# Development, Experimental Assessment, and Application of a Vacuum-Driven Soft Bending Actuator
## 2 Materials and Methods  
In this section, the design and development of soft pneumatic actuators with bending motion is presented. Based on three design requirements and a conceptual design approach, two novel VSBA actuators were developed and fabricated. The first approach utilizes thermoplastic rubber material, while the second uses heat-shrinkable material. Design and Development of a Vacuum-Powered Soft Bending Actuator Utilizing Thermoplastic Rubber Material  
After a methodical analysis of existing design solutions for soft bending actuators, it was observed that, despite their advantages, certain disadvantages still exist. The aim of this paper is to address these weaknesses through the development of a novel soft bending actuator that will meet three key design requirements. The first design requirement ensures safe operation without the risk of explosion, which can occur when positive pressure is used. As an alternative, vacuum pressure of up to \(-1\) bar is used. While this limits the actuator's maximum force, it reduces the risk of failure. Based on this safety requirement, it was decided that our VSBA would utilize vacuum pressure. The second design requirement focuses on achieving a large bending angle while being able to overcome significant forces relative to the actuator's dimensions. According to [PERSON]'s law, since vacuum pressure is limited, the actuator's force can only be increased by expanding its dimensions. However, the external dimensions of the VSBA must remain limited due to spatial constraints in real mechatronic systems. To address this, cylindrical ribbed geometry, also known as ribbed bellow, was used to increase surface area without expanding external dimensions. To achieve bending motion of the VSBA, a solution with a limiting element was chosen, which constrains contraction on one side of the actuator when vacuum pressure is applied, causing it to bend. The limiting element is located within the actuator and is designed as a flexible thin square strip. The third design requirement involves the use of soft materials that ensure actuator flexibility and durability without material fatigue. Therefore, we decided not to manufacture the ribbed bellow by casting silicone rubber or 3D printing with flexible materials. Instead, we focused on utilizing a commercially available ribbed bellow, with material durability verified by the manufacturer. The protection of the front suspension on motorcycles was chosen, as it meets the required geometric characteristics and material properties. This component is made from thermoplastic rubber (TPR) in large quantities using an injection molding process, which results in low cost. Also, thermoplastic rubber can withstand temperatures from around \(-30\)\({}^{\circ}\)C to \(120\)\({}^{\circ}\)C without significant damage or changes in properties. An additional advantage of using this component is its ability to return the actuator to its initial position after the vacuum is released due to its low stiffness. The mentioned advantages, along with other beneficial properties, have already been confirmed in our previous research [32,35]. Based on the mentioned design solution, the VSBA was developed, and its 3D model with main elements is shown in Figure 1a. To ensure the airtightness of the VSBA, the ribbed bellows must be sealed at both the top and bottom. Following that, upper and lower lids were designed, which not only seal the actuator but also transfer force to the mechatronic system via screws passing through both lids. Vacuum pressure on the ribbed bellow causes axial and radial contractions, with radial contractions negatively impacting the VSBA geometry and reducing the actuator's performance. To address this, reinforcement rings were designed and inserted along the inner side of the bellows. Additionally, reinforcement rings are designed with pockets through which the limiting element passes. The limiting strip should be tightly fixed with all rings at identical distances, as any deviation could cause uneven VSBA bending.