Machines for cutting large steel plates, produced by a steel mill, into smaller"child" plates require accurate positioning of cutting torches to ensure the cutting torches only act on the plate material. The torches also need to act on the edge of a plate to initiate cutting, otherwise undesired splatter deposits are formed on the plate material. Accurate positioning of the torches relative to a"mother"plate to be cut is normally achieved by manually positioning and adjusting the torches prior to a cutting operation. Automation of the plate cutting process has proved difficult to achieve primarily because cutting machines have been unable to cater for mother plates which do not have uniform perimeters and exhibit size variations between successive plates. Also the material handling systems of the machines invariably place mother plates on a cutting table in different positions which needs to be catered for when adjusting the torches. Providing a machine which is configured for automatic processing of mother plates, and child plates, test pieces and scrap pieces which are cut from the mother plates, would be advantageous and provide at least a useful alternative.

In accordance with the present invention there is provided an apparatus for cutting articles, including: a cutting station for supporting an article to be cut; camera means for scanning said article to generate image data representing an image of said article at said station; processing means for processing said image data to generate perimeter data defining a perimeter of said article and the position of the perimeter relative to said cutting station; control means, responsive to the perimeter data, for controlling the position of cutting means for cutting the plate.

Preferably the apparatus includes mounting means for mounting the cutting means and the camera means, and which is movable relative to the cutting table for scanning the article in a first direction and cutting the article in a second direction.

The present invention also provides an apparatus for cutting articles, including: a conveyor system for moving an article to be cut to a cutting station; mounting means for mounting cutting means and line scanning means, said line scanning means being arranged to scan a plurality of scan lines across said article at said cutting station; detection means responsive to the line scanning means for detecting a perimeter of the article; and cutter control means responsive to the detection means for controlling the position of the cutting means during cutting of the article.

Preferably the mounting means is arranged to execute a scanning pass in a first direction in which said line scanning means is operable and is arranged to subsequently execute a cutting stroke in a second direction in which said cutting means is operable.

Preferably said second direction is opposite to said first direction.

Preferably the apparatus includes auxiliary conveying means for conveying scrap and test pieces cut from the article laterally away from said conveyor system to sorting means, the sorting means being operable independently of the mounting means.

Preferably the article is a metal plate, such as a steel plate. Preferably the cutting means includes a plurality of gas cutting torches, such as plasma torches. Advantageously the mounting means includes a beam which extends across the cutting station and respective mounting modules for fixing the torches to the beam, said mounting modules including motors for controlled movement of the torches in the first, second and third directions relative to said beam. Preferably said cutting station includes a cutting table on which said plate is supported.

A preferred embodiment of the present invention is hereinafter described, by way of example only, with reference to the accompanying drawings, wherein: Figure 1 is a side view of a preferred embodiment of a plate cutting apparatus; Figure 2 is an end view of the plate cutting apparatus;

Figure 3 is a plan view of the plate cutting apparatus; Figure 4 is a schematic view of part of the apparatus showing plasma torches and line cameras; Figure 5 is a more detailed schematic view of a torch carriage assembly; Figure 6 shows part of a roller conveyor; Figure 7 shows part of the roller conveyor with a lifting frame elevated; Figure 8 diagrammatically illustrates camera line scans on a plate to be cut; Figure 9 is a schematic plan view of a plate to be cut; Figure 10 is a block diagram of a control system of the plate cutting apparatus; Figure 11 is a block diagram of a vision module of the control system; Figure 12 is a block diagram of image processors of the vision module; Figure 13 is a plan view of a calibration bar of the apparatus; Figure 14 is a flow diagram of a calibration process of the control system; Figure 15 is a flow diagram of a plate scan process of the control system; and Figure 16 is a schematic plan view of the plate cutting apparatus illustrating control of the torches by the control system.

