Case Study
1 INTRODUCTION
Tecvision SA has developed GOSPLAN for industries that are producing widely diversified products in large quantities and where the production time is relatively short (ranging from minutes to days). Typical industries are food factories, car builders, packing industry, etc.
2 APPLICATION
The application described here has been made for a company that produces corrugated paper boxes. The company produces also it own corrugated paper in more than 300 different qualities and with a very large number of options.
This company receives more than 200 orders a day. Each order is a special case with different sizes, paper quality, printing, etc. The average production delay is 10 days meaning that there a is an average of 2000 orders to plan. Each order consists of up to 5 successive tasks. Constraints do exist between tasks of he same order and between tasks of different orders. There is about 60 production centres or workstations Each one is hold by up to 5 workers. The production is scattered in the 3 factories that are about 200 km apart. Two of them are producing the corrugated paper.
Prototypes of packing are produced on a cutting table in one of the factory, at a Computer Aided Design centre. This CAD centre has been installed earlier by our company.
Before computer integration there was only weak planning links between factories. There was very few planning optimisations.
3 PLANNING
The purpose of the planning optimisation is to carry out the orders on time at the minimum possible cost.
Each order is entered the administrative computer where it is decomposed in tasks with a list of possible workstations. Earliest and latest production delays are introduced with all other relevant indications like quantity, size, model, etc.
Before computer integration the planning was made separately in the 3 factories with only weak links between them. The best planning was made in one of the factory (not the busiest one) by placing tickets on a planning board. Each ticket contains information like order No, operation, forecasted duration of the operation, etc. This solution was relatively efficient, but limited to the number of ticket one operator can handle in one day. Very little optimisation was possible
The fundamental idea of GOSPLAN is to replace the physical ticket by his picture displayed on a graphical screen.
The operator can grab a ticket with a tracking ball (or a mouse) and place it elsewhere. Alarms will ring if constraints are violated. Tickets are introduced semiautomatically by the system (there is some manual quality control in between), taking into account the constraints. The length of the ticket represents the forecasted duration. A moving real time line indicates the state of the production. Data from the production centre are fed to the data base in real time.
A Managment Center common to all factories has been built.
4 SOLUTION
Fig. Ticket (Part of the graphical display)
4.1 Real Time Computation
We have developed an original decentralised real time and parallel tasks concept that works on all the computers linked to the LAN -WAN network, independently of the operating system. The minimum resolution time is one second which is more than sufficient for production automatisation. The tick of each computer of GOSPLAN can be adjusted separately.
The most stringent requirement is the speed of operation of the planning station. The operator must be able to move a ticket on the display with two clicks of the mouse without waiting time. During this short period of time the system must recalculate all the database, flag alarms if constraints are violated, recalculate and display the new board of tickets. The necessary speed has been achieved by optimising the database, linking the database server to the planning station with 100MB fibre optic cable and decentralising calculations where is it possible.
4.2 Telecommunication network
Two kinds of networks has been installed: local area networks in each factory and wide area network between the factories. The LANs consist of a thick Ethernet cable going to all the production centre of the factory (approx. 400m). A thin Ethernet cable connects the servers to some dedicated stations. A Tokenring high speed fibreglass cable connects the database server to the planning station.
The Managment Center is connected to one of the other with a leased line at 64kB, to an other one with a 64kB ISDN link and to the main factory directly with thick Ethernet.
Peak traffic on is absorbed by other ISDN links at 64kB: the telecom bridges commute automatically to ISDN when the traffic is too high.
4.3 Links to the Administrative Computer Centre
Links between the Administrative Computer Centre and the factories already exist on leased lines at 19kB. Terminals are connected to the leased line with a multiplexer. GOSPLAN is connected to the administrative computer database through dedicated workstations and dedicated tasks on servers that simulate an administrative computer terminal This method separates totally the responsibility of GOSPLAN and of the Administrative Computer Centre.
4.4 Reliability
Reliability is extremely important for real time CIM application because a long failure can block the production of the factories.
4.4.1 Hardware Reliability
To achieve a long MTBF we have build up the workstations and servers, on industrial grade platforms (motherboard, power supply and casing) on which we have installed carefully selected components, e. g. Raid harddisks, etc. We have observed no failure on the 50 installed computers in 2 years. The power supply of the servers, the planning stations and the telecom bridges is backed with heavy duty UPSs . Workstation, servers and bridges are connected to the LAN through external transceiver: Transmission is not interrupted when a computer is disconnected.
4.4.2 Software Reliability.
Because of the real time and parallel task problems, we have set up our own development methodology. Great care has been taken to provide reliable goof-proof software (a software is "goof proof" if no unusual operation can damage or block the system). For example final tests of the software modules and subroutines are made by different engineers. For each line of instruction there is one line of comment. Detailed technical documentation fitted to the international standards exists for each software module, etc.
No software is bug free and no hardware is failure free, it is why we have set-up backup and recovery procedures. Every 30min a copy of the data base is made automatically to another disk of the same server. A copy is also made semi-automatically on a streamer 2 times a day. A database coherence test is run each time the planning station is switched. The system verifies that an order has the required tickets and that each ticket corresponds to an order. The operator is informed on missing tickets or orders.
4.5 Access Security
Access is secure by passwords at user level. External intrusion through the public network is secured with the call back technique: if password and user name are correct GOSPLAN servers call back to the initially registered phone number before giving access.
5 Success
The system is so efficient that it has been possible to deliver boxes to a customer who has forgotten to pass the order for his Beaujolais nouveau within a few hours. The company had his initial investment returned in 6 month by the increase of productivity.
6 Statistic
The sources consist of 70'000 lines of instructions and 70'000 lines of comments divided in 60 routines. The final documentation provided to the customer consists of 12 brochures totalling 267 pages, program listing not included. The total amount of paper edited is estimated to 3000 pages
The system (hard and soft) was developed, installed and tested in three years with a 5 man-years effort.
7 Copyright
GOSPLAN is a registered name of Tecvision SA.
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