Machine tools abstract
The invention provides a clamping device for machine tools capable
of preventing the occurrence of impressions. In a clamping device
for machine tools, a tailstock (movable carriage) is provided on
a top face of a fixed bed and the tailstock is positioned and fixed
with respect to the fixed bed. The tailstock is supported by linear-motion
bearings (guides) which are disposed between the tailstock and the
fixed bed. Blocks are slidably engaged with rails extending in the
travel direction with rollers interposed between them. Further,
a recess portion extending in the travel direction is formed in
the top surface of the fixed bed. A cylinder mechanism is arranged
so that left and right inner walls in the recess portion are pressed
by a pair of pistons provided on the undersurface of a headstock.
Machine tools claims
What is claimed is:
1. A clamping device for machine tools comprising:
a movable carriage movably provided on a top face of a fixed bed;
a guide disposed between said movable carriage and said fixed bed,
said guide extending in a direction in which said movable carriage
travels so that said movable carriage is supported by said guide;
a recess portion formed in the top face of said fixed bed and extending
in a travel direction of said movable carriage;
a cylinder mechanism disposed at an undersurface of said movable
carriage, said cylinder mechanism having at least two pistons oriented
in opposite directions so as to be respectively opposed to left
and right inner walls of said recess portion so that said inner
walls are pressed by said pistons when said pistons are extended;
a movable rack fixed to at least one of the pistons opposed to
one of the left and right inner walls; and
a fixed rack attached to one of said inner walls, wherein said
fixed rack is opposed to and engageable with said movable rack.
2. A clamping device for machine tools as claimed in claim 1 further
comprising a plurality of cylinder mechanisms disposed on the undersurface
of the movable carriage.
3. A clamping device for a lathe comprising:
a movable carriage movably provided on a top face of a fixed bed:
a guide disposed between said movable carriage and said fixed bed,
said guide extending in a direction in which said movable carriage
travels so that said movable carriage is supported by said guide;
a recess portion formed in the top face of said fixed bed and having
opposed left and right inner planar walls extending in a travel
direction of said movable carriage; and
a cylinder mechanism disposed at an undersurface of said movable
carriage, said cylinder mechanism having at least two pistons oriented
in opposite directions so as to be respectively opposed to said
left and right inner planar walls of said recess portion, said at
least two pistons having an extended position where said left and
right inner planar walls are pressed by said pistons and said movable
carriage is prevented from moving relative to said fixed bed and
a retracted position where said pistons are spaced from said left
and right inner planar walls and allow movement of said movable
carriage relative to said fixed bed.
4. A clamping device for a lathe as claimed in claim 3 further
comprising a plurality of cylinder mechanisms disposed on the undersurface
of the movable carriage.
Machine tools description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a clamping device for machine
tools in which a movable carriage, provided linearly movable on
a fixed bed, is positioned and fixed.
2. Discussion of the Related Art
In a lathe, for example, that has a headstock secured onto a fixed
bed and a movable tailstock, a workpiece is held by a spindle of
the tailstock and a chuck of the headstock. Thus, the machining
process is carried out by rotating the workpiece. In this case,
to prevent undesirable movement of the workpiece, the tailstock
must be securely positioned and fixed to the fixed bed with a clamping
device.
A conventional clamping device is shown in FIG. 1. In this clamping
device, a tailstock 50 is set on a fixed bed 51 with their sliding
surfaces 51a, 50a in sliding contact with each other. A piston member
53b is disposed in a hydraulic chamber 53a formed in a pinching
plate 53 of the tailstock 50. The piston member 53b is elevated
with oil pressure. A clamping force F is supplied to the hydraulic
chamber 53a so that a ceiling portion 51b of the fixed bed 51 is
pinched between the piston member 53b and the tailstock 50.
Japanese Utility Model Laid-Open Publication No. 2570872 discloses
a clamping device in which a protrusion formed at the undersurface
of a movable table is pinched by a pair of piezoelectric elements
provided on a fixed base.
A structure could be envisioned in which the tailstock 50 is movably
supported by linear-motion bearings 55 as shown in FIG. 2 instead
of the structure in which the tailstock 50 slides on the fixed bed
51. These linear-motion bearings 55 are generally structured, so
that rails 56 fixed to the fixed bed 51 and blocks 57 fixed to the
tailstock 50 are engaged with each other with rollers (not shown)
interposed in between. In this way, frictional resistance can be
reduced.
However, if this type of linear-motion bearing is used in the aforementioned
conventional clamping device, there is a possibility that the rails
56 and the blocks 57 may suffer impressions. This occurs as a result
of the rollers causing a reaction force f equivalent to the clamping
force F acting directly on the linear-motion bearings 55. In addition,
when using linear-motion bearings, the clamping force is inferior
in proportion to a decrement of friction coefficient, which causes
further problems.
