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1) Reconfigurable machining systems
2) Reconfigurable fixturing systems
3) Reconfigurable assembling systems
4) Reconfigurable material handling systems
5) Reconfigurable inspecting and calibrating systems
It is evident from the above that extensive research has been conducted in the field of reconfigurable manufacturing systems and reconfigurable manufacturing tools. There is still a need to develop formal design methodologies for these types of tools [5].
In the modular machine arena, libraries of mechanical components have predominantly focused on motion and function modules [3]. Motion modules allow the degrees of freedom of the machine to be varied from a single degree of freedom – such as in a drilling machine– to a machine with a full six degrees of freedom. Function modules, on the other hand,
deliver the machining process functions such as milling, boring, drilling, and turning.
Figure 1: An example of a library of modules for modular reconfigurable machines(adapted from [3])
Figure 2: Using different modules to vary a machine’s functionality [3]
A third category of modules, called accessory modules, are parts such as clamps and stabilisers. They might not have an active role in the cutting process, but they are critical to ensuring successful production. Tool storage and exchange systems may fall into this category, but the authors suggest that they should form part of a fourth set of modules called auxiliary modules. Auxiliary modules may also not form a direct part of the machining process, but they would add extra functionality to the machines, aiding the efficiency and quality of production. These modules might also include tool monitoring and quality control modules.
In the South African context, research has been completed by Estment, Gorlach & Wiens [7]in the area of adding an automatic tool changer and spindle to a reconfigurable machine tool. The machine tool was a gantry type CNC machine delivering 2.5 axis machining. The emphasis of the research was on the successful integration of these two new modules with
the existing machine. Mach 3 CNC programming software was used to generate the required G code. The tool changer module was mounted directly on the gantry machine bed, using a part of the machine that was not required for the workspace.
3.THE DEVELOPMENT OF A STAND-ALONE TOOL-CHANGING MODULE
The Mechatronics and Robotics Research Group (MR2G) of the University of KwaZulu-Natal has developed a tool-changing unit that presents a solution to the need for an autonomous module that offers a selection of tools to a reconfigurable manufacturing system. This section describes the specifications imposed on the design, and gives an overview of the various components that make up the unit.
3.1 The design specifications of the module
The first specification to be decided upon was the working space that the tool changer should cover. After a survey of typical production machines, it was concluded that the tool changer should be able to cover the 60th percentile of machine working area sizes. This would represent a good portion of commercially available machines. This requirement translates into a working area for the tool changer of 600 x 300 x 450mm above the worktable. The tool changer also had to occupy no more than 1.5m3.
The next consideration was the carrying capacity of the unit, along with the requirement for the speed of the tool exchange. The unit was required to house at least six industry standard tool holders and perform a tool change within 30 seconds.
Initially, it was thought to design the module around a BT-30 tool holder; but upon further investigation it was found that the BT-40 holder was more common in the South African manufacturing environment. The tool changer was therefore designed to handle a tool weight of up to 5kg and have an accuracy of 2mm at the tool insertion point.