GB2182625A - Controlling drive motor of conveyor - Google Patents

Abstract

Drive means for a conveyor 32, 50 to enable the latter to be positioned accurately relative to a delivery station 26, 28 or the like, comprises an electric stepper motor with control circuit means therefor to generate a sequence of electrical pulses the frequency and duration of which can be controlled so as to accurately position the motor and in turn the conveyor linked thereto. In a preferred arrangement the shaft of the stepper motor is held stationary and the outer casing is provided with a drive means for engaging the endless belt of the conveyor which is caused to pass around the motor casing. Typically teeth are formed around the motor casing for engaging in slots in the belt or a chain forming part of the conveyor. In order to obtain programmable control of the motor, the latter is conveniently controlled by means of pulses derived from a microprocessor control unit. Programming means is provided for entering programme information into a memory associated with the microprocessor. Preferably the microprocessor control unit includes input means for inputting electrical signals indicative of the arrival of objects at the delivery station or the arrival of a container or tray or the like below the delivery station. <IMAGE>

Description

SPECIFICATION Improvements in and relating to conveyors Field ofthe invention This invention concerns conveyors particularlythose which have to precisely move objects relative to a delivery station orthe like.

Background of the invention It is known to deliver a product from one conveyor to another and often the take-off conveyor operates transversely to the delivery conveyor so as to position collecting trays or boxes or the like at the output ofthe delivery conveyor so as to receive articles from the delivery conveyor.

Where accurate positioning of the articles in or on the trays or boxes is required, it is of course necessaryto accurately position the articles as they leave the delivery conveyor and also to accurately position the trays or boxes relative to the outlet end ofthe delivery conveyor, whilst it is rnlativelystraighfforward to provide deflecting fingers or guides to co-act with the delivery conveyor and position articles across the width thereof.

However, the positioning of receptacles by means ofthetake-offconveyor relative to the delivery station requires very accurate positioning ofthe take-off conveyor and it is with thisin mind that the present invention provides an improved drive mechanism for a take-offconveyor.

Summary ofthe invention According to the present invention drive means for a conveyor to enable the latterto be positioned accurately relativeto a delivery station orthe like comprises an electricstepper motorand control circuit means therefor adapted to generate a sequence of electrical pulses the frequency and duration of which can be controlled so as to accurately position the motor and in turn the conveyor linked thereto.

Sincethe stepper motor moves through a small arcuatedisplacement in responseto each control pulse and is locked at each stepped position, the conveyor will be driven incrementally by the same amount so that where the conveyor extends in a straight line path,the movementthereofwijl be made up of a series of incremental stepsthe lineardisplacement of each of which is proportional to the corresponding arcuate movements of the stepper motor.

The accuracy with which an article on the conveyor can be positioned will be determined by the size of a single step ofthe stepper motor and where high accuracy is required, a stepper motor having large number of incremental steps making up a single rotation is obviously required. It is not uncommon for stepper motorsto have steps corresponding to one degree of movement at the axis of the motor and using such a motor, it is relatively easy to obtain incremental movements ofthe order of 1 mm withoutgearing.

In a preferred arrangement, the shaft of the stepper motor is held stationary and the outer casing ofthe stepper motor is provided with a drive means for engaging the endless belt of the conveyor which is caused two pass around the motorcasing to engage the drive meansthereon.Typicallyteeth are formed around the motor casing for engaging in slots our a chain forming part ofthe conveyor.

It is advantageous if direct drive from the motor to the conveyor is utilised so as to avoid problems of backlash associated with gearing.

In orderto obtain programmable control ofthe motor, the latter is conveniently controlled by means of pulses derived from a microprocessor control unit. Preferably programming means is provided for entering programme information into the microprocessor and storing same in a memory associated with the microprocessor, whereby a series of commands can be given to the motor to operate incrementally by predetermined amounts so as to obtain desired movements of a conveyor driven thereby.

Preferably the microprocessor control unit includes input means for inputting electrical signals indicative ofthe arrival of objects atthe delivery station orthe arrival of a container or tray or the like belowthedelivery station.

The invention may be used in a variety of applications but as one example it may to advantage be employed in a system for handling and packaging cut pieces of meatsuch as chops, whereit is preferablethatthe chops are shingled as they are laid into a tray. To this end the invention will now be described byway of example with referenceto the accompanying drawings, in which:- Figure lisa diagrammatic plan view of a packaging line incorporating apparatus embodying the invention.

Figure2 is a general view in the direction the arrowA of part ofthe apparatus shown in Figure 1.

Figure 3 is a perspective view from above of the outlet end of one of the delivery conveyors shown in Figure 2.

Figure 4 is a perspective view ofthe lower end of the tray stack.

Figure 5is another perspective view of the tray stack, thistime shown empty, Figure 6 is an end view ofthe lower end of the tray stack support and shows the mechanism by which trays are removed from the bottom ofthe stack and loaded onto the tray conveyor, Figures 7A and 7B are diagrammatic side and top views ofthe delivery end ofthe tray conveyor, Figure 8 is a top view of a tray loaded with 4 meat chops after passing through the loading station shown in Figure 3, Figure 9 is a side view of the tray of Figure 8 with the nearer side of the tray removed to enable the lay ofthe chopsto be seen, Figure 10 is a perspective view of part of the main conveyor onto which the filled tray is delivered from the transfer conveyor of Figure 7A, Figure 11 is a perspective view of a buffer conveyor and gate to which thefilled trays are delivered bythe main conveyance of Figure 10, and Figure 12 is a perspective view ofthe gate mechanism of Figure 11 from the opposite side.

Figure 13 is a schematic block circuit diagram of part ofthe control system associated with the apparatus of Figures 1 to 12.

Figure 14 illustrates the basic control panel for a control system generally moddled on that of Figure 13, Figure 75illustratesthe same control panel with an overlay card fitted, Figure 16 shows the overlay card to a largerscale, Figure 17shows howthe central control unit of Figure 13 can be made up oftwo programmable control computers for delivering control signals to the left and right hand pair of chop cutting machines of Figure 1, Figure 18 is a listing of the l/O assignments for computer 252, Figure 19 is a listing ofthe I/O assignments for computer 254, Figure20, made up of 24 sheets) is a complete circuit/wiring diagram of the control system, Figure2 1 illustrates the connections to some ofthe chop cutting machines controls from the computer252, Figure 22 illustrates the same connections to the other chop cutting machine controls from the computer 254,and Figure 23 illustrates the essential parts ofthe speed control system for a stepper motor conveyor drive.

