| Summary: | 碩士 === 國立彰化師範大學 === 工業教育與技術學系 === 107 === A rotary mechanism is a key component of a computer numerical control (CNC) machine. Most advanced industrial machines employ fourth- and fifth-axis rotary mechanisms. Five-axis machine tools are now available at a reduced cost, providing two additional motion axes in the existing three-axis CNC machine tools and thereby increasing workpiece machining precision and flexibility. A CNC rotary mechanism is composed of the main structure, a motor, and a reduction unit. Traditional reduction units employed three common types include worm gear, roller gear cam, and eccentric gear. Due to the rolling contact and multiple rollers mating process, roller gear cam has a tendency to become a potential option for precision machining. Roller gear cam can be mainly divided into two types: radial mating drive and lateral mating drive. Both of these two driving mechanisms have specific characteristics in assembly. Radial roller gear cam have been prevalently applied in Japanese machines first; they enable mating of multiple rollers and meet the requirement of non-backlash. However, radial roller mating unit is much more difficult to assemble and involve 5-axis machining. For less assembly burden and reach high-precision non-backlash requirement with preload applied, this study employed the lateral roller mating design to fabricate variable lead and multiple roller mating cams for a reducer, which featured 4-axis machining; this design was intended to control costs
effectively and increase competitiveness.
The method to create cylindrical roller cams in this research is conjugate geometric envelope, in which the groove cut on the periphery of an end mill with the geometric diameter the same as that of the following roller. The manufacturing process between the cam raw material and the cutter was achieved through a simulation on the relative motions of the cam and the rollers. The generated variable lead cylindrical roller gear cam, which can be developed for a precision reducer, will be applied in multi-axial machine tools as rotary mechanisms. By propelling the cam shaft to drive roller disk will reduce the speed and improve the accuracy. The machining tool-paths include roller groove guiding neutral paths, leading entrance paths, preloading paths, relief exit paths, chamfer trimming paths, and edge engagement paths. According to the mating speed, motion type, and different preload curves applied, design parameters can be employed to adjust segments of the
full machining path.
Finally, a commercial reverse simulation system was employed to imitate a virtual machine tool for verifying all machining tool-paths. The simulated geometric models were applied to identify the preloading engagement through error comparison. Thus, the accuracy of the machining tool-paths could be verified, and the cost of invalid operating time could be reduced through simulation before real machining. Base on this developed model, the various design parameters are expected to determine the corresponding machining dynamic relationship, as well as identify the effect of the stress distribution between rollers and cams on the motion life and power consuming of the system. Inevitably a smart manufacturing system that optimizes parameters for assessments and settings can be established.
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