(5) Flexible Manufacturing Automation

2016-10-07

Production Management

Course Outline:

Flexible Manufacturing Automation (5) 8. FMS logistic system 9. FMS information system

Wacław Skoczyński room 2.17 B-4, tel. 71 320 26 39 [email protected]

8. FMS logistic system (automated material movement and storage)

Storage system The main goal of the storage system is:

FMS logistic system contains installations and devices realizing functions: storage, transportation, handling and control of this functions. •

Storage means causing of breaks in material flow,

•

Transportation - material moving,

•

Handling - moving with additional orientation changing.

Suppliers

Auxiliary material, fuel and repair parts store

Raw material store

Interoperation store

1. Introduction 2. Need for Flexible Manufacturing Systems 3. Organizational categories of flexible manufacturing 4. Functional structure of flexible manufacturing system 5. Machining subsystem 6. Tool management 7. Workpiece subsystem 8. FMS logistic system (automated material movement and storage) 9. FMS information system 10. FMS supervising and diagnostics system 11. FMS availability

”creating of parts, tools and fixtures inventory necessary for unmanned operation of FMS on extended period of time". Fulfilling of this task requires a store with suitable places and realization of following functions: • Identification of stored objects, • Incoming of this objects, they suitable placing and retrieve them when necessary, • Inventory management and remote control.

Depending on the factory size, production type, automation level and accepted organizational solutions, the particular kinds of stores, may act separately, or may be grouped in multi-task central stores. Each of the stores, which may act in the factory, presents a complex system realizing the above mentions functions. They are two types of storage systems: • Static, and • Dynamic.

MANUFACTURING

D

Finished goods store

Waste store

Receivers

In the static systems, the stored objects do not change their locations from the moments of their loading to the moment of leaving the store, whether the operations of loading/unloading are made at the same place. In the dynamic systems, the stored objects are displaced after loading. Loading and unloading may be followed in different places.

Figure 8.1. General structure of factory’s storage system

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Depending on the role in the company and in the manufacturing system, the stores may be divided onto: • Central stores providing services to production department, or for the whole plant, • Buffers used by several workstations, or by a cell, • With workstation integrated stores. Depending on the production plant size, organization of production, and the range of area occupied by the installed, flexible manufacturing system, there may be applied various types of stores, both, centralized, or “dispersed”. Therefore, out of among realized flexible manufacturing systems, -15% are equipped with only central store, -45% with only buffers and integrated stores, and -40% has both, the central and “dispersed” stores. From the organizational point of view of workpiece flow in FMS, all these stores fulfill the role of buffers containing inventory necessary for unmanned production. To the central store, there have a free access all workstations. The buffers are often the component part of transport system. These stores are used to balance the fluctuation in feeding associated with transport and machining.

Buffer stores holding different pallets, served by AGVs

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Figure 8.2. Example of a stacker crane construction: 1 - crane movement motor drive, 2 - vertical movement of platform drive, 3 - crane movement stabilizing guidance

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Stacker crane - animation

The basic structures of storage systems Stacker crane and pallet transport system

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High lift rack type store

Flexible assembly system

Flexible manufacturing system

Figure 8.3. Central high lift rack type store

These systems are located on two floors. Thanks to this, that the storage is developed vertically, there has been avoided the need of transport of plants from the machining to the assembly system. Such organization of storage systems markedly simplifies the transport system and the management of these both systems. This is particularly significant due to this fact, that in the plant in which this store has been installed, 40 various types of electric motors were produced, and the number of various machined parts were reached up to 900, at a batch number from 20 to 1000 pieces.

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1 4 5 3

7 6 8 9

Figure 8.4. FMS central storage system: 1 - automated high lift rack store for raw material and blanks, 2 - automated part and devices store, 3 - flexible manufacturing system (machining), 4 - flexible assembly system, 5 - production control, 6 - welding, 7 - central FMS control system, 8 - central monitoring system, 9 - AGV

The storage system has been integrated with the transport system realized as a suspended rail system. 3 The whole of the system covers two transport-storage systems: central 2 store and inter-station store. The machined subjects are placed in 5 containers suspended in transport system, whereas the central store 7 and the inter-station store constitute independent systems placed on 4 6 various transport levels. These levels are connected by a lifting station enabling the exchange of containers with subjects between Figure 8.5. Example of mobile storage system - suspended transport-storage system: 1 - second t-s system the stores: the central one and the level - central store, 2 - first t-s system level - interstation store and inter-station store. At each machine transport between work-stations, 3 - both level connecting lift station, tool there is a lifting station, and an 4 - work-station lift, 5 - mobile store, 6 - machine tool, 7 - load/unload installation of loading/unloading. installation

The central store has been divided into two units: materials and semi-product store, servicing the flexible manufacturing system, and finished parts and subassemblies store intended to service the assembling department. The plant is distinguished by a variety of products (13 types of robots), at relatively small number in a batch. In the flexible manufacturing system, these are made 450 various parts in batches of 5 to 20 pieces.

