Machine tools abstract
An operating head for automatic machine tools consists of a fork
(2) having a shaft (6) rotatably mounted to a support arm (1) for
rotating around an axis (C). A motor chuck (5) is rotatably mounted
between the arms of the fork and rotates around an axis (A). Axis
(A) is orthogonal to axis (C). Drive systems (1098) control the
rotation of the fork (2) around the axis (C) by directly engaging
the shaft (6). In order to transmit rotational motion for the fork
(2) around support arm (1) and for the positioning motion of the
motor chuck (5), a hypoid toothed crown wheel (813) and pinion
(914) are used.
Machine tools claims
I claim:
1. An operating head for automatic machine tools, the operating
head comprising:
a support arm (1);
a fork (2) having a shaft (6) and rotatably mounted around a first
axis (C) to the support arm (1) at the shaft (6), the fork (2) having
a pair of spaced apart arms (34);
a motor chuck (5) rotatably mounted between the arms (3 4) of
the fork (2), the motor chuck (5) being rotatable around a second
axis (A), the second axis (A) being orthogonal to the first axis
(C);
motor means (10 15) for driving the rotation of the fork (2) and
the motor chuck (5);
a first hypoid pinion (9) operatively connected to the motor means
(1015);
a first hypoid toothed crown wheel (8) fixed to the shaft (6) and
engaging the first pinion (9) for affecting the rotation of the
fork (2) around the first axis (C);
a second hypoid pinion (14) operatively connected to the motor
means (1015); and
a second hypoid toothed crown wheel (13) fixed to the motor chuck
(5) and engaging the second pinion (14) for affecting the rotation
of the motor chuck (5) around the second axis (A).
2. The operating head according to claim 1 wherein the motor means
(1015) is housed inside the support arm (1).
3. The operating head according to claim 2 wherein the first crown
wheel (8) and the first pinion (9), are housed inside the support
arm (1).
4. The operating head according to claim 2 wherein the second
crown wheel (13) and the second pinion (14) are housed inside one
of the fork arms (34).
5. The operating head according to claim 1 including means for
controlling the rotation of the fork (2).
6. The operating head according to claim 5 wherein means for controlling
the rotation of the fork (2) comprises a first pulley (20) fitted
to the shaft (6), a second pulley (22) operatively connected with
the first pulley (20), at least one cam (23) connected to the second
pulley (22) and at least one limit switch (24) activatedly connected
to the cams (23).
7. The operating head according to claim 4 wherein a thrust bearing
(16) is connected between the second crown wheel (13) and the fork
(2).
8. An operating head for automatic machine tools, the operating
head comprising:
a support arm (1);
a fork (2) having a shaft (6) and rotatably mounted around a first
axis (C) to the support arm (1) at the shaft (6), the fork (2) having
a pair of spaced apart arms (34);
a motor chuck (5) rotatably mounted between the arms (3 4) of
the fork (2), the motor chuck (5) being rotatable around a second
axis (A), the second (A) being orthogonal to the first axis (C);
drive means for driving the rotation of the fork (2) around the
first axis (C) and the motor chuck (5) around the second axis (A);
the drive means including a hypoid pinion (14) operatively connected
to the motor chuck (5), a crown wheel (13) engaged with the hypoid
pinion (14) for affecting the rotation of the motor chuck (5) around
the second axis (A), the crown wheel (13) and the hypoid pinion
(14) being housed inside one of the fork arms (34).
9. The operating head according to claim 8 wherein the drive means
further includes a support arm crown wheel (8) fitted to the support
shaft (6) of the fork (2) and a support arm hypoid pinion (9) engaged
with the support arm crown wheel (8), the pinion (9) and the crown
wheel (8) being housed inside the fork support arm (1).
10. The operating head according to claim 8 wherein a thrust bearing
(16) is connected between the crown wheel (13) and the fork (2).
Machine tools description
FIELD AND BACKGROUND OF THE INVENTION
This invention relates to an operating head for automatic machine
tools which uses bevel gear pairs with hypoid crown wheel and pinion
to transmit the chuck positioning motion.
In particular, the invention relates to operating heads of the
type comprising a fork fitted to a support with several degrees
of freedom and a motor chuck, hinged to the fork, which can be revolved
and positioned along one or more axes in relation to the fork.
The purpose of the invention is to obtain an operating head of
the type indicated above which, though equipped with a high-power
motor chuck (5-7 KW), is also very compact, so that work can be
performed inside hollow objects if required, and any play due to
assembly tolerances and to wear of the parts can be eliminated,
and sufficient rigidity is produced to enable the machine to withstand
the stresses transmitted by the tool during machining without buckling.
A further purpose of the invention is to obtain an operating head
in which, in order to improve the rigidity characteristics of the
machine, the head "pivot point" projects less in relation
to the chuck connection plane.
