GB2127582A - Scheduler for conveyor control system - Google Patents

Abstract

A computer is responsive to a scheduler to control a conveyor which transports workpieces from a load station to one or more machine bays and then to an unload station. The scheduler includes a first visual display unit (VDU) and a second visual display unit (VDU). The first VDU can display a menu of unscheduled work, and a series of options to the operator. The second VDU provides a visual indication of either an intended schedule or a running schedule as required. Any item of the menu of unscheduled work can be transferred from the first VDU to the second VDU and displayed as an intended schedule. The position of each item of the second VDU can be adjusted to provide a suitable arrangement, and then the intended schedule can be converted to a running schedule. <IMAGE>

Description

SPECIFICATION Control apparatus The present invention relates to apparatus for controlling a conveyor system having a conveyor to convey workpieces from a load station to one or more machine bays in sequence, and then to an unload station.

One example of a conveyor system for which the control apparatus of the invention is applicable, also includes first and second conveyors and an endless recirculation conveyor.

The workpieces are moved along the conveyors on pallets, and these pal lets may be transferred between the conveyors by suitable gates. A machine is located in each machine bay, and the workpieces may be transferred between the pallets in the bay and the machine by robots.

Object of the invention It will be appreciated that a sophisticated conveyor system of this type may be capable of carrying out several different machining operations on a large number of workpieces travelling on the system. It is clearly desirable that the conveyor system is operating as closely as possible to its optimum capacity in which all the machines are occupied during the entire operating time of the system. It is an aim of the invention to assist in reducing unwanted lost capacity in the system.

Statements of invention According to the present invention there is provided apparatus for controlling a conveyor system having a conveyor to transport workpieces from a load station to one or more machine bays and then to an unload station in which the apparatus includes a computer responsive to a scheduler to supervise the machining and feeding of the workpieces on the system, in which the scheduler can receive and display an intended schedule indicating the intended duration of the operations to be carried out on the workpieces in the various parts of the conveyor system, the intended schedule being adjustable by the operator to provide a desired future work programme for the system, and in which the scheduler is operable to convert the intended schedule into a running schedule to control the system.

The apparatus may include a first visual display unit (VDU) and a second visual display unit (VDU).

The first VDU provides a series of options to the operator, and is operable to display a menu of unscheduled work. The second VDU provides a visual indication of either the intended schedule or the running schedule as required. When displaying the intended schedule any item of the menu of unscheduled work can be transferred individually from the first VDU to the second VDU.

The position of each item can be adjusted on the second VDU until a suitable arrangement has been obtained, and then the second VDU can be operated to show the running schedule.

Specific embodiment One embodiment of the invention will now be described by way of example with reference to the accompanying Figures 1 to 6 which illustrate various displays provided by the embodiment.

This embodiment comprises a scheduler for providing a schedule for a conveyor system. This conveyor system includes first and second conveyors and an endless recirculation conveyor located between the first and second conveyors.

This conveyor system is used to convey workpieces from a load station to one or more machine bays in sequence where appropriate machining operations are carried out on the workpieces. The machined workpieces are then passed to an unload station for removal. The workpieces are moved along the conveyors on pallets, and conveniently each pallet contains a plurality of workpieces.

In operation, a pallet is loaded at a load station and then travels along the first conveyor to a load gate which transfers the pallet to the recirculation conveyor. The loaded pallet circulates round the recirculation conveyor until it is desired to carry out a machining or other operation on the workpieces. The loaded pallet is then passed to a machine entry gate and transferred to the second conveyor and passed into the appropriate machine bay. The workpieces are unloaded from the pallet, the appropriate machining or other operation is carried out on these workpieces, and these workpieces are then loaded onto another pallet which is transferred back to the recirculation conveyor. The loaded pallet is then guided in the aforementioned manner to one or more other machine or other bays until all the appropriate machining or other operations have been carried out on the workpieces.When the operations have all been completed, the loaded pallet is then transferred from the recirculation conveyor back to the first conveyor and passed to an unload station. In this conveyor system the pallets are transferred between the respective conveyors by means of gates which slide between either the recirculation conveyor and the first conveyor, or the recirculation conveyor and the second conveyor.

This conveyor system will be hereinafter referred to as a cell, and the cell is supervised by a computer which operates in response to appropriate software. This software comprises computer software which is concerned solely with running the computer itself, and cell software which operates the computer to control the cell.

