GB2127765A

GB2127765A - Conveying workpieces

Info

Publication number: GB2127765A
Application number: GB08216287A
Authority: GB
Inventors: Peter Henry Cook; Derek Hillyard; Dr Nigel Greenwood; Geoffrey Albert Giles; Edwards John Dalton
Original assignee: 600 Group PLC
Current assignee: 600 Group PLC
Priority date: 1982-06-04
Filing date: 1982-06-04
Publication date: 1984-04-18
Also published as: GB2127765B

Abstract

A method and apparatus for performing a series of machining operations on workpieces loaded on pallets, in which there is a first conveyor 2 on which pallets are moved and, when loaded, transferred to a recirculating conveyor 6 where they are stored in continuous motion to be transferred to a second conveyor 4 so that the workpieces may be removed by robots 52 and machined, the second conveyor and the adjacent active run of the recirculating conveyor moving continuously in opposite directions. <IMAGE>

Description

SPECIFICATION A method and apparatus for performing a series of operations on workpieces This invention relates to a method and apparatus for performing a series of operations on workpieces using a variety of machines.

Prior art It has been realised for some years that industry is more and more requiring flexible manufacturing systems for the production of components. Computer numerical control for the machining of components, particularly those manufactured from metal, is well established and goes a long way to achieving the desired goal of automated output. However, computer numerical control does not go far enough in automating manufacturing processes and flexible manufacturing systems which incorporate, for example, computer numerical control are coming to the fore.

Many different types of flexible manufacturing systems are already in existence. All of these aim towards optimum through-put of the components to be machined with the facility of being able to handle several different types of components each with its own special machining needs. These systems often utilise robots and computer control.

Object of the invention It is the main object of this invention to provide in a flexible manufacturing system for performing a series of operations on workpieces, a method of performing a series of operations which is facilitated by the configuration of conveyors which move the workpieces.

Statements of invention According to the present invention there is provided a method of performing a series of operations on workpieces, in which the workpieces are placed on pallets on a first conveyor at a loading station, the loaded pallets being transferred to a central recirculating conveyor on which they are stored; a loaded pallet being transferred from the recirculating conveyor to a second conveyor for operations to be performed and then back to the recirculating conveyor and subsequently back to the first conveyor all under computer control; said second conveyor having a plurality of work performing stations each having a machine and attendant robot for work to be performed on the workpieces; such transfers being effected at successive work performing stations where work is to be performed on workpieces; the second conveyor and the adjacent section of the recirculating conveyor continuously moving in opposite directions.

The invention also includes each loaded pallet being transferred from the recirculating conveyor to the second conveyor at the upstream end of the work performing station of the second conveyor and, after operations having being performed, being returned to the recirculation conveyor at the downstream end of the work performing station of the second conveyor.

The invention further includes each loaded pallet holding one or more workpieces, on reaching the second conveyor and immediately prior to a workpiece being removed by a robot, being held against forward movement by a latch mechanism distancing the pallet from an empty pallet immediately downstream thereof, each workpiece being removed from a pallet for an operation, after which, being relocated on the said pallet immediately downstream. The invention also includes apparatus for performing a series of operations on workpieces as recited above, comprising a plurality of pallets which carry workpieces; a first conveyor on which pallets are loaded with workpieces for operations to be performed, a central.

recirculating conveyor for the storage of loaded pallets; a second conveyor having a plurality of work performing stations, each work performing station having a machine and attendant robot; pallet transfer mechanism for transferring pallets from the first conveyor to the recirculating conveyor and back again and from the recirculating conveyor to the second conveyor and back again; latch mechanism for restraining forward movement of selected pallets, said latch mechanism being under computer control; and drive means for said conveyors, said drive means being adapted to move the second conveyor and the adjacent section of the recirculating conveyor continuously in opposite directions.

The pallet may each comprise a body with a top plate and a base plate fixed to the body, the said plates being rectangular in plan with a stop pin projecting from the body for co-operation with the latch mechanism. Each conveyor may include a series of free-wheeling rollers connected by chains, the chains riding over driven sprockets and being driven at a constant linear speed, the active run of each conveyor lying above the return run; and each conveyor having said rails for cooperation with the base plate of a pallet to guide the same in its movement along the conveyor.

