Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Improved Grinding Machine and Method of Grinding
'this is a division of co-pending Canadian Patent Application
Serial No. 2,191,069 filed internationally on April 20, 1995.
Field of Invention
'This invention relates to grinding machines.
Background of the Invention
When machining articles to a desired shape it is often necessary
to rotate: the article (usually termed the workpiece) so that
symmetrical machining can be achieved of a given cross section.
:Rotation of the workpiece to be machined can be achieved by
securing the workpiece into a rotating chuck. However if the
workpiece is not centralised correctly within the clamping jaws
of the chuck, it will not rotate in a 'true' fashion and
machining will be inaccurate.
.Alternative methods of transmitting rotation involve the use of
a tailstock and a headstock to support the article between
centres, the headstock transmitting the rotation, directly or
indirectly to the workpiece.
'The interengagement between the workpiece and the headstock or
driver ma.y be subject to misalignment and offset, which will
introduce errors in the machining.
;?fin improved drive transmitting device which will not transmit
misalignment or offset to the workpiece is described and claimed
in UK Patent Specification 2,289,742.
Summary of the Invention
'The invention lies in a method of grinding a crankpin of a
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crankshaft which latter includes a circular flange at one end,
comprising the steps of:
- mounting the crankshaft between centres
- attaching radially outer regions of the flange to a
rotational drive to rotate the crankshaft about its main axis,
via a coupling which is torsionally rigid in a plane generally
perpendicular to the axis of rotation of the crankshaft but
which is readily deformable in other planes to accommodate
misalignment,
- advancing the grinding wheel to engage a crankpin region of
the crankshaft, and
- synchronously controlling the position of the grinding wheel
whilst the crankshaft is rotated thereby to follow the
planetary motion of the crankpin so as to maintain grinding
contact between the wheel and the pin.
The advancement and retraction of the grinding wheel is
preferably under the control of a computer.
In a method as aforesaid, the crankshaft is preferably mounted
between headstock and tailstock centres for rotation about its
main axis.
The invention also lies in a machine tool (grinding machine)
for machining a crankshaft workpiece wherein drive of the
latter is provided by means of at least one drive decoupling
means.
The invention thus provides a grinding machine which is adapted
to grind a crankpin region of a crankshaft by synchronously
advancing and retracting the grinding wheel as the crankshaft
is rotated so that contact is maintained between grinding wheel
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and crankpin during grinding so as to grind a true cylindrical
surface on the crankpin, which includes drive means for
rotating the crankshaf t, an d a coupling means which is
torsionally rigid in a plane generally perpendicular to the
axis of the crankshaft but is readily deformable in other
planes to accommodate misalignment, for correcting the drive
means t.o the crankshaft.
Preferably the drive coupling means comprises a driving member,
a driven member which is attachable to the crankshaft so as to
rotate the latter, and a connecting means for transferring
torque between the driving and the driven members which
comprises a laminated device attached to the driving member via
at least or_e off axis connection and to the driven member by
at least one other off axis connection, the connections being
circularly spaced one from the other.
In one embodiment the laminations are formed frcm flexible thin
sheet s~~eel so that the connecting means is torsionally rigid
in a pl.arie perpendicular to the drive axis so as to ensure
rotation is transmitted reliai~ly to the driven member, and the
flexibi:Lity of the laminations accommodates any eccentricity
developed through misalignment of the driving member and driven
member, whereby the driven member and therefore the crankshaf t
is decoupled from the drivinc_r member.
Where the crankshaft is to be mounted between a headstock and
a tails~~ock of the grinding machine, the components of the
drive coupli ng means may be centrally apertured to accommodate
the headstock, which can thereby extend axially therethrough
to engage one end of the cra~:kshaft .
Preferaf>ly the driven mem~~,er is provided with radially
adjustable means for securi:ic it to the crankshaft.
Preferably the securing means is arranged symmetrically to
allow centering of the driven member relative to the
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cranks::~aft .
The adjustment may be provided by pneumatic, electrical or
hydrau:Lic means so that release and removal of a crankshaft can
be performed automatically.