A part of the cell software is a scheduler which provides a visual indication of the workload of the cell. This scheduler is used rather like a scratch pad to enable the operator to build up a desired intended work load for the cell. When the operator is satisfied with the intended schedule this intended schedule is converted into a running schedule which controls the cell to carry out the work indicated on this running schedule. An example of a running schedule is illustrated in Figure 1.

The scheduler includes a monochrome visual display unit (VDU) and a colour (VDU). The monochrome VDU is a data entry for instructing the computer software, and provides a series of options to the operator; one of these options being the operation of the scheduler. A main menu of the monochrome VDU is illustrated in Figure 2 as follows:- 1) Data entry and modification, 2) Cell control and status, 3) Install a file, 4) Event log analysis, 5) Scheduling, 6) New shift, 7) Statistics print-out, 8) Clear cumulative statistics.

9) Detach terminal.

Operation (9) allows the operator to detach from the cell software itself so as to communicate directly with the computer. This is important and useful if the computer is being used for any additional purposes. This facility is usually available only to the principal operators of the cell.

The required option indicated on the monochrome VDU is selected by pressing an appropriate button. If option (5)-scheduling, is selected then this provides the following schedule options illustrated in Figure 3: 1) Reschedule, 2) Create listing of operations, 3) Create listing of schedule, 4) Return.

If option (1)-Reschedule-is selected then an operator is able to reschedule the forward workload of the cell excluding those operations which have already been commenced.

The colour VDU displays a Gantt chart of the cell, and each machine bay of the cell is represented by two rows on the VDU display; the horizontal axis being used to represent time. The two rows are located above a visible row on the VDU screen which denotes a machine bay. The upper of the two rows is purely a buffer to indicate the duration of the various jobs under consideration and the lower row is the actual schedule which has been decided upon.

Each operation on a particular batch of components is automatically assigned a unique colour pattern. The machining of a particular batch at a particular machine bay can then be represented by a rectangle of the appropriate colour in the row representing that bay; the length of this rectangle occupying the required scheduled time interval. The length of this rectangle equals the machining time per component multiplied by the number of components in a batch.

To commence a rescheduling operation, the operator views the running schedule on the colour VDU and selects a time from which the running schedule is to be modified and the time scale illustrated on the screen. Any operations which are currently scheduled to start after this time are removed from the display. This part of the schedule is displayed to the operator who may now modify the schedule as follows:- A work scheduler menu of the unscheduled work intended to be scheduled is selected on the monochrome VDU, and if desired a computer print-out from the computer printer can be obtained of this unscheduled work. Any item of this unscheduled work can be transferred to the scheduler one at a time and displayed on the colour VDU.The position of each item of unscheduled work on the colour VDU can be altered using a cursor until a suitable arrangement has been obtained. Ideally, an entire line of the display would be filled without any spaces in between thereby avoiding any lost time on the cell. Two work scheduler menus are illustrated: in Figures 4 and 5.

In order to assist the operator, before a new schedule is prepared a list may be displayed on the monochrome VDU of the batches which will not have started by the selected time. A hard copy listing of the machining requirement of the batches may also be obtained, the appropriate operations are denoted by a line of characters whose length is proportional to the duration of the batch on that machine proportional to the duration time of the operation.

The operator may not reschedule any operation which has already started before the selected time; these operations being denoted by the appropriate display box being recoloured white. If a new batch is to be loaded at a loading bay, then the first operation may not be rescheduled once the first pallet of that batch has been registered by the operator. For secondary operations, none of the pallets for the operation must have reached the bay detailed for that operation.

Any operations which have not started or are not scheduled to start by the specified time are descheduled from the running schedule. These descheduled operations may be returned to the schedule by using the scheduler.

Each bay on the cell is represented on the colour VDU display by two lines. The first line contains the bay indent and information about the effects of the modifications being made to the schedule. This first line displays the unscheduled operations for that bay, that is those operations on any batch that already has some operations scheduled. This first line indicates the anticipated performance of the machine in that bay based on the sides of the gaps in the displayed schedule line and the deviation of this value from the required performance of the machine.

The second line contains the scheduled operations for that bay. The operation on the far left of the colour VDU screen may be a representation of the end of an operation currently being carried out on the cell, and this operation may not be moved. If the duration of an operation is less than one character position then some rounding up of the characters may be necessary. This is due to the limitation that a character may have one background colour and one foreground colour.