The pallet transfer mechanism may include at least one U-shaped terminal into which a pallet may enter to be restrained on three sides of its top plate; and means for traversing the terminal from one conveyor to another and hence transferring the pallet therein, said traversing movement being effected entirely in a horizontal plane. The pallet transfer mechanism may have oppositely facing U-shaped terminals, one terminal being used for transferring pallets from the recirculating conveyor and the other terminal being used for transferring pallets to the recirculating conveyor.

Drawings One embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which:~ Figures 1 a, 1 b and 1 c are schematic plan views of a system for machining workpieces, Figure 2 is a simplified schematic plan view of the system of Figure 1, Figure 3 is a perspective view of a pallet transfer mechanism in the form of a gate arrangement of the system of Figures 1 and 2, Figure 4 is a perspective view of a robot used in the system of Figures 1 and 2, Figure 5 is a plan view showing pallet transfer in the system of Figures 1 and 2, Figures 6a, 6,b and 6c show diagrammatic views of a pallet and part of a conveyor of the systems of Figures 1 and 2, Figure 7 is a perspective view of a pallet used in the system of Figures 1 and 2, Figure 8 is a perspective view of a load/unload machining station used in the system of Figures 1 and 2, and Figure 9 is a block schematic diagram of the computer control of the system of Figures 1 and 2.

Specific embodiment Referring particularly to Figures 1 and 2, a system for performing a series of machining operations on workpieces includes first and second conveyors 2 and 4 and an endless recirculation conveyor 6. The purpose of these conveyors 2, 4 and 6 is to convey pallets which support workpieces to be machined. As shown in Figures 6a and 6c, each of these conveyors 2 and 4 comprise an endless independently driven roller track approximately 40 metres long and 300 millimeters wide. This roller track is formed by longitudinally spaced rollers 8 extending transversely between endless chains 10. These rollers 8 are not driven but are independently mounted between the endless chains 10 which are supported by track side members 11 along their upper run and are free to rotate individually.

The recirculation conveyor 6 is made up of two such roller track conveyors 14 and 16 similar to the conveyors 2 and 4, and two connecting discs 1 2 located at opposite ends of the conveyors 14 and 16. As shown in Figure 2, the conveyors 14 and 16 are driven in opposite directions to one another and the connecting discs 12 are rotated in the same directions as one another to provide the endless recirculation path. A boundary rim 18 extends round the outer 1800 of the perimeter of each disc 12 to prevent a pallet on the recirculation conveyor 6 from coming off at the two ends. Rollers 20 are driven in unison with the conveyors 14 and 16 and the discs 12 to assist the pallets transferring between the connecting discs 12 and the conveyors 14 and 16.A horizontal guide plate 22 extends between the ends of the outer track side member 11 on each conveyor 14 and 16 and the transverse diameter of the adjacent connecting disc 12. As will be hereinafter described this guide plate 22 extends over the base plate of a pallet passing between the conveyors 14 and 16 and the connecting disc 12 to ensure that the pallet transfers correctly.

Referring to Figure 7, each pallet consists of an aluminium body 24, a nylon base plate 26 and a steel top plate 28; these three members being substantially square, and the base plate 26, to plate 28 being of slightly larger dimensions than the body 24 so that they project over the body 24.

It is this projecting portion of the base plate 26 which slides under the upper mentioned guide plate 22 and abuts the guide bar 21 extending between the connecting disc 12 and the conveyors 14 and 16.

An important feature is that the conveyors 2, 4, 14 and 16 are parallel to one another to provide four parallel conveyor tracks for the pallets 23.

