Note: Descriptions are shown in the official language in which they were submitted.
1131937
This invention relates to articu}ated or linked belts, and
particularly with a novel belt comprising modules each comprising
a plurality of preassembled link-liXe ele~ents.
It has long been known that en less belts, in the for~ of ~ I
loop, can be used particularly as a conveyor, for the trans-
mission of power, and for the transmission of precise angular
, ~ relationships, i.e. as a timing belt. The simplest form is
a loop of flat, flexible material driven by frictional engagement,
but such belts provide little, if ar.v, intrinsic resistance to
distortion under carrying load and :end to slip. Hence, their
virtue is primarily in their cost, but they find little applica-
tion for precision power transmission, timing or conveyance. For
lS the latter applications, the preferred belt is a chain drive.
Precision steel roller chains and inverted tooth or silent chains
are considered primarily power trans~ission andJor power timing
chains, particularly at average to high speed conditions.
The well known silent or "invertedH tooth driving chains
~ are generally characterized in that each driving link i9 usually
provided with a pair of teeth extending outwardly from the link
: . .
from approximately the pivotal axes of the latter, parallel to
one another and perpendicularly to the pitch line. While in
theory;these links have no sliding action in or out of the grooves
1 25 ~ of an associated sprooket wheel and are hence considered noiseless,
~ : . ' . ' ::
.'',: . ~ ' ~
. .
~C-22 CIP~
. . .. ' .
. ' ' . ':
" ,~ ~ ~, . . . '
. . ~k
'i ~ i , ,.. ___.,_.__,.. ,.__.,_.. _.. ~.__~... ._._.. __... ~.. ._.'
1: - .
.
,, . ' ' , ' ' .
. . ,, ,, , , '.
i~3~937
in practice, the link teeth and sprocket teeth engage one another
with a scuffing or rubbing contact, known as "scrubbing", with
attendant wear on the teeth. Additionally, in a typical operation
of a silent chain, the contact between the driving and driven
faces of the chain teeth and sprocket teeth is substantially along
a line or a narrow area of the tooth faces extending parallel to
the rotational axis of the sprocket wheel. The dri~ing pressure,
being thus concentrated over this very small area, typically
requires that the teeth surfaces be specially hardened to reduce
wear.
Prior art silent chains also claim to reduce the detrimental
effect of chordal action, i.e. the vibratory motion of the chain
as it engages the sprocket wheel. This vibratory motion is
anifes~ as a periodic acceleration and deceleration of the chain,
lS and a rise and fall of the links of the latter with respect to
its lineiof engagement with the sprocket wheel. Such chordal
action, of course, is not present in a fully flexible belt such
as a rubber timing belt, for the laiter simply conforms at every
point to the pitch circle of the sprocket wheel. However, for a
chain formed of substantially rigid links which are pivotally
joined to one another, flexible conformation to the pitch circle
of the sprocket wheel is impossible. Roller chains and the like
exhibit marked chordal a¢tion which limits high speed load
arrying capabillty and makes transfer of the load from the chain
o a stationary comb tangent to the sprocket wheel, particularly
. .
~`
~ rTP -2-
;:
~. , . .
:: , . . : .. . ~ ~
.. . ~ - :.. ,. : ,
1131937
perilous for fragile items being carried by the chain. In order
to reduce the chordal action of some current silent chains, the
designers have provided ingenious pin and rocker joints and
involute chain teeth and sprocket teeth. When such teeth engage
; 5 one another, the contact poin~ of the pin and rocker joint shifts
upward and causes the pitch of the chain to elongate, reducing
chordal action. -
In U.S. Patent 3,870,141 issued March 11, 1975, there is
disclosed a chain link belt particularly useful as a conveyor,
capable of carrying heavy loads and transmitting substantial
power at fairly high speeds. The chain belt therein disclosed
is particularly advantageous in that, being modular, it is very
easily assembled and repaired.
The modular belt of U.S. Patent 3,870,141 is generally
formed of a first plurality of link ends, each formed to circum-
scribe a pivotal hole and a second plurality of link ends, each
also formed to circumscribe a pivotal hole, the pivotal holes
` in each plurality of link ends being respectively aligned along
la common axis. The axes of the pivot holes of each plurality of
~ ~ ¦link ends are parallel with one another. Each link end of the
~ ? ~ ~
first plurality is joined to a corresponding link end of the
second plurality through at least one cross-rib which lies
etween and substantially parallel to the axes of the two plura-
lities of pivotal holes. The link ends are dimensioned and
spaced apart by a distance sli~htly greater than their respective
::'
rJC~22 CIP -3-
~, -
,~
11
.. . ~ .
