| Scientific research workers have developed some soft bionic robot which can be applied in complex environment by simulating flexible structure and its movement mechanism. Unlike the rigid robot, soft robot which can change its shape and size would play many major roles in many special field such as exploration, rescue, military and medical treatment. Four common actuation are used in the soft robot such as shape memory alloy (SMA) wire actuation, electroactive polymer actuation, hydraulic or pneumatic actuation which are physical actuation and chemical actuation where the chemical energy can be converted into mechanical energy. For four actuation, each have advantages and disadvantages, one of which SMA actuation is very similar to human muscle integrating sensor, driving with executive function. But the low response frequency problem resulting from slowly cooling limits its future development. In this paper, study aims to improve the frequency of SMA wires actuation.The paper reviews the current situation of soft robots at home and abroad, and the four common soft actuations. Shape memory alloy wires actuation taken as object are analyzed with the movement mechanism. Thesis points out the slow cooling is a major bottleneck for SMA wire, and several solutions are listed. Based on the water circulation cooling, a new method that is applied with the micro-channel cooling to SMAs actuation is presented which mixes the actuation and cooling together in one body. The main research content includes:the structure and model of SMA wire actuaction with micro-channel cooling are designed and established, the processes are followed by MEMS (micro electro mechanical system),3D printing technology and so on. At last, thermal and stability performance is tested. Detail content is as follows:Soft robot gradually becomes a new research field and is attracted many attentions of the researchers as it is the most close to biological flexibility. Currently, four kinds of actutions are used for soft robot:electroactive polymer actuation, shape memory alloy wires actuation, hydraulic or pneumatic actuation and chemical actuation. The advantages and disadvantages of each actuation are stated.Mostly, the SMAs actuation is studied in this paper. The current cooling methods can be classified as two types:reduction of the heat generated by the heat source (changing the diameter of SMA wires, employing the higher phase-transition temperature of SMAs, varying the heating duty ratio, changing the way of loading) and increasing external requipment(water cooling, air coolin, fan cooling and add heat conduction material). By imitating bionic water circulation system, the SMAs actuation is designed with micro-channel structure, where water cooling effect is obvious and the cost is low.According to several processes such as MEMS and 3D printing technology, the structure of SMA actuation is fabricated. After being a long process time investigation, the optimum process conditions are given. The structure with the most effective cooling is carefully chosen from a variety of actuation with different size and shape one by one.Coolant liquid flowing through channels can help heat transfer and cool SMA wires. Using water as cooling medium, the cooling effect is proved by two comparative groups between fluid-channel with water and other without water. In the experiment, the temperatures on the sample point at different frequencies and temperature distribution are presented by cloud picture are measured. The bending ratios changed with time are also tested with two comparative groups at different frequencies. These experiments could verify that this cooling method can improve the response frequency and output stability of SMA flexible actuator in the air. |
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