This research was motivated by the need to develop new production technologies that will enable the objectives of rapidly scalable system capacity and adjustable functionality to be achieved in reconfigurable manufacturing. Modular reconfigurable machines were proposed in this research as a possible solution to the machining requirements of RMSs. The modular nature of these machines permits a change in machining functions and degrees of freedom on a platform, thus enabling adjustable functionality in RMSs. The modular nature of the machines further permits the reconfiguration and redistribution of hardware resources in a system, thus enabling the synergistic scaling of production capacities in manufacturing streams or cells within the system.
The variable machining functionality and the ability to assist in scaling production capacities will enable MRMs to form part of the solution that addresses the primary challenges of coping with high product variety and product customization. The modularity of MRMs also creates the potential for the machines to be cost effectively used in the initialization of manufacturing configurations that are needed for the short term manufacturing of small product batches.
MRMs possess the expandable machine flexibility needed in RMSs, thus favoring their implementation above dedicated machine tools. MRMs also exhibit the features of convertibility and customization allowing a machine to be adjusted in its functionality to suit new product portfolios. MRMs therefore possess the potential to cost less than CNC machines, which have comprehensive inbuilt functionality and may have features that may never be used by a manufacturer. Although CNC machines are designed with high flexibility, a CNC may still not possess the functionality required by a manufacturer. In this instance a new CNC machine will have to be purchased or the job may have to be outsourced to another manufacturer who possesses suitable machines. The expandable flexibility in MRMs therefore creates a second advantage over CNC machines, as they may be upgraded as necessary. The expansion flexibility in MRMs increases the expansion flexibility of RMSs and the lifespan of a RMS is expected to be longer and more economical to extend than either DMSs or FMSs.
The MRM modules created during this research could be assembled into a drilling or turning center. The turning configuration displayed two automated axes and one manually adjustable axis.
The drilling configuration was able to display a variation from three up to six automated DOF.
The twelve modular units of hardware that formed the library of modules were used to create nine unique machine configurations in total. A high level of reconfigurability with limited hardware is therefore displayed in MRM technology.
A modular distributed control system was created for MRMs. The modularity of the system complimented the mechanical modularity and the computing capacity of the system was scalable.
The number of mechanical modules controlled by the system could be increased with an increase in the number of distributed control drives connected to the system. The use of standard communication protocols such as USB and I2C promoted the modularity and easy reconfigurability of the control system. The concentration of generic software functions on the host PC and the location of module specific control functions on distributed control drives created a hardware abstraction that further promoted mechanical and electronic modularity. Theoretically the hardware abstraction supports the augmentation of a platform with mechanical and electronic control modules from multiple vendors by providing a consistent style of integration with the rest of the control system.
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10. Conclusion
The facility for a manufacturer to augment his machine tools with modules from multiple vendors would ultimately result in a more competitive machine tool market. The potential to reconfigure and upgrade machine tools cost effectively, exists with MRMs a technology for future manufacturing.
The MRM software system on the host PC was created with full inbuilt functionality. The level of reconfigurability in the software system was limited to the selection of axes and the configuring of port addresses. Collision detection was only enabled locally between a mechanical module and a control module, and the host PC was only informed of collisions after a machining process had begun. For preemptive collision detections on the part of the host PC, a more extensive reconfiguration of the software system is required. A software system with full inbuilt functionality is also bound to be uneconomical if the technology is made commercially available.
Further research must be conducted into the development of a modular open architecture control system for MRMs.
The MRM platform developed in this research was limited to the machining of wax and soft materials. The machine displayed a lack of stiffness in certain machine configurations and low powered motors resulted in a decreased performance compared to similar machines that are commercially available. Low cost sliding mechanisms, power screws and other low cost drive mechanisms limited the performance of the machine. The overall performance of the mechanical system was sufficient to achieve the objectives of the research and the performance of the present MRM platform may be significantly improved with additional monetary investments.
Improvements that have been identified include the implementation of more suitable and higher quality mechanical components such as recirculating ball screws in linear axes; bevel and spur gearboxes in rotary axes and higher quality DC servo motors in all axes. The use of cast dove tail slide systems and bifurcated structures would also increase the stiffness of linear axes. Stiffer and heavier materials such as steel and cast iron would further increase the rigidity and vibration damping characteristics of individual modules. This would be complimented by an increase in the power capacities of all drive motors in modular axes.
Through the research performed on the existing library of modules, problems in MRMs have been identified. Some of these problems may be solved with improved design while others are an inherent and fundamental consequence of a modularized structure. Dimensional imbalances in machining structures are introduced when uncomplimentary machining processes are grouped together to create a set of modules. This problem was displayed by the current system where the use of a range extension arm was required to compensate for the uncomplimentary dimensions of the base module in drilling configurations. The range extension arm increased the susceptibility of the drilling configurations to large static and dynamic mechanical deflections. Imbalances in the dimensions of axes may be diminished by creating sets of modules centered on cutting processes that are grouped together on the basis of geometric commonality in the typical part shapes they machine (prismatic/non-prismatic, large length to breadth ratio/small length to breadth ratio, large length to diameter ratio/small length to diameter ratio, etc).
The second problem that has been identified in MRMs is an unfavorable mass distribution in the machine structure. The effect of this problem may be diminished to an extent by improved mechanical design; however the necessity to locate drive motors at the point of actuation creates a fundamental structural disadvantage with regard to the mass distribution.
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10. Conclusion
The third problem that was identified is the potential to drastically upset the balance of the structural rigidity and mechanical power available in the system by the integration of additional mechanical modules. This is a fundamental problem and modules may have to be designed with generally high powered motors and high stiffness; which will ultimately reduce the economic viability of the technology. The fourth problem that was identified was the need to increase the electrical power supply to the system as the number of modules in the system increases. Power supplies may be either created with excess capacity or further research may be performed on the development of modular scalable power supplies. A modular power supply system would be expected to cost more than a standard power supply system of equivalent capacity. The economic viability of both solutions appears fundamentally poor at present.
The final problem that was identified is the complexity of the reconfiguration process for MRMs.
Reconfigurations entail alterations to the mechanical, electronic, software and electrical power supply systems of a machine. The level of complexity will require the use of companies that possess lifting equipment, calibration equipment and trained personnel to complete the reconfigurations. The reconfiguration process is therefore expected to be costly and time consuming. MRMs have to be taken offline from a system to be reconfigured and the profit losses associated with the machine downtime further reduce the economic viability and practicality of the technology. It should be noted that the automated reconfiguration of a machine is an impractical solution to this problem. If a machine is to display automated transformability into different configurations this would imply that the machine would have to be created with full inbuilt functionality. This is a logical contradiction to the intentions of a modular structural design. In addition to containing full inbuilt functionality, an automated transforming machine would have to contain additional motors and mechanisms to enable the transformability. Such machines would be inherently expensive and therefore not applicable as reconfigurable technology in RMSs.
Further research must be conducted on solving the problems identified, before MRMs become industrially implementable and economically attractive machines. Novel solutions will have to be developed as many of the problems that were highlighted appear to be of a fundamental nature and plausible solutions are not easily identified. An investment into the further research of MRM technology is justified by the promising benefits of enhanced reconfigurability in system functionality and production capacity for RMSs.
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