Flexible Manufacturing Cell: development, coordination, integration and control

2005 International Conference on Control and Automation (ICCA2005) June 27-29, 2005, Budapest, Hungary WM-4.2 Flexible Manufacturing Cell: development, coordination, integration and control António Ferrolho and Manuel Crisóstomo Electrical Engineering Department Superior School of Technology of the Polytechnic Institute of Viseu Campus Politécnico de Repeses, 3504-510 Viseu PORTUGAL E-mail: antferrolho@elect.estv.ipv.pt ** Institute of Systems and Robotics University of Coimbra Polo II, 3030-290 Coimbra PORTUGAL E-mail: mcris@isr.uc.pt Abstract This paper describes the development, coordination, integration and control of a Flexible Manufacturing Cell (FMC). FMC has industrial characteristics and was developed to study these types of manufacturing systems. The FMC hierarchical structure is based on five layers: engineering, planning, scheduling, control and data acquisition. The connection of all of the equipment in the FMC (manufacturing equipment and information processing) is carried out via computer network. The connection of all the equipments in FMC (manufacturing equipment and processing of information) is done through a computer network. In this work we present the layout, the hierarchical structure and the four sectors (manufacturing, assembly, handling and storage) that make up FMC. For the coordination, integration and control of FMC several software programmes and hardware were created. An interface was developed - Direct Numerical Control (DNC) - to control the CNC machines used in FMC. For the robots used in the FMC the winats and RAPComm applications were developed. 1 Introduction Today two or more CNC machines are considered a Flexible manufacturing Cell (FMC) and two or more cells are considered a Flexible Manufacturing Systems (FMS) [4]. FMS are typical real time concurrent systems composed of a number of computer-controlled machine tools, automated material handling and storage systems [5,7]. FMS and Computer Integrated Manufacturing (CIM) systems using industrial control networks [3]. An FMC with industrial characteristics was developed with the objective of studying these types of manufacturing systems. The FMC has a hierarchical control structure based on five layers: engineering, planning, scheduling, control and data acquisition. Each layer communicates with whatever is immediately above or lower. The connection of all of the equipments in FMC (manufacturing equipment and processing of information) is done through an computer network. 2 PresentationofFMC The FMC is comprised of four sectors, which are controlled by PCs and different software. The four sectors are: Manufacturing sector, made up of two CNC machines (mill and lathe), one ABB IRB140 robot and one buffer; Assembly sector, made up of one Scorbot ER VII robot, one small conveyor and an assembly table; Handling sector, made up of one great conveyor; sector, made up of five warehouses and one robot ABB IRB1400. Control of existing equipment in each sector is carried out by four computers: PC1 manufacturing sector, PC2 assembly sector, PC3 handling sector and PC4 storage sector. The coordination, synchronization and integration of the four sectors is carried out by the of FMC computer Manager. 0-7803-9137-3/05/$20.00 2005 IEEE 1050

r Figure 1 presents the layout of developed FMC where the four sectors can be seen. PC CNC PC1+PC2 PC3+PC4 Raw materials Finished Products The third layer is scheduling. The process plans together with the drawing, the bill of materials and the customer orders are the input to scheduling. The output of scheduling is the release of the order to the manufacturing floor. The PCM FMC Manager is responsible for the engineering, planning and scheduling activities. ABB IRB140 robot Mill CNC Buffer Conveyor Assembly sector Scorbot ER VII Conveyor Manager of FMC ABB IRB1400 robot Finished Products Mill Raw materials Mill of Paletes The fourth layer is control. Manufacturing is controlled by a hierarchically structured real time computer system (PC1, PC2, PC3 and PC4). Its set points are the operating parameters used for starting and controlling the activities on the production floor. IRB140 Controller IRB1400 Controller Figure 1: Layout of Flexible Manufacturing Cell. Whenever a PC needs to communicate with another PC in a lower hierarchical layer, it sends a message through the net. The messages are composed of a command and a group of parameters: COMMAND PARAMETERS. The PC that receives the message will send two messages: the first indicates to the client that the command was received and whether or it will be executed. The second message indicates if the command was well executed or if an error occurred. The hierarchical structure implemented in FMC is shown in Figure 2. Messages cannot be sent from a higher hierarchical layer to an inferior layer without passing the intermediate layers [6]. The fifth layer is data acquisition. The operations of the machine tools and material movement equipment are monitored by a data acquisition system. The collected data represents the state of the manufacturing system and is the feedback information used for control. 