positions. This allows the support legs15,16to stably support the lathe21. Accordingly, the present embodiment maintains a state capable of performing highly accurate machining.

(9) Level difference is provided for the positions of the front support legs15and the rear support leg16that support the bottom of the bed22of the lathe21. More specifically, the position of the rear support leg16supporting the bottom of the bed22is higher than the positions of the front support legs15supporting the bottom of the bed22. This brings the position of a mounting base of the rear support leg16close to the center of gravity of the bed22. Thus, as compared with a case in which no height difference is provided for front and rear support positions, the vibration of the bed22caused by the movement of the spindle unit26is limited. This avoids a decrease in the machining accuracy.

(10) The rear lower plate78located below the spindle support24of the bed22has a curved shape that rises rearward. Thus, unlike a case in which the rear lower plate78extends straight in a horizontal manner, the bed22is reduced in size. Further, the cavity95is located below the spindle support24of the bed22. This reduces the size of the bed22. As a result, the amplitude of the natural vibration of the lathe21is reduced.

(11) Although the cavity95is located below the spindle support24of the bed22, the cavity95includes the reinforcement walls81,82,83and the like. This maintains the rigidity of the bed22. Also, the rear lower plate78is curved into a spherical shape. This further improves the rigidity of the bed22.

(12) The load produced by the spindle unit26and the like acts on the rear lower plate78as a tensile load. However, the rear lower plate78has an arcuate shape in the front-rear direction and thus effectively resists the tensile load, thereby properly limiting the deformation of the bed22that would be caused by the tensile load. Further, the load produced by the weights of the linear motors33and the like on opposite sides of the spindle58acts on the rear lower plate78as a compressive load. However, the rear lower plate78has an arcuate shape in the left-right direction and thus effectively resists the compressive load, thereby properly limiting the deformation of the bed22that would be caused by the compressive load. Accordingly, the substantial rigidity of the bed22improves without an increase in weight of the bed22. This contributes to high-accuracy machining.

(13) The rear leg coupling portion77receiving the rear support leg16is located higher than the front leg coupling portions73receiving the front support legs15. Thus, the shape of the lower part of the bed22rises rearward. This contributes to reduction of the bed22in size and weight as described above.

(14) Since the plate-shaped portion of the bed22includes the through-holes88, the weight of the entire lathe21is reduced. Further, when the through-holes88function as air vents, the temperatures inside and outside of the lathe21become uniform. This limits distortion and deformation of the bed22and the like.

Modifications

The present embodiment may be modified as follows. The present embodiment and the following modifications can be combined as long as the combined modifications remain technically consistent with each other.

The center of gravity a of the spindle unit26may be set in a range of the thickness of each linear motor61in the up-down direction. Even such a configuration provides almost the same advantages as those of the above-described embodiment.

Unlike the above-described embodiment, the spindle support24may support a tool such as a rotation grindstone and the rotation table39may support a workpiece.

The present embodiment may be applied to a machine tool other than a lathe. For example, a spindle may support a tool such as a drill and a rotation table may support a workpiece.

The bed22and the unit base51may be integrally arranged.

The oil hydrostatic bearing in each member may be changed to another type of bearing, such as a rolling bearing or an air bearing.

Several Technical Ideas in Present Disclosure

(A) A machine tool including:a bed;a table unit arranged on an upper surface of the bed; anda spindle unit including a spindle configured to rotate with respect to a rotational axis, the spindle unit being arranged on the upper surface of the bed, wherea lower surface of the bed including two first load receiving portions and one second load receiving portion, the first load receiving portions being arranged in a direction that is orthogonal to the rotational axis, and the second load receiving portion being located at a portion corresponding to the rotational axis, andthe lower surface of the bed includes a bulged portion between the first load receiving portions and the second load receiving portion, the bulged portion having a curved shape.

(B) The machine tool according to technical idea (A), wherethe table unit is configured to move in the direction that is orthogonal to the rotational axis, andthe first load receiving portions are located in correspondence with opposite ends of a movement range of the table unit.

(C) The machine tool according to technical idea (A) or (B), wherethe bed is configured to support the spindle unit at a higher position than the table unit, andthe second load receiving portion is located at a higher position than the first load receiving portions.

(D) The machine tool according to any one of technical ideas (A) to (C), further including a linear motor configured to move the spindle unit along the rotational axis, wherethe spindle unit includes a motor and a movable body, the motor being configured to rotate the spindle, and the movable body supporting the spindle and the motor, andthe linear motor includes a movable member arranged on the movable body.