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An Approach to Automated Warehouse Design
Copyright © IFAC Low Cost Automation 1986 Valencia. Spain. 1986
AN APPROACH TO AUTOMATED WAREHOUSE DESIGN J. Uceda, G. Ojea, H. L6pez, M. Rico Dpto. de Electr6nica y Automatica. Universidad de Oviedo Carretera de Castiello si n. Gij6n . Spain Abstract. In this paper an automated warehouse system is described. A des cription of the installation is included, considering the layout and thematerial handling equipment. The control system design is modular and the computer hierarchy is described. The sensors applied for accurate positio ning and the system operation are discussed. Manufacturing processes; Control engineering computer applications; Materials handling; Conveyors; sensors; Stock control; Transportation control.
~ords.
GENERAL DESCRIPTION
INTRODUCTION In today's factory, the warehouse has beco me increasingly integrated with the manufacturing process itself.
The warehouse installation for palletized goods are constituted for one or more rows of good cells. Between these rows there are one or more aisles with cells on both sides. This allows us to place there a mobile system responsible for good displacement.
The automated warehouse is an important element of any flexible manufacturing system. With the continuous development of automation in production, new demands are being made in automated materials handling in order to cut work in progress, stock and make internal transport efficient.
The mobile system (stacker crane) can give services at one or more aisles simultaneous ly and there is frequently to be found in one warehouse, various cranes working in co-ordination.
To remain competitive in today's market, the industries have to cut their manufactu ring costs. Large costs are hidden in exce sive stock of work-in-progress and raw ma= terial. The introduction of well disciplined and comprehensive stock control systems, and efficient transport systems will have a major effect on manufacturing costs and also in order to substantially increase the productivity of a manufacturing plant.
The prototype developped is a small-size installation of 5 m. high and 10 m. long. It consists of one aisle and two rows. Each row has 6 sections of 1 m. There sections have 3 or 4 levels at 500 Kg. weight per level. TWo different good-cell sizes are implemented, symmetrically distributed in both rows (5). Material handling is achieved by a stacker crane running on rails, through the aisle, picking up goods by an automatic fork, dis patching or retrieving pallets and allo- wing internal material movements. The input / output sections consists of two platforms where pallets are placed and picked up by the stacker crane.
Automated warehouses offer advantages that cannot be obtained with mannual operation at realistic costs. Stock control is an im portant function of any warehouse and itsautomation allows us to mantain a very accu rate inventory of articles in the factory,whether they are in the store, in the work shop, being transported or handled in anyother way.
The proposed solution ca be easily applied to large scale warehouse systems with seve ral aisles, rows, stacker cranes, etc. -
With automation of the production warehouse and the transport system between the wa rehouse and production, it is possible tolet the required articles remain in the warehouse control until the moment they are actually needed required.
Communication between computer and master control is achieved considering the computer as a primary station and the master con trol as a secondary one. In these structu-res the primary station has the responsibi lity for the information transfer. In the link operation there are three periods of time: - Waiting time between answers - Time between messages for link mainte nance Time between messages repetition in the case of broken link
err-AA
397
J. Uceda, G. Ojea, H. L6pez, M. Rico
398
POSITIONING AND MOVEMENT CONTROL PRINCIPLE In order to diminish the operation time si multaneously movement in both axis is pro= grammed. Both movements start at the same time and the maximum operation time is equal to the maximum traslation and elevation time. (Fig. 1).
Another characteristics of the movement lets the motor works at nominal speed as much as possible, improving working conditions and reducing the operation time.
ting the stacker crane in its working area, in cases of positioning errors, such as a positioning plate missed. This solution avoids the utilization of coded marks, sim plifying the system concept. The inicialization protocol locates the sta cker crane in the firsc plate in both axis and the system continues working in normal operation mode. There are digital encoders in both axis and a load cell, controlling the speed in close-loop operation. The speed diagram is re presented in figure 2.
)// Fig. 1.