As previously mentioned, the conveyor rollers 8 are not driven but are rotatably mounted between the endless chains 10. Friction fingers extend between adjacent rollers 8 on the conveyors to provide friction between these rollers 8 and pal lets 23 resting thereon. This friction ensures that the supported pallets 23 will be moved along the conveyors by the rollers 8. The conveyor 4 travels in the opposite direction to the conveyor 14, and the conveyor 2 travels in the opposite direction to the conveyor 16. The pallets 23 are transferred between the conveyors 2 and 16, and 4 and 14 when required by a series of gates which are mounted for slidable movement between the conveyors 2 and 16 and 4 and 14 respectively.All these gates are of an U-crosssection with the base of the U extending across an appropriate conveyor and the arms of the U extending in the direction of the conveyor over the conveyor track side members 11. The end gates 30 are single-U formation with the U's facing towards one another, and the intermediate gates 32 are of double-U formation with the two U's of each gate extending in opposite directions to one another along the appropriate conveyor. As shown particularly in Figures 1 and 2, a series of machine tools 34 are located along the length of the conveyor system adjacent to the conveyor 4 with each machine tool 34 located between adjacent gates. A series of longitudinally spaced load and unload station 36 extend along the conveyor 2 at the opposite side of the system to the machine tools 34.

Referring particularly to Figure 8, each load and unload station comprises an unload intermediate gate 38 and a load intermediate gate 40 downstream of the unload gate 38 on the conveyor 2. A manually operable pallet release mechanism 42 and a data entry and display terminal 44 are located between the gates 38 and 40 with the terminal 44 downstream of the release mechanism 42 and terminal 44 adjacent gate 40. Referring particularly to Figure 3, a series of pallet latch mechanisms 46 are located along the conveyor system, and upstream of each gate.

As will be hereinafter described there are three longitudinally spaced pallet latch mechanisms 46 upstream of all the gates on the conveyor 4 except for the end gate at the left hand end of the conveyor 4 as shown in Figure 1. In addition two pallet latch mechanisms 46 are located in each load and unload station downstream of the unload station and upstream of the load station. The upstream of these latch mechanisms 46 i.e.

mechanism nearer to the unload station, can be released by its associated manual pallet release mechanism 42 (see Figure 8). It will be appreciated that in each load and unload station, the unload station is upstream of the load station and that the end upstream and downstream stations include an end unload gate and load gate 30 respectively. Referring to Figure 8, a pallet 23 is loaded at a load station with two workpieces, one on top of the other, where it is held by a latch mechanism 46 upstream of its load gate 40. An operator informs the main computer control that the pallet is loaded by means of the terminal 44.

This terminal 44 also informs the operator what the load and unload situation is at his station and gives him appropriate instructions. When appropriate, the main computer control instigates release of the pallet by means of the pallet latch mechanism 46 and the loaded pallet enters the load gate 40. Any subsequent pallets along the conveyor 2 are held by the pallet latch mechanism 46 which has been reclosed. The computer then instigates movement of the load gate 40 which slides across from the conveyor 2 to the conveyor 16, and the loaded pallet travels down the conveyor 16 and circulates around the endless conveyor 6. Each latch mechanism 46 holds a pallet by means of its latch member abutting a stop pin 41 which projects from the pallet body 24. To release a pallet 23, the latch member is actuated to withdraw from the pallet stop pin 41.When it is required to unload the loaded pallet, this loaded pallet is held by the latch mechanism 46 immediately upstream of an unload gate 38 at a selected unload station. The unload gate 38 is then controlled by the computer control to slide across from the conveyor 2 to the conveyor 16, the pallet latch mechanism 46 is released to allow the loaded pallet to enter this unload gate, and this unload gate is then slid back over on to the conveyor 2. The loaded pallet then travels down the conveyor 2 and is held by the latch mechanism 46 in the load and unload station. If any preceding pallets are held by this latch mechanism 46, then the loaded pallet will simply abut the preceding pallet or pallets and queue up.Each loaded pallet is then unloaded by an operator at this unload station, and the operator then operates an associated pallet release mechanism 42 to release one or more empty pallets into the load station. Each unloaded pallet travels along the conveyor 2 and is held by the latch mechanism 46 immediately upstream of the load gate 40 where it is loaded ready for the previously described transfer to the main recirculation conveyor 6.

