GB2237256A

GB2237256A - Carrier supporting a load on a conveyor

Info

Publication number: GB2237256A
Application number: GB8923978A
Authority: GB
Inventors: David John Burke
Original assignee: CMB Foodcan PLC; CMB Packaging UK Ltd; Metal Box PLC
Current assignee: Crown Packaging UK Ltd
Priority date: 1989-10-25
Filing date: 1989-10-25
Publication date: 1991-05-01
Also published as: GB8923978D0

Abstract

A carrier 1a, 1b for supporting a load on a conveyor 2 is formed with a lower wedge 12 which rests on the conveyor chain 3 and an upper wedge which supports the load 4. The interface between the wedges is defined by upwardly and rearwardly inclined wedge surfaces 10 and 11. Limited fore-and-aft movement of the lower wedge 12 relative to the upper wedge moves the upper wedge between a relatively raised position in which flanges thereon are clear of the walls 5 of the conveyor, and a relatively lowered position in which the flanges rest on the walls such that the weight of the load is taken off the chain 3. Each carrier has a rearwardly extending projection 20 which engages the lower wedge of a following carrier to move it into its rearward position when the carriers form a queue. A linear roller bearing may be provided at the interface between the wedge surfaces. <IMAGE>

Description

CONVEYOR CARRIER In modern mass production systems there is an increasing use of conveyors to carry loads such as components, subassemblies and finished products between the various operations in the manufacturing process.

Where the load being conveyed is not suitable to be carried directly on the conveyor chain or belt, it is placed on a specially designed carrier.

This carrier is either formed as a pallet conveyed directly on the conveyor chain or as a pallet supported on two cylindrical packs which make contact with the conveyor chain to transmit the driving force to the pallet and thus to the product. The carrier is guided along the conveyor by means of vertical side walls positioned on either side of the conveyor chain. In the case of the pucked pallet, stability is increased by the use of horizontal wings or rails positioned close to the under side of the pallet.

During the production process the carriers are transferred from position to position on the continuously moving conveyor chain. Because the time taken by each operation can vary, it is often necessary for the carriers to form stationary queues in front of each operational station whilst the chain continues to move. This means that a carrier stop mechanism is introduced in front of the first carrier in the queue and the remaining carriers build up in a queue behind it. Under these conditions all the weight of the products and carriers is bearing down on the moving chain. As a result of the frictional forces generated between the moving chain and the stationary pallet or puck, the chain is subjected to high tensile loads and a high level of wear. Also as a result of these conditions, the stop mechanism is subjected to a high load as the number of carriers in the queue increases.The result of these high forces is that there is a limit to the number of carriers which can be held in the queuing mode within the conveying system.

When the.workstation is ready to receive the next carrier, the stop is withdrawn from the front carrier allowing it to move into position and inserted in front of the next carrier as it moves into the position vacated.

During this process the whole queue of carriers surge forward together and as they are arrested by the re-inserted stop mechanism, high shock loads are generated within the system. This condition is detrimental to the equipment and can damage the products if they are of a delicate nature.

The invention has as its object the provision of a carrier which will take the weight of the load and carrier off the conveyor chain whilst it is in a queuing position and then transfer the weight back onto the chain once the conveyor becomes clear ahead.

The basis of the invention is to make the pallet, or front puck of the pucked pallet, in the form of a double wedge with the upper wedge being attached to or forming the pallet itself and the lower wedge being allowed to move forwards or rearwards in line with the direction of conveyor chain travel relative to the upper wedge.

Accordingly the present invention provides a carrier for supporting a load on a conveyor comprising a lower wedge portion adapted to rest on the moving surface of the conveyor and an upper wedge portion supported on the lower portion; opposed wedge surfaces defining the interface between the upper and lower portions and inclined upwardly and rearwardly; and means allowing limited fore-and-aft movement of the lower portion relative to the upper portion between a forward position in which the upper portion is supported in a relatively raised position and a rearward position in which the upper portion is supported in a relatively lowered position.

The action of this double wedge arrangement is to transfer the weight off the moving surface provided by the chain or belt of the conveyor onto the wings or top of the guide walls when the bottom wedge is in the rearward position with the reverse action taking place as the bottom wedge is allowed to move forward.

