C-Axis driving system for machine tools

Abstract: In a C-axis driving system for machine tools including a worm wheel mounted on a spindle rotatably supported by a headstock, a worm shaft with a worm formed therein directed perpendicular to an axis of the spindle and placed so as to be pivotable about a pivotal shaft between an engagement position where the worm shaft is engaged with the worm wheel and a disengagement position where the worm shaft is disengaged therefrom, and a C-axis driving motor connected to the worm shaft and serving for rotationally indexing the spindle to a specified rotational angle, wherein the worm shaft is rotatably supported by a worm shaft base, the pivotal shaft is provided on the worm shaft base so as to be directed perpendicular to an axis of the worm shaft, and the pivotal shaft is supported by the headstock. Thus, the C-axis driving system for machine tools is capable of suppressing the upsizing of the C-axis unit as well as the increase in cost while implementing a smooth engagement with the worm wheel.

Description: BACKGROUND OF THE INVENTION The present invention relates to a C-axis driving system for machine tools for rotationally indexing and positioning a spindle, which is rotatably supported on a headstock, to a specified rotational angle. For example, some NC lathes are equipped with a C-axis driving system which allows C-axis machining by a rotating tool to be performed while controlling the rotation of the spindle that is rotationally driven by a spindle driving motor (see, for example, Japanese Patent Publication No. 2566543 & JP 63-191549 A, Japanese Patent Laid-Open Publication SHO 59-53140, Japanese Utility Model Laid-Open Publication HEI 1-114257). Conventionally, this type of C-axis driving system has been provided in the following structure, roughly. A worm shaft engageable with a worm wheel fixedly mounted on a spindle is placed perpendicular to the axis of the spindle and moreover supported by a unit casing. A pivotal shaft generally equal in length to the worm shaft is inserted into the unit casing parallel to the worm shaft, and the unit casing is driven by a drive mechanism to rotate about the pivotal shaft between an engagement position for engagement with the worm wheel and a disengagement position for disengagement therefrom. Further, a C-axis driving motor is connected to an end portion of the worm shaft of the unit casing. At the engagement position, the worm shaft is driven into rotation by the C-axis driving motor, by which the spindle is rotationally indexed and positioned to a specified rotational angle via the worm wheel. In this state, milling or other rotating work is performed. Otherwise, for turning work, the worm shaft is withdrawn to the disengagement position. In this connection, in order to obtain a smooth engagement between the worm wheel and the worm shaft, the rotational angle of the unit casing is preferably as small as possible. From such a viewpoint of making the rotational angle small, in some cases, the center distance "d" between the worm shaft and the pivotal shaft is set to a large one. However, with a structure in which the center distance "d" between the worm shaft and the pivotal shaft is set large as in the conventional system, there are problems that the C-axis unit as a whole is increased in size, causing the structure to be complicated accordingly and the cost to increase. SUMMARY OF THE INVENTION The present invention having been accomplished under the above circumstances of the prior art, an object of the invention is to provide a C-axis driving system for machine tools which is capable of suppressing the upsizing of the C-axis unit as well as the increase in cost while implementing a smooth engagement with the worm wheel. In order to achieve the above object, according to the invention, there is provided a C-axis driving system for machine tools including a worm wheel mounted on a spindle rotatably supported by a headstock, a worm shaft with a worm formed therein directed perpendicular to an axis of the spindle and provided so as to be pivotable about a pivotal shaft between an engagement position where the worm shaft is engaged with the worm wheel and a disengagement position where the worm shaft is disengaged therefrom, and a C-axis driving motor connected to the worm shaft and serving for rotationally indexing the spindle to a specified rotational angle, wherein the worm shaft is rotatably supported by a worm shaft base, the pivotal shaft is provided on the worm shaft base so as to be directed perpendicular to an axis of the worm shaft, and the pivotal shaft is supported by the headstock. According to another aspect of the invention, in the C-axis driving system as described above, the C-axis driving motor is connected in series to an end portion of the worm shaft of the worm shaft base, and the pivotal shaft is placed at a proximity