Hinge pivot for disk drive

This paper discusses the findings of a hinge pivot for use in hard disk drives (HDD). The actuator assembly in a HDD is supported by a pivot cartridge and controlled by a servo system to perform seek and track following operations for data recording. The cartridge is composed of a pair of pre-loaded ball bearings. Due to the demand for thin hard disk drives and hence, the need to reduce the height of the actuator assembly, a hinge pivot is proposed to replace the set of bearings. The shaft of the pivot is connected to the sleeve with thin hinges made of ultra-high heat-resistant polyamide film, such as Upilex. Measurement showed that the hinge pivot did not exhibit the nonlinear effects during low frequency actuation, such was inherent for ball bearing pivots. Experiment also showed that at least a million life cycles can be achieved without any performance degradation.     

Finite element modal analysis of an HDD considering the flexibility of spinning disk–spindle, head–suspension–actuator and supporting structure

This paper presents a finite element method to analyze the free vibration of a flexible HDD (hard disk drive) composed of the spinning disk–spindle system with fluid dynamic bearings (FDBs), the head–suspension–actuator with pivot bearings, and the base plate with complicated geometry. Finite element equations of each component of an HDD are consistently derived with the satisfaction of the geometric compatibility in the internal boundary between each component. The spinning disk, hub and FDBs are modeled by annular sector elements, beam elements and stiffness and damping elements, respectively. It develops a 2-D quadrilateral 4-node shell element with rotational degrees of freedom to model the thin suspension efficiently as well as to satisfy the geometric compatibility between the 3-D tetrahedral element and the 2-D shell element. Base plate, arm, E-block and fantail are modeled by tetrahedral elements. Pivot bearing of an actuator and air bearing between spinning disk and head are modeled by stiffness elements. The restarted Arnoldi iteration method is applied to solve the large asymmetric eigenvalue problem to determine the natural frequencies and mode shapes of the finite element model. Experimental modal testing shows that the proposed method well predicts the vibration characteristics of an HDD. This research also shows that even the vibration motion of the spinning disk corresponding to half-speed whirl and the pure disk mode are transferred to a head–suspension–actuator and base plate through the air bearing and the pivot bearing consecutively. The proposed method can be effectively extended to investigate the forced vibration of an HDD and to design a robust HDD against shock.     

磁悬浮硬盘中非记录磁场的研究

介绍了磁悬浮硬盘的概念，测量并分析了普通硬盘的音圈电机和主轴电机产生的非记录磁场以及磁悬浮硬盘中的磁力轴承产生的非记录磁场，分析了非记录磁场对记录磁场的影响，为磁悬浮硬盘的设计和研究提供了依据。     

VCM design with round coil and axe-shaped magnet for hard disk drive actuator

In this paper, we proposed a novel single-sided magnet voice coil motor (VCM) design that can reduce out-of-plane force. Out-of-plane force of a VCM causes the actuator vibration, which results in settling vibration and acoustic noise. The proposed single-sided magnet VCM consists of a round coil and an axe-shaped magnet. We designed the optimized configuration by using numerical magnetic field simulation and compared its performance with those of a conventional VCM. Torsional moment was reduced by 90% at the worst position of the middle track, and bending moment was reduced by 50% at the worst position of the inner track compared with a conventional VCM. Rotational moment in our VCM was almost the same as that of the conventional one. We manufactured an actuator with the new design VCM and confirmed that the new single-sided magnet VCM shows a good performance as expected, although its magnet volume and coil resistance were almost the same as a conventional design. The measured frequency response of the actuators from the coil current to the head displacement showed that the coil torsional mode vibration of the proposed VCM is reduced remarkably.     

Micro parts assembly system with micro gripper and RCC unit

This paper presents a new micro assembly system, which is composed of a micro gripper, a micro remote center compliance (RCC) unit, a voice coil motor-driving mechanism and precision motion stages. The micro gripper is actuated by two shape memory alloy (SMA) wires, and its grip is 1 mm. The micro RCC unit has low translational and rotational stiffness sufficient for micro parts assembly. The voice coil motor-driving mechanism can generate linear motion with an adjustable stiffness, and it can also measure external force in the moving direction. An algorithm for the automatic assembly of micro parts is also proposed, and assembly experiments are performed.     