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Steps when entering the part to the storage cell: • Identification of taking parts; • Marking a palette and assigning it to a specific location in the store; • Checking the suitability of the part and placing it in the store; • Protocolling of the activity and reporting it to the host computer. Activities in the course of order picking in the storage cell: • Giving the production management computer a command to deliver the appropriate part; • Checking the command by cell managing computer; • Formulating the command of part issue that the cell control exchanges for the command to run the stacker crane: • Getting stacker crane to the appropriate location in the store to carry out the required identification and transport required pallet to the position of order picking; • Placing pallet in the store after picking ended.

Functional structure of a storage cell

Transportation system The main goal of the transportation system in FMS is: „to assure continuity of material flow in order to increase utilization of machines and other production equipment". To have the possibility to fulfill the task in automated manufacturing system, there is the necessity to realize the following functions: • Material moving (workpieces, tools) along the given transportation path, • Flexible connections with the storage system and processing stations, • Identification of load and its condition and the processing stations, • Connections with the handling devices.

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Means of transport in manufacturing systems

Choice of means of transport for planned FMS depends on: • System type (machining or assembly), Conveyors

Cars

• Part spectrum (part type, size, weight),

Other

• Assumed system configuration (on-line, closed loop, open field), • Size of production (system size), Roller conveyors

Band conveyors

Link-belt conveyors

Overhead conveyors

Larry cars

Automated guided vehicles

• Assumed system productivity, • System automation level.

Figure 8.6. Classification of means of transport used in FMS’s

Conveyors – general characteristic Conveyors offer automated manufacturing users a variety of options from which to choose, depending on individual part characteristics and production requirements. They present a hardware-defined fixed path over which components travel to their destination. Conveyors are generally classified as either overhead mounted or floor mounted. Overhead conveyors may be either of the monorail power and free type or overhead chain type. Both power and free and chain-driven conveyors can handle medium to large part types such as automobile frames and bodies. Floor-mounted conveyors are classified as roller, chain, or belt driven. This type of transport is first of all used in closed loop systems and, because of workpiece permanent circulation, is not suitable to computer control of part flow. Then, the workstations must be provided with the read-write heads and the transport pallets with read-write microchips. Review of conveyors in FMS

Automated transport in the flexible manufacturing cell

Automation of transport and storage

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In case of roller conveyors the transport path consists of steadily rotating, driven rollers. The movement is transferred on pallets through friction on the rollers. There are two ways of situating the rollers: perpendicular and parallel to the path. In the first case, they fulfill the role of roller race. Conveyors of this type are used in transport between workstations, between workshops, on assembly lines and in storage transport. In the assembly transport are also used conveyors of single rollers situated in axis of the path drive. They are pressed with a steady force to pallets, which are moved on separate rolling guides.

The system is based on a concept of modular structure. The whole of the solution includes a series of types adapted to parts of different maximal masses (from 1.5 kg to 240 kg) and in this connection to pallets of different size (80mm × 80mm to 860mm × 1260mm)

An example of complex solution of conveyor transport in manufacturing system elaborated by the firm Bosh

The component who decides the design of the transport system is the workpiece pallet. They are used to carry the assembly pallets. Presented conveyor is intended to transport parts on workpiece pallets. The workpiece pallets ride on the surface of the conveying medium.

The chain conveyors displace the load by means of a chain band, to which are fixed the load carrying members in the form of plates and troughs. The chain conveyor is working on the same basis as the belt conveyors. The meshing plates form a chain of conveyor and are usually made of plastics. Thanks to their construction, this type of Link belt type 880, 882 conveyors may operate on arcs and can work both in a straight movement as well as on circumferential path

Link belt type 1700

Figure 8.7. Chain conveyor

The key element of the system is a twin-track modular conveyor. It is used to transport and transfer the assembly parts form the entrance of the system, between assembly stations and to the way out. All components of the system are modular.

The role of the longitudinal conveyor is to transport pallets in a closed loop

The structure of the conveyor is supported by an aluminium frame composed of pair of adjustable(only during the mounting stage) leg sets

The drive module (motor) drives the belt. The motor can be mounted suspended or horizontally.

Workpiece Pallet This transport method has many advantages for product assembly applications, including: • Positioning - pallets are positioned at workstations to ± 0.002 inches, permitting precision assembly operations. • Mounting - pallets can be tooled with fixtures to secure parts for manual or automated operations. Identification and data carrying devices (used to coordinate assembly sequences, identify model types, etc.) are also commonly mounted to pallets. • Stopping - pallets can be stopped on the leading or trailing edge - regardless of pallet orientation on the conveyor. Pallets can also be accumulated in queue and released one at a time. • Sensing - exciter plates on the pallet bottom and sides work with conveyor-mounted proximity switches to sense pallet presence. Pallet orientation and routing can be controlled using identification systems.

The electrical transverse conveyor is used to join two parallel longitudinal conveyor sections with a conveyor separation > 320 mm. All the transport belts for the electrical transverse conveyor are driven by the same motor. Along with the workpiece pallets, the lift transfer units are the key elements of the system.

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Loading/ unloading device

workpiece

Figure 8.8. Industrial car

The transport path is in this case strait lined, without curves and crossings. It is formed by exactly made pallet system of two rails on which the car is moving, usually numerically controlled. The larry cars are usually utilized Safety for transporting pallets, and zderzak bumper are used in manufacturing bezpieczeństwa systems for machining body rails szynyparts. They are equipped with a pallet loading/unloading device. The cars are provided with measuring systems transmitting information to the transport system control computer about position and velocity.

