Note: Descriptions are shown in the official language in which they were submitted.
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System and Method For Staking An Assembly Of Components Wit
Compensation For Comaonent Tolerances
FIELD OF THE INVENTION
[0001] The present invention relates to a system and method for staking an
assembly of
components in a mechanical device. More specifically, the present invention
relates to a system
and method of staking one or more components in a mechanical device to another
component in
the device whereby looseness of components in the resulting assembled device
can be reduced,
independent of tolerances in the assembly materials.
BACKGROUND OF THE INVENTION
[0002] It is known to make devices from assemblies of mechanical components,
which are
not expected to be disassembled, by staking the components together.
Generally, one or more
of the mechanical components will include at least one portion (the "staking
material") which is
permanently deformed during the staking process to fix (i.e. "stake") the
components together.
The compressive forces of the staking process are applied to the assembly of
mechanical
components via a pair of appropriately shaped dies to bend, curl, mushroom or
otherwise
permanently deform the staking material to fasten the components together to
form the device.
[0003] Staking provides several advantages over other assembly techniques such
as bolts or
welding, in that it is relatively inexpensive, requires little volume within
the assembly (unlike bolts
or screws which require volume in the assembly to receive the threaded portion
of the bolt or
screw) and results in a permanent connection of the assembly into the device.
[0004] However, staking also suffers from disadvantages. When a device is
assembled by
staking, the tolerances of the components in the staked device can result in
some looseness of
the components in the device, even though the device housing is staked,
allowing one or more of
the components to move with respect to others. When subjected to mechanical
vibration, the
loose component or components can move, resulting in undesired noises being
created in the
device. In particular, in the automotive industry, these noises are often
referred to as Buzz,
Squeak and Rattle ("BSR") and are very undesirable.
[ooos] Previous attempts to reduce undesired looseness by tighten tolerances
on the
feedstock materials have resulted in an unacceptable increase in manufacturing
costs. Other
attempts to mitigate the symptoms of the undesirable looseness, such as BSR,
have included
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adding elastomeric materials to the staked devices but such materials also
increase
manufacturing costs and may have unacceptably short lifetimes within the
devices.
[0006] It is desired to have a method for staking an assembly of components in
a mechanical
device which can avoid undesired looseness of components in the staked device.
SUMMARY OF THE INVENTION
[0007) It is an object of the present invention to provide a novel system and
method for
staking an assembly of components in a mechanical device which obviates or
mitigates at least
one disadvantage of the prior art.
[0008] According to a first aspect of the present invention, there is provided
a method of
method for staking an assembly of components in a mechanical device comprises
the steps of:
(i) forming at least one test device using a pair of staking dies in a press;
(ii) examining the at
least one test device to determine if a clearance between components in the
device has been
properly achieved; (iii) if the clearance has not been properly achieved,
changing at least one of
the pair of staking dies in the press and restarting the method at step (i);
(iv) if the clearance has
been properly achieved, producing devices with the pair of staking dies; and
(v) restarting the
method at step (i) if a batch change occurs to any component being staked in
the device wherein
a dimensional change in the changed component could affect the clearance.
[00091 Preferably, step (iii) comprises determining whether the clearance of
the at least one
test device was too large or too small and, if too small, changing at least
one of the pair of dies to
increase the clearance of the dies, or, if too large, changing at least one of
the pair of dies to
decrease the clearance of the dies.
[0010] According to another aspect of the present invention, there is provided
a method for
staking an assembly of components in a mechanical device wherein the resulting
devices have a
pre-selected clearance between two or more components, comprising the steps
of: (i) loading the
components into a staking press and staking the components to form a staked
device; (ii)
loading the staked device into a clearance setting press comprising a support
on which the
device rests and a compression die attached to a ram, the compression die
being operable to
engage a portion of the staked device to deform the portion of the device to
set the pre-selected
clearance; and (iii) moving the ram to bring the compression die into contact
with the portion of
the device with a pre-selected force to deform the portion to set the pre-
selected clearance.
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[0011] The present invention provides a novel method for staking components in
a
mechanical device to achieve a resulting staked device with at least one
desired inter-component
clearance independent of feedstock variations in the materials used to form
the components.
