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TITLE: STIFFNESS LOCALIZATION IN SOFT AND WEARABLE ROBOTICS

ABSTRACT: The inherent compliance of soft robots renders them safe for many applications such as object manipulation, surgery, haptics, and wearable devices. Stiffness modulation is thus an essential component of soft robot design so that these applications can implement compliance reversal and provide more rigidity when needed, often when force transmission is required. However, current variable stiffening mechanisms still struggle to provide adequate stiffness changes that are fast enough to avoid affecting robot dynamics, or be interfaced with electronic components for enabling electronic control. In this thesis, magnetorheological fluids (MRF), scaffolding structures, and electronically controlled magnetic field generation are investigated as a means to enable stiffening within soft robotic systems. Magnetically induced stiffening is first explored using permanent mag-nets and scaffolding materials immersed in MRF to discover stiffening ranges and how these may be amplified. Electropermanent magnets (EPMs) are then incorporated to electronically induce an instantaneous stiffening effect in a weight-bearing task. This variable stiffening mechanism is then applied in a wearable soft robotic glove targeted for hand rehabilita-tion. By exploiting rapid stiffness changes and magnetically attractive forces generated by EPMs, the glove aims to rehabilitate several motions at the digits. Also presented is an-other jamming technique that produces instantaneous and reversible stiffening by jamming stacks of thin, flexible metal sheets that are inherently magnetic. Using EPMs to supply magnetic fields required for jamming, a wearable haptic feedback application and miniatur-ized arcade game are developed to demonstrate the quasi-static and dynamic characteristics, respectively, of this technique. Driven by the need to develop variable stiffening technologies that address the shortcom-ings of current techniques used in soft robotics, the research presented in this thesis aims to provide alternative force transmission design choices for future wearable and soft robotic systems. In doing so, the magnetic stiffening strategies developed can be implemented in applications that require compliance reversal to exhibit portability, tunability, and fast re-sponse times.

COMMITTEE: ADVISOR Professor Tommaso Ranzani, ME/MSE/BME; CHAIR Professor Chuanhua Duan, ME/MSE; Professor Theresa D. Ellis, Department of Physical Therapy; Professor Douglas Holmes, ME/MSE; Professor Sheila Russo, ME/MSE