GB2073695A - Stacking elongate workpieces - Google Patents

Abstract

Groups of extruded side-by-side lengths 42 of aluminium are stacked in a skip 18 on spacers 17 which separate successive layers of the lengths. Each spacer 17, which supports the ends of a group of extruded lengths is gripped by a pair of jaws 29, which transfer the spacer to the skip on reciprocation of jaw mounting carriers 28. The extruded lengths are moved onto the spacers by conveyors 13, 14 and 23. <IMAGE>

Description

SPECIFICATION Method of stacking workpieces and apparatus for use in the method DESCRIPTION This invention relates to the stacking of elongated workpieces.

Elongated workpieces of aluminium are usually formed by extruding aluminium through a die to provide long lengths having the required crosssectional shape and size, cutting from the extruded lengths workpieces having the required length and then subjecting the workpieces to heat treatment termed ageing. In preparation for ageing, a substantial number of workpieces are stacked in a container referred to as a skip and the loaded skip is placed in an oven where heat is transferred to the aluminium workpieces by means of heated air. It is necessary to provide between successive layers of workpieces in the skip spaces which prevent vertically adjacent workpieces from contacting one another and provide between successive layers of workpieces a gap through which air can pass easily.

It is important that extruded aluminium workpieces should not be subjected to impact or abrasion since the surfaces of the workpieces are susceptible to damage in this way and the appearance, particularly after anodising, would be seriously impaired.

At the present time, elongated aluminium workpieces are loaded into heat treatment skips by hand. In order to avoid contact between successive workpieces, the workpieces are loaded one at a time and the procedure is therefore very labour intensive. A layer of workpieces is placed in the skip and then spacers are placed on that layer before a second layer of workpieces is placed in the skip. Since access to the interior of the skip is restricted by the skip itself, there is a substantial risk of impact between workpieces and each other or the skip. Long workpieces, for example having a length of six metres, give rise to a particular problem. Long workpieces are usually lifted and placed in the skip by two persons, one adjacent to each end of the workpiece. The workpiece may sag between its end sufficiently to impart a permanent curvature to the workpiece.

According to a first aspect of the invention, there is provided a method of stacking a plurality of elongated workpieces wherein a plurality of the workpieces are arranged side-by-side to form a group of the workpieces resting on a set of spacers in an assembly station, the respective lengths of the workpieces of the group being parallel to each other and the spacers being spaced from each other along the workpieces, wherein the spacers of the set are engaged by a transfer mechanism which moves the set of spacers bearing the group of workpieces from the assembly station to a stacking station and wherein the spacers are deposited from the transfer mechanism onto a previously transferred group of workpieces at the stacking station to form a stack comprising a lower group of workpieces spaced by the spacers from an upper group of workpieces.

In a method according to the invention, the risk of workpieces which form one layer in the stack contacting workpieces of another layer is avoided.

Furthermore, the transfer mechanism reliably moves the group of workpieces along a path which avoids contact between the workpieces and a skip or other structure occupying a predetermined position. Sagging of long workpieces is avoided by supporting the workpieces on an appropriate number of spacers during movement from the assembly station to the stacking station.

Preferably, the spacers are elongated and the transfer mechanism grips each spacer at at least positions adjacent to each of its ends. Grippping of a spacer enables the spacer to be supported by the transfer mechanism without engaging the underside of the spacer so that, whilst still gripped, the spacer can be deposited on a previously transferred group of workpieces.

In a case where the workpieces are to be stacked in a container having a length more than twice that of the workpieces, a plurality of groups of workpieces, each group resting on a respective set of spacers, can be moved concurrently from the assembly station to the stacking station, the groups being spaced apart in a direction extending along the workpieces.

By supporting the workpieces by gripping of the spacers, intrusion of the transfer mechanism into gaps between adjacent groups of workpieces can be avoided and these gaps can be small.

