Note: Descriptions are shown in the official language in which they were submitted.
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13~36S9 0234-IR-AS
FRICTION CONTROL FOR B~.~RING
S~RFA OE OF ROLL~R
This invention relates to the roller element o~ a
powered-rollex ~rans~er lin~, an~ mor- par~ieularly ~o tha
apparatus anc ~ethod embodia~ by a rollor ha~ing a pluxality o~
lubricant pr~ssure relie~ areas in o- about the bearing sur~aca
to provids consis~ent and incr~ased ro~tary powar tran3mission
rom z power~d a~le to t~.e rollar.
~ACKC-~U~D OF ~E INVENl'I~N
For certain auto~otive co~ponent3 such as engines or
tran~mis~ions, powered xoller t~ar.s~e. line.s are used ~o ~oYa
workpi~ces thro~lgh the manufacturing and assembly stations.
Workpieces are moun~ed on pall2~s which are carried through the
line by rollers d.i~en ~y slow ~ut continuously rotating axles.
~h~ rollers have a lubricated bushing-typ2 inner dizmat~r
b~ring surfacQ ad2pted to ~i~ on the axles. To propel the
p~llets, th~ powered a~les cause the roll~r~ to rotate ~y using
th,e ~rictian b~een tha a~la and tha baaring sur~ace Oc the
roller. At cQrtain p~itions on th~ ~ran3~er line, it is
de~ired to 3top th~ pallet~. At th~s in~nd~d stopping points,
a stopping ~wchanisul ph~ysicxlly rest-ain~ the pallet. The
rollers u~d~r the stoppad pallet al~c 3top rotating and slip on
the rotatins a~ . This ~lip~ing is facili~atad by the
lubric~nt between th2 axle and ~.a b~a_ing ~urfaca oP the
roller.
Th~ dri~g ~rcs to accelerate 2 ~allet fr~n a stopping
p~in~ or ~o dr~J~ a pall~t pa~ a ~inor resiPtanc~ ~uch ~s a
~all chang~ in ~levation i~ deter~ined by the coefficien~ of
~riction between the poware~ a~le ænd tne inner di~ et~r bearing
surface of the roller. Th~ cae~icient o~ ~ric~ion in turn is
af~ected by the lubrication condition e~ist~ng between the axle
and the bearing sur~ac2 o~ the roller. The desired lubrication
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0234-IR-AS
mode for the powered-roller in the transfer line described above
is boundary lubrication.
Under some working conditions however, additional
lubricant from the work process or the environment may gradually
enter the bearing gap. The additional lubricant changes the
lubricant mode from boundary to hydrodynamic . Hydrodynamic
lubrication substantially reduces the friction between the
roller and powared axle. ~herefore the driving force
trans~itted from the axles to the rollers is substantially
reduced. The reduced driving ~orce provided by the rollers to
the pallets causes the pallets to improperly accelerate and move
inconsistently. This is undesirable in automated manufacturing
and assembly lines.
SUMMARY OF T~E INVENTION
An ob~ect of this invention is to maintain at a consistent
and acceptable level the drive force transmitted to a roller
~rom a powered axle.
Another ob~ect i9 to maintain an acceptably high
coe~ficient of friction between the powered axle and the roller.
Another ob;ect is to prevent additional lubricant in the
bearing gap of a roller ~rom causing undesired transition from
boundary to hydrodynamic lubrication.
Another ob~ect is to relieve lubricant pressure locally
from about the bearing sur~ace by providing lubricant pressure
relie~ areas so as to maintain boundary lubrication about the
bearing sur~ace and thus maintain a high coefficient of friction
between the powered axle and the roller which results in
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consistent rotary power transmission from the powered
axle to the intermittently rotating roller.
The objects and advantages of the present
invention are attained by having a plurality of
lubricant pressure relief areas about the bearing
surface of an annular roller.