-` 1131937
widths. Thus, when the link ends of one module are nested or
enga~ed with the link ends of another module bv a common pivot
pin extending through the pivotal holes in the respective link
ends, the engagement of adjacent link ends tends to minimize
the transmission of twisting shear to the pivot rod. Consequently,
very advantageously the modules, chain belt and pivot pins of
U.S. Patent 3,870,141 can be formed of polymeric materials,
thereby minimizing costs~ providing high strength with light
. weight and avoiding lubrication problems. This chain belt can
withstand severe extremes of processing tem~eratures, and highly
corrosive environments such as are encountered frequently in
laundries, food proces.sing and other manufacturing processes.
~ To drive the chain belt of U.S. Patent 3,870,141, there is
: usually provided a sprocket wheel with extending teeth arranged
:~: 15 ~ in staggered relation alon~ the axis of rotation so that the
teeth can enaage a similarly .stagaered array of openings formed
by adjacënt engaged modules. These sprocket teeth bear against
: the portion of the link end wbich circumscribes the pivotal hole~
~The present invention is directed toward a novel chain link
.10 ~ having a driving tooth protruding therefrom intermediate pivot axes
;: located at opposite~:ends of the link, the tooth having working
surfaces of a unique configuration as hereinafter described. This
- ; novel chain link can be assembled to form a module for a c~ain
belt generally of the t~pe described in U.S. Patent 3,870,141 but
':
25: particularly adapted to provide very precise power transmission
and/or timing requlrements. To this end, the present invention is
also typically embodied in a modularly structured chain belt in
which each module is .formed of a plurality of lin~.s each having
a pair of link ends each formed to circumscrihe respective pivotal
'~ .
LC-22 CIP 11 -4-
,,' . '
. .
: .
1131937
holes, a number of links heing arranged so that a first set of
such holes in first plurality o~ such link ends are aligned along
a common first linear axis, and a second set of such holes in a
second plurality of such link ends are aligned along a second
common linear axis, the first and second axes being parallel to
one another. In t~e module formed of links of the present inven-
tion, each of the link ends of the first plurality is joined with
the corresponding ones of link ends of the second plurality throug
an intermediate portion. In emhodiments where the links are
integrally joined to one another, the intermediate portion ex-
tend substantially parallel to the first and second axes. Appende
to, and preferably formed integrally with each link is a single
driving tooth which protrudes intermediate the first and second
axes generally in a fixst direction perpendicular to a plane
com~on to those axes. The tooth is preferably formed with its
working surfaces as a like pair o plano-convex surfaces each
being typically a substantially cylindrical segment of like radius
of curvature, the respective cylindrical axis of each such seg-
ment being between the first and second axes through the pivotal
~ holes. The term "working surface" is intended to refer to that
surface of a tooth adapted to engage a driving element such as a
~- ~ ¦sprocket or an element to be driven, as the case may be.A particular object of the present invention is to provide a
link of the type descrihed which, in conjunction with a sprocket
wheel of appropriate configuration, exhihits substantially no
scrubbing action. Another object of the present invention is to
provide a link of the type described, a plurality of which when
formed into a hinged, endless belt used in conjunction with an
appropriate sprocket wheel, exhibits remarkably small chordal
action.
~C-22 CIP -5-
- ~3~;37
Other objects of the invention will in part be
obvious and will in part appear hereinafter. The invention
accordingly comprises the apparatus possessing the construction,
combination of elements, and arrangement of parts which are
exemplified in the following detailed disclosure, and the
scope of the application of which will be indicated in the claims.