In the preferred method of stacking in a container workpieces which are short, relative to the container, successive groups of workpieces are moved longitudinally to respective storage positions in which the groups are spaced apart in a direction along the workpieces and the groups are then moved concurrently from their storage positions in a direction transverse to the lengths of the workpieces to the assembly station. The gaps between adjacent groups of workpieces can be established during movement of the groups into their storage positions and subsequently maintained constant during movement of the groups to the assembly station and then to the stacking station.

According to a further aspect of the invention, there is provided apparatus for carrying out the method of the invention and comprising a delivery conveyor for delivering the groups of workpieces to the assembly station and a transfer mechanism for supporting a set of spacers at the assembly station and for moving the spacers of the set concurrently in a reference direction from the assembly station to the stacking station.

The transfer mechanism preferably comprises a plurality of pairs of jaws for gripping the spacers, the jaws being movable with one another between the assembly station and the transfer station. The length of each jaw preferably extends in the reference direction, the jaws of each pair being spaced apart in a horizontal direction transverse to the reference direction. With this arrangement, the spacers can be deposited on a previously transferred group whilst the spacers are still gripped by the jaws and the jaws can then be withdrawn from the spacers horizontally without engaging with the stacked groups of workpieces.

The apparatus preferably further comprises means for raising and lowering the stack of workpieces and spacers at the stacking station.

With this arrangement, it is necessary for the transfer mechanism to be capable only of moving the spacers with groups of workpieces supported thereon horizontally. After a group of workpieces has been added to the stack, the stack can be lowered to provide a space into which a subsequent group can be transferred and the stack can then be raised to deposit the newly transferred group of workpieces onto the stack.

For establishing the required spacing between adjacent groups of workpieces which are transferred concurrently to the stack, the apparatus may include a storage conveyor for moving successive groups of workpieces along a path to respective storage positions on the path, the length of the path being transverse to the reference direction, and an input conveyor for moving a group of workpieces in the reference direction onto said path, the delivery conveyor being arranged for moving a plurality of groups of workpieces concurrently from their respective storage positions in the reference direction to the assembly station.

The apparatus preferably includes a plurality of stops which are spaced apart along said path, each stop being movable independently of the other stops into and out of the path to limit the travel of groups of workpieces along the path and thereby establish respective storage positions.

One example of a method embodying the invention and of apparatus for carrying out the method will now be described with reference to the accompanying drawings wherein.

FIGURE 1 illustrates diagrammatically in plan view apparatus for stacking groups of workpieces in a container; FIGURE 2 shows diagrammatically and on an enlarged scale a side elevation of certain components of the apparatus shown in Figure 1; FIGURE 3 shows diagrammatically and on a scale intermediate those of Figures 1 and 2 an end eievation of certain parts of the apparatus of Figure 1, together with the container shown in Figure 1; and FIGURE 4 shows diagrammatically and on the scale of Figure 2 a part of a container in which there is a partially completed stack of workpieces, together with a part of a transfer mechanism for stacking workpieces in the container.

The apparatus shown in Figure 1 is intended to be used in conjunction with apparatus (not shown) for extruding long lengths of aluminium, cooling the lengths and feeding the lengths to a saw table 10 shown in Figure 1. The saw table may be identical with saw tables in use at the present time and has a settable gauge 11 which can be set at a required distance from a saw 12 to facilitate the sawing of the long lengths of aluminium into workpieces of required size. A plurality of extruded lengths may be supported on the saw table at the same time and all engaged with the gauge 11 so that a single sawing operation produces a group of workpieces arranged side-by-side. For convenience of illustration, groups of three workpieces are shown in Figure 1 but it will be understood that each group will normally comprise a larger number of workpieces.

There is associated with the saw table 10 in a known manner a conveyor 13 (called herein the input conveyor) for moving each group of workpieces sawn from the long lengths in a horizontal direction transverse to the lengths of the workpieces to a storage conveyor 14 situated beside the table. The direction of movement from the saw table to the storage conveyor is called herein the reference direction and is indicated in Figure 1 by the arrow 15.