Detailed description ofdrawings Figure lisa plan view of an overall packaging line. The apparatus is designed to cut large pieces of meat into chops orsimilarslices and two band saw automatic cutting machines shown at 10 and 12. Each includes a carousel 14 and 16 respectively on which can be mounted up to 4 pieces of meat from which chops can be cut as the carousel is rotated past a band saw. The cut pieces leave the cutting station in the direction ofthe arrow 18 in the case of cutter 10 and 20 in the case of cutter 12.

Conveyors generally designated 22 and 24 deliver the cut pieces to two loading stations generally designated 26 and 28 respectively which will be described in greater detail in relation to laterfigures.

Trays are stacked at 30 and are removed one by one and positioned on a tray conveyor generally designated 32 which incrementally movesthetraythrough the loading stations 26 and 28to atransfer conveyor 34 and from thence to a main delivery conveyor 36, part of which serves as a buffer conveyor at38 the outputfrom which is controlled bythe operation of a gate 40.

Two further meat cutting machines at 42 and 44 are also shown with associated conveyors 46 and 48 for supplying a second tray conveyor 50 having trays supplied from a second stack 52 for delivering filled trays to a second buffer conveyor 54whose output is controlled by a second gate 56. The second pair of meat cutting machines 42 and 44 are optional and simply indicate howthroughput can be increased by parallel operation.

In orderto accommodate outputfrom two gates 40 and 56, a two into one conveying station 58 is provided for supplying a single line offilled trays to awrapping apparatus 59 via a conveyor 61.

In its simplestform, the apparatus would comprise a single cutting machine such as 10, associated conveyor 22, and related tray conveyor 32 and tray stack and delivery station 30. The second cutting machine 12 simply allows a more efficient operation in thatwhilstthe first cutter is operating, the second cutter can be reloaded and cleaned ready to be put into action as soon as the meat in the operating machine is exhausted.

Figure 2 is a perspective view of the apparatus in the direction of arrow A in Figure 1. Thus the two meat cutting machines 10 and 12 can be seen in the background with their associated conveyors 22 and 24feeding the tray conveyor which will be described in more detail later and which is supported by a framework 60 which extends transversely to the two feed conveyors 22 and 24.

An upright tray magazine is shown at 62 within which are stacked trays. 64 one above the other. Each ofthe trays is generally square or rectanguiar in plan view, includes a depressed central region into which product can be laid and has a peripheral lip. Theform of each tray can best be seen from Figures8 and 9towhich reference will be made later.

The magazine 62 can be lifted clearfrom a su pport 66 to al low a fresh magazine to befitted orsimplyforthe magazine to be filled with trays.

A mechanism which will be described later removes each tray in turn from the bottom of the stack and each such tray is engaged on a conveyor having upstanding driving dogs, one of which is shown at 68which engage the rear edges ofthe trays and move them in a direction from beneath the magazine 62 towardsthe loading stations at the delivery ends ofthe conveyors 24 and 22.

The path ofthe conveyor (not shown) containing the dogs 68, is such that the latter rise up atthe right hand end ofthe framework 60, move across the framework 60 from right to left in Figure 2 and descend in a downward direction at the left hand end of the framework 60 in Figure 2. At that point the trays are delivered to a further conveyor as will be hereinafter described.

Controls, drives and powersuppliesforthe conveyors, tray magazine and for controlling the delivery of trays from the conveyors 22 and 24 onto the tray conveyor 32 are contained within units 70, 72 and 74 respectively.

Deliverystation Figure 3 ofthedrawings illustrates to a largerscaletheoutletend of the delivery conveyor 22 of Figures 1 and 2 and the interaction ofthis with the tray conveyor generally designated 32. This interaction formsthe delivery station or loading station where cut pieces of product such as meat chops or the like are loaded into a tray.

One such cut piece is shown at 76 and in practice will be preceded and followed by other similar cut pieces all travelling towards the tray conveyor 32.

To one side ofthe deliveryconveyor22 is an alignmentguide 78 made up of a metal leafspring anchored at 80 and adjustable in position at its downstream end by means of a screwed rod 82 and block 84. Positioning of the leaf 78 determines the precise position of the cut pieces across the width of the delivery conveyor 22 as they approach the exit end or outlet thereof.

Where the conveyor belt 86 of the delivery conveyor 22 passes around the end roller 88, the cut pieces 76 will fall in freeflightfrom the end of conveyor 22 onto awaitingtray, one of which is shown in dotted outline at 90.

Thetray90 is one of a number of such trays lying alongthetrayconveyor32andwhich are indexed ion a forward direction denoted by arrow B in Figure 3 by means of the tray conveyor drive dogs of which one is shown at 92. These are attached to an endless chain (not visible in Figure 3) and the latter is driven in aseries of incremental movements so as to shuntthe line oftrays past the loading station. As each tray is positioned in front of the loading station formed by the outlet ofthe conveyor 22, the cut pieces leave the conveyor belt 86 and after free flight land on the tray below.

Adjacent the exit of the conveyor belt 86 are located two sensors 94 and 96 with an optical link between them so that as a piece of cut product such as 76 arrives atthe exit end of the conveyor belt 86so the optical link is interrupted causing an electrical signal to be generated to serve as a control signal.

Further information is obtained when the optical link is re-established afterthe passage of a piece of cut material allowing a further electrical signal to be generated indicating that one piece has passed and another can now be expected.

