
NSF Org: |
CMMI Division of Civil, Mechanical, and Manufacturing Innovation |
Recipient: |
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Initial Amendment Date: | March 11, 2019 |
Latest Amendment Date: | March 11, 2019 |
Award Number: | 1855354 |
Award Instrument: | Standard Grant |
Program Manager: |
Y. Kevin Chou
CMMI Division of Civil, Mechanical, and Manufacturing Innovation ENG Directorate for Engineering |
Start Date: | March 15, 2019 |
End Date: | February 28, 2022 (Estimated) |
Total Intended Award Amount: | $220,334.00 |
Total Awarded Amount to Date: | $220,334.00 |
Funds Obligated to Date: |
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History of Investigator: |
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Recipient Sponsored Research Office: |
1109 GEDDES AVE STE 3300 ANN ARBOR MI US 48109-1015 (734)763-6438 |
Sponsor Congressional District: |
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Primary Place of Performance: |
MI US 48109-1274 |
Primary Place of
Performance Congressional District: |
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Unique Entity Identifier (UEI): |
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Parent UEI: |
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NSF Program(s): | AM-Advanced Manufacturing |
Primary Program Source: |
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Program Reference Code(s): |
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Program Element Code(s): |
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Award Agency Code: | 4900 |
Fund Agency Code: | 4900 |
Assistance Listing Number(s): | 47.041 |
ABSTRACT
Nanopositioning stages are mechanical devices used for precise positioning in a wide range of nanotech processes, ranging from spectroscopy to micro additive manufacturing. Hence, their precision, speed and cost are critical to precision engineering applications in the automotive, aerospace and defense industries, and therefore directly impact economic welfare and national security. Stages that use mechanical (i.e., sliding or rolling) bearings are currently the only commercially viable option for a growing number of large-displacement nanopositioning applications. However, mechanical bearing stages suffer from poor precision and low positioning speeds due to the adverse effects of friction. This award supports a scientific investigation into a simple but effective approach for mitigating the effects of pre-motion friction on mechanical bearing stages by connecting the bearing to the stage using a compliant joint. Knowledge created through this investigation will increase the positioning speed and precision of mechanical bearing stages without significantly increasing their cost, hence contributing to the commercial viability of nanotech processes. Its broader impact plan includes: (i) collaborations with Aerotech, Inc., a U.S.-based nanopositioning stage manufacturer, to facilitate knowledge and technology transfer; (ii) educational curriculum development at two universities and training of professional engineers through tutorials offered by the American Society for Precision Engineering; and (iii) outreach to underrepresented minority middle school students, aimed at inspiring and equipping the next generation of highly-skilled manufacturing engineers.
The objective of this research is to gain a fundamental understanding of the dynamics and compensation of nonlinear pre-motion friction acting on a servo-controlled mass through a friction isolator. Empirical studies have demonstrated significant improvements in positioning precision and speed when a servo-controlled mass (e.g., a nanopositioning stage) interacts with nonlinear pre-motion friction through a friction isolator (i.e., a compliant joint). However, very little is known about the dynamics of the friction isolator. The premise of this research is that, under certain circumstances, harmful dynamic phenomena (e.g., limit cycles) could occur when pre-motion friction acts on a servo-controlled mass through a friction isolator. This premise will be tested scientifically, to discover the harmful phenomena and circumstances that give rise to them, leading to insights on how to avoid them. To achieve this goal, mathematical characterizations of interactions between friction, friction isolator and servo parameters (e.g., mass, stiffness and damping) will be made using various tools, like the method of multiple scales, from nonlinear dynamic analysis. This will be complemented by rigorous numerical and physical experimentation on mechanical bearing nanopositioning stages, to guide, validate or refine the mathematical characterizations.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
Nanopositioning (NP) stages are used for ultra-precise positioning in a wide range of processes, ranging from spectroscopy to micro additive manufacturing. They can be constructed using flexure, fluidic, magnetic or mechanical bearings. Of these choices, mechanical bearing NP (MB-NP) stages are the most cost effective, and are currently the only commercially viable option for a growing number of large-motion-range NP applications that must be performed in high vacuum environments. However, MB-NP stages experience nonlinear pre-motion (or 'static') friction arising from their inherent rolling elements, end seals/wipers, and lubricants. Pre-motion friction adversely affects the precision and speed of MB-NP stages, making them inferior to those of other bearing types. Model-based friction compensation methods are commonly used to address this problem. However, the methods suffer from very poor robustness and limited practicality due to the complexity and extreme variability of friction dynamics at the micro scale. The PI's research group observed in experiments that the effectiveness and robustness of model-based friction compensation could be greatly enhanced by connecting a mechanical bearing to a NP stage using a joint that is very compliant in the motion direction (and stiff in non-motion directions). Such a joint is called a friction isolator. The beauty of the friction isolator is that it is very simple and practical, and holds potential to deliver large improvements in the motion precision and speed of MB-NP stages at low cost.