As will be described hereinafter, successive groups of workpieces are moved by the storage conveyor along a path to respective storage positions on that path and when the path is substantially entirely occupied by groups of workpieces all of the groups on the path are transferred concurrently in the reference direction to an assembly station 1 6 where each group is placed on a corresponding set of spacers 17. The sets of spacers, each bearing a group of workpieces, are then moved concurrently by a transfer mechanism in the reference direction to a stacking station situated immediately above a container 1 8 where the spacers are deposited on supports which can be lowered into the container or on groups of workpieces previously stacked on the supports.This operation is repeated to build up in the container a stack comprising layers of workpieces with spacers between adjacent layers.

The storage conveyor 14 comprises a plurality of units, one of which is shown in Figure 2 and which are arranged end-to-end, Each unit comprises a stationary frame 1 9 on which there are supported for rotation about respective axes three rollers 20. The axes of the rollers 20 lie in a common horizontal plane and are parallel to the reference direction. The rollers are spaced from each other along the path defined by the storage conveyor. For driving the rollers 20, there is provided drive means including a driving unit 21 and a belt and pulley drive 22 connecting the drive unit with the rollers.

The input conveyor 13 comprises a number of belt conveyors, each of which extends across the saw table 10 and into a space between adjacent rollers 20 of the storage conveyor. There is also disposed within each space between a pair of adjacent rollers 20 of each unit of the storage conveyor a further belt conveyor which extends across the storage conveyor and from the storage conveyor into the assembly station 1 6. These further belt conveyors collectively constitute a delivery conveyor 23 for moving groups of workpieces from their storage positions to the assembly station. The belt conveyors of the input conveyor 1 3 can be raised and lowered together for lifting workpieces clear of the saw table, moving them to the path defined by the storage conveyor and lowering the workpieces onto the storage conveyor.The means for driving and for raising and lowering the input conveyor may be constructed and arranged in a known manner.

Similar means for driving and raising and lowering the belt conveyors of the delivery conveyor 23 independently of the input conveyor 13 is also provided.

On the frame 1 9 of each unit of the storage conveyor 14, there is provided a stop 24 which can be moved into and out of the path along which groups of workpieces travel on the storage conveyor. The stop 24 is in the form of a plate connected with a respective carrier 25 for pivotal movement about an horizontal axis parallel to the reference direction 1 5. The carrier 25 is also movable relative to the frame 1 9 by means of a pneumatic piston and cylinder unit 26 between a first position in which the plate 24 is clear of the path of the workpieces and a second position in which the plate lies in the path. When the carrier 25 is in its second position, the plate 24 is urged by gravity into an upstream position indicated by a fuil line in Figure 2.Pivoting of the plate relative to the carrier is so limited that the plate can move from the upstream position only to the vertical position indicated by a broken line in Figure 2.

Limit switches, or other signalling devices 27 are associated with the plate 24 to provide to a control system a first signal when the plate leaves its upstream position and a second signal when the plate moves into its vertical position. By setting a selected plate 24 in the upstream position, a group of workpieces travelling along the storage conveyor 14 can be arrested in a required storage position when ends of the workpieces engage the plate and move the plate into its upright position.

In respective positions between the storage conveyor 14 and the assembly station 16, there are provided a number of further carriages 28, on each of which there is mounted a pair of jaws 29 of the transfer mechanism. Each carrier 28 is mounted on a stationary base structure 30 for reciprocation in the reference direction 1 5 and for limited pivoting movement about an axis 41 upwardly from the normal position illustrated in Figure 3, in which the carrier rests on the base structure. A common drive mechanism is provided for reciprocating all of the carriers 28 together.

This drive mechanism may include a rack associated with each carrier and a series of pinions secured on a common shaft to mesh with the racks.

The pair of jaws 29 mounted on each carrier 28 are spaced apart in a horizontal direction perpendicular to the reference 1 5 with the length of each jaw extending in the reference direction.

