U.S. patent application number 10/480050 was filed with the patent office on 2005-08-18 for spindle with axially acting collet-opening device.
Invention is credited to Ammann, Beat.
Application Number | 20050180832 10/480050 |
Document ID | / |
Family ID | 27740057 |
Filed Date | 2005-08-18 |
United States Patent
Application |
20050180832 |
Kind Code |
A1 |
Ammann, Beat |
August 18, 2005 |
SPINDLE WITH AXIALLY ACTING COLLET-OPENING DEVICE
Abstract
A spindle for machining at high rotational speeds, includes a
toll-holding taper collet with radial slits that is kept closed to
clamp a toool by pressing it axially against a seat of
complementary shape by the reaction force of precompressed elastic
elements interposed between the tool-holding collet and the body of
the spindle, and is opened by moving it axially away from the seat
by applying an axial force to it to further compress the
precompressed elastic elements. In the spindle the elastic means
are a sleeve of elastic material housed coaxially between the
inside wall of a cavity formed in the body of the spindle and a
shaped collar of epoxy resin applied coaxially around the outer
surface of the free end of the tool-holding collet.
Inventors: |
Ammann, Beat; (Chiasso,
CH) |
Correspondence
Address: |
YOUNG & THOMPSON
745 SOUTH 23RD STREET
2ND FLOOR
ARLINGTON
VA
22202
US
|
Family ID: |
27740057 |
Appl. No.: |
10/480050 |
Filed: |
December 9, 2003 |
PCT Filed: |
February 4, 2003 |
PCT NO: |
PCT/IB03/00365 |
Current U.S.
Class: |
409/233 |
Current CPC
Class: |
B23B 2250/12 20130101;
Y10T 408/95 20150115; B23B 31/265 20130101; H05K 3/0047 20130101;
Y10T 409/309464 20150115; B23B 2226/36 20130101; B23B 2226/33
20130101 |
Class at
Publication: |
409/233 |
International
Class: |
B23C 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 22, 2002 |
CH |
0317/02 |
Claims
1. Spindle (1) for machining at high rotational speeds, comprising
a tool-holding taper collet (2) with radial slits (2r) that is kept
closed to clamp a tool (3) by pressing it axially against a seat
(4) of complementary shape by the reaction force (F) of
precompressed elastic means (6) interposed between the tool-holding
collet (2) and the body (1s) of the spindle (1), and is opened by
moving it axially away from the said seat (4) by applying an axial
force (S) to it to further compress the said precompressed elastic
means (6), which spindle is characterized in that the said elastic
means are a sleeve (6) of elastic material housed coaxially between
the inside wall of a cavity (1e) formed in the said body (1s) of
the spindle (1) and a shaped collar (7) of epoxy resin applied
coaxially around the outer surface of the free end (8m) of an
extension (8) of the tool-holding collet (2).
2. Spindle according to claim 1, in which there is interposed
between that part (8n) of the said extension (8) of the
tool-holding collet (2) which is not surrounded by the said shaped
collar (7), and the body (1s) of the spindle (2), a bush (9) which
is also made of epoxy resin.
3. Spindle according to claim 1, in which the said free end (8m) of
the extension (8) of the tool-holding collet (2) is fitted securely
with a flange (10), the longitudinal section of which is an
inverted U, with the two sides of the U pressing via their ends
against that surface (7s) of the said sleeve (6) which is furthest
from the inner end of the said cavity (1e) of the spindle (1).
4. Spindle according to claim 2, in which the said free end (8m) of
the extension (8) of the tool-holding collet (2) is fitted securely
with a flange (10), the longitudinal section of which is an
inverted U, with the two sides of the U pressing via their ends
against that surface (7s) of the said sleeve (6) which is furthest
from the inner end of the said cavity (1e) of the spindle (1).
Description
[0001] The present invention relates to machine tools that use
spindles that rotate at high speeds, such as those of drilling
assemblies for printed circuit boards.
