Modeling and control of a bioinspired, distributed electromechanical actuator system emulating a biological spine

Ku, Bonhyun

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https://hdl.handle.net/2142/129376 Copy

Description

Title

Modeling and control of a bioinspired, distributed electromechanical actuator system emulating a biological spine

Author(s)

Ku, Bonhyun

Issue Date

2025-04-16

Director of Research (if dissertation) or Advisor (if thesis)

Banerjee, Arijit

Doctoral Committee Chair(s)

Banerjee, Arijit

Committee Member(s)

• Haran, Kiruba S.
• Hauser, Kris
• Kim, Joohyung
• Ramos, Joao

Department of Study

Electrical & Computer Eng

Discipline

Electrical & Computer Engr

Degree Granting Institution

University of Illinois Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Bioinspired actuator
• distributed actuator
• gearless actuator
• robotic spine

Abstract

The spine plays a crucial role in the anatomy and function of animals, serving as the central structural support that enables movement, flexibility, and stability. It not only protects the spinal cord, which is essential for transmitting neural signals between the brain and the rest of the body, but also provides the framework for muscle attachment, allowing for a wide range of motion. The spine's segmented structure, consisting of vertebrae, intervertebral discs, and associated ligaments, allows for both rigidity and flexibility, enabling animals to perform complex movements such as bending, twisting, and maintaining balance. In various species, the spine's design is adapted to meet specific locomotion needs, from the serpentine undulations of snakes to the upright posture of humans. The robotic spine holds significant promise for enhancing the mobility, flexibility, and overall functionality of snake-like, quadruped, and humanoid robots. A standard approach to developing an articulated spine uses geared motors to imitate vertebrae. However, rather than employing geared motors with 360-degree rotation, a bio-inspired gearless electromechanical actuator was proposed and developed as an alternative, specifically for humanoid spine applications. The actuator trades off angular flexibility for torque, while the geared motor trades off speed for torque. This thesis describes the actuation principle of the proposed actuator and dynamical model of the actuator that includes both the electrical and mechanical models. The analytical electrical and mechanical models are validated using finite element analysis (FEA), simulation, and experimental results. A system-level design methodology of the distributed actuator and a detailed clamp design is developed. The design procedure is based on a given constraints, such as box volume and bending angle for the spine. Module dimensions are determined while varying the module number and module length. Human-sized humanoid THORMANG 3’s torso volume was used for the volume constraint of the design procedure. Compared to the prototype that creates 1.42 Nm/kg specific torque developed, the system-level actuator design considerably increased specific torque to 10.2 Nm/kg. Moreover, the proposed trapezoidal limb design results in at least a 41.2\% torque improvement in the entire angular positions. The proposed actuator is also compared with conventional geared motors in terms of torque, acceleration, and copper loss for a vertebra's angular flexibility. When its angular flexibility is lower than 14 degrees, the proposed actuator achieves higher torque capability without gears than with conventional motors. Reduced angular flexibility, resulting in smaller airgaps between modules, allows the proposed actuator to generate significantly stronger torque for the same input power than geared motors. Control of an articulated spine is important for humanoids’ dynamic and balanced motion. Although there have been many spinal structures for humanoids, their actuation is still limited due to the usage of geared motors for joints. This thesis introduces position control of a distributed electromechanical spine in a vertical plane. The actuator's nonlinear electrical and mechanical dynamic models are utilized for position control in a six-module distributed spine. The spine mechanical dynamics model is approximated as an open chain. Gravitational and spring torques are compensated for the control. Moreover, torque-to-current conversion for the actuator is developed. Two position-control architectures are introduced: one featuring an outer-loop PI position controller with an inner-loop PI current controller, and the other combining an outer-loop PI position controller with an inner-loop PI torque controller. Experimental results show the implemented control of the electromechanical spine for undulatory motions. Additionally, the load capability of the spine is analyzed and validated with a load attached on top of the spine.

Graduation Semester

2025-05

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/129376

Copyright and License Information

Copyright 2025 Bonhyun Ku

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