A sizzling hand prosthesis: On the design and development of a pneumatically powered hand prosthesis for children

Mechanical, Maritime and Materials Engineerin

Comparison of mechanical properties of silicone and PVC (polyvinylchloride) cosmetic gloves for articulating hand prostheses

Current articulating electric and body-powered hands have a lower pinch force (15–34 N) than electric hands with stiff fingers (55–100 N). The cosmetic glove, which covers a hand prosthesis, negatively affects the mechanical efficiency of a prosthesis. The goal of this study is to mechanically compare polyvinylchloride (PVC) and silicone cosmetic gloves and quantify the stiffness of the finger joints, the required actuation energy, and the energy dissipation during joint articulation. Six cosmetic gloves, identical in size but made from different materials, were mechanically tested: three PVC and three silicone. The silicone gloves required less work and dissipated less energy during flexing. They also had a lower joint stiffness and required a lower maximum joint torque. Based on energy requirements, joint stiffness, and required joint torque, the tested silicone glove is most suitable for application on an articulating hand prosthesis.BioMechanical EngineeringMechanical, Maritime and Materials Engineerin

Efficiency of voluntary closing hand and hook prostheses

The Delft Institute of Prosthetics and Orthotics has started a research program to develop an improved voluntary closing, body-powered hand prosthesis. Five commercially available voluntary closing terminal devices were mechanically tested: three hands [Hosmer APRL VC hand, Hosmer Soft VC Male hand, Otto Bock 8K24] and two hooks [Hosmer APRL VC hook, TRS Grip 2SS]. The test results serve as a design guideline for future prostheses. A test bench was used to measure activation cable forces and displacements, and the produced pinch forces. The measurements show that the hands require higher activation forces than the hooks and 1.5 to 8 times more mechanical work. The TRS hook requires the smallest activation force (33 N for a 15 N pinch force) and has the lowest energy dissipation (52 Nmm). The Hosmer Soft hand requires the largest activation force (131 N for a 15 N pinch force) and has the highest energy dissipation (1409 Nmm). The main recommendations for future prostheses are the following: (1) Required activation forces should be below the critical muscle force (~18% of maximum), to enable continuous activation without muscle fatigue. (2) Hysteresis of mechanism and glove should be lowered, to increase efficiency and controllability.BioMedical EngineeringMechanical, Maritime and Materials Engineerin

Ipsilateral Scapular Cutaneous Anchor System: An alternative for the harness in body-powered upper-limb prostheses

Background: Body-powered prosthesis users frequently complain about the poor cosmesis and comfort of the traditional shoulder harness. The Ipsilateral Scapular Cutaneous Anchor System offers an alternative, but it remains unclear to what extent it affects the perception and control of cable operation forces compared to the traditional shoulder harness.Objective: To compare cable force perception and control with the figure-of-nine harness versus the Ipsilateral Scapular Cutaneous Anchor System and to investigate force perception and control at different force levels.Study design: Experimental trial.Methods: Ten male able-bodied subjects completed a cable force reproduction task at four force levels in the range of 10–40 N using the figure-of-nine harness and the Anchor System. Perception and control of cable operating forces were quantified by the force reproduction error and the force variability.Results: In terms of force reproduction error and force variability, the subjects did not behave differently when using the two systems. The smallest force reproduction error and force variability were found at the smallest target force level of 10 N.Conclusion: The Anchor System performs no differently than the traditional figure-of-nine harness in terms of force perception and control, making it a viable alternative. Furthermore, users perceive and control low operation forcesbetter than high forces.Biomechatronics & Human-Machine Contro

Design, fabrication, and preliminary results of a novel below knee prosthesis for snowboarding: A case report

Snowboarding with a below-knee prosthesis is compromised by the limited rotation capabilities of the existing below-knee prostheses, which are designed for use in normal walking. Based on snowboarding range of motion analyses, a novel below-knee prosthesis was designed with the aim to achieve similar range of motions like able-bodied snowboarders. The new prosthesis allows for passive inversion/eversion, passive plantarflexion/dorsiflexion and additional ‘voluntary’ plantarflexion/dorsiflexion initiated by lateral or medial rotation of the upper leg and knee. A prototype was tested on a single subject, a professional snowboarder. The results indicate that snowboarding with the new prosthesis is more comparable to able-bodied snowboarding.Biomechanical EngineeringMechanical, Maritime and Materials Engineerin

Design of a cosmetic glove stiffness compensation mechanism for toddler-sized hand prostheses

The addition of a cosmetic glove to an upper limb prosthesis has a distinct effect on the cosmetic value, but its viscoelastic behaviour adds a substantial amount of stiffness and hysteresis to the system. As a result, the overall usability of the prosthesis is degraded. A novel negative stiffness element is designed to compensate for the cosmetic glove’s stiffness. A combination of linear helical springs and the concept of rolling link mechanisms has resulted in a Rolling Stiffness Compensation Mechanism (RSCM). Results show that the RSCM is capable of exerting a progressive negative stiffness characteristic and can be built small enough to fit inside a 33 mm diameter wrist. Using the RSCM, an otherwise voluntary opening toddler-sized prosthesis is converted into a voluntary closing device, reducing maximum operation forces down to 40 N with a combined efficiency of 52%. Further adjustments to the design are possible to further improve the efficiency of the mechanism. Moreover, changes in geometric relations of the mechanism offers possibilities for a wide range of prostheses and other applications.Biomechatronics & Human-Machine Contro