Broadly speaking the present invention provides a
module for constructing linked structures for use as hinged,
endless belts, the module comprising, in combination: a
first plurality of link ends of substantially identical width,
each link end of the first plurality being formed to circum-
scribe a pivotal hole, the holes of the first plurality being
arranged coaxially along a first pivotal axis, the first
plurality of link ends being spaced from one another by
approximately the width; a second plurality of link ends of
substantially identical width, each link end of the second
plurality being formed to circumscribe a pivotal hole, the
holes of the second plurality being arranged coaxially along
a second pivotal axis parallel to the first axis, the second
plurality of link ends being spaced from one another by
approximately the width; an intermediate portion integrally
formed with and joining the first and second plurality of link
ends so as to preserve the parallel relation of the axes; a
driving tooth formed integrally with and protruding from the
intermediate portion substantially normal to the pitch line
between the first and second axes intermediate the latter;
the tooth having a pair of working surfaces, each of the
working surfaces having a shape in the range between and
.~
::~ including that of a cylindrical segment and a chord of the
- segment; the axis of each working surface being parallel with
the pivotal axes of the link and positioned intermediate the
pivotal axes or coincident with the pivotal axis furthest from
that surface; the pair of working surfaces being part of a pair of
sd/ ~ -6~
~ 7
intersecting loci; the shape of each of the working surfaces
being such that the -tangent angle of each such surface is not
more than 90, the tangent angle being defined between a
tangent at a point on one working surface and a line joining
that point to the opposite pivotal axis; and each of the
plurality of link ends of the module being pivotally engageable
to one of the plurality of link ends of adjacent modules.
Furthermore the present invention may be seen to
provlde a linked belt assembly comprising: a plurality of links,
each having at least a pair of opposite link ends each circum-
scribing a pivotal hole centered about a respective one of a
pair of parallel pivotal axes, and a rigid intermediate section :
joining the link ends; the link ends having no driving engage-
ment with an associated sprocket wheel; each of selected ones
of the links having at least one driving tooth protruding
from the intermediate section substantially normal to the pitch
line between the pivotal axes and intermediate the pivotal Y
axes; the tooth having a pair of working surfaces, each of the
: ~ . working~surfaces having a shape in the range between and
~lncluding that of a cylindrical segment and a chord of the
segment; the axis of each working surface being parallel with
the pivotal axes of the link and positioned intermediate the
~; pivotal axes or coincident wlth the pivotal axis furthest from
that surface; a pair of working surfaces belng part of a pair
: of intersecting loci; the shape of each of the working surfaces
being such that the tangent angle of each such surface is not
more than 90, the tangent angle being defined between a tangent
.~ at a point on one working surface and a line joining that point-
to the opposite pivotal axis; each of the link ends of each
link being pivotally connected to a link end of adjacent links
by means extending through the holes; a toothed sprocket wheel
having recesses between adjacent teeth thereof, each of the
; recesses including a pair of facing surfaces of shape corres-
~ . q ~. .
~ sd ~ -6A-
~131937
,,
ponding to the pair o working surfaces of the driving tooth;
and only the teeth of the connected links being in driving ~
engagement with the recesses of the sprocket wheel, the engaged
linked belt and sprocket wheel exhibiting minimal scrubbing
action and chordal action.
For a fuller understanding of the nature and objects
of the present invention, reference should be had to the
following detailed description taken in connection with the
accompanying drawings wherein:
Fig. 1 is a perspective view of a typical link formed
according to the principles of the present invention;
Fig. 2 is an enlarged view of a section taken along
the line 2-2 of Fig. l;
Fig. 3 is a perspective view of a module formed of
~; links of Flg. l;
~- Fig. 3A is a top plan view of the module of Fig. 3;
Fig. 4 is a section taken along the line 4-4 of Fig.
3A;
Fig. S is a side view of a portion of a linked belt
20 ~ ; formed of the modules of Fig. 3, in engagement with a driving
sprocket wheel, shown only in fragment;
Fig. 6 is a front elevation view of a modification
~ of the module of Fig. 3, particularly adapted for use with a
;-~ V-sheave sprocket drive7 t~
Fig. 7 is a front elevation of the mirror form of
the module of Fig. 6;
Fig. 8 is a fragmentary showing of a V-sheave
, . - ::.
~- sprocket drive only taken along the line 8-8 of Fig. 5;
,
:
,;
,, .
~. .
~ sd/~ ~ -6B-
. . , : .
~`` 1131~37
Fig. 9 is an end view of yet another modification of a link
formed according to the principles of the present invention;
Fig. 10, appearing on the same sheet as Fig. 1, is an end view
of yet another modification of a link formed according to the principles
of the present invention;
Fig. 11, appearing on the same sheet as Fig. 1, is an end view of
an extreme form of a link formed according to the principles of the
present invention;
Fig, 12, appearing on the same sheet as Fig. 1, is an end view of
a double-toothed version of a link formed according to the principles of
the present invention;
Fig. 13A is a diagram showing the relation of the teeth of links
of the present invention to a sprocket wheel formed according to the
present invention;
Eig. 13B is a simplified version of the diagram of Fig. 13
shcwing the displacement of a link tooth and sprccket wheel through an
angle of 15 relative to the sprocket center line;
Fig. 13C is a diagram similar to Fig. 13A but in which the link
~' ~ tooth surfaces æ e not formed within the teachings of the present invention;
- ~ 20 Fig. 13D is a diagram similar to Fig. 13A but in which the
centers of curvature of the tooth faces are coincident with the pivotal
axes of the l mk7
Fig. 14 is a side view of a portion of a belt formed from the
modules of Fig~ 3 arranged to serpentine through a pair of counter-rotating
driv m g sprcckets;
Fig. 15, appearing on the same sheet as Fig. 1, is an end view
of yet another modification of a link of the present invention.
