Machine tools abstract
Device for coupling in a reproducible position two coupling elements,
comprising a first coupling element (2) and a centering plate (4),
the centering plate (4) being designed to be fastened to a second
coupling element (3), the first coupling element (2) comprising
at least one peg (21) comprising at least one spherical portion,
the centering plate (4) comprising at least one hollow portion (41)
working with the peg (21) during the coupling of said second coupling
element (3) to said first coupling element (2) so as to determine
the position of said centering plate (4) relative to said first
coupling element (2), and equipment for pre-adjusting machine tools
comprising this device.
Machine tools claims
The invention claimed is:
1. Device comprising a first coupling element and a centering plate,
said centering plate being designed to be fastened to a second coupling
element to ensure the reproducible positioning of said second coupling
element onto said first coupling element, said first coupling element
comprising at least three pegs, said centering plate lying in a
plane and comprising at least three hollow portions working with
one of said at least three pegs during the coupling of said second
coupling element to said first coupling element so as to determine
the position of said centering plate relative to said first coupling
element, each one of said at least three pegs comprising at least
one spherical portion, wherein around each one of said at least
three hollow portions a flexible zone is demarcated by at least
one notch and connected to the rest of said centering plate by two
torsion zones allowing the pivoting of said flexible zone about
an axis in said plane relative to the rest of said centering plate
and out of the plane of the centering plate on each side of said
axis when said first coupling element is fastened onto said second
coupling element.
2. Device comprising a first coupling element and a centering plate
of generally constant thickness, said centering plate being designed
to be fastened to a second coupling element to ensure the reproducible
positioning of said second coupling element onto said first coupling
element, said first coupling element comprising at least three pegs,
said centering plate lying in a plane and comprising at least three
hollow portions, each one of said at least three hollow portions
working with one of said at least three pegs during the coupling
of said second coupling element to said first coupling element so
as to determine the position of said centering plate relative to
said first coupling element, each one of said at least three pegs
comprising at least one spherical portion, wherein around each one
of said at least three hollow portions a flexible zone is demarcated
by at least one notch and connected to the rest of said centering
plate by two torsion zones allowing the pivoting of said flexible
zone about an axis in said plane relative to the rest of said centering
plate and out of the plane of the centering plate on each side of
said axis when said first coupling element is fastened onto said
second coupling element.
3. Equipment for pre-adjusting machine tools, designed to work
with a reference surface of a pre-adjusting machine and comprising
at least one gauge, the position of said at least one gauge relative
to said reference surface being precisely determined, said at least
one gauge being fastened to a pallet capable of being coupled removably
and reproducibly to a chuck designed to be fastened onto said reference
surface, said equipment further comprising a centering plate designed
to be fastened onto said pallet to ensure the reproducible positioning
of said pallet onto said chuck, said chuck comprising at least three
pegs, said centering plate lying in a plane and comprising at least
three hollow portions, each one of said at least three hollow portions
working with one of said at least three pegs during the coupling
of said pallet to said chuck so as to determine the position of
said centering plate relative to said chuck, each one of said at
least three pegs comprising at least one spherical portion, wherein
around each one of said at least three hollow portions a flexible
zone is demarcated by at least one notch and connected to the rest
of said centering plate by two torsion zones allowing the pivoting
of said flexible zone about an axis in said plane relative to the
rest of centering plate and out of the plane of the centering plate
on each side of said axis when said first coupling element is fastened
onto said second coupling element.
4. Device of claim 1 wherein the pivoting of said flexible zone
occurs around an axis connecting said two torsion zones.
5. Device of claim 4 wherein the pivoting of said flexible zone
occurs towards the center of said device.
6. Device of claim 1 wherein said centering plate is of a generally
constant thickness.
7. Device of claim 1 wherein said at least three hollow portions
being circular holes of a diameter less than the maximal diameter
of said at least three pegs.
8. Device of claim 1 said first coupling element being a chuck
designed to support pallets.
9. Device of claim 8 said second coupling element being a pallet.
10. Device of claim 1 said at least three pegs being each constituted
by the protruding part of a ball driven home into a cavity of said
first coupling element.
11. Device of claim 2 wherein the pivoting of said flexible zone
occurs around an axis connecting said two torsion zones.
12. Device of claim 11 wherein the pivoting of said flexible zone
occurs towards the center of the device.
13. Device of claim 2 wherein said at least three hollow portions
being circular holes of a diameter less than the maximal diameter
of said at least three pegs.