If two adjacent operations have different background colours, then the foreground colours of each operation are not displayed in the character in which the operations meet. This is a limitation of the particular example now being described, and is not a limitation of the invention itself. The apparatus of this example is limited to two colours, in any one character location, and if no work is scheduled then one colour, black will be displayed. Consequently there can only be one other colour which in this example will be either yellow or blue but not both of them.

If the two adjacent operations have the same background colour then this background colour is displayed with the line in the character where the operations meet.

Underneath the schedule line a cursor may move from left to right, and this cursor is moved by means of a joystick or dedicated cursor keys.

The cursor may be made to point up to the scheduled work of the machine on the aforementioned line, or it may be made to point down to the unscheduled work on the machine below the line. The operator may move the joystick forwardly or backwardly to alter which way the cursor points, and the operator is able to point to an individual line on the display. The unscheduled work on the display is the work the operator is attempting to fit into a schedule.

Consequently until it has been decided to include that work in a schedule it is referred to as unscheduled work.

The time axis of the display is labled in week numbers, and each week is divided into hours.

The number of hours in each week is defined in a calender file previously created. The current date and time and the week number are displayed on the screen.

A list of batches which have not been scheduled can be displayed on the monochrome VDU. This list is added as batches are removed from the schedule being modified and displayed on the colour VDU. Each batch displayed on the monochrome VDU occupies one line and each line has a reference number against it. The operator can select a batch from the monochrome VDU display by entering the reference number, and if all the batches cannot be displayed on the monochrome VDU screen at the same time the operator may view further batches by pressing an "enter" key. For example if it is desired to display 20 items, and the monochrome VDU screen will only accept 10 items at a time, then it is possible to show the 20 items in two consecutive displays.

The operator interacts with the cell software by using function keys, the cursor joystick and alphanumeric keys. The operator identifies a batch either by moving the joystick such that the cursor points to an operation on the colour VDU and then pressing the function key "select" or by entering the batch identifier followed by pressing the function key "select". The batch may be identified either by a numbered choice from the monochrome VDU screen, or by entering the order number of the batch preceded by the function key "order number". Selection on the colour VDU screen of operations or "gaps" between operations is made by moving the joystick in the appropriate direction.

Forward/backward movement causes the cursor to move from one bay line to another. Left/right movement causes the cursor to move to the left or right at one increments under the schedule line of the bay. When the cursor is at the appropriate position the operator presses a function key.

When the "select" key is pressed, the order number and the component number of the selected batch are displayed, and the operation is linked.

To remove a batch from the colour VDU display the operator selects an appropriate operation on the batch or explicitly gives the order number. The operator then presses the function key "delete batch". The rectangles marking the positions of the operations disappear from the colour screen leaving blank spaces into which other work may be scheduled. The batch information then appears last on the list of unscheduled work on the monochrome VDU screen.

To add a batch to the schedule being prepared and displayed on the colour VDU, the operator makes a selection from the list of unscheduled work on the monochrome VDU by inputting the line number on which the batch indent is displayed, or directly inputs the order number. The cell software then calculates the length of each operation required on the batch. The operations are displayed on the right of the colour screen above the line of scheduled work for the appropriate bay. If there is already some unscheduled work for that bay then the new unscheduled work is placed as far right as possible. If there are options available for an operation, for example if the operation may be carried out on more than one machine, then the operation is displayed on the first named option in the component definition file.

These operations have not been scheduled for the cell, but they are simply being displayed so that the operator has a visual representation of the operation duration. This enables the operator to use the colour VDU screen to experiment with different intended workloads before finalising the schedule to be used for the cell.

To schedule an operation for the cell the operator moves the cursor to point to an unscheduled operation and then presses the "select" key. The operator then moves the cursor to an appropriate position on the schedule and indicates what function is required by pressing one of the following keys: "Move two"-the start of the selected operation is moved to the position in the gap above the cursor. If the operation cannot be fitted into that gap then all subsequent operations are shifted to the right. Any gaps between these subsequent operations are maintained.

"Move after"-the selected operation is moved to a position just after the operation to which the cursor is pointing. All operations subsequent to the operation being pointed to are shifted to the right to make way for the operation to be inserted.

