Note: Descriptions are shown in the official language in which they were submitted.
CA 02348656 2001-05-24
TITLE: Drive Mechanism For A Transfer Rail In A Press Transfer System
FIELD OF THE INVENTION
This invention relates to a drive mechanism for a transfer rail used in a
press transfer
system.
BACKGROUND OF THE INVENTION
The manufacturing industry, and in particular the metal fabrication and
stamping
industries, commonly utilize automated systems that allow a workpiece to be
conveyed
or transferred between equally spaced workstations where particular operations
are
carried out upon the workpiece. For example, many metal parts on automobiles
and
appliances are formed by means of a stamping procedure wherein a series of
separate
dies are situated on a series of aligned and equally spaced workstations
within a press
bed such that a workpiece will be stamped between a pair of dies upon each
stroke of
the press. Automated transfer systems are typically employed to grasp the
workpiece,
remove it from one set of dies, and transport it laterally through the press
bed to the next
adjacent workstation where the workpiece will be stamped a second time with a
further
set of dies upon the next stroke of the press.
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CA 02348656 2001-05-24
A press transfer system utilized in conjunction with a typical mufti-stage
press would
commonly include at least one transversely oriented transfer rail situated
adjacent to the
press bed and aligned with the various workstations. Depending upon the
particular
application and press design, a single transfer rail may be positioned along
one side of
the press bed or, alternatively, a separate transfer rail may be located on
each side of the
bed of the press. Regardless, the primary function of the transfer rail is to
provide a
mechanism by which grippers or fingers may be supported adjacent to the
workstations
for grasping a workpiece so that it may be transported to the next
workstation. Such
grippers or fingers would typically be mounted either to the transfer rail or
to a
secondary rail that is in some manner secured or attached to the transfer
rail. Movement
of the workpieces from workstation to workstation accordingly involves the
movement
of the transfer rail, often in a relatively complex three dimensional manner.
Described
generally, this movement involves (i) moving the rail toward the workstation
such that
the grippers may grasp the workpiece; (ii) lifting upwardly to remove the
workpiece
from the dies in the workstation; (iii) moving laterally and parallel to the
press bed to
align the workpiece with the next adjacent workstation; (iv) lowering to allow
the
grippers to release the workpiece onto the next adjacent set of dies; and, (v)
retracting
from the workstation and returning back to the starting position.
It will therefore be appreciated that to present an effective mechanism by
which a
workpiece may be moved in the above-described fashion, the transfer rails must
be
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relatively rigid, must be of a sufficient strength to support workpieces
without
significant flexure or deflection from the horizontal, and preferably of a
relatively light
weight construction so as to minimize the inertia of the moving transfer rails
to permit
more precise and faster movement of workpieces between workstations.
In order to maximize production efficiency in metal fabrication and stamping
operations,
press operators require a press transfer system that is capably of quickly
grasping and
transferring workpieces from one workstation to the next in synchronous
movement
with the cycling of the press. Optimum press throughput can only be achieved
when the
press transfer system is capable of moving parts through the press bed when
the press
is operating at its maximum speed. The requirement to grasp and move
workpieces
from workstation to workstation requires a press transfer system that is
capable of
quickly moving in the three dimensional manner as described above so that a
workpiece
may be placed upon the next adjacent set of dies before the next cycle of the
press. Such
movement necessitates very fast acceleration and deceleration of the transfer
rail and
other components of the transfer system, together with the workpiece itself.
The short,
fast and somewhat jerky movements of the press transfer system tend to place a
significant amount of strain upon the transfer rail and the various components
of the
transfer system. The strain and load borne by the transfer rail tend to be
considerably
enhanced when relatively large or heavy workpieces are involved and where
there is a
resulting increase in the inertia of the moving parts during acceleration and
deceleration.
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To help reduce the inertia of the moving parts in a press transfer system, the
elongate
transfer rails have traditionally been formed from aluminum extrusions.
Aluminum has
proven to provide a means to reduce the weight of the transfer rail while at
the same
time providing sufficient strength to support the workpieces and other
components
attached to the transfer rail. Unfortunately, with the advantages gained
through the use
of light weight transfer rails also come certain disadvantages. Currently
designed press
transfer systems, and more particularly systems known as "through-the-window"
transfer systems, employ methods of imparting movement to their transfer rails
that have
a tendency to cause the rails to be deflected from the horizontal during
operation. In
particular, during the very quick and somewhat jerky movements of the transfer
rail in
a direction parallel to the press bed, currently available systems have
demonstrated a
tendency to cause the rails to develop a wave-like or sinusoidal motion along
their
longitudinal axes. Such wave-like or sinusoidal motion is more pronounced in
press
transfer systems that are utilized on a multi-stage press having transfer
rails that are of
an extended length.