The jaws are connected together by a linkage which ensures that the jaws present towards each other faces which remain parallel. With the pair of jaws there is associated a piston and cylinder unit 31 for moving the jaws towards and away from each other into and out of gripping arrangement with respective spacers 1 7. Each spacer consists of a bar of timber having a square cross-section.

As shown in Figure 4, the jaws 29 engage each spacer only at opposite vertical surfaces and at positions spaced from upper and lower surfaces of the spacer.

Below the assembly station 1 6 there extends a conveyor 32 for conveying spacers 1 7 from a bulk supply (not shown) of spacers of respective positions lying directly below the pairs of jaws 29.

The conveyor 32 comprises a pair of belts which engage opposite end portions of the spacers. For clarity of illustration, a small part only of the conveyor 32 is shown in Figure 1. For arresting each spacer in the required position, there may be provided a pair of fingers which can extend into the path of travel of the spacers on the conveyor 32, engagement of a spacer with one pair of fingers giving rise to a control signal which brings about movement of an adjacent pair of fingers into the path of travel of the spacers.

For raising the spacers 1 7 from the conveyor 32 into the assembly station 16, there is provided on the base structure 30 a hoist 33 which extends upwardly between the belts of the conveyor 32.

The hoist 33 engages each spacer at its underside only, thereby leaving the opposed vertical faces of the spacer exposed for engagement by the jaws 29 in the assembly station.

The container 1 8 comprises a pair of horizontally spaced, parallel upper rails 34 and a pair of correspondingly arranged lower rails 35.

Each upper rail is connected with the corresponding lower rail by substantially upright ties 36 and the lower rails 35 are connected to each other by horizontal ties 37. The horizontal ties are spaced apart from each other along the container and are each aligned with corresponding ties 36. The upper rails 34 are provided with hooks (not shown) whereby the container may be lifted.

The container 18 rests on a base 38 on which there are carried by respective jacks 39 a number of support platforms 40. The bottom of the container 1 8 comprises a number of openings each defined between a pair of horizontal ties 37 and the lower rails 35. Each support plate 40 can be raised by the associated jack 39 through a corresponding opening in the bottom of the container up to a level slightly above the upper rails 34. When the jacks 39 are retracted, the support platforms 40 are withdrawn from the container.

Use of the apparatus to stack a number of groups of workpieces in the container 1 8 will now be described.

A number of extruded lengths of aluminium are moved along the saw table 10 into engagement with the gauge 11 which has been set at a predetermined position with respect to the saw 12. The extruded lengths are then sawn in a single sawing operation to provide a group of workpieces lying-on the saw table between the saw and the gauge. The workpieces of the group lie side-byside and may be spaced apart from each other in the reference direction 1 5. The respective lengths of the workpieces are parallel to each other.

The control system of the apparatus then automatically raises the belts of the input conveyor 1 3 to lift the group of workpieces off the saw table and move the group in the reference direction to a position overlying the storage conveyor 14. The input conveyor is then lowered to deposit the group of workpieces on the rollers 20 of the storage conveyor. A stop 24 adjacent to the end of the storage conveyor remote from the saw 12 is moved by the control system into its upstream position and all rollers of the storage conveyor are driven to move the group of workpieces along the storage conveyor into engagement with the raised stop. When the leading ends of the workpieces engage the raised stop 24, the stop is moved into its upright position.As the stop moves out of its upstream position, the control system de-energises at least those rollers 20 which are supporting the group of workpieces. As the stop 24 moves into its upright position, a further selected stop 24 is raised into the path of a subsequent group of workpieces.

Selection of the stop 24 which is to be raised is carried out by the control system in accordance with information concerning the lengths of workpieces which has previouly been fed into the control system.

Successive groups of workpieces 42 are sawn from the extruded lengths, transferred onto the storage conveyor and moved along the storage conveyor to respective storage positions until the storage position adjacent the saw 12 is occupied by a group of workpieces. The control system then raises the belts of the delivery conveyor 23 simultaneously so that all of the groups of workpieces are raised from the storage conveyor and are moved concurrently to the assembly station 1 6. The control system automatically moves the stops 24 out of the path defined by the storage conveyor 14, with the exception of the stop which is remote from the saw 12. This particular stop is returned by gravity to its upstream position.

