Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a broach sharpening
machine.
Broaches are tools which are normally of considerable
length and comprise a plurality of teeth which when brought
into contact in succession with a surface to be machined,
giveit a required finish and shape by each removing a determined
chip thickness which normally varies from one tooth to
another and depends on the increase in height of each tooth
relative to the preceding tooth. In addition, the fact
that the chip thickness removed varies from tooth to tooth
means that normally the distribution pitch of the teeth
also varies along the broach. Finally, the tooth profile
can vary along the broach according to the surface shape
to be obtained.
In this respect, it should be noted that broaches
are extremely specialized tools, the use of which is justified
only for mass production, and provided the broaches can
be sharpened a certain number of times.
In general, a broach is sharpened, or rather
the cutting edges of its teeth are reconditioned, by sharpening
machines of the grinding wheel type, in which a grinding
wheel head is moved manually in such a manner as to sharpen
the broach teeth one after another. For this purpose,
the operator has to identify the position of the cutting
edge of each tooth visually, then remove the same chip
thickness from each tooth while controlling the grinding
wheel such that its outer periphery does not touch the
base of the cavity between each pair of adjacent teeth.
Normally, the visual identification of the cutting
edge of the teeth with respect to the grinding wheel leads
to errors which automatically result in variations in the
geometrical form of the broach.
The object of the present invention is to provide
a broach sharpening machine in which the position of the
tooth cutting edges is identified rapidly and extremely
accurately, independently of the complexity of the shape
of the broach to be sharpened.
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Said object is attained according to the present
invention by a broach sharpening machine, of the type com-
prising a first sharpening slide arranged to impart, to
a grinding wheel supported by it, a movement having a constant
stroke away from and towards said broach in a direction
transverse to the longitudinal axis of the broach, a second
and a third slide mobile along two axes which form a contained
angle, the axis of movement of said second slide being
parallel to said longitudinal axis, and a feeler unit arranged
to determine the position of said grinding wheel relative
- to each tooth of said broach in succession, characterized
in that said third slide supports both said feeler unit
and said first slide, and that said feeler unit comprises
an articulated parallelogram constituted by a frame rotatable
relative to said third slide about an axis perpendicular
to the broach axis and to the axis of movement of said
second slide, a drag link, and two resilient cranks which
connect said drag link and said frame together; the feeler
unit also comprising first means for detecting the movements
of said frame about its axis of rotation, and second means
for detecting the axial movement of said drag link, this
latter comprising coupling means arranged to engage with
the teeth of said broach positively and in succession,
resilient means being connected to said frame in order
to move said coupling means towards said broach teeth.
Further characteristics and advantages of the
present invention will be apparent from the description
given hereinafter with reference to the accompanying drawings,
which show one non-limiting embodiment thereof, and in
which:
Figure l is a diagrammatic side elevation of
a detail of a broach sharpening machine constructed according
to the present invention;
Figure 2 is a detail of Figure l to an enlarged
scale; and
Figures 3 to 6 show the detail of Figure l during
different stages of operation.
Figure l shows part of a broach sharpening machine
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indicated overall by 1 and comprising a fixed bed (not
shown) on which a broach 2 to be sharpened is axially locked
in position. The broach, as shown in particular in Figure
2, comprises a plurality of teeth 3, which are distributed
along the broach 2 at a pitch P which is normally variable
according to a determined law, and comprise an outer surface
or back 4 forming a top rake angle A with the horizontal
axis of the broach 2, a front surface 5 defining a cutting
edge 6 with the surface 4 and forming a front rake angle
B with the pexpendicular to the axis of the broach 2, a
curved connection surface 7 between adjacent teeth, and
an increment H between adjacent teeth which is normally
vertical along the broach 2.
In the example shown in the Figures, the broach
2 is a round broach, which is fixed on said bed (not shown)
of the machine 1 by means of centres tnot shown). However,
the machine 1 can also be adapted to receive flat broaches
mounted directly on said bed.
Said bed supports an upper fixed slide guide
8 for a first slide 9 which is arranged to move along the
guide 8 under the action of drive means, not shown, in
a direction X parallel to the axis of the broach 2.