Adjacent the exit end is located an air pipe 98 having an outlet nozzle 100 which pipe is adjustable so asto direct an airstream from the nozzle 100 toward the flight path of cut pieces such as 76 as they leavethe conveyor. By appropriate adjustment of the nozzle and appropriate adjustment of the pressure and volume and duration of each air pulse leaving the nozzle, so a cut piece such as 76 leaving the conveyor86, can be deflected and tiled simultaneously so as to land in the tray in a tilted condition instead of lying flat on the bottom of thetray. This is of great advantagewhere chops and similartypes of meat product are involved since it allows the pieces to be layered in the pack to present the edge regions ofthe chops or other pieces of meat one overlying the other.

Opposite the delivery end of the conveyor belt 86 are located two spring fingers 102 and 1 04which are mounted on pivot blocks 106, 108 and are sprung in a direction so as to cause the fingers to protrude into the path ofthetrays.

The springing is very light and as each tray is pushed into the position aligned with the end of the conveyor belt 86, so the two fingers 102 and 104 are pushed out of the way by the side wall of the tray. However, there is just sufflicientfriction between the fingers and the tray edgeto restrain the tray so that the latter is prevented from overshooting as it is pushed in a series of incremental steps past the delivery end of the conveyor belt 86 by the movement of a dog 92.

In addition to the fingers 102 and 104, a tray sensor 110 is located immediately below the path ofthetrays which is itself engaged by the underside of each tray as the latter is moved into position. Control signals from the sensor are used to instigate the operation ofthe cutting machine and delivery conveyor drive.

In this connection the signals from the sensor link 94,96 serve to indicate that cut pieces have now arrived at the delivery end of the conveyor 22 and each piece can be counted as it passes between 94 and 96. Overall control of the apparatus is achieved by means of a microcomputer controlled device having a memory into which information is stored concerning inter alia a number of pieces to be laid in each tray and the distance through which tray must be indexed after it has arrived atthe loading station so as to accommodatethe desired number of cut pieces in a particular configuration within the tray.The signal from the sensor 11 Othus initiates the process,the signal from the sensor link 94,96 dictates the number of pieces which are laid in the tray and in the event that no tray supplants the first after the latter has been moved out ofthe delivery station region, the appropriate signal from the sensor 110 temporarily haltsthe cutting and delivery offurther pieces until the fault has been remedied.

The timing ofthe jet of air from the nozzle 100 is achieved using as a trigger the signal from the link 94,96.

As is best seen from Figures 3 and 4, the sides of the tray conveyor are made up of pairs of upper and lower guide rails 112 and 1 14on one side and 116 and 1 18ontheotherside.

The conveyor bed is stationary and is formed from a pair of elongate plates 120 and 122 separated by a groove 124 through which the dogs 92 extend and along which they can pass.

Tray magazine The tray magazine 62as shown in Figure 2, is shown in greater detail in Figures 4, 5and6.

Referring particularly to Figure 5, the magazine is constructed from a number of upright rods some ofwhich are denoted by reference numeral 126 in Figure 5, forming a cage and bounded atthetop and bottom and midway by means of bands 128, 130 and 132 respectively.

The lower band includes pairs of fixing knobs such as 134 and 136 (see Figure 6) on opposite sides by which the magazine can be secured to two uprightflanges 138 and 140 secured to and extending from the support 60.

Two tray support grants extend across the underside of the band 132 on wh ich the lips ofthe lowermost tray rest and the precise spacing between the rods is adjusted by means of cams 140 and 142 acting on pivoted levers 144,146.

Relative outward movement of the rods reduces the amount of overlap between the tray and the rods thereby making it easierto remove the lowermost tray whilst decreasing the spacing, increases the resistance to movement of the lowermost tray and removal thereof.

Actual removal of a tray from the lowest position in the stack is achieved by means of suction cups of which 2 are visible in Figure 5 and are designated 148 and 150. The suction cups are formed atthe upperends of piston rods ofwhich two are shown at 152 and 154 in Figure 6. Upward displacement ofthe rods 152,154 etc raises the suction cups 148,150 etc into contact with the underside of the lowermost tray as shown in dotted outline in Figure 6. Subsequent withdrawal ofthe piston rods causes the tray impaled on the4suction cups to be dragged in a downward direction and by virtue of the deformability of the material forming the tray, the latter can be pulled downwardly past the rods 156, 158.

Figure 6 shows by way of dotted outline the lowermost tray 160 in the stack of trays contained in the magazine and in solid outline belowthe lasttrayto have been removed at 162.

Also visible in Figure 6 arethetwo pairs of guide rails 112 and 114 and 116 and 118. Adjustment ofthe relative spacing between the two pairs of guide rails can be effected by adjusting knob 164. Rotation so asto move the knobtothe right in Figure 6 displaces the rails 1 16and 118 in one direction whilst rotating the knob in the opposite sense produces reverse movement of the arm bearing the rails 116,118.

Similar adjusters are provided at 166 and 168 (see Figure 5) and by appropriate adjustment so the rails 116 and 118 can be twisted from the position shown in Figure 6 where the tray will just rest on the upper rails 116 and 112, to the reverse of that shown in Figure 6 in which the tray can slip between the two upper rails and rest onthetwo lower rails 114 and 118 and be held captive in an upward sense by means ofthe two upper rails 116 and 112.

The transition from the position shown in Figure 6 to the position shown in Figure 6 to the position in which the rim of the tray is held captive between the pairs of rails on opposite sides ofthe track of the tray conveyor is effected as the tray is moved from below the stack in the magazine 62 towards the loading station.

Replacement of the magazine 62 with a freshly stacked magazine or simply to facilitate servicing or removal of jammed trays, is simply effected by undoing knobs 134 and 136 and lifting the magazine bodilyawayfrom thesidecheeksl38and 140 (see Figure6).

Tray conveyor Figures 7A and 7B illustrate the tray conveyor and also visible is the transfer conveyor onto which thefilled tray is passed.

The tray conveyor is an endless chain 170 on which are mounted the driving dogs such as 92. The chain passes around idlers such 172 and driven wheels 174.

In accordance with the invention the driveforthe chain is derived from a stepper motor (not shown) which will accurately indexthe chain through predetermined distances in response to an appropriate number of electrical pulses supplied to the motor.