~; Fig. 16 is a diagram according to the present invention useful
~' in analyzing the chordal action of the belt and sprccket wheel of the
~, .
~ 30 present invention;
'~
~ sd~ ~7~
31937 1~
ll '
I Fig. 17 is a graph showing the chordal variations in velocity
lusin~ a twelve tooth sprocket wheel in the pres~nt invention.
In Fig. 1 there is shown a typical link of the present inven-
tion designated generally at reference numeral 21 formed as an '
elongated element having a pair of parallel side surfaces (only one~
of which is shown). A first link section or end 22 is formed to
circumscribe a pivot hole 24 having a central pivotal axis A nor-
mal to the axis of elongation of link 21, the opposite link section
or end 26 being similarly formed to circumscribe another pivotal ',
` hole 28 having a central pivotal axis B parallel to axis A.
Appended to and preferably formed integrally with link 21 is
included at least one driving tooth 32 which protrudes generally
~ in a direction perpendicular to the common plane through the
1~ ~ first and second pivotal axes A and B and intermediate, prefer- ¦
ably midway, between the latter. The side surfaces of tooth 32
are, in this embodiment, coextensive with and coplanar with the
corresponding side surfaces (such as surface 23) of link 21. As
shown particularly in Fig. 2, the faces of tooth 32 are formed
preferably of a pair of plano-convex, e.g. cylindrical surfaces
J~
20~ 34 and 35 which intersect one~another. Surfaces 34 and 35 are
9hown as substantially right-angled cylindrical segments having
like radii of curvature, the cylindrical axes or axes of rotation
Pl and P2 respectively of surfaces 34 and 35 being parallel to
one another and disposed between and in a plane parallel t~ or
1 1 coplanar with first and second pivotal axes A and B. For example,
as shown in Fig. 2, surface 34 has a radius of curvature Rl, the
origin or center of curvature lyin~ at axis Pl, here show~ disposed
~'
LC-22 - -8-
~, ~ - .. " . - .
~", . . .
~ "'` ' ~' " ,~
` i 1~937
between and intersecting pitch line L through pivotal axes A and B
of holes 24 and 28. Similarly, surface 35 has a radius of curva-
ture which is centered as axis P2 similarly intersecting line L
and lies between the centers of pivotal axes A and B of holes 24
and 28. It will be seen therefore that the intersection of sur-
faces 34 and 35 lies along a line I (shown as a point) parallel to
and equidistant from the first and second axes A and B, so that
tooth 32 is preferably bilaterally symmetrical about line I.
The configuration of surfaces 34 and 35 of tooth 32 shown in
1~0 Fig. 2 are not only plano-convex, but the locations of the axes of
curvature thereof are of great importance. Specifically, axis P2
is at some distance d from axis A and axis Pl is the same distance
from axis B, i.e. they are equidistant from the nearest respective
pivotal axis. Axes Pl and P2 are in a common plane parallel to or
coplanar with the common plane of axes A and B. For any point X
on surface 34, there is a tangent T which, of course, is a perpen-
dicular to Rl the radius of curvature of surface 34 to point ~.
;~ The location of axis PI must then he such that an angle ~ between
¦tangent T and line D, which extends from point X perpendicularly
to the pivotal axis (here axis B) nearest to axis Pl, is not more
than 90 when observed looking into the convex surface of the
opposite face (here surface 35). Because as noted, the tooth
is bilaterally s~mmetrical, this constraint a~plies also to the
location of axis P2 with respect to axis A and any point on sur-
face 35. If angle ~, hereinafter in this specification and claims
referred to as the tangent angle, is 90 or less for each tooth
surface, then as discussed hereinafter, the tooth will seat
in a corresponding groove of a sprocket ~heel without
scru~bing. Not only does the structure of tooth 32 provide
a non-scruh action, but when used with appropriate sprocket
wheels, typically a minimum of twelve or more grooves matched to
Il ~ 1131~337
tooth 32, chordal action is reduced very suhstantially over prior
roller chain structures formed of links 21, as will be described
hereinafter.
