scholarly journals Ergonomic Design and Evaluation of Fabric Cutting Scissors with Regard to Pinch Force and Wrist Posture

2017 ◽  
Vol 5 (2) ◽  
pp. 61-66
Author(s):  
Soudabeh Asadollahi ◽  
Iman Dianat ◽  
Moein Nedaei
Keyword(s):  
Ergonomic Design ◽  
Pinch Force

scholarly journals Design of a 3D-printed hand prosthesis featuring articulated bio-inspired fingers

2020 ◽  
pp. 095441192098088
Author(s):  
Juan Sebastian Cuellar ◽  
Dick Plettenburg ◽  
Amir A Zadpoor ◽  
Paul Breedveld ◽  
Gerwin Smit
Keyword(s):  
3D Printing ◽  
Design Principles ◽  
Prosthetic Hand ◽  
Hand Prosthesis ◽  
Fused Deposition ◽  
Pinch Force ◽  
Actuation System ◽  
3D Printed ◽  
Energy Dissipated ◽  
Dual Material

Various upper-limb prostheses have been designed for 3D printing but only a few of them are based on bio-inspired design principles and many anatomical details are not typically incorporated even though 3D printing offers advantages that facilitate the application of such design principles. We therefore aimed to apply a bio-inspired approach to the design and fabrication of articulated fingers for a new type of 3D printed hand prosthesis that is body-powered and complies with basic user requirements. We first studied the biological structure of human fingers and their movement control mechanisms in order to devise the transmission and actuation system. A number of working principles were established and various simplifications were made to fabricate the hand prosthesis using a fused deposition modelling (FDM) 3D printer with dual material extrusion. We then evaluated the mechanical performance of the prosthetic device by measuring its ability to exert pinch forces and the energy dissipated during each operational cycle. We fabricated our prototypes using three polymeric materials including PLA, TPU, and Nylon. The total weight of the prosthesis was 92 g with a total material cost of 12 US dollars. The energy dissipated during each cycle was 0.380 Nm with a pinch force of ≈16 N corresponding to an input force of 100 N. The hand is actuated by a conventional pulling cable used in BP prostheses. It is connected to a shoulder strap at one end and to the coupling of the whiffle tree mechanism at the other end. The whiffle tree mechanism distributes the force to the four tendons, which bend all fingers simultaneously when pulled. The design described in this manuscript demonstrates several bio-inspired design features and is capable of performing different grasping patterns due to the adaptive grasping provided by the articulated fingers. The pinch force obtained is superior to other fully 3D printed body-powered hand prostheses, but still below that of conventional body powered hand prostheses. We present a 3D printed bio-inspired prosthetic hand that is body-powered and includes all of the following characteristics: adaptive grasping, articulated fingers, and minimized post-printing assembly. Additionally, the low cost and low weight make this prosthetic hand a worthy option mainly in locations where state-of-the-art prosthetic workshops are absent.

scholarly journals Influence of design of dentist’s chairs on body posture for dentists with different working experience

2021 ◽  
Vol 22 (1) ◽  
Author(s):  
F. Huppert ◽  
W. Betz ◽  
C. Maurer-Grubinger ◽  
F. Holzgreve ◽  
L. Fraeulin ◽  
...  
Keyword(s):  
Work Experience ◽  
Dental Treatment ◽  
Subjective Assessment ◽  
Body Posture ◽  
Control Group ◽  
Sitting Position ◽  
Ergonomic Design ◽  
Sitting Posture ◽  
Working Posture ◽  
Working Postures

Abstract Background Musculoskeletal disorders (MSD) are a common health problem among dentists. Dental treatment is mainly performed in a sitting position. The aim of the study was to quantify the effect of different ergonomic chairs on the sitting position. In addition, it was tested if the sitting position of experienced workers is different from a non-dental group. Methods A total of 59 (28 m/31f) subjects, divided into two dentist groups according to their work experience (students and dentists (9 m/11f) < 10 years, dentists (9 m/10f) ≥ 10 years) and a control group (10 m/10f) were measured. A three-dimensional back scanner captured the bare back of all subjects sitting on six dentist’s chairs of different design. Initially, inter-group comparisons per chair, firstly in the habitual and secondly in the working postures, were carried out. Furthermore, inter-chair comparison was conducted for the habitual as well as for the working postures of all subjects and for each group. Finally, a comparison between the habitual sitting posture and the working posture for each respective chair (intra-chair comparison) was conducted (for all subjects and for each group). In addition, a subjective assessment of each chair was made. For the statistical analysis, non-parametric tests were conducted and the level of significance was set at 5%. Results When comparing the three subject groups, all chairs caused a more pronounced spinal kyphosis in experienced dentists. In both conditions (habitual and working postures), a symmetrical sitting position was assumed on each chair. The inter-chair comparisons showed no differences regarding the ergonomic design of the chairs. The significances found in the inter-chair comparisons were all within the measurementerror and could, therefore, be classified as clinically irrelevant. The intra-chair comparison (habitual sitting position vs. working sitting position) illustrated position-related changes in the sagittal, but not in the transverse, plane. These changes were only position-related (forward leaned working posture) and were not influenced by the ergonomic sitting design of the respective chair. There are no differences between the groups in the subjective assessment of each chair. Conclusions Regardless of the group or the dental experience, the ergonomic design of the dentist’s chair had only a marginal influence on the upper body posture in both the habitual and working sitting postures. Consequently, the focus of the dentist’s chair, in order to minimize MSD, should concentrate on adopting a symmetrical sitting posture rather than on its ergonomic design.

Comparison of simulated key pinch after three surgical procedures for trapeziometacarpal osteoarthritis: a cadaver study

2021 ◽  
pp. 175319342110159
Author(s):  
Lionel Athlani ◽  
Damien Motte ◽  
Marie Martel ◽  
Florent Moissenet ◽  
Julie Mottet ◽  
...  
Keyword(s):  
Surgical Procedures ◽  
Total Joint Arthroplasty ◽  
Ligament Reconstruction ◽  
Cadaver Study ◽  
Joint Arthroplasty ◽  
Pinch Force ◽  
Trapeziometacarpal Osteoarthritis ◽  
Intact Sample ◽  
Significant Difference ◽  
Tendon Interposition

We performed a cadaver study using 18 fresh-frozen adult forearms and hands to compare the tendon loads required to generate progressively greater key pinch (0.5 kg to 2 kg) after three different surgical procedures to treat trapeziometacarpal osteoarthritis: isolated trapeziectomy, trapeziectomy followed by ligament reconstruction with tendon interposition and total joint arthroplasty using a Touch® implant. Thumb pinch was simulated by loading the main actuator tendons involved in the key pinch. Six specimens were randomly assigned to each of the three surgical procedure groups. Measurements were made before and after the joint surgery. Specimens that underwent trapeziectomy with or without ligament reconstruction with tendon interposition required significantly higher tendon loads than those with the implant to achieve the same pinch force. There was no significant difference between the isolated trapeziectomy and ligament reconstruction groups. Using the implant resulted in similar median tendon loads compared with those of the intact sample. Total joint arthroplasty with a Touch® prosthesis may yield a superior biomechanical profile in which the tendon loads needed to achieve a certain key pinch force are lower and better distributed between the actuator muscles compared with trapeziectomy with or without ligament reconstruction.

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