These angular displacements can be extracted from the NC program generated by some special sofwares that are specialized for cam mechanisms.
From machining point of view, the globoidal cam surfaces can be determined by corresponding angular displacements of both the cam and the driven member ( Koloc & Vaclavik, 1993). In general, the works mentioned above have used the mathematical expressions for the globoidal cam surfaces and various cam laws as the input data to generate the cam surfaces. In their study, the expression of a surface normal, a rule surface and its offset, meshing vectors and meshing angles were introduced to define the accurate swept surfaces generated by the roller follower, and a program in C++ language developed to generate the surface coordinates of the cam. They represented the surface geometry of the cam as the swept surfaces of the tool paths. In addition, some researchers studied to create the globoidal cam with conical rollers from machining point of view ( Tsay & Lin, 2006).
Some other researchers also described mathematicaly the cam surface, but they used computer to develop a package, which was a combination of AutoCAD R14, 3D Studio Max, and VBA, to generate the surfaces of the roller gear cam ( En-hui et al., 2001).
SWEEP COMMAND AUTOCAD 2004 WITH PICTURE SOFTWARE
Some can create the data of the cam curve profile which will be the input data for CAD/CAM software such as Unigraphics to build the CAD model ( Chen & Hong, 2008). Some programs can draw and display the draft of the cam contour, or create the solid model. They developed their own programs, which were written in Visual Basic, C or C++ languages, to assist themselves in studying. Some researchers derived mathematically expressions for the surface geometry of the globoidal cam with cylindrical, hyperboloid, or spherical rollers, based on coordinate transformation, differential geometry, and theory of conjugate surfaces ( Yan & Chen, 1994& 1995 Yan-ming, 2000 Cheng, 2002 Lee & Lee, 2001& 2007 Chen & Hong, 2008). Up to now, a number of works dealing with finding the way to describe accurately these surfaces have been proposed. These surfaces are very complex and it is very difficult to create them accurately. The working surfaces of the globoidal cams are the surfaces that contact with the roller surfaces. The most important task when modelling the globoidal cams is to represent their working surfaces. In term of the shape, globoidal cam is one of the most complicated cams. They are widely used in machine tools, automatic assembly lines, paper processing machines, packing machines, and many automated manufacturing devices. Compared to other cam-follower systems, the globoidal cam-follower mechanisms have many advantages, such as: compact structure, high loading capacity, low noise, low vibration, and high reliability. Globoidal cam mechanisms are widely used in industry.
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