Reference is now made to Figs. 3 and 3A inclusive wherein
there is illustrated one embodiment of a chain link module.incor-
porating tbe principles of the present invention. This module,
generally designated at 20, is designed to be formed as an inte-
gral unit typically, but not necessaril~ of poly~eric material by
any of a numher of conventional molding processes. The polymer
used is preferably a glass-reinforced polyproo~lene, but many
other materials can be used as well. ~qodule 20 comprises a mul-
tiplicitv of elongated, parallel, spaced-apart, links 21 which
for the sake of convenience in illustration and exposition, are
. shown to be five in number, although it is to be understood that
the module can and frequently does, comprise a substantially
~:~: greater or lesser number of such links 21. All of links 21 have
substantially the same length and width, and thus the length di-
mension of module 20 is determined by the length of the individ-
ual links while the width o$ module 20 is determined by the
~: 20 number of links, their width and the spacing there~etween. In
: : : the embodiment shown in Figs. 3 and 3A, all of links 21 are
~: ~ preferably rigidly joined together and held in substantially
parallel relation by an integrally ormed intermediate section
30, thus forming a rigid, open or slotted structure in which the
parallel link ends alternate with slots 31. Alternati~ely, module
:~ 20 can be formed of a plurality of links 21 and requisite spacers
to provide slots 31, all held together mechanically as by adhesive
or the like. The length of each slot is at least equal to twice
the distance between the center of a hole such as 24 and the
LC-22 CIP -10-
~,,,,
` 1131937
distal extr~mity of associated link 22, there~y provi~ing suffi-
cient space into which a corresponding link end of another like
module can fit so that the respective holes in the fitted link
ends are registered with coaxial pivot holes. Link ends 22 and
26 are held spaced apart by ad~acent surfaces by a distance just
slightly greater (e.g. 0.~03 inches or less) than the width of the
link ends so that the link ends of each module may fit snugly but
movably between the link ends of an adjacent module with parallel
facing surfaces in contact with one another.
Thus, as shown particularly in Fig. 3A, the module includes
a first plurality of pivot holes 24 which are all aligned coaxially
along first linear pivotal axis "A" and a second plurality of
pivotal holes 28 which are similarly coaxially al1gned along
second linear pivotal axis "B", the ~irst and second linear axes
lS A and B being parallel to one another. The respective pluralities
of aligned pivot holes are intended to receive pivot rods or pins
which arle adapted to pivotally connect module 20 with like modules
nd-to-end while laterally aligning the adjacent modules. In the
~ mbodiment shown wherein module 20 is formed of integrally molded
- 20 together links 21 and intermediate section 30, the face width ofeach tooth 32 is selected so as to form an integral unit tooth
which extends across the entire width of module 20, i.e. from one
end element 21 to the other end element 21. This form of tooth 32
lends itself to ready molding in the formation of the modules and
provides a large and stable driving surface, as will be described
later herein. However, unit tooth 32 can be molded to be of some-
what different width than the width of module 20 between end ele-
ments 21 and can be formed, instead, simply as a plurality of in-
dividual, arranged teeth 32 corresponding to the respective links.
The modules, subject to the above-described constraints on
the geometry of the working surfaces of tooth 32, may take
a number of slightly different configurations. Some
examples of alternative configurations are shown
, . .
"
` i` 1131937
in Figs. 9, 10 and 15 wherein respectively the module of Fig. 9
includes a dished portion or concavity 36 in the portion thereof
opposite tooth 32, concavity 36 being in the form of a trough
having its long axis substantially parallel to linear axes A and
B through holes 24 and 28. A linked belt formed of the modules
of Fig. 9 would have a corrugated upper surface with the corru-
- gations extending in a direction substantially perpendicular to
the direction of belt travel, and for example, would provide
either a high speed drainage surface for some articles to be
conveyed thereon or a surface capable of engaging and carrying
:~
various articles of appropriate size. It will be seen that
`~ tooth 32 of the module of Fig. 9 is formed of a pair of surfaces
~ 34 and 35 in substantially the same manner as the tooth shown in
`;; Figs. 1, 3 and 4. However, it will also be seen that the apex
of tooth 32 in Fig. 9 however has been provided with a separate
radius of curvature so as to blunt the apex somewhat.