In the structure of the aforementioned publication, the table is
pinched between piezoelectric elements provided on the base, with
a longer travel distance of the table. Therefore it is necessary
to set multiple piezoelectric elements in a number corresponding
to the travel distance, which disadvantageously increases the number
of component parts.
SUMMARY OF THE INVENTION
An object of the invention is to provide a clamping device for
machine tools capable of preventing the occurrence of impressions,
as well as the reduction in clamping force when linear-motion bearings
are adopted.
A further object of the invention is to provide a clamping device
that avoids any increase in the number of parts.
In one aspect of the invention, there is provided a clamping device
for machine tools comprising a movable carriage movably provided
on a top face of a fixed bed so that the movable carriage can be
positioned and fixed to the fixed bed. The clamping device also
comprises:
a guide disposed between the movable carriage and the fixed bed
and extending in a direction in which the movable carriage travels
so that the movable carriage is supported by said guide;
a recess portion formed in the top face of the fixed bed and extending
in the travel direction; and
a cylinder mechanism disposed at an undersurface of the movable
carriage, the cylinder mechanism having at least two pistons provided
in opposite directions so as to be opposed to left and right inner
walls of said recess portion, respectively, so that said inner walls
are pressed by the pistons, respectively when said pistons are extended.
In a second aspect of the invention, there is provided a clamping
device for machine tools further comprising:
a movable rack fixed to one of the pistons opposed to one of the
left and right inner walls, and
a fixed rack fixed to one of said inner walls, wherein the fixed
rack is opposed to and engaged with the movable rack.
In a third aspect of the invention, there is provided a clamping
device for machine tools comprising a movable carriage movably provided
on a top face of a fixed bed so that the movable carriage can be
positioned and fixed to the fixed bed. The clamping device also
comprises a guide disposed between the movable carriage and the
fixed bed and extending in a direction in which the movable carriage
travels, the movable carriage being supported by the guide. A strip
shaped plate is disposed on the fixed bed extending in the travel
direction; and a cylinder mechanism is disposed on an undersurface
of the movable carriage. The cylinder mechanism has at least two
pistons provided so as to be opposed to each other with the strip
shaped plate interposed therebetween so that said plate is pinched
by the pistons when the pistons are advanced.
As used herein, the term "guide" includes, for example,
a linear-motion bearing in which blocks are slidably engaged with
rails with rollers or balls interposed in between. Suitable guides
also include, for example, a slide guide allowing sliding contact
between the movable carriage and the fixed bed at their sliding
surfaces.
According to the clamping device in a first aspect of the invention,
since a pair of pistons are provided at the undersurface of the
movable carriage, and the movable carriage is positioned and fixed
by the pistons exerting pressing force on the left and right inner
walls within the recess portion of the fixed bed, the clamping force
acts only on the fixed bed and never acts on the guide surface.
Therefore, for example, when linear-motion bearings are used, the
occurrence of impressions as well as a lowering of the clamping
force can be prevented.
In addition, since the cylinder mechanism is provided on the movable
carriage, it is only necessary to provide a single or small number
of cylinder mechanisms regardless of the length of the travel distance
of the movable carriage. Thus, the invention avoids the problem
of having to increase the number of piezoelectric elements with
an increase in length of the travel distance. This problem arises
when piezoelectric elements of a conventional clamping device are
disposed on the fixed bed side. In contrast, the number of cylinder
mechanisms can be minimized, and the cost can be further reduced
when using the present invention.
In a second aspect of the invention, since the movable rack is
fixed to one of the pistons opposed to one of the left and right
inner walls, and the fixed rack with which the movable rack is engaged
is fixed to the fixed bed, the clamping force of the movable carriage
can be enhanced while utilizing a simple structure.
In a third aspect of the invention, since the strip shaped plate
provided on the fixed bed is pinched by a pair of pistons provided
on the undersurface of the movable carriage, the clamping force
never acts on the guide surface. This prevents the problems of impressions
and a lowering of the clamping force. Moreover, only a small number
of cylinder mechanisms are required regardless of the length of
the travel distance.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partial cross sectional view showing a problem that
is overcome by the present invention;
FIG. 2 is a partial cross sectional view showing a conventional
clamping device;
FIG. 3 is a right side view of a clamping device of a slant bed
type lathe according to an embodiment of the present invention;
FIG. 4 is a sectional side view showing an unclamped state of the
clamping device according to the present invention;
FIG. 5 is a sectional plan view showing a clamped state of the
clamping device according to the present invention;
FIG. 6 is a sectional view of linear-motion bearings in the embodiment
according to the present invention;
FIG. 7 is a schematic perspective view of the lathe; and
FIG. 8 is a right side view showing a clamping device according
to another embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiments of the present invention are described in further detail
with reference to the accompanying drawings.
