Machine tools abstract
A C-axis driving system for machine tools is disclosed that comprises
a worm wheel mounted on a spindle that is rotatably supported by
a headstock. The C-axis driving system also includes 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, and a disengagement position. The
C-axis driving system also includes a C-axis driving motor connected
to the worm shaft and serving to rotationally index the spindle
to a specified rotational angle. The pivotal shaft is provided on
the worm shaft base so as to be directed perpendicular to an axis
of the worm shaft. Thus, the C-axis driving system for machine tools
is capable of reducing the size of the C-axis unit as well as the
cost while allowing a smooth engagement with the worm wheel.
Machine tools claims
What is claimed is:
1. A C-axis driving system for machine tools, comprising: a worm
wheel engageable with a spindle rotatably supported by a headstock,
the headstock having an opening formed in a corner portion of the
headstock, a worm shaft with a worm formed therein, the worm shaft
being oriented 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, and a C-axis base being attached adjacent to the opening
in the headstock, and a portion of the C-axis base includes a triangular
cross section, wherein the worm shaft is rotatably supported by
a worm shaft base and the pivotal shaft is oriented relative to
the worm shaft base so as to be directed perpendicular to an axis
of the worm shaft, and the worm shaft base being pivotally supported
by the C-axis base.
Machine tools description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a C-axis driving system in a machine
tool having a spindle rotably supported on a headstock and for rotationally
indexing and positioning the spindle to a specified rotational angle.
2. Discussion of the Related Art
For example, some numerically controlled (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 Japanese
Patent Laid-Open Publication SHO 59-53140 and Japanese Utility Model
Laid-open Publication HEI 1-114257.
Conventionally, this type of C-axis driving system has been provided
in the following structure. As shown in FIG. 10 a worm shaft 82
engageable with a worm wheel 80 fixedly mounted on a spindle (unshown)
is placed perpendicular to the axis of the spindle and supported
by a unit casing 81. A pivotal shaft 83 generally equal in length
to the worm shaft 82 is inserted into the unit casing 81 parallel
to the worm shaft 82. The unit casing 81 is driven by a drive mechanism
(not shown) so as to rotate about the pivotal shaft 83 between an
engagement position for engagement with the worm wheel 80 and a
disengagement position for disengagement therefrom. Further, a C-axis
driving motor 84 is connected to an end portion of the worm shaft
82 of the unit casing 81.
When it is in the engagement position, the worm shaft 82 is rotatingly
driven by the C-axis driving motor 84. Thus the spindle is rotationally
indexed and positioned into a specified rotational angle via the
worm wheel 80. In this state, milling or other rotating work can
be performed. Otherwise for turning work, the worm shaft 82 is moved
into the disengagement position.
In this connection, in order to obtain smooth engagement between
the worm wheel 80 and the worm shaft 82 the rotational angle of
the unit casing 81 is preferably as small as possible. From the
viewpoint of making the rotational angle small, in some cases the
center distance "d" between the worm shaft 82 and the
pivotal shaft 83 is set to a large distance.
However, when the center distance "d" between the worm
shaft and the pivotal shaft is set to a large distance as in the
conventional systems, the entire C-axis unit increases in size thereby
causing the structure to be complicated and the cost increases.
SUMMARY OF THE INVENTION
The present invention has been made considering the above problems
and circumstances in the prior art.
An object of the invention is to provide a C-axis driving system
for machine tools that is capable of maintaining a smaller sized
C-axis unit as well as maintaining the costs while using a C-axis
driving system that implements a smooth engagement with the worm
wheel.
In order to achieve this and other objects according to the invention,
a C-axis driving system for machine tools is provided that includes
a worm wheel mounted on a spindle rotatably supported by a headstock.
The C-axis driving system also includes a worm shaft with a worm
formed therein that is directed perpendicular to an axis of the
spindle and is 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. The C-axis driving system also includes
a C-axis driving motor connected to the worm shaft that serves to
rotationally index the spindle to a specified rotational angle.
A worm shaft base rotatably supports the worm shaft. 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. Also the pivotal shaft is placed in 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 of a size that allows the worm shaft to be housed therein and
supported, thus allowing the unit to be smaller in size when compared
to the conventional systems where the worm shaft and the pivotal
shaft are placed apart with a distance therebetween. This thereby
allows the C-axis unit as a whole to be reduced in size.
