Experimental study on slider dynamics during touchdown by using thermal flying-height control

To investigate the possibility of further lowering the clearance in head?Cdisk interface systems, slider dynamic behavior during a touchdown sequence with a thermal flying-height control (TFC) function was investigated by using a spinstand-level evaluation utilizing an acoustic emission (AE) sensor and a laser Doppler vibrometer (LDV). Experimental results demonstrated that off-track vibration was easier to excite by head?Cdisk contact at the beginning of head?Cdisk contact. We then confirmed that the amplitude of pitch-mode vibration in the flying-height direction increased and sway-mode vibration in the off-track direction decreased when increasing heater power during the touchdown sequence. Moreover, we found that the peak frequency of pitch-mode vibration shifted to a higher frequency under over-push conditions. Time?Cfrequency domain analysis results showed that the peak shift occurred at several locations during a disk rotation. The mechanism of the peak shift is attributed to the increase in stiffness at the head?Cdisk interface (HDI) due to solid?Csolid contact or mode change occurred in such regions. During the touchdown sequence, the friction force at the HDI continues to increase, even though slider vibration and AE signal decrease when heater power is increased. The friction force at the HDI needs to be decreased to achieve further low-clearance HDI.     

Dynamics of droplet transport induced by electrowetting actuation

This study reports on the dynamics of droplets in the capillary regime induced by electrowetting-on-dielectric actuation. The configuration investigated allows for comparing the experimental results with respect to the predictions of Brochard’s theoretical model (Brochard in Langmuir 5:432–438, 1989). Firstly, side-view observations using stroboscopic recording techniques were used to measure and analyse droplet deformations as well as the front and rear apparent contact angles during motion. Secondly, the influence of viscosity on the droplet velocity as a function of the applied voltage was studied. This has revealed that low Reynolds number droplet motion can be described by the simple laminar viscous model of Brochard. Finally, the influence of the dielectric thickness on the droplet dynamics was studied. It is shown that droplet velocity is limited by a saturation effect of the driving electrostatic force and that this phenomenon is very similar to that occurring in static experiments.     

On the continuous contact force models for soft materials in multibody dynamics

A general and comprehensive analysis on the continuous contact force models for soft materials in multibody dynamics is presented throughout this work. The force models are developed based on the foundation of the Hertz law together with a hysteresis damping parameter that accounts for the energy dissipation during the contact process. In a simple way, these contact force models are based on the analysis and development of three main issues: (i) the dissipated energy associated with the coefficient of restitution that includes the balance of kinetic energy and the conservation of the linear momentum between the initial and final instant of contact; (ii) the stored elastic energy, representing part of initial kinetic energy, which is evaluated as the work done by the contact force developed during the contact process; (iii) the dissipated energy due to internal damping, which is evaluated by modeling the contact process as a single degree-of- freedom system to obtain a hysteresis damping factor. This factor takes into account the geometrical and material properties, as well as the kinematic characteristics of the contacting bodies. This approach has the great merit that can be used for contact problems involving materials with low or moderate values of coefficient of restitution and, therefore, accommodate high amount of energy dissipation. In addition, the resulting contact force model is suitable to be included into the equations of motion of a multibody system and contributes to their stable numerical resolution. A demonstrative example of application is used to provide the results that support the analysis and discussion of procedures and methodologies described in this work.     

Numerical modeling of electrowetting transport processes for digital microfluidics

Electrical actuation and control of liquid droplets in Hele-Shaw cells have significant importance for microfluidics and lab-on-chip devices. Numerical modeling of complex physical phenomena like contact line dynamics, dynamic contact angles or contact angle hysteresis involved in these processes do challenge in a significant manner classical numerical approaches based on macroscopic Navier–Stokes partial differential equations. In this paper, we analyze the efficiency of a numerical lattice Boltzmann model to simulate basic transport operations of sub-millimeter liquid droplets in electrowetting actuated Hele-Shaw cells. We use a two-phase three-dimensional D3Q19 lattice Boltzmann scheme driven by a Shan–Chen-type mesoscopic potential in order to simulate the gas–liquid equilibrium state of a liquid droplet confined between two solid plates. The contact angles at the liquid–solid–gas interface are simulated by taking into consideration the interaction between fluid particles and solid nodes. The electrodes are designed as regions of tunable wettability on the bottom plate and the contact angles adjusted by changing the interaction strength of the liquid with these regions. The transport velocities obtained with this approach are compared to predictions from analytical models and very good agreement is obtained.     

