Design And Control Of Vector Nozzle Actuated By Shape Memory Alloy Wire

Due to their high degree of flexibility and efficiency characteristics, biomimetic underwater robots have become a hot research in the field of robotics in recent years. Currently, the successful developments of biomimetic underwater robots have mainly focused on the imitation of fish. Squid, strange marine animals, swim mainly by jetting water, and its propulsive efficiency and flexibility can be comparable with the fish. Therefore, there is great value of bionic. Jet propulsion technology which control jet direction through vector nozzle structure has been mature in the application of ship. However, the traditional vector nozzle design is achieved by mechanical transmission structure, so it's difficult to apply in the small biomimetic underwater robot due to its complex structure. The structure of squid nozzle is simple, and it can bend flexible, thus it can control the direction of swimming squid. So, inspired from the structure and function of squid nozzle, this article has designed and realized the biomimetic squid vector nozzle which can be driven by shape memory alloy(SMA) and be bent flexible.First, this paper analyzes the squid nozzle muscle, action mechanism and function, and then designs two kinds of biomimetic squid vector structure. Through theoretical analysis, the nested structure is better than the hollow-type structure. And the mechanical model of the bending biomimetic squid vector is established.Second, the space curved geometry model of the biomimetic squid vector nozzle is established to determine the relationship between the SMA actuator and the space bending angle of nozzle. And the control system of the biomimetic squid vector nozzle based on the LM3S8962 MCU is developed.At last, the biomimetic squid vector nozzle is controlled using pulse width modulation(PWM) technology. Open-loop experiment is conducted, the results show that too long the PWM square wave cycle is will cause the nozzle oscillation, different bending angle of nozzle can be controlled by different duty cycle of PWM square wave, and different SMA wire resistance corresponds different bending angle. Semi-closed loop experiment is conducted, proportional integral control is used to improve the system response speed, obtain smaller steady-state error, and good control effect is achieved. Vector control is successful made, and injection test is carried out under the condition of a flow rate of 0.8m/s to verify its feasibility of control of water jet direction.