A second and a third slide indicated respectively
by 10 and 11 are mounted on the slide 9 in such a manner
as to be able to slide under the thrust of respective dri~e
means, not shown. The slide 10 is mounted on the slide
9 such that it slides relative to this latter in a direction
Y substantially perpendicular to the direction of movement
of the slide g, while the slide 11 is a sharpening slide
and is mounted on guides Inot shown) connected to the slide
9 in an angularly adjustable manner by means of a pin 12,
and lockable relative to the slide 9 in such a manner as
to enable the slide 11 to move in a direction Z which forms
a determined adjustable angle with the perpendicular to
the axis of the broach 2. The slide 11 can be moved by
drive means, not shown, in such a manner that it carries
out a fixed outward and return stroke in the direction
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Z between a first position controlled by a limit switch
lla carried by the slide 10, and a second determined
position closer to the broach 2~
A grinding wheel head 13 is mounted on the slide
11, and from which there transversely projects a spindle
14 onto the end of which is keyed a grinding wheel 15~
On that end of the slide 10 facing the broach
2 to be sharpened, there is disposed a guide 16 extending
parallel to the direction X and supporting a slide 17
mobile in one direction or the other along the guide 16
under the thrust of a pinion (not shown) which engages
with a rack 18 carried by the guide 16, and is keyed onto
a shaft (not shown) which is mounted rotatably through
the slide 17 and is provided with a hexagonal operating
head 19.
A second guide 20 is connected rigidly to the
slide 17 perpendicular to the guide 16, and supports a
plate 21 which is mobile along the guide 20 under the thrust
of a pinion (not shown) which engages with a rack 22 carried
by the guide 20, and is keyed onto a shaft (not shown)
mounted rotatably through the plate 21 and provided with
a hexagonal operating head 23. The slide 17 and plate
21 can be locked along the relative guides 16 and 20 by
respective locking devices 24 and 25 operated by respective
hexagonal nuts 26 and 27.
The guides 16 and 2Q, the slide 17, the plate
20, the said two pinion-rack couplings and the locking
devices 24 and 25 constitute together an adjustment device,
indicated overall by 28, by means of which the position
of a feeler unit, indicated overall by 29 and arranged
to determine the exact position of a tooth 3 to be sharpened,
can be ad~usted relative to the slide 10.
The feeler unit 29 comprises a rocker lever 30
consisting of a first arm 31 extending substantially in
the direction Y, and a second arm 32 perpendicular to the
arm 31 and rigid with that end of this latter which faces
the broach 2. The rocker lever 30 is mounted rotatably
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on a pin 33 rigid with the plate 21; and is perpendicular
to this latter and to the broach 2, and rotatably engages
in a through bore provided in the centre of the arm 32.
The arm 32 is in the form of a bar of parallelepiped
section, and constitutes the frame of a resilient articulated
parallelogram 34, of which the cranks are constituted by
two resilient strips 35 extending towards the broach 2
from a lateral surface of the arm 32, and of which the
drag link is constituted by a terminal portion of a feeler
rod 36 extending parallel to the arm 32 towards the grinding
wheel 15, and comprising a tooth or pawl 37 at that end
distant from the end connected to the strips 35 and extending
towards the broach 2.
The feeler unit 29 also comprises a linear actuator
38, which in this case is a pneumatic actuator, supported
by the plate 21 and comprising an exit rod 39 mobile between
a retracted limiting position in which a roller rotatably
mounted on the free end of the rod 39 is separated from
the arm 31 of the rocker lever 30, and an extracted position
in which said roller cooperates with a lateral surface
of the arm 31 which faces the grinding wheel 15, and by
overcoming the return force of a spring 40 stretched between
the free end of the arm 31 and the plate 21 keeps a protuberance
41 on the arm 31 in contact with one of the lateral faces
of a hexagonal stop can 42 rotatably mounted on the plate
21 by means of an eccentric pin 43.
The stoppage of the rod 39 in said two positions
is sensed by a sensor 44 mounted on one end of the linear
actuator 38.
Finally, the feeler unit 29 comprises two linear
differential electronic transducers 45 and 46, of which
the first is disposed on the plate 21 in a position to
the side of the actuator 38 and comprises a mobile rod
47, the end of which is arranged to come into contact with
the lateral surface of the arm 31 facing the grinding wheel
15, and of which the second is disposed on the plate 21
on the same side as the cam 42 relative to the arm 31,
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and comprises a mobile rod 48, the free end of which is
arranged to come into contact with that end of the feeler
rod 36 distant from the end which carries the pawl 37.
When in operation, the sharpening of the broach
2 fixed axially to the bed ~not shown) of the machine 1
is preceded by a setting-up stage which is of absolute
importance for the correct execution of the subsequent
sharpening cycles.
The setting-up of the machine 1 is carried out
on the first tooth of the broach 2 starting from the position
shown in Figure 6, and after deactivating all the automatic
control devices which may be present in the machine 1.
Normally, the first operation carried out by
the operator who sets up the machine is to position the
slide 11 about the pin 12 in such a manner that the direction
Z of movement of the slide 11 is perfectly parallel to
the front surfaces 5 of the teeth 3 to be sharpened. The
operator then operates the slide 11 by moving it towards
the broach 2 until it reaches its limiting position, and
then operates the slide 10 so as to move the slide 11, locked in
said limiting position, until the periphery of the grinding wheel
15 is in proximity to, but not in contact with, the curved sur-
face 7 located upstream of the first tooth 3 to be sharpened.