to the C-axis driving motor between the worm of the worm shaft and the C-axis driving motor. With the C-axis driving system of the invention, the worm shaft is supported by the worm shaft base, while the pivotal shaft is placed on the worm shaft base so as to be directed perpendicular to the axis of the worm shaft. Therefore, the worm shaft base can be set to such a size that the worm shaft can be housed therein and supported, thus allowing the unit to be smaller in size as compared with the conventional case where the worm shaft and the pivotal shaft are placed with a distance therebetween. This in turn allows the C-axis unit as a whole to be downsized. Also, since the worm shaft base can be downsized, the structure can be simplified as compared with the conventional unit casing. Resultantly, the parts count can be reduced and moreover the cost can be reduced. Furthermore, in the placement of the pivotal shaft on the worm shaft base, by such a setting that the rotational angle of the worm shaft base becomes a small one, a smooth engagement with the worm wheel can be achieved. According to another aspect of the invention, the C-axis driving motor is connected in series at an end portion of the worm shaft of the worm shaft base, and the pivotal shaft is provided at a proximity to the driving motor between the worm and the C-axis driving motor. Therefore, while a smooth engagement with the worm wheel is ensured, the driving force can be reduced, as compared with the conventional case where the whole unit including the C-axis driving motor is pivoted. Thus, the structure can be further simplified and the cost can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a vertical NC lathe in which a C-axis driving system according to an embodiment of the invention is provided; Fig. 2 is a left-hand side view of a headstock on which the C-axis driving system is provided; Fig. 3 is a plan view of the C-axis driving system; Fig. 4 is a cross-sectional plan view of the C-axis driving system taken along the line IV - IV of Fig. 5; Fig. 5 is a cross-sectional front view of the C-axis driving system; Fig. 6 is a cross-sectional side view of the pivotal shaft part of the C-axis driving system taken along the line VI - VI of Fig. 5; Fig. 7 is a cross-sectional side view of the engagement part between the worm wheel and the worm shaft of the C-axis driving system taken along the line VII - VII of Fig. 5; Fig. 8 is a schematic perspective view of the C-axis driving system; and Fig. 9 is a perspective view of the worm shaft base of the C-axis driving system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinbelow, embodiments of the present invention are described with reference to the accompanying drawings. Figs. 1 to 9 are views for explaining a C-axis driving system of a vertical NC lathe (machine tool) according to one embodiment of the invention. Fig. 1 is a perspective view of the vertical NC lathe; Figs. 2 and 3 are a left-hand side view and a plan view, respectively, of a headstock on which the C-axis driving system is provided; Fig. 4 is a cross-sectional plan view of the C-axis driving system taken along the line IV - IV of Fig. 5; Fig. 5 is a cross-sectional front view of the C-axis driving system taken along the line Va - Va and the line Vb - Vb of Fig. 4; Fig. 6 is a cross-sectional side view of the pivotal shaft part of the C-axis driving system taken along the line VI - VI of Fig. 5; Fig. 7 is a cross-sectional side view of the engagement part between the worm wheel and the worm taken along the line VII - VII of Fig. 5; Fig. 8 is a schematic perspective view of the C-axis driving system; and Fig. 9 is a perspective view of the worm shaft base. Referring to the figures, reference numeral 1 denotes a vertical NC lathe, which has the following structure, roughly. That is, a headstock 3 is fixedly mounted on a fixed bed 2, and a saddle 4 is provided upward of the headstock 3 of a column 2a so as to be movable in the X-axis direction (horizontal direction). Further, a tool post 5 is provided on the saddle 4 so as to be movable in the Z-axis direction (vertical direction), and a turret head 6 with turning tools, rotating tools or other cutting tools (not shown) loaded thereon is provided on the tool post 5 so that a required cutting tool can be rotationally indexed to a machining position. The headstock 3 is rectangular-parallelopiped box shaped, and a spindle 7 is inserted in the headstock 3 so as to be rotatable via bearings 8, 8. The spindle 7 is so positioned that its axis is directed vertical (along the Z-axis). A chuck 9 for gripping a workpiece W is mounted at an upper end portion of the spindle 7, while a hydraulic cylinder mechanism 10 for driving the opening/closing of a gripping claw 9a of the chuck 9 is connected to a lower end portion of the spindle 7. In the headstock 3, a spindle driving shaft 11 is inserted parallel