Slider Mass Research Articles

Effects of Design Parameters on Bouncing Vibrations of a Single-DOF Contact Slider and Necessary Design Conditions for Perfect Contact Sliding

The general characteristics of the bouncing vibrations of a IDOF contact slider model over the surface of a harmonic wavy disk were studied both by computer simulation and theoretical analysis. The necessary design conditions for a contact slider and the surface of a disk were discussed in terms of perfect contact sliding and wear durability. It was found that the bouncing vibrations change with the amount of waviness amplitude A(fr) at the contact resonant frequency fr(=(1/2π)kc/m) relative to static penetration depth δ, or fr relative to limiting critical frequency fcl, above which the downward acceleration of the surface of a disk is larger than that of a slider due to slider load. When the contact stiffness is large enough so that δ < A(fr) (fcl < fr), the slider bounces with a large amplitude similar to an elastic impact in a wide frequency range. When the contact stiffness is small enough so that δ > A(fr) (fcl > fr), bouncing vibrations occur near the contact resonance, similar to the resonance of a nonlinear soft spring system. Here, the bouncing vibration can be completely eliminatedby increasing the contact damping ratio and decreasing the slider mass and the waviness amplitude.

Effects of Slider Mass, Contact Stiffness and Contact Damping on Contact Force of a Single-DOF Contact Slider Model.

In this work, we elucidated the effects of slider mass, contact stiffness and contact damping on contact force of a single-DOF contact slider model in wide ranges of the parameter values by means of computer simulation. We found that contact force is mainly related to bounce height so that low bouncing height leads to low contact force. In general, at a larger slider mass the peak of maximum contact force shifts to a lower frequency region with no marked change in the maximum contact force. At the same slider mass, a decrease in contact stiffness can result in a marked decrease in the contact force. However the durability to wear is low because small contact stiffness can actually be realized by reducing contact area. At high contact stiffnesses of 1.5×107 N/m, large contact area can increase durability to wear, although bouncing height is large. In any contact stiffness, we can eliminate the bouncing vibration and suppress contact force by making the slider mass small and the disk surface ultra-smooth. As for the contact damping, an increase in the contact damping ratio has the remarkable effect of suppressing the contact force.

Effects of Slider Mass, Contact Stiffness and Contact Damping on Bouncing Vibrations of a Single-DOF Contact Slider Model.

In this work, we elucidated the effects of slider mass, contact stiffness and contact damping on bouncing vibration of a single-DOF contact slider model in wide ranges of the parameter values by means of computer simulation. We found that the bouncing vibration behaviors are governed by the contact resonance frequency and a critical frequency above which the slider downward acceleration is smaller than the wariness acceleration. At a low contact stiffness of 1.5×105 N/m, the bouncing vibration characteristics versus waviness frequency are similar to the forced vibration characteristics of a nonlinear soft spring system. In cases of high contact stiffnesses, 1.5×106 and 1.5×107 N/m, the slider bounces like in an elastic collision. In general, at a larger slider mass the peak of maximum bounce height shifts to a lower frequency region with no marked change in the maximum bounce height. At the same slider mass, a decrease in contact stiffness can result in a marked decrease in the bouncing vibration. In the case of high contact stiffness, we can eliminate the bouncing vibration by making the slider mass small and the disk surface ultra-smooth. As for the contact damping, an increase in the contact damping ratio has the remarkable effect of suppressing the bouncing vibration.

コンタクト記録におけるスライダ質量・押し付け荷重のヘッド跳躍への影響

The authors studied the effects of the slider mass and load force on the head jumping height in contact recording. The experiments were performed by using a contact-type model head and a measurement system consisting of an LDV and a piezo actuator. It has shown the results as follows. The jumping height decreased with an increase in the loading force. The jumping height had a complex dependences on the slider mass and load force. It was reduced for a slider of more than 1.0 mg under a suitable loading force. Lubrication lowered the jumping height. As regarding the jumping height, these findings suggest that, it is possible to design a contact recording head-disk interface (HDI) by using a high-mass slider such as conventional ones.

球面コンタクトスライダにおけるスライダ質量・押し付け荷重の摩耗・跳躍特性への影響

The authors investigated the effects of the slider mass and load force on both the jumping height and the wear of the contact pad for contact recording, using simulation and vibration energy experiments. The wear characteristics were determined by comparing the simulation results with those of the acoustic emission experiment, using a spherical contact pad with Hertz's contact. It was found that a low load leads to low wear on the contact pad. A high-mass slider, with a conventional magnetic head, can be used for contact recording. The use of liquid bearings with thick lubricant is an effective method for reducing highfrequency slider vibration.

Creep, stick-slip, and dry-friction dynamics: Experiments and a heuristic model.