Alternatively, as shown in Fig. 10, faaes 34 and 35 are
cylindrical segments and the surface of the module opposite
tooth 32 is maintained as a substantially flat surface (at least
20~ along the link-like elements 21). However, the apex of tooth 32
'r~ has been truncated~as at 37;so as to provide a relief spacc with
regard to a prooket grOGve, or so that the teeth of the ~procXet
;~ can be shortened if desired.
In a modification of the module of Fig. 10 shown in Fig. 15,
;25 tooth 32 is faced with substantially flat surfaces 34A and 35A
which can be chords or part of chords of the cylindrical segments
.
;
.
-12-
''. ~ ,,~, : 11
, ''~' .
~ ~ ,
11 ; 1131937 l l
constituting faces 34 and 35 o, the device of Fig. 10. Surfaces
34A and 35A need not be flat bu~ can assume a curvature lying
between the cylindrical curvature o,' faces 34 and 35 of Fig. 10
and a plane forming a chord to ihat cylindrical curvature so long
as the tangent angle is not more than 90 as noted.
A plurality of modules 20 are assembled in end-to-end (and
if desired side-to-side) relation to form belt 36 (shown in
fragment) when connected by pivot rods 38 as shown in Fig. 5.
~ oles 24 of one module and holes 28 of the next module are ioined
by pivot rod 38 to create a pin-and-bushing type of joint. It
will be appreciated that intermediate section 30 as reinforced
by its connection with tooth 32 unctions to support elemenrs 21
against lateral forces tending to separate the links as well as
on twisting or bending forces on the modules which would tend to
shear pivot pins 38. To drive belt 36 formed by linking a
pluralit~ of modules 20 together with pins 38, there is provided
a simple sprocket wheel 40 shown oDly in fragment, sprocket wheel
¦having a plurality of radial teeth 42. Each groove defined by
surfaces 44 and 45 lying between adjacent teeth 42 are shaped to
¦mate, at least in major part, with the corresponding surfaces
34 and 35 of teeth 32, i.e~ surfaces 44 and 45 are cylindrical
egments which are the inverse of surfaces 34 and 35 respectively,
n that the former surfaces are concave where the latter surfaces
re convex. It will be appreciated that when a pair of modules
~25 20 are coupled to oné another by pivot pin 38 because the modules
re staggered the width of the co~bined modules is greater than
', . . . .
'., .
-13-
~ - 11
,, ,
,. ..
ll 1131937
the width of a single module by at least a width of one link-like
element 21. The axial width of the driving teeth 42 on sprocket
wheel 40 should therefore preferably have a width at least equal
to or greater than the width of the coupled modules.
As noted earlier, the curves employed in shaping tooth 32
and the matching sprocket serve to insure that the tooth faces
cannot rub or abrade the sprocket surface during entry to exit,
i.e. obviates scrubbing action, thereby minimizing wear and
permitting high speed operation.
~his can be demonstrated by a numerical analysis of the
- relationship between the position of arc centers for tooth pro-
file relative to link pivot points, and the scrubbing action
of belt links on the driving sprocket. Assu~e for example that
conveyor belt 36 approaches the driving sprocket wheel 40 and
15 ~ is supported upon carrying ways so that the centers of the pivot
rods 38 connecting the individual conveyor belt links 20 approach
wheel 40 on a horizontal line. When any pivot rod center reaches
; the vertical center line of the driving sprocket, it is fully
supported by the sprocket. Referring particularly to Fig~ 16A
2~0 ~ ~ (in which only teeth-32 are shown as part of a link, and teeth 32
re in truncated form as in Fig~ 15) it can be seen that pivot
od 38A i~ on the vertica} cen~er line CL 90 that tooth 32A is
fully seated in an appropria~e groove on sprocket wheel 40, while
tooth 32B is approaching wheel 40 and quite separate from the
latter. As the c-nter of pivot rod 38A is carried around the
:"'
~,
`.:'.,.- . . ,
-14-
` ~13~37
¦sprocket wheel, it follows a circular path P. Therefore, the
¦center of any pivot rod approaches the drivin~ sprocket on a
¦straight horizontal line L to the s~rocket vertical center line
¦CL then follows a circular path P at the pitch radius R around
S ¦the sprocket wheel.
¦ The vertical height of ~he center of pivot rod 38A above
¦the sprocket center is equal to the pitch radius R. Radius R
is determined by the conveyor belt pitch pt of 1.1811 inches
¦(30mm) and the number of teeth in the sprocket. For a 12-tooth
¦sprocket, pitch radius R is (1.1811/2)/sin 15 = 2.2817 inches.