Grasping impact force control of a flexible robotic gripper using a piezoelectric actuator

This paper presents robust force tracking control of a flexible beam during a grasping operation using a piezoceramic actuator. Equations describing the motion of the gripper in conditions of contact and noncontact are derived based on the cantilever beam. In this study, contact force is regulated, in addition to the impact force generated at the instant of contact, based on variable structure model reference adaptive control theory using only force measurements. For the derivation of the control law, it is assumed that parameters of the beam and the stiffness of the object are unknown. Computer simulations show the effectiveness the controller. This work was presented, in part, at the Fourth International Symposium on Artificial Life and Robotics, Oita, Japan, January 19–22, 1999     

Dual track Wallace fly height measurement method to monitor slider motion in 2 dimension at near contact regime

Head media spacing of hard disk drive (HDD) is expected to continue its reduction in order to support areal density growth. At sub-nm clearance between the head and the disk, the intermittent head disk contact and interactions may happen. This does not only cause the fly height modulation but also induces the off-track motions as well. It is desirable to understand the characteristics of the 2D motions in the near contact regime, so as to enable further reduction of the clearance and to improve the reliability of HDD. This paper presents a method to measure instantaneous fly height (FH) motion and cross track motion concurrently by using read back signal from the dual data tracks written at different frequencies. The method is able to separate the FH motion and cross track motion of the head.     

Development of a touch probe based on five-dimensional force/torque transducer for coordinate measuring machine (CMM)

Systematic errors due to the pre-travel variation and the probe tip shape are irreducible to the traditional touch trigger probing systems. This paper describes the development of a probing system based on five-dimensional force/torque transducer for coordinate measuring machines. The compensation for pre-travel variation is accomplished through the five-dimensional force/torque information acquired by the integrated transducer and the stiffness matrix of the stylus. From the relationship between the obtained force/torque information and the geometrical shape equation, coordinates of the exact contact point immune from the contact error are acquired. After calibration, the combined measurement uncertainty is estimated to be less than ±0.3 μm.     

Dynamics of a three-module vibration-driven system with non-symmetric Coulomb’s dry friction

In the present paper, a three-module vibration-driven system moving on a rough horizontal plane is modeled to investigate the relation among the system’s steady-state motion, external Coulomb’s dry friction force and internal excitations. Each module of the system represents a vibration-driven system composed of a rigid body and a movable internal mass. Major attention is focused on the primary resonance situation that the excitation frequency is close to the first-order natural frequency of the system. In the case that the external friction is low, the internal excitation is weak and the stick–slip motion is negligible, both methods of averaging and modal superposition are employed to study the steady-state motion of the system. Through a set of algebraic equations, an approximate value of the system’s average steady-state velocity is obtained. Several numerical examples are calculated to verify the validity of the analytical results both qualitatively and quantitatively. It is seen that big quantitative errors will appear if stick–slip motions occur. Then, two mechanisms for the possible stick–slip motions are put forward, which explain the errors on the average steady-state velocity. Numerical simulations verify our analysis on the stick–slip effects and their mechanisms. Finally, to maximize the average steady-state velocity of the system, optimal control problem is studied. It is shown that, in addition to modifying the friction coefficients, the improvement of the system’s efficiency can be provided by changing the initial phase shifts among the three internal excitations.     

Mechanical characteristics of a contact optical head slider operating on a metal-layered medium

 Advances in a digital network society require both higher density and higher transfer rates in all sorts of storage systems. Even in optical recording, the trend toward higher density and larger capacity requires novel surface-recording technologies that can drastically diminish head-to-medium spacing, resulting in an improvement in spatial resolution and, finally, a higher recording density. In this paper, we propose a novel contact optical head slider that is able to almost cancel the suspension load by generating hydrodynamic pressure, thus realizing a lower net contact force. A trial-manufactured contact slider being processed four sliding pads on air-bearing surfaces has indicated a gentle variation of both the acoustic emission signal intensity and the friction force as the circumferential velocity changes. Furthermore, a time-domain simulation was performed to investigate the effects of the damping of a medium surface (lubricant) both on slider bouncing and on contact force. Received: 5 July 2001/Accepted: 1 November 2001     

Capillary and electrostatic limitations to the contact angle in electrowetting-on-dielectric

The shape of a conducting liquid droplet placed on a hydrophobic dielectric surface is simulated numerically by solving the Laplace–Young capillary equation. The electric force, acting on the conducting surface, distorts the droplet shape leading to a change in the apparent contact angle; its variation is compared with a theoretical Young–Lippman prediction. At sufficiently large values of voltage, applied to the droplet, the numerical algorithm fails to converge, which is interpreted as the break-up of the droplet surface with small droplets being ejected from the surface. These highly charged droplets, as well as any other electric charges near the triple contact line, generated for example by the electric corona discharge, cause a change of the distribution of the electric forces. This effect can be helpful in explaining saturation of the apparent contact angle: an appropriately selected surface charge near the contact line can completely stop droplet distortion, and the contact angle variation, despite the increased droplet voltage. Furthermore, the simulation results show the effect of the permittivity of the medium surrounding the droplet, on the contact angle variation.     