We perform an extensive study of the dry-friction dynamics of a paper-on-paper system. We explore the dynamical phase diagram by systematically varying the relevant control parameters (driving velocity V, slider mass M, and loading machine stiffness k). A set of experimental results gives strong proof that the low-velocity dynamics is controlled by a creep process, in agreement with previous results from rock mechanics and metals [C. H. Scholz, The Mechanics of Earthquakes and Faulting (Cambridge University Press, Cambridge, 1990), Chap. 2 and references therein; E. Rabinowicz, Proc. Phys. Soc. 71, 668 (1958) and references therein]. At higher velocities, a crossover to inertial dynamics is observed. In each regime, when k is increased, the system bifurcates from periodic stick-slip to steady sliding: in the creep regime, the bifucation is a direct Hopf one; in the inertial regime it becomes subcritical. We identify, from comparison of the time dependence of the static friction coefficient ${\mathrm{\ensuremath{\mu}}}_{\mathit{s}}$(t) and of the velocity dependence of the stationary dynamic one, ${\mathrm{\ensuremath{\mu}}}_{\mathit{d}}$(V), a memory length of the order of 1 \ensuremath{\mu}m. The V dependence of ${\mathrm{\ensuremath{\mu}}}_{\mathit{d}}$(V) changes from V weakening to V strengthening at the creep-inertial crossover. We propose a heuristic model of low-velocity friction based on two main ingredients: (i) following and extending the ideas of Ruina [J. Geophys. Res. 88, 10 359 (1983)], we define a phenomenological contact age accounting for the renewal of physical contacts on the scale of the memory length, and (ii) we assume that the dynamics is controlled by the Brownian motion of an effective creeping volume in a pinning potential, the strength of which increases with age.The crossover from creep to inertial motion then naturally appears as the runaway threshold between thermally activated and free motion. The bifurcation analysis in the creep regime is compared in detail with experimental results, yielding a very satisfactory agreement. When confronted with rock mechanics results, this study strongly suggests that low-velocity creep is quite generic; further studies of this process should in particular bear on models of earthquake dynamics.

The Dynamic Stability and Non-Linear Resonance of a Flexible Connecting Rod: Single-Mode Model

An analytical and computer simulation investigation of the dynamic behavior associated with the flexible connecting rod of an otherwise rigid, in-line, planar slider-crank mechanism is presented. The main goal of this work is to determine the manner in which this response depends on the system parameters, with a particular emphasis on non-linear analyses of the dynamic response near resonance conditions. A single-mode model is distilled from the governing partial equations and is used to describe the transverse deflection of the connecting rod. It is found that the slider mass is the primary source of the non-linearity, and that the connecting rod behaves as a system with a softening type of non-linearity, which is subjected to both external and parametric excitations. The effects of selected non-dimensional system parameters, such as the length ratio, damping ratios, frequency ratios and inertia ratios, are investigated in detail. A systematic numerical study is also carried out and compared with the analytical results.

Reducing flying height degradation due to track access acceleration acting on a magnetic head slider

Flying height fluctuations in a magnetic head slider were measured during track access using an optical interferometric technique. It was found that flying height of the front rail decreases while that of the rear rail increases due to acceleration during track access. Upon deceleration the situation is reversed. It is clear that flying height degradation is strongly influenced by deformation of the flexure element of a magnetic head suspension. An analytical model of the flying height degradation is presented to predict the flying height degradation for both Watrous and Winchester suspensions. By reducing installation angle of the flexure element, it is possible to reduce the flying height degradation. The flying height degradation can also be reduced by reducing slider mass and offset in the flexure mounting surface from the slider mass center and by increasing slider's air bearing stiffness.

A slotted-crank mechanism with a flexibly attached slider for path generation and its dynamic synthesis

Methods reported so far for the synthesis of 4-bar mechanisms with rigid links for path generation are very complex. In this paper a slotted link mechanism consisting of a flexibly attached slider is proposed for path generation. A pointer attached to the slider mass will trace a curve. Equation of motion for the slider mass and its solution are developed. The equation obtained for displacement of the slider mass is linear and can be used for the synthesis of a mechanism by closed form solution as well as for optimization through the method of least-square, etc. Example problems are included.

Synthesis of a mechanism with a flexibly attached slider for space curve generation

Generation of space curves is rather a difficult problem and not much work is reported in the literature. Planar 4-bar mechanisms with rigid links have been investigated for plane curve generation but the methods reported are complex. In this paper a slotted link mechanism with a flexibly attached slider is proposed for space curve generation. Equation of motion for the slider mass comes out to be nonlinear but the solution, i.e. the displacement of the slider mass is expressed in a linear form so that the synthesis either by precision point approach or through the method least squares becomes extremely simple. An example problem is included.

Dynamic synthesis of a 2-degree-of-freedom function-generator with flexible elements

Kinematic synthesis of planar 2-degrees-of-freedom linkages with at least seven links hitherto reported in the literature is very difficult due to the highly nonlinear equations that result. Special techniques are needed to solve these nonlinear equations. Both the formulation and the solution are extremely tedious and time consuming. In what follows a linkage with a flexibly attached slider is proposed. The differential equation of motion of the slider mass and its solution lead to a much simpler displacement equation which can be used for the closed form synthesis of a function generator for two independent variables. The resulting equations are linear simultaneous, the solution of which is a routine matter. The dimensions obtained can be used as starting values for optimisation by least squares method etc. An example problem is solved to illustrate the application.

Kineto-Elastodynamic Analysis of Slider-Crank Mechanism With a Flexibly Attached Slider

Kineto-elastodynamics is the study of the motion of mechanisms considering the elasticity of the links. The mechanism examined in this paper is the eccentric slider-crank mechanism in which the slider mass is connected with the coupler by means of a linear spring. Equations for kineto-elastodynamic analysis of the mechanism have been derived, and an iterative scheme is suggested for the solution. Friction is assumed small, and the effect of damping, clearances in joints, and tolerances on links have been neglected. Some example problems are worked out, and the results are compared with the available ones.