Before the groups of workpieces 42 reach the assembly station 16, a respective spacer 1 7 has been gripped by each pair of jaws 29. When the groups of workpieces reach the assembly station, the delivery conveyor 23 is lowered until the workpieces rest on the upper surfaces of the spacers 1 7 and the delivery conveyor moves clear of the workpieces. The jaws are then advanced to the stacking station directly over the container 1 8, thereby moving all of the spacers bearing their groups of workpieces concurrently to the stacking station.

Whilst the spacers 1 7 are supported by the jaws 29 at the stacking station, the jaws 39 are extended to raise the support plates 40 into engagement with the undersides of the spacers.

When the support plates reach this position, the control system energises the piston and cylinder units 26 to release the spacers from the jaws 29 and move the jaws sufficiently far apart to enable them to be withdrawn from the stacking station without disturbing the spacers and workpieces resting thereon. Once the jaws have returned to the assembly station, the jacks 39 are actuated to lower the support plates 40 by a distance exceeding the aggregate depth of the spacers and workpieces resting thereon.

It will be noted that, throughout the operation, the workpieces are supported on horizontal surfaces and are moved horizontally. The spacing between adjacent workpieces in each group is thereby maintained. The spacing between adjacent groups is established by the storage conveyor 14 and is maintained thereafter.

A number of further groups of workpieces are moved to respective storage positions on the storage conveyor 14 and are then moved to the assembly station where they are placed on respective sets of spacers. The spacers are then moved in the manner hereinbefore described to the stacking station, whereupon the jacks 39 are extended once more to raise the preceding groups of workpieces into engagement with the undersides of the spacers held between the jaws 29. When this engagement has been established, the jaws are moved apart and retracted from the stacking station, leaving a second layer of workpieces resting on spacers which in turn rest on the first layer of workpieces. The jacks are then at least partially retracted once more and the procedure is repeated until a stack of the required height has been built up on the support plates 40.

The jacks 39 are then fully retracted to withdraw the support plates 40 through the openings in the bottom of the container 18. The lowermost spacers may come to rest on the lower rails 35 of the container. Alternatively, the lowermost spacers may remain on the support plates 40 so that the lowest layer of workpieces comes to rest on the horizontal ties 37 of the container. The loaded container can then be lifted upwardly from the base 38 and transferred to a heat treatment oven.

Typically, the apparatus is capable of transferring concurrently from the storage conveyor to the assembly station and then to the stacking station six groups of workpieces wherein the length of each workpiece is approximately 1 m or three groups of workpieces wherein each workpiece has a length of approximately 2m or two groups of workpieces having a length of 3m or a single group of workpieces wherein each workpiece has a length of approximately 6m. The spacers bearing the workpieces may be spaced from each other by approximately 500 mm. The cross-section of the spacers is typically a 25 mm square. The jaws 29 are arranged to engage the spacers in a manner to provide adequate support for the spacers when bearing groups of workpieces. Each jaw engages the associated spacer at least adjacent to the ends of the spacer.

Adjacent to a mid portion of the spacer, the jaw may be relieved to provide a slight clearance between jaw and spacer and thereby ensure proper contact between the jaws and the end portions of the spacers.

For supplying to the control system signals indicating the positions of various moving components of the apparatus, there may be provided limit switches or transducers which provide an output representing movement of the components. The control system actuates the jacks 39 to raise the support plates 40 or a stack thereon, as the case may be, into engagement with the underside of the spacers at the stacking station. During initial setting up of the apparatus, upward movement of the support plates may be excessive. In this event, the spacers, jaws 29 and carriers 28 pivot upwardly relatively to the base structure 30 to avoid damage being caused to the apparatus.