Simplifying models and estimating grasp performance for comparing dynamic hand orthosis concepts

While designing a dynamic hand orthosis to assist during activities of daily living, the designer has to know whether a concept will have sufficient grasp performance to support these activities. This is often estimated by measuring the interaction force at the contact interface. However, this requires a prototyping step and limits the practicality of comparing several concepts in an early design stage. Alternatively, this study presents and compares basic static and dynamic models to numerically estimate grasp performance. This was applied on an exemplary concept for a hydraulically operated hand orthosis grasping a circular object. The models were validated with an experimental set-up that does not require sensors at the contact interface. Static and dynamic model results were almost identical, where the static model could be around 10 times faster and is generally more robust to a high contact stiffness. Both models were unable to make accurate quantitative predictions, which is believed to be due to differences in used contact stiffness. However, the models were able to make correct qualitative comparisons, making it a valid method to compare and choose concepts in an early design stage.Biomechatronics & Human-Machine ControlPrecision and Microsystems EngineeringMechatronic Systems Desig

Methods for reducing energy dissipation in cosmetic gloves

For cosmetic reasons, hand prostheses are provided with cosmetic gloves. Their pleasing appearance, however, is accompanied by poor mechanical behavior, resulting in a negative influence on prosthesis operation. Glove stiffness is high and nonlinear, and internal friction in the glove material causes energy dissipation (hysteresis). In this article, two methods for reducing hysteresis in cosmetic gloves are proposed, that may be applied independently or in combination. Glove modification. Altering the mechanical properties of the glove itself is the first method that is presented. It was found possible to reduce both stiffness and hysteresis about 50% by forming grooves into the inside of the glove. Together with the evaluation of this method, several properties of the cosmetic glove were determined. Motion optimization. Additionally, a second method for reducing hysteresis was developed. The amount of hysteresis is influenced by the way the glove is forced to deform. The prosthesis mechanism, determining this deformation, was designed for minimum hysteresis and maximum cosmesis. For the prosthesis-glove combination used in this study, thumb motion optimization reduced hysteresis by about 65%.Mechanical, Maritime and Materials Engineerin

A need for a more user-centered design in body powered prostheses

Users of body powered prostheses (BPP) complain about too high operating forces, leading to pain and/or fatigue during or after prosthetic operation. In the worst case nerve and vessel damage can occur [1, 2], leading to nonuse of prostheses. Smit et al. investigated cable forces and displacements required to operate commercially available voluntary closing and voluntary opening hands and hooks [3, 4]. The capacities of prosthetic users to operate these terminal devices remain unknown. Taylor reported in 1954 forces and displacements measured with 50 ‘normal’ subjects for arm flexion (280±24 N; 5.3±1.0 cm), shrug (270±106 N; 5.7±1.5 cm) and arm extension (251±29 N; 5.8±1.7 cm) (mean±SD) [5]. Unfortunately, the measurement procedure is unclear. Moreover, the study reported forces and displacements from isolated movements instead of combinations of movements typically used for BPP operation. Our recent pilot experiments on 10 male subjects (28±2 years old) also without arm defects using a BPP harness revealed average values of 475 N and a peak value of 970 N for one subject. Although these values are higher, it remains unclear if these force levels are sufficient to comfortably operate a BPP, or too low leading to non-use. Importantly, knowing the capacities and limitations of prosthetic users will aid in choosing and redesigning future BPPs to prevent non-use.Biomechatronics & Human-Machine Contro

Assessment of Body-Powered Upper Limb Prostheses by Able-Bodied Subjects, using the Box and Blocks Test and the Nine Hole Peg Test

Study Design: Experimental trial. Background: The functional performance of currently available body-powered prostheses is unknown. Objective: The goal of this study was to objectively assess and compare the functional performance of three commonly used body-powered upper limb terminal devices. Methods: Twenty-one able-bodied subjects (n=21, age= 22±2) tested three different terminal devices: TRS VC Hook Grip 2S, Otto Bock VO Hand, and Hosmer model 5XA hook, using a prosthesis simulator. All subjects used each terminal device 9 times in two functional tests; the Nine Hole Peg Test (NHPT) and the Box and Blocks Test (BBT). Results: Significant differences were found between the different terminal devices and their scores on the NHPT and the BBT. The Hosmer hook scored best in both tests. The TRS Grip hook 2S scored second best. The Otto Bock hand showed the lowest scores. Conclusions: This study is a first step in the comparison of functional performances of body-powered prostheses. The data can be used as a reference value, to assess the performance of a terminal device or an amputee.BioMedical EngineeringMechanical, Maritime and Materials Engineerin