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Simulation in Small and Medium Sized Companies
- 151 -
Simulation in small and medium sized companies
G. Kronreif, P. Kopacek
Institute of Robotics, Techllica/ Ulliversity of Viellna, Moe//wa/dp/atz 5/4, 1040 Vienna, Austria
Abstract: Modem production plants are characterized by enhanced complexity considering increased automation and enlarged integration of computers. Therefore duration and risks of planning are increasing. In addition putting into operation of new or modified plants b~ng about considerable complications with start-up operation and furthermore decreases in rate of production. The main source of this behavior is often the insufficient tuning of the single devices. The aim of this paper is to give stimulus to utilize "simulation", which is well known asa planning tool for a considerable time. However it is being used too less in order to fmd sOlution to the problems mentioned above. Keywords: Simulation; scheduling; modelling; manufacturing automation.
Introduction
decreasing life-time of certain products, another important factor, besides the reduction of planning costs, is the saving of time in the planning stage.
Modern manufacturing and assembling plants are more and more characterized by the high degree of automatization of their single sub-systems. High integration of computers in these plants complicates production planning and increases the risk of mis-investment (Schaif, 1990). Moreover, the lot sizes are becoming smaller and smaller. Market's imponderableness however, asks for a higher flexibility in the production. By means of "Just In Time" JIT and "Computer Integrated Manufacturing" CIM some production or assembly cells cannot be decoupled by storage banks any longer, and one would not be able to correspond with the troughput times (Furst, 1991). • Small and medium sized companies must therefore have high production flexibility to be able to meet the rapidly changing market situation, to meet the delivery dates and to provide for the inaeasing demands regarding quality.
There are only a few applications of simulation in small and medium sized companies. One of the reason are the costs of simulation Technique.
Because of the reasons mentioned before quality and costs of planning contribute extremely the overall costs. At an early stage of production system planning, in particular, the costs of production are already largely determined depending upon the plant layout and the choice of machinery (Milberg, 1992). Costs can be saved considerably in. this respect by means of an increase in the quality of planning. Because of the
rust and second generation's simulation software and the partly wrong way of the development of a model led to the wrong opinion of an extremely costy and highly complicated technique. The new simulation systems with their graphical interfaces, their user-oriented modelling concepts and their time saving experimental environment are supposed to open new areas of utilization and to plead for more acceptance.
Conventional planning techniques cannot be utilized for this discussion. The results of modifications of the structure and the utilization of the system can only be estimated vaguely at this point. When looking for innovative and economic solutions instruments which show the weaknesses in an integrated process and which support the acquisition and realization of solutions and their utilization, have to be taken into consideration. Under this point of view simulation seems to be the most appropriate device. This technique makes it possible to prove the expected productivity of the planned, complex system. The system can be tested without interfering into the real process
(VDI, 1983).
- 152 -
Advantages of slmulltlon Simulation is the imitation of the real plant in a computer model to deserve the dynamic behavior under several variants of load and eventual breakdowns. Based upon the costy and timeconsuming experiments which result from the real process, simulation offers a lot of help in the development and modification of complex systems. The financial benefit of simulation-based planning must not be rejected already nowadays. The utilization of simulation technique permits a reduction of time spent in planning and of planning risk and an improvement in the quality of planning. A positive side effect of the modelling is its extraordinarily high insight into the system. The plant is look at in a different way - from a different point of view. The formal description of the system, as it is necessary for the construction of a computer model, acts like a check-list (Flirst, 1991). In many cases, eventual errors are already discovered at this stage before the model itself is built up and existing but hidden reserves of the plant are recognized (Fig.l). Simulation in connection with animation of the manufacturing or the assembling process improve the communication between all the factors taking part in the process of planning. Fig. 1:
Simulation generates a "Feed-Back" just during the phase of planning (Fiirst, 1991)
New Irell of utilization A new sight of the simulation technique is growing increasingly. The simulation model is being serviced if possible improved and utilized from the phase of planning until the end of life-time of the manufacturing system. The renunciation of a oneway, so called "throwaway" simulation and the acceptance of a long-term utilization of the simulation model built long ago leads to a saving of costs. It is worth, therefore, applying the simulation during the operating phase of the plant too, as a support of a PPS-System for example. In this case simulation contributes to a higher transparency and security in short-time planning decisions. It is possible to schedule an inserted order more detailed by means of the model of the planning phase and by the operating data derived from the actual situation. If an eventual change of products, a change within the collection or a modification of the sequence of operations might be required, this model determines these effects in advance and tries to find the adequate measures.