In a particularly preferred embodiment, two drive coupling
means as aforesaid are connected in series, the driven member
of the first being connected to the driving member of the
second.. Such an arrangement allows even greater coupling to be
achievE:d than if only a single drive decoupling means is
employed and permits off set as well as misalignment to be
accommodated .
The invention is of value in that it permits an NC grinding
machine: to be used to cylindrically grind off-axis crankpins
of a crankshaft by synchronously advancing and retracting the
grindir..g wheel as the crankshaft is rotated.
Thus the invention provides a method of grinding a crankpin of
a crankshaft mounted for rotation between centres and driven
during the grinding process so as to rotate true about its main
axis, wherein a rotating grinding wheel is advanced and
retracted under computer control in synchronism with the
p~.anetary rotation of the crankpin caused by the rotation of
the crankshaft so as to maintain grinding contact between the
wheel a:nd the pin at all times during the grinding of the pin.
After grinding a crankpin to a desired diameter, the grinding
wheel m<~y be retracted and moved axially so as to register with
another crankpin on the crankshaft, to enable the latter to be
ground.
A grinding machine embodying the invention thus comprises a
headstock and a tailstock between which a crankshaft can be
mounted for true rotation between centres, means for driving
the crankshaft, and means fo r coupling the drive means thereto
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in a manner so as to remove errors due to offset and
misalignment, a grinding wheel which can be advanced and
retracted towards and away from a crankshaft when the latter
is mounted in the machine and aligned with a crankpin thereof,
and a computer for controlling the said advance and retraction
of the wheel thereby to cause the latter to advance and
retract in synchronism with the planetary motion of the
crankpin as the crankshaft rotates, so as to maintain grinding
contact between the wheel and the pin at all times during the
grinding of the pin.
In accordance with one aspect of the present invention there
is provided a method of grinding a crankpin of a crankshaft
which latter includes a circular flange at one end,
comprising the steps of: (1) mounting the crankshaft
between centres; (2) attaching radially outer regions of the
flange to a rotational drive to rotate the crankshaft about
its main axis, via a coupling which is torsionally rigid in a
plane generally perpendicular to the axis of rotation of the
crankshaft but which is readily deformable in other planes to
accommodate misalignment; (3) advancing a grinding wheel to
engage a crankpin region of the crankshaft; and (4)
synchronously controlling the position of the grinding wheel
whilst the crankshaft is rotated thereby to follow the
planetary motion of the crankpin so as to maintain grinding
contact between the wheel and the pin.
In accordance with another aspect of the present invention
there is provided a grinding machine adapted to grind a
crankpin of a crankshaft mounted in the machine, comprising
means for synchronously advancing and retracting a grinding
wheel as the crankshaft is rotated, so that contact is
maintained between the grinding wheel and crankpin during
grinding of the crankpin so as to grind a true cylindrical
surface thereon, drive means for rotating the crankshaft, and
a coupling means which is torsionally rigid in a plane
generally perpendicular to the axis of the crankshaft but is
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readily deformable in other planes to accommodate
misalignment, for connecting the drive means to the
crankshaft.
The present invention taken in conjunction with the invention
described in co-pending Canadian Patent Application Serial
No. 2,191,069 filed internationally on April 20, 1995, will be
described in detail hereinbelow with the aid of the
accompanying drawings, in which:
Figure 1 is an exploded view of a prior art flexible coupling
Figure 2 (a) is a perspective view of a drive decoupling means
as applied to a grinding machine;
Figure 2(b) is a section view through the grinding wheel and
workpiece as shown in Figure 2(a);
Figure 3(a) is a perspective view of the drive decoupling
means as applied to grinding crankpins;
Figure 3(b) is a section through the grinding wheel and
crankpin as shown in Figure 3(a)~
Figures 4(a) and 4(b) are views of a clamping ring for
clamping an end of a crankshaft to the drive decoupling means;
Figures 5(a) and 5(b) are views of a preferred embodiment of
the clamping mechanism;
Figure 6 is a view of part of a grinding machine with a
housing encasing a drive decoupling device; and
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Figure 7 is a vertical section through the grinding machine
housing as shown in Figure 6.
Detail.=d Description of emi~odiments
Referring to Figure 1, a fl exible coupling device 10 is shown.
The coupling device 10 is shown exploded to illustrate the
seDarat~e components .