14. Device of claim 2 said first coupling element being a chuck
designed to support pallets.
15. Device of claim 14 said second coupling element being a pallet.
16. Device of claim 2 said at least three pegs being each constituted
by the protruding part of a ball driven home into a cavity of said
first coupling element.
17. Equipment according to claim 3 wherein said centering plate
is of generally constant thickness.
Machine tools description
The present application claims the priority of European application
EP02011144.9 filed on May 21 2002 the contents of which are hereby
incorporated by reference.
FIELD OF THE INVENTION
The present invention concerns a device for coupling in a reproducible
position two coupling elements, in particular a pallet on a chuck,
as well as an equipment for pre-adjusting machine tools comprising
this device.
RELATED ART
The accurate and reproducible coupling of two coupling elements
is a central problem in mechanics, in particular in the field of
precision mechanics. The problem is all the more difficult to solve
in the case of a removable coupling, i.e. designed to be disassembled
and reassembled several times and where the two coupling elements
must be situated in the same relative position to one another at
each reassembling.
In order to avoid tedious positioning checks at each reassembling
by means of equipment that is sometimes complex and expensive, guiding
references are used on the surfaces of the coupling elements that
will come into contact with one another. Rigid pegs on one of the
two coupling elements and capable of being inserted in recesses
on the other coupling are often used and thus determine the relative
position of the two devices with a certain accuracy. This accuracy
is however limited by two main factors: the machining precision
of the references and the play necessary for coupling two rigid
elements, for example a peg in a recess. It is thus difficult to
obtain, with such systems, an accurate positioning of a coupling
device on another.
In order to remove the play between two coupling elements, an intermediary
element is sometimes used that is often flexible and that becomes
slightly deformed when the two coupling elements are coupled.
Such an intermediary element can also contribute to positioning
the coupling elements relative to one another, for example by integrating
part of the guiding references.
EP111092 describes for example a coupling system having a first
coupling element designed to drive the second coaxial coupling element
in its rotational movement. The intermediary element is a driver
plate fastened to the second coupling element. The driver plate
comprises bores into which are inserted partially conical driving
pegs worked onto the surface of the first coupling element, determining
thus the relative position of the two coupling elements. The conical
shape of the driving pegs causes the edge of the bores to become
at least partially deformed, thus ensuring the centering and correct
radial positioning, on the first coupling element, of the driver
plate and, consequently, of the second coupling element to which
it is fastened.
A system such as described in EP111092 comprising conical driving
pegs worked directly on the first coupling element is particularly
adapted to a coupling system in which a considerable rotational
force is transmitted between two coaxial coupling elements. However,
it has the major disadvantage that its aligning accuracy depends
essentially on the machining precision of the conical pegs. Yet
it is difficult and expensive to obtain a high precision during
the manufacture of such profiles.
In many applications, such as for example in the field of the pre-adjustment
of machine tools, the accuracy of the positioning, for example of
the tool to be pre-adjusted, is essential, whereas the need for
a force to be exerted, for example on the tool, is low or even non-existent.
Pre-adjusting a machine tool before using it on a machining center
makes it possible to shorten or even avoid adjusting the tool on
the machining center before using it. Thus, the machine tool can
be pre-adjusted on a pre-adjusting machine whilst the machining
center is operating with another tool, thus maximizing the productivity
rate of the machining center. In order to be pre-adjusted correctly
on the pre-adjusting machine, the machine tool must be in a configuration
similar to that which it will meet on the machining center. Pre-adjusting
systems thus resort to specific gauges for each machining center,
reproducing for example the configuration of the elements for fastening
the tool on the machining center. These gauges must also be very
accurately positioned relative to the reference of the pre-adjusting
machine so that the tool's pre-adjusting can be as accurate as possible.
On the other hand, practically no force is exerted on the machine
tool during this operation. For such an application, for example,
the system described by EP111092 is too complex and too expensive
if the necessary positioning accuracy is to be achieved.
Some of the prior art pre-adjusting machines are however adapted
to receive pre-adjusting equipment comprising several gauges, disposed
for example on a rotating barrel, allowing a single pre-adjusting
machine to pre-adjust the tool of different machining centers. The
number of gauges is however limited by the number of positions of
the barrel and their type is determined during manufacture of the
pre-adjusting equipment, thus preventing it from being adapted to
pre-adjusting tools of any new machining center.