¦This distance R is 1.93185 times the pitch. Conversely, the
¦pitch is .5176R for a 12-tooth sprocket. The radius to the pro-
¦file of the conveyor belt link was chosen as 0.748 inches. The
¦distance from the sprocket center to the line pt between centers
¦38A and 38B in Fig. 13A is 2.2817 cos 15 = 2.2040 inches. With
these factors known, it is possible to calculate the position of
a pivot rod center for any sprocket position or any point along
a straight line connecting the pivot rod centers of a conveyor
belt link. The reason for wanting to locate the position of
these points is that the centers of the arcs which define the
profiles of the conveyor belt link which engage the sprocket lie
along this line. For exemplary purposes, the centers for ~he
arcs which define the belt tooth faces or profiles have been
selected at a distance d which is one-quarter of a pitch in from
~25 the pivot rod centers or pivot points, so that the tangent angle
as noted is less than 90.
,, .
;~ -15-
~", 11
~,'
,,
~:
1~31937
~ext, consider the position shown in Fig. 13B, where the
pivot point 38A has advanced 15 with respect to Fig. 13A beyond
ihe vertical center line. The belt link center line pt connect-
ing the pivot points made an angle ~ with the horizontal line L.
The sine of the angle ~ is 1.93185(1 - cos a), where a is the
angle the line G connecting pivot point 38A and the sprocket
center makes with the vertical center line CL. For a = 15,
~ = arc sin 1.93185(1 - Cos 15) = 3.774. At a distance of
one-quarter the pitch left of pivot point 38A, i.e. at point H,
~ 10 the vertical distance below horizontal line L is .75(1.1811)
; sin 3.774 = .0583 inches. Point H is the center of the radius
to the tooth face or profile. The vertical distance to point J,
the center of the radius to the sprocket tooth face, from
horizontal line L is 2.2817 - 2.2040 or .0777 inches. This is
15 ~ .0194 inches below point H as as shown, tooth 32B will not rub
on the sprocket.
~;~ Next, consider the position shown in Fig~ 13C, again with the
; ngle a equal to 15. This time, the centers Of curvature for the
aces of tooth 32B are shown located one-quarter pitch outside
Z0~ the pivot points so that the tangent angle is greater than 90.
pgain~ ~ is 3.774 sinae a is ~till 15. Point H is 1.25(1.1811)
in 3.774 - .0972 inches below the horiæontal line. Point J
is 2.2040 inches above the sprocket center or .0777 inches below
he horizontal line. Therefore, point J is .0195 inches above
oint H. For this case, the link tooth face wCuld be theoretically
,
~,,..
~ -16-
11 1
,
, .' .
ll 1131937
below the sprocket tooth face. Since Ihis cannot happen prac-
tically, the link tooth face will rub on the sprocket tooth
face it drops into its seat (while the sprocket rotates 30),
and pivot point 38C will be lifted above horizontal line L.
As a fourth and final case, consider the position shown in
Fig. 13D. Again, the angle ~ is chosen as 15, but this time
the centers for the belt link tooth faces are selected in the
unique positions of exactly at the pivot points, and the tangent
angle equals 90. The distance o~ point H would be 1.000(1.1811)
sin 3.774 = .0777 inches below the horizontal line. Point J
would be 2.2817 - 2.2040 or .0777 inches below the horizontal
line. Therefore, point J and H would be coincidental, and
the link tooth face and the sprocke~ tooth face would be coinci-
dental. Theoretically r they would be in contact as the belt link
dropped into its sprocket seat, but with no rubbing pressure
between `the two.
As earlier noted, only the pivot points of the belt lie on
¦the pitch circle as they travel around the sprocket wheel, and
lines connecting the pivot points fall below the pitch circle.
The links approaching the driving sprocket, therefore, have a
; variable velocity characteristic of the chordal efect. The
belt made with links as hereinbeore described can be analyzed
for chordal effect by determining the distance traveled by a
ivot point as it approaches the driving sprocket for a small
angle of sprocket rotation~ `
I
~ -17-
11
~:
,
Il 113193'7
A twelve-tooth sprocket with a conveyor belt pitch of 1.1811
inches (30mm) will be assumed for this analysis as shown in Fig.