Variants are fabricated for at least one of the pair of stacking dies used in
the staking press and
the variant with an appropriate staking clearance is selected each time a
batch of components
changes. In this manner, variations between lots of feedstock materials used
to form the
components will not result in staked devices which suffer from lateral
looseness or other staking
results which do not meet the specifications for the device. In a second
embodiment, devices
are first staked in a conventional staking press and are then loaded into a
clearance setting
press which deforms at least a portion of the staked device to obtain the
desired clearance. By
carefully limiting the force with which the deformation is performed, the
desired clearance can be
obtained without requiring the batching of components in the manufacturing
process.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Preferred embodiments of the present invention will now be described,
by way of
example only, with reference to the attached Figures, wherein:
Figure 1 shows an exploded view of a disc recliner for an automotive seat back
which can
be manufactured in accordance with the present invention;
Figure 2 shows a partial section through a staked disc recliner of Figure 1;
Figure 3 shows a cross sectional view of a portion of a staking press in
accordance with
the method of the present invention with the press open and loaded with a set
of components for
the disc recliner of Figure 1;
Figure 4 shows a similar cross sectional view to that of Figure 3 with the
press closed to
stake the upper and lower components of the device together;
Figure 5 shows a side cross section of an upper die useful in the press of
Figure 2;
Figure 6 shows a perspective view of the die of Figure 5; and
Figure 7 shows a portion of side cross section of three upper dies which can
be employed
with the press of Figure 2.
DETAILED DESCRIPTION OF THE INVENTION
[0013] While the following discussion of the system and method of the present
invention
makes reference to the staking of a specific device, specifically a known disc
recliner, as an
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example of a device which can be advantageously manufactured with the system
and method of
the present invention, the present invention is not limited to use in
manufacturing this disc
recliner or any other specific device. Instead, the present invention can be
advantageously
employed to manufacture a wide variety of devices as will occur to those of
skill in the art.
[0014] As mentioned above, a known disc recliner is indicated generally at 20
in Figure 1.
Devices such as disc recliner 20 are commonly employed to provide for the
positioning of an
automotive seat back with respect to the set base.
[0015] As shown in the Figure, disc recliner 20 comprises a guide plate 24,
which can be
attached to a seat base, and a tooth piate 28 which can be attached to a seat
back. A set of
pawls 32 are located within guide plate 24 and are biased by a spring 36 to
lock the angular
position of tooth plate 28 with respect to guide plate 24 by engaging a set of
teeth located about
the inner peripheral lip of tooth plate 28. A shaft 40 includes a cam 44 which
is located within set
of pawls 32. Finally, a retainer ring 48 is staked to guide plate 24,
enclosing the other
components of disc recliner 20, to complete assembly of disc recliner 20.
[0016] When it is desired to alter the angular position of tooth plate 28 with
respect to guide
plate 24, thus altering the position of the seat back with respect to the seat
base, a lever (not
shown) attached to shaft 40 is moved, rotating shaft 40 and bringing the cam
surfaces of cam 44
into contact with the set of pawls 32.
[0017] Cam 44 moves pawls 32 out of contact with the teeth of tooth plate 28,
against the
biasing force of spring 36, which allows relative angular movement between
tooth plate 28 and
guide plate 24.
[0018] When the seat back is positioned as desired, the lever is released and
cam 44 allows
set of pawls 32 to reengage the teeth of tooth plate 28 under the bias force
of spring 36, thus
again fixing the angular position of tooth plate 28 with respect to guide
plate 24 and the seat
back with respect to the seat base.
[0019] As shown in Figure 2, when retainer ring 48 is staked to guide plate
24, a clearance 60
must be provided between tooth plate 28 and the radial upper surface 64 of
retainer ring 48 to
allow tooth plate 28 to rotate with respect to guide plate 28 and retainer
ring 48 when set of
pawls 32 are disengaged from tooth plate 28.
[0020] While clearance 60 must be sufficient to allow for rotation of tooth
plate 28, if
clearance 60 is excessive, tooth plate 28 will be capable of excessive
movement within disc
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recliner 20 and can thus produce undesired BSR noise. Accordingly, control of
clearance 60 is
important to avoid undesired BSR noise while still permitting correct
operation of disc recliner 20.
[0021] As mentioned above, the present invention is not limited to the
manufacture of disc
recliners 20, or the like, and many other staked devices have similar issues
with clearances
between components and the present invention can advantageously be employed in
the
manufacture of such devices.
[0022] Figure 3 shows a staking press 100, used in a method in accordance with
the present
invention. Press 100 can be generally conventional and preferably includes a
base portion 104,
to which a lower die 108 is affixed, and which also preferably includes a
locator 112 which
assists in loading and aligning the components to be staked by press 100.
[0023] In the illustrated embodiment, disc recliner 20 being staked by press
100, but as
mentioned above a variety of other devices can be staked in accordance with
the present
invention.
