Roller conveyor permitting low pressure accumulation of articles

A roller conveyor includes driven rollers, drive to which is transmitted through resilient drive belts looped about the rollers and about drive sleeves carried for rotation on and frictional engagement with a drive shaft, which extends longitudinally of the conveyor and adjacent the rollers. The drive sleeves consist of tubes carried on the shaft on nylon bush bearings and are restrained from axial movement along the drive shaft and the drive belts are in direct engagement with the surface thereof to assume a stable position thereon. When an article being transported is halted by external means the frictional drag between the bushes and the shaft is exceeded and the sleeve beneath the article and all associated rollers stall, thus preventing further articles being transported by those rollers.

This invention relates to roller conveyors used for transporting individual 
articles and is particularly concerned with a method and apparatus for 
allowing low pressure accumulation of articles to occur. 
Roller conveyors, in which rollers are driven by external means, frequently 
continue to transport articles even after one article has been stopped for 
example by becoming jammed against the side of the conveyor. As a result 
succeeding articles join the stoppage and are subjected to pressure from 
behind which can result in the build up of damaging pressure against the 
original stoppage. In order to clear such a stoppage it is generally 
necessary for the whole length of the driven conveyor to be stopped. The 
present invention is directed to preventing such an undesirable build up 
of pressure by providing for a section of the conveyor including a group 
of rollers adjacent the stoppage to be stalled thereby preventing further 
articles entering that section and allowing a low pressure accumulation of 
articles to occur. 
Accordingly the present invention provides a driven roller conveyor 
comprising a frame, a plurality of rollers carried by said frame for free 
rotation therein, a drive shaft supported for rotation and extending 
adjacent said rollers and at an angle thereto, drive means to drive said 
drive shaft and means acting between the drive shaft and at least a 
proportion of said rollers adjacent therewith to drive said rollers, 
characterised in that said second mentioned means comprises a plurality of 
sleeves rotatably mounted on said drive shaft for frictional engagement 
therewith, said sleeves being restrained from movement axially along the 
drive shaft and said means further including resilient drive belts looped 
between the sleeves and at least a proportion of the adjacent rollers and 
acting directly on the surface of said sleeves, each said sleeve being 
adapted to drive at least two rollers adjacent therewith. 
The invention further provides a method for transporting articles wherein 
the articles are carried by the rollers of a driven roller conveyor, at 
least a proportion of which rollers are driven by resilient drive belts 
frictionally connected to a common drive means running at an angle to the 
rollers, characterised in that the drive means consists of a plurality of 
drive sleeves rotatably carried on a drive shaft and powered by the 
frictional resistance between the sleeves and the shaft, each sleeve being 
arranged to drive a section of the conveyor including at least two driven 
rollers and being restrained from axial movement along the drive shaft, 
said drive belts being looped about the rollers and sleeves and acting 
directly on the surface of the sleeves, stoppage of an article being 
transported causing the drive sleeve immediately below the said article 
and all rollers associated with said sleeve to stall, thereby preventing 
further articles from entering that section of the conveyor. 
In a preferred embodiment each sleeve is associated with a group of rollers 
including at least two and up to about eight or more said rollers, the 
sleeve may be connected to each roller in the said group by a tensioned 
drive belt or only to certain of the said rollers, for example alternate 
rollers, provided that the last roller in each group is a driven roller 
connected directly or indirectly to the sleeve by a drive belt, e.g. the 
last roller may be driven by a belt looped about an adjacent roller which 
is driven by the drive sleeve. 
The rollers may each have an associated drive-pulley about which the drive 
belt is looped, or they may each contain a circumferential groove at or 
near one end arranged to receive the said drive belt. 
The drive to the rollers is by frictional drag acting between the drive 
shaft the rotatable sleeve, the tensioned drive belt and the rollers. 
The invention takes advantage of the fact that only small forces acting on 
the conveyor rollers are necessary to cause an article, such as a package, 
placed on drive rollers to be moved and transported along a horizontal 
plane. 