Claims (19)

1. A method of stacking a plurality of elongated workpieces wherein a plurality of the workpieces are arranged side-by-side to form a group resting on a set of spacers in an assembly station, the respective lengths of the workpieces of the group being parallel to each other, and the spacers being spaced from each other along the workpieces, wherein the spacers of the set are engaged by a transfer mechanism which moves the set of spacers bearing the group of workpieces from the assembly station to a stacking station and wherein the spacers are deposited from the transfer mechanism onto a previously transferred group of workpieces at the stacking station to form a stack comprising a lower group of workpieces spaced by the spacers from an upper group of workpieces.

2. A method according to Claim 1 wherein the spacers are elongated and the transfer mechanism grips each spacer at least at positions adjacent to each of its ends.

3. A method according to Claim 1 or Claim 2 wherein the transfer mechanism moves the spacers bearing the group of workpieces horizontally from the assembly station to the stacking station and, after the spacers have been deposited on the previously transferred group of workpieces, the stack of workpieces and spacers is lowered.

4. A method according to Claim 3 wherein after the stack has been lowered, a further group of workpieces on a further set of spacers is moved into the stacking station and the stack is then raised into engagement with the further set of spacers.

5. A method according to any preceding claim wherein the group of workpieces is moved into the assembly station in a direction transverse to the lengths of the workpieces and relative vertical movement of the group of workpieces and the set of spacers is then effected to cause the workpieces to rest on the spacers.

6. Apparatus according to any preceding claim wherein a plurality of groups of workpieces, each group resting on a respective set of spacers, are moved concurrently from the assembly station to the stacking station, the groups being spaced apart in a direction extending along the workpieces.

7. A method according to Claim 6 wherein each group is spaced from an adjacent group by a gap into which the transfer mechanism does not intrude.

8. A method according to Claim 6 or Claim 7 wherein sucessive groups of workpieces are moved longitudinally to respective storage positions in which the groups are spaced apart in the direction extending along the workpieces and are then moved concurrently from their storage positions in a direction transverse to the lengths of the workpieces to the assembly.station.

9. Apparatus for carrying out the method of Claim 1 and comprising the delivery conveyor for delivering the groups of workpieces to the assembly station and a transfer mechanism for supporting a set of spacers at the assembly station and for moving the spacers of the set concurrently in a reference direction from the assembly station to the stacking station.

10. Apparatus according to Claim 9 wherein the transfer mechanism comprises a plurality of pairs of jaws for gripping the spacers, the jaws being movable with each other between the assembly station and the transfer station.

11. Apparatus according to Claim 10 wherein the length of each jaw extends in said reference direction.

12. Apparatus according to Claim 9, Claim 10 or Claim 11 further comprising means for raising the spacers into the assembly station.

13. Apparatus according to any one of Claims 9 to 12 further comprising means for raising and lowering a stack of workpieces and spacers at the stacking station.

14. Apparatus according to Claim 13 further comprising a base structure below the stacking station, a container disposed on the base structure, the container having one or more openings in a bottom of the container, and wherein the means for raising and lowering the stack comprises a support disposed within or movable into the container and lifting means mounted on the base structure and arranged to extend through the openings of the container to raise the support.

1 5. Apparatus according to any one of Claims 9 to 14 further comprising a storage conveyor for moving successive groups of workpieces along a path to respective storage positions on the path and an input conveyor for moving a group of workpieces in the reference direction onto said path, the length of the path being transverse to the reference direction and the delivery conveyor being arranged for moving a plurality of groups of workpieces concurrently from their respective storage positions in the reference direction to the assembly station.

1 6. Apparatus according to Claim 1 5 further comprising a plurality of stops spaced apart along said path, each stop being movable independently of the other stops into and out of said path.

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17. A method of stacking elongated workpieces substantially as herein described with reference to the accompanying drawings.

18. Apparatus for use in the method of Claim 1 substantially as herein described with reference to and as shown in the accompanying drawings.

19. Any novel feature or combination of features disclosed herein and/or in the accompanying drawings.