Stability analysis of a disk-spindle supported by a plain journal bearing and pivot bearing

A hydrodynamic bearing is widely used for hard disk drives, and it is better than a ball bearing in terms of vibration suppression, noise reduction and shock resistance. However, its cost to performance ratio should be further improved. In this study we analyzed the stability of a disk-spindle assembly supported by a hydrodynamic plain journal bearing and a pivot bearing at the bottom of the shaft. As a result, we found that a half-frequency whirl of a vertical spindle caused by the plain journal bearing becomes stable if the gyro factor of the rotor is larger than 0.5. We examined the effects of the bearing design parameters on the stability of the disk-spindle assembly, including the flexibility of the shaft. We also compared the stability of a disk-spindle assembly supported by two plain journal bearings and found that the vertical spindle is always unstable. Thus, the bottom end of the shaft should be supported as a fulcrum.     

Design of a hybrid optical image stabilization actuator to compensate for hand trembling

In this paper, a novel hybrid optical image stabilization (OIS) actuator for digital camcorder is proposed. Image stabilization for this hybrid type consists of both radially and tangentially moving components to compensate for hand trembling. The proposed OIS actuator, which uses a voice coil motor method, is divided into two parts: a structure and a magnetic circuit. For the structural part, the driving mechanism consists of two systems: one system is based on a ball guide with a magnetic spring, and the other system is based on a pivot bearing. The former system is typically used as a driving mechanism in mobile devices, whereas the latter system has advantages such as mechanical stability and reduced friction. Overall, a magnetic spring between the magnet and yoke should be considered to select the best magnetic circuit part design and mechanism design. Regarding the electro-magnetic (EM) circuit, two types of EM circuits were designed to satisfy each direction: one circuit is a moving magnet circuit for the radial direction, and the other circuit is a moving coil for the tangential direction. In a digital camcorder, the space for the OIS actuator is limited, and thus, optimized actuator with adequate performances is required. To solve these problems, a sensitivity analysis was performed using the design of experiment procedure. Based on these results, an objective function was defined for the optimization procedure. Finally, the actuator was fabricated, and the dynamic characteristics and feasibility of adapting two types of mechanisms of the suggested OIS actuator were verified. The experimental results indicate that the proposed OIS actuator exhibits sufficient performance for the sensitivity.     

Prototype feedback-controlled bidirectional actuation system forMEMS applications

We have successfully developed a one degree-of-freedom microsuspension system, with active position control, as a paradigm of a micromagnetic bearing. This system integrates an electromagnetic actuator, a position sensor, and a feedback control system that provides active position control. This paper discusses the design and fabrication details of the microelectromechanical system (MEMS) components: the beam mass structure integrated with a drive coil and metallized targets, spacer plate, and sensor coils. It also discusses their integration with millimagnets and electronics. Noncontact magnetic bearings based on this principle have the potential of overcoming the tribo-physical issues associated with active MEMS devices     

Design of a hybrid magnetomotive force electromechanical valve actuator

We propose a novel axis-symmetric modified hybrid permanent magnet (PM)/electromagnet (EM) magnetomotive force actuator for a variable valve timing camless engine. The design provides a large magnetic force with low energy consump-tion, low coil inductance, PM demagnetization isolation, and improved transient response. Simulation and experimental results confirm forces of about 200 N (in the presence of coil current) at the equilibrium position and 500 N (in the absence of coil current) at the armature seat. We compared our proposed design with a double solenoid valve actuator (DSVA). The finite element method (FEM) designs of the DSVA and our proposed valve actuator were validated by experiments performed on manufactured prototypes.     

Shock effects on the performance of the interface between the moving suspension lift-tab and the ramp in a load/unload drive

The bouncing behavior of the suspension lift-tab at the tab–ramp interface during the unloading process of a hard disk drive subject to external shocks was studied by using a lumped-parameter dynamic model with one degree of freedom in a moving reference frame. A finite element model of the hard disk drive was used to generate the data as input to the lumped-parameter model. This simulation scheme allows easy examination of the effects of individual contributing factors. The effects of the peak acceleration of the external shock pulse, the pivot hub motion, the air bearing suction force and the disk motion on the bouncing characteristics of the lift-tab were studied by evaluating the bouncing distance and bouncing height of the lift-tab as well as the indentation depth at the tab–ramp interface. The simulation results indicate a different behavior of the suspension close to the base plate (B) compared to that close to the cover (C). The bouncing distance and bouncing height were larger for Suspension C compared to Suspension B. For the latter, the motion of the pivot hub is an important contributing factor to the bouncing distance and bouncing height. Moreover, the indentation depth increases significantly with increasing peak acceleration. For suspension C, both the bouncing distance and the bouncing height increase almost linearly with increasing peak acceleration. The vibration of the disk changes the dimple separation height and the air bearing force during an unloading process, thus affecting the bouncing behavior of the lift-tab. The effect of the suction force on the bouncing of the lift-tab is coupled with the disk position. When the lift-tab exceeds the dimple separation height for a disk raised relative to its original position, the suction force can decrease the bouncing height of the lift-tab significantly, compared to the condition without a suction force.     

