In this paper, the process control of a magnetostrictive-actuator-based microforming system is studied. Microforming has recently become an emerging advanced manufacturing technique for fabricating miniaturized products for applications including medical devices and microelectronics. Particularly, miniaturized desktop microforming systems based on unconventional actuators possess great potential in both high productivity and low cost. Process control of these miniaturized microforming systems, however, is challenging and still at its early stage. The challenge arises from the complicated behaviors of the actuators employed, the switching and the transition involved in the actuation/motion, and the uncertainty of the system dynamics during the entire microforming process. The dynamics and the hysteresis effects of the magnetostrictive actuator can be excited, resulting in positioning errors of the workpiece during both the trajectory tracking and the output transition phases. The rapid tracking-transition switching is also accompanied with substantial variation of the system dynamics. Moreover, the process control is further complicated by the use of multistage actuators and the augmentation of ultrasonic vibrations to the microforming process. In this paper, a control framework integrating iterative learning control and an optimal transition trajectory design along with feedforward-feedback control is proposed to achieve highspeed, high-quality microforming. The efficacy of the proposed control approach is demonstrated through experiments.Index Terms-Iterative learning control, magnetostrictive actuator, microforming, optimal output tracking transition.
Microforming requires high-precision motion due to scaling issues. A Terfenol-D transducer was considered to provide bulk motion for micro-extrusion. Because Terfenol-D cannot practically produce the necessary 2.5 mm displacement for this micro-extrusion experiment, a lever system was designed to amplify the output displacement. Compliant joints (flexures) were used to replace conventional bearings, resulting in a flexible, solid-state lever mechanism. By eliminating the backlash and static friction associated with conventional bearings, it should be possible to improve displacement precision as required to meet the geometric tolerance demands of microforming. A chief concern when designing flexure joints that see large amounts of axial loading is compliance, which leads to not only loss of motion but also loss of accuracy as the lever system responds differently under different loads. However, because Terfenol-D already has load-dependent response, this loss of accuracy is moot when coupled with a Terfenol-D prime mover, as it already requires load-dependent control. Preliminary FEM analysis has shown this design to have lever ratio losses of approximately 4% from half load to full load, with lower than predicted stress. Disciplines Manufacturing | Metallurgy CommentsThis is a conference proceeding from SPIE Proceedings 7645 (2010) ABSTRACTMicroforming requires high-precision motion due to scaling issues. A Terfenol-D transducer was considered to provide bulk motion for micro-extrusion. Because Terfenol-D cannot practically produce the necessary 2.5 mm displacement for this micro-extrusion experiment, a lever system was designed to amplify the output displacement. Compliant joints (flexures) were used to replace conventional bearings, resulting in a flexible, solid-state lever mechanism. By eliminating the backlash and static friction associated with conventional bearings, it should be possible to improve displacement precision as required to meet the geometric tolerance demands of microforming. A chief concern when designing flexure joints that see large amounts of axial loading is compliance, which leads to not only loss of motion but also loss of accuracy as the lever system responds differently under different loads. However, because Terfenol-D already has load-dependent response, this loss of accuracy is moot when coupled with a Terfenol-D prime mover, as it already requires load-dependent control. Preliminary FEM analysis has shown this design to have lever ratio losses of approximately 4% from half load to full load, with lower than predicted stress.
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