Spiral conveyor belt with ridged drive capstan

In a low tension spiral conveyor belt system, driving assistance is provided between the driving cage or capstan and a plastic conveyor belt via ridges formed generally vertically on the bars or caps on the cage bars. These ridges, preferably rounded at their exterior surfaces, interact with grooves provided in inner edge members of the belt, or with gaps between successive edge members. As the belt progresses up the spiraling incline of the system, the drive capstan ridges seat in belt grooves or gaps for a short period of time, assisting in driving engagement, then advance forward out of the groove due to the overdrive relationship of the capstan to the belt.

BACKGROUND OF THE INVENTION 
This invention is concerned with conveyor belts, and in particular the 
invention relates to a spiral conveyor belt driven in part by a driving 
tower or cage, and to improvement in driving engagement between the 
driving cage and the upwardly spiraling belt. 
In a related patent, U.S. Pat. No. 5,069,330, assigned to the assignee of 
the present invention, a spiral conveyor belt system was disclosed wherein 
an edge member or side plate includes one or more generally vertical 
grooves formed in its outer side. These vertical grooves were positioned 
to engage with protruding structure of cage bars of a spiral conveyor 
driving cage. The modular plastic conveyor belt had recessed rod heads on 
the connecting rods, and at least one of the generally vertical grooves 
was preferably positioned coincident with the rod head recess. The driving 
cage was disclosed as including ridges or protrusions, preferably formed 
in cage bar caps assembled onto the exterior of the cage bars. At any one 
time, at least some of the protrusions on the cage bars are engaged in 
grooves of the side plates, providing assistance in the driving of the 
spiral conveyor belt by the driving cage. 
Other approaches have been suggested for providing more positive gripping 
engagement or "positive drive" between a driving cage and a spiral 
conveyor belt, particularly for high speed spiral conveyors. See Irwin 
U.S. Pat. No. 4,941,566, Roinestad U.S. Pat. No. 4,741,430 and Roinestad 
U.S. Pat. No. 4,852,720. The Irwin patent describes jackets or caps for 
the cage bars of a driving cage, which are rectangular in cross section. 
These caps provide grooves at the outer side of each driving cage bar. The 
grooves cooperate with steel connecting rod heads of a metal spiral 
conveyor belt. Although not every rod head becomes engaged in a cage bar 
groove, due to phase shifting in the spacings involved, some of the rod 
heads do become engaged. The rod head and groove arrangement is supposed 
to provide some driving assistance and establish less slippage of the 
spiral conveyor belt against the driving cage, which moves 
circumferentially faster than the belt in "overdriving" relationship. 
The Roinestad patents disclose another type of "positive drive" for a 
spiral conveyor system. In the Roinestad patents, cage bar caps include 
linear vertical protrusions positioned to engage against protruding rod 
heads in a metal spiral conveyor belt. The vertical driving protrusions of 
the cage bar caps are square in cross-section and are intended to grip 
against the protruding belt rod heads and thus drive the belt, or a 
portion of the belt, at the same speed as the driving tower for a certain 
period or arc of movement. Since a spiral conveyor belt rises as it 
progresses, the rod heads in the Roinestad arrangement were to ride up on 
the cage bar protrusions until they were released at a vertical gap or 
interruption in the vertical protrusion of the cage bar. This would 
release the rod heads and allow the rod and belt edges to spring back, 
then subsequently engage a second, different cage bar protrusion farther 
back than the first. In this way, the Roinestad "positive drive" 
arrangement was intended to intermittently drive groups of protruding rod 
heads at the same speed as the driving tower. Thus, there would be a dwell 
time during which rod heads would be forced to travel with the bars of the 
driving tower, then the differential speed would cause a snapping or 
jerking disengagement, which was intended to occur at the vertical gap in 
the cage bar protrusion. 
It is a principal purpose of the present invention to provide improved 
driving engagement between a spiral conveyor driving cage and a plastic 
conveyor belt, with structure which is relatively simple and advantageous 
over prior apparatus aimed toward the same purpose. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, cage bars or cage bar caps are 
provided having generally vertical ridges or protrusions which are 
configured to cooperate with the grooves of plastic conveyor belt edge 
members or side plates as disclosed in U.S. Pat. No. 5,069,330. These 
protrusions, preferably provided on cage bar caps, function in the manner 
disclosed in U.S. Pat. No. 5,069,330, cooperating with the belt edge 
grooves by seating in grooves as the overdriving capstan or drive cage 
advances along the belt. They are fully seated in a groove momentarily or 
for a short period of time before advancing out of the groove. The cage 
bar protrusions or ridges preferably are shaped complementarily to the 
grooves of the belt edge, in a rounded or partial-cylindrical shape. No 
gaps in these cage bar protrusions or ridges need be provided. 