In this way the trays can be indexed along the path ofthetray conveyor by controlled distances so asto accurately position the trays relative to the discharge conveyor such as 22 and once in position can also be indexed accurately to receive different pieces of the cut product such as 76 at predetermined positions along the length of each tray thereby ensuring that the product is evenly distributed along the length of the tray and can be shingled, that is madeto overlay one piece on another, preferably with edge regions shown uniformly.

Beyond the tray conveyor is located a transfer conveyor best seen in Figure 7B. This is made up of a number of endless belts of which one is designated 176. There are 6 belts in all arranged in two groups ofthree on opposite sides ofthe central chain 170 of the tray conveyor.

Rollers such as 178 and 180 are provided at opposite ends ofthe transfer conveyor path and a constant speed drive (shown in Figure 7A) at 182 drives the endless belts such as 176. Idlers 184 and 186 take upthe slack and provide for the change of direction of the belts.

As shown in Figures 7A and 7B in dotted outline, astray 90 will be pushed bythe driving dogs 92 offthe platform ofthe tray conveyor onto the endless belts such as 176 which since they are moving in the direction of the arrow C in Figure 7A, will cause the tray 90 to be transferred to the left in Figure 7A.

Atake-off conveyor 36 (see Figure 1) picks up the trays from the transfer conveyor 34 and conveys the now filled trays towards a buffer conveyor 38 and the remainder of the wrapping apparatus.

Take-offconveyor Thetake-offor main conveyor is shown in part in Figure 10.

Positioned over the surface of the moving section of the conveyor (188) are located two rails 190 and 192 which are adjustable in position by slackening off the knobs 194 and 196 and sliding the arms 198 and 200 through the blocks 202 and 214 respectively to the desired positions. The knobs 194 and 196 can then be retightened.

The main ortake-off conveyor serves to convey the filled trays to a buffer conveyor which is made up of a series of rotatable but non-driven rollers on which the trays will queue and shunt towards the outlet as more trays are added from the take-off conveyor 188.

Bufferconveyor This item 38 is shown in Figures 11 and 12. The filled trays arrive from the main conveyor36 and are eventually halted in their forward movement over the bed of freely rotatable rollers 206 by means of a gate 208 which is raisable by means of a pneumatic ram 210.

Operation of the gate is controlled by means ofthe central control system for the overall apparatus and the gate serves to release trays from the buffer in response to the signals from the central control.

The latter is fed with signals from various sensors which are shown at 214,216 and 218. The signals from the various sensors indicate the arrival of a tray atthe gate (sensor 212), the arrival of a sensorjustin advance ofthe gate (sensor 214) and where signals are simultaneously received from sensors 216 and 218, the fact that numerous trays are now backing up on the buffer conveyor indicating that the supply oftraysto the buffer conveyor is exceeding the rate at which they are being released by the gate.

Beyond the gate 208 are located driven rollers 220 and a further transfer conveyor similarto the transfer conveyor 34 is provided beyond the driven rollers at 222.

System operation Figure 13 shows the control system for part ofthe apparatus of Figures 1 to 12. The heat ofthe system is a central, processor controlled, control unit 224 the operation of which will become evident from the following description.

On pressing ON-push button 226 CPU 224 sends a signal to a tray de-stacker 228 to remove a tray from the stack 64 (Figure 2) and initiate operation of tray conveyor drive 230. Passage of a tray past the decoder 232 produces a control signal for CPU 224to indicate the size of the tray in use and using a hook-up table orother devicethe CPU 224 generates appropriate control signals for the tray conveyor driveto enablethe correct step size movement to be achieved as each tray passes through the delivery station 26.

Atthe same timethe cutterdrive 234 and delivery conveyordriver 236 are energised and pieces of cut product are delivered to the input end of the delivery conveyor 22. If for any reason product fails to leave the exit end ofthe conveyor 22, the back-up of product on the conveyor 22 is sensed by a product sensor 238 causing CPU 224 to temporarily arrest drives 234 and 236.

Assuming delivery conveyor22 is functioningg correctly, cut pieces pass between 94,96 and electrical pulses are supplied to the CPU 224 to indicate the arrival and passage of cut product pieces to the waiting tray.

To this end a power supply 240 supplies currentforthe light source 94.

A counter 242 (which may form part of the CPU 224) accumulates electrical pulses corresponding to the passage of cut product pieces and provides an overflow signal after present members of pieces have been counted - the counter being reset after each present number has been counted.

CPU 224 is arranged to produce a small increment of travel of the tray atthe delivery station for each pulse counted until the overflow signal is generated, whereupon the tray conveyor drive 230 is caused to operate at a higher speed and/or for a longer period of time, so as to shiftthe tray well clear ofthe delivery station 26 and replace it with another empty tray.

If at anytime the apparatus must be stopped, the push button switch 224 can be pressed, to supply a further signal to the CPU 224, which in response thereto is arranged to haitall drives immediately.

CPU 224 also provides control signals at the correct point in time to a valve 246 for releasing air from a reservoir or pump 248 to the air nozzle 98 (see Figure 3).

General Where a second delivery conveyor such as 24 is provided adjacent the same tray conveyor, a second tray sensor similarto sensor 110 is provided within the tray conveyor opposite the end of the other discharge conveyor and control signals for the tray conveyor from the central control unittake account of the factthat trays are being filled at both locations and the control signals for the tray conveyor are arranged to accelerate the latter in the eventthat a tray has been filled by a first discharge conveyor 24 through the second loading station from the discharge conveyor 22so that the latter makes no attempt two discharge cut pieces onto a filled tray but is always presented with an empty tray.

Where a second line is provided also fed from one or two cutting machines and discharge conveyors such as 42,44,46 and 48 as described with reference to Figure 1, it is merely necessary to ensure that the outputs from the two buffer conveyors 38 and 54 arethemselves synchronised and phased so that the outputfrom one line is mixed with the outputfrom the other lineto provide a single line of filled trays ready forwrapping.

Further details of the air deflection nozzle and controls therefor are contained in my copending application filed concurrently herewith and entitled Improvements in and relating to article handling apparatus (8600418).