[00241 Press 100 further includes a ram 116 to which an upper die 120, an
example of which
is best seen in Figures 5 and 6, is mounted. Upper die 120 includes a cavity
124 with an
appropriate shape and volume to receive the upper portion of disc recliner
device 20 when upper
die 120 is brought into contact with lower die 108 as press 100 is cycled.
(00251 In the illustrated embodiment, much like a conventional staking
operation, guide plate
24 of disc recliner device 20 rests on lower die 108 with the remaining
components of disc
recliner 20 resting atop it. Press 100 is then closed, with retainer ring 48
being received in cavity
124 and the lower edge of retainer ring 48 engages lower die 108 which folds
the lower edge
over and onto the edge of the lower side of guide plate 24 to stake disc
recliner device 20
together as shown in Figures 2 and 4.
[0026] However, unlike known staking presses and methods, upper die 120
further includes a
first compression surface 136 and second compression surface 132 which engage
the upper
radial surface 64 of retainer ring 48 as press 100 is closed, such that upper
radial surface 64 is
compressed downward to reduce clearance 60.
(0027] Upper die 120 further includes an abutment surface 136 which abuts a
corresponding
abutment surface on lower die 108 to stop the closing of press 100 when upper
die 120 and
lower die 108 are fully closed and to thus prevent over compression of upper
radial surface 64 of
retainer ring 48.
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[0028] First compression surface 136 and second compression surface 132 are
vertically
spaced in upper die 120 at a specified distance which is selected such that
the deformation of
upper radial surface 64 will result in a desired clearance 60. This vertical
spacing is determined,
as is known to those of skill in the art, by the design of upper die 120, the
relative distances
between first compression surface 136 and second compression surface 132, the
thickness of
the material from which retainer ring 48 is formed and the vertical height of
the components of
disc recliner device 20 loaded into press 100 for staking.
[0029] Once the correct vertical spacing has been determined and upper die 120
fabricated,
changes in the thicknesses of components of disc recliner device 20, such as
changes in the
feedstock material from which retainer ring 48, tooth plate 28 or guide plate
24 are stamped or
otherwise formed, can result in clearance 60 being too small, leading to
failure of disc recliner
device 20, or too large, leading to BSR noise.
[0030] Accordingly, in the method of the present invention, a set of upper
dies 120 is
fabricated, each die differing to accommodate variations in feedstock
materials of device 20. In
a presently preferred embodiment, a set of three upper dies 120a, 120b and
120c are fabricated
as shown in Figure 7.
[0031] Upper die 120a is fabricated with the spacing 140 between first
compression surface
136 and second compression surface 132 being the nominally correct spacing,
determined as
described above.
[0032] Upper die 120b is fabricated with the spacing 144 between first
compression surface
136 and second compression surface 132 being a selected amount less than
spacing 140.
[0033] Upper 120c is fabricated with the spacing 148 between first compression
surface 136
and second compression surface 132 being a selected amount greater than
spacing 140.
[0034] In accordance with the method of the present invention, one of the set
of upper dies,
such as upper die 120a, is mounted in press 100 and the components for
assembling a disc
recliner device 20, or other device, are then loaded into press 100 and press
100 is cycled to
produce a test device 20. While only a single test device 20 need be produced,
it is presently
preferred to produce three or more test devices 20 to ensure that press 100 is
operating under
its normal operating conditions.
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[0035] Each test device 20 is removed from press 100 in turn and is examined
by the press
operator, or other individual or system, to determine if a desired value for
clearance 60 has been
properly achieved.
[0036] If the desired value for clearance 60 has been achieved for the test
devices 20, then
production of devices 20 can proceed until a batch change occurs for any of
the components of
device 20 which would affect clearance 60 of devices 20.
[0037] Specifically, each relevant component of device 20 is organized in
batches, each batch
being formed from a single lot of feedstock material for that component. Thus,
for example, if
the guide plate 24 of device 20 is formed by stamping from a steel feedstock,
when that lot of
feedstock is exhausted, those stamped guide plates 24 constitute a batch and
guide plates 24
stamped from a new lot of steel feedstock will constitute a new batch.
[0038] In the method of the present invention, one or more test devices 20 are
fabricated and
examined any time a batch of any of the relevant components of device 20
changes. As will be
apparent to those of skill in the art, the relevant components of device 20
are those where a
change of dimensional tolerances could affect the resulting dimension of
clearance 60.