Intellectual Merit
The objective of this research is to gain a fundamental understanding of the dynamics and compensation of nonlinear friction acting on a servo-controlled mass through a friction isolator (FI). Knowledge gained through this research will, at low cost, enable large improvements in the precision and motion speed of NP stages and other manufacturing machines guided by mechanical (i.e., rolling and sliding) bearings. Three tasks were proposed as part of its intellectual merit:
Task 1: Modeling and Exploratory Numerical Experiments on the FI
Task 2: Theoretical Analysis of the FI
Task 3: Experimental Validation of the FI
As part of Task 1, numerical studies on a rudimentary dynamic model of a PD-controlled motion stage with LuGre friction showed that the addition of FI shrinks the range of servo gains that can stabilize the motion stage. Linear stability analysis in the vicinity of equilibriums confirmed the numerical results. Further numerical studies showed that FI can reduce the amplitudes of limit cycles and prevent unbounded error, hence improve the precision of the motion stage.
As part of Task 2 of the proposed work, the effects of friction parameters on the stability of a precision motion system with and without a FI were analyzed theoretically and numerically. The following conclusions were reached:
- The dynamics of a motion stage with FI share similar characteristics as that without FI. Unless a very large integral gain is used in the motion controller, the stability of the system under the PID controller is dominated by the proportional and derivative gains.
- The FI can increase the stability region of the controlled motion system. Large stiffness or damping of the FI may lead to larger regions for stable PID gain selection, in particular, allowing larger stable integral gain to be paired with small proportional and derivative gain for faster steady-state error convergence. Raising FI damping and lowering integral gain also allow a more flexible table-bearing mass ratio and larger payload capacity.
As part of Task 3, a rigorous experimental study of a stage with FI was performed to provide guidelines on the effect of FI stiffness and damping on the performance of FI in point-to-point and tracking motions. The results indicate the following:
- The FI stiffness should be an order-of-magnitude smaller than the initial value of pre-motion frictional stiffness.
- The accuracy of model-based friction compensation improves when the stiffness of the FI reduces.
- When using FI for tracking applications, its stiffness should be designed as small as possible with a large enough damping coefficient.
Broader Impacts
The project team collaborated with Aerotech Inc. to help translate the FI to industry. Aerotech Inc provided in-kind support and industry advise for this project. This project also initiated a collaboration with researchers from the Korea Institute for Machinery and Materials (KIMM) who worked with our team to apply the FI to a roll-to-roll manufacturing system. Together, we demonstrated a 3x increase in roller speed without sacrificing precision using the FI.
The projects has trained a PhD student and an undergraduate student, while providing mentorship to a visiting scholar from industry. The PhD student mentored through this project is now a Senior Robotics Scientist at 3M.
The results of this project have been disseminated in manufacturing and vibration conferences. They have also been published in very reputable journals in manufacturing, mechatronics and vibration. A total of 5 journal papers, 6 conference papers and two US patents are associated with this project.
Last Modified: 07/12/2022
Modified by: Chinedum Okwudire
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