A more complete description ofthe control system forthe apparatus of Figures 1 to 12 now follows with reference to Figures 14 - 23. The system allows up to four chop cutting machines to be operated in any desired mode -i.e. singly or in pairs. Each chop cutting machine is an APS 200 machine as manufactured byAEW Engineering Co Limited of Norwich, England and each is referred to as an APS. Since there are two pairs of such machines arranged in leftand right hand lines,thetwo machines in each line are denotedAPS1 L,APS2L, and APS1 Rand andAPS2R respectively. Thus item 12 in Figure 1 isAPS1 L.

Figures 14-16 illustrate the control panel ofthis more complete system - Figure 16 showing one ofa number of overlay cards which can be selected and fitted thereto depending on the mode of operation desired. The cards fits over an array of light emitting diodes 250, which can be seen in Figure 14.

General description ofsystem and operation The control system is used to control the slicing, tray loading and converging of the two lines oftrays.

The control system uses two l.M.O. SYSMAC S6 programmable control computers252,254. Each computer controls one tray conveyor, left and right, independently. Additionally both computers drive different sections of the overall control system. For the system to operate correctly BOTHcomputers must be operational.

The master softwarefor each computer is contained in a programmable read-only memory (PROM) module. The modules plug directly into a receptacle on the central processing unit (CPU) of each controller.

Each memory module contains two full programs either of which can be selected by the PLC switch 256 cn the control panel.

P1 = PROGRAM 1 P2 = PROGRAM 2 It is essential that only PROM modules containing the correct software are plugged into the appropriate CPU. Each PROM is marked with CPU-L or CPU-R. lfthewrong PROM is in a CPU the system will notfunction and the PROGRAM ERROR lamp will light on the ALARM panel.

CONTROL PANEL The control panel is divided into logical sections which will now be described:- MIMIC DIAGRAMS The mimic diagram shows a diagrammatic representation of the system. Indicator lamps (red) showthe status ofthe 13 emergency stop buttons around the equipment. If an emergency stop button is operated,the whole system will shut down and the appropriate red indicatorwill lightonethe panel showing which button has been operated. The system cannot be restarted until the emergency stop button has been released and the corresponding indicator lamp extinguished.

Also on the mimic diagram each APS Slicer has an amber status indicator. These enable the operator to see the status of each machine dependant upon the state ofthe indicator.

STATUS INDICATOR APS STATUS OFF OFForloading FLASHING Standby CONTINUOUS Slicing Additionally these status indicators flash alternately - left pair- right pair for a period of time after pressing the system start button, before conveyors start.

These status indicators on the mimic panel correspond to the red status lamps mounted on top of each APS slicer.

ALARM DISPLAY In the centre of the panel is the alarm display section. This provides both visual and audible indication of alarm conditions.

SYSTEM PROGRAMMING The right hand end ofthe panel is dedicated to SYSTEM PROGRAMMING and enables anyof18 chop/tray/productcombinationsto be selected from preset values within each program of a PROM module.

Since each PROM module contains two complete programs a total of 36 chop/tray/product combinations is selectable from the panel without changing the prom module.

The program display accepts special overlay cards which refer to a particular program within a particular prom. The indicators which shine through the overlay give visual confirmation that the correct program has been selected.

Also in system programming section are the MODE selection switches.

RESET - stops the line and clears out the program registers.

L - left line only operative R - right line only operative B - both lines operative independently S - both lines operative in synchronism OPERATION To start both disconnect switches on the doors ofthe power console are turned on,the main STOP button is released byturning the key, and the POWER ON button is pressed. The red MAINS ON indicator on the control panel will light.

Select the correct overlay card forthe program to be run. Ensure that both CPU-Land CPU-R are fitted with correct PROM module and that the module number corresponds with the number written on top ofthe overlay card.

Place the overlay card over the program display so thatthe four pins are located in the corresponding holes in the card.

P1/P2 SELECT Turn the PLC switch to either P1 or P2 to select the program in the PROM modules which corresponds to the overlay card fitted.

PROGRAM LOAD Check that the program switches are now set as required. If correct, press the PROGRAM LOAD button. The program as set up on the switches is now loaded into memory and the computer confirms the loading by illuminating the appropriate LED indicators beneath the overlay card.

If wrong program has been selected, press the RESET mode button and repeat the programming process using the correct switch settings.

Once both lines have been programmed, either program may be confirmed by moving the LINE switch either to the L or R position. This simply switches the program display to either the left line or right linefor confirmation ofthe program which has been loaded.

The program load button is locked out once a line has had a program loaded. To reprogram a line the RESET mode switch must first be operated both lines reprogrammed as necessary.

if the system is running and the RESETswitch is operated the entire line including the APS slicers will SHUT DOWN.

To start the system once properly programmed simply press the SYSTEM START button. The amber status indicators on the mimic diagram will flash alternately in pairs (left pairthen right pair) at half second intervals for about 25 seconds. At the end of that period, the conveyors on the line or lines selected by the mode switches will start automatically.

In the computer selected forth is system, the RAM capacity is such that up to 512 single instructions can be stored in addresses 0000 to 0512.

Thus some ofthe addresses in each of the two computers are reserved for the operation of the tray conveyors of the lines to which the computers are connected. Other addresses provide for the operation of an airjetwhere chops are detected at the delivery end ofthe conveyors 46,48 etc. (see Figure 1) as required.

The computer chosen forthis system has an additional and useful facility - namely the production of control signals for a printer two enablethe logic instructions stored in the PROM to be printed out as either a mnemonic listing ora so-called ladderdiagram. TableAcomprisesthe mnemonic listing forthecomputer252 andTable B that for computer 254.

Figure 18 is a listing ofthe I/O assignmentfor computer252 and Figure 19 is the samefor computer 254. In the system described, only parts 000 - 064 are externally available and the higher number parts are only accessible within the software.

In addition to the I/O listing, Figures 18 and 19 describe the functions allocated to the software bistable relays KR00 - KR07, the 32 registers (outputs 00-31) of reversible up/down software counter RDM, the 32 outputs of the high speed software counter HDM (00-31 ),the eight software countersTlM0-TlM7 andthe eight software counters CNT0 - CNT7 in each ofthe two computers 252,254.