The advantages of rail transport are: • High carrying capacity, reaching several metric tons, depending on workpiece size, • Significant driving speed and transparent effectiveness, • Exact and quick docking at workstation pallet changer, • High reliability. The disadvantage of this transport solution is: • Significant cost of construction • Necessity to incur costs connected with rebuilding the railway by production changing (they are useful first of all in the system with rigid structure).

Automated Guided Vehicles (AGVs) - battery-powered driverless vehicles that can be programmed for path selection and positioning and are equipped to follow a changeable or expandable guidepath. The computer, communicating via FM radio signals, gave AGVs the ability to travel on both closed and multiple loop paths and also handled traffic control and the queuing of multiple-vehicle systems. This onboard microprocessor and “land-based” AGV computer allowed for material tracking as well. AGVs come in e variety of types and sizes and can be used in applications and environments wherever material is moved. AGV general types include: • Towing, • Pallet trucks, • Unit load, • Fork trucks, • Assembly vehicles. AGV pallet carrier

Automated transport using AGV

Various AGV applications

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AGV guidance systems

Passive guidepath

Metallic guidepath

Optical guidepath

Active guidepath

Wire guided

Virtual guidepath

Permanent tracing in whole travel area

The passive guidepath is determined by lines formed on the floor surface through placing various materials, such as metal tapes, paints, or chemical substance. Following the line may be realized e.g. with the use of camera. The disadvantages of these solutions are in sensitivity on impurities and ease of damage of placed line, and dependability of the way the floor surface was made

Discrete tracing in determined points

Figure 8.9. AGV guidance systems

The majority of AGVs in use are vehicles that follow energized wire embedded in the floor (active guidepath). Saw cuts are made in the AGV floor about one-half-inch deep based on a predetermined guidepath route. Wire is laid shop floor in the saw cut and then epoxied over to form a smooth, unbroken surface for sweeping and maintenance. In the wire flows alternating current of various frequencies b) (from 6 to 35 kHz) which generates concentric magnetic field along the running paths. In the cart, there are two coils: analyzing and reference coil. Their signals are continuously compared. The first of coils analyzes the magnetic field and if the cart goes away Figure 8.10. AGV wire guidance: (turns) from guidepath, measurement of the a) principle of wire guidance: 1 – in the floor embedded energized wire, 2 – groove, 3 – electromagnetic field, phase between signals delivers impulse to the control motor, which corrects the 4 – induction coil, b) path tracing movement direction. a)

Fundamental principles of AGV control

a)

G ~ ~

b) G ~ ~

f1 f3

There are many patterns of AGV guidepath: open in-line, open branched, closed loop and webbed (many loops connected in a net). By webbed guidepath in each loop is other current frequency (Fig. 8.11). The selection of path thereby follows through the recognition of given frequency.

f2 f4

Figure 8.11. Current supply of wire guidepath: a) simple path - one frequency, b) complex - several frequencies, G – generator, f - frequency AGV carrier components

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AGV moves on programmed running path. The travel program may be initiated manually, by pressing the button "drive", or remotely through the transport system control dedicated computer. In such a case, the orders for AGV are transmitted through the induction wire. Along the running path, there are placed stop-points: steady and alternating. Magnets in the floor usually indicate the first ones, whereas reflecting foils the other. They are locates at workstations, internal part queuing, stores etc. 2 5

7

4

1 3 6

Figure 8.12. Movable robot mounted on an AGV: 1 - wire guided AGV, 2 - industrial robot, 3 - robot control unit, 4 - rotary index table (4 x 90 0), 5 - pallet, 6 - safety bumper, 7 – power supply connector

At the stop-points there may be initiated the following special programs: • Automated the pallet back-up, • Reversing and automated the pallet taking up, • Automated drive of conveyor, handling the load onto the truck, or undertaking the load, • Automated disconnection the trailer coupling.

Power supply method used in AGVs: Carts are propelled by electric motors that are powered by industrial-grade, lead acid storage batteries (Ni-Cd) mounted in the AGV. They typically have a normal charged cycle life of around 20 hours. Then the cart must be routed to the AGV maintenance area for battery recharge or replacement. Battery replacement must be done manually, but recharging can be done either manually or automatically. Some carts can be programmed and routed to plug themselves in for recharging when battery power becomes low.

Safety features available on AGV: • Yellow caution beacons mounted on the front and back of the cart that flash when the cart gets ready to move and that continue throughout the move, • Audible, multiple-pitch and adjustable warnings signals, • Safety brakes on each drive wheel that automatically engage when the power is off, • Emergency stop buttons on each side of the vehicle, • Impact-sensing safety bumpers on each end of the vehicle that stop the cart when minimal contact and bumper compression are made. Initiating the cart travel again requires service intervention.