Referring to Figure 3, to transfer a loaded pallet from the conveyor 14 of the recirculation conveyor 6 onto the conveyor 4, the loaded pallet is held by a pallet latch mechanism 46 immediately upstream of a machine entry gate 48 operating between the conveyors 14 and 4. In response to computer control the latch mechanism releases the pallet which enters the gate 48, the gate transfers the pallet from the conveyor 14 to the conveyor 4, and the pallet travels down the conveyor 4 towards the next downstream machine exit gate 50. These gates 48 and 50 are located at opposite ends of a machine bay destined for a particular work operation on the pallet load. Each machine bay includes an appropriate machine tool 34, a robot 52 and a data entry and display unit 54. Upstream of this exit gate 50 there are three longitudinally spaced pallet latch mechanisms 46.The latch mechanism 46 nearest to the exit gate 50 will be referred to as the forward mechanism, and the other two will be referred to as the intermediate mechanism and the rear mechanism respectively.

An empty pallet is passed towards the exit gate 50 and is held by the forward latch mechanism 46. The upper mentioned loaded pallet is passed towards the exit gate 50 and held by the intermediate latch mechanism, and if desired, a subsequent loaded pallet is passed towards the gate 50 and held by the rear latch mechanism 46.

It may be that each pallet holds two workpieces one on top of the other. Referring to Figures 4 and 5, a robot 52 takes the upper workpiece on the pallet and may pass it directly to a machine 34 in the associated machine bay. When the machining operation has been carried out, the robot takes the workpiece and may place it directly on the previously emptied pallet at the forward latch mechanism 46. The robot 52 then takes the lower workpiece on the pallet and the intermediate hold mechanism, and passes it to the appropriate machine for the required machining operation.

When the machining operation has been carried out, the robot transfers this workpiece to the forward pallet so that the forward pallet now has the same two workpieces on it in reverse order.

The computer then releases the forward latch mechanism 46 to pass the now loaded pallet with the machine workpieces into the exit gate 50. The computer then controls this gate 50 to transfer this pallet back on to the conveyor 14, and the pallet then passes round the recirculation conveyor 6 to the next machining station. This loaded pallet is then passed into the next work station by the previously described series of operations. The upper mentioned three longitudinally spaced latch mechanisms 46 are provided to take account of the physical size of the gripper mechanism of the robot 52. The three latch mechanisms 46 are sufficiently spaced to enable the robot 52 to remove and replace a workpiece from and to a pallet without disturbing a workpiece on an adjacent pallet. If the gripper mechanism of the robot 52 was sufficiently small then the system would be workable with only a single pallet latch mechanism 46 immediately upstream of an exit gate 50.

This system is not limited to any specific way of carrying or mounting workpieces on the pallets 23. If for example, it is intended for a pallet to carry elongated workpieces such as shafts, a perforated holed member can be mounted on the pallet with each shaft mounted vertically in its associated hole.

Referring to Figure 1, there are eight machine bays each with an appropriate machine or machines. These nine machines comprise two computer numerical control latches, two turning centres, a gear shaper and a tooth rounder and deburrer in a single bay, a cylindrical grinder, a hob and a horizontal broach. It is, however, not necessary for a pallet to be passed into any one of these bays. If for example it is only required to have the machining operations which are carried out on three of these bays, then the pallet is passed round the recirculation conveyor 6 and only transferred into these particular machine bays by the above mentioned operation.

Upstream and downstream of every gate there is a sensor system which informs the main computer control that an appropriate pallet has correctly entered and left that gate. In addition, upstream of every gate of the main recirculation conveyor 6, sensor systems also identify the particular identification number of a pallet and operate a check so that the computer can always know where each particular pallet is at any given time.

Referring to Figure 9, the conveyor system is ultimately controlled by either of two computers 56 and 58. If the controlling computer goes out of service, then the standby computer is automatically switched into operation. This is to prevent the system becoming inoperative, and uncontrollable, due to a fault in a computer. A pair of hard discs 60 enables information to be read into and out of each computer at very high speed, and each computer is operated by the appropriate visual display units and other terminals 62. For slower information insertion and retrieval a magnetic tape 64 may be used, and a line printer 66 enables information to be extracted from each computer.

