MechE PhD Dissertation Defense: Ramón Sánchez

TITLE: FABRICATION STRATEGIES TO ENABLE RAPID PROTOTYPING OF HAPTIC DEVICES AND EXPERIENCES

ABSTRACT: The skin, with its high density of specialized neurons, provides a rich platform for discrete communication through haptic feedback technologies. Recent developments in these technologies have been applied to enhance virtual reality environments, human-machine interaction, navigation assistance, and prosthetics. However, current manufacturing techniques for haptic devices are labor-intensive, rely on specialized equipment, and do not facilitate hardware customization, thereby limiting accessibility and broader adoption. Furthermore, current haptic devices rely on external computing units for controlling tactile patterns and intensity, often decoupling the two, which limits the quality of the haptic sensation. Herein, we propose fabrication strategies ranging from benchtop 3D printing to hybrid techniques that integrate innovative materials with intuitive interfaces, enabling customizable and accessible haptic devices. We aim to create wearable haptic devices with direct, human-in-the-loop customization of haptic cues. To simplify the creation of haptic feedback devices, we developed a toolkit comprising five wireless, wearable haptic modules that deliver the three most common tactile sensations: vibrotactile, skin-stretch, and probing. These customizable modules can operate individually or collaboratively to enable multimodal haptic experiences, serving as a versatile platform for prototyping tactile displays. While these modules are designed to be easy to manually fabricate and program, they are inherently rigid, making them less suitable for applications demanding soft, stretchable, and body-compliant designs. To enable truly body-compliant stretchable haptic electronics, we developed a 3D-printed liquid metal (LM) emulsion for wiring that sustains high strains while maintaining electrical connectivity. To fabricate stretchable electronics, the LM emulsion was integrated into a soft polymer matrix through multi-material 3D printing, with manually placed off-the-shelf electronics. The LM emulsion is not conductive upon printing but can be render highly conductive with a single axial strain at low stress (< 0.3 MPa), resulting in activation stresses that are an order of magnitude lower than previous work. The LM emulsion also exhibits a maximum conductivity that is more than 300% higher than that of similar previous work. Its high conductivity and durability under strain make it ideal for use in stretchable electronics. To integrate the LM emulsion into stretchable electronics and automate the manufacturing process, we developed a computer-aided fabrication strategy that streamlined the design and production of haptic devices. First, we created an intuitive graphical user interface (GUI) for sketching haptic devices, compatible with direct ink writing. Next, we developed an algorithm to convert circuit schematics into 3D printing commands. This strategy combines direct ink writing with automated pick-and-place of electronics in a single fabrication step. Using this process, we fabricated a wireless, self-powered tactile display comprising a haptic input device and a haptic output device. Together, these devices enable immersive human-to-human interactions by mapping real-time pressure patterns through the input device and generating proportional vibrotactile feedback with the output device. This approach represents a significant step toward enabling rapid prototyping of both haptic devices and haptic experiences.

COMMITTEE: ADVISOR Professor J. William Boley, ME/MSE; CHAIR Professor Brian Walsh, ME/ECE; Professor Roberto Tron, ME/SE; Professor Sean Andersson, ME/SE; Professor Andrew Sabelhaus, ME/SE