Study on Compact Fine Positioner with Thermal Compensation Capability

针对超磁致伸缩材料在小型精密定位器中的应用，通过分析和设计改进，研制了两种样机。本研究的结果总结如下。现场预加载测量：对超磁致伸缩材料进行适当的预加载，对于材料的有效利用至关重要。通过测量定位器外壳的应变，可进行现场预紧力测量。这不仅提供了精确的预加载，而且还提供了定位器位移输出的传感能力。基于位移信号，可以通过反馈控制螺线管线圈的输入电流以调节输出。2.热补偿的设计阐述：当直流电供应到螺线管线圈时，线圈发出的焦耳热导致超磁致伸缩材料和附近部件的显著热膨胀，这显著降低了定位器的性能。在这项研究中，设计修改，使热膨胀是内部抵消。热效应测量系统：为了评估定位器各部件的热膨胀，新开发了一个测量系统。在该系统中，定位器的温度通过外部热源精确控制，并且可以同时采集多种测量信号，包括位移输出，应变输出和多个点的温度.通过有限元分析进行磁路设计：超磁致伸缩材料具有非常低的磁导率，需要注意，以便足够的磁通量通过材料。采用有限元法分析磁路，使产生的磁通量的约80%通过材料。

In view of the application of giant magnetostrictive materials to compact, fine positioner, two kinds of prototypes have been developed through analyses and design modification. Results of this study are summarized below.1. In-situ preload meassuring: Proper preloading to giant magnetostrictive materials vital for an efficient use of the material. In-situ preload measuring is available by means of strain measurement of the housing of the positioner. This not only provides accurate preloading but also serves sensing capability of the displacement output of the positioner. Based on the displacement signal, the input current to the solenoid coil can be controlled via feedback to adjust the output.2. Design elaboration for thermal compensation: When the direct current is supplied to the solenoid coil, joule heat emitted by the coil results in outstanding thermal expansion of the giant magnetostrictive material and nearby parts, which significantly degrades the performance of the positioner. In this study, design modification was made such that the thermal expansion is internally offset.3. Thermal effect instrumentation system: In order to evaluate the thermal expansion of the various parts of the positioner, a measuring system was newly developed. In this system temperature of the positioner is accurately controlled via external heat source and a variety of measurement signals can be gathered simultaneously including displacement output, strain output, and temperatures on more than one spots.4. Magnetic circuit design via finite element analysis: Giant magnetostrictive material has a very low permeability and a caution needs to be paid so that sufficient magnetic flux passes through the material. Finite element method was used to analyze the magnetic circuit so that about 80% of the generated flux passes through the material.