Simulation of thermal flying height control slider with built-in contact sensor

This work investigates the piezoelectric contact sensor in the thermal flying height control (TFC) slider. A finite element model is built for the thermal flying height control slider with a piezoelectric contact sensor, which is used to detect the contact between the slider and disk. A constant force is applied at the maximum thermal protrusion point of air bearing surface. The simulation results show that the ZnO sensor with shear-mode is more sensitive to contact force than that with transverse-mode. The sensitivity of contact sensor can be increased by reducing the cross-sectional area of sensor, increasing the thickness of sensor, and choosing a short distance of sensor to air bearing surface. In addition, the thermal-stress effects from TFC heater on contact sensor are significantly large and the amplitude of thermal-stress inducing output voltage is orders larger than that induced by contact force. However, by optimizing the distance of sensor to ABS, it is possible to eliminate the thermal-stress effects. Finally, the response time of thermal-stress induced electrical voltage of contact sensor is about 0.3?ms.     

Characterization of light contact in head disk interface with dynamic flying height control

This paper presents an investigation of the light contact in a head disk interface with dynamic flying height control. The touchdown test is conducted for a dynamic flying height control slider and the response is recorded using AE sensor. The bouncing instability and light contacts are observed during thermal actuated touching down process of the slider. The physics-based simulation is conducted to correlate with the experiments, so as to characterize bouncing instability and the factors affecting bouncing instability. The enhanced spectrogram and HHT approaches are used to extract and characterize the non-stationary characteristics of the weak signal of slider response under light contact. It is found that the light contacts are constituted by a series of intermittent transient impact responses with frequency identical to slider??s pitch mode.     

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.     

Investigation of wear resistance and lifetime of diamond-like carbon (DLC) coated glass disk in flying height measurement process

Flying height has been greatly reduced to less than 10 nm to achieve high-density magnetic storage. This leads to significant disk wear especially, glass disks used in flying height measurement process. This paper reports the utilization of diamond-like carbon (DLC) overcoat to increase the wear resistance and lifetime of commercial glass disks in a flying height tester. Wear resistance of the DLC coated glass disks was investigated in wear test using a triboindentor. The results showed significant wear resistance improvement of the coated disk where the wear depth reduced from 62.2 nm on an uncoated disk to 5–7 nm on 15-nm thick DLC coated disks. Furthermore, lifetime measurement of the coated disk has been performed in a flying height tester. As a result, lifetime of the coated disk has been drastically improved by more than 30 times in comparison to an uncoated disk.     

Servo signal processing for flying height control in hard disk drives

A novel method of measuring the relative head-medium spacing based on a measurement in the servo sectors is developed and simulated using a read back signal model. The spacing measurement is tested experimentally on a spin stand where the flying height is varied using the resistance heater element in a thermal flying height control slider. In addition, voltage step response measurements were obtained. The data were used to perform system identification and estimate the dynamics of the thermal actuator. The model can potentially be used for thermal flying height control.     

The flying height analysis of patterned sliders in magnetic hard disk drives

The ultra-low spacing of patterned sliders flying above a rotating disk with smooth surface in a hard disk drive is analyzed for high areal density recording. Three types of pattern (slender, square, and broad) with the same bump area are discussed. The molecular gas film lubrication (MGL) equation and the equations of motion of the patterned slider are solved numerically to obtain the steady flying attitude. The results show that the flying height of the broad patterned slider is the greater than either that of the square patterned slider or the slender patterned slider. In addition, we analyzed the effects of bump height and the bump pitch on the slider attitude, including flying heights, pitch angles, and roll angles, are discussed.The authors express their thanks for the foundation support from National Science Council, NSC 92-2212-E-151 -005, ROC.     

Numerical simulation of thermal flying height control sliders in heat-assisted magnetic recording

Heat assisted magnetic recording (HAMR) is one of the most promising techniques to extend the recording density in hard disk drives beyond 1?Tb/in². Although the diameter of the spot on the disk that is heated by the laser beam is very small, on the order of nanometers, high local temperatures on the disk and the heat dissipated in the slider during the light delivery process can cause thermal deformations of both the disk and the slider, thereby affecting the flying characteristics at the head-disk interface. In this paper, a finite element model is developed which incorporates a HAMR optical system into a thermal flying height control (TFC) slider with dual heater/insulator elements to study the effect of heat dissipation in the wave guide on the thermal deformation and flying characteristics of a HAMR-TFC slider. In addition, the power input of the laser and design parameters of the heaters are investigated.     

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.     

