CHAIN DRIVE MECHANISM

Abstract: An escalator or like conveyor incorporates a twin drive mechanism comprising two chain loops bridged by an axle, a wheel at each end of the axle, the axle being connected to the wheel by a joint which permits relative pivotal movement between the axle and the wheel whereby lateral float is avoided.

Description: CHAIN DRIVE MECHANISM Escalators and many other conveyors employ what is commonly known as a "twin chain" drive mechanism. The twin chain drive comprises two chain loops of the same length and arranged in synchrony. Steps or pallets are fixed between the two loops to corresponding points on each loop. The loops are driven in synchronism by synchronised sprockets. The loops are usually supported in space by wheels running on tracks to reduce frictional losses. These wheels are usually mounted externally to the chains for ease of servicing, at either end of an axle that is fixed either to or through corresponding points on each of the two chains. The through axle is present to resist large cyclic bending forces imposed on the axle by couples determined by the distance between chain centre and its corresponding wheel centre, without subjecting the steps or pallets to fatigue -inducing loading. These couples occur when a particular section of chains, axles and wheels is running over any area of the machine that causes the chains to be pulled either away from or toward the wheel running tracks. Escalators are subject to a phenomenon known as "lateral float" by which the steps exhibit a strong tendency to drive themselves into the side panels of the escalator adjacent to the steps, known as "skirt" panels. This damages the skirt panels, the edges of steps and often the wheels associated with steps. The available solution is to replace the main chains, at huge expense and disruption. It is one object of this invention to provide an escalator assembly or the like which is less prone to lateral float. According to the invention in one aspect there is provided a twin drive mechanism for an escalator or conveyor or the like, comprising at least two chain loops disposed in parallel relation, means for moving the loops in synchronism, at least one axle bridging the loops, a wheel at each end of the axle, a step or pallet mounted on the axle, the wheels being connected to the axle by a joint which permits relative pivotal movement of the axle. Preferably each wheel is fixed to the respective chain running parallel to the chains gearing rollers, mounted on an extended chain pin and not directly on to the axle as is the normal practice. While not limiting the scope of the invention in any way our investigations have suggested the following. Because the wheels are normally fixed to each end of the axle it is therefore reasonable to assume that the wheels are pointing in a direction exactly orthogonally to the axis of the axle. When two allegedly corresponding points on each of the two chain loops are not exactly opposite one another related to a line exactly peφendicular to the intended direction of motion of the system, the respective axle fixed to each chain at these points is also not exactly square to the direction of motion of the system. It follows that the wheels on each end of the axle are pointing in a direction other than the intended direction of motion of the conveyor or escalator. This has the effect of causing a "steering" movement to drag components in a direction other than that intended, as the machine runs, hence the tendency of an escalator to float laterally. The invention is based on the first realisation that one should arrange the supporting wheels to point only in exactly the desired direction of conveyor motion, irrespective of relative chain positioning. To achieve this, it is necessary to fix wheels to individual chains. The axle between the chains must be permitted to "articulate" about a known fulcrum at its chain attachment points in a free and unrestrained manner in the plane of motion of the system while preventing similar axle articulation in a direction peφendicular to that of the direction of motion. Simply fixing chain supporting wheels to the chains without allowing a small degree of free articulation in the plane of motion will not produce a mechanically correct solution on its own. This is because axles will still try to articulate where they are attached to or through the chains, even though this articulation is resisted by the chain interface. Without this free articulation at chain/axle interfaces, this resistance must cause unintended loading and deformation of chain in particular, resulting in some wheel steering effect, although somewhat reduced in level compared to the original arrangement with wheels attached to axle ends. Simply introducing uncontrolled looseness to provide clearance for axle articulation will preclude effective control of axle spacing around the chain loops, resulting in either excessive step or pallet spacing or collisions. The invention includes a method of running an escalator or the like in lateral float-free mode by running an escalator of this invention. In order that the invention may be well understood it will now be described by way of example only with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a plan view of a chainstep escalator, Figure 2 is a large scale view of one end of an axle, and Figure 3 is an enlarged sectioned end view of an axle shaft and extended chain hollow pin. The escalator shown in Figure 1 includes two chain loops, C1, 02, each made up of loops of identical length having aligned links. The loops are driven by sprockets not shown. The links are bridged at intervals by axles 1 which carry steps 2. A wheel 3 is present at each of the axle 1 and travels in a track 4 outboard of the respective chain. The escalator is mounted between walls 5, having side panels 6. Each axle 1, is connected to the chains 01 and 02 by a joint 10 which permits a limited amount of pivotal movement. As shown in Figure 2, each axle 1 terminates in a shaft portion 11 which is received in the bore 12, of an extended hollow chain pin 13, the extended portion passing through the wheel 3. The shaft 11 has two flats 14 machined at 180° on its outer diameter. The bore 12 of the chain hollow pin 13 has two keyways 18 cut at 180° and is stepped to define shoulders 15 which locate the outer diameter of the shaft portion 11, concentric to the chain hollow pins bore, both ends of which are enlarged into a lobed form 19 at 90° to the keyways. Keys 20 are inserted locating the flats on the shaft, preventing rotation, but allowing the axle to slew in the desired direction, the shaped form of the shoulders 15, providing the pivot point, and the enlarged lobed form of the bore ends enabling this slewing to take place. (Figure 3 shows the lobed end form in relation to the shaft end drawn to an enlarged scale). The hollow chain pin has an outer shoulder 16 to receive ball beaπngs 17, on which the wheel 3, runs. These are held in place by a circlip and which also retains the keys 20. The axle shaft has a reduced diameter end which locates the retaining cap 21 , which is held in place by the circlip 22. Because of the shoulders 15 the shaft portion 11 is held towards its inner end but can pivot within the bore 12 and can undergo significant free axle articulation with the plane of the chain motion. This articulation is further facilitated by domed end faces provided on the ends of the chain hollow pin 13. The wheel 3 however is held true in its track 4 so that the two parallel wheels will always tend to travel a parallel path. With time, chain parts will become worn, and a differential chain extension will take place; one would expect an escalator to move to one side, causing damage to panels 6, etc. Because of the pivotal linkage connection of the axle shaft 11 in the bore 12 any misalignment caused by wear and other factors will be accommodated by the joint, allowing both the wheels and the chains to travel true to their intended paths. The invention is not limited to the embodiment shown.