[0002] More particularly, the invention relates to a spindle of the
abovementioned type fitted with a tool-holding taper collet that
can flex elastically to clamp the tool owing to the existence of a
number of radial slits which give it the necessary elasticity. In
these spindles, as is known to those skilled in the art, closure of
the tool-holding collet is achieved by drawing it into a
complementary tapering cavity, causing the various sectors of the
end part of the clamp which are separated by the abovementioned
radial slits to flex, squeezing and clamping the tool between
themselves.
[0003] The collet is inserted into the said complementary cavity by
the reaction of precompressed elastic means interposed between the
body of the tool-holding collet and the body of the spindle. If an
axial force is then applied to the said collet, further compressing
the abovementioned elastic means by a suitable amount, the contrary
effect is obtained, that is the collet is opened allowing the tool
to be extracted from it.
[0004] In the prior art, the elastic means described above take the
form of a series of Belleville washers arranged coaxially around
the tool-holding collet, which are in contact with a special part
of the collet, on which they exert a predetermined pressure due to
the abovementioned precompression, keeping it closed during
machining. If an axial force is applied to the tool-holding collet,
via a rod passing through the interior of the spindle cavity
containing the Belleville washers, the latter are further
compressed to bring about this opening action of the collet.
[0005] However, the system described above has certain troublesome
drawbacks: firstly, at the extremely high rotational speeds of the
spindle that are currently achievable (over 100,000 rpm), the said
Belleville washers are drawn round by the rotation, creating
effects of unbalance which cause vibrations harmful to machining
accuracy. Also, to accommodate Belleville washers with
specifications suitable for the job, a large-diameter cavity must
be formed in the spindle, which means that the spindle itself must
have a large diameter and consequently a large mass.
[0006] Moreover, with the system currently in use, it is necessary,
as already discussed, to operate from the outside with a rod which
must move cyclically into contact with the end of the tool-holding
collet and exert upon it a force (of the order of some 2,000 N)
which, over time, owing in part to the situation of point loading
that occurs, can deform the tip and/or alignment of the rod,
causing problems of accuracy and service life.
[0007] In order to solve all the problems listed briefly above, the
inventor of the present innovation has devised a spindle of the
type defined above, in which the said elastic means are not
Belleville washers but instead a sleeve of elastic material (rubber
or another elastomer) which also, under conditions of
precompression, keeps the tool-holding collet in the closed
position as described. This sleeve is fitted onto the free end of
an extension of the said tool-holding collet, which ends near the
corresponding end of the spindle, and can be reached without having
to insert, as discussed, a long rod down into the body of the
spindle.
[0008] In order for the radial expansion of the said sleeve not to
create braking forces on the tool-holding collet, there is
installed between the collet and the sleeve a shaped steel collar
which, having a low coefficient of friction, does not significantly
oppose the axial movement of the tool-holding collet.
[0009] For similar reasons there is interposed, between the body of
the spindle and the tool-holding collet, in that part of its
extension which is not surrounded by the abovementioned sleeve, an
epoxy resin bush, which can be formed inside the spindle itself
during the assembly operation and has a low coefficient of friction
and permits movements in the axial direction of the tool-holding
collet with virtually zero play.
[0010] The subject of the present invention is therefore a spindle
for machining at high rotational speeds as described in the
appended claim 1.
[0011] A more detailed description will now be given of a preferred
illustrative embodiment of a spindle according to the invention,
selected from among the many that could be produced by a person
skilled in the art in keeping with the teachings contained in the
abovementioned claim 1.
[0012] In the course of this description reference will also be
made to the appended drawings, which show:
[0013] in FIG. 1, a longitudinal section, reduced in length,
through a spindle of the type described above produced in
accordance with the prior art;
[0014] in FIG. 2, a longitudinal section, reduced in length,
through a spindle of the same type as in FIG. 1, but produced in
accordance with the invention.
[0015] To begin with FIG. 1, this shows that a spindle 101 in
accordance with the prior art consists of a body 101s provided with
a cavity 101e in which a tool-holding collet 2 is inserted
coaxially, with a drilling tool 3 inserted in turn into the
latter.
