The stress analysis was conducted on Solidworks Simulation, as shown in Fig. \ref{MiddleFingerMechanismStressAnalysis} and Fig. \ref{MiddleFingerMechanismDisplacementAnalysis}.
As Ninjaflex material was not present on the material list, and customization of the material was not allowed in the software programme used by the writer, polyurethane (PUR) was been chosen, which closely resembles the physical properties of Ninjaflex, which is a thermoplastic polyurethane (TPU). From the stress analysis on the middle finger mechanism, it is observed that there are significant stress points on the tip of the origami folding. These stress points may have caused the folding unable to be folded completely. However, from the results, it also show that some joints were able to fold into the angle as expected. And from the results of the angle of movement, it can be shown that adding V-shaped cuttings at the side of the origami/kirigami foldings enables the finger mechanism to conduct flexion and extension in a more accurate angle.
Measurement of force need for maximum flexion of finger mechanism
The second experiment was to calculate how much force is needed for the finger mechanism to have the maximum flexion, which can be used as a reference for the choice of servomotor to be used for the hand exoskeletal system. The experimental setup for angle of movement was used for this experiment. And the data collection of the force is created using the AnalogRead Programme from Arduino.
The AnalogRead Programme has a range from 0-1024 units, which corresponds to the range of the input voltage from 0-5V. However, the reading has an error of +13 units at the neutral point, which means an addition or subtraction is needed from the obtained value. The force sensor can calculate a force from a range of 0-50N. As such, an equation is needed to convert the values obtain from Arduino.
Three fingers were subjected to this experiment to calculate the force needed to flex the fingers fully. The ring finger and the little finger was not been added into the calculation as the strength and grip of the prototype is mainly focus on the first three fingers, while the last two fingers are just assisting roles in the gripping action.
The equations and results for the experiment are as follow:
\(V=x/1025*5V\); \(F(inNewtons)=V/5*50N\).