Publications

Vibrotactile feedback enriches the use of wearable technologies for entertainment, navigation, and healthcare. The actuators of these portable systems, particularly fingertip devices, need to be compact, comfortable, and easy to integrate. Multiple vibrating elements could enhance perceptual realism, but how should they be arranged and oriented on the fingerpad? Here, we evaluate a simple approach that uses an audio input signal to drive an air coil that vibrates two magnets embedded in a soft fingertip sheath; the magnets are arranged in the radial-ulnar or proximal-distal direction with either the same or opposite polarity. We explore the effects of these new device configurations on both dynamic response and haptic perception. Experimental results indicate that the vibrations were perceived well across frequencies, with stronger sensations between 180 and 360 Hz, which aligns with the high vibration magnitudes our computational simulation predicts in this frequency range. Interestingly, perceptual responses showed that participants mainly classified vibrations based on the excitation frequency rather than the polarity of the magnets. Participants also rated vibrotactile feedback derived from recorded sounds and replayed for different interactions. Their evaluations offer promising evidence that this actuation approach could be used in extended-reality applications to improve transient user interactions with virtual objects.

The gold-standard treatment for children diagnosed with obsessive-compulsive disorder (OCD) is therapist-guided cognitive behavioral therapy (CBT), which includes exposure and response prevention (ERP) sessions that teach children to overcome compulsive responses when exposed to their anxiety-inducing triggers. CBT requires children to report frequent self-assessments of tension during both therapist-supported and therapist-free self-management ERP sessions. Videoconferencing-delivered CBT (vCBT) enables a psychotherapist to treat a child remotely in their home, where OCD symptoms often arise, but these remote therapeutic interactions lack physical presence and can be challenging to run. We propose using a robot as an input/output device during vCBT for young children diagnosed with OCD, and we introduce a stationary table-top koala robot for this application. We further describe the first of three planned participatory design phases: a co-design study comprising two sessions where child and adolescent psychotherapists role-played vCBT ERP exercises with this robot to help define its role.

Grounded force-feedback (GFF) devices, exoskeletons, and other haptic robots modulate human movement through carefully engineered mechanical, electrical, and computational designs. Given their significant societal potential and often high cost, it is essential to fairly and efficiently assess the quality of these intimate cyber-physical interfaces. However, existing device specifications and low-level performance metrics often fail to capture the nuanced qualities that expert users perceive during hands-on experimentation. To address this gap, this thesis introduces Haptify, a comprehensive benchmarking system that can thoroughly, fairly, and noninvasively evaluate GFF haptic devices. Haptify integrates multiple sensing modalities - a seven-camera optical motion-capture system, a custom-built 60-cm-square force plate, and an instrumented end-effector that can be adapted to different devices - to record the interaction between the human hand, the device, and the ground during both passive and active experiments. With this setup, users hold the device end-effector and move it through a series of carefully designed tasks while Haptify measures kinematic and kinetic responses. From this process, we establish six key ways to assess GFF device performance: workspace shape, global free-space forces, global free-space vibrations, local dynamic forces and torques, frictionless surface rendering, and stiffness rendering. These benchmarks enable systematic evaluation and comparison across devices. We first apply Haptify to benchmark two GFF devices produced by 3D Systems: the widely used Touch and the more expensive Touch X. Results reveal that the Touch X offers a slightly smaller workspace than the Touch, but it produces smaller and more predictable free-space forces, reduced vibrations, more consistent dynamic forces and torques, and higher-quality rendering of both frictionless surfaces and stiff virtual objects. To further validate and extend our approach, we conducted a user study with sixteen expert hapticians who used Haptify to evaluate four commercial GFF devices: Novint Falcon, Force Dimension Omega.3, Touch, and Touch X. Experts tested the devices in unpowered mode and across five representative virtual benchmark environments, providing extensive quantitative ratings and qualitative feedback. We distilled recurring themes from their input and analyzed correlations between expert opinions and sensor-based measurements. Our findings show that expert judgments of fundamental haptic quality indicators align closely with the metrics derived from Haptify. Moreover, device performance both unpowered and in active benchmarks can be used to predict its suitability for more complex applications, such as teleoperated surgery. By linking expert assessments with external measurement data, this thesis establishes a combined qualitative-quantitative framework for benchmarking haptic robots. This approach not only enables fair comparison across diverse devices but also establishes a direct connection between objective measurements and the subjective expertise of experienced hapticians. In doing so, it lays the foundation for more rigorous, transparent, and application-relevant evaluation of haptic technologies.

We describe the hardware design, force-rendering approach, and evaluation of a new reconfigurable haptic interface consisting of a network of hybrid motor-brake actuation modules that apply forces via cables. Each module contains both a motor and a brake, enabling it to smoothly render active forces up to 6 N using its motor and collision forces up to 186 N using its passive one-way brake. The modular design, meanwhile, allows the system to deliver rich haptic feedback in a flexible number of DoF and widely ranging configurations.