A pallet base plate 26 when travelling along each conveyor track, slides between the outer track side member 11, which ends just above the base plate 26 and the inner track side member 13 which is the same height as the member 11. In this way the pallet is controlled on two sides and its bottom, and when it is in a gate it is also controlled at a forward face. The gate side arms of the U also slide against the sides of the pallet top plate 28 and the gate cross arm abuts the forward edge of the pallet top plate 28. The track side members 11 of the conveyor do not extend into a gate area, otherwise the gate could not slide across. However, the inner track side members 13 of the recirculation conveyor 6 are uninterrupted.

In the foregoing, each work performing station has been described incorporating a machine tool such as a lathe, but any machine for carrying out work on a workpiece may be incorporated.

The particular configuration and movement of the second conveyor 4 and the adjacent run 14 of the recirculating conveyor in being accessible one from the other and moving in opposite directions has the advantage of enabling a pallet carrying a workpiece to be moved into a bay and emerging from that bay at its upstream end (in relation to the adjacent run of the recirculation conveyor) so that the pallet may even be readmitted immediately into that same bay for a further operation to be performed. Such contra-flow also permits simplification in the geometry of the transfer mechanism. Also, this contra-flow system, combined with the recirculation conveyor enables operations to be performed non sequentially in relation to the disposition of the machines.

Claims (Filed on 27 May 1983) 1. A method of performing a series of operations on workpieces, in which the workpieces are placed on pallets on a first conveyor at a loading station, the loaded pallets being transferred to a central recirculating conveyor on which they are stored; a loaded pallet being transferred from the recirculating conveyor to a second conveyor for operations to be performed and then back again to the recirculating conveyor and subsequently back to the first conveyor all under computer control; said second conveyor having a plurality of work performing stations each having a machine and attendent robot for work to be performed on the workpieces; such transfers to and from the second conveyor being effected at successive work performing stations where work is to be performed on workpieces; the second conveyor and the adjacent section of the recirculating conveyor continuously moving in opposite directions.

2. A method as claimed in Claim 1, in which each loaded pallet holds one or more workpieces and, on reaching the second conveyor and immediately prior to a workpiece being removed by a robot, being held against forward movement by a latch mechanism distancing the pallet from a sufficiently empty pallet immediately downstream thereof, each workpiece being removed from a pallet for an operation to be performed, after which, the said workpiece is relocated on the said pallet immediately downstream.

3. Apparatus for performing a series of operations on workpieces by the method claimed in either Claim 1 or Claim 2, comprising a plurality of pallets which carry workpieces; a first conveyor on which pallets are loaded with workpieces for operations to be performed, a central recirculating conveyor for the storage of loaded pallets; a second conveyor having a plurality of work performing stations, each work performing station having a machine and attendent robot; pallet transfer mechanism for transferring pallets from the first conveyor to the recirculating conveyor and back again and from the recirculating conveyor to the second conveyor and back again; latch mechanism for restraining forward movement of selected pallets, said latch mechanism being under computer control; and drive means for said conveyors, said drive means being adapted to move the second conveyor and

