Improving Fine Control of Grasping Force during Hand–Object Interactions for a Soft Synergy-Inspired Myoelectric Prosthetic Hand

Fu, Qiushi; Santello, Marco

doi:10.3389/fnbot.2017.00071

Cited by 27 publications

(16 citation statements)

References 50 publications

(73 reference statements)

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“…Grip performances of the "KIT Prosthetic Hand" were evaluated by using split cylinders with diameters of 31 mm and 49 mm, containing a six degrees of freedom (DOFs) force/torque sensor (Mini 40, ATI Industrial Automation ® ), that revealed a power grasp of about 24 N [4]. Grasp force tests of the "Soft Hand Prosthesis", were performed by means of a force/torque sensor (Nano 25, ATI Industrial Automation ® ) positioned inside a split cylindrical handlebar [5]. A multi-axis dynamometer was also presented with the purpose to evaluate the grip force of human hands in a range between 5 and 250 N. The device consists of three aluminum beams covered by caps to form a cylindrical shape.…”

Section: Introductionmentioning

confidence: 99%

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Evaluation of Grip Force and Energy Efficiency of the “Federica” Hand

et al. 2021

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The actual grip force provided by a hand prosthesis is an important parameter to evaluate its efficiency. To this end, a split cylindrical handlebar embedding a single-axis load cell was designed, 3D printed and assembled. Various measurements were made to evaluate the performances of the “Federica” hand, a simple low-cost hand prosthesis. The handlebar was placed at different angular positions with respect to the hand palm, and the experimental data were processed to estimate the overall grip force. In addition, piezoresistive force sensors were applied on selected phalanxes of the prosthesis, in order to map the distribution of the grasping forces between them. The electrical current supplied to the single servomotor that actuates all the five fingers, was monitored to estimate the force exerted on the main actuator tendon, while tendon displacement was evaluated by a rotary potentiometer fixed to the servomotor shaft. The force transfer ratio of the whole system was about 12.85 %, and the mean dissipated energy for a complete cycle of closing-opening was 106.80 Nmm, resulting lower than that of many commercial prostheses. The mean grip force of the “Federica” hand was 8.80 N, that is enough to support the user in many actions of daily life, also considering the adaptive wrapping capability of the prosthesis. On average, the middle phalanges exerted the greatest grip force (2.65 N) on the handlebar, while the distal phalanges a force of 1.66 N.

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Section: Introductionmentioning

confidence: 99%

“…Another study proposed an estimation of the grip force by measuring the current absorption of the prosthesis actuator. The current absorbed by the motor is proportional to the torque generated and, in turn, to the tendon traction force and to the gripping force; however, friction must be taken into account [5].…”

Section: Introductionmentioning

confidence: 99%

Evaluation of Grip Force and Energy Efficiency of the “Federica” Hand

et al. 2021

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“…A different approach to providing sensory feedback is based on mechanotactile stimulation, consisting in a force/pressure applied in a different area (the residual limb) from the original stimulus [ 30 ]. An example is an elastic armband connected to two DC motors [ 32 ], which rotate in opposite directions to tighten or loosen the band, in order to help the user adjust the gripping force. Current mechanotactile devices are more cumbersome and heavier than vibrotactile or electrotactile devices, also resulting in higher energy consumption [ 30 ].…”

Section: Introductionmentioning

confidence: 99%

The “Federica” Hand

et al. 2021

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Hand prostheses partially restore hand appearance and functionalities. In particular, 3D printers have provided great opportunities by simplifying the manufacturing process and reducing costs. The “Federica” hand is 3D-printed and equipped with a single servomotor, which synergically actuates its five fingers by inextensible tendons; no springs are used for hand opening. A differential mechanical system simultaneously distributes the motor force on each finger in predefined portions. The proportional control of hand closure/opening is achieved by monitoring muscle contraction by means of a thin force sensor, as an alternative to EMG. The electrical current of the servomotor is monitored to provide sensory feedback of the grip force, through a small vibration motor. A simple Arduino board was adopted as the processing unit. A closed-chain, differential mechanism guarantees efficient transfer of mechanical energy and a secure grasp of any object, regardless of its shape and deformability. The force sensor offers some advantages over the EMG: it does not require any electrical contact or signal processing to monitor muscle contraction intensity. The activation speed (about half a second) is high enough to allow the user to grab objects on the fly. The cost of the device is less then 100 USD. The “Federica” hand has proved to be a lightweight, low-cost and extremely efficient prosthesis. It is now available as an open-source project (CAD files and software can be downloaded from a public repository), thus allowing everyone to use the “Federica” hand and customize or improve it.

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“…While standard high-level control systems use EMG signals only to reconstruct a position reference, more sophisticated low-level control paradigms, as mechanical impedance control (Hogan, 1984 ) can be used to determine the dynamic relation between manipulator variables, such as end-point position and force, to adapt the system performance to different requirements. It is known that even a simple implementation of this approach, such as the active tuning of the proportional gain ( Kp ) of the motor controller, can strongly modify the performance of a robotic system (e.g., Fu and Santello, 2018 ). This tuning affects both the action velocity, e.g., closing or opening, and the grip rigidity (i.e., hand stiffness).…”

Section: Introductionmentioning

confidence: 99%

Exploring Stiffness Modulation in Prosthetic Hands and Its Perceived Function in Manipulation and Social Interaction

et al. 2020

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To physically interact with a rich variety of environments and to match situation-dependent requirements, humans adapt both the force and stiffness of their limbs. Reflecting this behavior in prostheses may promote a more natural and intuitive control and, consequently, improve prostheses acceptance in everyday life. This pilot study proposes a method to control a prosthetic robot hand and its impedance, and explores the utility of variable stiffness when performing activities of daily living and physical social interactions. The proposed method is capable of a simultaneous and proportional decoding of position and stiffness intentions from two surface electro-myographic sensors placed over a pair of antagonistic muscles. The feasibility of our approach is validated and compared to existing control modalities in a preliminary study involving one prosthesis user. The algorithm is implemented in a soft under-actuated prosthetic hand (SoftHand Pro). Then, we evaluate the usability of the proposed approach while executing a variety of tasks. Among these tasks, the user interacts with other 12 able-bodied subjects, whose experiences were also assessed. Several statistically significant aspects from the System Usability Scale indicate user's preference of variable stiffness control over low or high constant stiffness due to its reactivity and adaptability. Feedback reported by able-bodied subjects reveal a general tendency to favor soft interaction, i.e., low stiffness, which is perceived more human-like and comfortable. These combined results suggest the use of variable stiffness as a viable compromise between firm control and safe interaction which is worth investigating further.

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Improving Fine Control of Grasping Force during Hand–Object Interactions for a Soft Synergy-Inspired Myoelectric Prosthetic Hand

Cited by 27 publications

References 50 publications

Evaluation of Grip Force and Energy Efficiency of the “Federica” Hand

Evaluation of Grip Force and Energy Efficiency of the “Federica” Hand

The “Federica” Hand

Exploring Stiffness Modulation in Prosthetic Hands and Its Perceived Function in Manipulation and Social Interaction

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