Operation trajectories
Squirrel-cage motors are use in hoisting and travelling movements. A comertial PWM AC drive with regenerative braking and speed reversal capabilities worm-gear speed reducers have been used, due mainly to characteristics of irreversibility, and are specially indicated in the hoisting movement. Travelling maximum speed is 1 m/ s with 0,5 m/s2 of maximum aceleration. In the vertical movement the maximum speed and acelera tion are 0,2 m/s and 0,2 m/s2 respectively. The first level of positioning is achieved by photoelectric cells, detecting reflecting plates located at ground level in the horizontal movement, and on the mast in the vertical movement. Positioning is at first roughtly estimated by its coordinates. Then a second system starts working for more accurate requirements. The fine positioning system is based upon an optical sensor with reflecting plates 10 cated at every cells as it is shown in Figu re 2. Errors due to mechanical deformations in the structure can then be avoided.
Fig. 3.
Speed diagrams
The system starts at low speed, with constant aceleration, reaching the nominal speed. The positioning sensors indicate the vicinity of the final position, speed is smoothly reduced and, finally, when positio ning sensors indicate the final position, electric brakes are activated, locating the stacker crane in the proper cell. Additionaly the equipment includes a maximum and minimum weight alarms. Weight alarms can detect failures such as breaking or blokage of the elevation rope. The stacker crane also includes two ultrasonic sensors for obstacle detection in the aisle, avoiding eventual collisions.
PLATE
After the crane is properly positioned, the fork must be activated to pick up or drop off the load, depending of input or output operation.
OPTICAL SENSOR VISION FIELD
Input operation process can be divided in the following steps: 1) Both traslation and elevation aproximation positioning 2) Both traslation and elevation accura te positioning 3) Fork extension
Fig. 2.
Accurate positioning system.
Some other complementary protections at the boundaries in both axis are included. A position sensor activates a RESET signal, starting an inicialization protocol, loca-
4) Precision and elevation ( 100 mm) 5) Load weight computation 6) Fork taking back operation
399
Automated Warehouse Design Output operat ion proces s can be divide d in the follow ing steps: 1) Both trasla tion and elevat ion aproxi mation positio ning. 2) Trasla tion accura te positio ning
CONTROL SYSTEM STRUCTURE Block diagram and functio ns The contro l system is hierarc hized and includes three contro l levels . This is shown in figure 5.
3) Precis ion elevat ion (100 mm) STOC K AN D HATERI AL fLO W CONTROL
4) Fork extens ion 5) Precis ion descen t (100 mm) 6) Elevat ion accura te positio ning
CR ANE MASTER
CO NTROL
7) Fork taking back operat ion Accura te positio ning moveme nt implie s plate to plate displac ement and the crane moves at slow speed. Elevat ion accura te posi tionin g must be previo us to fork displace~ ment in order to ensure the proper alignment, avoidi ng errors in the load movem ent. There is not contro l loop in the fork move ment. Two speed induct ion motor is used. The follow ing speed values are select ed. - 6 m/ min. Loadin g fork - 12 m/ min. No loadin g fork Fork is moved at low speed with load avoiding slidin g effect s and at high speed with out load in order to improv e the speed op~ ration . An encode r (100 pulses / revolu tion) is coupled to the motor axis to ensure the proper positio ning. This system achiev es 5 mm. accura cy in the fork displac ement. In the fork there are three induct ive sensors definin g the moveme nt length . Two of these sensor s work like limit positio n sen sors. The other ensure the fork center ingacross the aisle. There are five more sensor s. Two of them determ ine "lhethe r the fork is loaded and proper ly locate d or not, to ensure that the crane can move withou t collis ions. Three proxim ity sensor s at both fork sides detect if there are goods in any cell. The se sensor s also check the fork and pallet alignm ent.
POR1( CONTROL
PALLET CONTROL
1 VERT ICA L ",NO
FURK CON 1 ROL , 1 l ____ _ ____ __ t CRANE CONTROL LER 1
Fig. 5.