An unexpected advantage of the present
invention is the increase in drive force transmitted
from the powered axle to the roller element under
operating conditions with excess lubrication present.
According to a broad aspect of the present
invention, there is provided a friction drive roller
for a continuously rotating axle of a conveyor. The
friction drive roller comprises an annular roller
element having an outer diameter surface for rollingly
transporting articles on the conveyor and an inner
diameter surface for frictional drive contact with the
rotating axle. Means is provided for reducing the
coefficient of friction between the inner diameter
surface and the rotating axle when the articles are
restrained from movement on the conveyor and
comprising a small gap between the rotating axle and
the inner diameter surface of the roller element and a
film of lubricant disposed in the gap so as to
substantially prevent the rotating axle from
contacting the inner diameter surface. Means is also
provided for increasing the coefficient of friction
between the inner diameter surface and the rotating
axle when the articles are free to move on the
conveyor and comprising a continuous helical groove
having circumferential loops spaced three to ten
groove widths apart in one of the inner diameter
surface and said rotating axle for reducing the
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lubricant pressure so as to allow frictional drive
contact of the rotating axle with the inner diameter
surface.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects, advantages and novel features of
the present invention will become apparent from the
following detailed description of the invention when
considered in conjunction with the accompanying
drawings.
Figure 1 is a partial cross-sectional and a
partial elevation of a portion of a transfer line;
Figure 2 is a front view of the roller;
Figure 3 is a cross-sectional side view of the
roller of the present invention;
Figure 4 is an enlargement of the circled
portion of the roller in Figure 3; and
Figure 5 is another embodiment of the present
invention.
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0234-IR-AS
DETAILED DESCRIPTION OF THE INVENTION
A typical powered axle-roller subassembly o~ a transfer
line is shown in Figure 1. The axle 12 is support for rotation
by bearings 14 in the frame member 16. A bevel gear arrangement
18 and 20 provides constant rotational power to the axle from a
power source, such as a motor, connected to drive shaft 22.
Two rollers 30 are mounted on the axle in the transfer
line shown in Figure 1. A spacer 24 and two collars 26 position
the rollers on the axle. Other configurations are possible. A
front view o~ a rcller is shown in Figure 2. The roller is
usually a solid metal annular cylinder having outer and inner
diameter surfaces. The outer diameter surface 32 provides the
roller contact sur~ace to carry a pallet such as 28 in Figure
1. The inner diameter sur~ace 34 provides a bearing surface for
the axle 12. The bearing surface 34 is formed by a bore through
the center of the roller and i9 usually concentric with
the outer diameter roller sur~ace.
The inner diameter bearing surface 34 is dimensioned such
that a small bearing gap exists between the powered axle 12 and
the bearing sur~ace. A lubricant is provided in the bearing
gap. In a pre~erred embodiment, the roller is constructed of a
lubricant-Lmpregnated sintered material. Alternatively,
lubricant may be Lntroduced into the bearing gap by other
conventional means such as a lubricant wick or pump. Another
known means of providing lubricant to the bearing gap is by a
supply passageway such as a supply groove on the axle or the
bearing sur~ace o~ the roller. A lubricant supply groove has
large dimensions and is widely spaced on the axle or roller
surfaces so as to best perform its supply function.
In normal operation a roller having a smooth bearing
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0234-IR-AS
surface operates as follows. The powered axle 12 rotates
continuously. A thin film of lubricant occupies the bearing gap
between the axle and bearing surface of the roller. The axle
rotational speed and other factors are such that the lubricant
effect is in the boundary lubrication mode. The coefficient of
friction between the axle and the bearing sur~ace of the roller
is high. This is well known from the Stribeck curve which
relates lubrication mode to coefficient of friction for sliding
bearings. Thus the axle causes the roller to rotate and
tangentially propel the pallet forward. The coefficient of
friction in the boundary lubrication mode is high enough that
the drive force supplied by the axle to the roller can overcome
any minor resistance a pallet may encounter on the line.