Humanoid robots and assistive devices have yet to match the efficiency and adaptability of able-bodied human walking in challenging environments. To bridge this performance gap, my projects explored the underlying mechanisms of human locomotion, focusing on the ankle push-off. Ankle push-off has a prominent role in walking due to its high-power output at the end of the stance phase, and due to the impact of its timing on the adaptability to diverse environments. The human leg catapult analogy provides a framework for the projects to understand and replicate the complex biological mechanisms that govern human walking gait. As a platform for the replication, the human-like bipedal EcoWalker robot was developed from version 1 to 3 in three consecutive projects, with iterative design and control updates tailored to each project's goals. Our findings provide insights into the separate roles of mono- and biarticular muscle-tendon units in the human leg catapult, while we also show functional details of the human leg catapult release mechanism through five distinct release processes on the EcoWalker robot. Utilizing the robot in the projects ensures that our findings are relevant to practical applications, allowing humanoid robot and assistive device developers to build on our insights, potentially reducing the performance gap in efficiency and adaptability between able-bodied human walking and artificial walking.

Keratin composites enable animals to hike with hooves, fly with feathers, and sense with skin. Mammalian whiskers are elongated keratin rods attached to tactile skin structures that extend the animal's sensory volume. We investigated the whiskers that cover Asian elephant (Elephas maximus) trunks and found that they are geometrically and mechanically tailored to facilitate tactile perception by encoding contact location in the amplitude and frequency of the vibrotactile signal felt at the whisker base. Elephant whiskers emerge from armored trunk skin and shift from a thick, circular, porous, stiff base to a thin, ovular, dense, soft tip. These functional gradients of geometry, porosity, and stiffness independently tune the neuromechanics of elephant trunk touch to facilitate highly dexterous manipulation while ensuring whisker durability.

Soft actuators offer lightweight, compliant, and safe alternatives to traditional mechanisms, but they often incur complicated actuation schemes, bulky support systems, and limited functionality when made solely from soft materials. Soft‑rigid designs that integrate rigid elements into primarily soft bodies are common, yet the potential of those rigid parts to shape actuation behavior without compromising the overall softness remains underexplored, and fabrication practices often lack reproducibility. This thesis presents two case studies of synergistic hybrid actuation systems that utilize the complementary roles of soft and rigid components to dictate temporal and spectral behavior in response to simple input commands. Between the soft and hard components, one is typically active, while the other is passive. The first case study implements a soft-active/rigid-passive approach for the medical robotics application of endoluminal locomotion. A thin hyperelastic balloon encased in an inextensible sleeve is coupled with a thicker, non-encased balloon on a single fluid supply to serve as front and rear anchors, respectively. Geometry and material selection reshape the pressure-stretch response so the rear anchor inflates and deflates before the front anchor, enabling asymmetric sequencing useful for peristaltic locomotion inside a lumen. Numerical simulation and experiments validate the characteristic curves of dip-molded balloons and alternating anchoring in rigid tubes. The approach can be extended to generate actuation patterns for sequential haptic feedback and other robotic applications. The second case study applies a soft-passive/rigid-active strategy in the domain of fingertip haptic actuation. A dip‑molded silicone sheath with embedded miniature magnets, excited by a single air‑core coil, produces localized, rich vibrotactile feedback. Simulations, mechanical measurements, and user experiments with a single-magnet design show consistent frequency‑dependent behavior and strong perceptual salience. In follow-on work, various dual‑magnet arrangements were also simulated, fabricated, and thoroughly evaluated. Classification tests indicate that frequency content is more important for perception than magnet orientation, while a realism‑rating experiment supports the feasibility of audio-driven simple commands for realistic haptic feedback. The device is demonstrated on the fingertip in virtual reality and could be adapted for other body locations for navigation, rehabilitation, or related applications. Together, these studies provide design rules, a simulation-fabrication-validation workflow, and reproducible fabrication practices for soft-rigid hybrid actuators that realize desired mechanical outputs from minimal actuation commands. The methods and findings generalize to other soft actuators and have potential applications in domains such as medical devices, wearable technologies, and soft sensing.

Vibrotactile feedback can enhance motor learning, sports training, and rehabilitation, but a lack of standardized tools limits its adoption. We developed a modular open-source hardware and software platform for delivering vibrotactile feedback that is spatially and temporally precise. The prototype device uses medical adhesive, linear resonant actuators (LRAs), and rigid 3D-printed components to standardize skin contact, avoiding the variability introduced by straps. The platform was validated by using the device's built-in accelerometers to fit a dynamic model of mechanical actuator vibration and examine how the anatomical site and body composition affect perceived vibration strength in 20 participants. Then, the platform was integrated with an optical motion-capture system to teach six participants a toe-in gait, showing potential for real-time, tailored clinical studies. By openly sharing the platform's hardware and software, we provide tools for delivering standardized vibrations and benchmarking feedback strategies in diverse applications.