Figure 20 is made up of 24 sheets and comprises the circuit diagrams ofthe numerous parts of the control system for the chop shingling apparatus of Figures 1 to 12.

Figure 21 illustrates the connections between the interface associated with the control system forAPSL1 and APSL2 and the control console containing the control panel of Figure 14while Figure 22 illustratesthe same connections from the APSR1 and APSR2 control system and the control panel.

In this system static inverters are used to power inductive motors for driving those conveyorswhose speeds need to be closely controlled and easily varied.

Astatic invertertakes a normal AC supply and applies itto a full wave rectifier. The resultant intermediate DC voltage is then applied to solid state output devices which are turned on and off in a three-phase switching sequence bythe internal control logic of the inverter. This produces an output which is effectively a rebuilt3 phase AC waveform. The switching logic is driven by a master oscillator so by varying the frequency ofthat oscillator, the frequency of the 3 phase output is also varied. Since the rotational speed of a standard squirrel cage induction motor is a function of the suppiy frequency, it is also varied by the change in master oscillator frequency.

The inverters used in this system are IMO JAGUAR units, lN1 -5, housed in the power console, as manufactured by IMO Precision Controls Ltd, 1000 North Circular Road, Staples Corner, London, England.

Inverters IN1-4aretheVN 75 model having a 1 hp rating and IN5 isthe2 hp,VN150 model. The output ofall these units is 220V 3 phase 2-100Hz and the input power is 220V 1 phase 60Hz. The master oscillator frequency is controlled by a 10K ohm linear track potentiometer. In the case of IN5which controlsthe converger speed,the 10k ohm potentiometer is replaced by speed selector module SSM-1 AEW 2158/2.

Speed control of the converger is achieved using a specially designed control module (SSM-1) and basically comprised 10 x 1 k-ohm resistors connected in series and this chain is connected across INS terminals 4 and 6, normally connected across the track of the speed control potentiometer. IN5terminal 5 normally connected to the wiper of the potentiometer is connected to the end of a chain of relay contacts. The relays are operated by the computer and enable itto select speeds from 0 to 100% of full speed in 10% steps by tapping off atthe junctions of the 10 x 1 k-ohm resistors. IN5 is set so that full speed ofthe converger represents an outfeed rate of 100 trays/min.The 10 speed tappings therefore each represent a change of 10 trays/min from the adjacent tappings.

The computer selects on of three speeds high (HI), normal (NORM) or low (LO) for each of three tray sizes (2P), (4P), (8P).

The Jaguar inverters have both acceleration and deceleration ramp controls. Since the speed ofthe converger materially affects the transfer timing of a tray from the buffer discharge release gate to the next set ofconvergerslats, it is important that acceleration and deceleration ramps of IN5 are setto match the inherent rate of change of the mechanical and electrical controls of that part of the system. In practice, these are quite slow ramps which have to be determined by trial and error.

The delivery conveyors (46,48; 22,24) are responsible for delivering a chop into a tray. The speed atwhich the chop is travelling is important. Too fast, and the chop will overshoot, too slow, and it will undershoot. The correct speed forthese conveyors has been found to be 43.7 meters/min (143.4feet/min).

The set-up is therefore quite simple. Using a tachometer with a linear speed wheel, the speed potentiometers are adjusted on each inverter IN 1-4 until the appropriate conveyor is running at the correct speed.

No acceleration ramp or deceleration ramp is required on these conveyors. They need to start and stop as quickly as possible.

Reference is madeto the IMO Jaguar Introduction Manual for details of the operation of these devices.

In accordance with the present invention, the tray conveyors 32 and 50 are driven by stepper motors. The drive system for one such motor 258 comprises the following major components shown in Figure 23; 1 x SLO-SYN TM 600U TRANSLATOR (260) as manufactured by The Superior Electric Co., of Bristol, Connecticut 06010, United States of America, and 1 x SLO-SYN My 12 FJ8030 STEPPER MOTOR (258), and 1 x PULSE STRETCHER AEW 2158/1(262) as as manufactured by AEW Engineering Co Ltd of Norwich, Norfolk, England. + the high speed counter(HDM) ofthe SYSMACS6 (264).

The rotor of a stepper motor rotates in discrete angular steps, in this case 200 steps per revolution or 1.8 degrees of rotation per step. A master oscillator (266) in the TM 600U drive electronics provides a stream of pulses to the translator logic. On each pulse of the oscillator, the translator connects the four phase windings ofthe stepper motor to a DC supply in a particular pattern and the rotor rotates just one step. By sending the translator a known number of pulses, the motorwill rotatethrough a pre-set number of degrees andthen stop. The frequency of the master oscillator's output determines the speed of rotation ofthe motor. Since the master oscillatorfrequency is variable, the speed of rotation of the motor is also variable.

The stepper motor directly drives the chain (170) of the tray of the conveyor (see Figure 7a) so one oscillator pulse rotates the stepper motor shaft 1/200th of a revolution which results in a known linear motion ofthe tray.

The extent of that linear motion is controlled in this system by the High Speed Counter (HDM) (264) ofthe SYSMAC S6 PC. After a chop has landed in a tray the PC starts the oscillator of the TM 600U and the stepper motor starts the oscillator of the TM 600U and the stepper motor starts rotating, driving the chain and moving the tray. The master oscillator pulses aretapped off and fed to the pulse stretcher module (AEW 2158). This acts as an interface between the TM600U and the SYSMAC S6. The HDM input of the SYSMAC S6 has a maximum frequency response of 1 kHz and the TM 600U oscillator produces pulses only 10 micro-seconds wide. The pulse stretcher therefore expands these pulses to a width of 1 milli-second to match the response of the HDM input.

It is important to note from this that in modes of operation where an extent number of steps is required in this system,the masteroscillatorfrequency must not exceed 1 kHz otherwise the HDM counterwill be unable to follow the pulse train. Thus as the tray moves, the number of oscillator pulses fed to the translator is counted by HDM. When this number is the same as the preset value ofthe appropriate HDM register,the SYSMAC S6 stops the master oscillator andconsequently, the movement of the tray.

