Actuator Arm Research Articles

The pulse width effect of single half-sine acceleration pulse on the peak response of an actuator arm of hard disk drive

For a head actuator assembly, its shock dynamic response and damage may be studied and assessed using vertical drop test simulation. The maximum relative deflection between the tip of the arm and the pivot can be used as an index of its response to shock. The pulse width effect on the peak response of the relative displacement of an actuator arm during a drop test was investigated by finite element method. The actuator arm was simplified as a single-degree-of-freedom (SDOF) system. It was found that for both the finite element analysis of the actuator arm, and the theoretical analysis of its simplified model as an SDOF system, when subjected to single half-sine acceleration pulses, the peak values of the maximum relative displacement occured at a certain frequency ratio, i.e., a pseudo-resonance phenomenon.

Numerical investigation of airflow inside a 1-in hard disk drive

The increasing application of the hard disk drive in consumer electronic devices has pushed the usage of the small form factor hard drives. At the same time, the data storage industry continues to enhance the capacity and performance of computer hard disk drive. The concerns of track mis-registration caused by various runout still remain with the form factor change. The objective of the current study is to numerically investigate the airflow characteristic inside a 1 in hard disk drive. The simulation model is constructed based on the currently available 1-in micro-drive in the market, with 3600 rpm disk rotation speed, thus the flow Reynolds number based on the disk tip radius is around 4.8×10 3. Two models with different actuator arm positions (outside and middle-disk) were studied. The simulation results show that the standard k-epsilon model used allows us to extract similar information and understanding as that from more developed numerical model. Good agreement in normalized velocity magnitude and flow pattern is observed between the numerical and experimental results. At different actuator arm positions, streamlines and velocity vectors plots show the effect of the actuator arm position to the flow pattern, especially around the arm. This arm position also affects the radial and tangential shear stress values over the disk, which may help to estimate the wind loss and power consumption.

Vibration and noise analysis of computer hard disk drives

Vibration and noise generated by some computer hard disk drives of different speeds have been analyzed. The vibration natural frequencies of disk platters were computed theoretically and by FEM. These were also verified experimentally by modal testing. The first four natural frequencies of the disk platters measured experimentally were 359, 525, 650 and 1080 Hz. The overall vibration amplitudes of rotating disk platters were also measured with the help of capacitance type of probe. Sound power levels of hard disk drives without covers were evaluated in seek and idle modes. The contribution of noise produced by different sources within the drives to total noise was assessed to find major noise sources. The measurement results showed that the major noise source in the lower speed hard disk drive was the actuator arm fly over the platter whereas in the case of higher speed drives, the main source was the disk platter air flutter noise. A weighted noise generated by the hard disk drives was mainly in the frequency range of 2–8 kHz.

Excitation pulse shape effects in drop test simulation of the actuator arm of a hard disk drive

For a head actuator assembly (HAA) of a hard disk drive, the deflection of the tip of the arm relative to the pivot can be used as an indicator of its response to shock. To study the pulse shape effects in a shock analysis, the actuator arm of an HAA subjected to different acceleration pulse shapes, such as half-sine, triangular and dual-quadratic, was simulated by using a dynamic finite element package. It has been found that, for the three acceleration pulses, the peak displacements have opposite behaviors for 0.1- and 1-ms pulse widths. The above phenomena have been explained in terms of a power spectrum analysis. It has been found that the relative magnitude of the peak displacement of the actuator arm is mainly determined by the power magnitude of the acceleration pulse at the resonant frequency. A simple mathematical theory was developed to predict the location of a cross-over interval which divides the power spectrum curve into two major regions where opposite behaviors are observed. The theoretical pulse width is correlated with a pulse width based on a threshold value as normally used in experiments.

Shock analysis of a head actuator assembly subjected to half-sine acceleration pulses

Shock robustness is an increasingly important design consideration for hard disk drives (HDD), as we move forwards toward consumer applications. For a head actuator assembly (HAA), which is the most important mechanical component of an HDD and consists of a cantilever arm fixed onto a pivot bearing, the maximun relative deflection between the tip of the arm and the pivot can be used as an index for its response to shock. The influence of pulse width/duration and pulse amplitude on the shock response of the relative displacement of the actuator arm is first investigated by the finite element method (FEM). The actuator arm is then simplified as a low-damping single-degree-of-freedom (SDOF) system. The shock response of the finite element model and that of the SDOF system are presented. It is found that, for both the finite element simulation and the theoretical analysis, when subjected to half-sine acceleration shock, the peak relative displacement occurs at a critical frequency ratio ( i . e . β = ω / ω n ≈ 0.6 ) , where ω and ω n are the characteristic frequency of the pulse loading and the first natural frequency of the system. In other words, a pseudo-resonance phenomenon occurs at this critical frequency ratio.