When the slide 10 has been locked in the aforesaid
position, the operator moves the slide 11 backwards until
it operates the microswitch lla, and operates the actuator
38 so as to move the rod 39 into its retracted limiting
position. In this manner, the operator releases the rocker
lever 30, which rotates under the thrust of the spring
40 about the pin 33 until it reaches a position similar
to that shown in Figure 4. In this position, the rod 36
is disposed with its lateral surface in contact with the
cutting edge 6 of the first tooth 3 of the broach 2, and
compresses the rod 48 of the transducer 46, whereas the
arm 31 of the rocker lever 3G compresses the rod 47 of
the transducer 45.
As is normally the case for all differential
linear transducers, the transducers 45 and 46 are arranged
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to emit an electrical signal which varies linearly with
the axial position of their mobile rod between a maximum
positive value, corresponding to the position assumed by
the mobile rod when unstressed, and, after passing through
zero, a negative maximum value which corresponds to an
intermediate position of the mobile rod.
When the rod 36 is in the position shown in Figure
4 on the first tooth 3 of the broach 2, the signals emitted
by the transducers 45 and 46 are in general strongly negative,
and are reduced by the operator moving the slide 9 to bring
the pawl 37 into engagement with the first tooth 3, then
continuing the movement in the direction X until the grinding
wheel 15 is aligned with the front surface 5 of the first
tooth 3 in a position analogous to that shown in Figures
1 and 5.
The engagement between the pawl 37 and tooth
3 leads to the stoppage of the axial movement of the rod
36, so that any further movement of the slide 9 in the
direction X results in deflection of the resilient strips
35. Simultaneously with this deflection, there is an axial
movement of the rod 36 relative to the transducer 46, the
rod 48 of which moves outwards, and a rotation about the
pin 33 (in the clockwise direction in the Figures) of the
rocker lever 30, the arm 31 of which withdraws from the
transducer 35, so enabling its rod 47 to move outwards.
In other words, the progressive deflection of the strips
35 leads to a progressive reduction, in absolute value,
of the output signals of the transducers 45 and 46.
The operator halts the slide 9 when that surface
of the grinding wheel 15 facing the spindle 14 is perfectly
aligned with the front surface 5 of the first tooth 3 to
be sharpened. He then completely zeroes the output signals
of the transducers 45 and 46 by means of the adjustment
device 28. For this purpose, the operator firstly loosens
the nuts 26 and 27, and then turns the heads 19 and 23
to move the slide 17 and plate 21 along the respective
guides 16 and 20 until the plate 21 becomes located in
a position corresponding to zero output of the transducers
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45 and 46. The setting-up stage for the machine 1 terminates
by locking the plate 21 in said position by means of the
nuts 26 and 27, and by the operator setting a feed value
for the slide 9 on a known automatic device (not shown),
5 this value corresponding to the chip thickness, which the
grinding wheel 15 is required to remove for each pass.
Summarising the aforesaid, it can be stated that
the setting-up of the machine 1 consists of adjusting the
feeler unit 29 in such a manner that zero output of the
transducers 45 and 46 corresponds to perfect alignment
of the surface of the grinding wheel 15 with the front
surface of the first tooth 3 to be sharpened.
When setting-up is completed, the operator operates
a knob (not shown) disposed on the control panel (not shown)
for the machine 1, to start the automatic sharpening cycle,
which is described hereinafter starting from the position
reached during the setting-up stage on the first tooth
3 to be sharpened, and corresponding to the position shown
in Figure 5.
In the automatic cycle, when the output signal
of the transducers 45 and 46 is zero, the actuator 38 operates
such that its rod 39 engages with the arm 31 to rotate
the rocker lever 30 (in a clockwise direction in Figure
6) until the protuberance 41 comes into contact with the
hexagonal cam 42, against which it stops. This rotation
of the rocker lever 30 causes the release of the pawl 37
from the first tooth 3, and the upward rotation of the
rod 36 (Figure 6), which stops in a position in which it
is raised to an extent which depends on the angular position
of the cam 42. The function of this latter is precisely
to allow adjustment of the raised position of the rod 36,
the pawl 37 of which must move higher the smaller the diameter
of the grinding wheel 15 used.
The stoppage of the rod 39 due to contact between
the protuberance 41 and cam 42 is detected by the sensor
44, which activates, in succession, said automatic feed
device (not shown) which causes the slide 9 to make a movement
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equal to a constant pass depth of the grinding wheel 15,
and a drive motor ~not shown) for the slide 11~ which moves
towards the broach 2 until the grinding wheel 15 is caused
to sharpen the first tooth 3~ and then withdraws from the
broach 2 and stops following operation of the microswitch
lla.
