Virtual manufacturing environment as a reference model for standardization
H.Hiraoka
Dept. of Precision Mechanics, Chuo University
13-27 Kasuga 1 Chome, Bunkyo-Ku, Tokyo 112 Japan
hiraoka@mech.chuo-u.ac.jp
abstract
Standardization plays a crucial role for manufacturers to achieve high customer satisfaction and rapid development of products.
To make various standards conform to each other, a reference model of manufacturing systems is required.
The concept of virtual manufacturing environment (VME) is introduced as the reference model.
VME is a proposal for a framework of totally computerized manufacturing system of the future.
Using the simulation based on accurate models, VME predicts what will happen in the life cycle of products and provides information on the necessary actions without actual activities.
Configuration of VME is explained and possible elements to be standardized is shown.
The frameworks of the construction and use of VME-based systems and their possible standardization are also discussed.
1. Introduction
Manufacturing companies seek distributed and autonomous manufacturing environment to achieve high customer satisfaction and rapid development of products.
Standardization plays a crucial role because distribution and autonomy require the existence of coherent and ubiquitous environment which only standardization can provide.
Many standards are being developed focusing various aspects of information systems for manufacturing. Unfortunately, these standards are not necessarily based on the same assumptions, nor avoiding overlaps of scopes.
To make these standards conform to each other, a reference model of manufacturing systems is necessary which will provide an uniform understanding of manufacturing systems to be standardized.
In this paper, the concept of virtual manufacturing environment (VME) is introduced as a reference model.
What portions should be standardized in the model is also discussed.
2. Virtual Manufacturing Environment
Manufacturing companies are required
- to shorten the delivery of their product
To respond customers' needs quickly, companies are required to deliver their product in more precise way, i.e., "Right products at the right place at the right time."
- to respond to various requirements
To meet customers' needs in more detailed and flexible way, concept of mass production has not work any more.
In some cases, companies have even to proceed "one of a kind" production.
Rapid changing of market is also a challenge to companies.
Furthermore, requirements have become complicated that are originated from problems such as product liability and environmental issues.
The concept of VME [1] is developed to provide a framework of totally computerized manufacturing system of next generation. The basic idea is to develop systems to meet the manufacturer's requirements arose from the above mentioned situation,
by employing fully the power of computers and relating information technologies.
Many troubles in manufacturing occur because we cannot foresee them in earlier stages of product development.
If we can forecast what will happen in later stages of manufacturing, operation, maintenance and discarding, we are able to resolve or prepare for the foreseen problems beforehand.
A VME system works based on physical simulations by which accurate and detailed prediction is made on the behaviors of products.
It can also perform simulations based on the compiled experiences.
With this capability of simulation, a VME system will be able to
- forecast what will likely to happen during the life cycle of products, i.e., in manufacturing, operation, maintenance and discarding, without actual activities, and
- examine characteristics and validity of various methods for life cycle activities of products without actual experiments.
To respond to these requirements in various fields, VME has configuration as shown in figure 1 which are composed from the following three layers.
- application specific objective systems,
- basic component models and
- modelling constructs.
An application specific objective system is a target system which fulfills the manufacturer's requirements. It is generated by selecting and combining basic component models.
Component models provides
- information on objects such as products, tools and manufacturing facilities
- information of manufacturing activities such as design, process planning, production and maintenance
Every component model is composed from modelling constructs that represent generic information on products and activities.
Product model contains all the technical information about the product including shape, assembly structure, shape tolerances, material, mass properties, kinematic properties and so on.
Product models are accompanied by physical process models such as mechanics of materials, kinematics, dynamics, structural analysis and finite element analysis for various purposes.
Physically accurate simulation of behaviors of products can be performed by using these physical process models.
Activity model contains information on basic processes in manufacturing such as machining, assembly, measurement and configuration management.
With this configuration, VME systems are expected to be easily generated and to fulfill the specific requirements of manufacturers.
3. Standardization for VME systems
VME systems are required to conform to each other as well as to fulfill each manufacturers' needs.
They should be inter-operable as companies want to use various systems seamlessly, i.e., without taking care of their differences.
Standardization can be a solution for this requirement.
In figure 1 possible elements of VME which would be suitable for standardization are shown in black.
Important areas of standardization in VME include the configuration of modelling constructs.
ISO TC184/SC4 and their standards called STEP [2] aims standardization of this area.
However, activity models have not yet been included in current version of STEP. Representation of activity is necessary if you want to handle various processes in manufacturing.
Some techniques should be developed for the representation of activity.
Higher layers are not necessarily to be standardized.
Component models may be standardized but more probably be provided by vendors as a set of library which generates arbitrary application specific systems.
I think the difference between component models and modelling constructs may be the level of maturity.
Information which everyone thinks to be fully matured and generic will be transferred from component models to modelling constructs.
Last but not least, underlying database for implementing modelling constructs should also be standardized for sharing data among various applications.
Technologies on object- oriented database can be applied for this purpose.
4. Construction and interfaces of VME systems
VME systems are not rigid nor static but are constructed at any time when the manufacturing companies' needs are identified.
