DRIVE SYSTEM FOR AN ENDLESS BELT AND A CONVEYOR SYSTEM INCORPORATING THAT DRIVE SYSTEM

Abstract: A drive system for an endless load-carrying belt comprises one or more drive stations adapted to propel the belt characterised in that at least one of the drive stations comprises a plurality of rollers (2) adapted to rotate about their longitudinal axes and to engage the belt (1) directly and to propel the belt (1), the rollers (2) having their axes of rotation within ± 20° of normal to the plane of the belt (1) at the point of contact when the belt (1) is in position, with the proviso that where the belt (1) is to travel around a path having one or more curves in the plane of the belt, at least one of those curves is provided with a drive station as defined above; and a conveyor system, notably one following an helical path through a food processing proccss, incor­ porating such a drive system.

Description: The present invention relates to a drive system for an endless belt and a conveyor system incorporating that drive system, notably to a conveyor system for use in a food processing operation. In freezing foodstuffs, the items of food are usually placed on a moving belt which is moved through a freezing station. Whilst the belt can be a linear belt, it has been proposed to cause the belt to follow a helical path through the freezing station around a central rotating drum. The frictional contact between the drum and the edge of the belt carries the belt around the drum in a similar way to that in which a rope is carried by a capstan drum. Typical of such a system is that described in British Patent No 1090630. However, in such a system the drive drum occupies a comparatively large volume of the whole freezing station and it is necessary to support the belt as it is carried vertically up, or down. Such support must be provided from the outer periphery of the belt by cantilever arm supports which are often of comparatively massive construction and which reduce the usable headroom above the surface of the belt. It has therefore been proposed, for example in BP 1420576, to form the belt with lateral walls so that the walls on one tier of the belt rest on and are supported by the walls of the tier below. The belt thus forms a self-supporting coil carried by a basal drive and support member. However, such a construction is costly and can cause problems with adequate circulation of air over the items carried by the belt. It has also been proposed in US Patent No. 3682295 to drive the belt by means of an intermediate belt carrying radial lugs on which the main belt rests. The intermediate belt is driven by means of a series of wheels engaging the inner surface of the intermediate belt and arranged around the arc of the curve which the intermediate belt follows. However, such a construction is complex and costly and the drive system for the intermediate belt occupies the area within the spiral path of the main belt. Also, the supports for the intermediate belt require considerable headroom between each successive level of the main belt. Such a system has in practice not proved feasible for multi-tier use and its commercial use has been restricted to the driving of the feed or off-take sections of a main belt being driven by a drum as in BP 1090630. We have now devised a form of drive system which, whilst retaining the low belt tension which is achieved using the above systems, reduces the problems encountered in the prior art. In the drive system according to the invention, the single drive drum used hitherto at each 180 0 or 360 curve in the path of the belt is replaced by a plurality of smaller drive rollers engaging directly with the edge of the belt. These rollers drive and support the belt and achieve a low tension drive system, but enable the belt to be supported from both sides without the use of space consuming cantilever or other supports; and also enable the volume hitherto occupied by the single drive drum or the intermediate belt drive system to be used to locate the heating or cooling mechanism, thus leading to a more compact system. By using a direct drive between the rollers and the belt a simple and effective system is achieved with we believe reduced power consumption. The drive system of the invention can be used to propel conventional belts along substantially straight paths, in which case the drive systems can be located at intervals along the run of the belt and thus reduce the overall tension in the belt. However, the drive system finds especial use where the belt follows a path which is curved in the plane of the belt, e.g. the belt travels around a helical or dog-leg path. In this case, at least one and preferably each curve in the path is provided with a drive system of the invention. Thus, the present invention provides a drive system for an endless belt adapted to carry articles through a path which system comprises one or more drive stations adapted to propel the belt characterised in that at least one of the drive stations comprises a plurality of rollers adapted to rotate about their longitudinal axes and to engage the belt directly and to propel the belt, the rollers having their axes of rotation generally, e.g. within +200 of, normal to the plane of the belt at the point of contact when the belt is in position, with the proviso that where the belt is to travel around a path having one or more curves in the plane of the belt, at least one of those curves is provided with a drive station as defined above. The present invention also provides a conveyor system which comprises an endless belt adapted to carry articles through a path, the belt being adapted to be propelled parallel