FIGS. 3 to 7 are views for explaining a clamping device for a slant
bed type lathe (machine tool) according to an embodiment of the
invention. In these figures, identical or corresponding elements
are designated by like reference numerals.
Referring to FIGS. 3 to 7 a slant bed type lathe generally has
a structure such that a tailstock 3 is right-and-left movably set
on the right side of the slant type bed 2 a headstock 4 is fixed
on the left side of bed 2 and a tool post 5 is back-and-forth,
right-and-left movably set behind the center line between the headstock
4 and the tailstock 3.
A chuck 6 for grasping the workpiece is fitted to the headstock
4 and a tailstock spindle 7 for holding the workpiece between itself
and the chuck 6 is fitted to the tailstock 3. In this tailstock
3 a tailstock body 3b is mounted on a base 3a, and the tailstock
spindle 7 is back-and-forth movably fitted to the tailstock body
3b.
As shown in FIG. 7 a turret head 8 for holding a plurality of
tools K is rotatably fitted to the tool post 5. A turret indexing
unit (not shown) for indexing the turret head 8 to make a required
tool selectively usable is provided inside the turret head 8 and
tool post 5.
The tailstock 3 is guided and supported by two linear-motion bearings
10 so as to be movable along the direction of the spindle. These
linear-motion bearings 10 which are disposed on the top face 2a
of the fixed bed 2 each comprises a rail 11 extending in parallel
to the travel direction and two blocks 12 disposed on the bottom
face of the tailstock 3 and slidably fitted to the rail 11.
As shown in FIG. 6 each rail 11 has a rod formed in a rectangular
shape in cross section and is tightly secured to the fixed bed 2
with a bolt 15 inserted through the central part of the rail 11.
Also, each block 12 is generally an inverted U-shape in cross section
and is in rolling contact with the rail 11 with a large number of
rollers 13 interposed between them. Each block 12 is tightly secured
to four corners of the undersurface of the base 3a of the tailstock
3 with bolts 16. In addition, balls may be interposed in place of
the rollers 13.
As shown in FIGS. 3 and 5 a clamping device 20 is provided between
the tailstock 3 and the fixed bed 2. This clamping device 20 comprises
one or more cylinder mechanisms 24 set within a recess portion 21
recessed between the two rails 11 of the fixed bed 2. In this example,
two cylinder mechanisms 24 are present. The clamping device 20 also
comprises a rack mechanism 45 which is driven into engagement and
disengagement by the cylinder mechanisms 24. The recess portion
21 comprises left and right inner walls 21a, 21b and a bottom wall
21c, as viewed from the right side of the lathe 1 and is formed
over the right-and-left overall length of the fixed bed 2.
The cylinder mechanisms 24 have a structure such that first and
second pistons 22 23 are provided in cylinder holes 27b, 27b formed
in a cylinder member 27 so that the first and second pistons 22
23 are advanceable and retractable alternately in opposite directions.
Rod portions 28a of the first and second pistons 22 23 are projected
outward from the cylinder holes 27b, respectively. In each of the
cylinder members 27 the cylinder hole 27b is bored through a rectangular
parallelepiped cylinder body 27a.
Lid plates 29 30 are tightened to both end faces of the cylinder
body 27a with a plurality of bolts 31 respectively. The rod portion
28a is projected from an opening 29a in one side of lid plate 29.
The cylinder member 27 is tightly fixed to the undersurface of the
base 3a of the tailstock 3 with a plurality of bolts 25. Further,
oil seals 32 are provided at the inner circumferential surface and
both end faces of the cylinder hold 27b, and at the inner circumferential
surface of the opening 29a of the lid plate 29 respectively.
The cylinder hole 27b is internally divided into first and second
hydraulic chambers 34 35 by the first and second pistons 22 23
respectively. The first and second pistons 22 23 are advanced by
oil pressure supplied into the first hydraulic chamber 34 and retracted
by oil pressure supplied into the second hydraulic chamber 35. The
first and second pistons 22 23 are set so as to be movable back-and-forth
along a direction parallel to the top face 2a of the fixed bed 2
and perpendicular to the travel direction of the tailstock 3.
The first piston 22 is opposed to the right inner wall 21b within
the recess portion 21 and the second piston 23 is opposed to the
left inner wall 21a on the opposite side. Thus, the first and second
pistons 22 23 are in pressure contact with the left and right inner
walls 21a, 21b in a mutually pressing fashion. In this way, the
cylinder member 27 and the tailstock 3 are positioned and fixed
at a specified position.