3 FMC Manager The central computer (PCM - FMC Manager) controls all of the FMC production, connecting the various computers and data communication networks, which allows real time control and supervision of the operations, collecting and processing information flow from the various resources. Figure 3 presents the main window of the software developed for the PC - FMC Manager. In this PC the first three layers of the hierarchical structure presented in Figure 2 are implemented: engineering, planning and scheduling. First layer: Internet PCM. Engineering CAD PC M Second layer: Planning Orders CAP PC M Third layer: M2 M1 PP&C Scheduling Fourth layer: PC1 PC2 PC3 PC4 Control Control Inputs/Outputs PCM Manager of FMC: Engineering + Planning + Scheduling PC1 Manufacturing sector: Mill + + IRB140 Robot + buffer PC2 Assembly sector: Scorbot ERVII Robot + small conveyor PC3 Handling sector: big conveyor PC4 sector: IRB1400 Robot + Automatic CAM. Fifth layer: Data acquisition Figure 2: Hierarchical structure of FMC. The first layer contains the engineering and design functions where the product is designed and developed. The outputs of this activity are the drawings and the bill of materials. The second layer is process planning. Here the process plans for manufacturing, assembling and testing are made. Figure 3: Main window of the software developed for the PC - FMC Manager. The PC - FMC Manager is responsible for: Developing and designing new products to manufacture the engineering layer; Production plans, assemblies and product tests the planning layer; Finding the optimum processing sequence so as to optimize CNC machine use the scheduling layer; Maintaining a database of jobs to manufacture, including the respective NC programmes; 1051

Synchronizing the various sectors so as to produce variable lots of different types of parts depending on the customer s orders; Monitoring the current state of the production; Guaranteeing tolerance of failures, safety and coherence of the data. 4 FMC Sectors carried out by DNC, and the robotics interface were used as redundancy. PC CNC state by robotics interface (redundancy) Machine state by DNC Send DNC commands PC1 In this section we will present the four sectors of the FMC. These sectors are controlled by four PCs - PC1, PC2, PC3 and PC4. These PCs are in the fourth layer (control) of the hierarchical structure of FMC, as shown in Figure 2. ABB IRB 140 Robot Robot state by RAPComm Send RAPComm commands 4.1 Manufacturing Sector The manufacturing sector has two CNC machines (CNC Mill and CNC ) responsible for the manufacturing of the jobs. In order to optimize the manufacturing jobs there is a buffer in this sector where small amounts of raw-materials for both machines are available and where finished-products are kept. 4.1.1 Control of the manufacturing sector The manufacturing sector is controlled by software, developed in C++ Builder, and has the following functions: Buffer Administration; CNC machine Administration; ABB IRB140 Robot Control. The state of the buffer is controlled by variables that are automatically updated whenever a load or unload operation of the machines or the buffer is requested. Table 1 shows the variables used. Table 1: Buffer Control Variables. Variables Meaning BUFFER_RM_L N.º of RM for the lathe BUFFER_RM_M N.º of RM for the mill BUFFER_FP_L N.º of FP for the lathe BUFFER_FP_M N.º of FP for the mill The load and unload operations of the machines and the buffer are executed by the ABB IRB140 robot. Whenever one of these operations is requested of the ABB IRB140 robot a thread is thrown (a task that runs parallel to the main programme). Mill CNC Mill state by robotics interface (redundancy) Machine state by DNC Send DNC commands Figure 4: Control of the manufacturing sector. 4.1.2 Developed software Figure 5 shows the developed software for controlling the manufacturing sector. This allows: Monitoring the buffer, the CNC machines and the ABB IRB140 robot; Loading and unloading the CNC machines; Controlling the machines through the developed DNC; Loading the buffer with raw-material for the mill and lathe; Unloading the finished-products of the mill and lathe from the buffer. Trytoconnectto lathe server. ABB IRB140 robot. Information information. Mill information. Buffer control. Buffer information. Control of the robot is carried out through RAPComm functions, procedures and events. Control of the CNC machines (Mill and ) is carried out by Direct Numerical Control (DNC) and robotics interface. The RAPComm and DNC were developed in C++ Builder. These applications are described in sections 5 and 6. Control of the manufacturing sector is carried out by the PC1 as shown in Figure 4. Control of the ABB IRB140 robot is carried out by RAPComm. Control of the Mill and is 1052 control. State of the connection with lathe server. State of the connection with mill server. Mill control. State of the server. Figure 5: Developed software for PC1. Trytoconnecttomill server. The developed software has a server which allows remote control of the manufacturing sector.