They should be easily constructed by combining necessary component models.
For that purpose, the framework of the construction of VME-based systems are considered as shown in figure 2.
Construction of VME systems includes generation of application specific objective systems.
Following techniques may be important and should be developed for the generation.
- Description of systems:
A method is required to describe the configuration of a specific system by formally specifying the combination and interaction of component models.
System description language should be clearly and logically defined to realize an unambiguous implementation.
- Viewing mechanism:
Core of the system generation methods is a viewing mechanism which creates a specific system as defined by the description.
The mechanism chooses appropriate (portion of) component models, makes them conform to each other and generates the required specific application system.
- Libraries:
Library is a set of component models which belong to an application domain.
With an appropriate library, target specific system is easily constructed or regenerated.
I suppose companies which have techniques or know-hows of specific domain could be a vendor which provides a library.
User companies construct their own specific systems based on those libraries.
- Description of database:
As for databases, description method is also necessary to create the required database.
Description language which can describe modeling constructs are necessary to define the contents of database.
One possibility is the efforts currently conducted in ISO TC184/SC4 including the development of EXPRESS language [3] and SDAI [4].
VME system has levels of communication interface, shown in figure 3, which are classified as
- application level exchanges,
- data level exchanges and
- data model exchange
Application level exchange:
Users want to get some component model from their libraries or through networks and plug it into their own system.
Technique such as applet mechanism will realize this level of exchange.
Data level exchange:
Data exchange/sharing between databases among companies or applications is still a strong requirement from many companies.
Unambiguity and completeness are the current target of development.
Data model exchange:
Not only data itself but its data model would be able to be exchanged.
Data model described by model description language will be sent from sender and expanded into receiver's system.
5. Standardization for the construction and interfaces of VME systems
Standardization is necessary to facilitate these activities, too.
Portions to be standardized are shown in black in figures 2 and 3.
Construction:
System description language and corresponding system generation methods should be standardized.
Often same concepts may be named differently in the different applications or slightly different concepts may be called under the same name.
These are obstacles when we combine different component models into one specific system and technique should be developed to resolve this problem.
Another area for standardization will be library for component models and modelling constructs.
Configuration of those libraries should be standardized to be used consistently.
Specification of library management system
which will manage libraries and templates
should be standardized as well.
Communication interface:
Appropriate component model will be picked up from libraries and plugged in the specific system.
To realize this methodology, the interface between specific system and plugged-in component model should be standardized.
When libraries are distributed in network, a mechanism is necessary which will find an appropriate component model through network.
This mechanism which we may call component request brokers should also be standardized.
Interface between models and underlying database should be standardized as well.
When databases are distributed in network, object request broker which will find the appropriate data via network should also be standardized [5].
6. Conclusion
In summary, this paper presents a reference model for standardization of information systems in manufacturing through the concept of VME system.
Concepts presented here has not been realized yet.
A lot of problems still exist to complete the virtual manufacturing environment.
Arguments may exist about the presented picture.
However, I believe that, based on the analyzed requirements, giving a future perspective and the preferable direction of development is important to avoid unnecessary overlapping of efforts.
References
[1] F.Kimura: Product and Process Modelling as a Kernel for Virtual Manufacturing Environment, Annals of the CIRP, 42/1, 1993, pp.147-150.
[2] N.N.: ISO 10303-1: Industrial automation systems and integration - Product data representation and exchange - Part 1: Overview and fundamental principles, ISO, 1994.
[3] N.N.: ISO 10303-11: Industrial automation systems and integration - Product data representation and exchange - Part 11: Description methods: The EXPRESS language reference manual, ISO, 1994.
[4] N.N.: ISO 10303-22: Industrial automation systems and integration - Product data representation and exchange - Part 22: Implementation methods: Standard data access interface specification, ISO DIS.
[5] T.J.Mowbray, R.Zahavi: Essential CORBA, The System Integration Using Distributed Objects, John Wiley and OMG, 1995.
[6] Y.Shiozawa: PROMINENCE, brochure for IMS Globeman 21 Japan National Initiative VME, 1996.
[7] K.Iwata, M.Onosato, K.Teramoto, S.Osaki: A Modelling and Simulation Architecture for Virtual Manufacturing Systems, Annals of the CIRP, 44/1, 1995, pp.399-402.
[8] W.Evarsheim, H.Rozenfeld, W.Bochtler, R.Graessler: A Methodology for an Integrated Design and Process Planning Based on a Concurrent Engineering Reference Model, Annals of the CIRP, 44/1/1995, 1995, pp.403-406.
About the author
Hiroyuki Hiraoka received Doctorate of Engineering from the University of Tokyo in 1983.
He joined Chuo University and became a professor of Department of Precision Mechanics in 1995.
He has been involved in activities of ISO TC184/SC4 for 6 years working for the development of draughting standards in STEP.
Now he is a member of WG10 Technical Architecture in SC4.
In addition to STEP, his current research interest includes product modeling, representation of assembly structures and the applications through computer simulations based on those representations, such as assembly planning, design for assembly, kinematics and maintenance planning.