# Development, Experimental Assessment, and Application of a Vacuum-Driven Soft Bending Actuator
## 2 Materials and Methods
### Design and Development of a Vacuum-Powered Soft Bending Actuator Utilizing Heat-Shrinkable Material  
An innovative fabrication approach using heat-shrinkable material will be implemented to develop a new VSBA with reduced dimensions compared to the VSBA-1. Made from polyolefin, this material has the ability to shrink when exposed to heat, enabling the fabrication of actuators in various shapes and dimensions. Furthermore, heat-shrinkable material is flexible and notable for its high durability and resistance to fatigue. Heat-shrinkable materials are commonly used in electrical installations to provide wire insulation and are typically available as tubes with standardized dimensions. Accordingly, heat-shrinkable tubes of various sizes will be employed in the fabrication of new VSBAs. We present two innovative manufacturing methods for fabricating the ribbed bellow of a VSBA using heat-shrinkable tubes. The first method involves positioning reinforcing rings on a cylindrical pipe, after which the heat-shrinkable tube is placed over the rings, as shown in Figure 3a. After heating, the tube shrinks and bonds tightly to the rings, creating an actuator with a ribbed bellows geometry. The goal of this method was to create a compact actuator without the need for an additional reinforcing ring assembly, but its practical application proved challenging. The main challenge appears because the heat-shrinkable tube shrinks until it makes contact with some constraint, which makes it difficult to achieve a uniform ribbed bellows shape. Therefore, the final shape of the bellows primarily depends on the amount of heat applied. Additionally, when the tube shrinks by more than 50% of its initial diameter, the heat-shrinkable material becomes stiffer, reducing the actuator's flexibility. To address this drawback, a second method was developed in which the heat-shrinkable tube conforms to the shape of a mold, as shown in Figure 3b. The mold is made of O-ring seals that are placed on the pipe at equal distances, with the heat-shrinkable tube placed over them. After heating and shrinking the tube, the mold is removed, resulting in the ribbed bellows shape. Reinforcing rings are then inserted into the newly formed ribbed bellows. This method allows for precise control over the tube's shrinkage, thereby sustaining the material's initial flexibility. Furthermore, the second method facilitates the easy fabrication of ribbed bellows in various sizes and shapes. Before developing actuators  
Figure 3: Fabrication of the VSBA ribbed bellow utilizing heat-shrinkable tubes: (**a**) the first method with non-removable rings; (**b**) the second method, which uses a mold. with reduced dimensions, a VSBA-2 with the same dimensions and shape as the previous VSBA-1 will be created, with the goal of comparing their performance and feasibility of production a VSBA with heat-shrinkable material. Next, the VSBA-3 version was fabricated, maintaining the same outer diameter as the VSBA-2, but incorporating increased spacing between the bellows ribs to evaluate the effect of this spacing on the VSBA's performance. Finally, a compact VSBA-4 version with a 50% reduction in outer diameter was fabricated. To fabricate the VSBA-2, a standardized heat-shrinkable tube with an outer diameter of 50.8 mm and a wall thickness of 2 mm was selected, as it closely matches the dimensions of the VSBA-1. The mold dimensions were selected as follows: the pipe has an outer diameter of 39 mm, and standard 5 \(\times\) 39 O-rings were selected, resulting in a total mold outer diameter of 49 mm. Additionally, the mold was created with ten O-rings spaced 8 mm apart, corresponding to the ribbed bellow shape of the VSBA-1 (Figure 3b). The selected heat-shrinkable tube starts shrinking at a temperature of 90 \({}^{\circ}\)C, so an industrial hot air blower was used to heat it, yielding the best results. Alternative heating methods, such as an open flame or hot water, have proven to be less effective.