Characterization of Dynamic Friction in MEMS-Based Microball Bearings

Abstract

ISR develops, applies and teaches advanced methodologies of design and analysis toAbstract-Rolling element bearing is a well-known concept in macroscale machinery applications. They are prospective candidates for friction reduction in microelectromechanical system (MEMS), as well as for providing stable, robust support for moving micromechanisms. The characteristics of rolling element bearings need to be investigated to facilitate their applications in MEMS. It is well understood that the measured data on the macroscale cannot be directly applied to the microscale. This paper presents an in-situ noncontact experimental system to characterize the friction behavior of microball bearings on the microscale. The methodology presented in this paper provides a useful template to study the dynamical behavior of linear microball bearings with a variety of materials, geometries, and surface qualities. The system, actuated by a motor, affords wide ranges of motion for measuring the dynamic friction using a vision system. It allows the determination of the coefficient of friction (COF) without any interference due to the measurement system. With careful optimization, the error in measurement has been reduced to 2%. Different designs of microball bearings are proposed to achieve lower friction. The studied microball bearings demonstrated an average static COF of 0.01 and an average dynamic COF of 0.007 between stainless-steel and silicon-micromachined contacting surfaces at 27 C and 40% relative humidity.Index Terms-Microelectromechanical systems (MEMS), microball bearings, rolling friction, silicon micromachining, V-grooves.

Vision-Based Microtribological Characterization of Linear Microball Bearings

“…By collecting motion data of the bearing elements through a CCD camera, one can infer the friction dynamics inside the system. For a more detailed description of the basic setup, see [2]. Several improvements have been made to upgrade the system reported in [2].…”

“…For a more detailed description of the basic setup, see [2]. Several improvements have been made to upgrade the system reported in [2]. A camera (Sony DCR-TRV22) with night-shot mode, a finepositioning stage, a 24 X magnification lens, and a halogen bulb as an infrared source enable one to see through the slider and observe the microballs closely.…”

“…A linear microball bearing structure was proposed and its static coefficient of friction (COF) measured by Ghodssi et al [1]. A vision-based experimental setup was developed to study the dynamic friction of linear ball bearings by Lin et al [2], where the underlying friction model consisted of the Coulomb friction only.…”

“…As a continuation of the work in [2], this paper contains indepth characterization and understanding of the microtribological behavior using infrared imaging, scanning electron microscopy (SEM) imaging, and analysis. The contributions of this paper include: a) verification of rolling motions of microballs by directly observing trajectories of all bearing elements (stator, slider, balls); b) observation of the hysteresis between the friction and the relative velocity; and c) investigation of the influences of the ball number and oxide formation on the frictional behavior.…”

“…A linear microball bearing structure was proposed and its static coefficient of friction (COF) measured by Ghodssi et al [1]. A vision-based experimental setup was developed to study the dynamic friction of linear ball bearings by Lin et al [2], where the underlying friction model consisted of the Coulomb friction only.As a continuation of the work in [2], this paper contains indepth characterization and understanding of the microtribological behavior using infrared imaging, scanning electron microscopy (SEM) imaging, and analysis. The contributions of this paper include: a) verification of rolling motions of microballs by directly observing trajectories of all bearing elements (stator, slider, balls); b) observation of the hysteresis between the friction and the relative velocity; and c) investigation of the influences of the ball number and oxide formation on the frictional behavior.…”