ABSTRACT
The aim of this paper is to present an analytical method of calculating forces acting on the thumb, index, middle finger, and metacarpal part of a hand prosthesis in a cylindrical grip. This prehension pattern represents a common operation of grabbing and manipulating everyday life objects. The design process assumed that such a prosthesis would have 5 fully operating fingers and 18 total degrees of freedom: three for each finger including the thumb, and another three for the wrist. The assumed load was 1 kg and the diameter equaled 70 mm, representing a water bottle. The method was based on analytical mechanics and as opposed to experiments or numerical methods does not require many resources. The calculations involved solving a system with seven unknown forces using an equilibrium equation for forces and moments in all three axes. The resulting equations were presented in a matrix form and solved using MATLAB software. The validation of the method with an experiment using FSR sensors and comparing it to other reports showed differences in index and middle finger involvement. However, the total sum of forces was similar, therefore it is reasoned that the grip can be performed and the prediction was accurate for the thumb and metacarpal. When using the model, the friction coefficient must be chosen with a safe margin as it influences the grip force. The presented method can be used for other models and designs by inserting their dimensions into the equations and solving them numerically to obtain forces useful in mechatronics design.
Subject(s)
Artificial Limbs , Hand , Fingers , Thumb , Hand StrengthABSTRACT
The aim of this paper is to compare two methods of epoxy adhesive bond gap control: one with a geometrical (mechanical) solution and the other with glass beads, which have the diameter of the desired bond gap and are mixed with an epoxy adhesive. The adhered materials were carbon fiber composite tubes and aluminum alloy inserts, which were used as wishbones in a suspension system of a motorsport vehicle. It was assumed that the gap thickness would be equal to 0.2 mm and the length of a bond would be 30 mm. The internal diameter of the tubes was 14 mm and 18 mm, whereas the inserts' external diameter was 13.6 mm and 17.6 mm. Their surface has been subjected to mechanical treatment with sand paper starting from 240 grit up to 400. The adhesives used were EA 3425 and EA 9466 cured at 80 °C for 2 h. The results showed that the glass beads method provides more consistent and better results as compared to the geometrical (mechanical) method. Further study in the area of fatigue and interfacial failure modes could be useful.
ABSTRACT
The aim of this study was to measure the energy absorbed by composite panels with carbon fiber-reinforced polymer (CFRP) skins and a 5052 aluminum alloy honeycomb core and to compare it to previous research and isotropic material-two 25 × 1.75 mm 1.0562 alloy steel tubes. The panel skins layup consisted of pre-impregnated Pyrofil TR30S 210 gsm 3K 2 × 2 twill oriented in directions 0/90 and -45/45 and having a consolidated thickness of 1 mm or 2 mm. The core consisted of a 15 mm or 20 mm honeycomb oriented along its lengthwise direction. The first test consisted of a three-point bending of specimens supported at a span of 400 mm with a 50 mm radius tubular load applicator in the middle. Second, a perimeter shear test was conducted using a 25 mm diameter punch and a 38 mm diameter hole. The results of the three-point bending test show that the energy absorbed by panels with 1 mm skins was similar to the energy absorbed by the tubes (96 J), which was better than the previously considered panels. In the case of perimeter shear, the average maximum forces for the top and bottom skin were 5.7 kN and 6.6 kN, respectively. For the panel with thicker skins (2 mm), the results were about 2 times higher.