The unscheduled operations are displayed on the colour VDU, and the list of unscheduled batches is displayed on the monochrome VDU.

"Move before"-the selected operation is moved to a position just before the operation to which the cursor is being pointed. If the selected operation cannot be fitted in, all operations subsequent and including the operation being pointed to, are moved to the right until the selected operation can be inserted.

If the operator attempts to move an operation to another bay, the software checks that the bay is a valid choice.

To delete an operation, the operator moves the cursor under the selected operation, and presses the "delete op" key. The operation is removed from the schedule leaving a gap, and is then placed on the right-hand side of the screen containing unscheduled operations.

Rescheduling an operation is essentially very similar to scheduling an operation. The operator selects which operation is to be rescheduled, and then indicates where to put the operation by the cursor and by pressing one of the keys "move to", "move before" or "move after".

To delete an interval of idle time between two operations on a particular bay the operator places the cursor under the gap, and then presses the key "delete gap". All operations subsequent to the gap are moved up to the end of the operation prior to the gap. Any gaps in between the subsequent operations are maintained.

The operator may press the function key "pallet loading" to obtain an estimate of pallet loading.

This appears as a histogram, three characters high, at the bottom of the display. The histogram is a representation of the number of pallets circulating on the conveyor at particular time instances. If the loading on the conveyor exceeds the preset value the relevant part of the histogram turns red. The pallet loading display remains on the schedule display until the schedule is modified. The estimate of pallet loading is calculated at the particular instance in time, based on the expected locations of the pallets of each batch in the system. This is based on the assumptions that the machining bays are full, and that pallets in transit to the first operation, and pallets in transit away from the final operation can be ignored. Travel times and distances between machines are also ignored.

The operator may press a function key "check".

This causes the software to check that the operations are consistent, and that the conveyor is not overloaded. Conveyor loading is displayed as a histogram of number of pallets circulating. If an operation fails any condition the operation is blinked. For each operation on the schedule the software checks that: The end of the operation does not occur before the last pallet load can be machined, that is the end must be after the end of the previous operation plus travel time plus machining time for that pallet.

The start of the next operation on this batch does not occur before the first pallet is available on the next machine, that is start time of this operation plus machining time plus travei time.

The last operation is completed on all the batch before the due date of the batch. If this test fails all the operations on the batch are blinked.

Re-synchronise This causes the lines of the schedule to be adjusted according to any slippage which may be occurring on the running schedule. This results in the left-hand side being adjusted. All gaps in the schedule being modified are maintained. The first operation (or gap) of each machine line is timed to begin when the current operation on the bay completes. If a machine is now found to be idle, the first operation or scheduled gap is moved to the left of the screen. Also passed to the manual scheduler is information to enable estimations of the pallet loaded for the start of the schedule to be obtained.

To clear the schedule the operator moves the cursor left or right to select a time after which the schedule is to be cleared. The operator then presses "clear schedule" and confirms the request by 'accept' or cancels the request by cancel'. Any batches which start after the selected time are removed from the screen and reappear as unscheduled work. Any other operations which start after the selected time are removed from the schedule and reappear as unscheduled operations on the right of the display.

The operator may at any time request a redraw of the display by pressing the 'redraw' key. This is used to cancel any blinking operations occurring as a result of performing a 'check' on the schedule.

Also the operator may modify the display to: Alter the scale Alter the start time of the display Pan the schedule View the original schedule The operator may change the scale of the display almost indefinitely, by continual pressing of the 'scale up' and 'scale down' bays. Each depression of the bay altering the scale by a predefined factor.

The operator enters the start time of the display as a week number and hour in the week, this information is then used to define the start time for that particular display.

Also the operator may, if he so desires, request that the original schedule be displayed, for the current scale and time setting, but he is not permitted to modify this schedule.

The operator may scan the schedule at the current scale. On selecting the function, the current display is replaced by schedule beginning at three quarters the way along the current display. When the operator presses the 'pan' key the action is repeated. Two keys are provided to permit panning of the display in either direction.

When the operator is satisfied with a schedule, the new schedule may be incorporated into the running schedule. The operator presses the 'commit' key. The software does a resynchronise on the schedule, and a consistency check, with a pallet loading calculation (checks if pallet loading higher than the optimum). The software informs the operator if there are any errors and requests confirmation or cancellation of the committing of the new schedule into the working schedule. The operator may commit the schedule even though there are errors in it. However, it is only possible to commit a schedule in which batches are either fully scheduled (all operations on the batches are scheduled) or the batch is not scheduled at all.

