# Bionic Design of the Vertical Bracket of Wide Angle Auroral Imager by Additive Manufacturing
## 3 Bionic Optimization Design of the Vertical Bracket of Wide Angle Auroral Imager
### Bionic Optimization Design of the Vertical Bracket  
As the only rigid support component, the lower extremity skeleton plays a bearing role during the movement process. Its strength and rigidity keep the external shape of the organism unchanged. Three typical lower limb bones including tiger, ostrich, and human are selected for research as shown in the Figure 4. Tigers, as a mammal with huge body and developed limbs, have developed lower limb bones, which are used for running and jumping (as shown in Figure 4a). The ostrich is the largest bird in the world and the only two-toed bird. Its lower limb bones are extremely load-bearing (as shown in Figure 4b). Humans are the most advanced mammals. Compared with other animals, humans have more developed lower limb bones, which are conducive to supporting body weight and completing other activities (as shown in Figure 4c).  
The characteristics of these three long bones have been discovered, including (1) the top of the bone is convex at both ends and concave in the middle; (2) the top is wide and the middle part is long and narrow; and (3) all are long bones with large width-to-diameter ratio. Further research on the lower limb bones finds that although there are great differences in the body size among different groups of animals, the morphology of bone shows a certain regularity. The structures of the head and greater trochanter of the lower limb bones in humans, tigers, and ostriches are basically symmetrical, and the relative heights are almost the same.  
According to the simplified diagram of human femur in Figure 4d, it can be seen that the topological structure of the vertical support is similar to the femur, which is also a symmetrical structure. The two top ends of the vertical support are convex and present a structural form of wide on the top and narrow in the middle. Taking the human femur as the reference object, the topology optimization model is further designed. Generally, the width-to-diameter ratio of the femur in adult males is 0.58-0.61 [38]. Since the width of the upper structure \(W1\) is determined to be 460 mm, by the position of shafting system and the imaging system. The width-to-diameter ratio 0.58 is chosen, the length of the middle  
Figure 3: Optimized structural configuration of the vertical bracket. (**a**) Topology optimization structural configuration. (**b**) Bionic optimization structural configuration. (**c**) Size optimization structural configuration.  
section W2 can be determined to be 266 mm, the size of the satellite is also determined due to it is connected to the bottom structure of the satellite. Then conical transition is adopted from the m.iddle to the bottom of the structure. It can be said that the general shape of the redesign model can be determined through the results of topology optimization. Further, the overall dimension of the redesign model can be determined through the width-to-diameter ratio of the femur, as shown in Figure 3b.  
Further, the study finds that the distribution of the bone density of the femur is related to the force. Intertrochanter is located at the junction of femoral body and femoral neck, which is the part bearing the largest shear force and stress. Correspondingly, the bone density of intertrochanter is also the largest. Bone density at greater trochanter and head is lower than in the intertrochanter region, while the lower end of the femoral body has the lowest bone density [39; 40; 41]. Therefore, the middle position of the vertical support is designed as a solid structure, and the upper and lower ends are designed as hollow thin-plate structures as shown in Figure 3c. As the main bearing structure, the solid structure in the middle section is designed to provide strong support for the imaging system, and the hollow thin-walled structure in the upper and lower sections is designed to minimize the structural quality. It ensures not only the lightweight of the structure, but also the rigidity of the structure.