The present invention relates to a toolhead for chip-forming machine
More specifically, the present invention relates to a toolhead of
the type presenting an axis and comprising an outer casing; at least one sleeve
coaxial with said axis and connected in axially-sliding, angularly-fixed manner
to the casing; a tool spindle connected in rotary, axially-fixed manner to the
sleeve; first drive means for rotating the spindle about said axis and in relation
to the sleeve; and second drive means for moving the sleeve along said axis and
in relation to the casing.
In known toolheads of the type described above, rotation of the spindle
in relation to the sleeve and axial displacement of the sleeve in relation to the
outer casing are achieved by means of a respective first and second motor located
outside the sleeve and connected respectively to the spindle and sleeve via respective,
e.g. gear or belt, drives and normally splined type couplings.
The location of the above motors and the presence of the drives connecting
the motors to the respective driven elements render the above known toolheads not
only cumbersome and complex in design but also relatively unreliable, especially
by virtue of comprising a large number of components in relative motion and, as
such, subject to wear.
In order to overcome the above drawbacks, it is known from US-A-5
009 554 and EP-A-0 362 781 to provide a toolhead of the type described above, in
which the above first and second motors, the respective drives and the sleeve,
which in EP-A-0 362 781 is integral with the aforementioned tool-carrying spindle,
are all aligned with one another along the axis of the casing.
The above arrangement simplifies the design of the toolhead, reduces
the number of components in relative motion, and increases reliability, but introduces
a limitation in the rigidity of the spindle and, therefore, in the torque and
share which may be applied thereto. This is due to the fact that the spindle and
the sleeve are to be mounted through at least one of the motors, and have limited
diameters if costs and bulk are to be maintained within acceptable limits.
It is an object of the present invention to provide a straightforward,
low-cost, highly reliable toolhead designed to overcome the aforementioned drawback.
According to the present invention, there is provided a toolhead
for chip-forming machine tools; said toolhead presenting an axis and comprising
an outer casing; at least a sleeve coaxial with said axis and connected in axially-sliding,
angularly-fixed manner to the casing; a spindle for supporting a tool and connected
to said sleeve in axially-fixed manner and so as to rotate about said axis; a first
motor for rotating the spindle about said axis and in relation to the sleeve;
a drive for moving said sleeve along said axis and in relation to the casing; and
a second motor for activating said drive; characterized by the fact that the spindle,
motors and drive are housed inside the sleeve in a substantially mutually aligned
arrangement along said axis.
In the toolhead set forth above, the sleeve is large enough to accommodate
the motors, and can, therefore, accommodate a spindle of suitable diameter; moreover,
such diameter is no longer limited by the internal diameter of the rotor of at
least one of the motors, since the spindle extends outside the motors for its
A non-limiting embodiment of the present invention will be described
by way of example with reference to the accompanying drawings, in which:
- Fig.1 shows a schematic view in perspective of a preferred embodiment of the
toolhead according to the present invention, connected to a chip-forming machine
- Fig.2 shows a larger-scale section along line II-II in Fig.1;
- Fig.3 shows a partial view in perspective of a machine tool featuring a number
of toolheads in accordance with the present invention.
Number 1 in Fig.1 indicates a chip-forming machine tool comprising
a base 2; and a work table 3 connected in known manner to base 2, and moved in
relation to base 2 by a known drive unit (not shown), so as to move a workpiece
4 in two horizontal, perpendicular directions 5 and 6.
Machine 1 also comprises an upright 7 having a bottom end portion
connected integral with base 2, and a top end portion fitted with a fixed arm 8
supporting toolhead 9.
In the Fig.1 example, toolhead 9 presents a vertical axis 10, and
provides for supporting and moving, along axis 10, any one of a number of interchangeable
tools 11 employed on machine 1.
As shown in Fig.2, toolhead 9 comprises an elongated outer casing
12 connected integral with arm 8 and presenting a first tubular portion 13 coaxial
with axis 10 and closed at a first end by a wall 14, and a second tubular cylindrical
portion 15 extending from a second end of portion 13 and coaxial with axis 10.
Portion 15 defines a guide for a cylindrical sleeve 16 coaxial with axis 10 and
connected in axially-sliding manner to portion 15 via the interposition of a liner
17 of antifriction material. According to a variation not shown, liner 17 is replaced
by a recirculating-ball bushing.
Sleeve 16 is locked angularly in relation to casing 12 by means of
an angular lock device 18 comprising a fixed guide rod 19 connected to portion
13 and parallel to axis 10; and a recirculating-ball bushing 20 connected integral
with the end portion of sleeve 16 facing wall 14, and connected in axially-sliding
manner to rod 19.
The end portion of sleeve 16 opposite that facing wall 14 houses
a spindle 21 for supporting tool 11. Spindle 21 extends coaxially with axis 10,
and is connected to sleeve 16 in rotary, axially-fixed manner by means of four
bearings 22 gripped against respective shoulders of sleeve 16 by a bushing 23 connected
to sleeve 16 by a number of screws 24.