Investigation of the electromechanical variables of the spindle motor and the actuator of a HDD due to positioning and free fall

This research investigates the electromechanical variables of a spindle motor and an actuator of an operating hard disk drive (HDD) due to the positioning and the free-fall of a HDD. Magnetic fields of a brushless DC motor and a voice coil motor are determined by the time-stepping finite element equation of the Maxwell equation and the driving circuit equation. The pressure of the fluid dynamic bearings (FDBs) is determined by solving the finite element equation of the Reynolds equation to calculate the reaction force and the friction torque. Dynamic equations of the rotating disk-spindle, actuator, and stationary bodies of a HDD are derived from the Newton–Euler’s equation. The speed control of the rotating disk-spindle and the servo control of the actuator are included to describe the head positioning between the rotating disk and the head. The simulation is performed to investigate the electromechanical variables of the spindle motor and the actuator due to the positioning and the free-fall of a HDD. This research shows that the positioning and the free-fall of a HDD change the electromechanical variables of the spindle motor and the actuator of an operating HDD, and that monitoring their electromechanical variables may identify the positioning and the free-fall of a HDD without using extra sensors.     

基于滑模控制的3D刚体摆姿态稳定性

研究3D刚体摆姿态稳定性的滑模控制问题.3D刚体摆由一个刚体绕一固定且无摩擦的支点旋转,刚体受到恒重力作用且具有三个转动自由度.针对3D刚体摆平衡位置处的姿态稳定控制问题,设计了滑模控制器并分析了角速度和姿态的渐进稳定性.由Lyapunov直接法找出了各个滑模系数取值的充分条件,并通过数值仿真实验验证了滑模控制方法的有效性.     

Analytical dynamic model for suspension with PZT actuators

Modern hard disk drive uses voice coil motor to move its actuator across spinning disk to access data stored on disk surfaces. To achieve higher area density with narrow tracks, piezoelectric (PZT) ceramics are deployed as secondary actuator in many high capacity drives to increase servo control bandwidth for better positioning accuracy. Piezoelectric secondary stage actuators, often called dual stage actuator or DSA, integrated on suspensions are discussed in this paper. An analytic model is presented to derive a secondary order equation of motion relating suspension dynamics to key suspension and PZT geometric parameters, material properties and voltage applied to PZT. DSA DC gain is then obtained from the equation of motion. By introducing a suspension configuration without PZT installed, the DSA DC gain is then further linked to suspension dynamics parameters. With the equation of motion and DSA DC gain model, design directions for higher stroke and tradeoffs for dynamics and robustness are discussed.     

Dynamic two arm hybrid position/force control

A useful two arm robot system will not only need to cooperatively manipulate the same object, but also need the ability for external force control. As an example, assume two robots are building a space station, which requires them to connect a structure to a partially built space station. This implies that they need to cooperatively move the object to the desired position, and then apply a force to connect it. Therefore, two arm hybrid position/force control is necessary. To accomplish this task quickly and accurately the dynamics of arm 1, arm 2, and the object must be taken into account. The external and internal forces must be clearly defined to be used in the servo control loop. There are several ways to choose the internal force: zero internal force, arbitrary force distribution, minimizing object strain energy, and minimizing the total torque. An example is shown to illustrate the trade-offs. A controller is presented which incorporates the dynamics of each arm, the dynamics of the object, and servos on the internal and external force. Experimental results show that servoing on the internal force will reduce the force error significantly.     

微硬盘的不确定性非线性系统及其跟踪控制

超大存储量、高精度定位、快速跟踪和强稳健性是微硬盘技术发展的重要目标,而控制技术的探讨是其主攻任务之一.鉴于影响磁头运动的主要因素包括摩擦力、惯性力和气流,本文在音圈马达驱动器的传统模型基础上,对这些扰动因素进行综合,引入磁头臂转动角度变量,建立该驱动器的不确定性非线性模型;利用Lyapunov稳定性理论及线性矩阵不等式凸优化技术,提出非线性观测器和自适应反馈控制器,获得所设计模型的跟踪控制方案.仿真结果论证了在所设计的控制方案下,系统的输出能跟踪任意给定的磁道,获得跟踪速度快、跟踪精度高的效果.     