An aim of the present invention is thus to propose a simple manufacturing
device allowing an accurate and reproducible positioning of two
coupling elements.
Another aim of the present invention is to propose a device allowing
an accurate and reproducible positioning of two coupling elements
at a reduced cost.
Another aim of the present invention is to propose an equipment
for pre-adjusting machine tools that is modular and adaptable for
pre-adjusting tools of any new machining center.
BRIEF SUMMARY OF THE INVENTION
According to the invention, these aims are achieved by the pre-adjusting
device and the equipment of the corresponding independent claims,
preferred embodiments being furthermore indicated by the dependent
claims.
In particular, these aims are achieved by a device comprising a
first coupling element and a centering plate designed to be fastened
to a second coupling element to ensure its reproducible positioning
on the first coupling element, the first coupling element comprising
at least one peg, the centering plate comprising at least a hollow
part working with the peg during the coupling of the second coupling
element to the first coupling element so as to determine the position
of the centering plate relative to the first coupling element, the
peg or pegs comprising at least one spherical portion allowing an
accurate positioning by means of elements that are less complex
and consequently less expensive to manufacture.
These aims are also achieved in particular by an equipment for
pre-adjusting machine tools, designed to work with a reference surface
of a pre-adjusting machine and comprising at least one gauge, the
position of the gauge relative to said reference surface being determined
with precision, the gauge being fastened to a first coupling element
that can be coupled removably and reproducibly to a second coupling
element designed to be fastened on the reference surface of the
pre-adjusting machine, thus allowing several pallets to be used,
each bearing a different gauge adapted each to the tools of a different
machining center and offering new possibility as regards modularity
and adaptability of the pre-adjusting equipment.
DESCRIPTION OF THE DRAWINGS
The invention will be better understood by reading the description
of a preferred embodiment given by way of illustrative and non-limiting
example and illustrated by the attached drawings in which:
FIG. 1 shows the first coupling element of the device,
FIG. 2 shows the device's centering plate,
FIG. 3 shows the second coupling element to which the centering
plate is designed to be fastened.
FIG. 4 shows a cross-sectional view of the device and of the second
coupling element in released position,
FIG. 5a shows a cross-sectional view of the device and of the second
coupling element in closed/tight position,
FIG. 5b shows a detail of the cross-section of FIG. 5a.
FIG. 6 shows a machine for pre-adjusting machine tools associated
to a pre-adjusting equipment using a device according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
In a preferred embodiment of the invention, illustrated in FIG.
4 the device comprises a first coupling element 2 comprising pegs
21 and a centering plate 4 fastened to a second coupling element
3.
The first coupling element (FIG. 1) is a chuck 2 onto which can
be fastened, in a removable manner and through not-represented fastening
means, for example interchangeable pallets. On the upper side of
the chuck 2 recesses 20 are machined that are preferably cylindrical
or semi-spherical and designed to receive pegs. With reference to
FIGS. 4 and 5 the pegs 21 are preferably constituted by balls 21
having a known and accurate diameter, driven home into the recess
20.
The centering plate 4 (FIG. 2) is preferably machined in a sheet
of hard material having a certain elasticity, for example in a steel
sheet. The centering plate 4 comprises hollow cavities 41 for example
circular holes 41 whose number and arrangement correspond to the
number and arrangement of the bores 20 on the chuck 2. Around each
circular hole 41 a flexible zone 42 demarcated by notches 43 44
is defined. Each flexible zone is connected to the rest of the centering
plate by a torsion zone 45 that allows the flexible zone 42 to pivot
around a not-represented axis connecting the two torsion zones 45.
It is also possible to demarcate the flexible zone 42 by zones where
the plate's thickness is diminished, thus rendering easier the deformation
of these zones under the effect of an external force. This variant
embodiment has however the disadvantage that the machining of the
plate is more complicated, and consequently more expensive, than
that of the plate according to the previously described preferred
embodiment of the invention wherein the notches 43 44 are preferably
formed by simple stamping. The centering plate 4 further comprises
holes 48 allowing it for example to be fastened, by means of screws
passing through these holes 48 to a second coupling element.
