The present device relates to devices for pushing the work-piece on
a lathe and for measuring its initial position in the axial direction relative to
the tool-holder turret, which uses a pusher head for work-piece sensing and an electrical
PRIOR STATE OF THE ART
A device comprising the features of the preamble of claim 1 is known
from GB-A-2 141 364.
Devices are known for measuring the position of the work piece on
a horizontal lathe. When the piece to be turned is, for instance, a camshaft which
is going to be machined at various points of its length along the axis "Z", the
control unit governing the turret movement "z" should first record the zero position
of the work-piece corresponding to the free end of the work piece, which will be
the datum point of the dimensional values "z" relative to the movement of the turret.
EP-877307 (ES-P9701007) describes a device for measuring the reference
position of the work-piece to be turned, which is secured on the lathe headstock
table. The measuring apparatus is of the optical type with a graduated scale and
a sliding reading head, which moves with the work-piece pusher head. The electrical
signal issued of the position of the work piece associates it with a reference position
of the tool-holder turret, by way of the lathe control unit, for axial movements
of the. turret during machining. Some lathes do not permit the installation of a
device in this way on the side of the headstock, which means that the device for
measuring the position of the work-piece has to be installed on the turret.
The same document EP-877307 discloses an earlier device for measuring
the "zero" position of the piece to be turned on the lathe. This device on the turret
has no head that pushes the work-piece towards the clamping chuck. It only has a
rocking feeler fitted perpendicular to the movement of the work-piece, which rocks
on coming up against the work-piece and actuates a switch that transmits a signal
of the position to the control unit. The position measurement obtained in this way
depends on the perpendicularity of the feeler relative to the axis "Z" of turret
movement and on the perpendicularity and state of the contact face surface at the
end of the work-piece. This feeler has to touch four different points of this face
in order to construct a datum plane of the work-piece.
DISCLOSURE OF THE INVENTION
The object of the present invention is a device for measuring the
position of the work-piece to be turned, installed on the tool-holder turret of
a lathe, as defined in claim 1.
The device according to the invention is attached to the turret tool-holder
disc and it has an external head that pushes the work - piece forward in the direction
of the machining axis "Z", up to the stop position inside the clamping chuck. When
the work-piece reaches this stop in the chuck, the pusher head retracts inside the
measuring device, overcoming the resistance of an inner return spring, and actuates
a feeler connected to a position sensor at the back of the device.
The position of the free end of the device detected is taken by the
lathe electronic control unit as the datum point of the work-piece machining dimensional
values "z" and as the reference for the axial movements of the turret. In this way
the work-piece is pushed and its initial position for machining is detected by a
single axial movement of the turret, after a single prior turn of the turret to
position the pushing and sensing device on the lower face of the tool-holder disc.
On its front contact face the pusher head has a detachable disc, which
can be removed for replacement when it is worn out.
DESCRIPTION OF THE DRAWINGS
FIG.1 is a cross-sectional view of a device for work-piece pushing
and sensing, according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
With reference to fig. 1, a preferred device 1 for pushing and sensing
the "zero" position of the work-piece 3 to be turned - indicated with number 2 -
is positioned on the turret 4 of a lathe on the tool-holder disc 4', and it comprises
a device support plate 5 attached to one of the peripheral flat surfaces of the
tool-holder disc 4', a pedestal 7 fixed to the support plate 5 provided with an
integral housing 7a, a pusher head 6 fitted in the housing 7a, an
electrical position sensor 8 with a feeler 9 attached, also supported on the plate
5 and situated behind the pusher head 6, on its side opposite to that of the work-piece
The pusher head 6 comprises an outer bushing 12, which stands proud
of the front of the housing 7a towards the work-piece 3, a detachable contact
disc 13 inserted in the front face of the bushing 12, a helical return spring 14
resting on an inner wall of the housing 7a, and a central measuring spindle
15a, 15b coaxial with the work-piece 3, which moves with the pusher
head 6 and makes contact with the feeler 9.
When the work-piece 3 is fitted in the lathe chuck, the turret 4 slides
in direction Z and the head 6 pushes the work piece 3 to a position stop inside
the chuck 11. The head 6 then retracts insides its housing 7a, overcoming
the resistance of the return spring 14, and the spindle 15a, 15b reaches
and touches the tip of the feeler 9 generating the electrical signal indicating
the position 2 of the free end 3a of the work - piece. The sensor 8 has an
inductive transmitter 10 for the electrical signal indicating detection of the feeler
The free end of the measuring spindle 15a, 15b passes
through the housing 7a towards the feeler 9, and it has an axial rear cavity
15a for housing the tip of the feeler 9, inside which it will make the contact
that energizes the position sensor 8.
The detachable pusher disc 13 offers up the impact surface of head
6 against the work-piece 3 and the spring 14 makes the pusher head 6 return to its
rest position. The pusher head 6 remains in the rest condition in a position relative
to the pedestal 7 that is always the same due to the fact that the measuring spindle
15a, 15b has a flange 15b at its free end outside the housing
7a which comes up against the latter, thereby restricting the return movement
of the pusher head 6.
After sensing the "zero" position 2 of the work-piece, the tool-holder
disc 4' revolves to select one of the tools and the turret carries out a movement
"z" in reference to this "zero" position of the work-piece 3 in order to perform
the machining. To assist the sliding of the pusher head 6 in the seat in the housing
7a, a bearing 16 is coupled to the pusher head bushing 12. The bearing and
the seat in the housing 7a are protected against dirt penetration by means
of a sealing ring 17.