Research On SMA Spiral Rotary Actuator

As a smart material with shape memory effect, Shape Memory Alloys(SMA) can change its shape for corresponding the change of temperature. So the functional devices, made by SMA materials, have the characteristics of integrating the sensor and driver. Because of the other inherent characteristics of this kind of material, the SMA actuator also have the characteristics of high power/weight ratio, no noise, no friction, no liquid or dust, which is especially suitable for the development of temperature adaptive control and drive device in aerospace.Aiming at solving the problems of structural complexity, low level of integration of the current SMA rotary drive, a type of rotary actuation device was invented. Avoiding the complicated motion converting mechanism and directly outputting torque and rotary motion, the actuator achieved the structure simplification. Based on the analysis of mechanical behavior, optimization of preparing technology, performance testing and active incentive effect, this article has carried on a systematic research to this kind of driver. The main works and achievements are as follows:(1) The segment of mechanical model construction of driving element: Along with Hook coil spring model and one-dimensional linear constitutive model of shape memory alloy, a segmental mechanical model of the driving element was established according to different changing processes of output twist moment, deformation and temperature to acquire the mechanical expressions during different working stages. The result proved that this model could effectively describe the basic status and features of the driving device before and after the phase change.(2) The segment of manufacturing of the actuator: The performance testing for the SMA strip samples has been conducted. These SMA strip samples had been trained in different heat treatment environment. Based on the middle temperature process and the criterion that low flexural rigidity of low-temperature state, large plastic deformation, high stiffness of high-temperature state and large hysteresis of material phase transition temperature, the proper SMA training method was tested to determine the basic parameters of heat treatment. The heat treatment mold was designed and made and desired functional SMA driving element was acquired.(3) The segment of development of testing system: While existing experimental device can’t test objects properly,a new testing system was developed. Through performance testing and actual using,the system was proved to meet the requirements of experiment on current research stage. And then in order to inprove testing efficiency, the system was automation retrofited based on PCI 1711 data card and Lab View software platform.(4) The segment of performance testing of the actuator: The test results of driving element showed that the angle deformation remained Archimedean spiral shape before 600°.The difference of angle deformation in the high and low temperature was about two times and the difference of torque output in high and low temperature was about 1.6 times. The test results of two-way actuator showed that the prototype could output maximum torque177 × 10-3N·m at high-temperature environments, output maximum reverse torque 75×10-3N·m at low-temperature environments, achieved a reciprocating stroke of 160 ° under no-load conditions.(5) The segment of integration study of the actuating devices and heaters: After comparing three different heat treatment and their influence on the output feature of SMA driving element, the carbon fiber adhesion layer was presented as a new type whole heating method for the SMA actuator. The integration method of carbon fiber adhesion layer and the SMA strip and the heat driving characteristics have been explored. Tests showed that: the adhesion layer made of 2K specification carbon fiber tow can provide a heating efficiency of 16.5×10-3℃·m/(W·S)per unit length,which can heat the actuating device from 11℃to over 100℃ within 55 seconds under 0.6A current excitation, to make incentive objects achieve expected torque and angular displacement output. With quick response, easy control and little demand of the driving power, this method will be very promising in future application.