Robustness and adaptivity: advanced control and estimation algorithms for the transverse dynamic atomic force microscope

Lead Research Organisation: University of Leicester
Department Name: Engineering

Abstract

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Description Practically validated methods

- A new improved, robust and more user friendly set-up of Bristol's Transverse Dynamic Force Microscope (relating to Objective 1)

- Development of a high speed x-y stage and positioning control (Objectives 1 and 2)

- Creation of a robust controller for non-contact scanning based on a secondary z-height signal (Objective 2)

- Improved control robustness after a redesign of existing controllers (Objective 2)

- Development of several practical procedures for creating a family of dynamic ordinary differential equations characterising the behaviour of the TDFM cantilever, starting from an accurate spatio-temporal approach (partial differential equations) and using measurements captured at a high sampling frequency from the TDFM rig. This is significant for easy design of advanced control-engineering based estimators and control laws. (Objectives 2 and 4)

- Creation of a real-time capable algorithm for the estimation of unmeasurable shear forces resulting from the cantilever interacting with a fluid layer above the specimen(Objective 4)

- Real-time identification of viscosity and elasticity coefficients within the fluid layer above the specimen (Objective 4)

In addition several other new methods have been validated in simulation (and possess solid theoretical underpinnings) but have not yet been implemented on the TDFM:

- Non-raster scanning approaches (relating to Objective 4)

- An adaptive approach for cantilever amplitude control which allows implicit estimation of the tip-to-sample distance (relating to Objectives 2 and 5)

Journal papers are under review or are being prepared with currently available results. We have addressed in our work all the 5 originally planned objectives. Further work on Objective 5 (Enhanced robust and adaptive control of the HS-TDFM cantilever system using observer based methods) is being carried out by a new PhD student Kaiqiang Zhang. Objective 5 is the most challenging and the most 'blue sky' of all the objectives. A slight change to the original objective, to the more general theme of 'nonlinear robust multi-variable control methods', was needed, as we understand now all requirements for control better. Note that the completion of the project was delayed for more than one year in 2012 by the extended construction work on a major building next to the Nano-science and Quantum Information (NSQI) Centre of the University of Bristol. The NSQI houses the experimental system, as it is, in the UK and world-wide, one of the most advanced nano-science research centres with its vibration reduced working environment. Much of the initial work in 2012 (although intense) was preparatory and directed towards redesign of the force microscope, while learning practical skills necessary for the effective use of the force microscope started only in 2013. This unplanned delay has certainly had an effect on the morale of the team. Moreover, the resignation of a researcher at the University of Bristol during that initial period in 2013 was not beneficial. (This researcher left for personal reasons.) It should be understood that the transverse dynamic force microscope is a probe microscope built from first principles. Thus, the hardware and in particular the control software has also been built in house using the most powerful FPGA-based control implementation equipment system on the market at the time of start of the project. Complete practical realization of objective 5 will require additional, upgraded FPGA-equipment. This fact has made the project challenging and exciting. Thus, in any respect, the team is very happy to have achieved the majority of the targeted objectives (while addressing them all), of which many additional results are to be published soon.
Exploitation Route Mr Kaiqiang Zhang, who worked as a research intern on this project, has successfully (co-)authored 5 conference and journal papers for this project. As a result, he obtained a PhD studentship from the University of Bristol (update of status as of 15 March 2017: 3 journal and 3 conference papers). He started his PhD research in March 2015 on advanced nonlinear control algorithms for Bristol's nano-precision devices such as the Transverse Dynamics Force Microscope under supervision of Dr Herrmann, Professor Miles and Dr Massimo Antognozzi. In preparation of further impact and the application for new funding, further actions on outcomes of the project are: The Transverse Dynamic Force Microscope has been successfully used for analysis of artificially engineered proteins (SAGE - Self-assembled peptide cages). This is a first collaboration with the Department of Chemistry: Professor Dek Woolfson is working on Protein design and its application in bionanotechnology and synthetic biology. This is a result of discussions in a funding oriented multi-disciplinary, cross university initiative at the University of Bristol has been successful (Long-term BristolBridge initiative): The objective is to use the transverse dynamic force microscope for non-contact scanning of biological specimen and the cell interior. Further discussions with the Infection and immunity research group, in the School of Cellular and Molecular Medicine, University of Bristol are being carried out. For instance, the sliding-mode based shear force detection method is a relatively generic approach with many other potential application areas and could be used in a larger scale device for viscosity and elasticity characterisation of viscous fluid layers. This has potential for investigating joint fluids in animals. This is a more speculative outcome of the discussions at the BristolBridge event. As a separate device, the development of the x-y stage for the force microscope has created a significant pool of expertise and knowledge in the design of electro-mechanical x-y stages, the use of laser-interferometry for position x-y measurements and the design and implementation of related controllers. Plans are underway to use this knowledge for projects targeting a higher technology readiness level.
Sectors Education,Healthcare,Pharmaceuticals and Medical Biotechnology
 