Parametric simulation of piezoelectric flying height control slider using shear-mode deformation

The piezoelectric flying height control slider has recently been implemented in magnetic recording disk drives to reduce the flying height. This paper performs the electromechanical simulation and air-bearing simulation to investigate the effects of the shear-model deformation on the static flying attitude of PZT slider. The location of PZT sheet and air bearing surface of slider are investigated to achieve a low flying height and robust head-disk interface. The results show that a short distance of the PZT sheet to the trailing edge of the slider can help to achieve a low flying height. A small center-trailing pad of the slider can also help to achieve a low flying height, but cannot prevent the reduction in pitch angle. The depth of the center-trailing pad does not change the reduction ratio of the pitch angle when increasing the drive voltage. A big pitch angle value is needed to avoid the pitch angle falling below zero at a high drive voltage.     

Effects of environmental temperature and humidity on thermal flying height adjustment

Thermal actuated sliders are being widely used in today’s hard disk drive industry for its advantages of easier control of flying height (FH) and less risk of contacts with the disk. This article uses a coupled-field analysis method, which includes an air bearing model, a heat transfer model and a thermal-structural finite element model to investigate the FH changes of thermal actuated sliders at various environmental conditions. The mechanism of water vapour’s contribution to air bearing pressure loss is explained and a new humidity model is proposed to calculate this pressure loss. The temperature effects are also considered in the simulation models. It is observed that the environmental temperature and humidity have significant effects on slider’s FH changes, but their effects on the thermal protrusion height are limited. A humidity sensitivity study is also made and the results are discussed. It is found that the slider with thermal protrusion on its trailing pad will be more sensitive to the humidity. Besides air bearing stiffness, some other factors such as peak pressure, protrusion shape and air bearing surface (ABS) design will also contribute to the slider’s humidity sensitivity.     

Experimental set-up for simultaneously measuring changes in LD temperature and flying height of HAMR-HGA

Heat-assisted magnetic recording (HAMR) is a promising technology for overcoming the performance limit of the conventional magnetic head in a hard disk drive. The HAMR-HGA consists of a HAMR-head slider, a suspension, and a laser diode (LD) mounted on the slider. An optical near-field transducer (NFT) and a waveguide are near the write-pole in the head slider. During the HAMR process, current is applied to an LD, and the laser beam is coupled into the waveguide and delivered to the NFT. The NFT further concentrate the focused optical spot and the optical spot locally heats the recording medium, thereby reducing the media coercivity. The temperature of the LD and the slider, however, increases. The slider is, moreover, locally deformed, and the flying-height (FH) changes. Therefore, an experimental set-up to simultaneously evaluate the FH change and LD temperature of the HAMR-HGA was required to develop the HAMR technology. We developed a novel experimental set-up for simultaneously evaluating laser characteristics (power, voltage, and wavelength), the increase in LD temperature, and the FH change of a HAMR-HGA. By using this set-up to measure these characteristics of our prototype, the HAMR-HGA showed that the FH decreased as the LD temperature increased. The LD temperature is directly related to the laser characteristics. The change in laser characteristics affects the read-write performance of HAMR. The FH change also affects the performance. Therefore, the developed experimental set-up should be useful in improving HAMR-HGA.     

Examination of flying height of magnetic head slider in simulations and measurements at nanometer-order spacing

This paper describes a comparison with the experimental flying heights and the simulated flying heights, which were calculated by using the linearized Boltzmann equation and the conventional modified Reynolds equations. The experiments were measured under the ambient pressure from atmospheric pressure to 6.7 × 10^?3 MPa. The calculated results of the linearized Boltzmann equation were almost the same as the experimental results from the high spacing range to the low spacing range of 10 nm. At the slider spacing of 10 nm, it was confirmed that the difference between the experimentally measured results and the calculated results of the linearized Boltzmann equation was less than 5%, and the differences in the conventional slip flow approximation equations were over 30%.     

时频分析在炮弹弹片飞行速率测量中的应用

炮弹爆炸产生弹片的数量不确定,弹片飞行方向和速率也各不相同,捕获所有弹片并测量其飞行速率的方法较复杂。鉴于此,设计了能捕获炮弹爆炸产生弹片的目标靶,并考虑目标靶靶区的实际电路特性,分析了目标靶靶区输出的信号特点。采用高速数据采集设备采集炮弹爆炸时刻至弹片全部穿过目标靶的一段时间内的各靶区输出信号,对该信号进行短时Fourier变换,分析各时间片段的信号幅频特性。再根据各时间片段的信号幅频特征,确定弹片刚触靶时刻点,由此计算得出弹片从爆炸点至触靶的飞行时间,测得爆炸点到目标靶的距离,就可计算得出弹片的飞行速率。最后举了个实例验证了该设计方案的可行性和正确性。     