Simulation can therefore be utilized for several tasks (depending upon the time of employment): •
at the beginning stage of planning to discover realistic and dynamic relationships of capacities, costs, bottlenecks etc.
•
during the planning phase to check the whole concept
• in the suppliance phase to check whether the means offered obtain the results requested before •
accompanying the phase of planning simulation may be used as testing environment to check the control software
•
in the operating phase eventual effects of planned modifications can be determined in advance
•
utilization of scheduling
simulation
in
optimal
The continuing improvement of calculating speed and of the capability of computer graphics offers a further area of utilization. The more and more realistic animation software makes it possible to use simulation as a means of support of marketing (wySIWYG - What you see is what you get). Equipped with an extensive module sample, the seller profits by the fact that visual aid is better than lots of words. Because of the increasing appearance of powerful portable computers in particular simulation technique could be growing up more and more to a helpful tool during the marketing and selling phase. Regardless of the utilization area of simulation, user-oriented software (graphical interface with interactive, menu- and window-driven modelling, block-oriented modelling concepts) are moreover preferred. Simulation can be utilized in those areas where it is requested - simulation is there for the planner and practitioner. Therefore, an initial period into the simulation technique and into the software used has to be offered to them which can easily be acquired by means of the new simulation software.
Costl and prejudlcel Insufficient knowledie about this techniQye and its advantaies Beside the presumably high costs of the simulation technique its utilization is prevented by other factors as well. The education program at schools and universities, for example, is far too limited. Moreover, people are still afraid of spending so much money on
- 153 -
Fig. 1.
SIMULATION
software or services in the software area. Finally, there is still this unfounded fear of this mighty and apparently complicated tool. ·User-oriented" interfaces of the first and second generation's simulation software have been reinforced this fear. User-orientation an functionality combined with a vast variety of utilization are available only within the last few years in modern software packages.
Costs of simulation From previous experience, the costs of simulation in general are up to 1-3 % of the total investment expenditure. It is difficult to understand in this respect why a technology .with such a low expenditure and such a high economizing potential is not utilized more intensively. In most cases the utilization of simulation in small and medium sized companies is prevented by high licence costs of the simulation software - efficient software packages require ATS 500.000,- on average. There are, however, other possibilities of how to get into simulation technique, like simulation studies as serviCe, testing installation, run-time licence and much more.. A step by step entrance is facilitated this way which leads to a reduction of the fmancial risk.
As was already mentioned, the turning away of a so called ·one way" simulation, which means the utilization of the simulation model during the whole life time of the manufacturing system, can be regarded as a further contribution to the reduction of simulation costs.
Ca •••tudy As an application example serves an assembly cell for the production of primary parts of welding transformers in a typical medium sized Austrian company. Three years ago this company started with the realization of a "Iow cost" CIM concept including an automated assembling station. Because of the market conditions, the trend goes towards smaller lots and therefore more variations of the six basic types are necessary. Today approximately 1300 product variations with an average lot size of 10 are produced. The necessary operations assembling station are:
in the
automatic
•
attaching two transistors, four diodes, two resistors and one Thermocouple
•
screwing these electronic parts
•
attaching the printed circuit 1
•
screwing the printed circuit 1 onto the diodes
•
screwing three power cables to the printed circuit 1
•
soldering the resistor cables and of some connections onto printed circuit 1
•
attaching and soldering a capacitor onto printed circuit 1
•
attaching a pressboard plate and the printed circuit 2
•
screwing these two parts
- 154 -
The major part of the overall processing time is consumed by the technological tasks (i.e. time for soldering, screwing, etc.). Therefore the simulation could only handle the following domains (Fig.2): •
the sequence of the single assembling operations
•
the single robot paths
•
the optimal layout of the assembling station (i.e. the arrangement of the storage units, of the used grippers, of the screwing devices, etc.).
Fig.2:
layout of the assembling station and some of the robot paths (Kronreif, 1990)
The simulation, we used the simulation package SIMAN/CINEMA, has taken up approximately three months (Fig.3). Fig.3:
snapshot of the simulation animation (Kronreif, 1990)
and
The benefit of the simulation is the reduction of the processing time from once 6 minutes to 3 minutes n~w (for the smallest of the six different types). Maybe this result could be reached without simulation too. Therefore they had to use the real process as an experimental enviroment. This way of optimizing - using the "trial and error" technique onto the real process - certainly is more time- and money consuming than using simulation technique.