A plate cutting apparatus 2, as shown in Figure 1, includes a main plate conveyor system 4 for moving plates 9, to be cut, generally horizontally through the apparatus. The conveyor system 4 moves the plates horizontally through the apparatus in a direction referred to as the x-axis. The conveyor system includes an inlet conveyor 6, cutting table 8 and outlet conveyor 10. The inlet conveyor 10 transports plates 9 to the cutting table 8. Once the plates 9 are on the table 8, the conveyor system is stopped so that scanning and cutting can take place as described below.

The apparatus includes a cutting beam 14 which is mounted for horizontal movement perpendicular to the direction of movement of the conveyor system 4, hereinafter referred to as the y-axis. The beam 14 is mounted on guide rails 16 and 18 which support the ends of the beam. Drive motors 20 are provided for accurately controlling movement of the beam 14 in the y-axis.

The beam 14 supports a number of cutting torches and in the illustrated arrangement there are four cutting torches 22,24,26 and 28. As will be explained hereinafter, the cutting torches are also each movable relative to the beam 14 in a controlled way, in the x-axis direction and in a direction referred to hereinafter as movement in the v-axis, which is parallel to the y-axis. The torches are also moveable up and down relative to the table 8. In the illustrated arrangement, the torch 22 at the upstream end of the cutting table 8 is fixed in the v-axis direction, the other torches being independently movable in the v-axis direction. As will be described below, each of the torches 22,24,26 and 28 is mounted on a torch carriage assembly 30,32,34 and 36. The assemblies permit adjustments to be made in the positions of the torches vertically and horizontally relative to the beam 14.

The beam 14 also supports a plurality of line cameras which are arranged to scan a line 12 on the cutting table 8 in the x-axis direction. In the illustrated arrangement there are four line cameras 38,40,42 and 44 which are carried by camera support beams 46,48,50 and 52, the camera support beams being equispaced on the top of the beam 14. As the beam 14 moves a plurality of lines 12 are scanned as diagrammatically shown in Figure 8. The cameras may comprise EE&G RETICON 4096 Pixel Line Scan cameras which are commercially available.

As will be explained in more detail below, each of the cameras is arranged to scan respective parts of the scan line 12 in the x-axis direction. The main function of the line cameras is to detect edges of the plates 9 in order to accurately determine the perimeter and the position of the plate on the table 8. A cutting control system 152, as described below, is used to accurately control the movement of the torches in order that the plates 9 can be accurately cut to size and shape.

The apparatus includes an elongate illuminating lighting system 56 which is supported on the beam 14, as best shown in Figure 4. The lighting system 56 directs light towards the cutting table 8 to illuminate the area beneath the line cameras so as to facilitate detection of the plate edges as the line cameras move over the plate. Signals from the line cameras are processed by respective line camera computers 180,182,184 and 186. Preferably the line camera computers are mounted on the support beams 46,48,50 and 52 respectively so that

they can be physically close to the cameras to avoid propagation delays in the signal transmissions from the cameras to the computers. This enables faster processing of the visual signals received by the line cameras.

In use of the apparatus, the beam 14 is initially at the left hand side of the cutting table 8, as shown in Figure 3. The apparatus is then activated so that the beam 14 moves in the y-axis at constant speed and the line cameras are triggered at fixed time intervals so as to effectively scan a plurality of closely spaced parallel scan lines 12 on the cutting table 8, as diagrammatically illustrated in Figure 8. In Figure 8, the plate 9 is shown at an exaggerated mis-orientation relative to the x-axis direction but in the apparatus 2 the torches can be controlled so that cuts are made perpendicular to the edges of the plate notwithstanding mis- orientations on the cutting table 8. The scan lines 12 are preferably spaced apart by a distance of say 1 mm, each of the scan lines being made up from signals derived from the respective line cameras 38,40,42 and 44. As will be described below, signals from the line cameras enable detection of the peripheral edges of the plate 9.