The ccupiirg device 10 comprises two identical connecting
members 12, 14, two laminated discs 16, 18 each formed from a
stack of thin sheet steel rings typically formed from shim
steel, ar_d a coupling sleeve 20, all the aforesaid being
centra7_ly apertured so as to allow a :~eadstock to extend
t he re t hrough .
The connecti ng member 12 ~urtizer comprises a cylindrical hub
22, and a circular flange 24 which is cutaway at three
circumferentially equally spaced positions. The three resulting
lobes 26, 28, 30 are apertured.
The second connecting member 14 is similar in construction.
The coupling sleeve 20 comprises a central cylindrical portion
32 with annular flanges 34, 36 at either end. The flanges 34,
36 are circumferentially cut away to leave lobes in a similar
manner as in the flange 24.
In use,. the coupling deTr'_ce 10 is assembled so that the
connecting members 12, 14 and coupling sleeve 20 are
interconnected by the laminated discs of thi n shim steel rings
16 , 18 .
The lobes of the flange 36 of the coupling sleeve 20 are
connected to the disc 16 by .tree hexagon bolts. One of which
is shown at 37. Three spaced apertures of the disc 16 are
connected to the flange 36.
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Similar bolts join the three lobes 26, 28 and 30 of member 12
to the disc 16 at points intermediate the bolts 37.
The sec:or_d connecting disc 18 is similarly connected to the
lobes of tie flange 34 by means of three bolts one of which is
shown at 39 and similarly to the lobes of the flange 14 by
similar bolts one of which is shown at 41.
The members 12, 14 are thus connected to the coupling sleeve
20 through the laminations of the discs 16, 18.
Thus on assembly the interconnection of the individual
connecting members 12, 14 and coupling sleeve 20 by use of the
flexible laminated thin sheet steel discs 16, 18 ensures a
torsion,all y rigid coupling which may be used in a machine tool
to transmit drive to a workp loco. The flexibility of the discs
16, 18 absorbs any misalignment or axial offset of the drive
member <~nd workpiece relative to each other.
Part of a grinding machine is shown in Figure 2 (a) . Here a
coupling device such as shown in Figure 1 is encased within a
housing 38.
The grinding machine comprises a grinding wheel 40, a headstock
42, a t:ailstock 44 and dri~re means 46 contained within a
housing 48.
The headstock 42 is free to pass through the centre of the
coupling device 10 contained within the housing 38. The
headstoc:k 42 and tailstock 44 support a workpiece 50.
The coupling device 10 is ccr~Lected at one end to the driving
means 46 and at the other en d is detachable secured to the
workpiece S0.
Rotation: of the drive means 46 by the motor 52 rotates the
coupling device 10. The wor'.tpiece 50 is supported between the
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headstock 42 and tailstock 44 and is rotated by rotation of the
coupling device 10 by the motor 52.
The dec:oupling of the workpiece 50 from the drive means 46 by
the coupling device 10 removes errors due to misalignment and
offset of the drive means 4 6 relative to the workpiece 50.
Figure 2 (b) shows the grinding wheel 40 and workpiece 50 during
a grinding operation. The grinding wheel 40 contacts the
workpiece 50 and grinds the surface to a desired diameter.
Figure 3(a) shows how a grinding machine can be used to
cylindrically grind off-axis crankpins of a crankshaft 54.
The cr<jnkshaft is supported between the headstock 42 and
tailstock 44, and includes a number of cranknins one of which
is denoted by reference numer al 56.
The drive means 46 rotates the crankshaft 54 via the coupling
device 10 as discussed in relation to Figure 2 (a) .
Rotation of the crankshaft 54 results in each off axis crankpin
describing a circle centred on the crankshaft axis as shown in
Figure :3 (b) .
The grinding wheel 40 synchronously advances and retracts as
the crankshaft 54 rotates and the crankpin 56 describes a
circle. This advance and rear action is controlled so that the
grinding wheel 40 maintains c:~ntact with the crankpin surface
at all times during the rotation of the crankshaft 54, thereby
grinding a true cylindrica= surface on the crankpin 56.
Although not shown, the cper ation of the grinding machine is
controlled by a computer.