4.2 Assembly sector The assembly sector is made up of a Scorbot ER VII robot, a conveyor and an assembly table. Responsibility for the control and coordination of this sector falls on PC2, as shown in Figure 2. The objective of this sector is to assemble and pack of some of the parts made in the manufacturing sector. For this sector the winats application was developed. 4.2.1 The developed WinATS software The developed Application Programming Interface (API), for the winats application, is based on a thread process running simultaneously with the main programme [1] and [2]. The ScorbotAPI library was developed with access to the controller s functions in mind, as shown in Figure 6. This API allows us to communicate with the robot s controller. PC ScorbotAPI Open(),Run(),SpeedA(), Close(),OnMotorsOff(), stopped in the appropriate sectors via stoppers. 4.3.1 Control of the handling sector Control of the handling sector is carried out through the PC3 and of a USB kit (hardware). The USB kit acquires the signals coming from the inductive sensors and sends them to PC3. When it is necessary to activate the stoppers, PC3 sends the control signals to the USB kit. 4.3.2 Developed Software Figure 8 shows the developed software which controls the handling sector. This enables the monitoring of the position of the all pallets on the conveyor and controlling the stoppers. In this way the required pallet can be stopped in the appropriate sector. Options menu. Indication of the pallet that is to pass in the assembly sector. RS232 Controller Scorbot ER VII Indication of the pallet that is to pass in the storage sector. Indication of the pallet that is to pass in the manufacturing sector. Figure 6: Scorbot API Library and the robot. Figure 7 shows the developed winats software and the teach pendant window. State of the USB kit. Figure 8: Developed software for PC3. State of the server. a) b) Figure 7: winats Programme. a) Editing mode. b) Teach pendant window. 4.3 Handling sector The handling sector is made up of a big conveyor in the center of the FMC which connects the storage sector, manufacturing sector and assembly sector. Pallets with raw-materials and finished-products circulate on conveyor. The position of the pallets on the conveyor is obtained through a group of inductive sensors and the pallets can be 1053 The software that controls the handling sector has a server application. The objective of this server is to allow remote control of the handling sector, through the. The software uses the communication protocol shown in Table 2. Table 2: Protocol of the handling sector. Message STOP_PALETE x,y STOP_PALETE WAIT STOP_PALETE X,Y START_PALETE _ RUNNING _ STOPPER y STOPPER_Y ACK command UNKNOWN Meaning Stop pallet x at stopper y. Waiting for pallet. Pallet x stopped at stopper y. Turn off all the stoppers. All the pallets moving. Turn on all stoppers y. Stopper y down. Command unknown. 4.4 sector The storage sector is made up of a raw-materials warehouse for the lathe, a raw-materials warehouse for the mill, a finished-products warehouse for the lathe, a

finished-products warehouse for the mill and a pallet warehouse for the conveyor. Control of the storage sector is carried out by PC4. There is always a full pallet on the conveyor, which is removed by the ABB IRB1400 robot to the warehouses and replaced by a new pallet. If the conveyor has an empty pallet of raw-materials, it is reloaded by the ABB IRB1400 robot. occurring in the warehouses and edit the respective values. The database can be used for the software that controls the storage sector, installed in PC4 as well as the software that controls the FMC, installed in the PCM- FMC Manager, as presented in Figure 10. PCM FMC Manager 4.4.1 Control of the storage sector The storage sector is controlled by software, developed in C++ Builder. The functions of this software are: Administration of the database of the whole warehouse; Controlling the ABB IRB1400 robot. The database can be updated at any moment by the operator, but it is also automatically updated whenever the ABB IRB1400 robot conducts a load operation, unloads or replaces pallets. Operations that involve the control of the ABB IRB1400 robot are executed in separate threads, that is to say: whenever a load operation, unload or replacement of the pallets is requested a thread is thrown. Control of the ABB IRB1400 robot is carried out by RAPComm functions, procedures and events. 