to the spindle 7 so as to be rotatable via bearings 12, 12. The spindle driving shaft 11 is linked with a driving gear 13 fixedly mounted on the spindle 7 via an unshown power transmission member. A pulley 11a is mounted at a lower end of the spindle driving shaft 11, and an unshown spindle driving motor is linked with the pulley 11a via a belt. By this spindle driving motor, the spindle 7 is driven into rotation via the spindle driving shaft 11, while the turret head 6 relatively moves in the X- and Z-axis directions so that a required turning tool cuts into the workpiece W. Thus, a specified turning work is performed. The headstock 3 is provided with a C-axis driving system 15. This C-axis driving system 15 is equipped with a worm wheel 16 mounted on the spindle 7 below the driving gear 13, a worm shaft 17 engageable with the worm wheel 16, and a C-axis unit 18 which drives the worm shaft 17 into rotation between an engagement position A where the worm shaft 17 engages with the worm wheel 16 and a disengagement position B where the worm shaft 17 is disengaged therefrom and withdrawn. The worm wheel 16, which is annular shaped, is mounted and fixedly bolted on an outer peripheral portion of a disc member 19 fixedly mounted on the spindle 7. The worm shaft 17 is positioned on the front side of the spindle 7 and perpendicular to the spindle axis (along the X axis), and a worm 17a is formed at an axially central portion of the worm shaft 17. The C-axis unit 18 is made up of a worm shaft base 20 for housing the worm shaft 17, a C-axis driving motor 21 for driving the worm shaft 17 into rotation, a C-axis base 22 for swingably supporting the worm shaft base 20, and a C-axis coupling hydraulic cylinder mechanism 23 for driving the worm shaft base 20 into rotation. At a corner portion defined by a front wall 3a and a left-side wall 3b of the headstock 3, an opening 3c is formed by cutting out the portion, and the C-axis base 22 is placed at this opening 3c. This C-axis base 22 is triangular shaped as seen in a plan view along the cut-out portion of the headstock 3, so that the headstock 3 is prevented from increasing in size due to the installation of the C-axis base 22. A flange 22a is formed at a peripheral portion of the C-axis base 22, and the flange 22a is fixedly tightened at an edge portion of the opening 3c with a bolt 24. In a left side wall 22b of the C-axis base 22, is formed a rectangular hole 22c having such a size as to allow the worm shaft base 20 to be passed therethrough. The worm shaft base 20, which is rectangular-cylindrical shaped with both ends opened, extends so as to be inserted through the rectangular hole 22c of the C-axis base 22 and the opening 3c of the headstock 3 and to confront the worm wheel 16. The worm shaft 17 is inserted into the worm shaft base 20, and supported so as to be rotatable via bearings 25, 25 mounted on both end portions of the worm shaft 17. Also, a window 20b having such a size as to allow a front end portion of the worm wheel 16 to be inserted therein is formed as a cutout in a rear side wall 20a of the worm shaft base 20. An outer end portion of the worm shaft base 20 protrudes outward of the C-axis base 22, and a flange 20d is formed at an outer end edge of the protruding portion. The C-axis driving motor 21 is fixedly bolted to this flange 20d. A rotating shaft 21a of this C-axis driving motor 21 extends into the worm shaft base 20 so as to be coaxially opposed to the worm shaft 17, and this rotating shaft 21a and the worm shaft 17 are fixedly connected to each other in series with a coupling member 27 (see Fig. 5). Also, an expandable/contractible seal cover 28 (see Fig. 4) is provided so as to cover between the flange 20d of the worm shaft base 20 and the C-axis base 22, thereby preventing invasion of dusts or the like from outside into the headstock 3. Pivotal shafts 30, 30 are provided on the worm shaft base 20 so as to be coaxial with each other. Each pivotal shaft 30 of these is so positioned that its pivotal axis is directed along the vertical direction (Z-axis direction), which is perpendicular to the axis of the worm shaft 17, and the pivotal shaft 30 is fixedly tightened with a plurality of bolts 31 to an upper wall 20e and a lower wall 20f of the worm shaft base 20 in proximity to the C-axis driving motor 21. The or each pivotal shaft 30 is inserted through an insertion hole 22g formed in a top wall 22e and a bottom wall 22f of the C-axis base 22 so as to protrude a little outward, and is rotatably supported by bearings 32, 32 fixedly mounted on an inner circumferential surface of the insertion hole 22g. The protruding portions of the pivotal shafts 30 are covered with caps 34, 34, respectively, the caps 34 being fixedly bolted to the C-axis base 22. In this way, the worm shaft base 20 is supported by the C-axis base 22 so as to be rotatable back and forth about the