With the minimum fly height less than 10 nm in contemporary hard-disk drives, understanding nanoscale heat transfer at the head-disk interface (HDI) is crucial for developing reliable head and media designs. While flying at near-contact, the fly height and spacing dependent nanoscale heat transfer are significantly affected by interfacial forces in the HDI (such as adhesion force, contact force etc.). Moreover, with the emergence of technologies such as Heat-Assisted Magnetic Recording and Microwave-Assisted Magnetic Recording, head failure due to overheating has become an increasing concern. In this study, we present a numerical model to simulate the head temperature profile and the head-disk spacing for a flying head over a spinning disk and compare our results with touchdown experiments performed with a magnetic recording head flying over a rotating Al-Mg disk. In order to accurately predict the fly height and heat transfer at near-contact, we incorporate asperity based adhesion and contact models, air & phonon conduction heat transfer, friction heating and the effect of disk temperature rise in our model. Our results show that the incorporation of adhesion force between the head and the disk causes a reduction in the fly height, leading to a smaller touchdown power than the simulation without adhesion force.

The frictional properties of a hybrid lubricant film composited from perfluoropolyether (PFPE) lubricant (Moresco DDOH) with single end group and PFPE film deposited from HT170 (Solvay) via photoelectron-assisted chemical vapor deposition (PACVD) were evaluated using a pin-on-disk tester and compared with that of a Z-tetraol dip-coated film. The frictional coefficient of only the HT170 film deposited via PACVD was considerably high; however, the hybrid lubricant film without the mobile fraction showed a friction coefficient equivalent to that of the Z-tetraol film with a mobile fraction of 40%.

This paper proposes a new concept of piezoelectric actuator. It is different from ordinary piezoelectric actuators which are actuated by friction, and wear becomes a major problem in long-term use. The main purpose of this research is to drive the motor without friction. Hence, the actuator driven by resonance force is proposed here. The foundation of the actuator is based on piezoelectric material which possess the inverse piezoelectric effect itself. The axial deformation of piezoelectric material is worked as excitation here, which makes the stator subjected to mutative equivalent force along the time. At the same time, the input frequency of sinusoidal voltage is controlled and applied to the stators which makes the stators resonated and in contact with motor for pushing the motor forward. In addition to proposing the preliminary design concept of linear piezoelectric actuator, the dynamic model of the piezoelectric actuator system is firstly studied by Hamilton’s Principle. Then, the finite element method is used to calculate the modal analysis of stator. Finally, the prototype is fabricated and experiment platform is established. The vibration response of stators is measured by laser Doppler vibration measuring system, which is able to verify reasonableness of the constructed finite element model and feasibility of linear piezoelectric actuator.

Conventional trains have used wheels while driving because of the friction between the rail and the wheels. However, the conventional train can’t drive fast. In contrast magnetic levitation (maglev) train can speed up to 600km/h. Because of driving so fast there are some vibrations on the car bodies. In this paper, we used multi-body dynamic analysis, ANSYS MAXWELL for determining magnetic forces and integrated with the MATLAB.

We examined the behaviors of the paper sheet in an overlap-type sheet separation mechanism and a pressing-type sheet separation mechanism. First, we introduced the models that can calculate the resistance force and feed force acting on the paper sheets in both sheet separation mechanisms. And, based on the calculation results of the resistance force and friction force between the paper sheets, we studied the behavior of the paper sheet in each separation mechanism. As a result, we found that an overlap-type sheet separation mechanism is superior to the pressing-type sheet separation mechanism but it is easily influenced by the feeding force caused by pick-up rollers, and also a pressing-type sheet separation mechanism has robustness for a thickness of paper sheet and for a feeding force caused by pick-up rollers.

Lubrication in nanometer-sliding gaps has attracted much interest along with the advance of processing technology. To clarify the lubrication phenomena in nanometer gaps, force measurement under accurate control of the gap between the sliding probe and sample surface is needed because the lubrication properties significantly depend on the gap size. In this paper, we aimed at realizing friction force microscopes that is capable of accurate control of sliding gap. A probe with an actuator that utilizes electrostatic force was proposed and its feasibility was demonstrated.

This paper deals with the influence of surface contamination on the frictional mechanisms of rubber rollers. The contamination which adhered on the rollers after feeding many sheets of papers is one of the predominant causes of paper jams. However, the mechanism has not been understood. The purpose of this paper is to clarify the relationships between the friction force and the real contact area of papers and contaminated rubber rollers. Carrying out paper feeding tests by using a commercial multifunction peripheral, we tested different types of papers produced by different manufacturers. The tests have been done with combinations of different manufacturer’s papers and different kinds of roller materials. Observations of the real contact area clarified that the roller surfaces covered with paper powders or lint reduces the friction coefficient.