It will be appreciated that any significant degree of deflection of a transfer
rail in either
an upwardly or downwardly direction can have a devastating affect on the
positioning
of component parts secured thereto, including the grippers or fingers. In such
cases the
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grippers may not properly grasp a workpiece causing the workpiece to be
dropped or,
alternatively, may result in the workpiece not being deposited upon an
adjacent
workstation in the required position causing the workpiece to be destroyed
upon the next
stroke of the press. Further, wave-like or sinusoidal movement of the transfer
rail has
the tendency of causing internal vibrations in the press transfer system and
creating
undesireable flexure and strain within its various components.
SUMMARY OF THE INVENTION
The invention therefore provides a drive mechanism for a transfer rail in a
press transfer
system that addresses a number of the limitations in prior drive mechanisms
through
providing a mechanism to drive the transfer rail in a direction parallel to
the press bed
without the tendency of imparting a wave-like or sinusoidal motion to the
transfer rail,
while at the same time not significantly increasing the mass of either the
rail or its drive
system.
Accordingly, in one of its aspects the invention provides a drive mechanism
for a
transfer rail in a press transfer system having a drive frame for imparting
reciprocating
movement to the transfer rail, the drive mechanism comprising a drive housing
securable to a transfer rail in the press transfer system; a drive bushing
received and
secured within said drive housing; and, a drive member slidably received
within said
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drive bushing and securable to the drive frame of the press transfer system
such that
movement of the drive frame causes movement of said drive member in a
direction
generally corresponding to the direction of the movement of the drive frame,
the
movement of said drive member transmitted through said drive bushing to said
drive
housing and the transfer rail causing movement of the transfer rail in a
direction
generally parallel to the movement of the drive frame.
In a further aspect the invention provides A drive mechanism for a transfer
rail in a press
transfer system, the drive mechanism comprising a drive bushing securable to a
transfer
rail of the press transfer system; a drive frame, said drive frame
reciprocated by the
press transfer system in a back and forth in a direction generally parallel to
the transfer
rail; and, a drive member having one end fixed to said drive frame such that
said drive
member and said drive frame move together, said drive member slidably received
within
said drive bushing such that movement of said drive frame results in movement
of the
transfer rail in a generally parallel direction to the direction of the
movement of said
drive frame.
Further advantages of the invention will become apparent from the following
description taken together with the accompanying drawings.
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BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the present invention, and to show more clearly
how it may
be carried into effect, reference will now be made, by way of example, to the
accompanying drawings which show the preferred embodiments of the present
invention
in which:
Figure 1 is an upper side perspective view of a press having attached thereto
a "through-
the-window" press transfer system employing an embodiment of the transfer rail
drive
mechanism according to the present invention;
Figure 2 is a side elevational view of the press shown in Figure 1;
Figure 3 is a rear side elevational view of a press transfer system generally
constructed
in accordance with the prior art;
Figure 4 is a side elevational view of the press transfer system shown in
Figure 3;
Figure 5 is a rear perspective view of a press transfer system employing a
drive
mechanism for a transfer rail in accordance with a preferred embodiment of the
present
invention;
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Figure 6 is a side elevational view of the press transfer system shown in
Figure 5;
Figure 7 is a sectional view taken along the line 7-7 of the Figure 6; and,
Figure 8 is an upper side perspective view of the transfer rail drive
mechanism according
to a preferred embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention may be embodied in a number of different forms. However,
the
specification and drawings that follow describe and disclose only some of the
specific
forms of the invention and are not intended to limit the scope of the
invention as defined
in the claims that follow herein.
Figures 1 and 2 represent a general schematic view of a press having attached
thereto
a through-the-window press transfer system that employs a drive mechanism for
its
transfer rails constructed in accordance with a preferred embodiment of the
present
invention. In Figures 1 and 2 the press transfer system is noted generally by
reference
numeral 1 and the press to which it is attached is identified by reference
numeral 2.