Design, modeling, and seek control of a voice-coil motor actuator with nonlinear magnetic bias

The research investigates the feasibility and trajectory tracking performance of an adaptive controller applied to a voice-coil motor actuator (VCMA) influenced by nonlinear magnetic bias. A magnetic bias feature on the actuator arm is designed to compensate for nonoperational shock. Because the resulting bias is nonlinear and uncertain, a model-based adaptive controller was developed to meet the seek performance requirements and simultaneously handle effects of the nonlinear bias. A VCMA with the bias feature was manufactured according to the design requirements. Extensive experiments were conducted to characterize the VCMA physical parameters and verify the controller performance. The effects of sample rate and bias modeling accuracy are also discussed. A representative sample of the results is presented.

Flow-Induced Vibration of Head Gimbal Assembly

This is a report on ways to reduce flow-induced vibration of a head gimbal assembly (HGA), i.e., windage. The relation between flow-induced force and windage was investigated; as was a statistical approach to optimizing an HGA-arm configuration. The investigated HGAs were set between disks in a spin stand, and their windages were measured by using a laser Doppler vibrometer. The amplitude of sway mode was found to be almost in inverse proportion to the square of its frequency because the power spectrum of the airflow between disks is in inverse proportion to the square of its frequency. Miniaturizing HGAs is therefore an effective way to reduce windage because its natural frequencies then become higher. The windage measured for a HGA with a part length of 12, for example, is 40% less than that of one with a part length of 14.5 mm. Optimizing HGA-arm configurations by the Taguchi Method is also useful for reducing windage. The Taguchi Method is a statistical technique for designing products whose performance is not affected by outside conditions. We used an L8 orthogonal array in this investigation and found that optimizing the actuator arm thickness could reduce windage most effectively, the load-beam bend angle, and the arm shape. The windage of an optimized HGA-arm configuration was reduced to about one third that of the initial configuration. This knowledge will be useful in optimizing the parameters of an HGA and a head stack assembly to obtain hard disk drives with higher track densities.

Performance Characteristics of a 32 mm Small Form-Factor Optical Disc and Drive

Experimental data obtained from testing the DataPlay 32 mm disc and drive are presented. Of particular interest, due to the unique rotary tilt arm actuator and front surface head/media architecture is the data concerning shock, vibration, and temperature and humidity stress environments. Results demonstrate that the DataPlay optical drive and media are sufficiently robust for use in portable consumer electronics devices.

Insights To Flow Induced Vibrations In ComputerHard Disks

Read/write operations in computer hard disk drives (HDD) are supported by a rotary actuator. Air movements in the drive are a consequence of still air dragged along by the flat surfaces of the spinning circular disks. Air flowing in the enclosed HDD induces severe mechanical vibration of the actuator that causes Track Mis-registration error (TMR) and limits the achievable TPI, an indicator of the storage capacity of a computer hard disk drive. The velocity fields of an enclosed HDD model were measured with a Laser Doppler Anemometer non-intrusively. The model retained most of the common dimensions and basic features of a 3½ ” HDD. The disks were spun at 10,000 rpm. From the spatial derivatives of the Reynolds shear stresses spatially distributed in the HDD model, the aerodynamic force distribution in the flow field was obtained. It was apparent that the highly fluctuating aerodynamic forces from the surrounding air acted on the arms and could have caused the tips of the arms to yaw back and forth. The aerodynamic action maybe closely related to the flow induced vibrations on arms widely reported by the hard disk drive industries. By modifying the cross sectional shape of the actuator arms, the attenuation of aerodynamic forces in the flow field was not observed.

粘弾性ダンパを用いた磁気ディスク装置用アクチュエータのセトリング振動低減(S62-2 機構・制御(2),S62 情報機器コンピュータメカニクス)

According to the areal density increase of HDDs, fine positioning is required. In this study, we focused on settling vibration of arm sway mode and we developed viscoelastic dampers for the actuator arm. The damper consists of 2 viscoelastic material sheets and a thin constraint plate. It is attached to the arm like ladder bar, over the arm hole. By applying this structure, the viscoelastic materials can withstand a higher stress load, and consequently, produce a high damping force. The dampers are attached to the top and bottom arms. The middle arms don't have any dampers. Our experimental results showed that the damper reduced the arm-sway mode settling vibration to less than half. The damping effect is effective, not only for the arm with attached dampers, but also for arms without dampers.

