Large load manipulation and controller design with flexible joint manipulators

Authors
Oakes, Kimberly
ORCID
https://orcid.org/0000-0002-7695-2900
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Other Contributors
Julius, Anak Agung
Mishra, Sandipan
Anderson, Kurt S.
Wen, John T.
Issue Date
2022-05
Keywords
Electrical engineering
Degree
PhD
Terms of Use
Attribution-NonCommercial-NoDerivs 3.0 United States
This electronic version is a licensed copy owned by Rensselaer Polytechnic Institute (RPI), Troy, NY. Copyright of original work retained by author.
Full Citation
Abstract
Recent years have seen an increased interest in the use of flexible joint robots. This is due to wider use of collaborative and space robots. Flexibility is desired for collaborative robots because the inherent compliance makes interactions with humans safer. Space manipulator flexibility results from harmonic drives used to amplify the torque generated by the small actuators used to keep arm mass low for launch. Both situations require precise tracking of desired movements. However, this is difficult to achieve due to the inherent nonlinearity of flexible joint manipulators. There exist model-based and neural network based methods of controller design. However, these methods may result in complex controllers that require a high computational load. In space applications, there exist computational limitations that prevent the use of such control methods. For this reason, most space manipulators use simple controllers such as PID. Tuning the gains is difficult not only because of the arm nonlinearity but also because the arm operates both without and with large loads. Gain scheduling may be used to address the various operation modes. However, it would be desirable to have a single set of controller gains to prevent non-smooth transitions in controller output resulting from the gain changes. Whether designing one set or multiple set of gains, the tuning process can be very time consuming. Common methodologies require understanding of complex mathematics (such as for H-infinity methods) or a lot of active time from the control designer (such as hand-tuning). Therefore a methodology that can be implemented with basic controller design knowledge and consumes less of the controller designer's time is desirable. This thesis seeks to develop a methodology to generate robust, simple controllers for flexible joint robots that achieve the desired performance while operating both without and with a large load. The methodology consists of experiment design to gather experimental frequency response data, path generation, trajectory generation, and optimization problem formulation for controller design. The methodology is tested using a simulated arm and Rethink's Baxter robot. The simulated arm is an approximation to a space manipulator with seven degrees of freedom and joint flexibility. The simulation is performed using Simulink and Simscape Multibody. Baxter is a dual-arm industrial robot with each arm containing seven degrees of freedom. Baxter's joint flexibility results from series elastic actuators.
Description
May 2022
School of Engineering
Department
Dept. of Electrical, Computer, and Systems Engineering
Publisher
Rensselaer Polytechnic Institute, Troy, NY
Relationships
Rensselaer Theses and Dissertations Online Collection
Access
CC BY-NC-ND. Users may download and share copies with attribution in accordance with a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 license. No commercial use or derivatives are permitted without the explicit approval of the author.