The lower wedge can be moved into the rearward position by coming into contact with a protrusion attached to the rear of the stationary pallet in front or rear puck of the pucked pallet in front. When the carrier in front moves away, the bottom wedge is driven forward by the action of the moving chain, re-engaging with the top wedge and thus lifting the weight of the carrier off the wings or top of the guide walls and restoring it to the chain or belt thus reinstating the normal driving force back to the carrier.

In order for the bottom wedge to be able to lift the weight of the carrier, the coefficient of friction between the chain and the underside of the bottom wedge must be greater than that between the two opposed sliding wedge surfaces of the wedges. In order to achieve this, the bottom wedge is made in two parts, with the lower part being manufactured out of a high friction, wear resistant material. In the case of particularly heavy products, small linear roller bearings are introduced between the sloping surfaces of the. two wedges, in order to reduce the friction at this point and thus allow the carrier to be lifted with a reduced driving force on the bottom wedge.

The action of this carrier design will be to sequentially disengage the carriers from the driving force of the chain as they come up against the rearmost carrier in the queue. When the front carrier is allowed to move away, each carrier in the queue will move forward into its next position individually, rather than the whole queue moving forward as a solid block. This will reduce the tension and wear rate in the conveyor chain. It will increase the number of carriers which can be held in a stationary position on any one conveyor. It will also increase the weight of individual products which can be carried by the conveyor. Finally it will reduce the shock loads experienced by delicate products when they are in the queuing mode.

Embodiments of the invention are now described below with reference to the accompanying drawings in which Figure 1 is a transverse cross-section through a prior art arrangement of a load carrying pallet on a conveyor; Figure 2 is a longitudinal section of the arrangement shown in Figure 1; Figure 3 is a transverse cross-section through a prior art arrangement showing a pucked pallet on a conveyor; Figure 4 is a longitudinal section through the arrangement of Figure 3; Figure 5 is a plan view of a section of a conveyor carrying a number of pucked pallets between workstations; Figure 6 is a transverse cross-section through a load carrying carrier on a conveyor in accordance with the invent ion; Figure 7 is a longitudinal cross-section through the carrier and conveyor of Figure 6;; Figure 8 is a longitudinal cross-section showing two pucked pallets in accordance with the invention on a conveyor; Figure 9 is a longitudinal cross-section through the front part of a pucked pallet in accordance with the invention; and Figure 10 is a similar view to Figure 9 showing an alternative embodiment.

Referring to Figures 1 and 2, a plain pallet 1 is shown travelling on a conveyor 2 which has a moving chain 3 or other continuous element. The pallet 1 supports a load 4. The pallet 1 is guided and restrained laterally by side walls 5 of the conveyor. Figures 3 and 4 show a similar arrangement to Figures 1 and 2 except that the pallet is supported on the conveyor chain 3 by means of front and rear pucks 6. Lateral flanges 7 on the conveyor improve the stability of the pucked pallet.

Figure 5 is a plan view of a section of conveyor extending between workstations 8 and carrying a number of pucked pallets queuing behind a stop 9. Other stops 9 are shown at the exit side of each workstation. As can be seen from Figure 5 the pucked pallets queue up behind one another with the leading puck of each pallet in contact with the trailing puck of the downstream pallet.

Figures 6 and 7 show a first embodiment of the invention in which the upper wedge of the load supporting carrier is provided by the pallet itself. The pallet is formed with an upwardly and rearwardly extending wedge surface 10 which is supported on a lower wedge 12 having a corresponding wedge surface 11. Wedge 12 rests on the conveyor chain 3. A key 14 formed on the lower wedge 12 is located in a downwardly open channel 16 formed in the pallet 1. The pallet 1 is also formed with laterally extending flanges 15 which overlie the top edges of the conveyor walls 5 and are spaced above these edges when the carrier is in its relatively raised position as shown in Figure 6. Referring to Figure 7 a leading carrier la is shown in the position where it has been stopped by a stop (not shown).The lower wedge 12 of this carrier remains in its forward position relative to the upper wedge formed by the pallet 1 and the weight of the carrier and its load continues to be supported on the chain 3 which slips beneath the lower wedge 12. At the rear of each pallet a depending wall 18 supports a rearwardly extending projection 20. When a following carrier Ib comes into contact with a stationary carrier the projection 20 on the stationary carrier engages the lower wedge 12 of the following carrier and moves it rearwards relative to the upper wedge of that carrier. As a result of this action the pallet forming the upper wedge of the carrier lb moves to a relatively lowered position and the flanges 15 engage the top edges of the conveyor wall 5 such that the weight of the pallet and its load is taken on the conveyor wall.