In a preferred embodiment, the device according to the invention
is preferably associated to a pallet 3 (FIG. 3) comprising on its
lower side threaded openings 34 whose arrangement corresponds to
that of the holes 48 of the centering plate 4 thus allowing the
latter to be fastened by means of screws or bolts. Other means for
fastening the centering plate 4 on the pallet 3 can be conceived
by the one skilled in the art. The centering plate 4 could for example
be riveted or soldered to the pallet 3. The pallet 3 has for example
a circular base of the same diameter as the centering plate 4 and
as the chuck 2 as well as a square upper plate, allowing to arrange
or fasten various elements, for example gauges for pre-adjusting
machine tools. The pallet 3 comprises not-represented fastening
means designed to work with the fastening means of the chuck 2 in
order to fasten it to the latter, preferably in a removable manner.
FIG. 4 shows a cross-sectional view along the axis A--A illustrated
in FIG. 1 of the preferred embodiment of the device according to
the invention associated to the pallet 3 before the fastening elements
are tightened. FIG. 5a represents a cross-sectional view along the
same axis A--A of the same elements, after tightening of the fastening
elements.
The centering plate 4 is fastened to the pallet 3 by means of screws
37. Clearances 28 are provided on the chuck 2 in order to avoid
all contact of the screw heads 37 with the chuck 2 when the pallet
3 is positioned on the chuck 2. The pallet 3 is equipped with wedges
35 determining the minimal distance between the chuck 2 and the
pallet 3. These wedges 35 are for example screwed in threaded openings
36 provided for this purpose on the pallet 3. Clearances are provided
on the centering plate 4 to allow a direct contact of the wedges
35 on the surface of the chuck 2.
The diameter of the circular holes 41 on the centering plate 4
is less than the diameter of the balls 21 so that the circumference
of each circular hole 41 rests on the balls 21 whereas the wedges
35 are at a distance d from the chuck 2. Preferably, this distance
d is less than 2 millimeter, preferably 0.3 millimeters. Other dimensions
are however possible.
During tightening of the not-represented fastening means, the pallet
3 is moved closer to the chuck 2 acting against the resting force
of the edges of the holes 41 on the balls 21. The circular holes
41 then slide on the circumference of the balls 21 thus causing
the torsion zones 45 to become deformed and the flexible zones 42
to pivot towards the center of the device. This pivoting illustrated
in FIGS. 5a and 5b is made possible by the clearances 32 provided
on the lower side of the pallet 3. The regularity of the deformation
of the torsion zones 45 during pivoting is ensured by the resting
zones 33 constituted by the edges of the clearances 32 visible
in FIG. 3 resting on the torsion zones 45 when the centering plate
4 is fastened on the pallet 3. The fact that the centering plate
4 is pinned against the lower side of the pallet 3 ensures that
the essential part of its deformation when the pallet 3 is tightened
on the chuck 2 occurs around the flexible zones 42 opposite the
clearances 32 in the torsion zones 45. The resting zones 33 thus
allow the regularity of this deformation to be controlled. Their
symmetrical arrangement around each circular hole 41 guarantees
in particular a repetitive and identical torsion to each flexible
zone 42. Additional clearances 31 are preferably provided on the
pallet 3 opposite the balls 21 so as to avoid any direct contact
between the balls 21 and the pallet 3 when the fastening means are
tightened.
The fact that the circumference of the hollow cavities 41 on the
semi-spherical part of the pegs 21 ensures that the flexible zones
42 pivot regularly when the fastening elements are tightened. The
forces causing the flexible zones 42 to pivot are spread more or
less regularly between the flexible zones, thus ensuring an accurate
and reproducible centering of the centering plate 4 and consequently
of the second coupling element 3 on the first coupling element 2.
The accuracy of the relative position of the two coupling elements,
for example of the chuck 2 and the pallet 3 thus depends only on
the precision and regularity of the diameter of the balls 21 on
the diameter and position of the bores 20 and on the diameter and
position of the circular holes 41. Calibrated balls are common and
relatively inexpensive mechanical components, produced industrially.
The machining of circular holes 41 or of preferably cylindrical
bores 20 of accurate dimensions and position is easy and can be
performed in a single operation, thus minimizing also the risks
of inaccuracies. The centering plate 4 with its holes 41 and its
notches 44 43 is thus for example preferably formed in a single
stamping operation from a steel sheet of uniform thickness. The
costs of such a machining are considerably lower than the costs
entailed by the machining of non-cylindrical and raised elements
having the same precision.
The manufacturing precision of the second coupling element 2 thus
has no influence on the reproducibility of the relative positioning
of the two coupling elements. The wedges 35 only must have accurate
dimensions in order to guarantee a correct and regular distance
between the two coupling elements.