Operating of safety system by AGV

AGV with virtual guidance systems The transport systems realizing the rigidly stated guidepaths characterizes only limited flexibility. The tendency to increase flexibility of system led to appear the concept “free programmable running path” (virtual guidepath). Problems, which in such a case arise, are associated with inaccuracy of driving mechanisms and with variability of surroundings (e.g. incidental unevenness of floor surface, or other obstacles as left of containers, loads etc.). They may lead to deviation of programmed running path, or to collision. Right realization of transport task requires than watching and possible correction the movements of vehicle. One of possible solutions is continuous supervision by way of observation through the watching system the entire surroundings in which the vehicle is moving. There may be used here vision, laser, or ultrasonic systems. Such solutions, which require processing by the on-board computer, high number of data, are not necessary in flexible machining, assembly, or storage systems.

P4

P5

P3 Sensor controlled obstacle by-passing

P6 P7 Reference point

Z1

P1 Pallet changing station

Sensor controlled positioning Sensor

controlled docking

P2 Sensor controlled Actual path path correction (incorrect) programmed path actual path onboard computer generated path correction

Machining centre

Figure 8.13. Realization of programmable AGV guidepath

The layout of FMS with such a solution of transport is typical and distances between workstations are usually not great. In such a case, it is sufficient to place in the programmed area of vehicle path some “reference points” and check whether the vehicle moves on proper path. The reference points are placed with the purpose to check the longer straight lined path sections where the danger of significant deviation of exists given running path. Correction of path, omitting obstacles and positioning by docking at the workstation is made with the use of ultrasonic sensors. The ease of changing the direction of running what is necessary by omitting the obstacles, or by precision docking, requires particular properties of truck driving system.

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The idea of navigation is sending laser beams through the navigation system, a reflection of its and return to the navigation system. On the basis of the distance information from the sensor to each of the reflectors AGV can be oriented in the working space. To correctly determine the orientation of the AGV is necessary to know placement of reflectors of the specific codes in the workspace.

2 1

Mobile truck FLEXL: 1 - drive for changes of travel direction with internal gear, 2 - drives for road wheels

The AGVs characterize the following advantages: • Short installation time, • High flexibility by FMS layout change, • Easy access to machine tools due to lack of any bearing and rail structures, • Favorable, with respect to industrial safety, smooth driving floor surfaces, • Unnecessary shield structures, • Space economy (there can be utilized normal communication ways), • Easily adaptable to increasing transport needs by increasing the carts number, • Not-blocking of transport path by cart failure, • Good traffic safety (small accident expectation). To their disadvantages may be included: • Relatively high price, • Some problems with accuracy of docking at loading/unloading stations.

Other transport solutions in FMS: 1.

2. 3. 4.

Linear and bridge-type robots - not only for part handling (loading and unloading), but also to realize many another functions associated with the material flow, as e.g. work-holding and work-changing, tool heads changing, and also fixture assembling and part clamping on the pallets (when the weight of devices and parts exceeds 20kg) or part handling in the assembling systems; Stacker cranes - they service the storage racks, but may also realize transport between the workstations by realizing tool exchanging in the tool matrices; Industrial robots - they find main application in machining cells and in plastic working (sheet metal forming); NC overhead traveling cranes – they may be also used in the transport of materials in the automated manufacturing system; they ensure realization of all transport of workpieces and tools; this solution is fully independent of the manufacturing system layout.

9. FMS information system

CAPACITY PLANNING

ORDER MANAGEMENT

The information aside of transport subsystem is the second functional system linking and integrating under central computer control all the facilities to flexible manufacturing system as a whole. It realizes many functions enabling this integration. The main goal of information system in FMS is: "minimization of idle machine times and shortening of production order realization time".

MANUFACTURING MANAGEMENT

COMUNICATION WITH FMS PERSONNEL

FLEXIBLE MANUFACTURING SYSTEM

MATERIAL MOVEMENT CONTROL

OPERATIONAL DATA COLLECTION CONTROL SYSTEM DATA MANAGEMENT TOOL DATA MANAGEMENT

COMMUNICATION WITH WORKSTATION

Figure 9.1. Functions realized by FMS information system

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The data management includes acquisition them in database and in case of need retrieval accessible all data associated with planning and control of part machining in flexible manufacturing system. Production planning and control – the main task is starting, monitoring and ensuring the realization of production tasks, considering the quantities, terms, quality, costs and working conditions. INFORMATION SYSTEM

Figure. 9.2. The main functional areas in FMS information system

In the basis of this type each element located on the certain level in the hierarchy can be linked to n elements located at the slave level. Addressing is only possible by the address of one of the fields of the base segment.

Rekord 0

Application of database may be of single-stand, or multi-stand. Bases belonging to the first mentioned above types consist of data set and set of functions, operating of them, implemented on one computer. Multi-stand bases allow for simultaneous operation many users. At the present stage of development of computer assisted production processes, the database fulfils the function of interface between various spheres of enterprise activity. This is associated with very large data sets, with simultaneously high requirements regarding the access time, and data security.

PRODUCTION PLANNING AND CONTROL

DATA MANAGEMENT

The basic database models: • Hierarchical database, • Network database, • Relational database, • Object-oriented database.

The majority of systems are based on relational database first of all because of the ease of adaptation to changing requirements. They enable easy access to data and quick data processing at ensured simultaneously using of resources by users working in the network.

Dependent records can be searched only sequentially. The advantage is a high speed of operations. Searching is carried out only unidirectionally.