Fuzzy bang–bang relay control of a single-axis active magnetic bearing system

Active magnetic bearings (AMB) are presently being utilized in various classes of rotating machinery. Although the rotor-AMB systems are open loop unstable, they are easily stabilized using feedback control schemes of which the PID controller is the most commonly used. The PID controller is however only effective at the vicinity of the rotor’s equilibrium position where the dynamics of the rotor-AMB system is linearized. Significant deviation of the rotor’s motion from this equilibrium position may occur due to large imbalance forces. In this situation, the nonlinearity in AMBs, which arises from the relationship between the electromagnetic force, coil current and air gap, may render the PID controller ineffective. For the control of nonlinear systems, artificial intelligence techniques such as fuzzy and hybrid techniques are effective. In this paper, a new fuzzy controller is proposed for the control of a single-axis AMB system. This controller is based on the bang–bang scheme, which is an old but effective technique to control nonlinear systems in optimal time. The performance of the proposed integrated fuzzy bang–bang relay controller (FBBRC) was found to be superior to that of the optimized PD controller and the conventional fuzzy logic controller. Comparison of the FBBRC with the fuzzy logic controller cascaded with a hard limiter (FBBC) relay revealed almost equal performance. High frequency chattering was however observed in the steady-state response of the FBBC. Such chattering is known to cause instability and distortion in the amplifiers that are used to supply current to the magnetic bearing actuators.     

Voltage driven hard disk drive with voice coil model-based control

In this paper, we describe a new solution for driving the voice coil motor (VCM) in hard disk drives (HDDs), in which the usual current driver for the voice coil motor has been replaced by a voltage driver. When used in conjunction with PWM power stages, this solution becomes fully digital and has proven advantages in terms of cost, power dissipation and silicon area. To achieve the same performance of the current driver, the voltage driver requires a pre-filter placed at its input, to cancel out the electrical pole of the VCM. In the paper, we describe the voice coil model-based control (VCMC), a solution for implementing the pre-filter, which replicates the behavior of a current loop by using a model of the voice coil motor and its driver, including the saturation of the power stage. It is worth noticing that VCM resistance may change by 30% during HDD operations, increasing when the disk is performing repetitive seeks or decreasing when the disk cools down during track following. Such variation may lead to an unsatisfactory performance of the VCMC, so an adaptation mechanism, capable of tracking variations of VCM coil resistance, must be set up. This paper presents a pair of on-line estimation procedure, used to get the value of the VCM coil resistance during seek and track following, respectively. The first one is based on a standard LMS approach, aimed at identifying a simplified model of the plant with the least computational effort. The second exploits the presence of repetitive disturbances (RROs) to detect variations of plant gain and, in turn, of VCM resistance. It will be shown that both procedures are quite accurate in estimating variations of VCM resistance and their output can be used to perform on-line tuning of the VCMC. Experimental results show that the servo performance with the adaptive VCMC is not affected by resistance variation and equivalent to that of the standard current driver.     

Fault-tolerant control of three-pole active magnetic bearing

Active magnetic bearings have many advantages over conventional bearings due to contactless operation and adjustable force dynamics. However, one of the obstacles associated with these bearings is failure modes, which may result in destructive rotor dynamic behaviour. One of the important failure modes is electric power outage which may be due to failure of power amplifier, coil or electric wiring. In the present work, a fault tolerant controller has been designed for three-pole magnetic bearings to provide unaltered performance in the event of fault occurrence. The controller has been designed by incorporating the nonlinear fuzzy logic control. The present design of fuzzy logic controller is done by reducing the number of rules of its rule base. Simulations have been carried out to test the performance of the controller for different failure conditions. The designed controller is able to stabilize the rotor for large deviations from the origin even in the presence of failure. The controller is found to be robust as it provides satisfactory operation in the presence of uncertainties.     

Two robot arms in assembly by using impulsive information

When two robot arms execute coordinated motions in assembly, collision between the two end-effectors cannot be avoided. The collision effects on the two coordinating robots include two aspects: abrupt velocity changes of the robot joints and impulsive forces exerting on the contact point as well as on robot joints. Since the direction of the impulsive force exerting on the contact point is related to the relative position and orientation of the two mating parts, the impulsive force can be used to detect the alignment errors of the two end-effectors. Thus a new assembly method is proposed in this article. The new method uses impulsive information to adjust the position and orientation errors of the two robot arms in assembly, rather than employing a compliance mechanism. The advantage of the new method is that the jamming problem, which is usually associated with compliance methods, never takes place. To make the method practically useful, wrist force sensors are suggested to installed at the wrist of each robot. Dynamic relations between the sensed information and the impulsive force at the contact point are then established. The sensed information thus becomes useful in analyzing the alignment situation. Finally, practical cases are studied to illustrate the use of the new assembly method.