1 1
,
1. __ _______ _ _ _ 1 CRANE CONTROLLER 2
The hierar c hy of contro l system
The higher level (stock and flow contro l) is essent ial in any wareho use system . It consis ts of one IBM PC XT and its main func tions are: - Input / output manage ment - Locati ons of pallet ized goods Optim ization of input / output trajec tories - File manage ment (suppl iers, custom ers, agents , articl es, etc). - Genera tion of invent ories - Physic al stock status for all storag e alloca tions - Commu nicatio ns with crane master control and manufa cturing contro l system The second level of hierarc hy consis ts of one Z-80 based microc ompute r system . The crane master contro l involv es input / output s pallet contro l and movem ents order to the crane contro llers. This master contro l monitors cell the stacke r crane in the warehouse system linkin g the IBM-PC -XT with the crane contro llers. The crane contro llers are based on two Z-80 microc ompute rs one of these involv es the horizo ntal moveme nt contro l and the other the vertic al and fork moveme nt contro l (see fig. 6). The IBM-PC -XT is linked to the crane master contro l throug h a RS-232 -C serial line (1200 baudio s) crane master contro l and the microc ompute r charge d of horizo ntal movement are connec ted in the same way (9600 baudio s). Both microc ompute r in the crane contro ller are connec ted throug h a parallel line (5). MANAGEMENT SOFTWARE
ACCURATE POSITION
The main functio ns of the inform atic system are: MOTOR DRIVE
Fig. 4.
Fork sensor s
-
Manage ment of the wareho use Input / output materi al contro l Produc tion of report s Contro l of the wareho use
1. Uceda, G. Ojea, H. L6pez, M. Rico
400
Fig. 6.
General structure of control system
The information system provides various 02 tions: -
File maintenance Stock control Goods location Charge and discharge paths control Warehouse inventory and listing of warehouse movements
Therefore, software tools are used to achie ve easier and faster modification and display of data values and automatic generation of reports. The user will be able to choose among different criteria by input! output. -
FIFO option Product expiry data Optimum trajectory of stacker crane The nearest empty cell Cell chosen by user
The set of data files containing information needed in the warehouse operation are: -
Articles file Products file Cell file SUppliers file Customers file Historial movements file Errors file
Tasks are codified in high level language (FORTRAN) and allow a standard operational logic of both data handling and report generation. It must be remarked that the finantial mana gement in the warehouse is achieved, inclu=
ding the following items: - Stock costs - Suppliers and customers results - Particular commercial conditions with suppliers and customers The aforementioned logic is based on control input! output information to screen, with an exhaustive test about the legality of the introduced information. The common operational sequence is structured in the following points: - Presentation on the scren of options index to select by user - Selection of the chosen option through the sequence shown on the screen - Presentation on the screen of input! output dialogue corresponding to the chosen option It is important to emphasize that the system offers two operational levels, according to the access password, namely: (a) supervisor, (b) operator. By means of these levels it is possible to stablish a set of privileges according to category, so that data input to the critical area is possible only from a high level. CONTROL SOFTWARE Master control functions Master control links the management computer and the crane controllers, synchronizing dialogs between the crane and the computer.
401
Automated Warehouse Design It also checks the auto/mannual state and communicates this situation to the computer. It also controls the height of palletized goods during input operations. This last function is specially important in warehou se installation with several all height. -
computer. CONCLUSIONS
Crane controllers functions
An automated system has been developed. A modular control system has been designed, allowing easy implementation of new control functions.
These microcomputer are involved in traslation, elevation and fork movement control. It also informs to the master control about the state of the crane at any instant.
All movements, including the horizontal and vertical ones, are achieved with induction motors. P~M inverters in slip-frequency closed-loop control are used.
Software is modulary developped including the following modules:
System operation and sensor techniques for accurate positioning have been verified in a small scale installation situated in the laboratory of the Departamento de Electronica y Automatica (DEA) in the school of Industrial Engineers in Gij6n. It has been done with the cooperation of the Duro Felguera S.A. (DF) enterprise and it has been sponsored by the Fundacion para el Fomento en Asturias de la investigacion Cientifica Aplicada y la Tecnologia (FICYT).