Conclusion Manufacturing industry is changing rapidly worldwide. Decisions have to be made more and more accurately and within shorter time of reflection. For this changing situation there is a tool at hand whose significant fmancial benefit has already been proved. Instead of using this tool for one's own economic success, one is afraid of its presumably high costs and runs the risk of investing a much higher amount in a wrong way. Simulation is an excellent instrument for experimenting promptly and cost saving. The simulation model and not the real factory serves as an experimental frame to optimize productivity and logistics. Simulation's utilization areas are transferred away from a single use of checking and controlling to a permanent function with the task of raising the benefit of the simulation model and saving time and costs for planning. Simulation should be growing up to a key technology of the nineties. The trend to a useroriented software, which can be used by everybody will be reinforced in the future. Simulation will be easier, more economical and more efficient this way. It must be a fIXed component of the CTechniques in planning in the future. Similar to the rapid development and distribution of these technologies, the CAD technology in particular, simulation will gain importance.
Fig. 2.
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- 155 -
Fig. 3.
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References AESOP GmbH (1992). Simulation - a key technologie of the nineties: high benefit but insufficient knowledge in this technique. (in German) Fachaufsatz Simulation, Stuttgart. Gangl P., and Hanisch R. (1992). A "guinea pig" made of bits and bytes. (in German) Luertechnik, 1114. Milberg J., and Burger C. (1991). Simulation as an aid for production planning und -control. (in German) ZwF 86, Z, 76-79. Seevers C. (1991). Utilization of simulation for many tasks. (in German) FOrdertechnik. 8. 62-65. Furst K. (1991). More sefety in planning because of Simulation. (in German) FOrdertechnik. 1 18-20. VDI (1983). Simulations for material flow planning. (in German) VDI-Richtlinie 3633. Milberg J., Amann W., and Raith P. (1992). Faster putting into operation because of tested sequence control. (in German) VDI-Z. 134/2, 32-37. Scharf P., and Spies W. (1990). Simulation 4" results of an interview of several users. (in German) VDI-Z, 132111, 62-65. Kronreif G. (1990). Contribute to the simulation technique in the area of automated assembling (in German), Diploma Thesis, Institute of Robotics and Handling Devices, TU Vienna.
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Simulation in small and medium sized companies
G. Kronreif, P. Kopacek
Institute of Robotics, Techllica/ Ulliversity of Viellna, Moe//wa/dp/atz 5/4, 1040 Vienna, Austria
Abstract: Modem production plants are characterized by enhanced complexity considering increased automation and enlarged integration of computers. Therefore duration and risks of planning are increasing. In addition putting into operation of new or modified plants b~ng about considerable complications with start-up operation and furthermore decreases in rate of production. The main source of this behavior is often the insufficient tuning of the single devices. The aim of this paper is to give stimulus to utilize "simulation", which is well known asa planning tool for a considerable time. However it is being used too less in order to fmd sOlution to the problems mentioned above. Keywords: Simulation; scheduling; modelling; manufacturing automation.
Introduction
decreasing life-time of certain products, another important factor, besides the reduction of planning costs, is the saving of time in the planning stage.
Modern manufacturing and assembling plants are more and more characterized by the high degree of automatization of their single sub-systems. High integration of computers in these plants complicates production planning and increases the risk of mis-investment (Schaif, 1990). Moreover, the lot sizes are becoming smaller and smaller. Market's imponderableness however, asks for a higher flexibility in the production. By means of "Just In Time" JIT and "Computer Integrated Manufacturing" CIM some production or assembly cells cannot be decoupled by storage banks any longer, and one would not be able to correspond with the troughput times (Furst, 1991). • Small and medium sized companies must therefore have high production flexibility to be able to meet the rapidly changing market situation, to meet the delivery dates and to provide for the inaeasing demands regarding quality.
There are only a few applications of simulation in small and medium sized companies. One of the reason are the costs of simulation Technique.
Because of the reasons mentioned before quality and costs of planning contribute extremely the overall costs. At an early stage of production system planning, in particular, the costs of production are already largely determined depending upon the plant layout and the choice of machinery (Milberg, 1992). Costs can be saved considerably in. this respect by means of an increase in the quality of planning. Because of the
rust and second generation's simulation software and the partly wrong way of the development of a model led to the wrong opinion of an extremely costy and highly complicated technique. The new simulation systems with their graphical interfaces, their user-oriented modelling concepts and their time saving experimental environment are supposed to open new areas of utilization and to plead for more acceptance.