Once the beam 14 has moved across the cutting table 8 in the scanning direction, the information is processed so as to accurately determine the position of the plate and required movement of the respective torches 22,24,26 and 28 in order to cut the plate in the desired shape and size. The torches are then activated and the beam 14 moves in a cutting pass or stroke in the direction of the y-axis but in the opposite direction to the scan direction. During the cutting pass of the beam 14, the torches cut through the plate 9 so as to cut a desired "child"piece 72 from the"mother"plate 9. Usually there will be a scrap piece 74 cut at one end of the mother plate 9 and a test piece 76 for testing of the material of the child piece 72 at the other end, and the position of these may be reversed at any time. The scrap piece 74 may be further cut into smaller parts so that the scrap portions do not exceed a predetermined size.

After the torches have completed the cuts required on the plate 9, a magnetically operated lifting gantry 78 is operated so as to lift the scrap piece 74 and test piece 76 from the cutting table 8. Two lifting gantries 78 are fixed to the beam 14, but are able to move along

the beam 14 in the x-axis independently and lift independently. Each lifting gantry 78 can move a scrap piece 74 and test piece 76 to a lateral conveyor 80 having two independently movable segments 82 and 84 for conveying the scrap and test pieces 74 and 76 to an unloading station 86, as best seen in Figure 3. A gantry crane 88 can then pick up the scrap pieces 74 and deposit them in scrap bins 90,92 and 94. The system can be arranged to deposit scrap of different grades in the respective bins. The gantry crane 88 can also move the test pieces 76 to test racks 96. Once the scrap and test pieces 74 and 76 have been moved from the cutting table 8, processing of the scrap and test pieces can be carried out independently of operation of the main conveyor system 4 and the cutting beam 14. This enables faster overall processing of material through the apparatus. The apparatus 2 includes a test piece marker 98 for applying coded information on the test pieces 76 so that they can be positively identified at a later stage.

Figure 5 schematically illustrates the torch carriage assembly 32 in more detail, the other assemblies being the same or similar. It comprises a housing 100 which is mounted for sliding movement on a guide rail 102 which is carried by the beam 14. Movement of the torch assembly 32 is controlled by means of a stepping motor 104 which is provided with a pinion 106 on its output shaft. The pinion 106 engages an elongate rack 108 which extends along the beam 14. The stepping motor 104 thus can be used to accurately control movement of the torch 24 in the x-axis, before and as the beam 14 moves across the table 8.

The assembly 32 also includes an arrangement for adjusting the horizontal v-axis position of the torch 24 relative to the housing 100. In the illustrated arrangement this is achieved by a horizontal adjusting screw 110 which is controlled by a stepping motor 112.

Vertical adjustment of the torch 24 is also possible by means of a vertical adjusting screw 114 which is controlled by a stepping motor 116. The adjustments afforded by the screws 110 and 114 are normally set before a cutting pass takes place and are not normally moved during the course of a cutting pass. The vertical adjustment afforded by the screw 114 is set so that the torch 44 is the correct distance above the plate 9 to cut the plate during a cutting pass or stroke, and adjustment of the v-axis position afforded by the screw 110 is set so that the torch 24 is positioned directly above the first side edge of the plate 9 to be cut during a cutting pass,

as described hereinafter.

The torches 22 to 28 can comprise plasma arc torches, oxy-torches or other cutting arrangements. Preferably, the torches comprise Kjellberg'or other commercially available plasma torches of known type.

Figures 6 and 7 illustrate part of the cutting table 8 in more detail. The cutting table 8 preferably comprises a wet table having a plurality of steel rollers 120 which can be rotated in order to move the plate there along. The rollers are suspended over a bath 122 of coolant, such as water. When the movement of the rollers 120 stops in readiness for scanning and cutting passes, a plate lifting mechanism 124 is operated in order to lift the plate 9 above the rollers 120, as diagrammatically illustrated in Figure 7, to avoid overheating, burning or cutting of the rollers during the cutting passes. The lifting apparatus 124 comprises a lifting frame 126 which includes beams located between adjacent rollers 120, the frame 126 being selectively movable by means of pneumatic bellows 128.

The cutting apparatus of the invention can be used for cutting relatively large plates.