-
Initial configuration module Communication module Starting and stopping module Movement module Error control module
In the master control there are two additio nal modules: - Exchange manual / auto module - Height control module Initial configuration module programs the operating modes of the microcomputer components (CTC, PlO, SITS, etc), defining baud rate, parity, stop bits. It is also defined some parameters needed in normal system op~ ration. Transmission-reception messages and communi cation line checking are achieved by the communication module. Starting/stopping module is activated by messages sent by the management computer (inicialization, stop, end of queue) or automatically through error messages. When inicialization is activated, crane is moved through the coordinates origin, the position is cheked, leavin9 the load in the output section, and waits for the first order. Movements orders are transmitted from the computer to the crane by movement rutines, picking up goods from the origin cell and leaving in other cell. This module achieves many tasks, such as movement identifica tion (input, output, desplacement), acelera tion and brake slope control, positioning sensor detection, precision positioning, synchronization of translation and elevation movements. Alarms and errors in the system operation are communicated to the master control from the crane controller microcomputers. Failu res are divided in two groups. One group includes these which the system can tolerate without interruption; the other, those which require operator action. The manual / auto state changes are detected by the master control. This unit communicates this information to the computer, and inicialization or stop order is trasmitted to the crane controller depending on the sense of state changes. In case of input operations, goods height must be controlled, defining what kind of cell must be used in this operation. (There are two different cell-heights in the warehouse). If overheight is detected a height error message in trasmitted to the
REFERENCES 1. Ranky P.G., "Computer integrated manufac turing". Prentice Hall. 1985. 2. Armstrong R.P. and Jack J., "Improving productivity by incorporation flexibility into an automated warehouse design". IFS 1 st International Conference on Auto mated Materials Handling. London 1983. 3. Duncan L.S., Booz-Allen and Hamilton Inc. "System design trends in automated warehousing". Stockholm 1985. 4. Lee R."., "Automated storage and handling of cores and moulds in a foundry". IFS 1 st International Conference on Auto mated Materials Handling. London 1983. 5. Uceda J., Ojea G., L6pez H. and Rico M. "An automated warehouse system for palle tized materials". IECON'86 Twelfth Annual IEEE Electronics Society Conference. Milwaukee 1986.
AN APPROACH TO AUTOMATED WAREHOUSE DESIGN J. Uceda, G. Ojea, H. L6pez, M. Rico Dpto. de Electr6nica y Automatica. Universidad de Oviedo Carretera de Castiello si n. Gij6n . Spain Abstract. In this paper an automated warehouse system is described. A des cription of the installation is included, considering the layout and thematerial handling equipment. The control system design is modular and the computer hierarchy is described. The sensors applied for accurate positio ning and the system operation are discussed. Manufacturing processes; Control engineering computer applications; Materials handling; Conveyors; sensors; Stock control; Transportation control.
~ords.
GENERAL DESCRIPTION
INTRODUCTION In today's factory, the warehouse has beco me increasingly integrated with the manufacturing process itself.
The warehouse installation for palletized goods are constituted for one or more rows of good cells. Between these rows there are one or more aisles with cells on both sides. This allows us to place there a mobile system responsible for good displacement.
The automated warehouse is an important element of any flexible manufacturing system. With the continuous development of automation in production, new demands are being made in automated materials handling in order to cut work in progress, stock and make internal transport efficient.
The mobile system (stacker crane) can give services at one or more aisles simultaneous ly and there is frequently to be found in one warehouse, various cranes working in co-ordination.
To remain competitive in today's market, the industries have to cut their manufactu ring costs. Large costs are hidden in exce sive stock of work-in-progress and raw ma= terial. The introduction of well disciplined and comprehensive stock control systems, and efficient transport systems will have a major effect on manufacturing costs and also in order to substantially increase the productivity of a manufacturing plant.
The prototype developped is a small-size installation of 5 m. high and 10 m. long. It consists of one aisle and two rows. Each row has 6 sections of 1 m. There sections have 3 or 4 levels at 500 Kg. weight per level. TWo different good-cell sizes are implemented, symmetrically distributed in both rows (5). Material handling is achieved by a stacker crane running on rails, through the aisle, picking up goods by an automatic fork, dis patching or retrieving pallets and allo- wing internal material movements. The input / output sections consists of two platforms where pallets are placed and picked up by the stacker crane.