Electroosmotic flow at a liquid–air interface

This paper presents the first experimental evidence on electroosmotic flow at a liquid–air interface. A PDMS microchannel with an opening to air was created to allow for the formation of a liquid–air interface. Polystyrene particles were used to visualize the liquid motion and the experiments found that the particle velocity at the liquid–air interface was significantly slower than the particle velocity in the bulk. This result agrees with a mathematical model that considers the effects of electrical surface charges at the liquid–air interface in electroosmotic flow.     

Performance-optimized design of electromagnetic micro-actuator for Probe recording storage device

In this paper the performance-optimized design of an electromagnetic micro-actuator for a Probe data-storage system is described. The Probe recording system considered in this study consists of a MEMS-based recording head array that can translate relative to a Ferroelectric media substrate. The probe device is slated to achieve 1 Tb/in2 recording density and a read/write data rate of 100 Mb/s while operating within a total power budget of 100 mW. Stringent requirements apply to the form-factor and packaging, power consumption, and operating environment making the design of the mechanical architecture and in particular, the actuator a challenging task. A methodology based on an analytical model framework for performance-optimal design of the actuator meeting these constraints is developed and presented.     

Six-DOF vibrations of partial contact sliders in hard disk drives

A six-degree-of-freedom slider dynamic simulator is developed to analyze the slider’s motion in the vertical, pitch, roll, yaw, length and width directions. The modified time-dependent Reynolds equation is used to model the air bearing and a new second order slip model is used for a bounded contact air bearing pressure. The simulator considers the air bearing shear acting on the air bearing surface and the slider–disk contact and adhesion. Simulation results are analyzed for the effects of the disk surface micro-waviness and roughness, skew angle, slider–disk friction and micro-trailing pad width on the vertical bouncing, down-track and off-track vibrations of a micro-trailing pad partial contact slider.     

Stochastic model for metastable wetting of roughness-induced superhydrophobic surfaces

A stochastic model for metastable wetting of roughness-induced hydrophobic surfaces is proposed. For a rough surface, increased solid–liquid interface area results in increased interface energy, and increases the contact angle (for non-wetting liquids) or decreases it (for wetting liquids). For a very rough surface, a composite solid–liquid–air interface may form with air pockets trapped in the valleys between asperities, as opposed to the homogeneous solid–liquid interface. Both the homogeneous and composite interface configurations correspond to local energy minima of the system and therefore, there are stable states associated with different energy levels. The system may transform from one stable state to the other due to small perturbations, such as capillary waves. Different probabilities are associated with these different stable states, depending on the energy levels. The contact zone consists of a large number of asperities and valleys, which may be in the homogeneous or composite state. The overall contact angle is calculated based on the statistical model. The model may be used for design of roughness-induced superhydrophobic surfaces.     

A self-propelled robotic system with a visco-elastic joint: dynamics and motion analysis

This paper studies the dynamics and motion generation of a self-propelled robotic system with a visco-elastic joint. The system is underactuated, legless and wheelless, and has potential applications in environmental inspection and operation in restricted spaces which are inaccessible to human beings, such as pipeline inspection, medical assistance and disaster rescue. Locomotion of the system relies on the stick–slip effects, which interacts with the frictional force of the surface in contact. The nonlinear robotic model utilizes combined tangential-wise and normal-wise vibrations for underactuated locomotion, which features a generic significance for the studies on self-propelled systems. To identify the characteristics of the visco-elastic joint and shed light on the energy efficacy, parameter dependences on stiffness and damping coefficients are thoroughly analysed. Our studies demonstrate that the dynamic behaviour of the self-propelled system is mainly periodic and desirable forward motion is achieved via identification of the variation laws of the control parameters and elaborate selection of the stiffness and damping coefficients. A motion generation strategy is developed, and an analytical two-stage motion profile is proposed based on the system response and dynamic constraint analysis, followed by a parameterization procedure to optimally generate the trajectory. The proposed method provides a novel approach in generating self-propelled locomotion, and designing and computing the visco-elastic parameters for energy efficacy. Simulation results are presented to demonstrate the effectiveness and feasibility of the proposed model and motion generation approach.     

The “Authoring on the Fly” system for automated recording and replay of (tele)presentations

We discuss the problem of capturing media streams which occur during a live lecture in class or during a telepresentation. Instead of presenting yet another method or system for capturing the classroom experience, we introduce some informal guidelines and show their importance for such a system. We derive from these guidelines a formal framework for sets of data streams and an application model to handle these sets so that a real-time replay becomes possible. The Authoring on the Fly system is a possible realization of a framework which follows these guidelines. It allows the capture and real-time replay of data streams captured during a (tele)presentation, including audio, video, and whiteboard action streams. This article gives an overview of the different AoF system components for the various phases of the teaching and learning cycle. It comprises an integrated text and graphics editor for the preparation of pages to be loaded by the whiteboard during the presentation phase. The recording component of the system captures various data streams of the live presentation. They are postprocessed by the system so that they become instances of the class of media for whose replay the general application model was developed. From a global point of view, the Authoring on the Fly system allows one to merge three apparently distinct tasks – teaching in class, telepresentation, and multimedia authoring – into one single activity. The system has been used routinely for recording telepresentations over the MBone net and has already led to a large number of multimedia documents which have been integrated automatically into Web-based teaching and learning environments.     