In this way, the spacing between chops is determined and controlled. It should be noted that only during this 'INDEX' phase of tray movement are pulses counted by the HDM. In other phases such as'TRAY LOAD' and 'TRAY CHANGE' the stepper motor is used as an ordinary drive in that it rotates continuously butthe STOP command is derived from tray position sensors rather than by pulse counting. In these other modes, therefore, the oscil lator frequency can exceed 1 kHz since it is not limited by the maximum frequency response ofthe HDM counter.

The TM 600U may also be connected in 'HALF STEP MODE'which results in a finer resolution at the stepper motor which then has as many steps per revolution i.e. 400 STEPS/REV. Half step mode gives smoother operation at low speeds.

Full details of the operation of the TM 600U are given in the manual forthat unit produced by The Superior Electric Co.

In this system, at 'TRAY LOAD' and 'TRAY INDEX' speeds, the stepper motor is used in HALF STEP MODE; and at 'TRAY CHANGE' speed, FULL STEP MODE is used.

The linear movement ofthe tray achieved per step of the stepper motor or per pulse of the oscillator is only of consequence in TRAY INDEX mode, since this is the only time when the HDM is used to count pulsesto determine the spacing between chops.

Since the stepper motor directly drives the chain on the tray conveyorthe distance per step may be determined asfollows: DRIVE SPROCKET = 30TEETH CHAIN PITCH = 3/8 in (9.525mm) thus 1 REV OF SPROCKET = 30 x 3/8 ins chain movement = 11 1/4 ins (285.75mm) and 1 STEPOFSTEPPER MOTOR = (111/4)200 ins chain movement = 0.0565 ins/step (1.429mm/Step) so 1/2 STEP OF STEPPER MOTOR = 0.028 ins/step (0.714mm/Step) The stepper motor is used in half-step mode for indexing the tray between chops so each oscillator pulse gives 0.028 ins of tray movement (0.714mm). If the appropriate HDM register was set to a value of 10, the tray would move for 10 oscillator pulses between chops of 10 x 0.02 ins = 0.28 ins (7.14mm).

However as detailed later under the section relating to differental spacing, the SYSMAC logic selects the value in the software counters C004 and C005 and effectively multiplythe HDM pre-setvalue by the value set in the C004 counterforfirst spacing and C005 counterforthe second spacing. Only if these counters are setto 1 wil a tray move as calculated above.

Thus the actual formula for calculating the chop spacing is asfollows: SPA CE BETWEEN FIRS TA ND SECOND CHOP SPACE 1 = HDM SETTING x C004 SETTING x 0.028 INS SPA CUE BETWEEN SUBSEOUENT CHOPS SPACE 2 = HDM SETTING x C005 SETTING x 0.028 INS EXAMPLE Suppose C004is set to 3, C005 is setto 2 and Program 1 is selected so HDM 000 is in use and setto, say, 10 SPACE 1 = HDM 000 x C004 x 0.028 = 10x3x0.028 = 0.84 ins (21.34 mm) SPACE 2 = HDM 000 x C005 x 0.028 = 10x2x0.028 = 0.56 ins(14.22 mm) Obviously if C004 and C005 both contain the same pre-set value then all chops in a tray will be spaced equally.

It can be seen that by adjusting the values ofthe HDM register settings and the values of C004 and COOS, a wide range offinely controlled spacings can be achieved.

Detailed description of operation with reference to the SYSMAC logic nmemonic listing of TABLE Afor computer 252. Specific addresses in the listing are identified and described below.

0000 CHOP DETECTION As a chop reaches the end of a delivery conveyor it breaks a light beam across the end of the conveyor between two fibre-optic cables.

Thechannel 1 sensoriscoupledtoinputOOOO The channel 2 sensor is coupled to input 0023 Obviously only one channel is operative at any one time so each sensor is enabled by the appropriateAPS RUN/STOP relay.

Thus channel 1 (0000) is enabled byAPS 1 RUN (0044) channel 2 (0023) is enabled by APS 2 RUN (0045) Since the sensors are through-beam types their inputs are assigned normally closed logic.

ihe entire chop detection circuit can be disabled bythe normally closed contact of timerT006 (100ms).This prevents the system cycling should a chop or any other material remain at rest in the sensor beam.

Thus considering channel 1 operation, only contact 44 is closed because APS 1 is operating and T006 is closed. Contact 65 is closed and bistable contact KOOO is closed. Contact 0000 is open because the sensor beam is unbroken. When a chop passes through the beam, the sensorturns off so the inputto 0000 is removed and contact 0000 closes operating the coil of relay 0064 and starting timerT00O (200ms). Relay0064 then latches via contact 0064.

After time delayT00O which allows transit time and settling timeforthe chop to transferfrom the launch conveyorto the tray and to settle in the tray the T000 contact at address 0020 closes and provided no alarm condition exists (0014) Relay 13 is energised and starts the tray conveyor advancing at index speed.

0019CHOPSPACINGCONTROL As the stepper motor rotates to advance the conveyor at index speed the pulses from the steppertranslator are processed by the pulse stretcher module in the power console to 1 .Oms width to match the CPU count input specification.

These pulses are applied to the EXT point of the High Speed Counter HDM and HDM starts counting the pulses when its STA (start) input is enabled by the contact of timer TOOO.

HDM has 32 outputs (HOO0 - H031 ) which can be individually programmed to change states and different values ofthe HDM counter.

In this system only 18 (H000 - H017) of the outputs are used. The outputs will have been selected bythe program set on the programming panel (See Program Decoding). For this description consider that program O is being run. Thus contact 0079 (address 0125) is closed and 80 through 96 are open. When the main HDM register has counted a number of stepper pulses equivalent to the number preset in HDM sub-registerHOOO, the contacts H00O will close and operate relay 97 via program 0 contact 79. The contacts of relay 97 at address 120 close and reset the main register of HDM to zero.

0179 DIFFERENTIAL SPACING Differential spacing is a provision in the Software to allow a large space between the first and second chops in a tray which in some cases gives a more stable load in a tray. It is controlled bytwo counters, C004and C005. C004 is shown setfora countof2and C005 is shown setfora countof2.