The display of the running schedule is modified to show the addition of a new schedule.

The operator may decide that the no improvement has been made over the original schedule and the original schedule should be put back into the running schedule. The operator presses the 'abort schedule' key and then the software requests confirmation or otherwise of the action. The modified schedule is lost and the original schedule is reinstated.

Should the operator wish to identify a particular component he may input the appropriate component number and the character which is used to identify the component will be displayed at the bottom of the display. The scheduler includes the previously described Manual Scheduler, a Low Level Scheduler and a High Level Scheduier.

Low level scheduler The Low Level Scheduler handles requests to perform gating operations, and requests for work.

It also handles requests from the running schedule display task and from the Manual Scheduler for information about the current status of all batches being machined. This is sent in terms of batch name and number of components machined.

The Low Level Scheduler maintains a data structure of the pallets in the system. It checks that when a pallet has been read, that it is passing the correct position based on its previous position. If it is not, the operator is notified. When the pallet is gated, the file containing the pallet information is updated. At closedown of the cell, the pallet file is updated to give the current positions of all the pallets which are circulating.

Each "train" of pallets for a batch is self contained, i.e. there are sufficient empty pallets to cope with the phase-shifting of components caused by unloading from one pallet to another.

When there is room in a siding after the last pallet comprising a preceding batch, the first pallet of the next batch may be gated into that particular machine bay.

All pallets associated with a batch (including any empty paliets) are gated out of the machining bays when a particular operation has been completed. Any empty-pallets created as a result of machining and sub-palletising processors are gated off at any unload bay which is using the same type of pallets.

Any empty pallets created by rejecting components etc. are routed to the nearest unload bay to the last operation, which satisfies one of the conditions: 1. The bay currently unloading the batch to which the pallet belongs.

2. The nearest bay which is loading components of the same type but is not unloading anything.

3. The nearest bay unloading components of the same type.

At the bays that have sub-palletisation stations, there will usually be one component in the machine and one in the input station. When an unmachined component is required and there is none available, the robot issues an index pallets request. The pallets in the siding are then indexed along. In general, this means that all but two components on a pallet are put onto the preceding pallet, the other two components are placed back onto the original pallet after the pallets have indexed along.

If there are any components on the inspection platform, the indexing of the pallets is held up until the component is either rejected or accepted.

The Low Level Scheduler is informed by the Loading Bay Monitor and Machining Bay Monitor when a pallet is ready to be gated onto the conveyor. The Low Level Scheduler is also informed by either of the two monitors when a pallet is at a sense switch, Low Level Scheduler then decides if it requires to operate the gate.

The local situation of a gate, that is whether there are any pallets in transit in the gating area, is handled by the conveyor controller for the particular pair of gates. The "rules" used by the Low Level Scheduler for gating depend on the type of gate, and are essentially as follows:- 1. The gating of a pallet out of a Load/Unload bay is permitted when: * The number of pallets on the circulatory conveyor is less than the optimal value, or if it is greater, then a secondary operation on the batch (or unloading of the batch) has started to be machined.

And * The number of pallets already in transit to the destination is less than the available space at the destination.

2. The gating of a pallet into a machine siding is permitted when: The pallet is allocated to the siding, and Sufficient room exists in the siding.

3. The gating of a pallet of a machine bay is permitted when: * There is less than a certain predetermined time interval (say, ten minutes) before the next pallet index.

or * If the number of pallets on the circulatory conveyor is less than the optimum.

4. The gating of a pallet into a Load/Unload bay is permitted when: The pallet has been allocated to the siding, and Sufficient room exists in the siding.

High level scheduler This task handles requests from the Low Level Scheduler when a change from one batch to another occurs in any of the bays for any reason.

When a machine bay has room for a pallet after the last pallet of a batch has been gated in, the High Level Scheduler checks if the next operation is a first operation on a batch. If it is the High Level Scheduler selects a loading bay from which the new batch is to be loaded. The selection of a bay is the nearest loading bay to the first machining bay which satisfies one of the following conditions (in preferential order).

* The nearest unallocated bay which is receiving from the circulatory conveyor pallets of the same type.

* The nearest unallocated bay which is not being used to gate off components.

