*2.2.2. Mechanism design*

After the above analysis by the calculator, we found out the appropriate gas cylinder and airbag, and designed the corresponding mechanism parts for the selected gas cylinder and airbag. We are going to elaborate on the design concept of the inflator mechanism in the following. **Figure 4** illustrates a double-trigger inflator including a servomotor, horn, spring, Design and Estimation of an AUV Portable Intelligent Rescue System Based on Attitude Recognition Algorithm http://dx.doi.org/10.5772/intechopen.79980 53

**Figure 3.** The result of calculation specification analysis. (a) The front panel of the specification calculator. (b) The growth rate between the water depth and the airbag volume.

spring case, crowbar-striker, water-soluble PVA fiber, release button, and CO2 cylinder. The designed double-trigger inflator can be triggered not only by electricity but also by water damage when the waterproof cabin is severely broken.

After the above analysis by the calculator, we found out the appropriate gas cylinder and airbag, and design the corresponding mechanism parts for the selected gas cylinder and airbag.

There are two operating mechanisms to trigger the inflator. To begin with the electricity trigger mechanism as shown in **Figure 4**(**b**), we assume that the waterproof cabin is watertight; after detecting the failure of AUVs, servo motor rotates for pushing the crowbar-striker, and the crowbar-striker punches the release button, which needs 35 N normal force to release into the airbag through the air tube. We chose MG995 for servomotor, which has product size 40.7 19.7 42.9 mm and weight 55 g; MG995 is sufficient to move the horn for the release button with its maximum torque 127 N-cm.

Besides, if the AUV is severely impacted and causes cabin seepage, so that the power system is damaged, the AUV cannot resurface by the thruster or the electricity-trigger inflator. Hence, we designed the water-trigger inflator for this kind of case. When the cabin is broken, water

**Figure 4.** The design diagram of a double-trigger inflator. (a) before release. (b) release by servo motor. (c) release by spring.

melts the water-soluble PVA fiber and releases the spring case as shown in **Figure 4**(**c**). Within the spring case, the music wire is selected to spring; the true maximum load of spring is 27.985 N, which is not enough to press the release button. Thus, we extended the striker into a crowbar-striker, and amplified the spring force by the lever principle to release the push button. The final part is the airbag, which is made of nylon 6/6 and folded under a cover. The airbag weighs 150 g and the value of tensile strength is 809.3 atm, which can withstand the pressure caused by gas cylinders.
