Design And Research Of Differential SMA Spring Actuator

Due to the increasing demand for intelligence and automation,intelligent actuators that can quickly rely on their own to respond to environmental changes by sensing the external environment continue to emerge.Among them,the electrothermal differential shape memory alloy(SMA)coil spring actuator is the most common driving device in mechanical and electronic equipment,which has the advantages of simple structure,high energy utilization rate,and large driving displacement.However,electrothermal differential SMA coil spring actuator has some problems in the process of commercialization,such as lack of a complete,accurate and unified design model,SMA characteristic parameters are greatly affected by the manufacturing process,and the actuator indicators are mutually restricted.In view of this,the design and performance optimization of electrothermal differential SMA coil spring actuator are deeply studied in this paper.Firstly,the basic formulas in the driving model of the electrothermal differential SMA coil spring actuator were compiled.Then,the 50.4 at% Ni-Ti alloy coil springs after heat-setting at 475 ℃ for10 min were wound by the cold rolling method and then the performance parameters were tested.Combine with MATLAB design,the spring performance parameters and the stress-strain curve yield platform were applied to determine γH and establish a set of simple and comprehensive electrothermal differential SMA coil spring actuator driving model in stable phase and transition state.The accuracy of the driving model was verified by actual driving.Secondly,according to the actual driving situation of the actuator,the system resistance method based on the driving displacement deviation to correct model was proposed.Base on the influence of the bias force on the phase transition temperature,the CA and CM phase transition temperature influence coefficients were proposed to correct model and the effect of rising rate/cooling rate on the phase transition temperature was further analyzed.Therefore,the model was further optimized and the model error was reduced.On this basis,in order to realize the synchronous optimization of the driving index,the regularity between the driving index of the actuator and the spring wire diameter,winding ratio and maximum shear strain was researched through MATLAB simulation calculation.Thirdly,the Ni element in 50.4 at% Ni-Ti alloy was replaced by 5 at% Cu element,and the Ni-49.6 at%Ti-5 at%Cu alloy spring after heat setting at 475 ℃ for 10 min was prepared.And then the performance of NiTiCu alloy spring and spring actuator was compared with NiTi alloy spring and spring actuator.The results show the NiTiCu alloy is more suitable as the actuator material,and the NiTiCu alloy actuator has greater effective output force,driving displacement and faster driving frequency at room temperature.Finally,the effect of the cooling method after heat setting and temperature and time of heat setting on 50.4 at%Ni-Ti alloy and Ni-49.6 at%Ti-5 at%Cu alloy was studied under the response rate of 5 ℃/min heating and cooling.The research results show that,for the two alloys,furnace cooling is beneficial to the low-power and stable driving of the electrothermal spring driver at room temperature and at a response rate of 5℃/min heating and cooling.For 50.4 at% Ni-Ti alloy,thermal setting at 475 ℃ for 10 min and then cooling with the furnace is the most suitable for low power and stable driving of electrothermal spring actuator at room temperature and 5 ℃/min response rate.For Ni-49.6 at%Ti-5 at%Cu alloy,thermal setting at 425 ℃ for 10 min and then cooling with the furnace is the most suitable for low power and stable driving of electrothermal spring actuator at room temperature and 5 ℃/min response rate.