to its plane characterised in that the belt is provided with one or more drive stations, at least one of which comprises a plurality of rollers rotatable about their longitudinal axes, which rollers engage directly with and are adapted to propel an edge of the belt, the axes of rotation of the rollers being generally, i.e. within +200 of, normal to the plane of the belt at the points of contact. Preferably the belt is one which can be longitudinally collapsed across its width so that the belt can be curved in its plane and the path which the belt follows is preferably one containing at least one curve. In this case there is provided at that curve a drive system of the invention. Accordingly, the present invention further provides a conveyor system which comprises an endless belt which is adapted to carry loads and is progressively longitudinally collapsible across its width, whereby it can conform to a path having curves in the plane of the belt, which belt is formed into a circuit having one or more curves in the plane of the belt characterised in that at least one curve of the belt is provided with a drive station comprising a plurality of rotatable drive rollers which engage directly with and are adapted to propel an edge of the belt, the axis of rotation of the rollers being within +20 of, normal to the plane of the belt at the points of contact. Preferably the drive rollers are located at the inner radius of each curve in the path through which the belt travels and act also to support that edge of the belt with which they engage. To aid understanding of the invention it will now be described with respect to a preferred form thereof shown in the accompanying drawings in which: Figure 1 is a plan view of a typical assembly; Figure 2 is a side elevation of the assembly of Figure 1; and Figures 3 and 4 are detailed views of parts of the assembly of Figure 1. A collapsible belt 1 is caused to travel around a generally helical path. The path need not be of oval plan as shown in Figure 1, but could be circular or of a more complex and convoluted form. However, it is preferred to have a simple path in which the belt is carried through several complete turns of 3600, e.g. 3 to 40 turns, around the vertical axis of a substantially symmetrical e plan-view path. The belt 1 is of any suitable form, e.g. - a chain link, slatted or corrugated rubber belt, which can collapse longitudinally along its inner edge to follow a curved path. Preferably, the belt is made from stainless steel or plastic-coated metal and many suitable forms are commercially available. A particularly suitable form comprises a series of rods or bars linking two collapsible chains which form the outer edges of the belt. The bars can carry a mesh or expanded metal platform to provide a plane surface to the belt. Such a belt can be collapsed along one edge to adopt an arcuate form as shown in Figure 4, the radii of curvature of the edges of the belt having a common centre. Typical of suitable belts for present use are those sold by Ashworth Brothers Inc of the United States of America. In the present invention, the central drive drum used hitherto is replaced by a series of smaller drive rollers 2 disposed around the inner radius of the path around which the belt is carried. We prefer that the rollers 2 are mounted at 5 to 200 intervals along each curve to provide a smooth carriage of the belt around each curve of the path. However, larger intervals between rollers may be acceptable. We prefer that the rollers are arranged so that the belt travels around each curve with its outer edge 3 fully extended and its inner edge 4 fully collapsed. The rollers serve to support the belt radially as it travels around the arc of the curve and also to drive the belt. Each roller can be driven, e.g. by suitable chain drive, belting or gearing from a prime mover (not shown). However, if desired some (e.g. every other one) of the rollers can be undriven and merely act as idling supports. The rollers can take the form of simple cylindrical rollers or can be provided with longitudinal ribs or flutes which support the belt and act as drive ribs. If desired the roller or its ribs or flutes can be given an anti-slip coating where excessive slip between the roller and the belt might otherwise occur. Thus, a stainless steel roller can have high density polyethylene ribs affixed thereto, or be fitted with a rubber sleeve. However, we prefer to form the roller from a material with a high co-efficient of friction, eg an hard nylon. As shown in Figure 2, we prefer that the belt follow a generally helical path, for example with the belt rising (or falling) as it travels through each curve and remaining level between the curves, or vice versa. To achieve a rise or fall of the belt through each curve the longitudinal axes about which each roller rotates can be inclined, e.g. at from 5 to 100,,to the vertical. Where the axes are inclined toward the centre of the arc of the curve, the belt will ascend as it travels around the curve, and when outward the belt will descend. Alternatively, the rollers can be formed as frusto cones and rotate about substantially vertical axes to achieve a similar effect. However, a particularly preferred form of roller is that shown in Figure 3 and comprises a substantially cylindrical roller mounted with its longitudinal axis of rotation substantially vertical. The surface of the roller is provided with circumferential grooves 5 or ribs 6 to form circumferential recesses adapted to receive the inner edge 4 of the belt. If desired, the recesses can be provided with an annular rubber or similar sleeve to improve the frictional contact between