Rekord 1

Rekord 5

Rekord 1.1

Rekord 2.1

Rekord 1.2

Rekord 2.2

Rekord 1.3

Rekord 2.3

Rekord 1.4

Rekord 3.1

Rekord 2

Rekord 1.5

Rekord 3.2

Rekord 4

In the network model elements are treated equivalently and mutual relationships of all the elements are possible. Relationships between the elements can be bilateral, which allows to start searching at any place and carry it in any direction. These database structures are usually complicated and more difficult in the practical application then the hierarchical databases.

Rekord 3

Scheme a network database model

Scheme of the hierarchical database model

The logical structure of a relational database form relationships. Data are stored in tables, which form rows of data records, and the columns their attributes. In the fields of tables may be only elementary data types (such as number, date, time, etc.) and not the structure. Table (relation) has defined key (highlighted one or more attributes of the table), whose value uniquely identifies a row. The result of the selection of data is a subset of the database in the form of a table.

The object model database is a combination of the network model, object-oriented programming and expert systems. It uses concepts such as classes, attributes, methods. The main features of object-oriented databases are: abstract data types, inheritance, object-identity and complex objects. In the such databases can be stored data which are a mapping of complex objects. With object-oriented mechanisms the independence of the data from the application can be increased through the transfer of data handlers to the database management system.

Example of relational database

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The main task while production control is: „Starting, monitoring and ensuring the realization of production tasks considering the quantities, terms, quality, costs and working conditions."

Planning material requirements and the number of batches of products is included in the short-term planning of the production program. To be able to produce the planned number of a particular type products, it is necessary to determine the amount necessary to purchase or produce raw materials, assemblies or components . This is done either on the basis of the product documentation or on the prognosis based on consumption occurring in the past. So designated general material demand is divided into production lot sizes during determining the size of the manufacturing batch. The next step is scheduling the course of accepted for realization orders. The initial and final time points of production are set, taking into account the technically conditioned order of operations and seeking to balance the potential of workstations. In turn, it is possible to determine ultimately the course of the technological process and make the assignment of individual operations specific manufacturing means. This completes the planning phase and begin the manufacturing process associated with the realization of order.

The difficulty in the access and utilization of data used in the production Simulator systems is, that they often are in bases of various independent from itself computer aided systems. There exists Planning system Documentation a tendency to elaborate a platform of company integrating the use of information technology in the enterprise, from Model Diagnostics editor system planning the manufacturing system, DISTRIBUTED through the product development, to DATABASE the production process, with consideManaging CAx ration of the cost account, or e.g. system systems training the personnel. Such an integrated model of enterprise data would Real allow also for better utilization of manufacturing system simulation techniques in planning and Figure 9.3. Platform to integration of all computer aided operating of production systems and also for decreasing the simulation applications in a company - company data model costs. PPC system

001101010010011111001 100110001010110010010 000110101010111100010 001010001110101101110 111001010010001000100 0110111110111100101

with a variety of drawing tools. You can use the pencil tool to draw both lines and arcs. As you begin to draw with the pencil tool, Visio quickly calculates the path the mouse is traveling and draws

The initiating point in the sequence of these actions, are data referred to production orders and terms of realization, given by the plant host computer. They allow defining the kind and quantities of parts to be machined and to state the earliest time points in which should be ready the semi products and materials, and the latest acceptable terms of realization the complete machining of all the parts. Planning the material demand and product quantities in a batch, are contained in a short term planning of production program. To enable production of defined product quantities, there is the necessity to know the quantities to purchase, or manufacture, material, assemblies or elements. After the acceptance of orders and planning the material demand, there follows creating and structuring the routing of pieces to be run through the system and to manage, control, and dispatch workpieces and resources within the FMS. Work-order preparation must be completed well in advance of the part’s scheduled run time. Any workpiece introduced into an FMS must be identified to the system by means of work order. Identification of each workpiece type generally includes defining the number of parts to be processed, start date, due date, and routing sequence.

Production programm planning

Material requisition and batch quantity planning

Order realisation scheduling and workpiece load balancing

Plannnig

The second functional area of FMS control system is short-term (operational) planning and control. The purpose of this area is the detailed specification of the production process course in the existing system, wherein the fundamental task of operational planning is: "Systematic searching, classification and defining the production tasks and resources to reach the stated aims."

Process visualization

Part processing planning

Starting up of order realisation

Control

Multi-database architecture: • A central database, • Database Client-Server type, • Distributed database. Central database is characterized by carrying out all activities related to the processing of data on a central computer. Users are connected with the terminals. They can call programs on the computer, and perform operations based on the data stored in it. Architecture of database Client-Server type differs from the previous in that not all operations on data are performed on the main computer (Server). Some of the tasks are transferred to the cooperating computers (hosts) coupled with this computer. In this arrangement, the central computer (server) provides only certain types of services (eg search procedures selected records in the database). A distributed database is based on a client-server architecture, with the difference that there is no specified units, which would realize completely only the Server tasks. Each PC system both provides other services related to certain operations on the data, and uses the services provided by other computers. The aim is to split a single logical data structures into smaller fragments that can be stored in various nodes of net.