16 because, as well known, sprockels with more teeth will exhibit
less chordal aciion proporiionalely. The pitch radius R is again
assumed to be (1.1811/2)/sin 15 = 2.2817 inches, i.e. 1.93185
times ihe pitch. The angle ~ is ~he angle between an ex~ension of
the horizontal line L upon which ~he pivoi points approach and a
line pl connecting piVOI points 38A and 38B. The sine of Ihis
angle is 1.93185 (1 - cos ~) where ~ is the angle line G through
the sprockel center and pivot point 38B makes with the sprocket
verlical center line CL. The horizontal distance from che vertical
cenler line Ch to ~he pivot poin~ 38~ is Rsina. The horizontal
distance between pivot points 38B and 38A is Qcos~. Therefore,
pivol point 38A is shown at Qcos~ - Rsina to the left of the sprock ~t
; 15 vertical center line CL.
; To determine the velocity variation, the distance from pivot
~:
poinl 38A lo the sprocket vertical cenler line was calculated for
every two degrees of sprocket rotation and a plot of the velocity
varia~ion for about 30 of driving sprocket rotation is shown in
ig. 17.
With ~his analysis in hand, ic is seen that the conveyor
belt action and veloaicy variation are considerably different
from that of a roller chain running on a sprocket with the same
number of teeth. For example, a similarly dimensioned roller
~25 chain would rise and fall approaching a Iwelve-iooih sprocket,
and the velocity variation from chordal action would be about
7.2 percent. The preseni invention exhibits an improvement of
abou~ 700% over such a chain.
-18-
,- . .
1131937 ~ ~
In one particularly desir~ahle form of the present invention
as shown in Figs. 6 and 7, module 20 is formed with at least one
edge or end element 21 designated as edge guide 43 having a width
which is smaller at or near tooth 32 (the bottom portion as shown)
than at the top (as shown) so that the edge of end link or element
21 is tapered or beveled through an angle a as sho~m in Fig. 6.
A helt can then be formed of modules such as is shown in Fig. 6,
by providing that each alternative module is simply a reversed
form of the module of Fig. 6 so that edge guide 43 alternates
~10 from left to right along the belt. ~hen this belt is assembled
by joining the alternately reversed modules with pivot pins 38,
the cross section of the belt will have a ~7-shaped configuration,
thus providing a link belt which also then possess attributes of
V-belts. To drive such a link belt with a V-shaped configuration,
;~ sprocket wheel 40 of Fig. 5 can have the configration of a pitched
¦chain sheave~ such as is shown in Fig. 8 where the central hub or
sprocket with teeth 42 is disposed between a pair of circular
¦flange~s shaped as shallow conical discs 44. The conical angle
of discs 44 should be matched to the taper angle, u, of the module
~ ~ shown in Fig. 6 to gain the advantages of V-belts.
The links of the present invention, such as are shown in
Fig. 1 can also be assembled to form a belt in which only evexy
other (or third, fourth, etc.) pivotally coupled link (or
module as the case may be) ~ears a tooth 32 particularly when
the links or modules are very small. Further, one can assemble
.
'':.
~ -19-
, .... .
,
~ 113~37 ~
a belt in which teeth 32 do not necessarily all ~rotrude in the
same direction radially either inwardly or outwardly with respect
to the endless loop formed by the helt. For example, as shown
in Fig. 14, the links or modules formed therefrom may be assembled
so that teeth 32 protrude radially (with respect to the loop
formed by the belt) in alternately opposite directions. When
used with a pair of counter-rotating driving sprockets 4OA and
40B (similar to sprocket 40 of Fig. 5) the belt of Fig. 11 can
be driven along a tortuous or serpentine path with substantially
no slippage or power loss and therefore provides a very precise
timing belt. Alternatively, one can employ a double-tooth link
such as is shown in Fig. 12 which includes a second tooth 32A
extending on the opposite side of the module fram tooth 32 and
formed of two cylindrical surfaces centered on axes denoted as
P2 and Pl or even other pointæ.
As shown in Fiq. 11, when the pitch of a link (i.e. the dis-
tance between axes A and B) is sufficiently large in relation to
the thickness or height of the link, one can generate both sur-
faces 34 and 35 about a single axis shown as point P3 lying
~20 ~ equidistant between axes A and B. It will be apparent that the
closer to the midpoint between A and B one places the axes o
revolution of surfaces 34 and 35, the shallower will become toot~
~, 32 (the extreme case being the clrcular segment shown as tooth
32 in Fig. 11), but the tooth separation (i.e. the spacing be-
tween tooth and sprocket surfaces per angular degree of movement
of~ the link about either pivotal axis A or B) is maximized.
,.~ . .
:; ~
-20-
: 11 i
,
.