Also, since the worm shaft base can be downsized, the structure
can be simplified when compared with the conventional unit casing.
This also results in reductions in the parts count and the cost.
Furthermore, when placing the pivotal shaft on the worm shaft base
so that the rotational angle of the worm shaft base becomes small,
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. Also the pivotal shaft is provided in 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 when compared to 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 further reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects and features of the present invention
will be clearly understood from the following description with respect
to the preferred embodiment thereof when considered in conjunction
with the accompanying drawings and diagrams, in which:
FIG. 1 is a perspective view of a vertical NC lathe having a C-axis
driving system according to an embodiment of the present invention;
FIG. 2 is a left-hand side view of a headstock provided on the
C-axis driving system according to the present invention;
FIG. 3 is a plan view of the C-axis driving system according to
the present invention;
FIG. 4 is a cross-sectional plan view of the C-axis driving system
taken along line IV--IV in FIG. 5;
FIG. 5 is a cross-sectional front view of the C-axis driving system
taken along lines Va--Va and Vb--Vb in FIG. 4;
FIG. 6 is a cross-sectional side view of the pivotal shaft part
of the C-axis driving system taken along line VI--VI in 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 line VII--VII in FIG. 5;
FIG. 8 is a schematic perspective view of the C-axis driving system
according to the present invention;
FIG. 9 is a perspective view of the worm shaft base of the C-axis
driving system according to the present invention; and
FIG. 10 is a schematic view of a C-axis driving unit according
to the prior art.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereinbelow, embodiments of the present invention are described
with reference to the accompanying drawings.
Referring to the figures, a vertical NC lathe 1 includes a headstock
3 fixedly mounted on a fixed bed 2 and a saddle 4 is provided above
the headstock 3 on 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). 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. The spindle 7 is positioned so that its axis is directed
vertically (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. 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 moves in the X- and Z-axis directions relative thereto so that
a required turning tool cuts into the workpiece W. Thus, the specified
turning work is performed.
The headstock 3 is also 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 annularly 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 is perpendicular to the spindle
axis (it extends along the X axis). 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
a portion. The C-axis base 22 is placed at this opening 3c. This
C-axis base 22 is generally triangularly shaped as seen in a plan
view along the cutout portion of the headstock 3. This substantially
prevents the headstock 3 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. The flange 22a is fixedly attached to an edge portion of the
opening 3c with bolts 24. A rectangular hole 22c is formed in a
left side wall 22b of the C-axis base 22. The hole 22c has a size
that allows the worm shaft base 20 to be passed therethrough.
The worm shaft base 20 is rectangularly shaped with both ends opened
and 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 so as
to be disposed adjacent to the worm wheel 16. The worm shaft 17
is inserted into the worm shaft base 20 and is supported so as
to be rotatable via bearings 25 mounted on both end portions of
the worm shaft 17. Also, a window 20b is provided that has a size
that allows a front end portion of the worm wheel 16 to be inserted
therein and 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 outwardly
from the C-axis base 22. A flange 20d is formed at an outer end
edge of the protruding portion and the C-axis driving motor 21 is
fixedly bolted to this flange 20d. A rotating shaft 21a of the 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 by 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 dust or the like on the outside from invading into the
headstock 3.
Pivotal shafts 30 are provided on the worm shaft base 20 so as
to be coaxial with each other. Each pivotal shaft 30 is positioned
so that its pivotal axis is directed in the vertical direction (Z-axis
direction), which is perpendicular to the axis of the worm shaft
17. The pivotal shafts 30 are respectively fixedly tightened by
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 respective pivotal shaft 30 is inserted through a respective
insertion hole 22g formed in a top wall 22e and a bottom wall 22f
of the C-axis base 22 so as to protrude outwardly a small amount.
The respective pivotal shafts are rotatably supported by bearings
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 respectively. The caps 34 are 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 shafts 30.
An opening 3e is formed as a cutout at a portion of the front wall
3a of the headstock 3 adjacent to an inner end portion of the worm
shaft base 20. The C-axis coupling hydraulic cylinder mechanism
23 is inserted in the opening 3e. This hydraulic cylinder mechanism
23 has a rough structure that allows a piston rod 36 to be advanceably
and retreatably inserted in a cylinder 35. The hydraulic cylinder
mechanism 23 is also installed on a plate 37 that is fixedly bolted
to the front wall 3a so as to close the opening 3e.
