This study presents a comprehensive experimental analysis of Twisted String Actuators (TSA), focused on enhancing contraction modelling accuracy and establishing a baseline for TSA tension and impedance control efficacy. A novel TSA string radius function is introduced, computing effective radii for multi-strand bundles based on axial actuator tension. The proposed model was validated in physical experiments, resulting in a reduction of maximal errors between measured and simulated actuator contraction trajectories from up to 60 % in established models to around 10% in our work. Additionally, the tension-dependent radius modification effectively reduced errors between the estimated and the measured bundle tension by an order of magnitude, marking an essential step towards TSA control independent of bundle tension measurements. TSA tension control was assessed based on four metrics: accu-racy, precision, impact stability, and bandwidth, following ISO 9283:1998 standards. The quality of tension control was found to be dependent on bundle tension, twisting angle and strand quantity, whereas impact stability was maintained in all config-urations. Joint impedance control with TSA was evaluated for perturbation stability and position control bandwidth, where the latter was enhanced with increasing joint stiffness. The presented analysis informs designers about the capabilities of TSAs in different configurations, and their respective suitability for desired applications.

This study addresses the absence of an identification framework to quantify a comprehensive dynamic model of human and anthropomorphic tendon-driven fingers, which is necessary to investigate the physiological properties of human fingers and improve the control of robotic hands. First, a generalized dynamic model was formulated, which takes into account the inherent properties of such a mechanical system. This includes rigid-body dynamics, coupling matrix, joint viscoelasticity, and tendon friction. Then, we propose a methodology comprising a series of experiments, for step-wise identification and validation of this dynamic model. Moreover, an experimental setup was designed and constructed that features actuation modules and peripheral sensors to facilitate the identification process. To verify the proposed methodology, a 3D-printed robotic finger based on the index finger design of the Dexmart hand was developed, and the proposed experiments were executed to identify and validate its dynamic model. This study could be extended to explore the identification of cadaver hands, aiming for a consistent dataset from a single cadaver specimen to improve the development of musculoskeletal hand models.

Markerless motion capture devices such as the Leap Motion Controller (LMC) have been extensively used for tracking hand, wrist, and forearm positions as an alternative to Marker-based Motion Capture (MMC). However, previous studies have highlighted the subpar performance of LMC in reliably recording hand kinematics. In this study, we employ four LMC devices to optimize their collective tracking volume, aiming to enhance the accuracy and precision of hand kinematics. Through Monte Carlo simulation, we determine an optimized layout for the four LMC devices and subsequently conduct reliability and validity experiments encompassing 1560 trials across ten subjects. The combined tracking volume is validated against an MMC system, particularly for kinematic movements involving wrist, index, and thumb flexion. Utilizing calculation resources in one computer, our result of the optimized configuration has a better visibility rate with a value of 0.05 ± 0.55 compared to the initial configuration with -0.07 ± 0.40. Multiple Leap Motion Controllers (LMCs) have proven to increase the interaction space of capture volume but are still unable to give agreeable measurements from dynamic movement.

Recent advancements in artificial hand development have primarily concentrated on enhancing adaptive grasping, dexterity, as well as the integration of biomimetic skin. However, few designs have successfully combined lightweight, cost-effective solutions, and tactile sensing along with adaptive grasping in a human-sized prototype. We propose, an open-source, highly integrated artificial hand. It leverages a compliant linkage mechanism for versatile grasping capabilities, featuring six degrees of actuation and MEMS-based tactile sensors on every fingertip.

This study addresses the critical need for diverse and comprehensive data focused on human arm joint torques while performing activities of daily living (ADL). Previous studies have often overlooked the influence of objects on joint torques during ADL, resulting in limited datasets for analysis. To address this gap, we propose an Object Augmentation Algorithm (OAA) capable of augmenting existing marker-based databases with virtual object motions and object-induced joint torque estimations. The OAA consists of five phases: (1) computing hand coordinate systems from optical markers, (2) characterising object movements with virtual markers, (3) calculating object motions through inverse kinematics (IK), (4) determining the wrench necessary for prescribed object motion using inverse dynamics (ID), and (5) computing joint torques resulting from object manipulation. The algorithm’s accuracy is validated through trajectory tracking and torque analysis on a 5+4 degree of freedom (DoF) robotic hand-arm system, manipulating three unique objects. The results show that the OAA can accurately and precisely estimate 6 DoF object motion and object-induced joint torques. Correlations between computed and measured quantities were > 0.99 for object trajectories and > 0.93 for joint torques. The OAA was further shown to be robust to variations in the number and placement of input markers, which are expected between databases. Differences between repeated experiments were minor but significant (p < 0.05). The algorithm expands the scope of available data and facilitates more comprehensive analyses of human-object interaction dynamics.

Prosthetic limb abandonment remains an unsolved challenge as amputees consistently reject their devices. Current prosthetic designs often fail to balance human-like performance with acceptable device weight, highlighting the need for optimised designs tailored to modern tasks. This study aims to provide a comprehensive dataset of joint kinematics and kinetics essential for performing activities of daily living (ADL), thereby informing the design of more functional and user-friendly prosthetic devices. Functionally required Ranges of Motion (ROM), velocities, and torques for the Glenohumeral (rotation), elbow, Radioulnar, and wrist joints were computed using motion capture data from 12 subjects performing 24 ADLs. Our approach included the computation of joint torques for varying mass and inertia properties of the upper limb, while torques induced by the manipulation of experimental objects were considered by their interaction wrench with the subject’s hand. Joint torques pertaining to individual ADL scaled linearly with limb and object mass and mass distribution, permitting their generalisation to not explicitly simulated limb and object dynamics with linear regressors (LRM), exhibiting coefficients of determination R = 0.99 ± 0.01. Exemplifying an application of data-driven prosthesis design, we optimise wrist axes orientations for two serial and two differential joint configurations. Optimised axes reduced peak power requirements, compared to anatomical configurations, by exploiting high torque correlations (r = −0.84, p < 0.05) between Ulnar deviation and wrist flexion/extension joints. This study offers critical insights into the functional requirements of upper limb prostheses, providing a valuable foundation for data-driven prosthetic design that addresses key user concerns and enhances device adoption.

Tactile sensors are becoming more prevalent in numerous research domains, including robotics, human-robot interaction, and grasping. As the development of customized soft tactile skin for various applications continues to gain momentum, there is an increasing demand for the automation of design and manufacturing processes based on user specifications. Our work presents a partially automated framework for designing and customizing silicone-based skin-like sensors for objects of arbitrary shapes. We assess the performance of stretch and contact sensors featuring custom patterns on complex surfaces, subjecting them to position control, grasping, and manipulation scenarios. Our study's findings demonstrate the feasibility of fabricating skin-like sensors effectively within a semi-automated framework, with potential applications in the aforementioned research domains.

This study reports the initial testing of a gait exoskeleton for Spinal Muscular Atrophy (SMA) patients having variable muscle strength with no balance or ambulation capabilities. To improve the quality of life of such patients, a pediatric gait exoskeleton was developed. The ATLAS exoskeleton has 8 active degrees of freedom (DOF): 2 at the hip (adduction/abduction and flexion/extension), 1 at the knee and ankle joint for flexion and extension. A feasibility test was performed to gauge the initial response of the patients. This study demonstrates that the exoskeleton was able to provide gait assistance and sit-to-stand movements effectively to the subjects. This kind of wearable exoskeleton will play a key role in the rehabilitation of SMA patients and delay further metabolic degeneration in the future.