Order realisation and system productivity control

Activities in operational planning and production process control

In a flexible manufacturing system may be simultaneously executed multiple production orders, with significantly different number of parts in a batch. The variety of parallel jobs should result in increased complexity of planning, but in the FMS there are a number of factors that reduce this complexity : • In the FMS are mainly used machining centers that integrate the functions of many conventional machine tools, which greatly reduces, compared with conventional generation , the number of objects that must be taken into account when planning the flow of materials, • Use centers also reduces the number of operations performed on the workpiece, • Computerized linking automated manufacturing equipment allows for better recognition of operational data and thus improves the data reality of planning

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The main functions associated with the current production control: 1. Making a daily timescale of initiations for lots of particular products, 2. Assigning operations to isolated groups of workstations exact to working shifts, and preparing time schedules for: • Completing the machining aids, • Arranging of stations and pallets. 3. Detailed determining the sequence of production operations; the result thereof is the operations timescale of different flexibility level: • Timescale of basic flexibility level, which define the terms of beginning and ending operations on particular stations, taking in consideration also the stations which realize the auxiliary works e.g. the transport cars, • More flexible time scale defines sequence of operation, without defining the term of beginning and termination, • Timescale of the higher flexibility level is defined in the form of set of rules characterizing servicing of the queues arising by particular workstations. These rules are the basis for current sharing of operation between workstations. They are determined for a defined production task according to the accepted criterions.

a).

b).

The centralized system shows a range of non-advantageous properties such as: relatively high installation costs due to complicated and expensive parallel wiring system, high sensibility to failures and external influences, limited possibility of remote defining the parameters of installations (e.g. motor drive controller) due to lack of appropriate communication network, difficulties and costs associated with modification or expanding the system. The decentralized control system consists of arrange of computers and terminal installations, making in parallel various prescribed them functions

Figure 9.5. Architecture of FMS control systems: a). centralized computer environment, b) decentralized

The other functions of the control system: • Dispatcher function: assigning the operation to be made, for defined stands, • Distribution of control programs, • Monitoring of realization progress of particular work orders, • Recording of the part (and other displaceable resources) flow, • Inspection of equipment operation condition, • Reporting, • Running the statistics, • Communication with other systems of enterprise.

The main features of the centralized control system: • Direct parallel connection of the control unit, for example, managing computer with drivers of devices, or PLC or CNC driver with actuators or sensors, • A main computer performs the basic functions of the control system associated with the operative production planning and disposition of production operations, as well as tasks related to the exchange of information with the environment, in particular the master production scheduling system, • The operating system of the computer provides the opportunity to work in multi program and multi-access mode; centralized system is usually a one-level structure, • A main computer performs all calculations and data processing; it cooperates directly with drivers and terminals of individual stands and FMS equipment, • Such systems dominated in the past; they are now even used in small industrial applications.

The main features of the decentralized control system: Disadvantages of the centralized control system: • Relatively high cost of installation because of the complicated and expensive parallel wiring, • High sensitivity to damage and external disturbances, • Remote parameterization of devices is limited (eg drivers for drives) due to lack of proper communication network, • Difficulties and costs associated with the modification or extension of the system.

• Consists of a number of computers and terminal devices performing alongside various functions assigned to them, • Computers supervise working of FMS equipment and task- specialized units, such as a operator’s computer that realizes a computer-aided production scheduling, • Despite the possibility of communicating with each other all the computers, often one of them is assigned to the function of the communication processor; its role is limited to the analysis of reports , selection of their content from the perspective of users' needs and the degree of urgency, as well as the formatting of reports and their resulting emissions in accordance with established priorities, • Allows the use of distributed databases (local computers manage data of local importance which shortens the time to access data), • Such a system provides greater freedom of choice until the moment of data transmission, • Uses a specialized industrial fieldbus communication networks, which joints the individual peripherals automation equipment, • High flow capacity and speed of data transmission in a communication network .

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Principal differences in a centralized versus a decentralized computer environment CENTRALIZED

DECENTRALIZED

High hardware cost

Lower hardware cost

High software cost

Lower software cost

High in-plant wiring and connection costs

Lower in-plant wiring and connection costs

Software complex, time consuming, and difficult to change and maintain

Software application specific, designed for local use, easy to write, modify, and maintain

Easy to trace overall operating costs and control expenses

Harder to track overall operating costs and control expenses

Low computer transaction response time, priorities assigned and controlled by corporate data processing

Fast computer response time; user controls own application environment and assigns own priorities

Expandability difficult and hard to justify cost

Expandability easy, less expensive, and less difficult to justify

All plant communications shut down with computer failure

Only isolated location shut down with computer failure

Expensive backup resources required

Less expensive backup resources required; spare computer can be available as standby

Application program changes time consuming to implement; central data processing must evaluate, prioritize, analyze, and determine system impact

Application changes easy to make and in control of local users

Figure 9.6. Structure of FMS control system

The control system of a developed FMS creates a hierarchic structure in which there can be distinguished four levels: • The highest level of the system control and monitoring of the realized manufacturing process state, • Plane of direct monitoring of machine tools and other NC equipment operation; within this plane may be also situated computer which controls the quality of manufacturing, • Plane of the machine tools and other NC equipment control, • Plane of sensors and functional elements of machine tools and equipment,

The FMS control system consists of: • • • •

Host computer, Controllers of machine tools, manufacturing equipment, robots etc., Digital and analog sensors and executive elements, motor drive controllers, control panels, control devices, counters etc., Communication system.