A thorough understanding of the dynamic behavior of friction modifier additives added to lubricating oil is crucial for improving the performance of boundary lubrication. However, such understanding is still lacking due to difficulty in measurements. In this study, we used coarse-grained (CG) molecular dynamics (MD) simulations to gain insight into the behavior of stearic acid additives physically adsorbed on corrugated or smooth hematite surfaces which were separated by lubricating oil of dodecane at a nanometric distance and sheared relative to each other. Compared with all-atom MD simulations, our CG MD simulations provided comparable accuracy and 40 times faster computational speed. The simulation results showed that, in contrast to the case of smooth solid surfaces, shear-induced desorption of stearic acid molecules and re-adsorption during rest occurred at the convex portions of the corrugated solid surfaces. This demonstrates that roughness of sliding surfaces largely influences the dynamic behavior of additives in lubricating oil.

The purpose of this paper is to use the hydrostatic bearing technology with a permanent magnet synchronous motor to develop a high-load, high-precision and heavy-cutting indexing plate, and the PI algorithm is used for developing the precise positioning control technology of the indexing plate system. Compared with the conventional ball bearing systems, hydrostatic bearings have the advantageous characteristics of high stiffness, small friction, long life and superior shock absorption. Therefore, equipment like linear motion platform and indexing plate which apply hydrostatic bearing can achieve a high positioning accuracy. It is expected that the indexing plate system with the PI controller can be used as a fourth or fifth axis for high precision processing machines.

We investigated the effect of the friction coefficients of a barrel on grinding performances in a planetary ball mill. The linear velocity of chips, impaction and shear energy according to the friction coefficients were simulated by the discrete element method (DEM). The increase of the friction coefficient of the barrel not only improves the shear energy due to increasing the relative velocity between chips, but also reduces the impaction due to decreasing the average linear velocity of the chips. Finally, we validated the simulated result by measuring the removal amount of chips before and after grinding test and comparing with shear energy. The experimental results show the similar trend as the simulated results.

It is well known that two ideally confident surfaces should give the effect of superlubricity, e.g. should slide without friction. In principle, the superlubricity deals with absence of energy dissipation mechanism. If we consider interatomic interactions, we see that the number of atoms, which resist sliding is equal to the number of atoms that push slider. In the case of noncontact quantum friction interacting surfaces are divided by some spatial interval. This sliding can take place in probe (atomic force or scanning tunneling) microscopy. However, experiments usually show nonzero friction force in this case. Nowadays there are several mechanisms of the noncontact friction. According to all of these models the noncontact friction arises from photons momentum transfer between surfaces. But there is much more efficient mechanism of noncontact friction dealing with electron tunneling. Two tunneling electron flows or tunneling currents between close conductive surfaces transmit momentum from a moving body (slider) to the fixed one (substrate) and at the same time in backward direction. At the thermodynamic equilibrium conditions these two counter-flows are equal. We have calculated these flows. Two different approaches have been applied — quantum mechanical and quasi-classical ones. The complex shape of the sliding surface have been taken into account by introduction of special function for the distribution of the tunneling gap width. In this model, noncontact friction is similar to Newtonian viscous friction in the fluid. Friction force has been calculated for both variants. Numerical evaluations according to both formulas have shown rather similar results. It has been found that in both cases friction force is proportional to the slider’s speed and exponentially decreases with increase of the tunneling gap. In addition, the friction force disappears at zero temperature. The tangential stresses have been obtained from numerical calculations for different surfaces with different roughness and for the atomically smooth surfaces. These values are close to macroscopic friction stress in experiments.

The reduction of head-media separation (HMS) results in a decreased flying height. Consequently, the contact probability between the slider and the lubricant layer or hard overcoat surface on the disks will increase greatly. Therefore, investigating the contact stress of the disk is vital for improving the reliability of the head disk interface. In this study, a rigid hemisphere sliding over a multilayer thin film half-space is implemented to simulate the contact between the recording slider and the magnetic storage multilayer disk under the quasi-static condition. The effects of different parameters such as normal load, friction coefficient and radius of slider on the von Mises, shear and principal stresses in the multilayer system are analyzed by using finite element method (FEM).

Cable driven parallel robots (CDPRs) are a class of parallel robots in which the rigid links are replaced by cables. It consists of a moving end-effector and a number of active cables connected to the end-effector.