Automated warehouses offer advantages that cannot be obtained with mannual operation at realistic costs. Stock control is an im portant function of any warehouse and itsautomation allows us to mantain a very accu rate inventory of articles in the factory,whether they are in the store, in the work shop, being transported or handled in anyother way.
The proposed solution ca be easily applied to large scale warehouse systems with seve ral aisles, rows, stacker cranes, etc. -
With automation of the production warehouse and the transport system between the wa rehouse and production, it is possible tolet the required articles remain in the warehouse control until the moment they are actually needed required.
Communication between computer and master control is achieved considering the computer as a primary station and the master con trol as a secondary one. In these structu-res the primary station has the responsibi lity for the information transfer. In the link operation there are three periods of time: - Waiting time between answers - Time between messages for link mainte nance Time between messages repetition in the case of broken link
err-AA
397
J. Uceda, G. Ojea, H. L6pez, M. Rico
398
POSITIONING AND MOVEMENT CONTROL PRINCIPLE In order to diminish the operation time si multaneously movement in both axis is pro= grammed. Both movements start at the same time and the maximum operation time is equal to the maximum traslation and elevation time. (Fig. 1).
Another characteristics of the movement lets the motor works at nominal speed as much as possible, improving working conditions and reducing the operation time.
ting the stacker crane in its working area, in cases of positioning errors, such as a positioning plate missed. This solution avoids the utilization of coded marks, sim plifying the system concept. The inicialization protocol locates the sta cker crane in the firsc plate in both axis and the system continues working in normal operation mode. There are digital encoders in both axis and a load cell, controlling the speed in close-loop operation. The speed diagram is re presented in figure 2.
)// Fig. 1.
Operation trajectories
Squirrel-cage motors are use in hoisting and travelling movements. A comertial PWM AC drive with regenerative braking and speed reversal capabilities worm-gear speed reducers have been used, due mainly to characteristics of irreversibility, and are specially indicated in the hoisting movement. Travelling maximum speed is 1 m/ s with 0,5 m/s2 of maximum aceleration. In the vertical movement the maximum speed and acelera tion are 0,2 m/s and 0,2 m/s2 respectively. The first level of positioning is achieved by photoelectric cells, detecting reflecting plates located at ground level in the horizontal movement, and on the mast in the vertical movement. Positioning is at first roughtly estimated by its coordinates. Then a second system starts working for more accurate requirements. The fine positioning system is based upon an optical sensor with reflecting plates 10 cated at every cells as it is shown in Figu re 2. Errors due to mechanical deformations in the structure can then be avoided.
Fig. 3.
Speed diagrams
The system starts at low speed, with constant aceleration, reaching the nominal speed. The positioning sensors indicate the vicinity of the final position, speed is smoothly reduced and, finally, when positio ning sensors indicate the final position, electric brakes are activated, locating the stacker crane in the proper cell. Additionaly the equipment includes a maximum and minimum weight alarms. Weight alarms can detect failures such as breaking or blokage of the elevation rope. The stacker crane also includes two ultrasonic sensors for obstacle detection in the aisle, avoiding eventual collisions.
PLATE
After the crane is properly positioned, the fork must be activated to pick up or drop off the load, depending of input or output operation.
OPTICAL SENSOR VISION FIELD
Input operation process can be divided in the following steps: 1) Both traslation and elevation aproximation positioning 2) Both traslation and elevation accura te positioning 3) Fork extension
Fig. 2.
Accurate positioning system.
Some other complementary protections at the boundaries in both axis are included. A position sensor activates a RESET signal, starting an inicialization protocol, loca-
4) Precision and elevation ( 100 mm) 5) Load weight computation 6) Fork taking back operation
399
Automated Warehouse Design Output operat ion proces s can be divide d in the follow ing steps: 1) Both trasla tion and elevat ion aproxi mation positio ning. 2) Trasla tion accura te positio ning
CONTROL SYSTEM STRUCTURE Block diagram and functio ns The contro l system is hierarc hized and includes three contro l levels . This is shown in figure 5.