Basic tasks of DNC computer: • Management of machining programs for workpieces, • Transfer programs to other NC devices, such as measuring machines, manipulators, robots, etc. • Tool data transfer (corrections, tool life), • Forwarding instructions for staff (eg plans of fastening parts on pallets), • Collecting, processing and maintenance data transfer, • Programming (when DNC computer is not fully utilized for other purposes).

Transfer of programs from DNC is made in the following way: • In double direction, from DNC to CNC and reversely, • Semi-automatic, that means the manual calling by the operator, or automatic i.e. without the interference of operator, • With the protection, i.e. by checking the correctness of transmission with automatic correction through repeating the transmission by appearing an error, • With receiving the correction data and managing correction of tools (data are coming from the tool room, or from CNC by exchanging the tools in the tool matrix; correspondence with the stand of preliminary tools setting-up my be carried up manually or automatically, • With individual set-up of transmission speed for each attached CNC controller.

The management of machining programs related functions: • Receiving the machining programs; the new-ones from the programming system, and the used-ones from CNC, • Collecting data in appropriate mass memories, • Management of NC programs according to defined criterions, e.g. required memory capacity, demand on the tools, machine tools on which the program will be realized etc., • Transferring the machining programs to the machine tools in appropriate time, • Making copies of machining programs to secure them against any losses, • Comparing the programs transferred back from CNC, to the original ones and revealing the changes made, • Blocking the transferred programs from CNC until releasing them by the programmer.

Central gathering of machine operational data means the collection of necessary, actual data from the area of manufacturing, and transferring them in the form suitable for processing, to the system of operational planning and control of the production process in order to designate the new input data for the costs calculating and materials management. It covers: • Recording the working time and standstill, • Statistic analysis of recorded data, according to number of machined parts, number of spoilages, times of failures, time of standstills caused by awaiting, • Central reporting of disturbances (errors), monitoring of machine tool, service and inspection orders, • Loading the data on optional information carrier.

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Requirements for CNC controllers in the flexible manufacturing automation (1): 1. Memory capacity - possibility to store many part programs, what makes the machine tool independent from the DNC computer (sub-programs, technological tables (tool correction data, displacement of zero point, dimensional correction due to tool wear, tool life tables)). 2. Data management - should ensure the machine tool operator an easy access to it, in order to check the resources, manual searching of programs, their activation, erasing, correction, securing against changing etc. There should be also ensured the possibility of visual and automatic inspection, through the host computer of free memory capacity in order to check whether this capacity will be sufficient to introduce next part machining program. 3. Remote control (by a host computer) is necessary by a full automatic FMS operation. The host computer must have the following possibilities: • Bringing the tool to a reference point, • Changing the operating mode, • Starting the machining program, • Automatic stoppage the machine tool in case of disturbances in working (failures). 4. External machining program calling - possibility to call appropriate program by the pallet code, or by the DNC computer, and to erase the useless program by this computer. Comparison of information flow NC systems (a) and CNC type (b)

Requirements for CNC controllers in the flexible manufacturing automation (2): 5. Reporting of the errors and warnings - possible errors by data input or reading must be immediately captured and if possibly corrected by multiple input repeating and reported to the managing computer in order to record in the central error statistic. 6. Acquisition the machine and operational data (AMOD) - the data about the reasons of disturbances in working and standstills are taken automatically, or introduced by the operator. The host computer can automatically made the statistic of disturbances for each machine tool and manufacturing equipment. 7. Tool management - optimization of tool spacing in the tool matrix (where big, over-dimensional tools occur) and minimizing the loss of time in exchanging the damaged and worn tools for new in the machine tool magazine. 8. Pallet management - it appears first of all in the closed-loop FMS systems, because the host computer cannot practically control their actual positions. The CNC control checks then the code of the pallet and decides about accepting it for machining, or send it further. When operating in the unmanned system, there additionally appears the task to determine the priority of machining of various parts being in circulation.

1

2

4

3

5

6

Additional quantities should be calculated by measurement system: • Coordinates describing the part position in reference system, • Boundary values of dimension and allowances, • Diameters of holes and riser heads (in castings), • Lengths and widths of grooves, • Correction of zero point, • Correction of tool wear, • Compensation of part fixing allowance, • Tool dimensions.

Figure 9.7. Example of measurement cycles realized using touch probe: 1 - incorrect part clamping detection, 2 - part type identification, 3 - part measurement before, during and after machining, 4 - compensation of thermal deformation, 5 - allowance identification, 6 - defining of zero point on the part

Requirements for CNC controllers in the flexible manufacturing automation (3): 9. Controlling the measurement cycles - the application of measurement probe on the machine tool requires that the CNC controller would have programmed measurement cycles and programs for data processing at its disposal. 10. Protections against exceeding the workspace – in order to avoid collision and in consequence tool damage, each of NC axes must have a kind of program end switch. Appearance in the machining program the tool position beyond limited space should cause stoppage of the machine tool and reporting the error. 11. Ensuring the possibility of use the test mode on the machine tool - necessary by testing the new part machining programs. 12. Automatic correction of tool wear - the tool wear, especially by turning and boring, is a constant factor influencing the machining accuracy. Therefore, it is desirable that conside-ring it, take place automatic, independently of data input of other correction values. 13. Communication with DNC system - each of the CNC controllers in the FMS should have the possibility of connection with DNC computer. This connection should ensure suitable speed of data transmission.