Thermocapillary convection and interface deformation in a liquid film within a micro-slot with structured walls

Thermocapillary convection in a thin liquid film inside a micro-slot with structured walls kept at different temperatures is studied. The liquid film is wetting the substrate wall and is separated from the cover wall by a gas layer. If the slot walls are structured, the temperature at the liquid–gas interface is non-uniform. The temperature variation induces thermocapillary stresses which bring the liquid into motion and lead to the interface deformation. We investigate the film flow inside the micro-slot, the heat transfer, the liquid–gas interface deformations and the film stability in the framework of the long-wave theory. We show that the amplitude of the interface deformation increases with increasing of the wall structure period. We demonstrate that the structured walls lead to the heat transfer enhancement, which effect is for the studied range of parameters stronger if the cover wall is structured. We also show that the wall structure enhances the long-wave Marangoni instability. The destabilizing effect of the substrate structure is stronger than that of the cover wall structure. This work has been originally presented at the 3rd International Conference on Microchannels and Minichannels, 13–15 June 2005, Toronto, Canada.     

Profile-based roughness discrimination with pen-type texture sensor

Tactile discriminations of surface roughness using artificial sensors have been challenging. The modeling methods and parameters that have been using to describe the mechanical properties of rough surface are insufficient for haptic roughness. This paper proposes a method to characterize surface roughness based on the profiles of the surface. A compact handheld pen-type texture sensor with a right probe is developed for the measurement of surface profiles. Based on the contact force and the motion of the senor, profiles in the paths of scanning are estimated. The height variations of a profile are converted to a series of tactile stimuli to represent the contact stimulations in haptic explorations. The mean and the standard deviation of the amplitudes of stimuli are identified as haptic features that indicate the required tangential force to slide on the rough surface and how rough the surface is, respectively. Experiments show that the roughness on four kinds of sandpapers can be clearly distinguished by the proposed discrimination method.     

Water droplet properties on periodically structured superhydrophobic surfaces: a lattice Boltzmann approach to multiphase flows with high water/air density ratio

Surface roughness affects the contact angle (CA) due to the increased area of solid–liquid interface and due to the effect of sharp edges of rough surfaces. Roughness may also lead to another non-wetting regime, by forming a composite solid–liquid–air interface between the water and the textured surface; this composite interface exhibits strong water repellency due to the various pockets of air entrapped between the surface textures. The contact between water and a hydrophobic textured surface leads to one of these two regimes depending on the thermodynamics stability of the regimes. In this study, the projection method of lattice Boltzmann method is used to analyze the large density difference at the air and water interface. The method is applied to simulate two-phase flows with the density ratio of up to 1,000. A numerical model is presented to provide a relationship between roughness and CA, which is used to develop optimized texture topography and create a biomimetic superhydrophobic surface. The numerical models encompass the effects of contact area, solid–liquid–gas composite interface and shape edges. The models are reused to analyze different possible roughness distributions and to calculate the effect of the cross-sectional area of pillars, including rectangular, triangular, cross, and pyramidal pillars. The energy barrier is investigated to predict the position of the transition between the Cassie and Wenzel regime observed for each roughness parameter as well as a theoretical free surface energy model.     

Modeling, control, and stability analysis for time-delay TLP systems using the fuzzy Lyapunov method

In this study, we present a Takagi–Sugeno (T–S) fuzzy model for the modeling and stability analysis of oceanic structures. We design a nonlinear fuzzy controller based on a parallel distributed compensation (PDC) scheme and reformulate the controller design problem as a linear matrix inequalities (LMI) problem as derived from the fuzzy Lyapunov theory. The robustness design technique is adopted so as to overcome the modeling errors for nonlinear time-delay systems subject to external oceanic waves. The vibration of the oceanic structure, i.e., the mechanical motion caused by the force of the waves, is discussed analytically based on fuzzy logic theory and a mathematical framework. The end result is decay in the amplitude of the surge motion affecting the time-delay tension leg platform (TLP) system. The feedback gain of the fuzzy controller needed to stabilize the TLP system can be found using the Matlab LMI toolbox. This proposed method of fuzzy control is applicable to practical TLP systems. The simulation results show that not only can the proposed method stabilize the systems but that the controller design is also simplified. The effects of the amplitude damping of the surge motion on the structural response are obvious and work as expected due to the control force.