pivotal shaft 30. An opening 3e is formed as a cutout at a portion of the front wall 3a of the headstock 3 confronting an inner end portion of the worm shaft base 20, and the C-axis coupling hydraulic cylinder mechanism 23 is inserted in the opening 3e. This hydraulic cylinder mechanism 23, having a structure, roughly, that a piston rod 36 is advanceably and retreatably inserted in a cylinder 35, and the hydraulic cylinder mechanism 23 is fixedly installed on a plate 37 fixedly bolted to the front wall 3a so as to close the opening 3e. A rectangular-plate shaped coupling block 38 is fixedly bolted at the inner end portion of the worm shaft base 20. In this coupling block 38, a recessed portion 38a having a U-shaped cross section is formed in the rear side wall, and a rectangular window 38b communicating with the recessed portion 38a is formed at a central portion of the front wall, where a fore end portion 36a of the piston rod 36 is inserted into the rectangular window 38b. In a front right end face of the coupling block 38, is formed a tapered stopper portion 38c which makes surface-contact with the rear end face of the plate 37 at the disengagement position B, so that the worm shaft base 20 is restricted to the disengagement position B by this stopper portion 38c (see Fig. 4). In the recessed portion 38a, a columnar coupling pin 39 is inserted with its axis vertical. At an axially central portion of this coupling pin 39, is formed a cutout portion 39a, to which the fore end portion 36a of the piston rod 36 is fixedly screwed. This coupling pin 39 functions to absorb the rotational motion of the worm shaft base 20 due to the advance and retreat of the piston rod 36. At a portion within the headstock 3 confronting the inner end face of the worm shaft base 20, is provided a positioning guide block 40, which is fixedly bolted to the headstock 3. This positioning guide block 40 is L-shaped in a right-hand side view, having a rearwardly extending guide portion 40b integrally formed at the lower end of a vertically extending positioning portion 40a, where a guide groove 40c extending in the back-and-forth direction is formed in the left-hand side wall of the guide portion 40b. A guide portion 41 which slidably engages in the guide groove 40c is integrally formed at an inner end portion of the lower wall 20f of the worm shaft base 20. As a result of this, the worm shaft base 20 is allowed to rotate only in the back-and-forth direction while prohibited from swinging in the up-and-down direction, thus the worm shaft base 20 being prevented from shifts during the rotation. A positioning portion 42 confronting the front face of the positioning portion 40a is integrally formed at an inner end portion of a front wall 20h of the worm shaft base 20, and a contact block 43 is fixedly bolted to the positioning portion 42. This contact block 43, when making contact with the positioning portion 40a, positions the worm shaft base 20 to the engagement position A. As a result of this, the pressing force of the piston rod 36 of the hydraulic cylinder mechanism 23 is prevented from acting on the engagement portion of the worm 17a and the worm wheel 16. The spindle 7 is also equipped with a hydraulic clamp mechanism 50 for fixing the spindle 7 to a rotational index position, as shown in Figs. 4 and 5. This hydraulic clamp mechanism 50 has four pairs of pistons 51, 51 disposed circumferentially, each pair being opposed to each other with the driving gear 13 interposed therebetween. Each piston 51 is inserted in a common cylinder block 52, and driven to advance and retreat between a clamp position where the driving gear 13 is fixedly clamped by hydraulic pressure and an unclamp position where the driving gear 13 is unclamped. It is noted that in Fig. 5, the upper piston 51 shows an unclamped state while the lower piston 51 shows a clamped state. Next, functional effects of this embodiment are described. When a lathe machining is performed with the vertical NC lathe 1 of this embodiment, the worm shaft base 20 is withdrawn to the disengagement position B and the piston 51 of the hydraulic clamp mechanism 50 is withdrawn to the unclamp position. In this state, the spindle 7 is driven into rotation by the spindle driving motor, and the turning tool indexed to the machining position by the turret head 6 cuts into the workpiece W. When a rotating tool machining is performed, the spindle 7 is stopped from rotating, then the piston rod 36 of the hydraulic cylinder mechanism 23 advances and the worm shaft base 20 is pivoted until the contact block 43 makes contact with the positioning guide block 40. As a result, the worm shaft base 20 is fixedly positioned to the engagement position A where the worm 17a engages with the worm wheel 16. In this case, the contact block 43 is in contact with the guide block 40, thereby blocking the worm shaft base 20 from pivoting