The operation of the microswitch lla causes the
actuator 38 to operate, such that its rod 39 is moved into
the withdrawn position, so releasing the rocker lever 30
which rotates (in the anticlockwise direction in Figure
3) under the thrust of the spring 40, until the end of
the pawl 37 rests on the back 4 of the first tooth 3 which
has been previously sharpened.
The stoppage of the rod 39 in its withdrawn position
is detected by the sensor 44, which activates a control
device (not shown) for two drive motors (not shown) for
the slides 9 and 10.
When the rocker lever 30 and rod 36 are in the
position shown in Figure 3, the signals emitted by the
transducers 45 and 46 are certainly other than zero, and
are fed to said control device (not shown) as error signals,
to respectively cause operation of said two drive motors
(not shown) for the slides 10 and 9, which move until said
signals are zeroed.
With regard to the aforesaid, it should be noted
that the value of the signal emitted by the transducer
46 is influenced, except for very small variations, only
by the engagement between the pawl 37 and a tooth 3 of
the broach 2. Consequently, the slide 9, controlled by
the transducer 46, moves (towards the right in Figures
3, 4 and 5) with a substantially constant speed, to slow
down when the pawl 37 engages with the second tooth 3 of
the broach 2, and finally to stop when the output signal
of the transducer 46 is zero. In contrast, the value of
the signal emitted by the transducer 45 is normally positive
when the pawl 37 (Figure 3) rests on the back 4 of the
f irst tooth 3 of the broach 2, and then suddenly passes
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to a negative value when the pawl 37 precipitates (Figure
4) into the space between the first a~d second tooth. Con-
sequently, the slide 10, controlled by the transducer 45,
moves firstly such as to withdraw from the broach 2, and
then reverses its movement so as to approach the broach
2, until it stops (Figure 5) when the output signal of
the transducer 45 is zero.
When the slides 9 and 10 reach the new zero position,
the position assumed by the grinding wheel 15 relative
to the cutting edge 6 of the second tooth 3 is exactly
identical to that assumed by the grinding wheel 15 relative
to the cutting edge 6 of the first tooth 3 in the preceding
zero position reached during the setting-up stage. In
other words, the feeler unit 29 has controlled the movement
of the slides 9 and 10 in such a manner that the final
movement made by the slide 9 is exactly equal to the pitch
P between the first tooth 3 and the second, and the final
movement of the slide 10 corresponds to a withdrawal of
the grinding wheel 15 from the axis of the broach 2 which
is exactly equal to the increment H between the first tooth
3 and the second.
As stated heretofore, when the zero position
is reached, this automatically causes the rod 39 to operate,
and its stoppage in the extracted position (Figure 6) causes
the sensor 44 to automatically cause the slide 9 to advance
through a distance equal to the constant pass depth, and
to subsequently cause the slide 11 to operate.
At this point, the stages heretofore described
are repeated, and the sharpening cycles automatically follow
each other until all the teeth 3 of the broach 2 have been
sharpened.
Although in the embodiment heretofore described
by way of non-limiting example, the broach 2 is fixed and
the grinding wheel 15 is made to move along the X axis,
it is obviously possible to construct a sharpening machine
in which the broach 2 itself moves along the X axis.
Furthermore, although the machine 1 described
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by way of non-limiting example is a sharpening machine
of completely automatic cycle, it is clear that the feeler
unit29 can advantageously be mounted on semi-automatic
or manual sharpening machines, i.e. on machines in which
at least part of the movements along the X, Y and Z axes
are not controlled automatically by the tracer unit 29.
With regard to the aforegoing, it should be noted
that the working capacity of the described machine 1 does
not depend so much on the fact that once a position has
been reached corresponding to zero output of the transducers
45 and 46, the machine 1 is capable of automatically effecting
the sharpening cycle, nor on the fact that the zero output
position of the transducers 45 and 46 is sought automatically,
but rather on the fact that the feeler unit 29 enables
a simple, rapid and extremely precise determination to
be made of the position in which the grinding wheel head
13 has to be disposed for the grinding wheel 15 to be perfectly
aligned with the front surface 5 of the tooth 3 to be sharpened.
In other words, by using the feeler unit 29, it is possible
to sharpen all the teeth of a broach 2 with extreme accuracy
and in the same manner, and the broach, even after numerous
sharpening cycles, will preserve its geometrical characteristics
substantially intact.
Finally, it should be noted that if all the operations
described with reference to Figures 3 to 6 are carried
out but excluding the operation of the slide 11, this being
excluded by a simple operation carried out on the control
panel (not shown) of the machine 1, and if the output of
the feeler unit 29 is connected to any visual display device
of known commercial type, it is possible to operate the
machine 1 as a test bench able to check the geometrical
characteristics of any broach mounted on the machine bed 1.
Numerous modifications can be made to the described
machine 1 within the principle of the invention, without
leaving the scope of the inventive idea.