Dynamics of ultra low flying sliders during contact with a lubricated disk

In this paper, laser Doppler vibrometry is used to study the motion of a femto slider in the vertical, pitch, roll, off-track and down-track direction due to slider–lubricant interactions. The change in slider dynamics is determined by comparing the laser Doppler vibrometer signals from the slider for time increments of 2 min. The time evolution of this signal is analyzed. The data suggest that slider–lubricant interactions at the head-disk interface have a strong effect on slider dynamics. Spectral analysis of the slider motion indicates that excitation occurs at the same frequency for all degrees of freedom. The excitation frequency is slightly lower than the free vibration frequency, suggesting that lubricant damping plays a role in the excitation of the slider.     

Adaptive flying height modulation control of hybrid active slider with thermal and piezoelectric actuators

Hybrid active slider is an effective means to increase the storage density of hard disk, but its effectiveness is compromised by the flying height modulation (FHM), the bounding vibrations associated with the slider. There is a need to reduce the FHM through real time control. The hybrid active slider exhibits a very complex dynamic behavior which causes a big challenge for the traditional controller relying on an exact dynamic model. Without the requirement of an exact knowledge of the dynamics of the slider, this paper proposes an adaptive control scheme to control the flying height modulation. It is designed from the model with uncertain parameters and can guarantee the convergence of FHM. The details of the controller design and the proof of its performance are presented, and simulation results are provided to verify the effectiveness of the controller.     

一种新型波高测量系统的设计

波高测量是海洋工程模型试验中的一项重要内容,为了能够准确、稳定地实时测量实验水池中的波浪,采用了一种新型的波高测量系统设计方法:首先利用液位高度与波高传感器电容量的线性关系将波高测量问题转化为电容量测量问题;其次利用波高传感器的电容量与其充放电时间的关系将波高传感器的电容量测量问题转化为充放电时间的检测问题;然后运用单片机片内模拟比较器和定时器的输入捕获功能将电容充放电时间转化为计数值;接下来将计数值通过USB接口送到上位机进行数据处理及波形显示;最后进行实验测试,实验结果表明所采用的波高测量方法是有效的,且具有线性度好、灵敏度高、精度高的优点。     

专家系统在车辆宽高检测中的应用

基于目前在动态宽高检测中由于车头后视镜而引进的宽度误差,从而设计了基于专家知识库的宽高检测系统。该系统采用专家知识库和数据库相结合的方法,有效滤去了车头的后视镜宽度。通过采集安装有该系统的某超限检测站的现场数据进行验证。结果表明：宽度的测量准确率符合《超限运输车辆行驶管理规定》,并且准确率高达98.8%。     

光电码盘技术在尾矿库高程测量中的应用

干滩高程测量是矿山企业尾矿库监测系统中一项重要的检测内容,用于检测矿山尾矿(废料)排放湖面的高度。尾矿库一般都地处偏远山区,要求检测设备具有很强的恶劣环境适应能力,因而迫切需要开发出一种新的测量技术,以用于满足数字化矿山建设的需要。光电码盘计数测距法就是为了满足这项实际需求而研发的。文章介绍了此项技术的工作原理、电路实现方法,并对波形处理、精度控制、数据处理等几方面也做了详细的阐述。     

临近空间太阳能飞翼无人机气动性能设计仿真

目前在进行临近空间太阳能无人机的设计时,通常采用常规布局,但常规布局的无人机在空气密度低的飞行环境中,速度小、动压小,气动性能较差,且常规布局飞机的表面不平整,不利于太阳能电池的大面积铺设。为此,特设计了一种飞翼布局的临近空间太阳能无人机,通过对翼型的气动仿真分析,优选出适合临近空间飞行环境、适用于飞翼无人机的反S型低雷诺数翼型,并采用翼梢外洗设计以改善无人机的稳定性,最后使用数值计算方法进行仿真计算,检验所设计飞翼无人机的气动性能。结果表明,根据数值方法仿真,所设计的临近空间太阳能飞翼布局无人机气动性能得到显著改善。     

Synthesis of optimal control systems with near sensitivity feedback

Design of optimal control systems with reduced sensitivity to parameter variations is attempted by employing trajectory sensitivity feedback and minimizing a cost term that includes the trajectory sensitivity. Since the trajectory, sensitivity, cannot be assessed directly, a successive approximation method that results in "near" sensitivity feedback is given for the case of linear regulators. The method may be extended to more general optimal control problems.