Conventional planning techniques cannot be utilized for this discussion. The results of modifications of the structure and the utilization of the system can only be estimated vaguely at this point. When looking for innovative and economic solutions instruments which show the weaknesses in an integrated process and which support the acquisition and realization of solutions and their utilization, have to be taken into consideration. Under this point of view simulation seems to be the most appropriate device. This technique makes it possible to prove the expected productivity of the planned, complex system. The system can be tested without interfering into the real process
(VDI, 1983).
- 152 -
Advantages of slmulltlon Simulation is the imitation of the real plant in a computer model to deserve the dynamic behavior under several variants of load and eventual breakdowns. Based upon the costy and timeconsuming experiments which result from the real process, simulation offers a lot of help in the development and modification of complex systems. The financial benefit of simulation-based planning must not be rejected already nowadays. The utilization of simulation technique permits a reduction of time spent in planning and of planning risk and an improvement in the quality of planning. A positive side effect of the modelling is its extraordinarily high insight into the system. The plant is look at in a different way - from a different point of view. The formal description of the system, as it is necessary for the construction of a computer model, acts like a check-list (Flirst, 1991). In many cases, eventual errors are already discovered at this stage before the model itself is built up and existing but hidden reserves of the plant are recognized (Fig.l). Simulation in connection with animation of the manufacturing or the assembling process improve the communication between all the factors taking part in the process of planning. Fig. 1:
Simulation generates a "Feed-Back" just during the phase of planning (Fiirst, 1991)
New Irell of utilization A new sight of the simulation technique is growing increasingly. The simulation model is being serviced if possible improved and utilized from the phase of planning until the end of life-time of the manufacturing system. The renunciation of a oneway, so called "throwaway" simulation and the acceptance of a long-term utilization of the simulation model built long ago leads to a saving of costs. It is worth, therefore, applying the simulation during the operating phase of the plant too, as a support of a PPS-System for example. In this case simulation contributes to a higher transparency and security in short-time planning decisions. It is possible to schedule an inserted order more detailed by means of the model of the planning phase and by the operating data derived from the actual situation. If an eventual change of products, a change within the collection or a modification of the sequence of operations might be required, this model determines these effects in advance and tries to find the adequate measures.
Simulation can therefore be utilized for several tasks (depending upon the time of employment): •
at the beginning stage of planning to discover realistic and dynamic relationships of capacities, costs, bottlenecks etc.
•
during the planning phase to check the whole concept
• in the suppliance phase to check whether the means offered obtain the results requested before •
accompanying the phase of planning simulation may be used as testing environment to check the control software
•
in the operating phase eventual effects of planned modifications can be determined in advance
•
utilization of scheduling
simulation
in
optimal
The continuing improvement of calculating speed and of the capability of computer graphics offers a further area of utilization. The more and more realistic animation software makes it possible to use simulation as a means of support of marketing (wySIWYG - What you see is what you get). Equipped with an extensive module sample, the seller profits by the fact that visual aid is better than lots of words. Because of the increasing appearance of powerful portable computers in particular simulation technique could be growing up more and more to a helpful tool during the marketing and selling phase. Regardless of the utilization area of simulation, user-oriented software (graphical interface with interactive, menu- and window-driven modelling, block-oriented modelling concepts) are moreover preferred. Simulation can be utilized in those areas where it is requested - simulation is there for the planner and practitioner. Therefore, an initial period into the simulation technique and into the software used has to be offered to them which can easily be acquired by means of the new simulation software.
Costl and prejudlcel Insufficient knowledie about this techniQye and its advantaies Beside the presumably high costs of the simulation technique its utilization is prevented by other factors as well. The education program at schools and universities, for example, is far too limited. Moreover, people are still afraid of spending so much money on
- 153 -
Fig. 1.
SIMULATION
software or services in the software area. Finally, there is still this unfounded fear of this mighty and apparently complicated tool. ·User-oriented" interfaces of the first and second generation's simulation software have been reinforced this fear. User-orientation an functionality combined with a vast variety of utilization are available only within the last few years in modern software packages.
Costs of simulation From previous experience, the costs of simulation in general are up to 1-3 % of the total investment expenditure. It is difficult to understand in this respect why a technology .with such a low expenditure and such a high economizing potential is not utilized more intensively. In most cases the utilization of simulation in small and medium sized companies is prevented by high licence costs of the simulation software - efficient software packages require ATS 500.000,- on average. There are, however, other possibilities of how to get into simulation technique, like simulation studies as serviCe, testing installation, run-time licence and much more.. A step by step entrance is facilitated this way which leads to a reduction of the fmancial risk.