The material forming the rotatable sleeve and the tension in the drive belt 
are therefore arranged to provide sufficient friction between the driving 
components to transmit a force to the rollers which will cause a package, 
of maximum weight for which the conveyor is designed, placed on the 
conveyor to be transported between driven rollers. That is, the frictional 
resistance between the drive shaft and the sleeve must be just greater 
than the rolling resistance of the rollers. Generally this is achieved by 
forming the sleeve of low-friction material or by using a continuous or 
discontinuous lining on the inside surface of the sleeve or the outside 
surface of the drive shaft. Preferably the sleeve is a steel tube carried 
on the drive shaft by low friction bearing bushes at each end. 
The friction drag existing between the rotatable sleeve and the drive shaft 
and therefore the maximum force available for driving the rollers, can 
additionally be controlled by varying the diameters of the sleeve and/or 
drive shaft to change the arc of contact therebetween of varying the belt 
diameter or initial tension. 
We have found that when a package, being transported by the conveyor of the 
present invention, is stopped at some point along the conveyor, the 
frictional resistance between the package and the rollers is sufficient to 
bring the driven rollers in contact with the package at that point to 
rest. Because of the low friction existing between the sleeve and the 
drive shaft rotation of the sleeve is also arrested with the result that 
all of the rollers in the group being driven by that particular sleeve 
also stop. 
The package being transported by the next adjacent up-line group of rollers 
is then moved onto the stationary rollers and stops without colliding with 
the already stationary package. Either that second package, or the next 
succeeding package in line, will then cause the said next up-line group of 
rollers to be arrested. Packages thus accumulate in a spaced-out 
arrangement without damaging collisions occuring. 
When the resistance to movement of the first package is removed, 
transportation of the accumulated packages restarts. 
The conveyor may include means to permit sections of the conveyor to be 
selectively halted by providing a non-rotatable friction member capable of 
bearing against a sleeve, or against drive belts acting on the sleeve, 
with sufficient pressure to provide a force exceeding the frictional 
resistance between the sleeve, or the low friction bearings carrying the 
sleeve, and the drive shaft to cause the sleeve and associated rollers to 
stall.

The conveyor comprises a plurality of rollers 1 to 6 mounted for free 
rotation in a frame member having parallel support members 10 running the 
length of the conveyor. 
A drive shaft 20 is located at right angles to the rollers 1 to 6 and runs 
parallel with the frame member being supported in bearings 21 carried on 
cross members 22 positioned along the shaft at distances of one meter 
apart. Midway between each bearing the shaft carries an integral collar 
portions 23 which substantially increase the diameter of the shaft at that 
point, the collar including two flat faces 24 and 25. 
Steel drive sleeves 26, 27 and 28 each defining a section of the conveyor, 
are carried by the drive shaft and supported thereon by nylon bushes, 30, 
31, 32 and 33 and having flanges 34, 35, 36 and 37 respectively. The 
bushes are mounted on the drive shaft for slipping engagement therewith. A 
running clearance only is provided between flanges 34 to 37 and the faces 
of the collars 23 or bearings 21. 
In this embodiment each section of the conveyor includes six rollers driven 
directly from the sleeves as hereinafter described. 
Rollers 1, 3, 4 and 6 each contain grooves 7 which are in alignment with 
the drive shaft. Drive is transmitted from the drive sleeves 26, 27 and 28 
to the rollers by means of twisted drive belts 8 which are located in 
grooves 7 of the rollers and are in direct contact with the surface of the 
drive sleeves. 
Rollers 2 and 5 are slave rollers being positioned over a bearing (21) or a 
collar (23). These rollers include grooves 9 (not shown) corresponding to 
an equivalent groove 9' included in rollers 3 and 4 and are driven by 
drive belts 11 from rollers 3 and 4. 
Drive shaft 20 is driven by any conventional means (not shown). When a 
conveyor is running under "no load conditions" i.e. not transporting any 
articles, the frictional resistance between the shaft 20 and for example, 
the bushes 31 and 32 supporting the drive sleeve 27, the sleeve 27, belts 
8 and rollers 3 and 4 is sufficient to cause the rollers to rotate at a 
constant speed, the tension in both legs, (8a and 8b) of belts 8 being 
equal. 