A rectangular-plate shaped coupling block 38 is fixedly bolted
to 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. An 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 when
in the disengagement position B, so that the worm shaft base 20
is restricted in the disengagement position B by this stopper portion
38c (see FIG. 4).
A columnar coupling pin 39 is inserted in the recessed portion
38a so that its axis is vertical. A cutout portion 39a is formed
at an axially central portion of this coupling pin 39. The end portion
36a of the piston rod 36 is fixedly screwed to the cutout portion
39a. This coupling pin 39 functions to absorb the rotational motion
of the worm shaft base 20 due to the advancing and retreating action
of the piston rod 36.
A positioning guide block 40 is provided at a portion within the
headstock 3 adjacent the inner end face of the worm shaft base 20.
The positioning guide block 40 is fixedly bolted to the headstock
3. This positioning guide block 40 is L-shaped in a right-hand side
view. Also it has a rearwardly extending guide portion 40b integrally
formed at the lower end of a vertically extending positioning portion
40a. A guide groove 40c extends back-and-forth and is formed in
the left-hand side wall of the guide portion 40b.
A guide portion 41 slidably engages the guide groove 40c and is
integrally formed with 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 back-and-forth while being prohibited
from swinging up-and-down. Thus the worm shaft base 20 is prevented
from shifting during rotation.
A positioning portion 42 adjacent to the front face of the positioning
portion 40a is integrally formed with an inner end portion of a
front wall 20h of the worm shaft base 20. Also, a contact block
43 is fixedly bolted to the positioning portion 42. The contact
block 43 positions the worm shaft base 20 to the engagement position
A when making contact with the positioning portion 40a. As a result
of this arrangement, the pressing force of the piston rod 36 in
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 in a rotational index position, as shown
in FIGS. 4 and 5. This hydraulic clamp mechanism 50 has four pairs
of pistons 51 disposed circumferentially. Each pair of pistons 51
being opposed to each other with the driving gear 13 interposed
therebetween. Each piston 51 is inserted in a common cylinder block
52. Each piston 51 can be driven to advance and retreat between
a clamped position, where the driving gear 13 is fixedly clamped
by hydraulic pressure, and an unclamped position, where the driving
gear 13 is not clamped. It is noted that in FIG. 5 both the clamped
position and the unclamped position are shown. Specifically, the
upper piston 51 shows the unclamped state while the lower piston
51 shows the clamped state.
Next, the functional effects of this embodiment are described.
When a lathe machining operation is performed with the vertical
NC lathe 1 of this embodiment, the worm shaft base 20 is moved to
the disengagement position B and the piston 51 of the hydraulic
clamp mechanism 50 is moved to the unclamped 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 operation is performed, the spindle
7 is prevented from rotating, then the piston rod 36 of the hydraulic
cylinder mechanism 23 is advanced 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
in 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 so as 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 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. Further the C-axis base 22 rotatably supports the pivotal shaft
30. Therefore, the worm shaft base 20 can be set to a size so that
the worm shaft 17 can be housed therein. This allows the worm shaft
base 20 to be smaller in size when compared to 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 reduced in size. Also, since the
pivotal shaft 30 is placed perpendicular to the worm shaft 17 the
axial length of the pivotal shaft 30 can be reduced compared with
the conventional case where the pivotal shaft is equal in length
with the worm shaft. From this point as well, the C-axis unit 18
can be reduced in size.
Further, since the worm shaft base 20 can be reduced in size, the
structure can be simplified when compared with the conventional
case where a large size unit casing is provided. As a result, the
number of parts can be reduced as well as the cost.
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 reduced 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
with the outer end of the worm shaft base 20. Also, 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 reduced, allowing the hydraulic cylinder mechanism
23 to be reduced in size when 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 for the case where the
invention is applied to a vertical NC lathe where the spindle axis
is vertical. However, the machine tool according to the present
invention is applicable also to lathes where the spindle axis is
horizontally oriented as well as to any machine tools capable of
C-axis machining.
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. 2000-156815 filed
May 26 2000 is hereby incorporated by reference. |