3) Precis ion elevat ion (100 mm) STOC K AN D HATERI AL fLO W CONTROL
4) Fork extens ion 5) Precis ion descen t (100 mm) 6) Elevat ion accura te positio ning
CR ANE MASTER
CO NTROL
7) Fork taking back operat ion Accura te positio ning moveme nt implie s plate to plate displac ement and the crane moves at slow speed. Elevat ion accura te posi tionin g must be previo us to fork displace~ ment in order to ensure the proper alignment, avoidi ng errors in the load movem ent. There is not contro l loop in the fork move ment. Two speed induct ion motor is used. The follow ing speed values are select ed. - 6 m/ min. Loadin g fork - 12 m/ min. No loadin g fork Fork is moved at low speed with load avoiding slidin g effect s and at high speed with out load in order to improv e the speed op~ ration . An encode r (100 pulses / revolu tion) is coupled to the motor axis to ensure the proper positio ning. This system achiev es 5 mm. accura cy in the fork displac ement. In the fork there are three induct ive sensors definin g the moveme nt length . Two of these sensor s work like limit positio n sen sors. The other ensure the fork center ingacross the aisle. There are five more sensor s. Two of them determ ine "lhethe r the fork is loaded and proper ly locate d or not, to ensure that the crane can move withou t collis ions. Three proxim ity sensor s at both fork sides detect if there are goods in any cell. The se sensor s also check the fork and pallet alignm ent.
POR1( CONTROL
PALLET CONTROL
1 VERT ICA L ",NO
FURK CON 1 ROL , 1 l ____ _ ____ __ t CRANE CONTROL LER 1
Fig. 5.
1 1
,
1. __ _______ _ _ _ 1 CRANE CONTROLLER 2
The hierar c hy of contro l system
The higher level (stock and flow contro l) is essent ial in any wareho use system . It consis ts of one IBM PC XT and its main func tions are: - Input / output manage ment - Locati ons of pallet ized goods Optim ization of input / output trajec tories - File manage ment (suppl iers, custom ers, agents , articl es, etc). - Genera tion of invent ories - Physic al stock status for all storag e alloca tions - Commu nicatio ns with crane master control and manufa cturing contro l system The second level of hierarc hy consis ts of one Z-80 based microc ompute r system . The crane master contro l involv es input / output s pallet contro l and movem ents order to the crane contro llers. This master contro l monitors cell the stacke r crane in the warehouse system linkin g the IBM-PC -XT with the crane contro llers. The crane contro llers are based on two Z-80 microc ompute rs one of these involv es the horizo ntal moveme nt contro l and the other the vertic al and fork moveme nt contro l (see fig. 6). The IBM-PC -XT is linked to the crane master contro l throug h a RS-232 -C serial line (1200 baudio s) crane master contro l and the microc ompute r charge d of horizo ntal movement are connec ted in the same way (9600 baudio s). Both microc ompute r in the crane contro ller are connec ted throug h a parallel line (5). MANAGEMENT SOFTWARE
ACCURATE POSITION
The main functio ns of the inform atic system are: MOTOR DRIVE
Fig. 4.
Fork sensor s
-
Manage ment of the wareho use Input / output materi al contro l Produc tion of report s Contro l of the wareho use
1. Uceda, G. Ojea, H. L6pez, M. Rico
400
Fig. 6.