[0016] On the free end of the said tool-holding collet 2 is a
flange 110 that is in contact with the series 15 of superposed
Belleville washers arranged coaxially around the said tool-holding
collet 2. The Belleville washers are precompressed by a suitable
amount when the spindle 101 and the tool-holding collet are
assembled, so that their elastic reaction exerts a force F on the
abovementioned flange 110 such as to push the tapered part of the
tool-holding collet 2 into a cavity 4 of complementary shape formed
in the body 101s of the spindle. This causes it to contract
elastically and clamps the tool 3 inside it. As already mentioned,
this contraction is made possible by the existence of a number of
radial slits (not shown in the drawings but obvious to those
skilled in the art) formed in that part of the tool-holding collet
which is intended to accommodate the shank of the tool.
[0017] To open the tool-holding collet 2, which will be abbreviated
to "collet" below, a force S is applied in the opposite direction
to the said reaction force F of the series of Belleville washers
15. This further compresses the washers and causes the collet 2 to
move axially far enough to disengage its tapered part from the seat
4, so that it opens due to the elastic return of the sectors of its
part that contains the tool 3 shank, these sectors being separated
from each other by the abovementioned radial slits.
[0018] This force S is applied through a rod 13 aligned coaxially
with the collet 2, which is cyclically pressed against the
aforesaid end part of the collet 2 to which the flange 110 is
attached.
[0019] FIG. 2 by contrast shows that a spindle 1 according to the
invention likewise has a body 1s provided with a coaxial cavity 1e
that contains the tool-holding collet 2 to which a tool 3 is fixed.
In this case the collet 2 is provided with an extension 8, on the
free end 8m of which is fitted a flange 10, the longitudinal
section which is in the shape of an inverted U, with the two sides
of the U pressing via their ends against the surface 7s of a sleeve
6 of precompressed elastic material, for example rubber, which is
housed coaxially between the inner wall of the said cavity 1e of
the body is of the spindle 1 and a shaped steel collar 7 applied
coaxially to the outer surface of the said end 8m of the extension
8 of the collet 2. As already stated, the function of this shaped
collar is to prevent interference between the sleeve 6, when it
deforms radially, and the collet 2, which could otherwise
undesirably increase the force S necessary to move the collet 2
axially to open it.
[0020] The operations of closing and opening the collet 2 are
similar to those already described with reference to the case
discussed earlier: the elastic reaction F of the precompressed
sleeve 6 on the said inverted-U flange 10 of the collet 2 holds the
latter in the closed, tool-clamping position, and to open the
collet 2, the said force S is applied to the end 8m of its
extension 8, further compressing the elastic sleeve 6 and moving
the said collet 2 axially the necessary distance. To facilitate the
axial movement of the collet the inventor has interposed, between
the part 8n of the said extension 8 of the collet 2 which is not
surrounded by the said elastic sleeve 6 and the body Is of the
spindle 1, a bush 9 of epoxy resin with a low coefficient of
friction, which as mentioned earlier can be injected during the
actual assembly stage, producing a fit with virtually zero play
that permits relative movements between the collet 2 and the
spindle 1 in precise alignment with their longitudinal axes, which
coincide precisely with each other.
[0021] As already noted, owing to the characteristics of the
component parts of the spindle 1 of the invention, and in
particular those of the elastic sleeve 6, the spindle 1 according
to the invention achieves the desired object, making the cavity 1e
of the spindle 1 of a much smaller diameter compared with spindles
of conventional type: a comparison of FIGS. 1 and 2, which
basically show the spindles at the same scale, will show that the
outside diameter .O slashed..sub.1 of the spindle 1 of the
invention is about 25% less than the outside diameter .O
slashed..sub.101 of a spindle 101 of conventional type.
[0022] Though this is well known to those skilled in the art, it is
relevant to add a final detail on how both spindles 1 and 101
described above work: when the said force S is being applied to the
collet 2 to open it by moving it axially relative to the body of
the spindle, the body is prevented from moving by supporting it
against a fixed contact surface 5.
* * * * *