Flying Height Variation Research Articles

Using Multi-Spectral UAV Imagery to Extract Tree Crop Structural Properties and Assess Pruning Effects

Unmanned aerial vehicles (UAV) provide an unprecedented capacity to monitor the development and dynamics of tree growth and structure through time. It is generally thought that the pruning of tree crops encourages new growth, has a positive effect on fruiting, makes fruit-picking easier, and may increase yield, as it increases light interception and tree crown surface area. To establish the response of pruning in an orchard of lychee trees, an assessment of changes in tree structure, i.e., tree crown perimeter, width, height, area and Plant Projective Cover (PPC), was undertaken using multi-spectral UAV imagery collected before and after a pruning event. While tree crown perimeter, width and area could be derived directly from the delineated tree crowns, height was estimated from a produced canopy height model and PPC was most accurately predicted based on the NIR band. Pre- and post-pruning results showed significant differences in all measured tree structural parameters, including an average decrease in tree crown perimeter of 1.94 m, tree crown width of 0.57 m, tree crown height of 0.62 m, tree crown area of 3.5 m2, and PPC of 14.8%. In order to provide guidance on data collection protocols for orchard management, the impact of flying height variations was also examined, offering some insight into the influence of scale and the scalability of this UAV-based approach for larger orchards. The different flying heights (i.e., 30, 50 and 70 m) produced similar measurements of tree crown width and PPC, while tree crown perimeter, area and height measurements decreased with increasing flying height. Overall, these results illustrate that routine collection of multi-spectral UAV imagery can provide a means of assessing pruning effects on changes in tree structure in commercial orchards, and highlight the importance of collecting imagery with consistent flight configurations, as varying flying heights may cause changes to tree structural measurements.

Near Contact Thermal Flying Height Control in Hard Disk Drives

A modeling and optimization approach is proposed and implemented for minimizing variations in flying height of thermal flying height control (TFC) sliders. The method utilizes the resistive heater element of TFC sliders for adjustment of spacing and the embedded thermal contact sensor (TCS) as a relative measurement for changes in flying height. In the modeling approach, the static and dynamic behavior of the TCS as a function of heater power is characterized. A model of the system is identified from experimental step excitation data using a realization algorithm. In the optimization approach, the optimal feedforward heater input profile is calculated via convex optimization techniques based on the static and dynamic behavior of the system. The modeling and optimization approach was verified experimentally, showing that the proposed approach reduces the difference between the maximum and the minimum value of the TCS measurements by a factor of two, indication a twofold reduction of flying height variations.

Numerical Simulation of Thermal Flying-Height Control Sliders to Dynamically Minimize Flying Height Variations

Thermal flying-height control (TFC) sliders have been used for active flying height control of hard disk drives. It is of particular interest to investigate if TFC sliders can be used to minimize both repeatable and nonrepeatable flying height variations. To that end, the power input to the heater must be dynamically optimized at each time step in order to minimize changes in flying height. In the current study, a numerical procedure is implemented to simulate the time dependent response of a TFC slider to changes of the heater element power input. The dynamic Reynolds equation and slider equilibrium equations are solved simultaneously to determine the dynamic change in flying height as a function of time. The change of thermal protrusion as a result of the optimized power input to the heater is computed using a TFC slider finite element model. The reduction of flying height variation is studied using past and present flying height histories and optimization of the power input to the heater. It is shown that the dynamic approach can be successfully used to minimize both repeatable and nonrepeatable flying height changes at the hard disk interface.

Time dependent simulation of active flying height control of TFC sliders

A time-dependent numerical simulation procedure is implemented to simulate the flying height response of a typical thermal flying height control (TFC) slider as a function of the power input to the heater element. The Reynolds equation is used in conjunction with a TFC slider finite element model to determine the change in the thermal protrusion and flying height of the slider. The power input signal to the heater element is optimized using convex optimization to minimize flying height variations of the slider. The optimization procedure is applied to a typical experimentally measured flying height profile. The numerical simulation results are in excellent qualitative agreement with experimental measurements.

