# Development, Experimental Assessment, and Application of a Vacuum-Driven Soft Bending Actuator
## 4 Vacuum-Driven Soft Robotic Gripper Assembly
In most cases, the gripper achieved a proper grasp, except in situations where the object's dimensions were incompatible with the dimensions of the developed soft robotic gripper. The next experimental assessment focused on analyzing the gripping force, defined as the force exerted by the actuators on an object, which is a critical parameter in applications involving the handling of fragile objects. To measure the gripping force, the robotic gripper was modified by removing the third actuator, leaving two actuators aligned with their operating axis. Also, the gripping parts were removed to allow the actuators to directly engage with a load cell, as illustrated in Figure 8b. Gripping an object with the robotic gripper requires a certain bending angle of the actuators. However, since previous experimental tests demonstrated a significant drop in force beyond a bending angle of 30\({}^{\circ}\), all experimental measurements were conducted at bending angles up to 30\({}^{\circ}\). The external dimension of the load cell, including mounting screws, was set to 80 mm. Therefore, to precisely adjust the bending angle, the spacing between the actuators was altered. This was achieved by drilling additional holes in the support plate, resulting in a first spacing of 200 mm between the actuators, and the second spacing was set at 240 mm. Figure 8: Soft robotic gripper: (**a**) design approach; (**b**) experimental measurement of the gripping force; (**c**) results of the gripping force and holding force. The gripping force results are shown in Figure 8c. The measurements revealed that a smaller spacing of 200 mm resulted in a greater gripping force, because the bending angle of the VSBA-1 was \(\theta=30^{\circ}\). The maximum gripping force measured was \(F=16\) N, achieved at \(p=-0.8\) bar. The results show that each actuator contributes approximately half of the total force (\(F=8\) N) applied to the gripped object. Consequently, the obtained relationship between force and vacuum pressure represents a key parameter for the precise control of gripping force using a proportional pressure control valve. In the next experiment, the maximum holding force that the soft robotic gripper, equipped with three VSBA-1s, could apply to an object was investigated. The experiment was conducted by allowing the robotic gripper to strongly hold a cylindrical object while a pulling force was gradually applied from below, until the object slipped off the gripper's contact surface, as shown in Figure 1f. A polypropylene rope, previously used for its resistance to stretching under load, was employed again. The rope was connected to a load cell, and weights were gradually added to generate the pulling force while data were simultaneously recorded. The outer diameter of the cylindrical object was 80 mm, and the spacing between the actuators was set to 200 mm, resulting in a bending angle of approximately \(30^{\circ}\), as in the previous experiment. Figure 8c shows the maximum holding force as a function of vacuum pressure, with results indicating a maximum holding force of \(F=28\) N at \(p=-0.8\) bar. These results demonstrate the soft robotic gripper's capacity to strongly hold a cylindrical object with an 80 mm diameter and a mass of up to 2.8 kg and highlight the potential of the novel VSBA for integration into a soft robotic gripper.