Furthermore, in normal operation, the lubrication about
the bearing sur~ace of the roller allows the roller to slip on
the axle if the pallet encounters a stif~ resistance such as a
~topping mechanism. The lubrication in the bearing gap
facilitates the continued rotation of the powered axle relative
to the stopped roller.
During operation of the line, excess lubrication may
gradually enter the bearing gap. The increased lubrication
causes the lubrication effect to change from the boundary mode
to the hydrodynamic mode. The coefficient of friction between
the axle and the roller decreases as the lubrication mode
changes from boundary to hydrodynamic lubrication. Again this
is known from the Stribeck curve.
In a hydrodynamic lubrication mode, the drive for~e
supplied by the axle to the roller is not strong enough to
overcome minor resistance. Thus the rollers begin to slip on
the axles and the pallets in the line are subject to
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0234-~R-AS
inconsistent movement. In other words, when excess lubrication
enters the bearing gap the rollers tend to slip on the powered
axle rather than drive the pallets.
The present invention overcomes the above problem. Even
with excess lubrication, the lubricant can be maintained in the
boundary lubrica~ion mode ~y dividin~ the hearing surface into
narrow lands separated by narrow lubricant pressure relief
areas. The recessed relief areas bleed off the excess lubricant
pressure and prevents transition to hydrodynamic lubrication.
In the preferred embodiment of the roller 30A shown in Figure 3,
and enlarged in Figure 4, narrow or thin grooves 36 having a
substantially circumferential orientation provide localized
lubricant pressure bleed off. The grooves preferably are narrow
so as not to substantially reduce the bearing area. The bearing
lands between the grooves are also relatively narrcw but
preferably are three to ten times the groove width. This
relationship appears important to provide both adequate bearing
support area and relief area to bleed off lubricant pressure.
It is apparent that these narrcw, closely spaced lubricant
pressure relief grooves differ substantial in construction,
purpase an~ e~ect from the large, widely spaced lubricant
supply groove~ discussed earlier.
A thread-like helical groove on the inner diameter bearing
sur~ace of the roller, as shown in Figures 3 and 4, is the
preferred embodiment for providing lubricant relief areas for
the bearing sur~ace of the roller. The groove has a groove root
width of about .005", a thread pitch between .015" and .050",
and a thread depth between .003" and .006". The groove
sideWalls have a 60 included angle. A helical thread
configuration is preferred due to ease of machining.
Unexpectedly, it was found that dividing the bearing
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surface into narrow lands surrounded by lubr1cant pressure
relief areas such as circumferential grooves machined into the
bearing surface increased the drive force transmitted to the
rollers when excess lubricant is present. For example, a new
roller having a smooth, ungrooved bearing sur~ace was found to
initially generate about 25 lbs. of drive force on a pallet with
450 lbs. of weight. When excess lubrication was introduced into
the bearing gap the drive force was reduced to 4-7 lbs.
In the above situation, installing rollers with
circumferential grooves machined into the bearing surface as
provided by the present invention produced 28-30 lbs. of drive
force. When excess lubrication was introduced into the bearing
gap, the grooved roller produced 25-30 lbs. o~ force, about 4
times the drive force transmitted by the smooth ungrooved
bearing sur~ace with excess lubricant.
Other configurations o~ lubricant pressure relief areas
are possible and are considered within the scope of this
invention. Thin axial grooves on the roller inner diameter
would also allow the excess lubricant pressure to bleed off.
Alternatively, as shown by Figure 5, axial or circumferential
grOOVQS 38 can be prov~ded on the axle 12A, oppo~ite the bearing
sur~ace o~ the roller inner diameter.
Obviously, many modi~ications and variations of the
present ihvention are possible in light of the above teachings.
It is there~ore to be understood that, within the scope of the
;appended claims, the invention may be practiced otherwise than
as specifically described.