General structure of control system
The information system provides various 02 tions: -
File maintenance Stock control Goods location Charge and discharge paths control Warehouse inventory and listing of warehouse movements
Therefore, software tools are used to achie ve easier and faster modification and display of data values and automatic generation of reports. The user will be able to choose among different criteria by input! output. -
FIFO option Product expiry data Optimum trajectory of stacker crane The nearest empty cell Cell chosen by user
The set of data files containing information needed in the warehouse operation are: -
Articles file Products file Cell file SUppliers file Customers file Historial movements file Errors file
Tasks are codified in high level language (FORTRAN) and allow a standard operational logic of both data handling and report generation. It must be remarked that the finantial mana gement in the warehouse is achieved, inclu=
ding the following items: - Stock costs - Suppliers and customers results - Particular commercial conditions with suppliers and customers The aforementioned logic is based on control input! output information to screen, with an exhaustive test about the legality of the introduced information. The common operational sequence is structured in the following points: - Presentation on the scren of options index to select by user - Selection of the chosen option through the sequence shown on the screen - Presentation on the screen of input! output dialogue corresponding to the chosen option It is important to emphasize that the system offers two operational levels, according to the access password, namely: (a) supervisor, (b) operator. By means of these levels it is possible to stablish a set of privileges according to category, so that data input to the critical area is possible only from a high level. CONTROL SOFTWARE Master control functions Master control links the management computer and the crane controllers, synchronizing dialogs between the crane and the computer.
401
Automated Warehouse Design It also checks the auto/mannual state and communicates this situation to the computer. It also controls the height of palletized goods during input operations. This last function is specially important in warehou se installation with several all height. -
computer. CONCLUSIONS
Crane controllers functions
An automated system has been developed. A modular control system has been designed, allowing easy implementation of new control functions.
These microcomputer are involved in traslation, elevation and fork movement control. It also informs to the master control about the state of the crane at any instant.
All movements, including the horizontal and vertical ones, are achieved with induction motors. P~M inverters in slip-frequency closed-loop control are used.
Software is modulary developped including the following modules:
System operation and sensor techniques for accurate positioning have been verified in a small scale installation situated in the laboratory of the Departamento de Electronica y Automatica (DEA) in the school of Industrial Engineers in Gij6n. It has been done with the cooperation of the Duro Felguera S.A. (DF) enterprise and it has been sponsored by the Fundacion para el Fomento en Asturias de la investigacion Cientifica Aplicada y la Tecnologia (FICYT).
-
Initial configuration module Communication module Starting and stopping module Movement module Error control module
In the master control there are two additio nal modules: - Exchange manual / auto module - Height control module Initial configuration module programs the operating modes of the microcomputer components (CTC, PlO, SITS, etc), defining baud rate, parity, stop bits. It is also defined some parameters needed in normal system op~ ration. Transmission-reception messages and communi cation line checking are achieved by the communication module. Starting/stopping module is activated by messages sent by the management computer (inicialization, stop, end of queue) or automatically through error messages. When inicialization is activated, crane is moved through the coordinates origin, the position is cheked, leavin9 the load in the output section, and waits for the first order. Movements orders are transmitted from the computer to the crane by movement rutines, picking up goods from the origin cell and leaving in other cell. This module achieves many tasks, such as movement identifica tion (input, output, desplacement), acelera tion and brake slope control, positioning sensor detection, precision positioning, synchronization of translation and elevation movements. Alarms and errors in the system operation are communicated to the master control from the crane controller microcomputers. Failu res are divided in two groups. One group includes these which the system can tolerate without interruption; the other, those which require operator action. The manual / auto state changes are detected by the master control. This unit communicates this information to the computer, and inicialization or stop order is trasmitted to the crane controller depending on the sense of state changes. In case of input operations, goods height must be controlled, defining what kind of cell must be used in this operation. (There are two different cell-heights in the warehouse). If overheight is detected a height error message in trasmitted to the
REFERENCES 1. Ranky P.G., "Computer integrated manufac turing". Prentice Hall. 1985. 2. Armstrong R.P. and Jack J., "Improving productivity by incorporation flexibility into an automated warehouse design". IFS 1 st International Conference on Auto mated Materials Handling. London 1983. 3. Duncan L.S., Booz-Allen and Hamilton Inc. "System design trends in automated warehousing". Stockholm 1985. 4. Lee R."., "Automated storage and handling of cores and moulds in a foundry". IFS 1 st International Conference on Auto mated Materials Handling. London 1983. 5. Uceda J., Ojea G., L6pez H. and Rico M. "An automated warehouse system for palle tized materials". IECON'86 Twelfth Annual IEEE Electronics Society Conference. Milwaukee 1986.