For instance the mother plates may range in length from 6 to 15 metres and in width from 1.5 to 3.1 metres. Various materials can be cut but the torches would need to be suited to the material being cut. For steel plate, plasma arc torches are appropriate. The thickness of the material being cut is normally in the range from 3 to 10 mm but again different thicknesses of material can be accommodated provided suitable torches are provided.

The cutting table 8 is about 17 metres long and about 3.6 metres wide. The line cameras 38,40,42 and 44 are approximately 3.9 metres above the level of the cutting table 8. The beam 14 can be driven at a rate of up to 20 metres per minute in the y-axis direction.

The control system 152 for triggering the line cameras can be triggered at fixed time intervals, say at 5 millisecond intervals or at selected multiples of 5 milliseconds (e. g. 10 milliseconds, 15 milliseconds, etc.).

The cutting apparatus 2 can be coupled to rolling mills or other treatment plants as

required.

The computer control system 150 of the apparatus 2, as shown in Figure 10, includes a cutting subsystem 152, a material handling subsystem 154 and a process manager or supervisor computer 156 connected by an Ethernet local area network 158. The process manager 156 is a workstation which includes control software to receive messages from the subsystems 152 and 154 concerning data collected from the status of their components and send instructions to the subsystems 152 and 154 to control the timing and actions performed during the cutting process and handling of all plate material. The process manager 156 can also be connected by a level one gateway 160 to a network 162 of the plant to receive and send messages on the plant network 162 concerning the status of and actions to be performed by the cutting apparatus 2. A management interface system 164 and a planning system 166 may be connected to the plant network 162. The systems 164 and 166 are used to display information on all plant equipment and send instructions to the process manager 156 to control aspects of the cutting apparatus 2, such as the type of plates the apparatus 2 is to handle, and the profiles that need to be cut in the mother plates.

The subsystems 152 and 154 each include computer numerical control (CNC) units 168 and 170 connected to the Ethernet network 158 and for use in controlling the positions of respective machine components of the apparatus 2. The CNC 168 of the cutting subsystem 152 controls, movement of the beam 14, activation of the cutting torches 22 to 28, movement of the v and x-axes of the carriage assemblies 30 to 36, triggering of the line cameras 38 to 44, and the lifting gantries 78. The CNC 168 also triggers activation of a vision module 172.

The CNC 170 of the material handling subsystem 154 controls the conveyor system 4, gantry crane 88, the side conveyor 80, and a marker controller 174 for controlling the marker 98.

Text to be printed by the marker 98 is passed by the CNC 170 to the marker controller 174 using an RS 232 interface. Both CNCs 168 and 170 execute compiled program logic control (PLC) programs and at run time each execute interpretively numeric control (NC) programs which have been generated and forwarded by the process manager 156. The PLC and NC programs provide position data to set the positions of controlled components, tool data to select and initiate components, and path data to define the speed and direction of a travel path,

and any offset from the path, i. e. from the speed and direction. The specific programs executed and their sequence are described below. The CNCs 168 and 170 communicate with one another to coordinate control of the components by exchanging TCP/IP messages on the Ethernet network 158. Both CNCs 168 and 170 are PDF 32 CNCs manufactured by Farley Cutting Systems Australia Pty. Ltd. The cutting cycle controlled by the process manager 156 consists of four main steps which are: 1. Calibrate the line cameras 38 to 44 using the vision module 172 and a calibration bar 200 fixed to the cutting table 8.

2. Scan the mother plate 9 on the cutting table 8 using the line cameras 38 to 44 and determine the coordinates defining the perimeter of the plate.

3. On the basis of the plate perimeter data obtained, position the cutting torches and move the cutting torches across the plate to execute a cutting stroke during which the mother plate is cut as desired.

4. Use the gantry 73 and crane 88 and side conveyor 80 to remove and deposit any scrap and test pieces, during which test pieces may be marked via the marker 98.