Dynamic Flying Height Adjustment in Hard Disk Drives Through Feedforward Control

A dynamic model of the resistance heater element in a thermal flying height control (TFC) slider of a hard disk drive is identified and used for dynamic flying height control. Experimental data obtained on a spin stand and a generalized realization algorithm are used for identification of a discrete-time dynamic model of the thermal actuator. The flying height change is measured in two different ways: using servo burst information written onto the disk surface and using information written in the data sectors only. The resistance change of the thermal actuator based on the input power level is measured. Based on the identified discrete-time model of the heater and using convex optimization techniques, a computational scheme is proposed to obtain optimized feedforward input profiles to the heater element that minimize repeatable flying height variations and enable low flying heights.

Optimal Feed Forward Profiles for Dynamic Flying Height Control in Hard Disk Drives

AbstractA dynamic model of the resistance heater in a thermal flying height control (TFC) slider of a hard disk drive is identified and used for dynamic flying height control. Experimental data obtained on a spin stand and the generalized realization algorithm are used for identification of a discrete-time dynamic model of the resistance heater (thermal actuator). The flying height change is measured using servo burst information written onto the disk surface. Based on the identified discrete-time model of the heater and convex optimization techniques, a computational scheme is proposed to obtain optimized feed forward input profiles to the heater element that minimize repeatable flying height variations and enable low flying heights.

Flying-Height Measurement With a Symmetrical Common-Path Heterodyne Interferometry Method

To enhance the magnetic storage capacity of hard disk drives, the areal density of recording has to be increased continuously. But as the areal density of recording increases to over 100 Gb/in2, the head-disk physical gap, also called flying height (FH), decreases to less than 10 nm. Measurement of FH becomes a significant challenge. In this paper, we propose a symmetrical common-path heterodyne interferometry method to measure FH, utilizing a transverse mode Zeeman laser and a high-speed phase measurement technology, which has the sampling frequency of 100 kHz. We have developed a prototype FH tester based on the method. To effectively compensate influences of the tilt of the rotating disk, vibration of the optical system, and other environmental disturbances on measurement accuracy, we introduced a tri-spot distribution compensation method. Theoretical analysis indicates that the resolution of the FH measurement method reaches 0.1 nm. We carried out a series of experiments of FH measurement with this system, and the results indicate that the measurement system is sensitive enough to FH variation and can measure FH with a high precision and high response. We compared the experimental results with the predictions of FH by numerical simulation of thin-film gas lubrication of sliders, with good agreement.

Numerical Quasi-Static Analysis of Ultralow Flying Slider During Track-Seeking Motion Over Discrete Track Media

It is important to accurately estimate the flying height (FH) of the ultralow flying slider in hard disk drive (HDD). Especially, during the track-seeking motion, the FH can change by the motion from inner diameter (ID) to outer diameter (OD) and vice versa. The FH variation induced by the track-seeking motion happens over discrete track media (DTM). Therefore, the FH variation during track-seeking is an important issue and it certainly should be considered for DTM. In this research, we performed the track-seeking simulation using quasi-static approximation to reduce the computation time. The effects on groove depth, width, and pitch with the effective skew angle taken into account were investigated with the simulation. As a result, we calculated the absolute change in FH as a function of the effective skew angle and groove depth. Finally, we proposed that the model that considers the effective skew angle over DTM should be adopted in the track-seeking motion-studies.

Effect of thermal pole tip protrusion and disk roughness on slider disk contacts

Ultra-high areal density for hard disk drives requires a stable head disk interface at a flying height lower than 8 nm. At such a low flying height, small flying height variations may cause slider/disk contacts. Slider/disk contacts can also occur when a write-current is applied to the write coil since the flying height between slider and disk can be affected by the thermal expansion of the pole tip. In this paper, we investigate the vibration characteristics of sliders during thermally induced contacts using laser Doppler vibrometry. We perform a parametric study of contact events using disks with different surface roughness and lubricant thicknesses, and analyze the slider motion statistically. For a given write current, we observe that the slider vibrations increase with disk roughness and lubricant thickness.

