More Like this

1. Friction-induced instability and vibration in a precision motion stage with a friction isolator

   https://doi.org/10.1177/1077546321999510  

   Wang, Jiamin; Dong, Xin; Barry, Oumar R; Okwudire, Chinedum (March 2021, Journal of Vibration and Control)

   null (Ed.)

   Motion stages are widely used for precision positioning in manufacturing and metrology applications. However, they suffer from nonlinear premotion (i.e. “static”) friction, which adversely affects their speed and motion precision. In this article, a friction isolator is used as a simple and robust solution to mitigate the undesirable effects of premotion friction in precision motion stages. For the first time, a theoretical study is carried out to understand the dynamic phenomena associated with using a friction isolator on a motion stage. Theoretical analysis and numerical simulation are conducted to examine the dynamical effects of friction isolator on a proportional–integral–derivative-controlled motion stage under LuGre friction dynamics. The influence of friction isolator on the response and stability of the system is examined through theoretical and numerical analyses. Parametric analysis is also carried out to study the effects of friction isolator and friction parameters on the eigenvalue and stability characteristics. The numerical results validate the theoretical findings and demonstrate several other interesting nonlinear phenomena associated with the introduction of friction isolator. This motivates deeper nonlinear dynamical analyses of friction isolator for precision motion control. 

   more » « less
2. BIFURCATION ANALYSIS OF A PD CONTROLLED MOTION STAGE WITH A NONLINEAR FRICTION ISOLATOR

   Ehab E. Basta, Sunit K. (January 2023, ASME: IDETC-CIE 2022)

   The utilization of mechanical-bearing-based precision motion stages (MBMS) is prevalent in the advanced manufacturing industries. However, the productivity of the MBMS is plagued by friction-induced vibrations, which can be controlled to a certain extent using a friction isolator. Earlier works investigating the dynamics of MBMS with a friction isolator considered a linear friction isolator, and the source of nonlinearity in the system was realized through the friction model only. In this work, we present the nonlinear analysis of the MBMS with a nonlinear friction isolator for the first time. We consider a two-degree-of-freedom spring-mass-damper system to model the servo-controlled motion stage with a nonlinear friction isolator. The characteristic of the dynamical friction in the system is captured using the LuGre friction model. The system’s stability and nonlinear analysis are carried out using analytical methods. More specifically, the method of multiple scales is used to determine the nature of Hopf bifurcation on the stability lobe. The analytical results indicate the existence of subcritical and supercritical Hopf bifurcations in the system, which are later validated through numerical bifurcation. This observation implies that the nonlinearity in the system can be stabilizing or destabilizing in nature, depending on the choice of operating parameters. 

   more » « less
3. Stability and Bifurcation Analysis of Precision Motion Stage With Nonlinear Friction Isolator

   https://doi.org/10.1115/1.4062266  

   Gupta, Sunit K.; Basta, Ehab E.; Barry, Oumar R. (August 2023, Journal of Computational and Nonlinear Dynamics)

   Abstract The application of servocontrolled mechanical-bearing-based precision motion stages (MBMS) is well-established in advanced manufacturing, semiconductor industries, and metrological applications. Nevertheless, the performance of the motion stage is plagued by self-excited friction-induced vibrations. Recently, a passive mechanical friction isolator (FI) has been introduced to reduce the adverse impact of friction in MBMS, and accordingly, the dynamics of MBMS with FI were analyzed in the previous works. However, in the previous works, the nonlinear dynamics components of FI were not considered for the dynamical analysis of MBMS. This work presents a comprehensive, thorough analysis of an MBMS with a nonlinear FI. A servocontrolled MBMS with a nonlinear FI is modeled as a two DOF spring-mass-damper lumped parameter system. The linear stability analysis in the parametric space of reference velocity signal and differential gain reveals that including nonlinearity in FI significantly increases the local stability of the system's fixed-points. This further allows the implementation of larger differential gains in the servocontrolled motion stage. Furthermore, we perform a nonlinear analysis of the system and observe the existence of sub and supercritical Hopf bifurcation with or without any nonlinearity in the friction isolator. However, the region of sub and supercritical Hopf bifurcation on stability curves depends on the nonlinearity in FI. These observations are further verified by a detailed numerical bifurcation, which reveals the existence of nonlinear attractors in the system. 

   more » « less
4. Robust planar dynamic pivoting by regulating inertial and grip forces

   Hou, Y.; Jia, Z.; Johnson, A.M.; Mason, M.T. (January 2020, Algorithmic Foundations of Robotics XII)

   In this paper, we investigate the planar dynamic pivoting problem, in which a pinched object is reoriented to a desired pose through wrist swing motion and grip force regulation. Traditional approaches based on friction compensation do not work well for this problem, as we observe the torsional friction at the contact has large uncertainties during pivoting. In addition, the discontinuities of friction and the lower bound constraint on the grip force all make dynamic pivoting a challenging task for robots. To address these problems, we propose a robust control strategy that directly uses friction as a key input for dynamic pivoting, and show that active friction control by regulating the grip force significantly improves system stability. In particular, we embed a Lyapunov-based control law into a quadratic programming framework, which also ensures real-time computational speed and the existence of a solution. The proposed algorithm has been validated on our dynamic pivoting robot that emulates human wrist-finger configuration and motion. The object orientation can quickly converge to the target even under considerable uncertainties from friction and object grasping position, where traditional methods fail. 

   more » « less
5. Velocity Dependence of Dynamic Rock Friction Modulated by Dynamic Rupture in High‐Speed Friction and Stick‐Slip Tests

   https://doi.org/10.1029/2024JB030402  

   Chen, Xiaofeng; Saber, Omid; Chester, Frederick_M (March 2025, Journal of Geophysical Research: Solid Earth)

   Abstract Rock friction tests have made profound contributions to our understanding of earthquake processes. Most rock friction tests focused on fault strength evolution during velocity steps or at specific slip rates and the characteristics during stick‐slip events such as dynamic rupture propagation and the transition from stable sliding to instability, with little attention paid to the transient acceleration and deceleration periods. Here, we present Westerly Granite fault friction test results using a unique pneumatically powered apparatus with high acceleration of up to 50 g, focusing on the transient stages of fast fault acceleration and deceleration during both high‐speed sliding and stick‐slip events. Our data demonstrates the dominating velocity‐weakening behavior at transient stages of fault acceleration and deceleration, with a 1/V dependence for peak friction and deceleration lobe consistent with the flash‐heating model but with the acceleration lobe consistently deviating from the 1/V dependence. Our analysis of velocity‐dependent friction between dynamic rupture events, stick‐slips, and high‐speed friction tests reveals the significance of high acceleration in influencing transient fault weakening during dynamic weakening. We further demonstrate that the deviation of the friction‐velocity curve from the 1/V trend during fault acceleration is associated with the contribution of the dynamic rupturing process during the initiation of fault slip. 

   more » « less