Claims: CLAIMS 1. A twin drive mechanism for an escalator or conveyor or like apparatus, comprising at least two chain loops disposed in parallel relation, means for moving the loops in synchronism, at least one axle bridging the loops, a wheel at each end of the axle, a step or pallet mounted on the axle, the wheels being connected to the axle by a joint which permits relative pivotal movement of the axle. 2. A mechanism according to Claim 1, wherein each wheel is fixed to the respective chain running generally parallel to gearing rollers associated with the chain. 3. A mechanism according to Claim 1 or 2, wherein a pin extends between the axle and the wheel, and comprises a shaft received in a bore, the shaft being capable of pivotal movement therein. 4. A mechanism according to Claim 3, including means to prevent rotation of the shaft in the bore while allowing the pivotal movement. 5. A mechanism according to Claim 3 or 4, wherein the shaft includes shoulders located to define the pivot point for the pivotal action. 6. A method of running an escalator or conveyor or like apparatus in a lateral float- free mode, the method comprising incoφorating a mechanism according to any preceding Claim in the apparatus, and running the apparatus with the wheels being held true in the tracks through which the chain loops travel by the pivotal connection of the axle relative to the wheel.

Inventors: HAYCOCK BRYAN, HAYCOCK, BRYAN
Applicants: HAYCOCK BRYAN, PRECISION CHAINS, RCS DESIGNS LTD, HAYCOCK, BRYAN, RCS (DESIGNS) LTD.
Application year: 1997
Main classification: B66B23
IPC codes: B66B23