Requirements for CNC controllers in the flexible manufacturing automation (4): 14. Control of additional NC axes - additional NC axes are used to handling (during machining) the tools and/or the machined part. Their programming is independent from the machining programs. Application of such NC axes gives additional possibilities such as optimization of speed of movements connected with the tool exchanging. 15. Diagnostics of disturbances - it is necessary to determine quickly and securely the causes of disturbances resulting in standstills and work interruptions. Thanks to a special program-ming, the screen is changed into oscillograph with a memory, enabling the graphical presen-ting registered values and storage them. It fulfills the following diagnostic functions: • Drawing theoretical and real movements trajectory in particular NC axes, • Visualization of dynamic behavior (time characteristic) of NC axis, • Drawing (multi-channel) of control processes time running (switch in/out) with selective time scale, • Recording of all warnings and reported errors, • Recording of all “manual” interferences (the data inputs).

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The tasks to be solved by the transport system and control thereof:

correction

• Recognition of a machine tool with free input station (i.e. one of parts is being

machined, and on the output place one part is already finished), • Checking the given priorities in case when several machine tools are simultaneously called the readiness state, • Transporting the pallet with appropriate part from pallet storage, or fixing station, to the machine tool, • Drive to the machine tool, docking and changing the pallet, i.e. taking away the pallet with ready part and leaving a new one on the input station, • Checking , whether the wash-station is free, • Drive to the wash-station, leaving the pallet with the part to machining and taking away the washed part, • Calling the readiness of the car to the next working cycle realization.

workpiece

tool wear touch probe deviation workpiece

Figure 9.8. Automatic tool wear correction

REQUIREMENTS LEVEL

4.4. PRODUCTION PRODUCTION MANAGEMENT LEVEL LEVEL

Production management aiding computers

min

Mbyte

s

3. MANUFACTURING SYSTEM LEVEL

Manufacturing system computers, SCADA and DNC systems

Kbyte

0,1 s

2. CONTROLLER AND PERIPHERAL DEVICES LEVEL

PLC, CNC and RC controllers, IPC computers, I/O module, drivers

byte

ms

LAN

Cellbus

Devicebus 1. OBJECT LEVEL

Sensors, execution units

7

Application layer

6

Presentation layer

WAN Gbyte

bit

0,5 ms

Transmitted information volume

Data transmission time

5

Session layer

4

Transport layer

3

Network layer

2

Protection layer

1

Physical layer

Sensorbus

Open system Application process

Communication system

Applications oriented layers FIELDBUS

Data transmission oriented layers

Figure 9.10. The OSI reference system

Figure 9.9. Application areas of communications networks and suitable requirements

Application process

4

Application

FTP File transfer protocol

Telnet

SMTP Simple mail transfer protocol

Plug connection

DoD layers

The tasks, which has to fulfill in each of OSI reference model layer: 1. Physical layer - in the layer there are determined details of information transfer between open systems, such as methods of modulation or coding, or else electric properties of medium transmitting the data. The function of this layer is to ensure the flow of nonstructuralized stream of information bites. 2. Protection layer - this layer contains mechanisms, which ensure correct transfer of data in the form of blocks of information bites. It monitors the access to physical information carrier, defines the addressing system and enables the data flow control. 3. Network layer - it enables the information exchange between two open systems by the use of different segments, with the use of interface devices (e.g. the routers). It chooses the transport path and addresses the datagrams. 4. Transport layer - it enables stability of connection between optional application programs in open systems. It ensures the continuity of information flow. 5. Session layer - it ensures realization of functions necessary to begin, correct carrying out and finishing of communication connection, called the session. 6. Presentation layer - it enables realization of different methods of coding, visualization, forming, or else conversion of exchanged information. 7. Application layer - it is directly designed for application process and encloses e.g. passing on commands connected with realization of defined process.

3 Computer

TCP Transmission control protocol

UDP User datagram protocol

2

Internet

IP Internet protocol

1

Internet access

ISO 8802 or CCITT X.25

Physical transmission medium

Figure 9.11. TCP/IP model

Communication system

Strategic production planning aiding computers

OSI model layers

5.

5. COMPANY MANAGEMENT COMPANY LEVEL

In the open control systems are also used communications protocols TCP/IP (Transmission Control Protocol/ Internet Protocol). The communication system of this network has been based on the layer model, which can be recognized as an archetype of the later reference OSI model. Originated from the name of department of defense, it is called DoD model. Its structure is based on four layers. The open system in TCP/IP model, similarly as in the OSI model, is divided onto two parts: • Application process and • Communication system. The layers 1, 2 and 3 are in this model oriented on information transport,and the layer 4 on application (application process).

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