Only the weight of the lower wedge 12 continues to bear on the conveyor chain 3.

Figure 8 shows a similar view to that of Figure 7 in relation to carriers formed by pallets supported on front and rear pucks 6. In this case the upper wedge is formed as an upper portion 22 of the leading puck of each carrier and the lower wedge 12 is formed of a lower portion of this puck. A bolt 24 retains the upper and lower wedge portions of the puck on the pallet 1. The bolt 24 passes through a longitudinal slot 25 formed in the lower wedge of the puck. This slot allows limited fore-and-aft movement of the lower wedge 12 relative to the upper wedge 22.

The trailing puck 6 of each carrier is not formed with upper and lower wedges but is formed with a rearwardly extending projection. When a queue of carriers is formed the projection 20 on the trailing puck of a downstream pallet engages the lower wedge 12 of the leading puck of an upstream pallet to move it to its rearward position. The front of the upstream pallet thus drops onto the conveyor walls 5. A strip 26 extending underneath the pallet 21 transversely of the conveyor also then comes into contact with the top edges of the conveyor walls 5. This strip is located at or about the centre of gravity of the carrier so that when the front end drops the weight of the carrier and load is largely taken on the strip 26.

Figure 9 is an enlarged view of the puck construction shown in Figure 8. The lower wedge 12 of the puck is made with a lower part 30 of high friction material. In a further embodiment shown in Figure 10 small linear roller bearings are provided between the opposed wedge surfaces 10 and 11. Such an arrangement is particularly advantageous when heavy loads are being carried.

Claims

Claims:

1. A carrier for supporting a load on a conveyor comprising a lower wedge portion adapted to rest on the moving surface of the conveyor and an upper wedge portion supported on the lower portion; opposed wedge surfaces defining the interface between the upper and lower portions and inclined upwardly and rearwardly; and means allowing limited fore-and-aft movement of the lower wedge portion relative to the upper wedge portion between a forward position in which the upper wedge portion is supported in a relatively raised position and a rearward position in which the upper wedge portion is supported in a relatively lowered position.

2. A carrier according to claim 1 in which an upstanding key on the lower wedge portion is received in a downwardly open guide channel in the upper wedge portion; the guide channel and the key extending in the direction of the conveyor to guide the lower wedge portion in fore-and-aft movement relative to the upper wedge portion.

3. A carrier according to claim 1 or claim 2 wherein the lower wedge portion is formed in two parts and the lower part which rests on the conveyor surface is made of a high friction material.

4. A carrier according to any preceding claim wherein a bearing is provided at the interface between the opposed wedge surfaces.

5. A carrier according to claim 4 wherein the bearing is in the form of a linear roller bearing.

6. A carrier according to any of claims 1 to 5 in which the upper wedge portion is formed as part of a load supporting pallet.

7. A carrier for supporting a load on a conveyor comprising a load supporting pallet supported on a front puck, formed as a carrier according to any of claims 1 to 5, and a rear puck.

8. A carrier according to claim 6 or claim 7 further comprising means extending rearwardly of the carrier for engaging the lower wedge portion of a following carrier on the conveyor to move it from its forward to its rearward position.

9. A carrier according to any preceding claim in combination with an endless conveyor, the carrier being supported on the conveyor and the conveyor having guide and support means for the carrier; wherein a part of the upper wedge portion of the carrier overlies the guide and support means with clearance when the upper wedge portion is in its relatively raised position and is supported on the guide and support means when the upper wedge portion is in its relatively lowered position.

10. A carrier for supporting a load on a conveyor substantially as described herein with reference to Figures 5-10 of the accompanying drawings.