Effects of the Suspension Interconnect on ESD Failures of the Head Stack Assemblies

With increasing recording density and shrinking size of giant magnetoresistive (GMR) read/write heads, the GMR sensor is getting more sensitive to electrostatic discharge (ESD) events. In this study, two different types of head stack assembly (Type A and Type B) were studied in terms of ESD sensitivity. Both head stack assemblies (HSA) consist of head gimbal assemblies (HGA), preamplifier, E-block, flexible printed cable (FPC), voice coil motor (VCM) coil, and 20-pin connector for 3.5-in drive. Type A is a conventional HSA consisting of two or four HGAs with long tail suspensions whereas Type B is a head stack consisting of one HGA with FPC interconnect instead of a long tail. ESD events were simulated by zapping 20-pin connector with an ESD gun. A quasi-static tester (QST) was used for amplitude and resistance measurement of GMR heads after each ESD event. The test results showed that the failure voltage of Type B (1.0-1.2 kV) is much lower than Type A (4.0-5.0 kV). Furthermore, failed HSAs showed different failure modes: preamplifier damage for Type A and read sensor damage for Type B. To understand the main reason for low failure voltage for Type B, we investigated ESD sensitivity by modifying Type B with different interconnects, bonding methods, and arm actuator structures. These results indicate that the write-to-read crosstalk of interconnect (from preamplifier to head slider) during ESD events caused low failure voltage for Type B. It was found that the metallic structure surrounding the VCM coil is another cause for the low failure voltage of Type B.

MODAL TESTING AND FINITE ELEMENT MODELLING OF SUBSYSTEM IN HARD DISK DRIVE

Residual vibration is one of the primary mechanical problems that affect the dynamic characteristics of the head actuator assembly in hard disk drives, and the data access speed and positioning resolution. This paper presents the experimental modal testing and finite element modelling that are tailored to vibration testing in the head actuator assembly. The special excitation method has been applied for modal testing of the head actuator assembly, based on voice coil motor without altering the modal property of the structure in actual operating condition. The finite element models of the head actuator assembly have been developed, and various modes have been analysed. It is shown that the dynamic characteristics of the head actuator assembly are very complicated, in particular the vibration due to the lateral quasi-rigid body mode caused by the flexibility of the pivot, and mass and structure of the head actuator arm. It is thus essential to develop effective approaches to reduce the vibration of the lateral quasi-rigid mode and improve the dynamic characteristics of the head actuator assembly, so that high-performance HDD can be developed.

Unsteady analysis and experimental verification of the aerodynamic vibration mechanism of HDD arms

The authors investigate the flow structure in 3.5-in hard disk drives with a rotation speed of 10033 rpm, especially the unsteady flow around actuator arms with and without a weight-saving hole, and clarify the unsteady flow in detail. In the method of approach utilized in this investigation, they used: 1) a direct numerical simulation of the Navier-Stokes equations to analyze the flow field; 2) a laser Doppler velocimeter to measure the velocity field; and 3) a laser Doppler vibrometer to monitor unsteady displacement of the actuator arm. The authors find a three-dimensional spiral vortex in the wake region of the arm and the flow spilled from the weight-saving hole. These flows can be considered to be an excitation source for the actuator arm. The power spectrum of the arm torque generated by calculated wind disturbance agrees with that of measured wind disturbance. This verifies the existence of the predicted vortices and the flow spilled from the weight-saving hole.

Multirate digital control for high track density magnetic disk drives

A computationally effective fixed-order multirate digital control scheme is presented for disk drive actuator control. The proposed multirate controller outputs control commands at each control update instant, while the multirate control scheme is evenly computed for every measurement sampling period, thereby eliminating the need for very powerful processors for implementation. Application results demonstrate that the proposed multirate control scheme is useful to smooth control inputs so as not to excite the flexible mode dynamics of the actuator arm and suspensions.

Time and frequency response of two-arm micromachined thermal actuators

This paper examines the time and frequency response characteristics of two-arm micromachined thermal actuators. Two types of thermal actuators are considered: hot/cold arm actuators and ‘V’ or ‘chevron’ shaped actuators. A heat transfer equation governing the temperature profile along the thermal actuators is derived. Equations for the thermal time constants and the frequency responses are presented. The thermal time constants and frequency responses are measured experimentally and compared to analytical predictions.

Optimization of a magnetic disk drive actuator with small skew actuation

Currently the utilization of the voice-coil motor for actuating read/write head elements in magnetic hard disk drives results in a skewed actuation, which necessitates an involved microjogging process and thus a complicated servo system. Furthermore, in perpendicular recording systems, a small skew actuation will relax the requirement on pole trimming. This article presents a magnetic hard disk drive actuator and suspension assembly with small skew actuation. In the present study, the distance from the actuator pivot to the read/write head is chosen so that the skew angle variation is minimized. After that, the suspension head is assembled to the actuator arm at a slant angle with respect to the actuator longitudinal direction to achieve an absolute small skew actuation. Finite element modeling and experimental measurements reveal that there are no significant changes of the actuator assembly dynamic performance with and without the slant angle.