[0039] If, when test devices 20 are examined, it is determined that clearance
60 of the test
devices 20 is too large, the upper die 120 (120a in this example) is removed
from press 100 and
is replaced with an upper die (120b in this example) with a reduced spacing,
relative to the
removed upper die 120, between first compression surface 136 and second
compression
surface 132.
[0040] One or more additional test devices 20 are then formed in press 100
with the
replacement upper die 120 and these additional test devices 120 are then
examined to
determine if clearance 60 is within the desired range. If clearance 60 is
acceptable, then
production of devices 20 can proceed until the next occurrence of a batch
change occurs for any
of the relevant components of device 20.
[0041] If clearance 60 is above the desired range, then upper die 120 is
removed from press
100 and is replaced with another upper die which has a reduced spacing between
first
compression surface 136 and second compression surface 132, relative to the
removed upper
die, and one or more test devices 20 are again fabricated and examined.
[0042] Alternatively, if test devices 20 are examined and it is determined
that clearance 60 is
below the desired range, then the upper die 120 in press 100 is removed and
replaced with an
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upper die 120 (such as upper die 120c) with an increased spacing, relative to
the removed upper
die 120, between first compression surface 136 and second compression surface
132. One or
more test devices 20 are then fabricated with the replacement upper die and
are examined. If
the test devices now have a clearance 60 within the desired range, production
of devices 20
proceeds under the next batch change. Conversely, if the test devices are not
staked within
specification, then upper die 120 is exchanged with an appropriate alternate
upper die 120,
either one with increased spacing in the case of clearance 60 being below the
desired range, or
one with reduced spacing in the case of clearance 60 being greater than the
desired range.
[0043] As will be apparent to those of skill in the art, the present invention
is not limited to the
use of any particular number of variant upper dies and the appropriate number
of variant dies will
be depend upon the expected variations in feedstock materials. In a current
use of the method
of the present invention, it has been found that three variant upper dies 120
are sufficient but it
contemplated that in other circumstances more or fewer variants may be
appropriate.
[0044] In a second embodiment of the present invention, the staking of the
components of
device 20 and the compression and/or deformation of surface 64 to set
clearance 60 have been
separated into separate manufacturing steps. In this embodiment, devices 20
are staked in a
conventional staking press. Staked devices 20 are then loaded into a clearance
setting press
which comprises a lower rest having a complementary shape to, and supporting,
the lower
surface of device 20 and a ram to which a compression die is mounted. The
compression die is
shaped to engage and appropriately deform surface 64 when the ram is moved
toward the lower
rest.
[0045] To set clearance 60, the ram of the clearance setting press is moved
toward a device
20 on the lower rest, bringing the compression die into contact with surface
64. A control
system, such as a microcontroller, monitors the force which the ram exerts on
surface 64, via the
compression die, and controls the ram such that a pre-selected force is
exerted on surface 64,
after which the ram is retracted.
[0046] The pre-selected force can be determined in a variety of ways,
including through
empirical testing, and is the force which is sufficient to deform surface 64
to obtain a clearance
60 within the desired range of clearances.
[0047] In one presently preferred embodiment, the pre-selected force is
selected such that
surface 64 (or features on surface 64, such as dimples, etc.) is brought into
contact with tooth
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plate 28 and clearance 60 is formed by the rebound of surface 60 as the ram
and compression
die are retracted.
[0048] As will be apparent to those of skill in the art, the pre-selected
force and rebound of
surface 64 are substantially independent of expected tolerance changes in the
components of
device 20 and thus in this embodiment of the present invention the manufacture
of devices 20
need not be arranged in batches and the manufacturing can be performed as a
continuous
process.
[0049] The present invention provides a novel method for staking components in
a
mechanical device to achieve a resulting staked device with at least one
desired inter-component
clearance independent of feedstock variations in the materials used to form
the components.
Variants are fabricated for at least one of the pair of stacking dies used in
the staking press and
the variant with an appropriate staking clearance is selected each time a
batch of components
changes. In this manner, variations between lots of feedstock materials used
to form the
components will not result in staked devices which suffer from lateral
looseness or other staking
results which do not meet the specifications for the device. In a second
embodiment, devices
are first staked in a conventional staking press and are then loaded into a
clearance setting
press which deforms at least a portion of the staked device to obtain the
desired clearance. By
carefully limiting the force with which the deformation is performed, the
desired clearance can be
obtained without requiring the batching of components in the manufacturing
process.
[0050] The above-described embodiments of the invention are intended to be
examples of
the present invention and alterations and modifications may be effected
thereto, by those of skill
in the art, without departing from the scope of the invention which is defined
solely by the claims
appended hereto.
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