# Bi-Stability in Flexure Beams: Introducing a Setup for Experimental Characterization
## 2 Materials and Methods
### Test Setup and Component Specifications  
To characterize the bi-stable behavior of the mechanism, a setup was designed, fabricated, and integrated into a TVT 6700 Perten Texture Analyzer (Perten Instruments, New South Wales, Australia). The main components of the setup are shown in the exploded view in Figure 3a. The actual setup is shown in Figure 3b.  
The components of the bi-stable mechanism (flexure beams, slider-triggers, and anchors) are made of commercial materials that are easy to acquire and affordable. The flexure beams are made of different calibers of commercially available styrene plastic sheets. To create stripes, the sheets were laser cut in an STM-L1390 CO\({}_{2}\) CNC laser cutter. The stripes  
Figure 3: (**a**) Enlarged 3D model of the setup on the texture analyzer. (**b**) Picture of the setup placed on the texture analyzer. All of the experiments were documented using a smartphone.  
Figure 2: (**a**) Design and dimensions of the base of the setup. The layout of the flexure beams and components can be seen in thin lines. (**b**) Schematic of the components of the bi-stable mechanism.  
have a total length of 55 mm and a height of 3 mm. On their part, the rigid components (the slider and the anchors) have holes for screws and slots for press-fit assembly of the flexure beams. The shape of the slot locks the flexure beam in place. These components were made of 3 mm cast acrylic (Acrylite(r)) and fabricated with the same laser cutter. The physical components are shown in Figure 4a.  
The setup consists of a base with circular perforations in different places to position the components with M3 screws fixed with M3 cap bolts. As shown in Figure 2a, it also has a slender slot in the center to guide the slider as it moves. The setup is limited to an area of 146 mm by 83.5 mm. The distance of the linear displacement of the slider is 45 mm; this length is determined by the position of the screws in the trigger, which constrain the movement when meeting the slider ends. The base is also made of 3 mm acrylic cast fabricated with the same laser cutter. In turn, the two sides of the acrylic base are press-fit inserted into 3D printed fixtures bolted to the base of the machine. These fixtures were 3D printed with the blue eSun(r) 2.85 mm Polylactid Acid (PLA) filament in a Zortrax M300 FDM 3D printer.  
To determine the range of operational actuation forces, different thicknesses of flexure beams were tested. The thickness was defined by the length of the calibers available on the market. Table 1 lists the five calibers used for this study, their nomenclature, and their thickness in millimeters. To join the flexure beams, the width of the slots in the anchors and triggers was adapted to meet each styrene thickness. The tailored designs for each thickness can be seen in Figure 4b. As shown in Figure 4c, one end of the styrene stripes is press-fit assembled to one slot of the anchor, and the other end to the trigger, shortening the 55 mm original length to an operative length of 53 mm.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Nomenclature** & **Caliber** & **Thickness** \\ \hline C10 & Caliber 10 & 0.25 mm \\ C15 & Caliber 15 & 0.38 mm \\ C20 & Caliber 20 & 0.50 mm \\ C30 & Caliber 30 & 0.75 mm \\ C40 & Caliber 40 & 1.00 mm \\ \hline \hline \end{tabular}
\end{table}
Table 1: Nomenclature, caliber, and thickness of the five styrene plastic stripes used in this study for making the flexure beams.  
Figure 4: (**a**) Picture of actual components. The anchor is made of acrylic and the flexure beam of styrene plastic. (**b**) Schematics of anchor components. The width of their slots gets larger according to the caliber of the flexure beam. (**c**) The flexure beams are press-fit assembled to the anchor and trigger.