Description Dissemination of the results on both a formal and informal level within the two universities (University of Bristol and University of Exeter), has led to extended interest. In particular, the Institution of Mechanical Engineering (IMECHE) supported a talk at the University of Bristol on 19 March 2015 and generated the first significant impact on engineers within the region of Bristol and Bath and other researchers within the Faculty of Engineering and university wide. Moreover, a public talk at schools have created further interest in STEM subjects.
Sector Education
Impact Types Societal
 
Title FPGA-based control and estimation algorithms 
Description Implementation of robust nano-precision H_infinity-based-control algorithms and of nonlinear estimation algorithms in a fixed-point format on FPGA systems at high-implementation frequency of up to 4 MHz. This is to achieve high bandwidth for estimation or control in a real-time environment subject to limited computational resources. 
Type Of Material Computer model/algorithm 
Year Produced 2017 
Provided To Others? No  
Impact (1) Nano-precision control has enabled the non-contact scanning of bio-specimen (2) Fast real-time estimation has enabled real-time identification of shear forces, viscosity and elasticity coefficients within the fluid layer above the specimen to identify material parameters in real-time scans at nano-precision 
 
Description IMECHE Public Talk 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Professional Practitioners
Results and Impact "Engineering and its impact on biomedical research at nano-scale", 11 March 2015 19:00 - 20:00, talk held by Dr Guido Herrmann (P-I), Dr Toshiaki Hatano (Postdoctoral Researcher) & Gavindu De Silva (Research Intern)
This activity was part of the public talks organised by the Institution of Mechanical Engineering (IMECHE) within the region of Bristol and Bath.
https://nearyou.imeche.org/near-you/UK/Western/Bath---Bristol-Area/event-detail?id=10247
http://research-information.bristol.ac.uk/en/activities/engineering-and-its-impact-on-biomedical-research-at-nanoscale(897b4958-7567-40ed-aa66-68f27411154d).html
These talks are usually attended by engineers working and living within the region of Bristol and Bath. In addition, post-graduate and post-doctoral researchers, undergraduate students, members of other faculties within the University of Bristol attend. This is an ideal way of disseminating the research outcomes. This talk has sparked discussions across the Faculty of Engineering and the University.
Year(s) Of Engagement Activity 2015
URL https://nearyou.imeche.org/near-you/UK/Western/Bath---Bristol-Area/event-detail?id=10247
 
Description Talks on STEM subjects and current engineering research, e.g. the transverse dynamic force microscope, to primary, secondary and A-level students 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact Professor Stuart Burgess, one of the co-investigators, has been highly active in disseminating engineering and engineering research to schools to increase the interest in STEM and in particular in engineering subjects among primary, secondary and A-level students. During the following talks, the work on the high precision control and mechanical design problems for the Transverse Dynamics Force Microscope have been particularly mentioned:

- St Mary's, http://www.stmaryscalne.org, a secondary / A-level girls' school, SN11 0DF, Calne, Wiltshire, 28 Jan 2014
- Clifton High School, http://www.cliftonhigh.bristol.sch.uk, a primary, secondary & A-level school, BS8 3JD, Bristol, 10 March 2014
- forthcoming: Emmaus School, http://www.emmaus-school.org.uk, a primary school, BA14 6NZ, Wiltshire, 23 June 2014


Professor Stuart Burgess has been very successful with these presentations at schools. As a result, he has hosted summer placement students within the Faculty of Engineering at the University of Bristol. It is expected that similar summer placement activities will take place in the near future.
Year(s) Of Engagement Activity 2014