When a load is placed on the conveyor for example a package "A" the 
frictional resistance between package "A" and the rollers tends to cause 
the rollers with which it is in contact to stall and increased drive power 
is required for the rollers to transport packages. To provide this 
increased power the tension in the drive belts 8 increases. This increase 
initially takes place in the downward moving leg, 8b of belt 8, (referring 
for example to roller 3) with a reduction in tension of the upward moving 
leg 8a. To compensate for this imbalance in tension in the legs of the 
belt, the belt tends to creep along the drive sleeve in the direction as 
the rotation of the rollers until the tension in both legs equalises at a 
higher level than under no load conditions. The rollers are then able to 
move the packages forward at the same speed as the rotation of the 
rollers. The effect of an increase in tension of the belt is to pull the 
drive sleeve 27 and bushes 31 and 32 against the drive shaft 20, thereby 
increasing the frictional resistance between the shaft and the bushes 
reducing any tendancy to slip. The movement of the belt acting on the 
sleeve also increases the force acting longitudinally of the sleeve in the 
opposite direction to the direction of rotation of the rollers the result 
of which, for example, is to cause sleeve 27 to move towards collar 23 
causing the flange of bush 32 to press against face 25 of collar 23, 
thereby providing extra drive to the sleeve. 
It is clear, therefore, that the sleeves should be restrained from any 
tendancy to move axially along the drive shaft. If such movement were 
permitted the forces acting longitudinally of the sleeve would cause the 
sleeve to move along the shaft rather than the belt being permitted to 
creep along the sleeve. 
It can be readily understood that the greater the tension in the belts the 
greater the forces acting on the bushes and flanges to increase the 
frictional resistance between the bushes and the drive shaft. However 
because the bushes are made of a low friction material, nylon, a point is 
reached when the forces acting on the drive sleeves exceed the frictional 
resistance between the bushes and the drive shaft. At this point slippage 
occurs between the bushes and the drive sleeves and rollers associated 
therewith are stalled. The drive shaft 20 continues to rotate however and 
drive other sleeves and rollers associated therewith. 
Such a situation will occur if package "A" is obstructed during its 
movement along the conveyor and caused to stop, or an operator is in 
contact with the moving parts of the conveyor. The pressure acting on 
rollers 2 and 3 for example, derived from the frictional resistance 
between the rollers and the package, is then sufficient to overcome the 
frictional resistance between bushes 31 and 32 and drive shaft 20 with a 
result that sleeves 27 and rollers 2, 3, 4 and 5 are stalled and that 
section of the conveyor is halted. Since the sleeve 27 is no longer 
rotating with the shaft 20 the natural hysteresis in the drive belts 8 
causes them to creep back along the sleeve to their initial position, 
releasing the tension in the belts and thus reducing the pressure acting 
on the stationary package. 
A second package "B" being transported by rollers associated with drive 
shaft 28 passes from the last of those rollers, 6, onto the stationary 
rollers 4 and 5 and stops. Since packages "B" has stopped whilst still in 
contact with roller 6 that roller also stalls and causes sleeve 28 and the 
remaining rollers associated therewith to stall also thus halting the next 
adjacent section of the conveyor. 
Any succeeding packages moving along the conveyor are also stopped, halting 
further sections of the conveyor and a line of stationary packages builds 
up i.e. a low pressure accumulation of packages occurs. 
As soon as the obstruction is removed from in front of package "A" the 
force acting on rollers 1, 2 and 3 causing their rolling resistance to 
exceed the frictional resistance between sleeve 27 and drive shaft 20 is 
reduced, sleeve 27 is therefore again enabled to drive the rollers and 
packages "A" or "B" and forwarded along the conveyor. As a result sleeve 
28 again provides drive for roller 6 and the other rollers in that section 
permitting the next package upstream to be forwarded and so on until the 
whole line of packages is again moving along the conveyor. 
It can be appreciated that if the number of slave rollers in each section 
of conveyor is increased then power available for transporting packages is 
reduced. By the same token the force necessary to stall a section of 
conveyor is also reduced. Thus the conveyor can be designed to transport 
light weight packages but to operate as described above.