When the HDM register has completed its count relay 97 closes, resets HDM to zero and bumps counter C004 and C005. These now both contain a value of 1 so their outputs to do not change state, thus relay 0065 (address 0185) remains unenergised so the chop detection circuit (address 0000) remains latched and HDM starts counting up from zero again (tray still moving). This time when HDM reaches its preset value, H000 again closes and operates relay 97.97 again zeroes HDM and bumps counters C004 and C005. On this pass both counters now contain 2 so their outputs change state. At address 185, therefore C004 and C005 close.

Since we are considering the first chop into a tray only C004 has an effect because RDM counter ouptut R031 is setto change state at a count of 2 or greater (see CHOPS/TRAYCOUNT). Thus the closure of CO04energises 0065 whose normally closed contact at address line 0000 opens the entire chop detection circuit is unlatched and readyforthe second chop.

It can be seen from the above that the full movement of the tray indexforthe first chop required two complete cycles of HDM controlled byCO04. For all subsequent chops intothattraythe number of HDM cycles will be controlled by C005 becausethe chop counter RDM will have counted morethan one chop into thetray so R031 (address 0185) changes state.

If a greater spacing is required between the first and second chops in a tray then the value of C004 is simply increased.

i.e. ifC004 = 3 and C005 = 2 then the space between the first and second chops in a tray will require 3 HDM cycles as opposed to 2 HDM cycles for subsequent chops. Thus the space between the first and second chops in a tray will be 50% greater than that between subsequent chops.

C004 and C005 can be loaded with any value orcombination orvaluesto give differentspacing arrangements.

0193 CHOPS/TRAY CONTROL The chops/tray control uses the RDM reversible counter in the SYSMAC which has 32 outputs each ofwhich may be programmed to changed state atdifferentvalues ofthe main RDM counter.

The count input IN is driven by a contact oftimerT00O which closes a short time after a chop has landed in a tray.

The counter can be reset by the tray change bistable K000 or the tray load push button 0019 oratpower-up bye109.

Thus after initial tray loading thecounteris setto zero and as slicing commences, it then countsthe number of closures of the T000 contact which is the same as the number of chops in the tray. One of the outputs ofthe RDM counter R000 - R01 7 will be selected by the program decode contacts 0079 - 0096 (see PROGRAM DECODING).

When the counter reaches the pre-setvalue of the selected output, the corresponding output contact closes and energies the COUNT DONE relay 0069 (address line 0200). This signal is used to indicate TRAY FULL i.e.

the tray now contains the required number of chops. The operation of 0069 initiates the tray change sequence.

0279 TRAY CHANGE CONTROL When the appropriate RDM chop count is reached the 0069 contact closes and since this count is based on chops breaking the detector beamtheTOOOcontact also closes and the bistable (latching relay) K000 is set.

The contacts of K000 change state and perform the following functions: 1. Resets chop detection circuit (address line 0000) 2. Selects tray conveyor high speed by operating relays 0013 and 0019 (address lines 0020 and 0030) 3. Inhibits RDM counter (address line 0193) 4. Zeroes RDM counter (address line 0196) Thus the full tray is moved away from the chop discharge position at tray change speed. When the next empty tray approaches the chop discharge position its leading edge is sensed by the sensor at the channel two tray position, connected to input 0024.The contact 0024 at address line 0256 operates relay 0070which self latches through the normally closed contact of timer and and at the same time starts timer T001 timing.

Similarly, at address line 0260 another contact 0070 operates relay 0072.0072 is then de-energised when T001 times out.

The contacts of relay 0072 therefore pulse when the channel 2 tray detector is switched by a tray giving a one-shot output. At address line 0281 the pulse from contact 0072 resets the tray change bistable KR000 which in turn releases relays 0013 and 0019 stopping the tray conveyor and bringing new tray to rest inthe correct position for receiving the first chop.

Itis importantto notethattrays are always aligned to the channel 2 sensor regardless ofwhich channel is currently discharging chops. The channel 1 tray sensor is used only to check for the presence or absence of a tray in that position.

Reference is madeto Tables A and B for the complete description ofthe software command to effectthe stepper motor control.

Claims (9)

1. In combination with a conveyor, drive meanstherefor comprising an electric stepper motor and control circuit means adapted to generate a sequence of electrical pulses the frequency and duration of which are controlled whereby the motor and in turn the conveyor are accurately positionable.

2. A conveyor and drive therefor comprising a stepper motor which moves through small arcuate displacements in response to control pulses supplied thereto and is locked at each stepped position whereby the conveyor is driven in a series of incremental steps the linear displacement of each of which is proportional to the corresponding arcuate movement of the stepper motor in response to each control pulse supplied thereto.

3. A conveyor drive comprising an electric stepper motor having an outer casing attached to a stator and an output shaft rotatably mounted in the casing, attached to a rotor, wherein means is provided forfixedly mounting the shaft ofthe motor to hold the shaft stationary and the outer casing is provided with drive means for engaging and driving an endless belt associated with the conveyor, which belt extends around the outer casing to be driven thereby as the casing rotates aboutthefixed shaft.

4. Aconveyordrive as claimed in any of claims 1 to 3 wherein teeth reformed around the casing for engaging in slots in the endless belt.

5. A conveyor drive as claimed in any of claims 1 to 3 wherein teeth reformed around the casing for engaging between links of a chain, which lattercomprisesthesaid endless belt.

6. Aconveyordrive as claimed in any of claims 1 to 3 in combination with circuit means adapted to generate electrical pulses for driving the stepper motor and a microprocessorfor controlling the circuit means.

7. A conveyor drive as setforth in claim 6 further'comprising programming means for entering programme information into a memory associated with the microprocessor, whereby a series of commands can be given to the motor to operate incrementally by predetermined amounts so as to obtain desired movement of the conveyor belt.

8. A conveyor drive as setforth in claim 6 in combination with a conveyor to which objects are supplied via a delivery station, which further comprises input means for inputting electrical signals indicative of the arrival of objects at the delivery station.

9. A conveyor drive as set forth in claim 6 in combination with a conveyor on which containers are carried past a delivery station, which further comprises input means for inputting electrical signals indicative ofthe arrival of a container atthe delivery station.