* The nearest unallocated bay which is being used to gate off components of a different type.

If this last condition fails, an error is iogged and the batch is queued for when a bay becomes available. Once a bay has been allocated for a batch it cannot be used for loading any other batch onto the conveyor until either the batch has been completely loaded onto the conveyor or the batch is withdrawn from the cell.

The allocation of a bay for pallets coming off the conveyor is done by a similar set of rules. The selection of an unload bay is made from the nearest bay to the last machine bay which satisfies one of the following conditions (in preferential order).

* The nearest unallocated bay which is being used to load pallets of the same type.

* The nearest unallocated bay which is not being used to load pallets.

* The nearest unallocated bay which is being used to load pallets of a different type.

The High Level Scheduler also interacts with the Manual Schedulen This occurs when the manual scheduler takes the current schedule from a particular time, for the purposes of modification, and then again when the modified schedule is returned to the High Level Scheduler.

After the completion of a particular batch the computer views the current running schedule and where necessary sends machine tool and robot programmes to the respective equipment together with the routing of pallets with the appropriate components to that bay.

Also, in addition to regular consistency checks the computer iooks at each machine bay periodically. If it detects any spare capacity in a machine bay it will arrange for the work for that operation to be carried out as soon as possible.

i.e. before the scheduled start time. If work is being carried out on the machine in that bay i.e. it is being modified or prepared, this is detected by the computer which ensures that the loaded pallets will enter the bay but that the robots will not transfer the work-pieces from the pallets to the machine or to the buffer pallets.

If the running schedule should have two scheduled work operations for a particular bay, and if the machine for that bay starts working at half speed then the first operation will take longer than was calculated. This is acceptable provided that it does not intrude into the available time period of the second operation. This is also acceptable provided that there is sufficient time for the second operation to be carried out and then for the workpieces to undergo their subsequent scheduled operations. This situation is referred to as the schedule remaining consistent. If there is not sufficient time for the second and subsequent operations to be carried out, i.e. the schedule cannot remain consistent, then the computer informs the operator. It will be appreciated that the computer has some freedom of action.

Claims (filed on 15-7-83) 1. Apparatus for controlling a conveyor system having a conveyor to transport workpieces from a load station to one or more machine bays and then to an unload station in which the apparatus includes a computer responsive to a scheduler to supervise the machining and feeding of the workpieces on the system, in which the scheduler can receive and display an intended schedule indicating the intended duration of the operations to be carried out on the workpieces in the various parts of the conveyor system, the intended schedule being adjustable by the operator to provide a desired future work programme for the system, and in which the scheduler is operable to convert the intended schedule into a running schedule to control the system.

2. Apparatus as claimed in Claim 1 in which the scheduler includes a first visual display unit to provide a series of options to the operator, and a second visual display unit to provide a visual indication of either the intended schedule or the running schedule as required.

3. Apparatus as claimed in Claim 2 in which the first visual display unit is operable to display a menu of unscheduled work.

4. Apparatus as claimed in Claim 3 in which the scheduler is operable to transfer individually any item of the menu of unscheduled work from the first visual display unit to the second visual display unit when displaying the intended schedule.

5. Apparatus as claimed in Claim 4 including means to adjust the position of each item on the second visual display unit until a suitable arrangement has been obtained, said second visual display unit being operable to convert this suitable intended schedule to a running schedule.

6. Apparatus as claimed in Claim 3 in which the first visual display unit is operable to display a list of workpieces on which work will not have commenced by a selected time.

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

Claims (14)