The vision module 172, as shown in Figure 11, includes the four personal computers 180,182,184 and 186 which are all connected to the Ethernet network 158 and are used to execute image processing for each of the cameras 38 to 44. The PCs 180 to 186 operate in a master/slave relationship, where one of the PCs 180 acts as the master and coordinates the image processing executed by the slave PCs 182 to 186. The master PC 180 is able to communicate with the process manager 156 to provide status messages and receive instructions. The master PC 180 also communicates with the cutting CNC 168 to obtain data on the position of the beam 14, which is controlled by the CNC 168. The master PC 180 also combines all image data segments obtained by the slave PCs 182 to 186 to provide complete perimeter data on the mother plate on the cutting table 8.

To commence a plate scan, the cutting CNC 168 will generate the camera trigger signals on a line 188 using a trigger circuit 190 following receipt of plate scan command instruction from the process manager 156 on the network 158. The trigger signals are received

by a camera interface board 192 of the master PC 180 and passed to similar camera interface boards 192 of the slave PCs 182 to 186. The interface boards 192 generate a camera trigger signal on a line 193 for the cameras 38 to 44. The cameras 38 to 44 will acknowledge receipt of the trigger signals by forwarding acknowledge signals on line 195 to the interface boards 192 and will execute a line scan for each trigger signal to provide a total of 4096 pixels per line. As the beam 14 is moved, a total of up to 4096 lines (in multiples of 512 lines) are obtained in one scan across the cutting table 8. The pixel values obtained each represent a grey level which can range from 0 to 256. On receipt of the trigger acknowledgement signals, the PCs 180 to 186 initialise a buffer in frame grabbers 194 to receive the pixels generated by the cameras 38 to 44. The PCs 180 to 186 provide direct memory access (DMA) for the frame grabbers 194. Segments of 256 lines can be transferred by DMA to each PC 180 to 186 whilst its respective frame grabber 194 is storing a succeeding 256 lines. The frame grabbers 194 of the vision module 172 are cycled on a 512 line basis. Once a 256 line segment is transferred to the memory of a PC 180 to 186 it is processed before receiving the next 256 lines from its frame grabber 194.

Along the first edge of the cutting table 8 which the vision module 172 scans, a calibration bar 200, as shown in Figure 13, is fixed in position on the cutting table. The dimensions of the calibration bar 200 are accurately predetermined, and the bar 200 includes a row of black rectangular boxes 202 on a white background which have the same dimensions and are spaced the same distance apart. The row of boxes 202 is perpendicular to the scanning direction of the cameras 38 to 44. The positions of the calibration bar 200 and the boxes 202 are known relative to the cutting table.

The process manager 156 and the cutting CNC 168 will act on a calibration mode command message to instruct the vision module 172 to execute a calibration process, and in particular the calibration mode procedure 204 shown in Figure 14. The PCs 180 to 186 will firstly initialise their frame grabbers 194, their line scan cameras 38 to 44 and allocate memory to store a received image frame or segment at step 206. The cameras 38 to 44 at step 208 then scan the calibration bar 200 to each have an image segment of the bar 200. The image segments are forwarded to a memory of the PCs 180 to 186 for processing at step 21Q,

and the image is processed to remove the grey level values for the pixels and simply provide a binarised sub-sampled image of the bar 200, at step 212, where dark pixels are represented by a binary 1 and light pixels are represented by binary 0. The binarised image segments are then passed to the master PC 180 where the complete binarised image is compared with the actual known dimensions, and position with respect to the cutting table, of the calibration bar 200, and any differences due to lens distortion or magnification are determined, at step 214.

The differences due to lens distortion and magnification and any other imaging factors are then used to produce a look-up table of correction factors Ax and Ay for each pixel, based on the x, y position of the pixel across a line image. The correction factors are subsequently used, as discussed below, to convert x, y pixel coordinates to real x, y coordinates to represent positions on the cutting table 8.

