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1. Robotically adjustable kinematics in a wrist-driven orthosis eases grasping across tasks

   Chang, Erin; McPherson, Andrew; Stuart, Hannah (December 2024, IEEE)

   Without finger function, people with C5-7 spinal cord injury (SCI) regularly utilize wrist extension to passively close the fingers and thumb together for grasping. Wearable assistive grasping devices often focus on this familiar wrist-driven technique to provide additional support and amplify grasp force. Despite recent research advances in modernizing these tools, people with SCI often abandon such wearable assistive devices in the long term. We suspect that the wrist constraints imposed by such devices generate undesirable reach and grasp kinematics. Here we show that using continuous robotic motor assistance to give users more adaptability in their wrist posture prior to wrist-driven grasping reduces task difficulty and perceived exertion. Our results demonstrate that more free wrist mobility allows users to select comfortable and natural postures depending on task needs, which improves the versatility of the assistive grasping device for easier use across different hand poses in the arm’s workspace. This behavior holds the potential to improve ease of use and desirability of future device designs through new modes of combining both body-power and robotic automation. 

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2. Improvement of hand functions of spinal cord injury patients with electromyography-driven hand exoskeleton: A feasibility study

   https://doi.org/10.1017/wtc.2020.9  

   Yun, Youngmok; Na, Youngjin; Esmatloo, Paria; Dancausse, Sarah; Serrato, Alfredo; Merring, Curtis A.; Agarwal, Priyanshu; Deshpande, Ashish D. (January 2020, Wearable Technologies)

   null (Ed.)

   Abstract We have developed a one-of-a-kind hand exoskeleton, called Maestro, which can power finger movements of those surviving severe disabilities to complete daily tasks using compliant joints. In this paper, we present results from an electromyography (EMG) control strategy conducted with spinal cord injury (SCI) patients (C5, C6, and C7) in which the subjects completed daily tasks controlling Maestro with EMG signals from their forearm muscles. With its compliant actuation and its degrees of freedom that match the natural finger movements, Maestro is capable of helping the subjects grasp and manipulate a variety of daily objects (more than 15 from a standardized set). To generate control commands for Maestro, an artificial neural network algorithm was implemented along with a probabilistic control approach to classify and deliver four hand poses robustly with three EMG signals measured from the forearm and palm. Increase in the scores of a standardized test, called the Sollerman hand function test, and enhancement in different aspects of grasping such as strength shows feasibility that Maestro can be capable of improving the hand function of SCI subjects. 

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3. A Hybrid Active-Passive Actuation and Control Approach for Kinesthetic Handheld Haptics

   https://doi.org/10.1109/HAPTICS45997.2020.ras.HAP20.12.af578b0a  

   Dills, Patrick; Colonnese, Nick; Agarwal, Priyanshu; Zinn, Michael (March 2020, 2020 IEEE Haptics Symposium (HAPTICS))

   Handheld haptic devices are often limited in rendering capability, as compared to traditional grounded devices. Strenuous design criteria on weight, size, power consumption, and the ungrounded nature of handheld devices, can drive designers to prioritize actuator force or torque production over other components of dynamic range like bandwidth, transparency, and the range of stable impedances. Hybrid actuation, the use of passive and active actuators together, has the potential to increase the dynamic range of handheld haptic devices due to the large passive torque capability, the stabilizing effects of passive actuators, the high bandwidth of conventional DC servomotors, and the synergy between actuators. However, to date the use of hybrid actuation has been limited due to the highly nonlinear torque characteristics of available passive actuators that result in poor rendering accuracy. This paper describes a hybrid actuation approach and novel control topology which aims to solve actuation challenges associated with nonlinear passive actuators in hybrid and handheld haptic devices. The performance of the device is assessed experimentally, and the approach is compared to existing handheld devices. 

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4. Stability and Rendering Limitations of a Parallel Hybrid Active-Passive Haptic Interface

   https://doi.org/10.1109/HAPTICS52432.2022.9765621  

   Dills, Patrick; Dawson-Elli, Alexander; Gruben, Kreg; Adamczyk, Peter; Zinn, Michael (March 2022, IEEE Haptics Symposium 2022 (HAPTICS))

   Impedance based kinesthetic haptic devices have been a focus of study for many years. Factors such as delay and the dynamics of the device itself affect the stable rendering range of traditional active kinesthetic devices. A parallel hybrid actuation approach, which combines active energy supplying actuators and passive energy absorbing actuators into a single actuator, has recently been experimentally shown to increase the range of stable virtual stiffness a haptic device can achieve when compared to the active component of the actuator alone. This work presents both a stability and rendering range analysis that aims to identify the mechanisms and limitations by which parallel hybrid actuation increases the stable rendering range of virtual stiffness. Increases in actuator stability are analytically and experimentally shown to be linked to the stiffness of the passive actuator. 

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5. Haptic Feedback Relocation from the Fingertips to the Wrist for Two-Finger Manipulation in Virtual Reality

   https://doi.org/10.1109/IROS47612.2022.9981392  

   Palmer, Jasmin E.; Sarac, Mine; Garza, Aaron A.; Okamura, Allison M. (October 2022, IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS))

   Relocation of haptic feedback from the fingertips to the wrist has been considered as a way to enable haptic interaction with mixed reality virtual environments while leaving the fingers free for other tasks. We present a pair of wrist-worn tactile haptic devices and a virtual environment to study how various mappings between fingers and tactors affect task performance. The haptic feedback rendered to the wrist reflects the interaction forces occurring between a virtual object and virtual avatars controlled by the index finger and thumb. We performed a user study comparing four different finger-to-tactor haptic feedback mappings and one no-feedback condition as a control. We evaluated users' ability to perform a simple pick-and-place task via the metrics of task completion time, path length of the fingers and virtual cube, and magnitudes of normal and shear forces at the fingertips. We found that multiple mappings were effective, and there was a greater impact when visual cues were limited. We discuss the limitations of our approach and describe next steps toward multi-degree-of-freedom haptic rendering for wrist-worn devices to improve task performance in virtual environments. 

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