As each crankpin is group d to the desired diameter, the
grinding wheel 40 is retracted and moved a~cially along the
crankshaft 54 to register w=th another crankpin. In this way
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an entire crankshaft can be ground automatically.
Attachment of the coupling device 10 to crankshaft 54 is
preferably achieved by a clamping ring as shown in Figures 4(a)
and 4(b) and 5(a) and 5(b).
In Figure 4(a) a clamping ring 58 is shown having two fixed
jaws 60, 62 and an adjustable jaw 64.
Figure 4(b) is a section (not to scale) along line A-A of
Figure 4 (a) .
In use the crankshaft 54, is inserted between the three jaws
60, 62, 64 and the adjustable jaw 64 is tightened onto the
crankshaft 54 by means of a threaded thrust member 66 such as a
screw. Adjustment of the threaded member 66 may be by way of
an Allen key spanner 68 so as to cause the j aw 64 to grip the
crank 54 against the two fixed jaws 60, 62.
Loosening the threaded member 66 allows removal of the
crankshaft 54.
The headstock 42 passes through the central aperture to contact
the crankshaft 54 for support.
An alternative clamping device 70 is shown in Figures 5(a) and
(b) .
Figure 5(a) shows a clamping ring 70 having as before two fixed
jaws 72, 74 and an adjustable jaw 76. A hydraulic piston and
cylinder 78 is provided to facilitate insertion and removal.
Figure 5(b) is a section (not to scale) along line B-B of
Figure 5(a) and illustrates the adjustable jaw 76 in more
detail.
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In the clamped position a flange 55 of the crankshaft is held
between the adjustable jaw 76 and the fixed jaws 72, 74. The
spring 90 acts to urge the adjustable jaw 70 against the flange
55.
As before the headstock 42 passes through central apertures in
the drive coupling device 10 and clamping ring 70 to support
the crankshaft 54.
To release the crankshaft 54, the hydraulic cylinder 78 is
actuated to push down on touch pad 77.
The spring 90 is sufficiently strong as to initially resist
this downward force, which is thus transmitted to the ring 70
and the latter displaces downwards until it hits bed 80.
Thereafter continued movement of the piston in the cylinder 78
results in compression of the spring 90 and pivoting of the jaw
76 into the position shown at 76', so all three jaws 72, 74, 76
are now clear of the flange 55.
The crankshaft 54 is now clear and can be removed from the jaws
72, 74, 76.
The bed 80 is spaced by a running clearance from the clamping
ring 70.
The interaction of the flange 55, the bed 80 and the spring 90
ensures that all three jaws 72, 74, 76 are moved clear of the
flange 55.
Figure 6 shows a grinding machine housing 92 containing a drive
means for operating the grinding machine, with a housing 94
attached, to encase a drive decoupling device such as is shown
in Figure 1.
The housing 94 encases the drive decoupling device except for a
drive plate 96 and jaws 100, 102, 104. An annular attachment
98 fits over the housing 94 and attaches to the grinding
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machine' drive housing 92. This ensures that no gap is left
between the housing 94 and the housing 92 so as to improve
safety and reduce the entry of dirt and swarf during machining.
Jaws 100, 102, 104 are provided for clamping the flanged end
of the crankshaft . An adj ustable jaT.v 104 grins the flange
against: the two f fixed j aws 10 0 , 102 . Rotat i on of the dri ve
plate 5~6 by the drive means, contained within the housing 92,
causes rotation of the flanged crankshafts. A headstock 106
passes through the central aperture of the coupling device so
as to allow for support of the crankshaft during machining .
The control panel 106 and bed of the machine 108 are shown.
As shoo~n. in Figure 7 the headstock I06 passes through the
central aperture of the coupl ing device. The latter comprises
connecting members 108, 110 and a coupling sleeve 112 which are
interconnected by laminated discs in the form of thin shim-
steel rings 114, 116. The coupling device is connected at one
end to the driving means and at the other end is detachably
securable to the flange of the crankshaft by means of the jaws
100, 10:?, 104 (only 102, 104 of which are visible in Figure 7) .
A faceplate I18 is shown surrounding the headstock 106, with
the cover 94 enclosing the entire coupling device shown.