A movable rack 36 is provided so as to be stretched to the rod
portion 28a of the first piston 22 and tightly fixed with bolts
37. Also, a fixed rack 38 having a length corresponding to the travel
distance of the tailstock 3 is disposed on the right inner wall
21b of the recess portion 21. This fixed rack 38 is securely tightened
with bolts 39 to a bracket 38a securely bolted to the right inner
wall 21b. Further, the movable rack 36 is opposed to and engageable
with the fixed rack 38.
Next, the operation and effects of this embodiment are explained
below.
In the lathe 1 of this embodiment, the tailstock 3 is positioned
and fixed. The workpiece is held by the chuck 6 of the headstock
4 and the tailstock spindle 7 of the tailstock 3. In this manner,
specific machining processes are carried out with the tool while
the workpiece is being rotated.
In order to position and fix the tailstock 3 the fixing position
of the tailstock 3 is determined, then the first and second pistons
22 23 are advanced. The movable rack 36 fixed to the first piston
22 is engaged with the fixed rack 38 while the second piston 23
presses the left inner wall 21a of the recess portion 21. Thus,
the cylinder member 27 and the tailstock 3 are positioned and fixed.
According to the present embodiment, the cylinder member 27 is
fixed to the undersurface of the tailstock 3 and then the tailstock
3 is positioned and fixed by pressing the left and right inner walls
21a, 21b of the recess portion 21 of the fixed bed 2 by means of
the first and second pistons 22 23 provided within the cylinder
member 27. The resulting clamping force acts only on the left and
right inner walls 21a, 21b of the fixed bed 2 and the clamping
force never acts on the linear-motion bearings 10. As a result,
the occurrence of any impressions on the rails 11 11 and the blocks
12 is prevented, and there is no lowering of the clamping force.
This makes the linear-motion bearings 10 particularly practical,
and frictional resistance can be reduced.
Further, since the cylinder member 27 for holding the first and
second pistons 22 23 is fixed to the tailstock 3 it is only necessary
to dispose a small number of pistons regardless of the travel distance
of the tailstock 3. Therefore, the number of pistons can be reduced,
and thus the cost for component parts can also be reduced, as compared
with the use of piezoelectric elements disposed on the base side.
In this embodiment, since the movable rack 36 is fixed to the first
piston 22 and the fixed rack 38 is fixed to the right inner wall
21b of the recess portion 21 the clamping force of the tailstock
3 can be enhanced with a simple structure and wearing out of the
workpiece can be prevented with higher reliability. Further, since
the first and second pistons 22 23 are placed in parallel to each
other and alternately in opposite directions, the pressing force
to the fixed bed 2 can be exerted with good balance. Moreover, the
placement space within the recess portion 21 can be ensured with
ease.
FIG. 8 is a view for explaining a clamping device according to
another embodiment of the invention. In the figure, the same reference
numerals as in FIG. 3 designate like or equivalent component parts.
In the clamping device 40 of this embodiment, a strip shaped plate
41 having a length corresponding to the travel length of the tailstock
3 is provided in the recess portion 21 of the fixed bed 2 and secured
with a bolt 41a. Further, a housing 43 is fixed to the undersurface
of the tailstock 3. A pair of pads 42 42 are provided opposite
to each other within the housing 43 with the plate 41 interposed
between them. Further, pistons 44 for pressing the individual pads
42 using oil pressure are provided within the housing 43. The pads
42 when released from being pressed, are returned by return springs
(not shown).
According to this embodiment, since the plate 41 fixed to the fixed
bed 2 is pinched by a pair of pistons 44 set on the undersurface
of the tailstock 3 the clamping force acts only on the plate 41
and never acts on the linear-motion bearings 10. Thus, in this case
also, effects generally similar to those of the foregoing embodiment
can be obtained. For the clamping device 40 it is also possible
to use, for example, commercially available disc brake parts for
vehicles, in order to lower costs.
Although the above embodiments have been described with respect
to the case where the tailstock of the lathe is clamped, the clamping
device of the present invention is not limited to this. The invention
is also applicable for clamping steady rest, movable tables, pallets
and the like.
Also, although the tailstock is guided and supported by linear-motion
bearings in the above embodiments, the present invention is not
limited to this arrangement. For example, the present invention
is also applicable to slide guides implemented by bringing into
sliding contact the sliding surfaces of the fixed bed and the tailstock
into sliding contact. In this case also, the clamping force does
not act on the slide guide surface and thus does not result in undesirable
indentations on the guide. |