COMBINED CONTROL BY SPACE ROBOTIC MODULE WITH USING MANIPULATOR'S MOBILITY

An approach of designing of combined energy-economic control of a freeflying robotic module, used e.g. as a transport unit at its flight near by a manned orbital station is considered. The fuel consumption economy for the control of the configuration is achieved by stabilising the module's main body angular position with the help of a motion “exchange” between the module's main body's and the manipulator's links activated by their arm actuators. The control algorithms are suggested and the dynamics of the operation of all interacting subsystems module's for the combined control are investigated. A mathematical simulation was carried out taking into account the nonlinear properties of Lagrange module's equations and the nonlinear characteristics of the control subsystem's elements.

Scapular plane isokinetic shoulder elevation: Effect of shoulder and motor centres of rotation transient misalignment on moment data

During isokinetic shoulder elevation in the coronal and sagittal planes, the centre of rotation of the glenohumeral joint was displaced 8-cm vertically relative to the centre of rotation of the dynamometer’s actuator arm. It was suggested that in order to account for this displacement, the recorded maximum moment values should be reduced by 12.5%. The aim of the present study was to measure the displacement of the glenohumeral centre of rotation (DGCR) during isokinetic shoulder elevation in the scapular plane and to conduct an error analysis of the dynamometer’s moment recordings. The DGCR was assessed in twenty healthy volunteers, during isokinetic concentric elevation of the left shoulder, in the scapular plane, using a two-dimension motion analysis system. Measurements were performed at 30, 60 and 120 ◦ ·s −1 , between 30–90 ◦ of shoulder elevation and were analysed every 12 ◦ . The glenohumeral centre of rotation was superomedially displaced relative to the centre of rotation of the actuator arm, throughout shoulder elevation ( P< 0.001). The effect of isokinetic velocity on the DGCR was not significant. The DGCR resulted also in changes of humeral lever arm orientation and length relative to the pre-set orientation and length of lever arm. As a result of these changes, dynamometer’s recordings underestimated corrected angle-based maximum moments by 6.2%. The DGCR during isokinetic elevation of the shoulder in the scapular plane was probably attributed to normal kinematics of shoulder elevation that requires synchronous function of both the scapulothoracic and glenohumeral joints. The cutaneous markers and the 2-D kinematic analysis system used for the assessment of a 3-D shoulder motion may effect the precision in detecting movements of the shoulder under the skin. The present findings are also limited to the position, stabilisation method and range of motion tested.

Monitoring of residual stresses in injection-molded plastics with holographic interferometry

Residual stresses are often trapped in injection-molded plastic parts due to the rapid cooling of the material in this manufacturing process. These stresses are a common source of failure in plastic components in automobiles, appliances and computers and are difficult to measure with conventional residual-stress experimental methods. Real-time holographic interferometry appears to be a viable technique to identify and monitor these stresses in plastic parts. In this investigation, holographic interferometry was used to monitor the relaxation of residual stresses in the plastic-molded actuator arm of a computer hard drive. In the first phase of this study, the relaxation of these residual stresses as a function of temperature was observed. In the second phase, the time to completely relax the residual stresses in the plastic part at an elevated temperature, the annealing temperature, was determined. In the third phase of this investigation, the rate of relaxation of these residual stresses as a function of time at various operating temperatures, was studied. Based on the results of this study, holographic interferometry appears to be a powerful research tool in the study of residual stresses in plastic parts. It also has the potential to be a practical tool for the inspection of manufactured plastic parts for the presence of residual stress.

Finite Element Analysis of a Computer Hard Disk Drive Under Shock

Shock of computer hard disk drives (HDD) in both portable and desktop computers is a common problem. Shock of an HDD can occur during installing the HDD into the computer, HDD testing, HDD handling, and so forth. It is important to identify key design parameters to improve HDD shock performance. This paper presents the finite element studies of a HDD under a non-operational linear drop shock. A complete HDD model is built in ANSYS finite element package. GP commands are used to apply the preload and define the interface between the head and the disk. Shock pulses with different amplitudes and pulse widths are applied to the HDD. The minimum shock amplitude required to lift off the head from the disk is determined for different shock pulse width. Discrete Fourier Transform studies are used to identify critical frequency ranges for different shock pulse widths. The design guideline for the minimum space required between the swage plates and the disk is provided. The effects of drive base stiffness, disk thickness, actuator arm stiffness, and bearing stiffness on HDD shock performance are investigated.