Skin Sensitivity Assessment Using Smartphone Haptic Feedback.

Goal: This work presents a smartphone application to assess cutaneous sensory perception by establishing Vibrational Perception Thresholds (VPTs). Cutaneous sensory perception diagnostics allow for the early detection and symptom tracking of tactile dysfunction. However, lack of access to healthcare and the limited frequency of current screening tools can leave skin sensation impairments undiscovered or unmonitored. Methods: A 23-participant cross-sectional study in subjects with a range of finger sensation tests Smartphone Established VPTs (SE-VPTs) by varying device vibrational intensity. These are compared against monofilament test scores, a clinical measure of skin sensitivity. Results: We find a strong positive correlation between SE-VPTs and monofilament scores ([Formula: see text] = 0.86, p = 1.65e-07). Conclusions: These results demonstrate the feasibility of using a smartphone as a skin sensation screening tool.

A Wearable Testbed for Studying Variable Transmission in Body-Powered Prosthetic Gripping.

For those with upper limb absence, body-powered prostheses continue to be popular for many activities despite being an old technology; these devices can provide both inherent haptic feedback and mechanical robustness. Yet, they can also result in strain and fatigue. Body-powered prosthetic graspers typically consist of a simple lever providing a relatively constant transmission ratio between the input forces from the user's shoulder harness and the grip force of their prosthetic prehensor. In the field of robotic hand design, new continuously varying transmissions demonstrate particular promise in generating a wide range of grasping speeds without sacrificing grip strength. These benefits, if applied to shoulder-driven prosthetic grippers, have the potential to both reduce shoulder exertion and fatigue. This work presents the integration of a continuously variable transmission into a body-powered, voluntary close prosthetic testbed. We introduce the design and validate its performance in a benchtop experiment. We compare constant transmission conditions with a force-dependent, continually varying condition. The device is mounted on a prosthetic emulator for a preliminary wearable demonstration.

Characterizing the Force-Motion Tradeoff in Body-Powered Transmission Design.

Upper-limb prosthesis users continue to reject devices despite continued research efforts. Today, the passive topology of body-powered prehensors, which physically transmits grasp force and position data between user and device, results in improved performance over myoelectric alternatives. However, the loads and postures on the user's body also result in discomfort, fatigue, and worsened grasp force control. Despite the long history and everyday adoption of body-powered prehensors in society, the measurement of how specific body loads and postures affect grasp performance and user experience has yet to be systematically studied. In this work, we present a body-powered prosthesis emulator to independently change required input forces and motions to study the positive and negative effects provided by the inherent haptic feedback. Using a simulated grasping task, we collect functional and qualitative data from 15 participants using a shoulder harness interface. Outcomes show that lowering required input motions and forces independently reduces negative outcomes, with diminishing returns below 1:1 output mappings. Given the tradeoff between force and motion in traditional body-powered transmissions, a transmission ratio of 1:1 balances both requirements. The purpose of this study is to inform future prehensor designs that leverage the transparency of body-power to deliver high functionality while mitigating user discomfort.

Effect of variable transmission on body-powered prosthetic grasping.

Body-powered upper-limb prostheses remain a popular option for those with limb absence due to their passive nature. These devices typically feature a constant transmission ratio between the forces input by the user and the grasp forces output by the prosthetic gripper. Work incorporating continuously variable transmissions into robotic hands has demonstrated a number of benefits in terms of their motion and forces. In this work, we use a custom prosthesis emulator to evaluate the viability of applying variable transmissions to a body-powered prosthetic context. With this haptics test bed, we measured user performance during a grasping and lift task under a variety of transmission ratio conditions and with three different test objects. Results indicate that use of a variable transmission leads to the successful manipulation of a wider variety of objects than the constant transmission ratio systems, while requiring less shoulder motion. Analysis also shows a potential tendency for users to apply higher grasp forces than necessary, when compared to constant transmission conditions. These findings suggest a multifaceted effect on grasp performance with both benefits and drawbacks when considering a variable approach that supports the continued study of variable transmissions in assisted grasping.

Motor-Augmented Wrist-Driven Orthosis: Flexible Grasp Assistance for People with Spinal Cord Injury.

This paper presents the design of a motor-augmented wrist-driven orthosis (MWDO) for improved grasp articulation for people with C6-C7 spinal cord injuries. Based on the traditional passive, wrist-driven orthotic (WDO) mechanism, the MWDO allows for both body-powered and motorized actuation of the grasping output thus enabling more flexible and dexterous operation. Here, the associated control scheme enables active decoupling of wrist and finger articulation, which can be useful during certain phases of manipulation tasks. An additional modification to the traditional WDO is the integration of a magnetic latch at the Distal Interphalangeal (DIP) joint allowing for improved pinching. These abilities are demonstrated with common activities of daily living (ADL).