As was already mentioned, the turning away of a so called ·one way" simulation, which means the utilization of the simulation model during the whole life time of the manufacturing system, can be regarded as a further contribution to the reduction of simulation costs.
Ca •••tudy As an application example serves an assembly cell for the production of primary parts of welding transformers in a typical medium sized Austrian company. Three years ago this company started with the realization of a "Iow cost" CIM concept including an automated assembling station. Because of the market conditions, the trend goes towards smaller lots and therefore more variations of the six basic types are necessary. Today approximately 1300 product variations with an average lot size of 10 are produced. The necessary operations assembling station are:
in the
automatic
•
attaching two transistors, four diodes, two resistors and one Thermocouple
•
screwing these electronic parts
•
attaching the printed circuit 1
•
screwing the printed circuit 1 onto the diodes
•
screwing three power cables to the printed circuit 1
•
soldering the resistor cables and of some connections onto printed circuit 1
•
attaching and soldering a capacitor onto printed circuit 1
•
attaching a pressboard plate and the printed circuit 2
•
screwing these two parts
- 154 -
The major part of the overall processing time is consumed by the technological tasks (i.e. time for soldering, screwing, etc.). Therefore the simulation could only handle the following domains (Fig.2): •
the sequence of the single assembling operations
•
the single robot paths
•
the optimal layout of the assembling station (i.e. the arrangement of the storage units, of the used grippers, of the screwing devices, etc.).
Fig.2:
layout of the assembling station and some of the robot paths (Kronreif, 1990)
The simulation, we used the simulation package SIMAN/CINEMA, has taken up approximately three months (Fig.3). Fig.3:
snapshot of the simulation animation (Kronreif, 1990)
and
The benefit of the simulation is the reduction of the processing time from once 6 minutes to 3 minutes n~w (for the smallest of the six different types). Maybe this result could be reached without simulation too. Therefore they had to use the real process as an experimental enviroment. This way of optimizing - using the "trial and error" technique onto the real process - certainly is more time- and money consuming than using simulation technique.
Conclusion Manufacturing industry is changing rapidly worldwide. Decisions have to be made more and more accurately and within shorter time of reflection. For this changing situation there is a tool at hand whose significant fmancial benefit has already been proved. Instead of using this tool for one's own economic success, one is afraid of its presumably high costs and runs the risk of investing a much higher amount in a wrong way. Simulation is an excellent instrument for experimenting promptly and cost saving. The simulation model and not the real factory serves as an experimental frame to optimize productivity and logistics. Simulation's utilization areas are transferred away from a single use of checking and controlling to a permanent function with the task of raising the benefit of the simulation model and saving time and costs for planning. Simulation should be growing up to a key technology of the nineties. The trend to a useroriented software, which can be used by everybody will be reinforced in the future. Simulation will be easier, more economical and more efficient this way. It must be a fIXed component of the CTechniques in planning in the future. Similar to the rapid development and distribution of these technologies, the CAD technology in particular, simulation will gain importance.
Fig. 2.
28
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- 155 -
Fig. 3.
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.-~
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""-
..... _ _ ' . . . 1
--
Tt-. . . . . . . I _ _ _
~."I
.'
References AESOP GmbH (1992). Simulation - a key technologie of the nineties: high benefit but insufficient knowledge in this technique. (in German) Fachaufsatz Simulation, Stuttgart. Gangl P., and Hanisch R. (1992). A "guinea pig" made of bits and bytes. (in German) Luertechnik, 1114. Milberg J., and Burger C. (1991). Simulation as an aid for production planning und -control. (in German) ZwF 86, Z, 76-79. Seevers C. (1991). Utilization of simulation for many tasks. (in German) FOrdertechnik. 8. 62-65. Furst K. (1991). More sefety in planning because of Simulation. (in German) FOrdertechnik. 1 18-20. VDI (1983). Simulations for material flow planning. (in German) VDI-Richtlinie 3633. Milberg J., Amann W., and Raith P. (1992). Faster putting into operation because of tested sequence control. (in German) VDI-Z. 134/2, 32-37. Scharf P., and Spies W. (1990). Simulation 4" results of an interview of several users. (in German) VDI-Z, 132111, 62-65. Kronreif G. (1990). Contribute to the simulation technique in the area of automated assembling (in German), Diploma Thesis, Institute of Robotics and Handling Devices, TU Vienna.
I
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cmJ
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.
..--
----. ::~
\_,." z.ot :