By means of a number of screws 25, spindle 21 is connected integral
with a hollow shaft 26 coaxial with axis 10 and connected to sleeve 16 by a pair
of bearings 27, and is rotated about axis 10 by an electric motor 28 housed coaxially
inside sleeve 16. More specifically, motor 28 is a quill-drive type with its stator
29 secured integral with the inner surface of sleeve 16 by a cylindrical casing
30, and its rotor 31 fitted to an intermediate portion of shaft 26.
Spindle 21 presents a taper seat positively engaged by a known toolholder
32 for supporting tool 11 and which is retained inside the taper seat by a known
releasable retaining device 33. More specifically, device 33 comprises a jaw 34
for positively engaging the shank of toolholder 32; and a control rod 35 connected
to jaw 34, extending inside shaft 26, and loaded by a spring 36, also housed inside
shaft 26, for maintaining jaw 34 closed when in use.
Still with reference to Fig.2, toolhead 9 also comprises an actuating
device 37 for moving sleeve 16 in relation to casing 12 and between a fully extracted
and fully withdrawn position along axis 10. Actuating device 37 comprises a recirculating-ball
drive 38 substantially inside sleeve 16 and coaxial with axis 10; and a motor
39 for activating drive 38.
Motor 39 is a quill-drive type housed inside sleeve 16, with its
stator 40 secured to the inner surface of sleeve 16 by casing 30. Motor 39 also
presents a hollow rotor 41 fitted to a hollow supporting shaft 42 coaxial with
axis 10 and connected to sleeve 16 in rotary, axially-fixed manner by means of
a pair of bearings 43 on casing 30.
Drive 38 comprises an externally threaded shaft 44 coaxial with axis
10, engaging in axially-sliding manner shaft 42 and at least part of shaft 26,
and having an end portion connected integral with wall 14, and an opposite end
portion which, when sleeve 16 is close to the withdrawn position, contacts the
end of and so defines an axial stop for rod 35.
Drive 38 also comprises a nut 45 connected to shaft 44 via the interposition
of a number of balls 46, and connected integral with shaft 42 by means of a number
of screws 47.
Still with reference to Fig.2, toolhead 9 also comprises two position
and angular speed transducers 48 and 49 for respectively controlling motors 28
and 39. Transducers 48 and 49 are housed inside sleeve 16, and present respective
stators 50 secured integral with the inner surface of sleeve 16 by casing 30, and
respective rotors 51 fitted respectively to shafts 26 and 42.
Finally, toolhead 9 comprises a pair of limit sensors 52 for determining
said two limit positions of sleeve 16; and a further position sensor 53 for determining
a zero position of sleeve 16. Sensors 52 and 53, transducers 48 and 49, and motors
28 and 39 are connected by respective wires A (only part of which is shown) and
by a connector 54 to a known control system (not shown) for controlling and driving
Finally, on toolhead 9, motors 28 and 39 are cooled and bearings
22, 27 and 43 lubricated by oil filling all the gaps inside casing 12, which is
sealed by a dynamic seal 55, a rotary seal 56, and static seals 57. Outwards,
dynamic seal 55 also presents a scraper element for preventing dirt from infiltrating
inside casing 12.
According to a variation not shown, and which is particularly suitable
for heavy-duty applications, toolhead 9 also comprises a unit for cooling the oil
inside casing 12; and an electromagnetic brake, connected to shaft 42, for locking
rotor 41 under given operating conditions.
In actual use, spindle 21 and, consequently, tool 11 are rotated
about axis 10 by motor 28, and are controlled as to speed and angular position
by the control system (not shown) as a function of the signals supplied to the
control system by transducer 48. Axial displacement of spindle 21, on the other
hand, is controlled by motor 39, which acts on sleeve 16 via drive 38, and is
also controlled by the control system (not shown) as a function of the signals
supplied to the control system by transducer 49.
By virtue of the internal configuration of toolhead 9, this is therefore
extremely straightforward in design and considerably more compact and lightweight
as compared with known toolheads. What is more, the internal configuration of
toolhead 9 also provides for a high degree of reliability due mainly, though not
exclusively, to the relatively small number of mutually sliding components involved.
Fig.3 shows a machine tool 58 differing slightly in design from machine
1 and the component parts of which are indicated, where possible, using the same
Machine 58 is a multispindle machine comprising, in place of table
3, a turret 59 supporting a number of workpieces 4, and rotated in steps in relation
to the base (not shown) and about a substantially horizontal axis 60, for successively
feeding workpieces 4 through a number of work stations 61. Instead of a single
toolhead 9, machine 58 comprises a number of variously-oriented toolheads 9, each
positioned facing a respective workpiece 4 in a respective station 61, for performing
a specific machining operation on workpiece 4.
According to a further variation not shown, at each station 61, machine
58 comprises two or more toolheads 9 for performing different machining operations
on workpiece 4 simultaneously.