Press 2 has a press bed 3 and a series of aligned workstations 4. So as to
create a frame
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of reference with respect to the movement of the components of transfer system
l,
movement in a horizontal direction parallel to press bed 3 is generally
referred to as
movement in the "X" direction, movement horizontally inwardly and outwardly
from
workstations 4 is designated as movement in the "Y" direction, and vertical
movement
is designated as movement in the "Z" direction. In the particular embodiment
of the
press transfer system shown in Figures 1 and 2, movement in the X, Y, and Z
directions
is accomplished by means of one more "X" drive motors 5, "Y" drive motors 6,
and "Z"
drive motors 7.
Press transfer system 1 includes a transfer rail 8 extending through the press
window and
positioned parallel to workstations 4. Depending upon the particular operation
in
concern and the configuration of press 2, a single transfer rail may be
positioned along
one side of the press bed or, alternatively, a pair of transfer rails may
extend along both
sides of press bed 3. In the embodiment of the press transfer system shown in
Figures
1 and 2, a foot 9 is positioned at each corner of the press in order to secure
each end of
transfer rail 8 to the press transfer system. In Figures 1 and 2 feet 9 are
also the
components which impart movement to transfer rail 8 in the "Y" direction.
Figures 3 and 4 represent a typical press transfer system having a drive
mechanism for
its transfer rail generally designed in accordance with prior existing
devices. As shown
in Figures 3 and 4, press transfer systems currently in use typically employ a
transfer rail
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8 connected to an "X" drive frame 10 by means of a pair of generally
vertically oriented
bars or posts 11. Posts 11 are rigidly secured to the upper surface of
transfer rail 8 to
resist movement therebetween. Posts 11 are permitted to slide upwardly or
downwardly
within a set of drive bushings 12 so as to permit transfer rail 8 to be raised
or lowered
in the "Z" direction movement of transfer rail 8 in the "X" direction is
accomplished
through the operation of an "X" drive member 13 which would typically be
comprised
of a belt, chain, jack screw or similar device, the function of which is to
move "X" drive
frame 10 in a direction parallel to transfer rail 8 and press bed (ie in the
"X" direction).
It will be appreciated that movement of "X" drive frame 10 will cause a
corresponding
movement of drive bushings 12 that are attached thereto, which in turn
transfer
movement in the "X" direction through posts 11 to transfer rail 8.
While the above described structure is relatively efficient in the transfer of
energy from
the drive system to transfer rail 8, imparting movement to transfer rail 8 by
the
application of force applied through rigidly attached posts 11 that are driven
at a vertical,
spaced apart, distance from the upper surface of the transfer rail imparts a
bending
moment to the transfer rail. That is, since the transfer rail is being driven
through posts
11 that are rigidly fixed to the transfer rail, the distance along the length
of the posts
between the upper surface of the transfer rail and drive bushing 12
effectively represents
a moment arm that causes torque to be built up within the transfer rail. It
will therefore
be appreciated that as the press transfer system cycles through its various
movements
CA 02348656 2001-05-24
when transporting a workpiece between workstations on the press, a series of
cyclical
bending moments will be established within posts 11 and transfer rail 8.
Furthermore,
the bending moments (and the resulting torque) will alternate, in terms of
direction, as
the movement of transfer rail 8 in the "X" direction is constantly reversing.
The result
of the complex forces that are applied to the transfer rail through this
structure is a
tendency for the rail to be deflected vertically from its horizontal position
and the
establishment of a wave-like or generally sinusoidal motion within the
transfer rail. The
extent and amplitude of the wave-like motion is enhanced with an increase in
the length
of the transfer rail and/or an increase in the weight of workpieces and other
components
attached thereto.
In contrast to the drive mechanism shown in Figures 3 and 4, Figures 5, 6, and
7 depict
a drive mechanism for a transfer rail in a press transfer system in accordance
with a
preferred embodiment of the present invention. Refernng specifically to Figure
6, there
is shown a press transfer system having an "X" drive system 14 for imparting
movement
to a transfer rail 8 in a direction that (as described previously) is
generally parallel to the
press bed. "X" drive system 14 is itself comprised of a number of different
components.