the roller and the edge of the belt. The recess serves the function of providing the drive surface of the roller and also acts to support the inner edge of the belt. In order to achieve a rise of the belt as it travels around a curve, the recesses on successive rollers on that curve can be formed higher up the roller; or rollers of essentially identical construction can be mounted at progressively increasing heights around the arc of the curve. If desired, support members can also be provided between rollers to provide additional support to the belt. Also,the surface of the recess which supports the belt can be shaped so as to maximise the area of contact between the roller and the belt. The outer edge of the belt also requires to be supported. This can be achieved by providing support fingers or rails 7 under each tier of the belt or by providing the belt with upstanding lateral walls as in BP 1420576 to form a self-supporting stack. Alternatively, a series of rollers similar to those used at the inner radius of the curve can be used. If desired, these outer rollers can be driven to supplement the driving effect of the inner rollers, or can merely be idler rollers. As shown in Figure 1, there may be straight sections of belt between the curves where the drive rollers are located. It is preferred to support both edges of the belt over these straight portions, which can be inclined as shown in Figure 2, or can be level. Suitable support means include lateral support fingers or rails or further rollers. If desired, the support means can provide lateral restraint, for example as when a vertical upstand 8 is provided to the support means 7 as shown in Figure 3. Also, the bearing surfaces of the support means can be given a low friction surface coating or layer, e.g. of high density polyethylene or polytetrafluorethylene. Whilst it is not always necessary, it may be desired to provide a belt take-off means for drawing the belt 1 off the generally helical path at the desired point and to provide a tensioning effect on the belt. Suitable take off means include a separate belt drive station 10 in which the belt is drawn off the generally helical path, e.g. by an opposed pair of vertical drive rollers of the type used in the generally helical path, or a conventional horizontal drive roller which can carry teeth to engage in the lateral slats of the belt. The belt is then returned by a suitable path to the feed in to the generally helical path to form a closed loop of belt. If desired, the belt in this return portion can be subjected to steam cleaning or other treatments;further,the strip can be twisted in this return portion so that the closed loop of belt adopts a Mobius configuration to reduce lateral wear on the belt by alternating the edges carried on the drive rollers. In operation, the drive rollers 2 and the take-off means 10 are actuated and cause the belt 1 to come under tension and bear in slipping frictional contact directly against the drive rollers 2. The belt is moved through the generally helical path at the desired rate under the influence of the drive rollers. The take-off means operates at a speed of belt travel the same as or slower, e.g. 5 to 50% slower, than the linear rate of travel of the belt along the generally helical path. Articles, e.g. pieces of foodstuff, are fed to the feed-in'point (A) of the belt; are carried through the generally helical path; and are removed at the of f-take point B having undergone the desired treatment. The rate of travel of the belt can be varied over wide ranges to suit the items carried on the belt and the treatment to be carried out. By providing the drive system as a series of individual drive rollers in direct contact with the belt, the central space within the helical path is no longer obstructed and can be utilised to aid optimum flow of, e.g. coolant or heating, medium over items carried on the belt. Also, it is possible to support the belt from both edges without the need to provide heavy cantilever constructions, thus enabling a compact construction to be achieved. Whilst the invention has been described above in terms of a belt driven by rollers on the inner radius of each curve, it is possible to provide the drive rollers on the outer radius in addition to or in place of the drive rollers on the inner radius. In this case the belt requires radial support, e.g. by means of driven or idling rollers on the inner radius of the belt radially opposed to those on the outer radius. This ability to drive the belt from either or both edges provides further flexibility in design and operation of the conveyor system not possible with a centre drive drum system. Also where drive rollers are provided on both edges of the belt it may be possible to increase the load which the belt can carry as compared to conventional systems. The conveyor system of the invention finds widespread use wherever it is desired to carry items on a path. Thus, for example the system finds use in carrying items through a warehouse or store, in which case the path will not be the generally helical path described above, but could be a series of straight runs connected by 450, 900, 1800 or other angled bends to form a tortuous path serving the various bays of the warehouse or store. However, the invention is of especial use where it is desired to cause a treating medium (e.g. steam or air) or a coating agent (e.g. chocolate) to flow over items carried on the belt which follows a helical or other path within an enclosed treatment zone. Thus, the invention is of especial use in the food processing industry in the coating, chilling, freezing, cooking or sterilisation of food items.