The process manager 156 and the cutting CNC 168 on generation of a plate scan mode command will cause the vision module 172 to enter a plate scan mode and execute a plate scan process 220, as shown in Figure 15. Firstly the frame grabbers 194, the cameras 38 to 44 and the PCs 180 to 186 are initialised by executing step 206 to receive line images. The beam 14 is then moved in the y axis direction across the cutting table 8 to scan the mother plate at step 209. The, image lines are obtained, and for every 256 lines the image segment block is loaded into the memory of the respective PC 180 to 186 for image processing at step 211. The processors 180 to 186 first determine the x, y boundaries for each image segment which is being processed at step 213, based on position information for the beam 14 provided by the cutting CNC 168. To remove pixels which relate to noise and the background lifting frame 126, an adaptive threshold procedure, at step 215, is applied to all of the adjacent pixels in an image segment which first determines the differences between grey levels. The pixels which relate to differences that exceed a threshold will correspond to the edge of an object of interest. These pixels which are considered to represent, and are contained within, a large enough object of interest are set to a high value, whereas all of the remaining pixels are effectively eliminated by setting them to a low value. This binarised image data represents possible plate edges and is further processed at step 217. A binary image which provides a continuous perimeter profile for objects in the image is generated at step 217 by examining each edge pixel forwarded by step 215 and attempting to form a continuous profile from

adjacent edge pixels. This involves applying a perimeter traversal or snaking algorithm to each edge pixel which looks in all directions from a pixel to find and create an edge boundary. If an edge pixel is found within a predetermined distance from another edge pixel in a direction which correlates with part of the profile already generated, then a boundary is formed to extend the profile. Once a binary image has been produced with complete perimeters or profiles for objects or features in an image segment, a labelling process step 218 applies labels to those features which are sufficiently large enough that they may form part of a scanned mother plate. Other smaller features are rejected by the labelling process. The x, y coordinates are then determined for the boundaries or perimeters of the image features which have been labelled, at step 220. The x, y coordinate boundary data is corrected at step 222 based on the x, y correction factors 224 obtained during the calibration process 204. The corrected boundary data or perimeter data for each segment is then passed to the master PC 180 at step 224. The master PC 180 will then join all of the perimeter data segments together so that the perimeter data is continuous to define a complete profile for a mother plate, at step 226. As the perimeter represented by the x, y perimeter data may have sharp deviations, such as erratic protrusions or indents, which could not apply to a milled mother plate, the perimeter data is smoothed at step 228 by applying a smoothing algorithm. The algorithm removes image artefacts along the located edges and at junctions between the sides of polygonal features of the image. Haar transforms are used to decompose the data into sets of straight line components, as described in T. J. Davis,"Fast Decomposition of Digital Curves Into Polygons Using the Haar Transform", CSIRO Manufacturing Science and Technology technical report CMST-P-97-02,1997. The distribution of the directions of the line components and their connectivity relative to one another are used to cluster line components on the perimeter or boundary and to identify any erroneous boundary features. The erroneous features on the perimeter are removed either by interpolating between significant clusters or by interpolating between points of intersection of the line clusters. The smoothing algorithm simply adjusts the x, y data to ensure it represents a smooth edged plate perimeter without any uncharacteristic deviations. The perimeter data is then forwarded to the process manager 156 indicating the end of the plate scanning process 220.

The lights of the elongate illuminating lamp 56 are positioned along the lamp 56 so as

to be closer together at the extremities on the x-axis of each field of view of the cameras 38 to 44, and are spaced further apart at the central optical axes of the cameras 38 to 44. The lights of the lamp 56, in particular, are spaced in this manner to provide correct illumination distribution for the cameras 38 to 44, bearing in mind that when a uniformly bright object plane is focused by a lens of a camera on the plane of the sensor for the camera, the illumination of the sensor is no longer uniform but falls off steadily from the centre to the edge. According to the optical cosine law, the illumination varies as cos40, where 0 is the angle between the optical axis of a camera lens and a lens axis to the image point in question.

The illumination intensity profile for the cameras 38 to 44 is configured to offset the lens affects to provide even illumination for each sensor of the cameras 38 to 44.