Voltage assisted wear at the head and the disk interface is investigated with the motive of understanding the head overcoat wear processes. In this work, we report the quantitative analysis of voltage assisted wear on head carbon overcoat at high sliding speed interfaces. We found that voltage assisted TFC head wear acts asymmetrically at the interface with positive voltage leading to high wear. We quantitatively analyzed the interface using a strain gauge based friction measurement.

Reduction of head-media spacing (HMS) keeps crucial during the increase of areal density of hard disk drives (HDD). The design of hard disk drive with a superlubric interface is reported with two schemes for HDI design to realize superlubricity. For the first scheme, the DLC layer is kept on the disk while removing the lubricant layer. The DLC layer on the transducer is replaced by graphene-like layer. The direct contact between head and disk could reduce the HMS to about 2.3 nm. For the second scheme, the DLC layer on disk is further replaced by graphene and the HMS could be reduced to below 1 nm. For the first scheme, the basic proof of concept experiments are conducted using micro-scale graphite island samples. Ultralow COF, with the average of 0.0344 on the interface of single crystalline graphite surface and DLC substrate is demonstrated by AFM. What’s more, the temperature dependence of friction between single crystalline graphite and DLC is measured by micro-force sensor mounted on micro-manipulator. The results show that heating helps to significantly decrease the friction. Desorption of contaminants along the interface is speculated to be the key mechanism for temperature dependence of friction. This work provides the concept of large-scale superlubricity relevant in HDD applications, which could be a promising technology to ultimately reduce HMS for future HDI development.

A computationally efficient five-degree-of-freedom dynamic model was developed to simulate the motion of a magnetic head slider under the conditions of moving-bump collision and of contact due to an expanding protrusion on the slider for thermal flying-height control, with consideration of intermolecular forces. Compared to results obtained without intermolecular forces for a bump on the rotating disk, the intermolecular forces cause a significantly greater normal contact force, a larger roll angle and a larger off-track displacement under nonzero skew. When an expanding protrusion on the slider reaches a position close to the disk surface, the intermolecular forces pull the slider into contact at an earlier time and keep the protrusion in contact for a longer duration, which, with friction under nonzero skew, results in a substantially greater off-track displacement.

The dynamic friction and wear at the head and the disk interface is investigated with the motive of understanding the head overcoat wear process associated with physical contact between the head and the disk. In this work, the results from systematic experiments under overpush conditions are presented. Various regimes of head wear are identified based on the individual wear rate of the participating overcoat layers. A strain gauge based friction measurement is used to extract the friction coefficient and the adhering shear strength between the head and the disk.

In the pursuit of high areal recording density towards 10 Tb/in 2 , it is necessary to improve the positioning accuracy of the magnetic head in the hard disk drive head-positioning control system. Ultrasonic motors (USMs) are novel electric motors used for positioning controls. Due to the drive characteristic of USMs, wear and fatigue of friction material at the contact friction interface are inevitable. Contact deformation can cause local damage of USMs. Therefore, obtaining the details of the stress distribution in the friction material due to the inelastic deformation is important. In this work, a contact model of traveling wave ultrasonic motor (TWUSM) is proposed. A three dimensional finite element model with cohesive zone elements embedded between friction material and rotor is then developed. Infinite finite elements are incorporated in this modeling as the boundary condition as the model thickness is typically many orders smaller than the longitudinal dimension. The evolution of deformation in friction material and rotor due to the mechanical surface loading is presented. The possible interfacial delamination process between friction material and rotor is numerically studied. And the friction coefficient effect of the friction material on the delamination propagation is also investigated.

The effect of normal load on fretting wear of the dimple-gimbal interface is investigated. The wear volume, the wear coefficient and the friction-displacement loops are studied as a function of the number of fretting wear cycles. The wear volume of the dimple is calculated from the radius of the wear scar obtained using scanning electron microscopy. The results show that the wear coefficient decreases with an increase in the number of fretting wear cycles.

This research investigates the Monte Carlo simulation of manufacturing tolerance of FDBs to identify the sensitive design variables for the friction torque of fluid dynamic bearings (FDBs) and the critical mass of disk-spindle system supported by FDBs. We analyze the characteristics according to design variables of FDBs and it shows that the clearance of journal bearing is most sensitive design variable of both friction torque and critical mass. Also the groove to groove and ridge ratio and groove depth of grooved journal bearing which are manufactured by ECM are also sensitive to determine the friction torque and the critical mass of the FDBs, respectively. This research can be utilized to manage manufacturing tolerance to maintain the consistent performance of FDBs and a disk-spindle system in a HDD.