The research objective of this award is to develop distributed actuators in nanosteppers with staggered stepping schemes to maintain force control continuously in time. Currently, the loss of force control limits the use of such nano-steppers in precision trajectory tracking applications. The research will solve the following controls-related challenges: (i) manage the applied force in each nanostepper without inducing unwanted vibrations due to actuator dynamics; and (ii) design the actuator recruitment (i.e., the number of active nanosteppers at different time instants) based on the required force level. Analysis methods will be developed to investigate the effect of the recruitment procedures on the stability and performance of closed-loop systems with the distributed nanostepper. Additionally, the proposed work will design and build a proof-of-concept distributed nanostepper, and the theoretical developments will be verified experimentally.
If successful, the results of this research will improve the performance of nanopositioners used in research and development of nanosciences and nanotechnologies. Example applications include: probe positioning in scanning probe microscopy (SPM) and alignment of optical components in the opto-electronics industry. The proposed work will provide research-training and education to undergraduate and graduate students in nanotechnology. The proposed research will be introduced into undergraduate curriculum through mechatronics design projects in a senior-level capstone design class. Moreover, the resulting undergraduate projects will be used in outreach/recruitment activities in annual open houses for high-school students. Additionally, the research efforts will be disseminated through seminars, publications, and conferences. Thus, the proposed work will build the research and human resource infrastructure needed to remain competitive in high-tech and emerging-nanotechnology industries.
The goal of the project was to develop systems with distributed actuators, and design control of such distributed systems to optimize performance. For example, typical nanopositioners do not have both large range and high bandwidth. An approach is to develop multi-actuator-based steppers that can achieve infinite range without sacrificing bandwidth. However, precision could be lost due to oscillations induced during each stepping motion. The main contribution of this work was to show that appropriate control of the relative phase between the driving waveforms for the different actuators, osciall With the application of multiple actuators, we can reduce the oscillations, and lead to constant velocity for a motion stage. A modified Poincar´e map approach was used for evaluating the stability of the stepper dynamics in the presence of Coulomb-friction nonlinearity, which has a jump discontinuity with velocity. Additionally, inversion of the stepper-dynamics model was used to find the piezo input for controlling the stepper velocity, and model-based predictions of the stepper velocity were evaluated using an experimental-stepper system. Impact Research in nanotechnology is critical to US competitiveness in high-tech industries such as the development and manufacturing of future electronics and optical applications. Additionally, the study of chemistry, physics and biology at the nano-scale has applications in human health (National Nanotechnology Initiative: Leading to the Next Industrial Revolution, a Report by the Interagency Working Group on Nanoscience, Engineering and Technology, 2000). Therefore, the proposed work to improve nanopositioners (a key enabling tool in nanoscience and nanotechnology) will have broad impact on the economy and on health. Impact on training and professional Development: The research of three PhD graduate students (Scott M. Wilcox, Nathan Banka and Jiradech Kongthon) was supported by the grant. Additionally, one undergraduate student (Kurt J. Stalsberg) participated in the research through a research experience for undergraduates (REU) supplement. Impact on Courses: Research issues in piezo actuators were introduced and discussed in courses 1) Undergraduate Course: Automatic Controls, ME471, Autumn 2010 The range versus bandwidth tradeoff in piezo actuators were discussed in the Automatic Controls class. The ability to use controls to increase the bandwidth was studied. Students designed a control system to increase the bandwidth of an experimental piezo actuator. 2) Undergraduate Course: Mechanical Vibrations, ME470, Winter 2011 and Winter 2012 Vibration issues in piezo actuators were discussed in this undergraduate course. In particular, the need to increase bandwidth and the effect of the resonance vibrational frequencies in determining positioning bandwidth were used to motivate the modeling techniques. 3) Undergraduate Course: Capstone Design, ME495M, Spring 2011 and Spring 2013 Control issues (such as control of smart materials such as shape memory alloys used in high-precision positioning) were introduced into a number of capstone projects. A list of projects completed can be found at the website http://faculty.washington.edu/devasia/Teaching/Example_projects.htm . Publications Journal 1 S. Devasia "Nonlinear Minimum-Time Control With Pre- and Post-Actuation." Automatica, Vol. 47 (7), pp. 1379-1387, July 2011. 2 S. Devasia "Time-Optimal Control with Pre/Post Actuation for Dual-Stage Systems," IEEE Transactions on Control Systems Technology, Vol. 20 (2), pp. 323-334, March 2012. 3 J. Kongthon and S. Devasia "Iterative Control of Piezoactuator for Evaluating Biomimetic, Cilia-Based Micromixing," IEEE/ASME Transactions on Mechatronics, Vol. 18 (3), pp. 944-953, June 2013. 4 S. Wilcox and S. Devasia "Stability of Velocity Control for a Piezoelectric Stepper," Accepted for publication, IEEE/ASME Transactions on Mechatronics, June 2014. Conference S. Wilcox and S. Devasia. "Modeling and Feedforward Control of a Large-Range, Piezo Nano-Stepper." American Control Conference, San Francisco, CA, June 29 - July 1, 2011, pp. 2855-2860. S. Devasia. "Time-Optimal, Dual Stage, Output Transition: with Pre / Post Actuation." Proceedings of the 18th IFAC World Congress, Milan, Italy, Aug. 28 – Sept. 2, 2011. J. Kongthon and S. Devasia. "Feedforward Control of Piezoactuator for Evaluating Cilia-Based Micro-Mixing." Proc. of the 18th IFAC World Congress, Milan, Italy, Aug. 28 – Sept. 2, 2011. J. Kongthon and S. Devasia. "Iterative Inversion-Based Control of Piezoactuator for Evaluating Cilia-Based Micro-Mixing." American Control Conference, Montreal, Canada, June 22- 29, 2012. N. Banka and S. Devasia. "Nonlinear Models for Optimal-Placement of Magnetially-Actuated Cilia", Presented at the 2013 ASME Dynamic Systems and Control Conference. S. Wilcox and S. Devasia. "Precision Control through Vibration Suppression in Piezoelectric Stepper Response", Presented at the 2013 ASME Dynamic Systems and Control Conference. Scott Wilcox won the best student paper award for this paper.