toward engagement. Thus, the hydraulic pressure of the hydraulic cylinder mechanism 23 never acts on the worm wheel 16. Further, since the worm shaft base 20 is guided by the guide groove 40c of the guide block 40, the worm shaft base 20 is allowed to smoothly pivot without occurrence of up-and-down shifts. At the engagement position A, the C-axis driving motor 21 drives the worm shaft 17 into rotation so that the spindle 7 is rotationally indexed to a specified rotational angle. At this index position, the pistons 51 of the hydraulic clamp mechanism 50 clamp the driving gear 13 to fix the spindle 7. Subsequently, the tool post 5 turns the turret head 6 to rotationally index a required rotating tool to a machining position, so that the workpiece W is subjected to rotating work such as milling or drilling with the rotating tool. According to this embodiment, the worm shaft 17 is placed and housed within the rectangular-cylindrical shaped worm shaft base 20, while the pivotal shaft 30 is placed on the upper wall 20e and the lower wall 20f of the worm shaft base 20 so as to be directed along the vertical direction, which is perpendicular to the axis of the worm shaft 17, and further the pivotal shaft 30 is rotatably supported by the C-axis base 22. Therefore, the worm shaft base 20 can be set to such a size that the worm shaft 17 can be housed therein, thus allowing the worm shaft base 20 to be smaller in size as compared with the conventional case where the worm shaft and the pivotal shaft are housed in a unit casing with a distance therebetween. This in turn allows the C-axis unit 18 as a whole to be downsized. Also, since the pivotal shaft 30 is placed perpendicular to the worm shaft 17, the axial length of the pivotal shaft 30 can be made shorter as compared with the conventional case where the pivotal shaft is set equal in length to the worm shaft. From this point as well, the C-axis unit 18 can be downsized. Further, since the worm shaft base 20 can be downsized, the structure can be simplified as compared with the conventional case where the large-size unit casing is provided. Resultantly, the parts count can be reduced and moreover the cost can be reduced. In this embodiment, since the pivotal shaft 30 is placed in proximity to the C-axis driving motor 21 at the outer end portion of the worm shaft base 20, the rotational angle of the worm shaft base 20 can be made small by setting a large distance between the worm 17a and the pivotal shaft 30. As a result, a smooth engagement with the worm wheel 16 can be achieved. Furthermore, the C-axis driving motor 21 is connected in series at the outer end of the worm shaft base 20, and the hydraulic cylinder mechanism 23 is connected to the inner end portion of the worm shaft base 20. Thus, the pivotal operation force of the worm shaft base 20 can be made small, allowing the hydraulic cylinder mechanism 23 to be downsized as compared with the conventional case where the whole unit including the C-axis driving motor is pivoted. From this point as well, the whole unit can be decreased in size. The above embodiment has been described on a case where the invention is applied to a vertical NC lathe in which the spindle axis is directed vertical. However, the machine tool according to the present invention is applicable also to lathes in which the spindle axis is directed horizontal, and further to any machine tools capable of C-axis machining.

Claims: A C-axis driving system (15) for machine tools including a worm wheel (16) mounted on a spindle (7) rotatably supported by a headstock (3), a worm shaft (17) with a worm (17a) formed therein directed perpendicular to an axis of the spindle and provided so as to be pivotable about a pivotal shaft (30) between an engagement position where the worm shaft (17) is engaged with the worm wheel (16) and a disengagement position where the worm shaft is disengaged therefrom, and a C-axis driving motor (21) connected to the worm shaft and serving for rotationally indexing the spindle to a specified rotational angle, wherein the worm shaft is rotatably supported by a worm shaft base (20), characterzized in that the pivotal shaft (30) is provided on the worm shaft base so as to be directed perpendicular to an axis of the worm shaft, and the pivotal shaft is supported by the headstock (3). The C-axis driving system according to Claim 1, wherein the C-axis driving motor (21) is connected in series to an end portion of the worm shaft (17) of the worm shaft base, and the pivotal shaft (30) is placed at a proximity to the C-axis driving motor between the worm (17a) of the worm shaft (17) and the C-axis driving motor (21).

Inventors: SASABE NOBUAKI, UEDA TOSHIO, UEMURA YOSHITANE, SASABE, NOBUAKI, UEDA, TOSHIO, UEMURA, YOSHITANE
Applicants: MORI SEIKI SEISAKUSHO KK, MORI SEIKI CO., LTD.
Application year: 2001
Main classification: B23Q5
IPC codes: B23Q16, F16H1