4. Modular Reconfigurable Machines
4.2 Design Concept
Figure 4.2: Sequence of Operations - Mechatronic Design Process (Adapted from [53], [54])
4.2 Design Concept 4.2.1 Design Perspective
The design of reconfigurable machinery has yet to converge on a single set of principles. The primary division in design philosophies is based on views of machine flexibility. The matter arising is if a reconfigurable machine should assume an intermediate level of flexibility between DMTs and CNC machines, or should it be designed to exceed the flexibility of typical CNCs. The Arch Type RMT is the only prototype machine that has been developed for RMSs to date. This machine was developed with intermediate flexibility between DMTs and CNCs, having been designed around a family of V6 and V8 engine blocks.
In a dynamic manufacturing environment problems may be encountered with designs that are either highly customized or excessively generic. With regard to machine design around a part family, the manufacturer bears the risk of machinery becoming redundant if drastic changes in products are expected. In the case of the Arch Type RMT, designs on automotive engines are not expected to change drastically over a short period of time, and the design of the machine around a part family was acceptable. In many other industries such as industries based on trend driven consumer products, product lifecycles are short and improvements in technology are rapid.
Machines employed in the manufacturing of consumer goods with short production lives must be adaptable to dynamic changes in product portfolios and cannot be strictly designed around a part family. Conversely machines may be designed to possess comprehensive inbuilt flexibility, potentially exceeding that of current CNC machines; however such machines would be expensive, complex and will inevitably possess unused features in different manufacturing implementations.
To avoid the problems associated with rigidly customized or excessively generic designs, the concept of Modular Reconfigurable Machines (MRMs) has been developed.
1 •Identify the Need
2 •Problem Analysis
3 •System Conceptualisation and Specifications
4 • Design and Modelling
5 •Manufacturing/Fabraction
6 •System assmbly/ integration
7 •Testing and Optimisation
8 •System Operation
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4.2 Design Concept
MRMs are oriented towards customized flexibility as in the case of the Arch Type RMT;
nonetheless the flexibility of the machine may be extended through the process of reconfiguration.
It is envisioned that through design for reconfigurability the machining envelope of a MRM could ultimately exceed that of similar CNC machines, although at each configured state the machine will possess only the functionality required for the operation at hand. The concept of customized, yet extensible flexibility in MRMs is realized by a modular design approach. MRMs are machines that are defined to be fully modular in their mechanical and control architectures. Although the idea of modular machines has been pre-existent, no fully modular machine has been developed by industry or academia.
4.2.2 Adopted Principles for MRM Design
The principle of machine design from a library of precompiled modules is indispensable in the synthesis of MRMs. This concept is essential for the rapid development of production machinery to capitalize on market opportunities. The concept of developing machines from a library of modules has been previously exploited in virtual machine tool design environments such as PREMADE and VRAx, as discussed in Section 3.4. The idea has nonetheless, never been extrapolated for the fabrication of a physical library of machine modules. Neither have machine tool builders developed individual automated modules for the synthesis of complete machining systems, with the possibility of after market reconfiguration. The main differences between the MRM library of modules and those developed elsewhere [37] are:
the library exists at a physical level,
modules within the library are intended for the complete synthesis of modular machine structures,
modules are intended to be assembled and disassembled in a “building block” fashion,
modules are intended to be mechanically autonomous and
modules are intended to enable the after market reconfiguration of machinery.
The complete library of mechanical modules may be considered as the general solution to machining systems for reconfigurable manufacturing. Through the modular, interchangeable capability of the modules, customized solutions may be extracted from the general solution and the property of customized flexibility is present in this approach. The mathematical methodology for module selection developed by Moon and Kota, as discussed in [42, 44] may be implemented to extract the desired machining solution from the generic solution i.e. the identification of the necessary modules for the synthesis of a machine that is exactly matched to the application.
4.2.3 Conceptualization of MRMs: Virtual Mock-Up
The concept of MRMs was first tested in the virtual environment provided by the Autodesk Inventor 11 software package. Within this environment a conceptual library of mechanical modules was created for the synthesis of machinery (see Figure 4.3). The conceptual library was first created to clarify the concept of modular machine design and explore decisions on module connectivity and module functions. Modules within the library were categorized according to three classes: Process, Motion and Accessory Modules.
Process Modules
Process modules are those modules within the library that provide a single manufacturing process.
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4.2 Design Concept
Figure 4.3: A Conceptual Library of MRM modules [55]
The focus of MRM development in this research has been on material removal processes, and modules in the conceptual library were created for milling, drilling and boring processes.
Process modules are envisioned to be the end effectors of a platform and a reconfiguration of the processing functionality is to be achieved by the interchange of MRM cutting heads. Figure 4.4 illustrates the concept where by a 3-axis milling machine is reconfigured into a 3-axis line boring machine by the substitution of a single module. Reconfigurability of this nature has not been illustrated by previous RMT designs.
Figure 4.4: The Reconfiguration of a 3-Axis Boring Machine to a 3-Axis Milling Machine [55]
Motion Modules
Motion modules are units that contribute to the axes of a machine and are responsible for the DOF available to the cutting tool. One motion module corresponds to one axis of a machine. In total six types of motion modules were conceptualised enabling translations along the three axes of a conventional Cartesian system (X, Y, Z) and rotations about those axes (A, B, C). Although six types of motion modules are intended to be made available only the necessary combination for a specified operation will be integrated into the machining platform.
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4.2 Design Concept
Figure 4.5 illustrates the kinematic reconfiguration of a 3-axis milling machine into a 4-axis milling machine through the integration of an additional motion module.
Figure 4.5: The Reconfiguration of a 3-Axis Milling Machine to a 4-Axis Milling Machine [55]
Accessory Modules
Accessory modules are units of hardware that are not directly responsible for the material removal process; however these units enable a machine to perform the required operation more efficiently.
Such modules include cutting fluid supply and work-clamping modules, steady rests, flow rests etc. In certain instances a machine may not be able to perform an operation without a critical accessory module, e.g. a work table module.
4.2.4 Digital Electronic Control
The concept of a mechanically modular machine required a similar approach to the conceptualization of a suitable electronic control system. Mechanical modules are to possess dedicated electronic control modules that map to the mechanical hardware on a 1:1 basis. The creation of a monolithic control system for MRMs would not suffice due to the scalable nature of the mechanical hardware. The electronic control system is therefore specified to be modular and scalable to exactly match the physical characteristics of a MRM platform.
Figure 4.6: Reconfigurable Software and Modular Electronic Control Systems for MRMs
MRMs are also specified to possess OAC systems, implemented on PC-based hardware. OAC is essential for software scalability in correlation to changes in the mechanical and electrical architectures of the machine tool. It is recommended that the MRM host control software be created in C++ to promote a modular programming approach. The architectural style of C++
presents an advantage in the object oriented nature of the programming language. The ability of an object to hide its representation from other client software makes it possible to change the software implementation without affecting the client. This is an essential feature for MRM software, as the system is expected to reconfigure with every reconfiguration of the physical hardware.
Reconfigurable Software
Digital Electronic
Control Module Mechanical Module
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