Numerical and Experimental Analyses of Nanometer-Scale Flying Height Control of Magnetic Head With Heating Element

Hard drives featuring sliders with active flying-height (FH) control using thermal expansion of a heating element have been recently introduced in products. This approach allows to actively compensate for static FH variations and achieves sub-3-nm clearance during read/write operation. This paper describes a nonlinear numerical model of a perpendicular magnetic recording head for accurate simulation of pole-tip protrusions and their effect on FH change under various conditions, such as at an elevated drive temperature, with the heater activated or during write operation. The model integrates an electrical-thermomechanical finite-element model of slider and a full air-bearing solver, and includes lapped pole-tip recession and slider/disk deformation due to air-bearing pressure. We are able to predict key parameters that are not easily measurable (e.g., minimum/reader/writer FH, different protrusion profiles for ambient temperature, heater actuation, and during writing). We also present novel experimental methods for measuring protrusion and clearance delta profiles with angstrom-level resolution. The modeling results are compared to experimental data under various test conditions showing excellent agreement. From this method, we are able to quickly evaluate and optimize different heater, head, and ABS designs.

Method for In Situ Motion Measurement of Head-Slider in Both Flying Height and Off-Track Directions

We present a novel method to determine the motion of the slider's flying height and off-track direction simultaneously in a hard disk drive. The results show the relative movement of the slider in two dimensions, both during thermal actuator controlled contact and full flying condition. The method separates the position error signal (PES) and the flying height signal from the readback signal. The method includes writing dual-frequency pattern tracks adjacently, with the readback signals from the tracks filtered for the in situ motion measurement. The harmonic ratio method is used to determine the flying height variation of the head, whereas the conventional servo burst detection method is used to determine the PES.

Slider Dynamics With Adhesive Force in Near-Field Recording

A near-field optical disk drive uses near-field optics to read/write disk data at a flying height of about 50 nm. Effects of interfacial adhesive forces, including van der Waals forces and electrostatic forces, become more evident during ultralow flying. However, the pickup head-flying-height variation is affected by the suspension, disk flutter, and air flow between the flying head and disk. An analysis model consisting of a simplified suspension and an air-bearing model with springs and dampers in three directions (focusing, pitching, and rolling) is used to simulate the dynamic behavior of the flying head. This study proposes an improved method for measuring the slider's flying-height variation. Simulation results with and without interfacial adhesive forces are compared

An optical lever approach to photodetector measurements of the pickup-head flying height in an optical disk drive

In order to increase the storage capacity and the density of near-field optical disk drives, a flying pickup-head has to allow a slider to fly at a stable height above the disk surface with the use of near-field optics. Since both the precision of the track pitch and the flying height are of a nanometre scale, it is necessary to increase the motion accuracy of the pickup-head. In this study, a piezoelectric bender is used as an actuator of the pickup-head, and two quadrant photodetectors are used to sense the pickup-head displacement and the rotating disk deformation. Based on an optical lever method that magnifies a small displacement, the flying height variation of the pickup-head above the disk is measured. Further results show that using the proposed measurement method in the real-time control of flying height is feasible.

High air-bearing stiffness slider design

This paper discusses the approach to design air bearing surface (ABS), which can achieve high air bearing (AB) stiffness and high air pressure (AP). Generally, in order to reduce flying height variation and improve the slider's flying stability, high AB stiffness and high AP are preferred. AB stiffness and AP is very sensitive to the slider's ABS design. The flying height and flying attitude of slider is realized by ABS design. According to our study, flying stability of slider is also affected by ABS design. The slider has higher AB stiffness and higher air pressure; it is going to fly more stable. [E.M. Jayson, J. Murphy, P.W. Smith, F.E. Talke. J. Tribol. 125 (2003) 343; W.C. Choi, Y.H. Shin, J.H. Choi. JSME Int. J. 44 (2001) 470.] In order to increase highly the AB stiffness and AP, a dual shallow step structure in a slider is explored. It proved that the dual shallow step structure-increases the air bearing stiffness and the AP on the head area significantly. The structure of central trailing pad is found to have much higher influences on the AB stiffness and AP than the other pads. Optimizing the structure of central trailing pad in the dual shallow step structure slider can further increase the AB stiffness and AP. Finally, the optimized dual shallow step structure slider has much higher AB stiffness and much greater AP on the head area than the normal single shallow step slider. Therefore, the flying stability of the slider with optimized dual shallow step structure should be better.

