Design And Control Of Underwater Vector Deflection Actuator Based On Ni Ti Shape Memory Alloy

Vector propulsion system is a key part of the underwater vehicle,which can precisely adjust the propulsion direction according to the mission.The vector deflection actuator is the core part of the propulsion system,which is used to perform the attitude control of the propeller.Hydraulic or motor as deflection actuator is utilized in a traditional underwater vector propulsion system,which is usually large in volume and complex in structure.Those features make the miniaturization and light-weight of the systems hard for the system designers.In order to simplify the structure of vector deflection actuator and improve its compactness,it is necessary to develop a new actuator for these vector deflections.The fundamental research on the actuation characters of smart materials provides a new technical perspective for the design of vector deflection actuator.Ni-Ti shape memory alloy(SMA)is a kind of metallic intelligent materials with light-weight and high-strength.Its unique shape memory effect makes it suitable to be used as an actuation element to realize vector deflection.The main purpose of this thesis is to develop a kind of SMA vector deflection actuator and its control system with adequate response rate,accurate action and stable operation.The vector propulsion system requires that the position alternation can be realized in a global space,the maximum deflection angle is 25 °,the deflection speed is not less than 3 ° / s,and the deflection output torque is not less than 5 N·m.Under the guidance of the top-down design principle,the mechanical structure design and the selection of the actuation elements were carried out according to the functional requirements of the actuation subsystem and the transmission subsystem.And three types of vector deflection schemes based on SMA elements are proposed.Through the comprehensive consideration of action stability and output torque of three schemes,it was determined that the rotary SMA vector deflection actuator was the final scheme.According to the selected scheme,Ni-Ti shape memory alloy wire was selected as the actuation element,and the required output performance of the element was pointed out.In order to master the output characters of the actuation elements,the SMA wire was studied by experimental characterizations and numerical simulations.The SMA element with a wire diameter of 0.5 mm is determined.When the recovery stress output range is between 166 MPa and 300 MPa,it can work safely for long time under the condition of satisfying the torque output of the rotary actuator.In order to describe the deflection process quantitatively,the dynamic model of SMA rotary actuator was built.Combined with the SMA element model,the model of rotary driving system is established.Based on previous models,the open-loop simulation and experimental studies of the system were carried out.The results show that the maximum rotation angle only increases with the increase of driving current in a certain range(1.0A ? 1.3A),and the maximum rotation angle does not change when the driving current exceeds the critical value.When the driving current increases,the total response time monotonously decreases,and the rotation process duration period decreases and then increases.The minimum value appears when the driving current reaches 1.2A.Anti-windup PID closed-loop control system of rotary drive is established with the rotation angle as the feedback value.The simulation results show that the rotary drive system can satisfy the requirements of vector deflection in response rate and control accuracy(not more than 0.9%).Finally,the feasibility of the rotary drive system is illustrated by an example of vector propulsion position control.