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. pallet with each shaft mounted vertically in its associated hole. Referring to Figure 1, there are eight machine bays each with an appropriate machine or machines. These nine machines comprise two computer numerical control latches, two turning centres, a gear shaper and a tooth rounder and deburrer in a single bay, a cylindrical grinder, a hob and a horizontal broach. It is, however, not necessary for a pallet to be passed into any one of these bays. If for example it is only required to have the machining operations which are carried out on three of these bays, then the pallet is passed round the recirculation conveyor 6 and only transferred into these particular machine bays by the above mentioned operation. Upstream and downstream of every gate there is a sensor system which informs the main computer control that an appropriate pallet has correctly entered and left that gate. In addition, upstream of every gate of the main recirculation conveyor 6, sensor systems also identify the particular identification number of a pallet and operate a check so that the computer can always know where each particular pallet is at any given time. Referring to Figure 9, the conveyor system is ultimately controlled by either of two computers 56 and 58. If the controlling computer goes out of service, then the standby computer is automatically switched into operation. This is to prevent the system becoming inoperative, and uncontrollable, due to a fault in a computer. A pair of hard discs 60 enables information to be read into and out of each computer at very high speed, and each computer is operated by the appropriate visual display units and other terminals 62. For slower information insertion and retrieval a magnetic tape 64 may be used, and a line printer 66 enables information to be extracted from each computer. A pallet base plate 26 when travelling along each conveyor track, slides between the outer track side member 11, which ends just above the base plate 26 and the inner track side member 13 which is the same height as the member 11. In this way the pallet is controlled on two sides and its bottom, and when it is in a gate it is also controlled at a forward face. The gate side arms of the U also slide against the sides of the pallet top plate 28 and the gate cross arm abuts the forward edge of the pallet top plate 28. The track side members 11 of the conveyor do not extend into a gate area, otherwise the gate could not slide across. However, the inner track side members 13 of the recirculation conveyor 6 are uninterrupted. In the foregoing, each work performing station has been described incorporating a machine tool such as a lathe, but any machine for carrying out work on a workpiece may be incorporated. The particular configuration and movement of the second conveyor 4 and the adjacent run 14 of the recirculating conveyor in being accessible one from the other and moving in opposite directions has the advantage of enabling a pallet carrying a workpiece to be moved into a bay and emerging from that bay at its upstream end (in relation to the adjacent run of the recirculation conveyor) so that the pallet may even be readmitted immediately into that same bay for a further operation to be performed. Such contra-flow also permits simplification in the geometry of the transfer mechanism. Also, this contra-flow system, combined with the recirculation conveyor enables operations to be performed non sequentially in relation to the disposition of the machines. Claims (Filed on 27 May 1983)

1. A method of performing a series of operations on workpieces, in which the workpieces are placed on pallets on a first conveyor at a loading station, the loaded pallets being transferred to a central recirculating conveyor on which they are stored; a loaded pallet being transferred from the recirculating conveyor to a second conveyor for operations to be performed and then back again to the recirculating conveyor and subsequently back to the first conveyor all under computer control; said second conveyor having a plurality of work performing stations each having a machine and attendent robot for work to be performed on the workpieces; such transfers to and from the second conveyor being effected at successive work performing stations where work is to be performed on workpieces; the second conveyor and the adjacent section of the recirculating conveyor continuously moving in opposite directions.

the adjacent section of the recirculating conveyor continuously in opposite directions.

4. Apparatus as claimed in Claim 3, in which each pallet comprises a body with a top plate and a base plate fixed to the body, the said plates being rectangular in plan with a stop pin projecting from the body for co-operation with the latch mechanism.

5. Apparatus as claimed in any one of the preceding claims, in which each conveyor includes a series of free-wheeling rollers connected by chains, the chains riding over driven sprockets and being driven at a constant linear speed, the active run for each conveyor lying above the return run; and each conveyor having side rails for co-operation with the base plate of a pallet to guide the same in its movement along the conveyor.

6. Apparatus as claimed in any one of the preceding claims, in which the pallet transfer mechanism includes at least one U-shaped terminal into which a pallet may enter to be restrained on three sides of its top plate; and means for traversing the terminal from one conveyor to another and hence transferring the pallet therein, said traversing movement being effected entirely in a horizontal plane.

7. Apparatus as claimed in Claim 6, in which the pallet transfer mechanism has oppositely facing U-shaped terminals, one terminal being used for transferring pallets from the recirculating conveyor and the other terminal being used for transferring pallets to the recirculating conveyor.

8. A method of performing a series of operations on workpieces substantially as herein described.

9. Apparatus for performing a series of operations on workpieces by the method claimed in any one of Claims 1,2 or 8, substantially as herein described with reference to the accompanying drawings.