旋转MEMS中微球轴承的滚动摩擦测试与减摩机制研究

Nowadays the micro rolling bearing is considered as the best mechanical support for the rotary MEMS owing to its lower friction coefficient than planar contact bearing mechanisms and increased stability over noncontact bearing while simplifying the fabrication processes. However, the influences of the size effects and surface effects on the micro rolling friction and micro wear have been still unclear so far, which has become the bottleneck of the development of this kind of bearing technique.The followings will be investigated in this project.First, the test rig will be fabricated by DRIE and bonding techniques in which the realistic contact conditions for microball bearing are demonstrated. Next, the experimental studies will be undertaken under the diffetent scales and working conditions through the UMT-2 Tribometer and the test rig developed in this project, in order to investigate the influences of the size effects and surface effects on the micro rolling friction torques and micro wear behaviors. Furthermore, the diamond like carbon (DLC) films are prepared on the silicon raceway of the ball bearing by the radio-frequency plasma enhanced chemical vapor deposition (rf-PECVD) technique, and then the microscopic features of the DLC films and the film-forming conditions under micro rolling contact are examined so as to clarify its mechanisms of friction reduction and antiwear. The objectives of this project are to provide the tribological design theory for the micro rolling bearing in rotary MEMS and the key technology for its friction reduction and antiwear.

微滚动轴承比平面接触式微轴承摩擦系数低，而比非接触式微轴承支承稳定并且硅微制造工艺简单，因而被当作未来旋转MEMS器件的首选支承。然而迄今为止，对于尺度效应和表面效应影响微滚动摩擦和磨损的机制尚不清楚，已成为阻碍微滚动轴承发展的瓶颈。本项目拟开展如下研究：（1）利用体硅DRIE和键合工艺研制一台能模拟微球轴承真实工况的试验装置，为研究微滚动摩擦学特性提供实验手段；（2）分别通过UMT-2球盘试验机和所研制的微轴承测试装置进行不同尺度和工况条件的实验研究，揭示尺度效应和表面效应对滚动摩擦力矩以及磨损行为的影响机制；（3）在微球轴承的单晶硅滚道上利用射频等离子体增强化学气相沉积方法(rf-PECVD)制备类金刚石(DLC)膜，探讨类金刚石膜在微滚动接触下的微观结构特征和成膜条件，阐明其减摩和耐磨机理。本项目研究将为旋转MEMS中微滚动轴承的摩擦学设计提供理论依据，并为其减摩抗磨提供关键技术。

微滚动轴承比平面接触式微轴承摩擦系数低，而比非接触式微轴承支承稳定并且硅微制造工艺简单，因而被当作未来旋转MEMS器件的首选支承。然而迄今为止，对于尺度效应和表面效应影响微滚动摩擦和磨损的机制尚不清楚，已成为阻碍微滚动轴承发展的瓶颈。本项目开展了如下研究：（1）利用体硅DRIE和键合工艺研制一台能模拟微球轴承真实工况的试验装置，实现了转子角位移和法向载荷的在线监测，并通过减速实验获得了微尺度滚动摩擦力矩随法向载荷的变化规律。结果表明：单个微球-滚道接触副的滚动摩擦力矩与载荷成亚线性关系，这一规律与数值模拟结果相同。（2）提出了考虑黏附滞后的微尺度滚动摩擦理论模型，考察了微球尺度参数、相对黏附滞后量、Tabor数以及外载荷对最大滚动摩擦力矩的影响。结果表明：由于黏附作用，微尺度下的最大滚动摩擦力矩与外载荷呈亚线性的关系，且零载荷下的最大滚动摩擦力矩不为零，其无量纲值不仅随微球尺度参数的减小而增大，表现出明显的尺度效应，而且随相对黏附滞后量及Tabor数的增加而增加。（3）在微球轴承的单晶硅滚道上利用射频等离子体增强化学气相沉积方法(rf-PECVD)制备类金刚石(DLC)膜，研究了类金刚石膜在微滚动接触下的磨损机理。实验结果表明，微球轴承磨损机理主要包括两个方面：即微球与类金刚石薄膜之间的接触面在瞬时高温下受很高的接触应力作用而产生粘着磨损，以及微球对类金刚石薄膜施加周期性的循环应力而产生薄膜表面疲劳磨损。此外，还研究了微球与表面涂覆DLC薄膜的滚道之间的接触力学行为，考察了不同DLC薄膜弹性模量和厚度，以及不同微球材料和直径对微球轴承接触特性的影响。结果表明，高弹性模量的厚DLC薄膜可以降低微球轴承滚道表面的最大径向拉应力和界面剪切应力，但提高了最大接触压力；轴承轴向最大von Mises等效应力和界面应力梯度可通过减小DLC薄膜的弹性模量或增加薄膜厚度来降低。本项目研究将为旋转MEMS中微滚动轴承的摩擦学设计提供理论依据，并为其减摩抗磨提供关键技术。