It is therefore among the objects of the present invention to enhance the 
driving relationship between a driving cage and side plates or edge 
members of a plastic modular conveyor belt in a spiral conveyor belt 
system, and to make less critical the speed relationship between an 
overdriven cage and a belt, this being accomplished through the provision 
of ridges on the driving cage and grooves at the edge of the belt. These 
and other objects, advantages and features of the invention will be 
apparent from the following description of preferred embodiments, 
considered along with the accompanying drawings.

DESCRIPTION OF PREFERRED EMBODIMENTS 
In the drawings, FIG. 1 shows a side plate 10 formed according to the 
principles of the present invention. The plastic side plate 10 is adapted 
for inclusion as a side member in a modular plastic conveyor belt, 
particularly such a belt as used in a spiral conveyor belt system. The 
side plate 10 as conventionally used on a spiral conveyor belt system 
provides a surface 12 for engagement against the driving cage bars of the 
driving cage or driving tower. In U.S. Pat. No. 4,901,844, for example, 
these side plates were disclosed as having recesses or countersink bores 
for receiving the plastic rod heads of the modular conveyor belt, in order 
to prevent excessive wear on the rod heads in the spiral system. 
In the present invention, as shown in FIG. 1, the rod bore 14 of the side 
plate 10 also has a countersink or recess 16. This is formed in the outer 
cage-engaging surface 12, which is on an outer leg 18 of the side plate as 
shown. A second leg 20 is inwardly offset and has a slot 22 which provides 
for expansion and collapse of the plastic conveyor belt in straight and 
curving paths. A central angled portion 24 of the side plate 10 connects 
the two offset legs 18 and 20 together. 
In the side plate and system of the present invention, a groove o slot 26 
is formed generally vertically in the driving engagement face 12 of the 
side plate, i.e. generally transverse to the length of the side plate. As 
indicated, the groove 26 preferably is formed on a common center with the 
rod bore and countersink 16. Preferably the groove is rounded as 
illustrated, for smooth entry and exit of a cage bar protrusion or a 
protrusion or ridge formed on a cage bar cap. 
It should be understood that one or more additional grooves or slots 26, 
similar to the groove 26 shown, can be provided in the outer surface 12 of 
the side plate 10. Such additional groove would be spaced from and 
parallel to the groove 26, although not formed at the location of any bore 
or countersink. The groove not located at the countersink could be the 
sole groove. 
FIG. 2 shows another side plate 30 in accordance with the principles of 
invention. The side plate 30, which may be of a longer length or pitch 
than the side plate 10 of FIG. 1, is shown with a groove or slot 32 
similar to that of the side plate 10, that is, the groove 32 is formed on 
a common center with a rod bore 34 and countersink or recess 36. However, 
FIG. 2 also shows an additional groove or slot 38, similar in shape, 
spaced from and parallel to the groove 32. This groove 38, as mentioned 
above, is not formed at the location of any bore or countersink. The 
groove 38 could be the only groove if desired, or several grooves can be 
located outside the countersink. 
FIG. 3 is a sectional plan view, showing a series of side plates 10 of the 
type shown in FIG. 2 engaged against a cage bar 40 according to the 
present invention. The side plates 10 are part of a modular plastic 
conveyor belt, the remainder of the belt not being shown in FIG. 3. The 
side plates 10 are at the inside of a curve of the conveyor belt, i.e. 
that side of the belt which engages against the driving tower or cage as 
the conveyor progresses in a curving and spiral path around the driving 
tower. 
In FIG. 3 a driving cage bar is shown generally identified by the reference 
number 40. The cage bar 40 has one or more bumps or vertical extending 
protrusions or ridges 42, which may advantageously be formed in a cage bar 
cap 44 which is fitted over and secured to a metal cage bar 46 inside. As 
indicated, the protrusions 42 of the cage bars engage in the generally 
vertical grooves 26 of the side plates 10, which may be rounded as shown. 
Generally, the spacing between cage bars 40 is greater than the spacing 
between successive side plates 10 in the conveyor belt; thus, not every 
side plate 10 will be engaged by a driving cage bar at any given instant. 