4.4.2 Developed software Figure 9 shows the software developed to control the storage sector. IRB1400 robot informations. View/Edit the data base. Robot configurations. Load the RM pallet of the lathe. Unload the FP pallet of the mill. sector DB PC4 ABB IRB 140 Robot ABB IRB 140 Robot Figure 10: sector database. 5 Direct Numerical Control Two programmes in C++ Builder were developed, that allow controlling the CNC machines through Direct Numerical Control (DNC). These programmes allow control of all of the functionalities of the CNC machines remotely. For the lathe the PC TURN 55 CONTROL programme was developed and CONCEPT MILL 155 CONTROL for the mill. DNC is an interface that allows a computer to control and monitor one or more CNC machines. The DNC interface creates a connection between PC1 and the CNC machine computer. After activating the DNC mode, PC1 starts to control the CNC machines through the, as shown in Figure 11. Client software CONCEPT MILL 155 CONTROL PC TURN 55 CONTROL PC1 PC2 PC3 PC4 Server software CONCEPT MILL 155 CONTROL DNC DNC Server software PC TURN 55 CONTROL State of the server. Figure 9: Software developed for PC4. This software allows: Visualizing and updating the warehouse database; Reloading the raw-materials pallets; Unloading the finished-products pallets; Replacing pallets on the conveyor. At any moment it is possible to visualize the situation 1054 Figure 11: Direct Numerical Control for the Mill and. Figure 12 presents the DNC software. These programmes allow two operation modes: Manual operation in this mode we can control the machines manually through available buttons in the programmes; Remote operation the developed software has a server

to allow client application of PC1 to send and receive information through the. 7 Conclusion In this paper, development, coordination, integration and control of the FMC is presented as well as the layout, the hierarchical structure and the sectors (manufacturing, assembly, handling and storage) that make up the developed FMC. The objective of the development of this FMC was to study coordination problems, integration and control in these types of production systems. The software and hardware developed for FMC have been shown to be effective and highly functional. The Direct Numerical Control (DNC) applications, winats and RAPComm, developed for FMC were fundamental for a good operation. The experimental results show the viability and success of the developed FMC. Figure 12: DNC software. 6 RAPComm The RAPComm is a library developed in C++ builder. It allows development of simple and fast applications for the ABB robots (IRB 140 and IRB1400). PC1 and PC4 communicate with the robots through RAPComm, as shown in Figure 13. PC1 ABBIRB IRB140 Robot RAPComm ABB IRB140 Robot Figure 13: RAPComm PC4 RAPComm ABB ABB IRB1400 Robot As an example, the S4ProgramLoad procedure is presented and shown in Figure 14. This shows how to load a programme in the ABB robot controller. long ResultID; short ResultSpec=3; String spathtofile= /hd0a/14-26239/cff/load_m.prg ; wchar_t *pathtofile=new wchar_t[spathtofile.widecharbufsize()]; spathtofile.widechar(pathtofile,spathtofile.widecharbufsize()); Interface1->S4ProgramLoad(0,pathToFile,ResultSpec,ResultID); Figure 14: S4ProgramLoad of the RAPComm. References [1] António Ferrolho and Manuel Crisóstomo, Development of a Flexible Manufacturing Cell, WSEAS Transactions on Electronics. Issue 2, Volume 1, April 2004, ISSN: 1109-9445, pp. 404-409. [2] António Ferrolho and Manuel Crisóstomo, Software Development to Control the Scorbot ER VII Robot With apc,wseas Transactions on Circuits and Systems. Issue 2, Volume 3, April 2004, ISSN: 1109-2734, pp. 247-253. [3] Kim B. H., Cho, K.H. and Park K.S., Analysis and feedback control of Lon works-based network systems for automated manufacturing, 2000 IEEE International Conference on Systems. Man and Cybernetics, Univ of Ulsan, Ulsan, South Korea. [4] Mikell P. Groover, Automation, Production Systems, and Computer Integrated Manufacturing, Prentice Hall, New Jersey, 2001. [5] Najjari, H., Steiner, S.J., Integrated and intelligent control system for a flexible manufacturing cell, Industrial Electronics, 1997. ISIE 97, Proceedings of the IEEE International Symposium, Volume 1, July 1997, pp. 165-170. [6] U. Rembold, B. O. Nnaji and A. Storr, Computer Integrated Manufacturing and Engineering, Addison-Wesley, 1993. [7] Wang Jiacun and Deng Yi, Incremental modelling and verification of flexible manufacturing systems, Journal of Intelligent Manufacturing, vol. 10, nº 6, 1999, pp.485-502. 1055