Disk clamping distortion and slider crown sensitivity induced flying height variation

The disk clamping distortion and slider crown sensitivity induced flying height (FH) variation is investigated. The experimental results which were measured with in situ method were compared with simulated numerical results. Both results indicate that the disk clamping distortion has significant influence on the FH variation. Crown sensitivity of the sliders is one of the factors that determine the amplitude of the FH variation. Higher crown sensitivity sliders exhibit greater FH variation.

Thermo-resistive flight attitude measurements of flying heads in near-field magnetooptical data storage

The development of an optical recording system which is based on the flying head technology requires to determine the head's dynamic flight behavior. To do so, a thermo-resistive test head was created. It uses thermo-resistors embedded in the air-bearing surface (ABS). Joule heating by the sensing current generates a heat flow across the head-disk spacing which highly depends on the distance between ABS and disk. Due to the thermal sensors located on each of the four corners of a slider, pitch, roll, and flying height variations may be measured.

An Optical Flying Head Assembly for a Small-Form-Factor Plastic Disk in PCMCIA-Like Drive

In a small-form-factor (SFF) optical disk drive (ODD), the optical flying head (OFH) on a thin-cover-layered plastic disk requires not only uniformity of the cover layer thickness of the disk media, but also the flying stability of OFH on the plastic disk surface with low flying height variation, as well as precise tolerance management in the OFH assembly. Therefore, in order to develop a practical optical pickup head interfaced to the plastic disk, we designed the OFH with a parallel-plate electrostatic actuator for the vertical positioning of the objective lens for better flying characteristics. The flying height of the OFH is designed to be 200 nm to increase air-bearing stiffness. On the other hand, a UV resin cover layer is adopted as a protective layer and a hard and stiff plastic substrate is also adopted to increase the durability of the disk. In the evaluation of the stability of the OFH and the durability of the disk, we introduce computational and experimental results on the flying height variation of the OFH, additionally we investigated the characteristics of the durability of various plastic disks.

浮上スライダの耐衝撃特性(情報機器コンピュータメカニクス1 -ヘッド・ディスク・インターフェース,IIP2004 情報・知能・精密機器部門講演会)

The report is about a simulation of a negative pressure slider due to a shock. In the simulation, a shock with downward direction and a shock with upward direction are used. The shock is set as a triangle wave with maximum value 9800m/s^2(1000G) and varied duration. It is clear that squeeze effect of air bearing surface play an important role when a shock is gave to slider. In the case under downward shock, the flying height variation in short duration is smaller than in long duration, and in the case under upward shock, the suction face in short duration is larger than in long duration.The suction force of ABS under a upward shock is larger than the suction force that occurs in normal flying situation.

Head slider designs using approximation methods

This paper presents an approach to optimally design the air bearing surface (ABS) of the head slider by using the approximation methods. The reduced basis concept is used to reduce the number of design variables. In the numerical calculation, the progressive quadratic response surface modeling (PQRSM) is used to handle the non-smooth and discontinuous cost function. A multi-criteria optimization problem is formulated to enhance the flying performances over the entire recording band during the steady state and track seek operations. The optimal solutions of the sliders, whose target flying heights are 12 nm and 9 nm, are automatically obtained. The flying heights during the steady state operation become closer to the target values and the flying height variations during the track seek operation are smaller than those for the initial one. The pitch and roll angles are also kept within suitable ranges over the recording band.

Spacing fluctuation induced by disk clamping distortion

This paper reports the results of study on the spacing fluctuation of sliders induced by the disk clamping distortion. The investigations were carried out with in situ flying height testing technology introduced by the authors. Various shapes of disk deformation were studied in the experiment. Results obtained show that the spacing fluctuation is a function of the amplitude of the disk clamping distortion. Results also exhibit that higher air bearing stiffness reduces the amount of flying height (FH) variation. Also, it is interesting to notice that the lower FH slider can introduce a higher percentage of FH variation compared with the slider of higher FH. Investigations are also extended to study the effect of slider's loading force on the FH variation of the slider. Results indicate that the changes of the loading force for the low FH slider could intensify the FH variation.