Often even a pair of successive cage bars such as the cage bar 40 and the 
cage bar 40a shown in FIG. 3 will have bumps 42 that do not both engage 
side plate grooves simultaneously. However, a sufficient number of the 
bumps or ridges 42 will be engaged in side plate grooves at any given 
instant, that a significant driving engagement assistance results. Since 
the driving cage is used in an "overdrive" condition, wherein the driving 
cage rotates slightly faster than the movement of the spiral conveyor belt 
itself, the bumps 42 will engage in grooves 26 only momentarily, and will 
engage in different side plate grooves successively over time. This 
momentary engagement is different from the engagement over a prescribed 
dwell time as in the Roinestad patents described above, with the resulting 
tension forces such dwell induces in an overdriven belt. 
In FIG. 3 two grooves 26 and 48 are shown in each side plate. In this case, 
the cage bar cap 44 can have either one or two ridges or protrusions 42. 
If two are included they should be at the same spacing as the grooves 26 
and 48. 
The cage bar caps 44 may be produced from plastic, for optimum frictional 
engagement with minimum wear. However, other appropriate plastics may be 
used if desired. 
FIG. 4 shows another embodiment of the invention, wherein integral side 
plates 50 of conveyor belt modules 52 are used and are each provided with 
at least one cage bar driving engagement groove 54. The module 52 with the 
integral side plate 50 may be as described in copending application Ser. 
No. 594,623, filed Oct. 9, 1990 and commonly owned with the present 
invention, now U.S. Pat. No. 5,181,602. The module 52 includes oppositely 
extending projections 53 and 55. It should be understood that "side plate" 
as used herein and in the claims refers to the side plate 10 or 30, or the 
side plate 50. 
As indicated, the generally vertical grooves 54 on the integral side plates 
50 are preferably positioned across and concentrically with rod bores 56 
and countersink recesses 58. The operation of the embodiment of FIG. 4 is 
similar to that described above. The groove 54 may be located other than 
over the countersink bore if desired, provided the side plate has 
sufficient thickness at the selected location. 
FIG. 5 shows another spiral conveyor driving arrangement involving a belt 
with similar side plates 10 to those shown in FIG. 1, with a single groove 
26 positioned concentrically with the rod bore. In this driving 
arrangement, the cage bars 60 of the driving cage are positioned 
angularly, such that a vertical edge 62 of each bar acts as a protruding 
ridge for engagement with the conveyor belt. The protruding edge 62 may be 
rounded or radiused (as shown at 62a) for engagement in the side plate 
grooves 26 of the conveyor, in accordance with the principle of momentary 
engagement and smooth entry and exit of the edges or driving protrusions 
in the grooves. The angling of the driving cage bars 60 eliminates the 
need for any cage bar capping having ridges or protrusions. 
FIG. 6 shows a cage bar cap 44 in perspective, indicating that the 
protrusions 42 may be in the form of continuous vertical ridges, formed by 
extrusion of the cap 44. As noted above, these ridges have smooth, 
generally rounded exterior contours in the lateral direction, i.e. as 
viewed from above or in sectional plan view. This in combination with the 
generally rounded grooves in the side plates 10 or 50 assures smooth entry 
and exit of the ridges with the grooves, for momentary engagement, without 
hard snagging and with a simplicity and smoothness of operation. Even if 
the cage bar ridges or protrusions are used with a belt not having the 
illustrated grooves the rounded contour of the ridges will engage gaps 
between successive side plates or plastic modules (see the gap 64 in FIG. 
3) with smooth, non-snagging entry and exit. 
FIG. 7 shows in perspective an alternative form of cage bar cap 65, similar 
to the cap 44 of FIG. 6 but having a single vertical ridge or protrusion 
66. 
It is therefore seen that the improved cage bar and cage bar cap 
construction and the system of the invention, including both the side 
plates and the cage bar caps, significantly improve the driving engagement 
between a driving cage and a modular plastic spiral conveyor belt. The 
engagement apparatus of the invention is used in an overdriving spiral 
system, and it makes less critical the speed relationship between the 
overdriven cage and the belt. Overdrive is required, but the degree of 
overdrive is more flexible with the system of the invention. 
The above described preferred embodiments are intended to illustrate the 
principles of the invention, but not to limit its scope. Other embodiments 
and variations to these preferred embodiments will be apparent to those 
skilled in the art and may be made without departing from the spirit and 
scope of the invention as defined in the following claims.