**WARNING** start of CLMS field may overlap end of DESC **. 4. The gating of a pallet into a Load/Unload bay is permitted when: The pallet has been allocated to the siding, and Sufficient room exists in the siding. High level scheduler This task handles requests from the Low Level Scheduler when a change from one batch to another occurs in any of the bays for any reason. When a machine bay has room for a pallet after the last pallet of a batch has been gated in, the High Level Scheduler checks if the next operation is a first operation on a batch. If it is the High Level Scheduler selects a loading bay from which the new batch is to be loaded. The selection of a bay is the nearest loading bay to the first machining bay which satisfies one of the following conditions (in preferential order). * The nearest unallocated bay which is receiving from the circulatory conveyor pallets of the same type. * The nearest unallocated bay which is not being used to gate off components. * The nearest unallocated bay which is being used to gate off components of a different type. If this last condition fails, an error is iogged and the batch is queued for when a bay becomes available. Once a bay has been allocated for a batch it cannot be used for loading any other batch onto the conveyor until either the batch has been completely loaded onto the conveyor or the batch is withdrawn from the cell. The allocation of a bay for pallets coming off the conveyor is done by a similar set of rules. The selection of an unload bay is made from the nearest bay to the last machine bay which satisfies one of the following conditions (in preferential order). * The nearest unallocated bay which is being used to load pallets of the same type. * The nearest unallocated bay which is not being used to load pallets. * The nearest unallocated bay which is being used to load pallets of a different type. The High Level Scheduler also interacts with the Manual Schedulen This occurs when the manual scheduler takes the current schedule from a particular time, for the purposes of modification, and then again when the modified schedule is returned to the High Level Scheduler. After the completion of a particular batch the computer views the current running schedule and where necessary sends machine tool and robot programmes to the respective equipment together with the routing of pallets with the appropriate components to that bay. Also, in addition to regular consistency checks the computer iooks at each machine bay periodically. If it detects any spare capacity in a machine bay it will arrange for the work for that operation to be carried out as soon as possible. i.e. before the scheduled start time. If work is being carried out on the machine in that bay i.e. it is being modified or prepared, this is detected by the computer which ensures that the loaded pallets will enter the bay but that the robots will not transfer the work-pieces from the pallets to the machine or to the buffer pallets. If the running schedule should have two scheduled work operations for a particular bay, and if the machine for that bay starts working at half speed then the first operation will take longer than was calculated. This is acceptable provided that it does not intrude into the available time period of the second operation. This is also acceptable provided that there is sufficient time for the second operation to be carried out and then for the workpieces to undergo their subsequent scheduled operations. This situation is referred to as the schedule remaining consistent. If there is not sufficient time for the second and subsequent operations to be carried out, i.e. the schedule cannot remain consistent, then the computer informs the operator. It will be appreciated that the computer has some freedom of action. Claims (filed on 15-7-83)

1. Apparatus for controlling a conveyor system having a conveyor to transport workpieces from a load station to one or more machine bays and then to an unload station in which the apparatus includes a computer responsive to a scheduler to supervise the machining and feeding of the workpieces on the system, in which the scheduler can receive and display an intended schedule indicating the intended duration of the operations to be carried out on the workpieces in the various parts of the conveyor system, the intended schedule being adjustable by the operator to provide a desired future work programme for the system, and in which the scheduler is operable to convert the intended schedule into a running schedule to control the system.

2. Apparatus as claimed in Claim 1 in which the scheduler includes a first visual display unit to provide a series of options to the operator, and a second visual display unit to provide a visual indication of either the intended schedule or the running schedule as required.

3. Apparatus as claimed in Claim 2 in which the first visual display unit is operable to display a menu of unscheduled work.

4. Apparatus as claimed in Claim 3 in which the scheduler is operable to transfer individually any item of the menu of unscheduled work from the first visual display unit to the second visual display unit when displaying the intended schedule.

5. Apparatus as claimed in Claim 4 including means to adjust the position of each item on the second visual display unit until a suitable arrangement has been obtained, said second visual display unit being operable to convert this suitable intended schedule to a running schedule.

6. Apparatus as claimed in Claim 3 in which the first visual display unit is operable to display a list of workpieces on which work will not have commenced by a selected time.

7. Apparatus as claimed in Claim 6 in which

the second visual display unit is operable to display both scheduled work, and unscheduled work.

8. Apparatus as claimed in Claim 7 including indicating means operable to point to any desired item of displayed scheduled or unscheduled work.

9. Apparatus as claimed in Claim 8 which is operable to transfer a workpiece batch from the first visual display unit to a gap in a displayed schedule on the second visual display unit indicated by said indicating means.

1 0. Apparatus as claimed in any preceding Claim in which the scheduler is operable to transfer individually any item of work from the second visual display unit to the first visual display unit.

11. Apparatus as claimed in any preceding Claim in which the scheduler is key operated.

12. Apparatus as claimed in Claim 11 operable to reschedule an operation to a selected position.

1 3. Apparatus as claimed in Claim 11 operable to delete a gap in the displayed schedule.

14. Apparatus substantially as herein described and shown in the accompanying drawings.