In order for the positioning to be reproducible, it is also necessary
for the deformation of the centering plate 4 when the fastening
elements are tightened to be completely reversible. It must thus
be performed in the flexible zone of the material used for its manufacture.
In the illustration given here above of a preferred embodiment
of the device according to the invention, the centering plate is
fastened to a pallet 3 as represented in FIG. 3. The centering plate
4 according to the preferred embodiment of the invention can however
be fastened to any other second coupling element whose position
relative to the first coupling element 3 must be precisely guaranteed.
In the preferred embodiment of the invention described here above,
the pegs 21 comprising at least one spherical portion are formed
by the protruding part of a ball 21 driven home in a bore 20 of
the chuck 2. The one skilled in the art will however understand
that it is also possible to form pegs comprising at least one spherical
portion through other means, for example by means of cylindrical
pins having a semi-spherical extremity and lodged in the bores of
the first coupling element, or by spherical portions, for example
half-spheres, fastened onto the surface of the first coupling element,
for example by gluing, soldering or screwing. It is also possible
to machine pegs comprising at least a spherical portion directly
on the first coupling element. This latter embodiment has however
the disadvantage of considerably increasing the production costs
of the device.
The one skilled in the art will also understand that the number
of pegs 21 and their arrangement can be different. Preferably, at
least three pegs 21 will be used in order to define precisely the
plane of the pallet 3.
One application of the present invention is for example in the
field of pre-adjusting machine tools.
The application to an equipment for pre-adjusting a device allowing
the precise and reproducible positioning, on a fixed chuck relative
to the guiding references of the pre-adjusting machine, of one or
several interchangeable pallets having for example each a different
gauge, offers new and unexpected possibilities as compared to the
prior art pre-adjusting equipment. Such an application allows a
pre-adjusting machine to be equipped so that it can pre-adjust the
tools of any existing machining center. Such an application further
allows the number and type of machines to be chosen precisely according
to which the pre-adjusting machine must be equipped. Such an application
also allows the pre-adjusting machine to be equipped at any time
for pre-adjusting the tools of a new machining center, including
a machining center that was unknown at the time the pre-adjusting
machine was designed.
FIG. 6 represents an example of pre-adjusting machine associated
to a pre-adjusting equipment comprising such a device. The pre-adjusting
machine 1 has a reference surface 10. A column 5 associated to an
arm 50 allows a pre-adjusting control system, for example an optical
aim system 51 to move, for example in a plane perpendicular to the
reference surface 10. The position of the center of the optical
aim system 51 relative to the reference plane 10 is known perfectly.
A display 52 generally allows an enlarged representation 53 of the
image captured by the aim system 51 to be visualized in order to
allow a higher precision in the visual control of the pre-adjusting
of the machine tool 8.
At least one gauge 7 is fastened on a pallet 3. A chuck 2 is fastened
onto the reference surface 10. The position of each gauge 7 on its
pallet 3 is determined in such a manner that when the pallet 3 is
removably coupled to the chuck 2 the position of the gauge 7 relative
to the reference surface 10 is known precisely and is adapted to
the pre-adjustment of the corresponding machine tool 8.
The pre-adjusting equipment associated with the pre-adjusting machine
1 can comprise several pallets 3 preferably equipped each with a
different gauge 7 thus offering a high modularity to the pre-adjusting
machine 1. The number of pallets 3 is not limited and it is possible
at any time to add a pallet 3 provided with a new gauge 7 to the
pre-adjusting equipment.
In order to ensure the accuracy of such a pre-adjusting machine
1 it is necessary that each time a pallet 3 is coupled again to
the chuck 2 the position of the gauge 7 relative to the reference
surface 10 should be identical. Thus, the positioning of the pallet
3 on the chuck 2 must be reproducible with the highest precision.
For this, the pre-adjusting equipment comprising the chuck 2 and
at least one pallet 3 is equipped, for example, of centering plates
4 as described previously fastened to each pallet 3 and the chuck
2 is equipped of pegs comprising at least one spherical portion,
constituted for example by the protruding part of balls inserted
in bores on its upper surface. The accurate positioning of each
pallet 3 during each coupling to the chuck 2 is thus guaranteed
in the manner described here above.
The one skilled in the art will however understand that the first
coupling element equipped with pegs comprising at least one spherical
portion and the centering plate described here above can also be
adapted to other applications, in particular to any application
where two coupling elements must be associated with a high precision
and in a reproducible manner. |