Claims: Claims 1. A drive system for an endless load carrying belt which system comprises one or more drive stations adapted to propel the belt characterised in that at least one of the drive stations comprises a plurality of rollers (2) adapted to rotate about their longitudinal axes and to engage the belt (1) directly and to propel the belt (1), the rollers (2) having their axes of rotation within +200 of normal to the plane of the belt (1) at the point of contact when the belt (1) is in position, with the proviso that where the belt (1) is to travel around a path having one or more curves in the plane of the belt, at least one of those curves is provided with a drive station as defined above. 2. A system as claimed in claim 1 characterised in that the rollers (2) each comprise a substantially cylindrical roller having circumferential grooves (5) or ribs (6) forming circumferential recesses adapted to receive and support the edge of the belt (1). 3. A system as claimed in either of claims 1 or 2 characterised in that the rollers (2) are positioned at intervals of from 5 to 200 around a curve in the path of the belt. 4. 7A system as claimed in any one of claims 1 to 3 characterised in that rollers (2) are provided to engage each side of the belt. 5. A conveyor system having an endless belt (1) adapted to carry articles through a path, the belt (1) being adapted to be propelled parallel to its plane characterised in that th belt (1) is provided with one or more drive stations, at least one of which comprises a plurality of rollers (3) rotatable about their longitudinal axes, which rollers (2) engage directly with and are adapted to propel an edge of the belt (1), the axes of rotation of the rollers (2) being within +20 of normal to the plane of the belt (1) at the points of contact. 6. A conveyor system which comprises an endless belt (1) which is adapted to carry loads and is progressively longitudinally collapsible across its width, whereby it can conform to a path having curves in the plane of the belt, which belt (1) is formed into a circuit having one or more curves in the plane of the belt characterised in that at least one curve of the belt (1) is provided with a drive station comprising a plurality of rotatable drive rollers (2) which engage directly with and are adapted to propel an edge of the belt (1), the axis of rotation of the rollers (2) being within +200 of normal to the plane of the belt (1) at the points of contact. 7.. A conveyor system as claimed in either of claims 5 or 6 characterised in that the belt (1) follows a helical path and the rollers (2) are located at from 5 to 200 intervals around the inner radius of the curves in that path. 8. A conveyor system as claimed in any one of claims 5 to 7 characterised in that the drive station comprises a drive system as claimed in any one of claims 2 to 4. 9. A conveyor system as claimed in any one of claims 5 to 8 characterised in that a treating medium is adapted to flow over items carried on the belt (1). 10. A conveyor system for use in the treatment of food which comprises an endless belt (1) formed from a series of metal rods linking two peripheral collapsible chains, the belt being carried around a helical path so that at the curves the inner edge of the belt is fully collapsed and the outer edge is fully extended, the belt being driven by frictional engagement with driving means located at each curve in the path of the belt characterised in that the driving means comprises a series of substantially cylindrical rollers (2) rotating about their; substantially vertical longitudinal axes, the surface of the rollers (2) being provided with circumferential recesses into which the inner edge of the belt (1) is located, which recesses serve to support and to drive the belt (1) by frictional engagement therewith r successive curves in the path of the belt being linked by inclined substantially straight sections, whereby the belt (1) is raised as it traverses its path, the rollers (2) being positioned at intervals of o from 5 to 20 around each curve of the path of the belt (1).

Inventors: PERRYMENT, ALAN JOHN
Applicants: APV BAKER LTD
Application year: 1982
Main classification: B65G21
IPC codes: B65G23, B65G21, B65G15, A23L3