Another purpose of the invention is to produce an operating head
which is simpler to assemble than the ones currently used.
These purposes are achieved with an operating head in accordance
with the characterising part of the claims. Various types of operating
head are already known which comprise a fork, fitted to a support
with several degrees of freedom, which is equipped with a motor
chuck.
For example, U.S. Pat. No. 4904131 describes an operating head
which presents the general structure described above, in which the
chuck positioning motion (axis A) is transmitted from a motor located
in the fork support arm to the electric chuck via an inclined shaft
with bevel gears at the ends which engage corresponding cogwheels,
one built into the fork support arm and the other into the chuck
support.
This system produces a very compact head. German patent application
no. 3.809.750 also describes an operating head in which the chuck
positioning motion is transmitted via a set of bevel gears subject
to an axial elastic force, in order to eliminate play due to wear.
This system, however, is quite complex and too bulky.
An operating head of the type with fork and electric chuck is also
described in Italian Pat. No. 1.220.733 which illustrates a machine
tool comprising an arm that moves along three cartesian axes; a
fork fitted to the end of the arm can rotate around the arm axis
and is equipped with a motor chuck presenting three degrees of freedom
in relation to the fork.
These automatic machines are used to perform precision tasks such
as milling, contouring, countersinking and other jobs involving
the removal of material and assembly work, especially in the aeronautical
industry.
SUMMARY OF THE INVENTION
The present invention also falls into this category; it is designed
to further improve this type of equipment by offering a head which
simultaneously presents all the above-mentioned advantages of compactnesss,
rigidity and elimination of play.
BRIEF DESCRIPTION OF THE DRAWINGS
This invention will now be described in detail, by way of example
but not of limitation, by reference to the annexed drawings in which:
FIG. 1 is a view in cross-section of an operating head in accordance
with the invention along a plane passing through the fork arms,
and also showing the lower part of the support arm at the point
where the fork is connected to it;
FIG. 2 is a view in cross-section of the fork shown in FIG. 1
along a plane orthogonal to the preceding plane;
FIG. 3 is a top view of the fork showing in cross-section the systems
which control its rotation around the support arm axis;
FIG. 4 is a view in cross-section taken along line I--I shown in
FIG. 3;
FIG. 5 is a view in cross-section taken along line II--II shown
in FIG. 3;
FIG. 6 illustrates a view in cross-section of the systems which
control the fork rotation;
FIGS 7 and 8 schematically illustrate an operating head in accordance
with a known technique and an operating head in accordance with
the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In FIGS. 1 2 and 8 1 indicates a support arm of the operating
head, the body of which, indicated at 2 basically consists of a
fork 2 with a motor chuck 5 fitted between fork 2 arms 3 and 4.
Fork 2 is fitted to arm or sleeve 1 via a hollow shaft 6 built
into the fork, whose axis coincides with the axis of arm 1.
FIG. 1 shows hollow shaft 6 together with the fork 2 which can
rotate around the axis of arm 1 (axis C), while the motor chuck
5 can rotate around an axis (axis A) which passes through the fork
arms 3 and 4 and which is orthogonal to axis C. Both these movements
are numerically controlled in a known way, and serve to position
and revolve the chuck 5 and a tool.
As shown in FIGS. 1 4 and 5 shaft 6 of fork 2 is fitted to arm
1 on bearings 7 (FIG. 4); a crown wheel with hypoid toothing 8
is fixed to the shaft 6 and engages a corresponding bevel pinion
9 and activated by a motor 10 which can be pushed axially by Belleville
washers or the like to press against the crown wheel toothing 8
in order to eliminate any play due to wear on the parts.
Both motor 10 and the linkage constituted by crown wheel 8 and
pinion 9 are housed inside arm 1.
This configuration eliminates the need to use a reducer, (axis
C) which is employed in known heads in order to attach the fork
2 to the sleeve 1 (FIG. 1).
In order to appreciate this difference fully, reference should
be made to FIGS. 7 and 8.
As can be seen from FIG. 7 in known heads, fork 2 having an electric
chuck 5 is fitted to a reducer 50 which in turn is fitted to sleeve
1.
This configuration means that the axis of reducer 50 must be aligned
with the axis of sleeve 1 and after the fork 2 is installed. After
the fork 2 has been fitted, the electric chuck axis is aligned with
the sleeve 1 and the axis of the reducer.
In accordance with the invention, the axis of motor chuck 5 can
be aligned with the fork axis during bench assembly and then, when
the fork 2 has been fitted to the sleeve 1 its axis is aligned
with the sleeve axis by adjusting the locking screws used to attach
hollow shaft 6 to the fork.
In this way assembly is simplified, because one regulation operation
is eliminated and the chuck 5 can be aligned on the workbench.