The lights of the lamp 56 are wired to an AC supply in a manner which minimises the supply producing any ripples in the illumination for the plate and the cutting table 8. The thermal inertia filtering of a single light filament produces approximately 10% peak to peak ripple in the illumination levels. By connecting the three AC phases of the supply in a distributed and alternate manner to the lights across the lamp 56, effective additional filtering is obtained to provide less than 2% peak to peak ripple. In other words the first phase is connected to the first lamp, the second phase is connected to the next lamp, the third phase is connected to the third lamp, the first phase is connected to the fourth lamp, etc. This provides a suitable level and consistency of illumination for the apparatus 2.

With the complete x, y coordinates for the mother plate perimeter, the process manager 156 is able to generate x, y cutting data for the cutting CNC 168 to cut the child plates, test pieces and scrap pieces required in a mother plate. The cuts to be made to the plate 9 are normally dictated by plant systems 164 and 166. In particular, the process manager 156 is able to provide precise v-axis data to the cutting CNC 168 to position the cutting torches directly at the edges of the mother plate before the beam 14 executes a cutting stroke, as shown in Figure 16. Once the cutting CNC 168 has positioned the cutting torches 22 to 28 at the correct v-axis positions, the beam 14 can be moved to commence the cutting stroke across the plate 9, in the reverse direction to the scanning direction, and the x-axis positions of the carriage assemblies 30 to 36 can be adjusted on instructions from the cutting CNC 168

to move the torches 20 to 28 to cut any desired profile which fits within the plate 9.

Movement of the beam 14 adjusts the y-axis coordinates of the torches. If further control is required, the v-axis positions could also be adjusted during a cutting process, but normally these positions are not further adjusted once the torches have been placed at the nearest edge of the plate 9, as shown in Figure 16. The v-axis positioning of the torches 22 to 28 based on the perimeter data obtained from the vision module 172 is particularly advantageous as it adjusts the torches to the optimum position on the plate 9 to strike or start a cutting arc at the commencement of a cutting stroke and avoid producing splatter deposits on the plate 9. The perimeter data obtained by the vision module 172 also ensures the torches 22 to 28 can be controlled by the cutting CNC 168 to remain within the mother plate 9 on the cutting table 8, without any manual positioning of the plate or the torches.

A complete cutting and material handling process and the sequence of steps executed is described below with reference to the particular NC and PLC programs which are executed.

The initial conditions for the sequence is that the apparatus 2 has completed a cut for a mother plate 9, retracted the torches 22 to 28 and a gantry 78 has picked up a scrap and test piece.

1. A cutting NC part program of the cutting CNC 168 signals the process manager 156 that scrap and test pieces from the last mother plate have been picked up.

2. The process manager 156 signals the planning system 166 that a new mother plate can be conveyed on and the child sheets can be conveyed off.

3. The cutting NC part program sets or resets a"marking enable"bit.

4. The cutting NC part program sends marking text if required to the handling CNC 170 which downloads the text to the marker 98.

5. The cutting NC part program causes the gantry 78 to deposit first piece (scrap or test) on conveyor 80 when a"conveyor load stage 1 ready"message from material handling CNC 170 is received by the cutting CNC 168.

6. Material handling CNC 170 compiled PLC turns on both conveyor stages 82 and 84 when second conveyor stage 84 is clear and triggers marker 98 as the first piece enters the marking station if marking enabled.

7. Material handling CNC 170 compiled PLC turns off first conveyor

stage 82 when first piece has cleared first stage.

8. Cutting NC part program sets or resets"marking enable"bit.

9. Cutting NC part program sends marking text if required to handling CNC 170 which downloads the text to the marker 98.

10. Cutting NC part program causes a gantry 78 to deposit second piece (scrap or test) on conveyor when"conveyor load stage 1 ready"message from material handling CNC 170 is received by the cutting CNC 168. Cutting NC part program terminates.

11. Material handling CNC compiled PLC turns off second conveyor stage 84 so that first piece stops at crane pickup point.