It will be appreciated from a thorough understanding of the invention that the
precise
construction and configuration of the "X" drive system could vary
substantially from
press transfer system to press transfer system without affecting the scope of
the present
invention. For illustrative purposes, the "X" drive system shown in the
attached
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drawings is comprised of a generally horizontally mounted drive frame 15
(shown most
clearly in Figures 1 and 5) that is moved in the "X" direction by means of "X"
drive
motor 5, in conjunction with one or more belts, chains, jack screws, or other
commonly
used mechanical structures that transmit motion. In the embodiment of the
press
transfer system shown in Figures 5 through 7, a number of the components of
"X" drive
system 14 and other features of the transfer system are concealed within a
nose cone 19.
To transfer the reciprocating motion of drive frame 15 to transfer rail 8, in
the preferred
embodiment there is utilized a drive member 16 having one end rigidly
connected to
drive frame 15 and an opposite end slideably received within a drive bushing
17 secured
to one end of transfer rail 8. Drive bushing 17 may be attached directly to
the end of the
transfer rail or, alternatively, may be received and secured within a drive
housing 18,
that is in turn secured to the end of transfer rail 8. Regardless, with the
fixation of one
end of drive member 16 to drive frame 15, and through the receipt of the drive
member
within drive bushing 17 which is either directly connected to transfer rail 8
or indirectly
connected by means of drive housing 18, reciprocal movement of drive frame 15
in a
direction parallel to the press bed will result in a corresponding reciprocal
movement of
the transfer rail in the same direction. In the embodiment depicted in the
attached
drawings drive member 16 is rigidly secured to a bearing attachment plate 20
through
the use of one or more collars 21. Bearing attachment plate 20 is in turn
fixed to drive
frame 15.
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The attachment of the drive bushing and/or drive housing to the end of
transfer rail 8,
rather than to its sides or top surfaces, helps to reduce the torque and
bending moment
developed within the rail as it is driven by drive member 16. To further help
minimize
the bending moment applied to transfer rail 8, in the preferred embodiment
drive
bushing 17 is a self aligning bushing and drive member 16 is a post slideably
received
within bushing 17. Through utilizing a self aligning bushing to transmit force
between
the drive post 16 and transfer rail 8, it will be appreciated that there will
be presented
the ability for the angle between drive post 16 and transfer rail 8 to be
automatically
adjusted in accordance with the reciprocal motion of the drive post. That is,
in essence
the connection between self-aligning bushing 17 and drive post 16 will be
"free
floating" allowing the drive post to be deflected in a direction either toward
or away
from the end of transfer rail 8 as the post is reciprocated back and forth. In
this manner
the moment arm imparted to transfer rail 8 will be minimized and less than
would be the
case if the drive post were rigidly fixed directly to the transfer rail. The
use of self-
aligning bushing 17 to transfer movement between drive post 16 and transfer
rail 8
allows for the angle of the post relative to the transfer rail to be
automatically varied as
the drive housing reverses direction during its reciprocal movement.
Self-aligning drive bushing 17 also helps to accommodate any deflection that
may occur
within drive post 16 upon the reversing of direction of movement of drive
housing 15.
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Specifically, upon the reversal of the reciprocating moment of drive frame 1
S, there will
be an inertia within the moving transfer rail having a tendency to deflect
drive post 16
from its generally vertical orientation. Self aligning drive bushing 17
permits any such
deflection to be accommodated without a significant increase in the moment arm
or
torque applied to the transfer rail. The combined affect of the function and
operation of
drive post 16 and self aligning drive bushing 17 is to reduce the moment arm
and torque
applied to transfer rail 8 and the resulting wave-like or sinusoidal motion
that is often
imparted to a transfer rail through the use of prior existing drive
mechanisms.
With drive post 16 slideably received within self-aligning drive bushing 17,
there will
also be presented the ability for transfer rail 8 to be raised or lowered in
the "Z"
direction without affecting the "X" drive assembly. That is, a separate drive
mechanism
(not shown) would typically be utilized to raise or lower transfer rail 8 at
which time
self aligning drive bushing 17 merely slides upwardly or downwardly along
drive post
16. Once again, due to the nature and relationship between self-aligning drive
bushing
17 and drive post 16, inertia in the "X" direction that is present within
transfer rail 8
when it is moved in an upwardly or downwardly direction can be accommodated
through self-aligning drive bushing 17.
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It is to be understood that what has been described are the preferred
embodiments of the
invention and that it may be possible to make variations to these embodiments
while
staying within the broad scope of the invention. Some of these variations have
been
discussed while others will be readily apparent to those skilled in the art.
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