In addition, the elimination of reducer 50 (FIG. 7) allows the
fork 1 to be shortened, thus reducing the degree to which the pivot
point projects in relation to the point at which the support arm
1 is connected; thereby considerably improving the rigidity characteristics
of the unit. As shown in FIGS. 1 and 2 chuck 5 is fitted to fork
2 via a pair of hubs or pins 11 and corresponding bearings 12 (FIG.
1).
A crown wheel 13 also with hypoid toothing, is fitted to one of
the arms 3 or 4; this crown wheel 13 engages a bevel pinion 14
activated by a motor 15 housed in the fork support arm 1 and positioned
inside hollow shaft 6 (FIG. 1). Via hypoid gear pair, i.e. bevel
pinion 14 and crown wheel 13 motor 10 (FIG. 5) activates the rotations
of the fork around the axis of arm 1 (axis C), while motor 15 (FIG.
1) activates, via hypoid gear pair 5 the angular movements and/or
swivel of the chuck 5 around axis passing through the fork arms
3 and 4 perpendicular to axis C.
The bottom of crown wheel 13 fitted to the support hub 11 of motor
chuck 5 should preferably rest on a thrust bearing 16 located between
the bottom of the crown wheel 13 and wall 17 of the fork 2.
In this way any bending stresses to which the crown wheel 13 is
subject are passed onto the fork structure, which thus helps absorb
these stresses and thereby increases the rigidity of the system.
The rotations of the chuck 5 around axis A are detected by an encoder
18 or similar system, while air, lubricants, coolants, etc. are
supplied to the motor chuck 5 through a series of pipes (the piping
system being shown as reference numeral 19) passing though the chuck
support hub 11 in the arm 4 of the fork 2.
In known machines of this type, the fork can rotate around the
axis of the support arm through an angle close to 360.degree., but
the extent of its rotation is limited by the presence of one or
more cams which activate limit and reset switches.
However, in some cases it would be useful for the fork to rotate
through a full 360.degree., if not slightly more.
For example, this applies to machining performed on the outer surface
of patterns, when it is useful for the tool, having machined all
round the pattern until it reaches the starting point, to carry
on for a period of time in order to ensure the continuity of the
machined surface, without leaving grooves or the like at the point
where the machining started.
For this purpose, the head in accordance with the invention is
fitted with cams, which activate limit switches, not fitted directly
to the fork shaft but located on a support connected to the shaft
via a suitable reducer.
As shown in FIG. 6 a pulley 20 is fitted to fork shaft 6 coaxial
with it; via a belt 21. Pulley 20 drives a corresponding pulley
22 fitted idle on a shaft 30 built into the casing of arm 1 (FIG.
8). The ratio between pulleys 20 and 22 is such that the second
pulley rotates at a lower speed than the first. For example, the
ratio between pulleys 20 and 22 might be 1:2.
Cams 23 which activate limit and/or reset microswitches 24 built
into the structure of fork support arm 1 (FIG. 1), are integral
with pulley 22.
Here again, the rotations of the fork arm 1 are detected by an
encoder 25.
During operation, the numerical controls of the machine activate
motors 10 and 15 (FIGS. 5 and 1) in order to position the tool correctly.
For this purpose, motor 10 rotates the shaft of pinion 9 via a
drive of a known type.
This shaft engages with crown wheel 8 built into fork shaft 6
which is thus made to rotate around axis C (FIG. 1). Pinion 9 can
be suitably loaded in such a way as to eliminate play due to wear
on the parts.
The rotation of shaft 6 and therefore of the fork 2 is transmitted
via pulleys 20 and 22 to cams 23 which activate limit switches 24.
The extent of the fork rotations is detected by encoder 25 connected
to the numerical control of the machine.
As the number of revolutions of pulley 22 is suitably geared down
in relation to those of pulley 20 the fork can rotate through more
than 360.degree. before the cams 23 fitted to pulley 22 engage the
limit switches 24.
Thus with a ratio of 1:2 between the toothing of pulleys 20 and
22 the fork 2 can be made to rotate through over 400.degree. around
axis C (FIG. C).
Moreover, the use of a hypoid gear pair to transmit motion to the
fork 2 means that fewer gears are required, thus enabling the projection
of the pivot point to be reduced and space to be saved and, without
any change in the overall size of the operating head, providing
more room for tools, which can therefore be selected from a wider
range.
In the same way, the chuck 5 is positioned around axis A by hypoid
gear pair 14 and 13 and activated by motor 15 (FIG. 1). In this
case the use of a large crown wheel produces greater resistance
to the stresses transmitted by the tool, as the arm of the lever
(distance between axis A and toothing of crown wheel 13) which transmits
these stresses to the remaining mechanisms is larger. The fact that
a thrust bearing 16 is positioned between the crown wheel 13 and
the fork casing means that these stresses are transmitted to the
head structure, which combines with the other devices to make the
unit more rigid. |