12. Material handling NC part program of CNC 170 causes crane 88 to pick up the first piece.

13. Material handling NC part program causes crane 88 to carry piece to appropriate bin or cassette.

14. Material handling NC part program causes crane 88 to drop scrap into appropriate bin 90 to 94; or to lower test piece to cassette 96, release test piece, and return hoist of crane 88 to travel height.

15. Material handling NC part program causes crane to move back to crane loading station.

16. Material handling CNC compiled PLC turns on both conveyor stages 82 and 84 when second conveyor stage is clear (crane 88 has picked up first piece) and triggers marker 98 as the second piece enters the marking station if marking enabled.

17. Material handling CNC compiled PLC turns off first conveyor stage 82 when second piece has cleared first stage.

18. Material handling CNC compiled PLC turns off second conveyor stage 84 so that second piece stops at crane pickup point.

19. Material handling NC part program causes crane 88 to pick up the second piece.

20. Material handling NC part program causes crane 88 to carry piece to appropriate bin or cassette.

21. Material handling NC part program causes crane 88 to drop scrap into appropriate bin; or to lower test piece to cassette, release test piece, and return hoist to travel height.

22. Material handling NC part program causes crane 88 to move back to crane loading station and the handling NC part program terminates. The pieces just handled were from the previous mother plate, and steps for the newly conveyed mother plate are activated by the process manager 156.

23. Process manager 156 sends message to vision module 172 to prepare for a calibration pass.

24. Process manager 156 waits for a"continue"message from the vision module 172.

25. Process manager 156 activates a vision calibration NC part program for cutting CNC 168.

26. Vision calibration NC part program triggers the cameras 38 to 44 and causes scanning of the calibration bar 200.

27. Vision calibration NC part program sends a"end capture"message to the vision module 172.

28. Vision calibration NC part program terminates.

29. Process manager 156 sends message to vision module 172 to prepare for a full plate perimeter scan.

30. Process manager waits for continue message from the vision module 172.

31. Process manager 156 receives the details of the mother plate from the planning system.

32. Process manager receives message that mother plate is in position.

33. Process manager activates a full plate perimeter identification NC part program for cutting CNC 168.

34. Plate perimeter identification NC part program raises plate 9.

35. Plate perimeter identification part program commences scan.

36. When at speed plate perimeter identification NC part program sends camera trigger signals to vision module 172.

37. Plate perimeter identification NC part program sends"end capture" message to vision module 172 and then terminates.

38. Vision module 172 determines plate profile and sends to process manager 156. Processor manager 156 generates new cutting and handling NC part programs based on plate profile.

39. Process manager activates a cutting NC part program for CNC 168.

40. Cutting NC part program positions torch carriages 30 to 36 for cutting, lifting gantries 78 for next pickup and the crane 88 for next pickup.

41. Cutting NC part program lowers torches and fires torches.

42. Cutting NC part program performs cutting pass.

43. Cutting NC part program turns off plasma and raises the torches.

44. Cutting NC part program causes pick up of the scrap and test piece.

45. Cutting NC part program lowers the plate.

Many modifications will be apparent to those skilled in the art without departing from the scope of the present invention as hereinbefore described with reference to the accompanying drawings. For example, the apparatus 2 may be configured to enable the vision module 172 to scan a mother plate in two directions which are transverse to one another to obtain the plate parameters, such as perimeter, position of the plate on the cutting table, and area of the plate. The apparatus can, as mentioned, cut a number of different shapes and profiles in the mother plate 9. Also at least one additional torch can be added and, for example, positioned behind a main cutting torch, and then moved during a cutting stroke along the x-axis so as to cut tapered scrap pieces from a child plate being cut by the main torch. The main cutting torch would only move in the y-axis, whereas the additional torch positioned behind it would move in both the y and x-axis to produce tapered cuts to the plate edge from the primary cut. Various different types of components can also be used, for example the roller conveyor may be placed by a chain slat conveyor or other alternatives.